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Cutting endodontic access cavities— for long-term outcomes
This is not a critique so much as an admission of the ways that teeth and their root canal systems have taught me, usually the…
This is not a critique so much as an admission of the ways that teeth and their root canal systems have taught me, usually the hard way, to spend whatever time is needed to create perfect entry paths into canals, before I attempt to work in them. So why do I have to have a talk with myself before beginning every access cavity—even after doing this for 35 years—to be certain to hit the mark I know must be met before it is safe to venture further?
Zen and the art of endo access
Robert Persig, in his book “Zen and the Art of Motorcycle Maintenance,” described being deeply frustrated when a bolt stripped as he was attempting to remove the side covers to the engine of his motorcycle, before rebuilding it. The rebuild could not continue until he was able to circumvent this problem. He had expected to spend several days completing the mission, yet he was amazed at the fury he experienced when faced with this conundrum.
The more he thought about it, the more mystified he became about his instinctual response, until he realized that he was tweaked because he had grossly undervalued this part of the long rebuild procedure, thinking mostly about the more dramatic routines to follow, such as cracking the cylinder case, honing the cylinder, replacing the piston and putting it all back together afterward. When he realized that nothing was going to progress until he had successfully removed the side cover, he made removing that side cover a separate and important mission, an accomplishment that would deliver satisfaction in and of itself, if it could be completed during the next several hours spent.
So it is with endodontics. When we realize how critical the quality of our access preparations is to the remainder of the case, it feels like fingernails on a chalkboard to head into a canal before securing an ideal path into it. Aristotle got it right—excellence is a habit, not a character trait. So what do the habits of access excellence look like in this 21st century?
Failing to plan is planning to fail
Atul Gawande, in his book “The Checklist Manifesto,” describes the importance of planning not just which procedure to do, but how every single aspect of that procedure must be planned in detail, from start to finish, if consistently ideal results are the goal. Does the preoperative imaging accurately describe the anatomical challenges? Does the clinician have adequate magnification and light? Are the cutting tools adequate and well chosen? Are the locations, angles and depths of entry determined before beginning the procedure? Have maximal safe cutting lengths been marked on access burs? Are there procedures in place to deal with calcified canals that defy location? And so on.
In other words, the Alfred E. Neumann attitude of “What, me worry?” is not appropriate during this critical event. Conversely, when each of these critical elements is included in the treatment planning and execution of an ideal access cavity preparation, the rest of the procedure becomes progressively simpler as the finish is approached.
We wouldn’t even attempt RCT without Roentgen’s invention of the dental radiograph, so it is not much of a stretch to claim the critical necessity of ideal preoperative radiography. Ideal preoperative X-ray imaging must include a straight-on angle that splits the mesial and distal contacts perfectly—taken either as a periapical or as a bitewing X-ray image, then at least one ideal off-angle view in order to capture data from the Z-plane (buccolingual) of the tooth in question.
In my practice, a mesial off-angle view of anteriors and premolars works well, because it is much easier to capture than a distal angle, and in anteriors and premolars the mesial view reveals as much radicular anatomy as a distal view. In molars it is different. In molars a distal view is far preferable to a mesial off-angle view, as the mesial view superimposes the body of the root over the distally curved root structure, while the distal view casts the apical root end sideways, where it can be more easily seen on the radiographic image.
Of course, cone-beam CT (CBCT) imaging is the unfair endodontic imaging advantage. If told I could have either a microscope or a CT machine, but not both, I would choose 3-D imaging every time. Only CBCT imaging can capture the mesial view of root structure—the view in which we see “The Secret Life of Root Canals”—the bucco-lingual plane containing the greatest degree of anatomic complexity. One of the greatest joys of having a CT machine in practice is knowing, for sure, before the access procedure is begun, that there is only a single canal in the mesiobuccal root of an upper molar. Conversely, one of the few negative experiences to be had with this technology is when the reconstructed volume shows two or three canals, in a root that has given up only one to the clinician’s exhaustive search.
The first gift of CBCT imaging to the field of endodontics has been the gift of finding all canals in a given tooth. Its second gift is the great diminution of access size possible, because the access cavity is no longer the primary viewing port into the pulp chamber and beyond. In fact, CT imaging is the only view needed into the anatomic verities of root canal spaces, allowing access cavities to be used exclusively as treatment, rather than as exploratory portals. Ultimately, RCT access procedures will be done with CT-generated drill guides, allowing molars to be treated through three to four 1-mm pea-holes, rather than the 2- to 4-mm access cavities used today.
So what are the objectives we consider when planning the invasion of a root canal space? Basically, all the best access cavities are cut in a balance between conservation and convenience form. We cut as little tooth structure as possible, while ensuring ideal pathways into each canal. Access outline form objectives become fairly simple then; we demand convenience form, otherwise we cannot complete our task, yet we always strive to preserve the structural integrity of the tooth. This boils down to three easily remembered objectives:
1) In anteriors and premolars, conservation form is found in the mesial-to-distal dimension. Traditionally, anterior access cavity outline form has been triangular because of the mesial and distal pulp horns in these teeth—logical until we consider the structural consequences, a needless weakening of coronal tooth structure to insure these lateral pulp horns are cleaned out, when the smallest undercut with a #2 Mueller Bur or Buc-1 ultrasonic tip (Spartan) could suffice as well. Premolars have pulp chambers like the shape of a hand, which is fortunately arranged in a bucco-lingual direction, the angle of the recommended slot-like access cavity outline form is bucco- lingual as well, simultaneously combining convenience and conservation form.
In anterior teeth, convenience form is harder won as the incisal edge is to be avoided, out of respect for postendodontic aesthetic objectives, thus requiring a deeper cut under the cingulum, to allow a more straight-line entry path, while minding the “no-fly zone” of the incisal edge. The most dangerous anterior access cavity error is not cutting adequately through what Dr Schilder called the “lingual dentinal triangle” under the cingulum, and this can be accomplished with minimal structural weakening when the mesio-distal dimension is kept to a 1 to 1.5 mm width (Fig. 1).
2) In posterior teeth, premolars and molars, it is important to remember that their occlusal surfaces are not centred over the root structure, but are skewed toward the idling cusp side of the root structure. As pulp chambers are centred in the root structure, not centred under the occlusal surface, access in posterior teeth is best accomplished by cutting near working cusps, while staying 1–2 mm away from idling cusps (Fig. 2).
3) In molars, conservation form is held by avoiding the distal half of the occlusal plane, as ideal file paths from the distal canals of upper and lower molars are canted severely to the mesial, so much so that distal canals of lower molars are best referenced to the MB or ML cusp tips, and distobuccal canals of upper molars are best referenced to the palatal cusp tips. Convenience form is achieved by cutting the mesial wall of molar access cavities parallel to the mesial surface of the tooth (Fig. 3).
Back from the abyss
I was taught Schilder technique at University of the Pacific by Dr Michael Scianamblo and after grad school by Dr Cliff Ruddle. I understood the clinical imperative Dr Schilder had placed on cutting an access adequate to treat the entire root canal system in a predictable manner, and I enjoyed working through the large access cavities and the generous coronal canal shapes he recommended until I was broughtup short by Dr Carl Reider, a well-known prosthodontic lecturer from Southern California.
When I asked what he most wanted from the endodontists he referred his patients to, he said he wished we could “just suck the pulp out, without cutting any tooth structure.” As we talked, I came to better understand the structural imperative of saving teeth in the long term, setting me on a quest for tools and methods that would allow us to achieve the same consistently ideal endodontic outcomes, through smaller access openings and coronal canal shapes.
Ultimately, it was the inspiration for my invention of the Maximum Flute Diameter (MFD) limitations on GT and GTX rotary files (DENTSPLY Tulsa Dental Specialties), the LAX (line angle extension) GuidedAccess Diamond Burs by SybronEndo, as well as obturation methods using flexible condensation devices, such as System-B Continuous Wave electric heat pluggers (SybronEndo) and GT/GTX Obturators (DENTSPLY Tulsa Dental Specialties).
The Itty Bitty Access Committee
Since that initial awakening in the ’80s, it has felt like being a lone voice in the wilderness until the past 10 years, when a new generation of dentists and endodontists, steeped in the new reality of implant dentistry as an alternative to RCT, have taken up the cry for longer-term outcomes through improved structural preservation, ultimately becoming what I jokingly call The Itty Bitty Access Committee (IABC).
As so often happens, somebody outside of our specialty, a general dentist named Dr David Clark, started lecturing on the access elephant in the endodontic living room. He got my buddy Dr John Khademi turned on to the possibilities that more conservative access cavities could offer the specialty, 4 and one by one a group of young endodontists joined the game of who can do a perfect RCT through the smallest access cavity. This ad hoc group of talent began the IBAC club.
The cases shown in Figures 4 through 10—mostly done by IBAC members—make me very happy and afraid at the same time. What the heck are they doing? Little, tiny entries, leaving pulp chamber roofs intact, lateral pulp horns unroofed as well, or just total RCT through previously cut restorative cavities!
After getting over my initial shock at what they were accomplishing, I came to understand that the future of endo is very good in these extremely talented hands, and I saw that the procedure I was developing for endodontic surgery—CT-guided endodontic surgery (CT-GES)—could be applied to conventional treatment as well (Figs. 11a–12d).
And morning breaks over the field of endodontics.
Editorial note: This article was published in roots – international magazine of endodontology No. 04/2016.
Stairs to the Apex
Sometimes endodontic specialists have to go the extra mile to save teeth. Only with the proper endodontic instruments success can be ensured in the most…
Sometimes endodontic specialists have to go the extra mile to save teeth. Only with the proper endodontic instruments success can be ensured in the most challenging situations. This case shows how the aid of HyFlex CM-files can help to deal with multiple iatrogenic deformations after several previous temporary root canal therapies. The use of these pre-bendable NiTi-files help us to get the root canal preparation “back on track”.
Endodontic intervention after a previous temporary treatment can sometimes pose a real challenge even for the most skilled endodontist. Some patients have a long history of unsuccessful root canal treatments. In a situation like this it becomes quite difficult to shape the canal when the natural path of the root canal is almost completely lost. The loss of dentin is often considerable after several dentists have literally tried to “push their luck”.
An 18-year old male patient presented with a painful lower right first molar. After thorough examination, both clinical and radiographic, tooth #46 was diagnosed to be the cause of his pain. On the pre-operative radiograph a (symptomatic) apical periodontitis could be recognized together with a leaky temporary restoration with decay underneath. Two mesial and a distal canal were filled with calcium hydroxide. Looking even more into detail a step could be observed in the distal root canal. Clinical the tooth was painful on percussion and biting forces, there was no reaction to cold or warmth and no pockets could be probed although the gum was inflamed due to the temporary restoration and decay that was left behind.
After further examination the patient explained the tooth had been treated in the recent past by no less than three different dentists. Recurring pain had forced him to seek treatment time and again after each provisional non-surgical root canal treatment (nsRCT). Apparently, each colleague had tried to work his or her way around the imperfect preparation of their predecessors leading to a root canal with the shape of a staircase. The absence of a good coronal seal lead to improper healing and thus caused a chain reaction of re-interventions which resulted in iatrogenic damage of the root canal walls.
Re-shaping the root canal preparation
After applying a dental dam the first step was to remove the temporary filling and decay, the pulp floor was checked for perforations and all orifices were located. The canals were then scouted, patency was regained and with small hand files (K-flexofiles ISO 06 up to ISO 20) a manual glide path was established in all four root canals. After scouting it was clear that several steps, luckily without any perforation, were present in the distal and in the mesio-buccal canals. In a case like this it is important to redefine the shape of the previous preparation and first and foremost an endodontic file system is needed that is flexible and prevents further unproportional loss of tooth substance.
For the canal preparation a renowned nickel titanium file system by Swiss dental specialist COLTENE (Fig. 2) was used. Thanks to a clever combination of unique material properties, pre-bendable HyFlex CM files are virtually unbreakable. The reason for this phenomenon is simple: the well-known “Controlled Memory”-effect is flexible enough to find its way around the distorted canals. It improves certain physical qualities of the alloy itself. Similar to classical stainless steel files the instruments can be prebent, but they do not bounce back like conventional NiTi files. This typical characteristic makes “CM”-treated NiTi files extremely flexible. Highly versatile files are particularly helpful if you have to move around abrupt curves or—in this case—a mutilated anatomy. After usage their form adaptation can be quickly reversed in the sterilization process. During autoclaving the instruments turn back to their original shape (Fig. 3). The refined NiTi files are very resistant to cyclic fatigue and can be reused safely, as long as they are not plastically deformed.
The Hyflex CM-files respond to excessive resistance with straightening of the spirals, which avoids binding to the walls. To create any form of steps in the canal shape is incredibly hard and instrument separation is almost impossible, as long as the files are applied correctly. A good preparation technique is to move the file in a soft pecking motion through the canal. In addition to that it is highly advisable to irrigate the canal thoroughly every time a file in the sequence is changed.
Once the manual glide path was created, it was very easy to bypass the various steps and ledges with the pre-bendable HyFlex files (Fig. 4). The mechanical rotation was started on the endodontic motor only after the insertion of the pre-bent instrument in the canal beyond the step. By this approach the risk of perforation is generally eliminated and no further damage of the root canal wall takes place at the level of the step. Beyond the step we used the rotating files as usual at the normal operating mode of 500 rpm. With only a few files per canal it was possible to instrument the root canal up to a working length of 21 mm. The mesio-lingual canal was finally instrumented with a pre-bent .35/0.06 file (Fig. 5). The file was inserted into the canal with two to three subtle movements, then withdrawn before it re-entered the canal. Similarly, the mesio-buccal canal was shaped with a size .35 file with a taper of 0.04 (Fig. 6). To enlarge the apical aspect of both the disto-lingual and the disto-buccal canal a 45/0.04 file was used (Fig. 7).
All files kept their pre-bent shape during the procedure and moved safely in the centre of the canal. Even unexpected angles could be managed almost effortlessly with the swift moving instruments. Despite the numerous steps that got sculptured into the root canal before a smooth shape was finally regained, which would ensure a tight and reliable obturation of the root canal system (Fig. 8).
Successfully preventing re-infection
As mentioned above, a thorough rinsing protocol was performed throughout the whole nsRCT. The constant copious irrigation helped to clear the canal of remaining debris or necrotic tissue. As cleaning irrigants we used sodium hypochlorite (NaOCl) in a concentration of 5.25 % and citric acid (40 %). Both irrigants were activated by ultrasound as well as manual dynamic activation (cone pumping). Corresponding paper points were inserted to dry the canals afterwards.
In the end a bioceramic sealer and gutta percha were used in the hydraulic condensation technique for permanent obturation (Fig. 9). After curing, bioactive filling material can form so-called hydroxyapatite crystals on the surface. The crystals help to stimulate the regeneration of bone and dentin tissue in particular. The coronal restoration was topped off with a composite and a core build-up of glass fibre reinforced composite. Further indirect restoration is planned to be done by the referring dentist.
The post-operative X-rays illustrate two interesting aspects (Figs. 10 & 11): first of all, the obturation material was safe in place and together with the tight seal of the coronal restoration should keep another reinfection at bay. Secondly, the steps were still visible. Especially the mesio-buccal and distal canals looked imposing in relation to their normal size. However, the composition as a whole appeared to be stable with enough dentine surrounding the apex. We were able to save the tooth and the patient left our endodontic practice with an uplifting prognosis despite his unfortunate entry.
Experts for root canal treatment
In our line of work, we often witness patients that dread visiting an endodontic specialist. This sometimes leads to a situation were the general practitioner tries to perform a complex nsRCT himself turning it in an even more complex treatment. Of course, the enormous technical progress in endodontic instruments helps dentists to work professionally and confidently—almost irrespective of their level of experience. Modern endo equipment like a state of- the-art NiTi system allows newcomers and colleagues who do not perform endodontic treatments on a regular basis to create convincing results in a short period of time.
Dentists who have not got the time or desire to personally invest in endo should nevertheless improve the service level of their practice by cooperating with a skilled and well-versed endodontic practice. In Belgium, dentists specialize in a three year intensive course to become experts in root canal treatments. Equipped with the latest instruments experienced endodontists therefore can offer a lot of advice and help with cases that are otherwise deemed to be untreatable. A good working referral system can bring huge benefits for both general practitioners and endodontists who know their way around the root canal.
Modern rotating instruments help the endodontist and general dentist to operate both confidently and safely. Refined NiTi systems with “Controlled Memory”- effect are extremely flexible and fracture resistant due to their special material properties. With pre-bendable files root canals can be shaped efficiently without making any concessions to the natural anatomy of a given root canal. Even referral cases with an eventful history can have a promising prognosis, if the RCT is performed according to the rules, i.e step by step.
Editorial note: This article was published in roots – international magazine of endodontology No. 04/2016.
The role of the operating microscope – in conjunction with ultrasonic in preparation of root canal systems
A review of preparation techniques states that “because of limited efficacy of irrigation in such recesses, debris and smear layer may accumulate and remain on…
A review of preparation techniques states that “because of limited efficacy of irrigation in such recesses, debris and smear layer may accumulate and remain on these unprepared root canals walls, decrease the quality of obturation and jeopardize the long-term treatment success” (Hulsmann et al., 2005).
Preparation of root canal system
The cause of failure of endodontic treatment has been attributed to the presence of microorganisms persisting in the apical part of the root canal (Siqueira 2001). Much attention has therefore been focused on preparation and obturation of the apical part of the canal thereby depending on the apical seal to prevent toxins from leaking out into the periradicular tissues. While success rates of endodontically treated teeth without periradicular lesions is very high, there can be a significant reduction in success in both teeth with periradicular periodontitis and in those teeth where endodontic treatment has failed (Ng et al., 2011). This is predominantly due to the failure to remove microbes form the root canal system. The quest is to find more effective irrigants and irrigation techniques, as well as rotary files and preparation techniques to overcome these difficulties.
An ideal preparation shape with a rotary instrument can only be achieved in a canal with a matched cross section. Many canals are variable in shape. They may have irregular and oval cross-sections and while much of the debris is captured within the flutes of the instruments, some is compacted into those spaces between the instrument and the canal wall (Fig. 2). The incidence of isthmuses in both maxillary and mandibular first molars is very high (von Arx 2005). They are particularly liable to have an accumulation of compacted debris after preparation and the inability to clean these areas effectively has been implicated as a major cause of failure of root canal treatment, particularly in both mandibular and maxillary first molars (Fig. 3) (Hsu & Kim, 1997; Tam & Yu, 2002).
The more the debris is compacted, the more difficult it is for chemicals such as sodium hypochlorite and calcium hydroxide to penetrate through the interface. Paque et al. (2010) reported that approximately half of the debris that accumulated during rotary instrumentation of the mesial canals of lower molars remained in the canal system after irrigation.
Failure of endodontic treatment in maxillary molars has been attributed to the failure to locate and treat the mb2 canal (Weine, 1969; Wolcott et al., 2005). Various studies have shown the presence of the mb2 canal in up to 90 % of maxillary first molars. A study by Somma et al. (2009) showed that in 58 % of teeth, the mb1 and mb2 merge apically into one canal. In a proportion of these failed cases where the mb1 canal has been located, cleaned, shaped and obtruded well, the question should be asked, “Was the failure due to inadequate treatment of the apical part of the mb1 canal, or because the mb2 canal and isthmus between the two canals had been missed?” Identification and treatment of the mb2 canal with concomitant re-treatment of the mb1 canal often leads to healing. This suggests that the seals are not always good enough to “entomb” the bacteria. Indeed coronal microleakage has been implicated as a major cause of failure of endodontic treatment (Saunders and Saunders, 1990). Undoubtedly tracts of debris running along side root fillings are conduits for bacteria to cause failure by this method.
In an in vivo study by Nair (2005) the mesial canals of sixteen lower molars with infected root canals were root treated by conventional techniques in a single visit and the apical portions removed by flap surgery and evaluated by corrective light and transmission electron microscopy. In the majority of cases residual microbes were located in inaccessible recesses, uninstrumented areas of the main canals, accessory canals and intercanal isthmuses.
If the lateral extensions feed into the apical part of the canal, then removing bacteria and nutrients from these areas reduces the bacterial load and this has to be beneficial for the outcome of treatment. A variety of techniques have been proposed to overcome the inadequacies of mechanical preparation in non-circular canals including circumferential filing using both hand and rotary files and the use of a rotary self-adjusting file that adjusts to the shape of the canal. The SAF system has been shown to be more effective in cleaning oval canals that conventional rotary nickel titanium instruments, however in the study by De Deus et al. (2011) using mandibular canines, even this technique did not render the canals completely clean. They showed that rotary files were unable to access the recesses of oval canals and that sodium hypochlorite had a “limited ability to compensate for the inadequacy of the file itself”. They further suggested that the common belief that “the file shapes; the irritant cleans” is based more on wishful thinking than on experimental facts. In a review article by Metzger (2014), it was recognised that SAF was unable to prepare the narrow isthmus of less than 0.2 mm. In the case of the narrow isthmus the challenge is to deliver sufficient quantities of irrigant effectively into a very small area in which debris has been compacted during preparation.
Recently new concept files XP 3-D Finisher (Brassler, USA) that change their shape with temperature have been developed with the expectation that they can deal with canal irregularities. While these may be helpful in removing soft tissue in non-circular canals, they may be of limited value in situations where tissue or root filling materials are strongly adherent to the root canal wall.
Among the numerous irrigation techniques that have also been proposed there are those that include the use of ultrasonic energy. Ultrasonic have played a role in endodontics for many years. Initially ultrasonic canal preparation was introduced by Richman (1957) and in subsequent years there was a vogue for using the ultrasonically energised file to cut dentine in root canals. The technique fell out of favour because lack of control produced ledges, apical perforations and instrument separation (Lumley et al., 1992). In the 1980s research showed that passive ultrasonic energy, PUI rendered canals clean more effectively than ultrasonic irrigation with simultaneous instrumentation (UI), where the file is intentionally brought into contract with the canal wall (Weller et al., 1980; Ahmad et al., 1987a). PUI uses an ultrasonically energised file to irrigate the canal and to remove debris utilising a combination of acoustic microstreaming and and cavitational energy (Ahmad et al., 1987a, b; 1988; 1992) (Fig. 4).
PUI was found to be effective in apical part of curved canals and in the isthmus area between two canals. The technique has been shown to remove tissue more effectively than hand irrigation and does not cause damage to the canal wall (Gutarts et al., 2005). Variation in the efficacy of PUI reported in some studies were explained by difficulties in standardizing the position of the instrument in the centre of the canal (van der Sluis, 2007).
Since the introduction of the operating microscope, it has been possible to carry out endodontic treatment at varying magnifications up to approximately 25x with the aid of direct light that can penetrate into the depths of the root canal. This means that visual inspection of the prepared root canal is possible. Once the canal has been shaped by conventional techniques and dried, the canal can be visually inspected both apically and laterally into the extensions of the canal. Straight canals can be inspected to the apical constriction. Since the rotary files straighten the coronal and middle thirds of curved canals, most of these prepared canals can be inspected to within a few millimetres of their full working length.
Inspection through the microscope at about 10x and above can identify those parts of the canal system that have not been touched by the rotary files and contain residual tissue (Fig. 5). These are usually the extensions of oval and flattened canals, isthmuses and fins.
The challenge is to prepare these areas producing a smooth predictable shape, without removing excessive tissue, allowing irrigants to penetrate into the canals more fully and therefore producing cleaner canals. Our expectations are that delivery of irrigants and medicaments using a variety of techniques into these parts of the canal anatomy will digest residual tissue material and entomb remaining bacteria, rendering them ineffective. While they have undeniable advantages in the parts of the canal system that cannot be inspected under the microscope, a significant part of the bacterial load within the canal can be removed by the use of a cutting instrument directed towards a specific part of the root canal such as a fin or isthmus. In the coronal part of the canal this can be done with either a long shank rosehead bur or a dedicated ultrasonic instrument. Long shank burs are very limited in their use, however because of the length of the shank, relatively large diameter of the bur, lack of visual access and they can only be used in the straight part of the canal. In the deeper parts of the canal ultrasonically activated instruments can be used to great effect.
A very effective solution is to use an ultrasonically energised K-file (UEFK), the very instrument that was discarded after the problems identified with ultrasonic instrumentation in the 1980s. The difference between then and now is that in conjunction with the use of the operating microscope the instrument can be used with a great deal of control. Also power settings have been considerably reduced to minimise the possibility of instrument separation. In many situations the UEKF overcomes many of the limitations presented by other ultrasonic instruments. The file can be curved in multiple directions so that the head of the ultrasonic handpiece does not impair visual access and the file can be shaped to follow the curvature of the canal. When used in conjunction with the operating microscope, the file can be directed to the part of the canal that has not been prepared by the rotary files. A size 20 UEKF with a 2 % taper is an optimal size although occasionally a larger file may be used. Because the file is relatively flexible and removes only 0.2 mm of tissue, unnecessary removal of dentine is kept to a minimum (Fig. 6).
The file works in multiple ways; it can be easily pre-curved to follow the canal curvature and can be used as either a cutting instrument by engaging the tip or as a planning instrument by using the flutes along its working length. When used as a planning instrument, it can be used with variable pressure against the walls of the canal such as in an oval canal extension or in an isthmus. The greater the pressure applied, the more effectively the file cuts dentine in the same way as a hand file, at the expense of the ultrasonic effect. As the pressure on the file is reduced, so the ultrasonic effect is increased, achieving the benefits of PUI. The effectiveness of this technique is enhanced by both the flexibility of the k-file so that it can be pre-curved and by its rigidity so that it can cut efficiently into a targeted area. The instrument can be used in both modes interchangeably just by varying the lateral pressure placed on the ultrasonic handpiece.
In endodontic retreatment cases both the UEKF and the dedicated ultrasonic tips can be used to great effect to remove endodontic obturation materials, separated instruments and posts using minimally invasive techniques. While the UEKF has to be used at low power settings to minimise the possibility of fracture, it allows for excellent visual control. The dedicated ultrasonic tips such as the EndoSucess ET 25 tip can be precurved to improve visual access and can be used at higher power settings. It is however only effective at its end. This tip is particularly useful for removing separated instruments. Other ultrasonic tips that cannot be pre-curved can only be used in straight parts of the canal.
The removal of gutta-percha from oval canals often presents a challenge as rotary instruments are not completely effective. A rigid ultrasonic tip is more like to plasticise the gutta-percha, while the UEKF with its increased tip amplitude, fragments the material.
Both ultrasonic and the microscope have become an essential part of the armamentarium in endodontics. When used together they can produce minimally invasive preparations, which produce cleaner canals in both primary and retreatment cases. Conventional irrigation strategies should always be employed, particularly in those areas of the canal system that cannot be visually inspected with the operating microscope such as in the curved apical third. However, the technique described above can aid in the reduction of the bacterial load within the canal system and this can result in more predictable outcomes.
Editorial note: A complete list of references are available from the publisher. This article was published in roots – international magazine of endodontology No. 04/2016.
An indirect method for provisionalisation: The team approach in a complete mouth hybrid reconstruction
Her chief complaint was to improve her aesthetics and comfort with a desire for a permanent and quick solution to replace her failing dentition. She…
Her chief complaint was to improve her aesthetics and comfort with a desire for a permanent and quick solution to replace her failing dentition. She also desires a reduction of her maxillary anterior gummy smile in the final prosthesis. She arrived at our office for a third surgical consult for an immediate load maxillary and mandibular hybrid restoration using the Straumann Pro Arch treatment concept (tilting of the distal implants to avoid anatomic structures of the maxillary sinus, mandibular mental foramina). This treatment concept reduced the need for additional surgeries and number of implants needed to provide a fixed hybrid restoration with a first molar occlusion. A medium to high lip line was noted upon a wide smile with a bi-level plane of occlusion. Also noted was supraeruption of her maxillary and mandibular anterior teeth (FDI: #12, 11, 21, 22 and #41–43, US: #7–10 and #25–27) creating a deep bite of 6 mm (Fig. 2). A Class I canine relationship was recorded with 6 mm overjet and 6 mm overbite. Due to her medication-related dry mouth issue, generalized recurrent caries were noted. Periodontal probing depths ranged generally from 4–7 mm in the maxillary jaw and from 4 to 6 mm in the mandibular jaw with moderate to severe marginal gingival bleeding upon probing in both jaws. Tooth #6 (FDI: #13) was noted to have a vertical fracture clinically. There was generalised heavy fremitus in her maxillary teeth and mobilities ranging from 2–3 degrees on the following teeth: #3, 7 thru 13, 20–26 and 29 (FDI: #16, 12, 11, 21–25, 31–35, 41–42 and 45). Her compliance profile was good with her previous dentists, however, she states that she has always had “issues with my gums.”
The tentative treatment plan discussed at the initial visit with the patient and her husband included the following diagnosis: generalised moderate to advanced periodontitis; generalised recurrent caries related to medication-related dry mouth; posterior bite collapse with loss of occlusal vertical dimension (“mutilated dentition”). Prognosis: all remaining teeth are hopeless.
Based on CBCT analysis it was decided to place five implants in the upper jaw at the following sites: #4 (FDI: #15) (tilted), #7 (FDI: #12), between #8 & #9 (FDI: #11 & #21) (midline), #10 and #12 (FDI: #22 and #24) (tilted) after vertical bone reduction for prosthetic room. Four implants were anticipated to be placed in the lower jaw at sites #21 (FDI: #34) (tilted), #23 (FDI: #32), #26 (FDI: #42), & #28 (FDI: #44) (tilted). The anticipated position of each implant is ideally palatal in the maxilla to the original teeth and lingual to the original mandibular teeth. This is to allow for screw-access holes exiting away from the incisal edges anteriorly, and if possible, lingually to the central fossae in the posterior sextants. An additional benefit of palatal and lingual placement of each implant is that their final position will be at least 2–3 mm from the anticipated buccal plates, which is beneficial for long-term bone maintenance and implant survival. If the necessary 2 mm buccal bone to the final implant position is not available, then contour augmentation (bone grafting) is recommended to create that dimension. The goal is to prevent buccal wall resorption over time using slowly resorbing inorganic bovine bone and a resorbable collagen membrane. This membrane allows easy contouring and flexibility over the graft material when wet. It is also important to evaluate tissue thickness. It is ideal to have at least 2 mm of buccal flap thickness over each implant as thin tissues are associated with bone loss and recession over time. Either connective tissue grafts from the palatal flap or tuberosity can be harvested and sutured under the buccal flap. Alternatively, an allograft connective tissue or a thick collagen material can be used to thicken the buccal flaps when necessary.
The patient was pre-medicated with oral sedation (triazolam 0.25 mg), amoxicillin, a steroid dose pack and chlorhexidine gluconate (CHG) rinse, all starting one hour prior to surgery. The patient’s chin and nose were marked with indelible marker, and the OVD was measured using a sterile tongue depressor with similar markings while the patient’s mouth remained closed. The patient was then given full-mouth local anaesthesia.
Starting with the maxillary arch, full-thickness flaps were raised and sutured to the buccal mucosa with 4-0 silk to provide improved surgical access and vision. The teeth were removed with the goal of buccal plate preservation using the PIEZOSURGERY (Mectron: Columbus, OH) for bone preservation (tips EX 1, EX 2, Micro saw: OT7S-3). The sockets were degranulated with PIEZOSURGERY (tip: OT4) and irrigated thoroughly with sterile water.
With the anatomically correct surgical guide in position and firmly held in place by the surgical assistant, measurements were made from the midbuccal of each tooth. Surgical cuts were made going from the anticipated cantilever of site #3 (FDI: #16) to site #14 (FDI: #26) using the PIEZOSURGERY saw (tip: OT7). Our team goal was to create the prosthetic room necessary for a hybrid restoration i.e. 10–12 mm. The cuts were intentionally extended beyond the anticipated cantilever length to create adequate strength and thickness of the final prosthesis in these unsupported cantilever areas (Figs. 5–6). The mandibular arch was treated in a similar manner. Additionally, bilateral mandibular tori reduction was accomplished with the aid of the PIEZOSURGERY saw (tip: OT7) after the extractions and prior to the vertical bone reduction of the mandibular ridge. Subsequently, the implants were placed.
The implant sites were prepared per the manufacturer’s protocol (except for bone tapping) for the Straumann BLT implant. The implants were placed using the surgical guide template with the following insertion torques measured: site: FDI: #15, #12, #11, #21, #23, #25, #34, #32,#42/US: #4, #7, #8-9, #11, #13, #21, #23, #26. All torques were >35 Ncm with #28 (FDI: #44) recording 20 Ncm insertion torque values. All implants were 4.1 mm in diameter and 14 mm in length except FDI: #12, #11, #21, and #23/US: #7, #8–9, and #11, which were 12 mm in length (Fig. 7). All 17 and 30 degree angled implants were bone profiled prior to SRA abutment placement. This allowed the complete seating of the SRA abutment at the recommended 35 Ncm torque. Using the available Straumann bone profilers with the appropriate Narrow Connection (NC) or Regular Connection (RC) inserts was a critical step for an abutment to fit correctly. The following SRA abutments (all were 2.5 mm gingival heights) were then chosen: straight: FDI: #32, #42/US: #23, #26; 17 degrees: FDI: #15, #12, #11, #21/US: #4, #7, #8–9; and 30 degrees: FDI: #23, #25, #34, and #44/US: #11, #13, #21, and #28. Tall protective healing caps were then placed (Fig. 8), and the dentures were checked to evaluate that there was adequate space for the pink acrylic to allow for bite registration material thickness. All sockets and buccal gaps to the immediately placed implants were bone grafted. Prior to suturing, the tissue flaps were scalloped with 15c blades to reduce overlap of the flaps over the protective caps. This not only aided in post-operative healing, but also aided in the visualisation of the abutments by the restorative dentist for the provisional insertion. The patient was sutured with resorbable 4-0 chromic gut and 5-0 Vicryl sutures (Ethicon: Johnson & Johnson) and was released to be seen immediately by Dr Randel for the coordinated restorative visit.
As discussed below, his responsibilities included: bite registration, impressions, and the dental lab conversion of the complete denture to a metalreinforced fixed transitional prosthesis (indirect provisionalisation technique). Our team of restorative dentists have been treating full-arch immediately loaded cases on 5–8 implants (depending if restoration is a hybrid or C&B) since 1994. Our earlier experiences, for approximately the first two years (1994–1996), have resulted in us all presently using the indirect technique, which in our hands is easier for everyone involved (especially the patient). We handle these coordinated visits between offices, the dental lab, and our Straumann representative weeks in advance so we are all on the same page with timing. These coordinated efforts could be compared to a symphony orchestra, where each musician knows their specific part and when and where they are expected to be. Many of our patients have described this fluidity as a seamless experience that they witness first hand and greatly appreciate.
Same-day restorative appointment
The patient was seen in Dr Robert Levine’s office for restorative records with Dr Randel (prosthodontist) in preparation for immediate load protocol. The previously processed dentures were first checked with pressure paste to ensure the absence of contact between the intaglio surface and the tall healing caps. Bite registration material was then used to confirm there was no contact (Fig. 9), and later will be used by the lab to articulate the models. Efforts were made to confirm the OVD (with the marked tongue depressor provided by Dr Levine), incisal position, midline, plane of occlusion, and centric position with the prosthesis in place. Adjustments were made as needed. Photographs were acquired to document and relay information via e-mail to the lab technician. The lab will use the registration material left in the intaglio surface of the prostheses, as healing caps will be placed on the newly fabricated models. This allows the index to transfer the OVD and centric relationships with contact just on the healing caps. The soft tissue plays no role in this relationship. A bite registration was made to confirm centric relation. Healing caps were then removed and open tray impression copings were placed. If the connection between the implant abutments and the impression copings are not visualised, then X-ray confirmation of the connection is needed. Transfer impressions were made using a custom tray and rigid impression material of choice, in this case polyether was used.
Our lab courier delivered the dentures and impressions to the lab for the conversion to metalreinforced, screw-retained provisionals, which were delivered back to the restorative office within 24 hours. The next afternoon, the prostheses were inserted (Fig. 10) and panoramic radiographic confirmation of proper seating was obtained (Fig. 11). Any necessary occlusal adjustments were then completed. The patient was then seen every two to three weeks for deplaquing and plaque control review per our earlier discussed protocol. The occlusion was also refined as needed. The patient’s TMJ symptoms were significantly reduced within the first three weeks. A water irrigation device was given and reviewed at six weeks post-surgery. As the patient was in Florida for the winter, and unable to come in after the typical three-month protocol, she was seen 4 1/2 months after the surgery. At that time, periapical X-rays of each implant were done to confirm bone healing. The prostheses were removed and cleaned. GC verification jigs (Fig. 12), made on the original models and fabricated prior to the appointment, were tried in. If passivity is not confirmed, then the GC jig can be cut and re-indexed.
Once the fit of the verification jigs was confirmed, custom trays were used to transfer the relationships (Fig. 13). During the following appointments, OVD and centric relations were obtained, and the waxtry-ins were confirmed for aesthetics, phonetics, and occlusion prior to the milling of the framework (Fig. 14). It is important to confirm tooth location prior to milling the framework so that the framework was designed within the parameters of the acrylic/tooth borders. At the insertion appointment, the healing caps were removed and cleaned with chlorhexidine. Figure 15 demonstrates the excellent healing of the soft tissue prior to insertion of the prosthesis. Once inserted, aesthetics, phonetics, and OVD of the prosthesis were confirmed. The occlusion was adjusted as needed. Screws were tightened to 15 Ncm, screw access openings were filled with Teflon tape to within 2 mm of the surface, and a soft material such as Telio or Fermit was used to seal the access. A maxillary acrylic nightguard was fabricated to help protect the occlusal surfaces from wear and reduce any parafunctional habits. The completed case is shown (Figs. 15–18). At subsequent appointments, the prostheses were evaluated to determine if they needed to be removed to assess the soft tissue or if any contouring of the acrylic was necessary. Eventually, the soft material used to close the access can be replaced with a hard composite material.
A Complex-SAC Straumann Pro Arch Case was presented. Management of this treatment utilised the advantages of the team approach for maximising our combined knowledge to benefit the patient, consistent with ITI doctrine. The use of the BLT implants, due to excellent initial stability, gave us the confidence in our ability to not only use immediate extraction sites (Type 1 implant placement), but also to increase avoidance of anatomic structures. In this case, the structures include the maxillary sinuses, nasopalatine and mental foramina, as well as the inferior alveolar nerve canals. In addition, with the tapered design of the BLT implant, maxillary anterior areas could be utilised by the surgeon to avoid apical fenestrations where undercuts could become problematic using straight-walled bone level implants. The coordinated appointments, along with the symphony-like steps in the procedure, created a positive, “seamless” experience for the patient.
This article was published in CAD/CAM international magazine of digital dentistry No. 04/2016.
Guided surgery for single-implant placement: A critical review
Case description Electronic and manual literature searches of clinical studies published between January 2002 and May 2015 were carried out using specified indexing terms. Outcomes…
Electronic and manual literature searches of clinical studies published between January 2002 and May 2015 were carried out using specified indexing terms. Outcomes were accuracy, Pink Esthetic Score, and clinical outcomes (implant and prosthetic survival rates, complications, and marginal bone loss).
A total of 706 titles and abstracts were found during the electronic and manual searches, but 563 publications were excluded (inter-reviewer agreement k = 0.78). The full texts of the remaining 143 publications were evaluated. A total of 125 papers had to be excluded because they did not fulfill the inclusion criteria (k = 0.99). Three manuscripts were added from the reference lists of all of the selected articles. A total of 21 articles were thus selected that fulfilled the inclusion criteria of and quality assessment required for this critical review.
Despite the high accuracy and a cumulative survival rate of 100%, there is little evidence to support the hypothesis that there is a clinical advantage of computer-assisted, template-based implant placement over conventional treatment protocols for the placement of an implant-supported single-tooth restoration. Long-term randomized clinical trials are needed to confirm these preliminary results.
Editorial note: The full article was published in the 4/2016 issue of the Journal of Oral Science and Rehabilitation. It can be access free of charge at www.dtscience.com.
Augmentation and implant treatment: Two-stage surgery in the severely resorbed edentulous mandible
Distant donor sites like the anterior and posterior iliac crest and intraoral areas like the retromandibular and the interforaminal region of the chin are common…
Distant donor sites like the anterior and posterior iliac crest and intraoral areas like the retromandibular and the interforaminal region of the chin are common sources for harvesting autogenous bone-grafts. Depending from the donor site, patient and surgeon should be aware of the possible confrontation with various advantages but also disadvantages when harvesting the bone. Harvesting bone from the iliac crest requires patient hospitalisation, and surgery under general anaesthesia, whereas intraoral bone harvesting can be performed ambulatory and under local anaesthesia.[2,3] The main problem with autogenous bone grafting is represented by the high risk of patient morbidity, causing pain, swelling, and healing problems at the donor site.
The aim of this case presentation is to demonstrate a predictable, two-stage operating protocol for the horizontal augmentation of the severely resorbed, edentulous anterior mandible with an autogenous bone graft, harvested from the crestal alveolar ridge at implant site, in order to create a sufficient bone volume for the later implant therapy, without donor morbidity for the patient.
The 47-year-old male patient visited our dental office in order to renew his old and poor fitting prostheses in the lower and in the upper jaw. The remaining five teeth 32–43 in the front of the lower jaw had been removed three months previously due to a chronic periodontitis in our dental practice. Nearly all remaining teeth in the upper and the lower jaw showed significant signs of progredient chronical periodontitis, insufficient root treatments and prosthetic suprastructures as well (Fig. 1). The medical history of the patient was without any significant pathological findings.
In cases of long-term edentulism, the dental surgeon is almost always confronted with a reduced bone volume, representing both a major challenge and a significant demand for the use of diagnostic imaging methods prior to augmentation and implant treatment. Conventional X-ray images contain only a two-dimensional information concerning the vertical height of the alveolar bone. Therefore, they represent an insufficient method for the appreciation of the horizontal bony dimensions. In comparison, three-dimensional (3-D) diagnostic tools like cone beam computed tomography (CBCT) offer the advantage of the visualisation of the so called ‘z-axis’, representing the bone volume in the horizontal, i.e. bucco-lingual dimension of the alveolar crest respectively. A proper treatment planning and the use of 3-D diagnosis are therefore crucial parameters for a predictable and sustainable final treatment outcome in implant therapy, especially in patient cases with severe resorption of the jawbone, like in our presented patient case.
The oral examination and the CBCT scan (SCANORA, SOREDEX, Schutterwald, Germany) revealed a distinct bone resorption in the lower jaw, showing a more pronounced horizontal atrophy in the anterior part of the mandible (Figs. 2 & 3). According to the clinical measurements and the values of the 3-D CBCT scan, the interforaminal vertical bone height was between 22.0–25.0 mm. The horizontal bone volume amounted to between 1.0–3.0 mm in the implantation zone. The CBCT scan revealed a horizontal crestal bone thickness of 1.09 mm in region 32, and 1.74 mm in region 44.
Treatment planning and augmentation procedure
After patient-consultation, we opted for a twostage surgery with an intraorally harvested autogenous bone-graft and a delayed implant treatment after a healing period of at least four months. As the vertical dimension of the implant region appeared to be sufficient enough for placement of implants with a standard length, we decided to cut off 5.0 mm of the thin and sharp-edged alveolar ridge by osteotomy, in order to create an autogenous lateral onlay bone-graft for horizontal augmentation in the anterior alveolar ridge. This protocol comprised in our view the advantage of the avoidance of donor morbidity, because the donor site was the receptor site as well. After creation and mobilisation of the mucoperiostal flap, the very thin and sharp edge of the atrophied alveolar crest became visible (Fig. 4). The osteotomy of the bone was performed with a saw (Bone splitting system, Helmut Zepf Medizintechnik GmbH, Seitingen-Oberflacht, Germany; Fig. 5). Subsequently, the graft was detached from the anterior mandible with chisel (Bone splitting system, Helmut Zepf, Medizintechnik GmbH, Seitingen-Oberflacht, Germany; Fig. 6) and a cortico-cancellous bone block was obtained (Fig. 7). The bone graft was fixed at the buccal side of the anterior mandible (region 34–44) with four 8.0 mm long titanium microscrews (Storz am Mark GmbH, Emmingen-Liptingen, Germany; Fig. 8). A combination of autogenous bone chips and particulated xenograft (BEGO OSS, BEGO Implant Systems, Bremen, Germany) was placed in the small remaining space between the bone block and the alveolar processus, as well as around and on the bone graft. The augmented site was covered with a platelet rich in growth factors (PRGF) membrane (BTI Biotechnology Institute, Blue Bell, USA) and additionally with a barrier membrane for guided bone regeneration (GBR, Bio-Gide, Geistlich Biomaterials Vertriebsgesellschaft mbH, Baden-Baden, Germany; Fig 9). The healing of the graft was uneventful and without any complications, like membrane exposure, being classified as a frequent post-operative complication. The patient was provided with a removable provisional prosthesis.
Re-entry and implant surgery
The re-entry for the delayed implant placement protocol was planned after a healing period of four months. With regard to the soft aspect of the augmented area of the anterior mandible, the dimensions of the alveolar ridge appeared sufficient enough for implant placement (Fig. 10). The CBCT data confirmed the assumption, demonstrating a significant gain of bone volume in the interforaminal region of the mandible after augmentation. The horizontal thickness of the crestal alveolar bone was 5.53 mm in region 44 and 4.43 in region 32. The augmentation procedure resulted in a horizontal bone gain of about 3.9 mm in region 44 and 3.3 mm in region 32 respectively, representing a mean bone gain of 3.6 mm (Fig. 11). After elevating the flap, an apparently good osseointegration and stabilization of the autograft with the underlying pristine bone could be noticed (Fig. 12). Prior to implant placement, the fixation screws were removed. The four implants with a diameter of 3.75 mm and a length of 11.5 mm (BEGO Semados RSX, BEGO Implant Systems) were inserted epicrestally in regions 33, 31, 41 and 43 using the freehand-method without a surgical guide (Fig. 13). The insertion torque of the implants was 35 Ncm with good primary stability.
Pre-prosthetic surgery and prosthetic rehabilitation
After three months of uneventful submerged healing, the panoramic X-ray showed a successful implant osseointegration without any signs of bone resorption (Fig. 14). Due to a lack of keratinised gingiva, we decided for an enlargement of the ratio between attached and free gingiva by performing muco-gingival surgery with the Edlan-Mejchar method (Figs. 15, 16 & 17). After an additional healing period of one month, the final bar retained, a removable acrylic overdenture was incorporated. The bar was constructed with bar abutments (PS TiBA, BEGO Implant Systems) and a non-precious alloy (Wirobond, BEGO Dental, Bremen) and was screw-retained on the four implants (Figs. 18, 19 & 20).
In our case presentation, the patient suffered from an extremely horizontal bone resorption, resulting in a 1.0–3.0 mm thin, and knife-edged alveolar crest. Since standard diameter dental implants need a certain crestal bone volume for an adequate stabilisation and a good and predictable osseointegration, augmentation procedures had to be performed prior to implant treatment.
A recently published meta-analysis showed that dental implant survival has probably to be seen independently of the biomaterial used in augmentation procedures.[7,8] Since this evidence is limited by the fact, that defect size, augmented volume, and regenerative capacity are scarcely well described in literature, autogenous bone is still recommended as the ‘gold standard’ for augmentation in the deficient alveolar ridge. Simultaneous grafting and augmentation is the standard procedure in ridge augmentation, resulting in an extended operating time. Fortunately, as the vertical dimension of the anterior mandible was high enough in our clinical case, we were able to harvest an adequate autogenous bone block from the thin alveolar crest, in order to use it as an onlay graft for the horizontal augmentation of the anterior mandible. This procedure avoided donor site morbidity, and resulted in less operating time and a reduced patient discomfort. The dimensions of the graft were ideal for lateral augmentation, so that there was no need for any additional carving of the bone block. As mean bone gain after healing of the autogenous graft was 3.6 mm in our patient, it was slightly smaller compared to the average bone gain of 4.3 mm, as reported in a systematic review by Jensen and Terheyden in 2009, but was comparable to the findings of a recent review by Sanz-Sanchez et al., showing a mean bone gain in horizontal defects of 3.9 mm in a staged approach. Nonetheless, we gained enough bone volume for insertion of four standard diameter implants. Considering the fact that the fixation screws had to be removed, and with regard to a number of benefits of a delayed implant placement in augmented deficient alveolar ridges, we opted for a two-stage protocol. Even though delayed implant placement with flap elevation required a second surgical intervention and therefore an additional burden for the patient, it comprised the additional advantage of a visual and tactile assessment with respect to the osseointegration of the autograft in our patient case. Another crucial advantage of the staged approach comprised inter alia the possibility for an implant placement in an ideal position for the later prosthetic restoration under visual control. Another reason for open access for implant placement was the use of non-resorbable microscrews for the stabilisation of the bone graft. The decision to utilise non-resorbable titanium screws in favour to resorbable screws out of poly (D,L-lactide) acid, was supported by the findings of a systematic review of the Cochrane Collaboration. Thus, resorbable screws seem to have a high susceptibility for fracture during fixation of onlay grafts. As the combination of autogenous grafts with guided bone regeneration (GBR) is apparently associated with superior outcomes, we decided to use a barrier membrane. With the additional application of a PRGF membrane, we aimed to utilise the beneficial effects of platelet-derived rich plasma for an advanced wound therapy, and the reduced risk of post-operative infection. The vestibuloplasty with the Edlan-Mejchar method was performed for two purposes. Firstly it was done in order to create a sufficient amount of keratinised mucosa. According to findings of a systematic review, published by Linet al., a lack of keratinised mucosa around implantsfosters plaque accumulation, inflammation, and soft-tissue recession. Secondly we aimed to create enough space for the final overdenture.
The staged approach with the use of an autogenous bone graft, harvested from the surgical site in the anterior mandible, resulted in a significant horizontal bone gain, and took to a good osseointegration of both, autograft and implants. Obviously, the described grafting procedure has not been previously reported in literature. Despite the lack of any experience reports, our method revealed nonetheless a successful rehabilitation with an implantsupported, screw-retained prosthetic rehabilitation, and is still in function without any biological or technical problems after a three-year follow up.
Special thanks to Dr Pantelis Petrakakis.
Editorial note: A list of references is available from the publisher. This article was published in CAD/CAM international magazine of digital dentistry No. 04/2016.
Exploring the fracture resistance of retentive pin-retained e.max press onlays in molars
Introduction The loss of tooth structure, from disease or biomechanical stress, requires the replacement of tooth structure through dental restoration techniques.This may occur either directly…
The loss of tooth structure, from disease or biomechanical stress, requires the replacement of tooth structure through dental restoration techniques.This may occur either directly or indirectly. Extensive tooth restorations typically require indirect restorations. Indirect dental restorations benefit from excellent form, function, esthetics, and strength; however, the retention of indirect restorations can prove problematic. This is primarily due to variable technique-sensitive chemical bond of the restorative material with the tooth. The type of restoration used largely depends on the magnitude of tooth destruction and dictates unique preparation design characteristics.
With the increasing demand in esthetics, use of ceramics has become more prevalent in restorative dentistry. E.max, a ceramic and metal-free restorative material, has been demonstrated to be an extremely strong, dependable restoration with ideal esthetics. It is a highly biocompatible glass ceramic composed of lithium disilicate. E.max is also among the most durable dental materials to date. Previous studies have concluded that e.max poses no health risk to dental patients and has little potential to cause irritation or sensitizing reactions, when compared to composite or gold restorations.
Although the primary retention of an indirect restoration is based on bond strength, secondary elements can be introduced to further increase surface area and retentive strength, such as pins. Traditionally, retentive pins were employed to offer significant retention to direct restorations when minimal tooth structure remained. Effective utilization of pins required proper application of biomechanical principles in each clinical case. Adequate dentin, to support the pin, remains an important factor in the evaluation of the clinical success of retentive restorations. The type of pin used also determines the success rate of the restoration. Among the two pin types, titanium retentive pins have been found to be highly biocompatibility with minimal corrosive activity.
Due to the sensitivity of indirect restoration bonding and resultant retention, an investigation on whether the use of titanium retentive pins would offer an increase in fracture resistance seemed fitting. If there was a significant increase in fracture resistance between the restorative material and the tooth, pin reinforced e.max press restorations could justify further investigation. In addition, with advances in 3-D intra-oral imaging and CAD/CAM, a digital work flow would provide a simple and predictable clinical alternative.
Materials and methods
Human extracted molar teeth were used for this investigation. They were sorted and randomized. A total of 20 extracted molar teeth were used. The control group contained ten molar teeth. Each tooth was prepared for a four surface onlay restoration which did not incorporate pins. The test group included ten molar teeth. Each tooth was prepared for a four surface onlay restoration which did not incorporate pins. Each four surface e.max onlay restoration preparation had either the buccal or lingual wall remaining intact (Fig. 1) following standard pin-retained amalgam guidelines. Titanium pins with a diameter of 0.6 mm were used (Stabilok; Fairfax Dental Inc.). Two pins were placed in each tooth at the appropriate line angles; pin 1 was placed on the mesial side whereas pin 2 was placed on the distal side of each molar tooth (Fig. 2). Pins were inserted to a 2 mm depth. The top 1mm was sheared off and smoothed. Pin length was slightly variable among the teeth. Radiographs were taken in a buccolingual and mesiodistal fashion to verify pin placement (Fig. 3). All tooth specimens were packaged and sealed in a moisture controlled container and shipped to a dental laboratory (DentUSA) for restoration fabrication with e.max press (IPS e.max Press; Ivoclar Vivadent). Specimens were returned in the same manner along with the e.max onlay restorations (Figs. 4 & 5). Tooth specimens and restorations were prepared and bonded (Fig. 6) using Multilink adhesive cementation system (Multilink Automix; Ivoclar Vivadent) following manufacturing recommendations.
Cement flash was removed and the restorations were polished following standard Schulich Dentistry protocols. The prepared tooth was fixed with ortho resin (Fig. 7) (acrylic resin, DENTSPLY Caulk) in the stabilization ring (Fig. 8). A universal loading machine (Instron laboratory testing unit: ITW) was utilized to apply an axial load to the tooth until the tooth fractured (Fig. 9). The machine applied pressure at a maximum crosshead speed of 0.5 mm/min. Tooth fracture was assessed visually and measured in Newtons for all the teeth in the control and test groups (Fig. 10).
The force (Newtons) required to cause fracture of either the restoration or tooth, or a combination of the two, was extremely variable (Table I). The test group suggested greater variability among the values and the highest fracture resistance value. There was no significant difference in the fracture resistance between the non pin-retained e.max press restorations and the pin-retained e.max press restorations (Fig. 11). An unpaired t-test result using P < .05 was P = .4443 in this assessment. Data were obtained by using an analysis of variance (ANOVA). Significant differences were set at a .05 level (Fig. 11).
Table1: Fracture resistance values for samples (Newtons)
Control Group (N)
Test Group (N)
There was no statistical difference between the control group (non pin-retained restorations) and the test group (pin-retained restorations) in fracture resistance. The results indicated that the test group exhibited greater variability. This could be due to pin location, pin length, differences in pin angulations or variations in the width of the onlay preparation margin. The highest fracture resistance value was a pin-retained e.max onlay, which could be related to the increased surface area and subsequent bond strength. Pin-retained e.max onlays had a tendency to fracture in a very controlled manner, with much of the tooth-restoration complex remaining intact. Conversely, non pin-retained e.max onlays typically fractured in such a violent manner that the tooth-restoration complex was destroyed.
Due to the degree of variability, further laboratory testing would be warranted with a larger sample size. A clinical investigation, highlighting the procedural aspects, would also be an ideal extension of the research. Further studies should isolate variables and establish a greater sample size. With advances in technology, the digital workflow of records, design and output could be easily implemented for pin-retained restorations. It has been previously shown that digital impressions have the ability to capture all aspects of a pin-augmented substructures (Fig. 12). It has also been demonstrated that CAD/CAM technology has the precision and accuracy to mill (Fig. 13) the subsequent pin-bored restoration from an e.max CAD block. A digital approach seems to represent a simple and predictable chair-side alternative for the clinician.
This study explored combining retentive titanium pins with indirect e.max press onlay restorations in extracted human molar teeth. Teeth were then subjected to axial loading in a universal loading machine. There was no statistical difference in fracture resistance between the two groups. However, the highest fracture resistance was displayed from a pin-retained e.max onlay. This may be related to the increased surface area and subsequent bond strength. Observationally, pin-retained e.max onlays fractured in a manner that seemed more controlled than non pin-retained onlays.
Digital dentistry could simplify this potential alternative by providing the clinician with the tools required to acquire the digital impression, design and fabricate the final restoration. Although pin-retained was termed for the investigative restorations, perhaps pin-reinforced would seem more logical. Further investigations are required to substantiate the research and identify whether this approach may be considered as a clinical alternative.
Conflict of Interest
Research was supported by the Schulich Dentistry Summer Research Project and by Research Driven Inc. Les Kalman is the co-owner and President of Research Driven Inc.
The authors thank Victoria Yu, a dental summer student, who assisted with aspects of the methodology, and Dr. Amin Rizkalla, BSc, MEng, PhD, Associate Professor & Chair of the Division of Biomaterials Science, who facilitated the testing.
Editorial note: A complete list of references is available from the publisher. This article was published in CAD/CAM international magazine of digital dentistry No. 04/2016.
Manager versus clinician
Creating and managing realistic expectations Expectations are difficult to control and impossible to turn off. According to Brazos Consulting, “Expectations are deeper and broader than…
Creating and managing realistic expectations
Expectations are difficult to control and impossible to turn off. According to Brazos Consulting, “Expectations are deeper and broader than ‘requirements’. Expectation is your vision of a future state or action, usually unstated but which is critical to your success.” By learning to identify and influence what you expect, and by ensuring it is clearly communicated, understood and agreed with your manager, you can dramatically improve the quality, impact and effectiveness of your business.
Expectations are created by many different circumstances. It may be something you said or the way that you said it, something you or someone else did, or an expectation of your prospective manager based on his or her previous experience. The vital point here is that expectations, whether right or wrong, rational or otherwise, are not developed in a vacuum. You should consider instances when you were let down by your manager and ask yourself how that expectation was derived. Was it based on an agreement with your manager after a discussion or was it based on something you said or thought in passing? In retrospect, you may wonder how realistic that expectation was and why you thought your manager was in the strongest possible position to fulfil it.
In my experience, the following scenarios are typical of how unrealistic expectations are created:
- The practitioner is busy and needs someone to take charge. He or she chooses the “best of the bunch”, hoping he or she will learn on the job.
- The new manager has his or her expectations of the job and these are often unrealistic.
- No detailed job description or objectives are ever provided. No on-the-job or any other type of training is provided; the practitioner simply assumes the manager will learn as he or she goes along.
- The manager is excited about the new position. For some, the empowerment, the title and the kudos mean a great deal; for others, the challenge and the task at hand mean more. When reality hits, so does the realisation that the original motivating factors are no longer as important.
- Both practitioner and manager are reticent to discuss what is not working and often brush the issues under the carpet until it is too late.
- Resentment grows and what is at stake—the patients, the practice and the staff—outweighs the actual issue, which is poorly managed expectations.
Of course, there are many practices managed by very capable staff members. However, for all the well-functioning practitioner–manager relationships, there are more people in these roles who prefer not to talk about the problems inherent within and who are only too glad for someone else to address the issues.
One of my aims is to facilitate management teams to assess where they are at present, to plan for appropriate change and to implement that change. The outcome is that a weight is lifted from your shoulders and focus moves to a united partnership working towards the success of the practice. In order to move forward, however, you must recognize where you are now.
An alternative approach
The first step towards achieving a successful management partnership is to honestly appraise your current situation. If anything I have said so far has touched a nerve, if frustration exists between you and the manager, or if you simply think things could be better, then acknowledge the fact and take action. Knowing what action to take for the best is probably the most difficult thing to assess.
The following are tips on getting started: Vocalize your vision, agree that your vision is realistic and share it with your team. Create a job description with and a training plan for your manager, as well as identify skills gaps and create smart objectives with and for her or him. Also agree and schedule regular one-to-one meetings and plan to assess and review with your manager. Most importantly, however, keep communicating.
Drive your success
Expectations always exist, even if we do not know what they are and despite them often being unrealistic. Managers have expectations of their roles and their employers have expectations of the person given responsibility for managing the practice. The problem is that mismatched expectations can lead to misunderstanding, frayed nerves and ruffled feathers. More seriously, they often lead to flawed systems, failed projects and a drain on resources.
There is nothing wrong with having expectations; the trick is to communicate them and to agree how they might be satisfied over time and with the right support. Managed expectations drive your success.
Editorial note: This article was published in CAD/CAM international magazine of digital dentistry No. 04/2016.
MIS announces release of B+ implant surface
Dr Björn-Owe Aronsson, who developed this unique surface together with his team at Nano Bridging Molecules, has presented case studies in which B+ proved very…
Dr Björn-Owe Aronsson, who developed this unique surface together with his team at Nano Bridging Molecules, has presented case studies in which B+ proved very efficient in maintaining the bone level over time. This is particularly beneficial for patients with compromised bone healing and poor blood supply. The specific bone-bonding properties of the surface have proved to produce greater fixation of the implant in the early stages post-placement, as well as greater stability later on.
Aronsson explains: “Titanium is used as implant material due to its inertness and high acceptance by the body. Over the years, however, a wish for faster and more predictable integration with the bone has been driving research on the importance of the surface structural and chemical properties.”
The surface consists of a monolayer of multi-phosphonate molecules. These have a very high affinity to titanium dioxide, enabling a true covalent bond. The unique properties of this layer also make it extremely hydrophilic, which facilitates the colonisation of cells on the surface naturally. Research has even shown that blood vessels grow directly into the surface of the implant, which is unaffected by the oral environment and has been proved very stable in different pH levels.
“With the initial results from testing of the B+ surface, it was discovered that, for the first time, specific biochemical bonding can be obtained already at the very early healing phase after implantation,” Aronsson said.
MIS was very excited to learn about these discoveries and immediately saw the potential for a major breakthrough. Having been seeking a suitable company to partner with, Aronsson and his team were equally enthusiastic about embarking on the commercialisation phase with a company able to achieve rapid implementation in clinical practice and with a strong position in the market to advance their product.
Most recently, MIS has launched a user experience project involving 250 participants worldwide, who will be placing ten implants each with the B+ surface and reporting their experiences. The results of studies conducted by Aronsson and his team are extremely promising and both partners are exploring future applications for this advancement.
Long-term analysis of primary, non-surgical root canal treatments – A retrospective study
Introduction Studies feature the evaluation of factors with the treatment aim of healing and retention in a symptom- free environment. Evaluation of success/failure is partly…
Studies feature the evaluation of factors with the treatment aim of healing and retention in a symptom- free environment. Evaluation of success/failure is partly based on X-rays only, and partly on X-rays plus clinical situation. According to Schmalz1, X-rays are not an absolutely reliable parameter. Furthermore, studies[2,3] show that the bias of the reviewer influences the interpretation of the X-ray. Finally, various improbabilities affect evaluation.
Ng et al.4 evaluated 76 studies from 1922–2002 in a systematic review. Various studies showed an average success of 74.7 % based on strict criteria, and a success rate of 85.2 % based on loose criteria. When using strict criteria, the success rate increased with duration of follow-up period—from 67.3 % after 24 months to 85.4 % after 48 months. In a follow-up publication based on 63 studies, the authors analysed parameters regarding their influence on the success of the root canal treatment (RCT). Using strict criteria, they determined four main factors: apical periodontitis (AP), quality of root canal filling (RF) homogeneous versus nonhomogeneous, length of RF, and quality of restoration. They ascribed a success of 82.5 % to vital teeth, and a success of 73.1 % to non-vital teeth. The lowest success rates could be observed in mandible molars, patient age > 50. In a systematic review of 14 survival studies Ng et al. showed that survival rates concerning extractions showed better results than success rates. The study of Lee et al. features a clear comparison of the evaluated comparison parameters success/survival.
Materials and methods
The author, who started as a dental practitioner in 1969, used the 9,988 non-surgical endodontic treatment cases registered in his patient files from 1985 to 1999. Of these, X-rays were no longer available in 518 cases. Five teeth were extracted immediately upon noticing of via falsa. Eight hundred and twenty-one cases had not returned to the practice after RCT, however they were included in the dropout rate without further analysis. Thus, 8,644 cases of vital and non-vital teeth at 3,951 patients remained for analysis. The non-vital cases had been applied to a former study8 with shorter follow-up-time, exclusion of molars and X-ray-rating of three reviewers. The observation period ended in September 2006. A recall of the patients did not take place. Considering extractions and remaining cases after 5, 10, 15 and 20 years, drop-out rates amounted to 40.6, 58.5, 72.2 and 81.7 %.
RCTs were carried out according to the N2-method of Sargenti. This method includes the use of the paraformaldehyde-containing zinc oxide root canal cement N2 and canal preparation without canal rinsing. Canal preparation was solely done manually by reamer: using step-back technique in vital teeth, crown-down technique in non-vital teeth. The creamy N2 composition was applied to the root canal by lentulo instruments. A gutta percha point was added in wide canals only. The RF-sitting were always finished by a definite filling as well as a provisional crown, if needed. The adequate length of the RF was considered to end in the area of the radiological apex up to –2 mm, an RF level of < –2 was determined as underfilling, an RF level of > 0 as overfilling. RF-quality was judged according to its homogeneity. X-rays were taken and diagnostics were performed by the author himself. Follow-up X-rays were only evaluated one year or more after RCT. According to the European Society of Endodontology (ESE) quality guidelines, the ‘follow-up’ diagnoses were classified into three criteria:
- Diagnosis 1 (success): Regular periodontal gap in X-ray, no symptoms, no fistula, no swelling;
- Diagnosis 2 (uncertain result): AP after < 4 years, incomplete healing, not to be evaluated, scar tissue, remaining shadow around overfilled root-canal;
- Diagnosis 3 (failure): AP still existing > 4 years, newly developed AP, clinical symptoms.
In multi-canal teeth, the root canal with the poorest prognosis was selected as being relevant for the analysis. The present study contains an analysis of success/failure and survival of root-filled teeth with reference to re-intervention: extraction, retreatment (RTR), root-end-resection (RER), trephination (TR), hemisection (HEM). Failures were divided into:
- Clinical failure: no follow-up X-ray accompanying acute exacerbation, pain, swelling, fistula;
- Failure with follow-up X-ray.
The statistic evaluation was executed with program R: R Core Team. The survival rates were estimated by nonparametric estimation according to Kaplan & Meier. Group comparison was done by Log Rank test. A p-value of < 0.05 was judged as being significant statistically. Survival publications depending on 14 influence factors (Table 1) in reference to failure and extraction were determined with the help of the multiple Cox regression (Table 2). This include the findings which were relevant in vital and non-vital cases.
The observation period of the 8,644 analysed teeth lasted up to 25 years after the RCT (median 6 years). 8,098 (93.7 %) were attributed to vital extirpations (VitE) and 546 (6.3 %) to conservative initial treatment of non-vital teeth. During the observation pe-riod, an average of 5,295 cases attained a minimum of one follow-up X-ray after 7.14 years: 4,886 (60.3 %) in vital teeth, 409 (74.9 %) in non-vital teeth. The follow-up X-ray diagnoses are shown in Table 3.
X-ray diagnosis < 4 years after RCT (n = 1,482) revealed a radiographical failure of 9.9 %. This radiographical failure rate decreased to 8.3 % when diagnosis was made > 4 years after the RCT.
Out of the entity of 713 failures (8.2 % of all RCTs), 514 (5.9 % of all RCTs) were incorporated with X-ray. In doing so, the failure of 465 cases (90.5 %) was proved radiographically; 49 failures (9.5 %) were not substantiated in the X-ray. Another 199 cases (2.3 % of all RCTs) in form of acute exacerbations had to be judged as clinical failures without follow- up X-ray: 139 (1.72 %) in vital, 60 (10.98 %) in non-vital teeth. Fifty-five failures remained without therapy. In 13 cases, therapy was limited to a noncontact grinding. Four hundred and twelve failures (57.8 %) were extracted, failures increased extraction rate to the 2.8-fold.
Fourteen factors had been evaluated (Table 1) regarding extraction and failure rate. Five of these factors (operator, vitality status prior to RCT, preoperative AP, preoperative symptoms, number of appointments) did not have a significant influence to the extractions statistically, whereas three factors (sex, insurance condition, preoperative symptoms) did not have a significant influence to failure.
Of the RCTs, 58.7 % were carried out by the author himself, and 41.3 % by his assistant doctors. Cox regression showed a higher failure risk for the assistant cases versus the author: however, there was no higher extraction risk.
The clientele consisted of 51.4 % male and 48.6 % female patients. Regarding failures and extractions, a significant statistic difference between the sexes could not have been observed in the multivariate analysis (p = 0.417).
With regards to insurance, 59 % of the patients were insured by the RVO health insurances (legal health insurance for workers), 26.6 % by insurances for employees, 12.6 % had private health insurance, and 1.7 % were insured elsewhere. The failure analysis revealed no difference between the individual insurances (p = 0.629). Cox regression showed a lesser (approx. 24 %) extraction risk in employees and privately insured patients.
The average age of the patients amounted to 36.7 years (6–84). Regarding age, the highest failure rate was observed in patients < 30 years, however, they had the lowest extraction rate. According to Cox regression, the middle age group of 30–50 years had nearly 2-fold and the age group of over 50 years a 3.1-fold higher extraction risk versus the patients under the age of 30.
Analysis revealed significant differences (< 0.0001) regarding failures connected with the kind of tooth: molars 18.2 %, premolars 8.8 %, front teeth 8.1 %. Extraction rate of upper incisors was the lowest, extraction rate of the lower incisors the highest. Details can be seen in Table 4. According to univariate analysis, age and kind of tooth were not relevant regarding failure. Considering all analysed influence factors, premolars had a lower extraction risk of 81.5 % versus front teeth, molars a lower extraction risk of 73.1 %.
Aside from 19 teeth (0.23 %), all vital teeth were treated in one appointment. The multi-appointment of non-vital teeth in 257 cases (47 %) led to more failures (p = 0.0496).
Significant failure rate differences could be observed regarding pulp vitality prior to RCT (p < 0.001). Cox regression showed the significantly lower failure risk for vital teeth, which amounted to 30.9 % of non-vital teeth.
Two hundred and fifty-six (46.9 %) of the non-vital teeth featured an apical lesion when starting RCT. These were diagnosed with a failure rate of 34.9 % after 10 years. The difference with/without AP was significant (p = 0.0028 %).
Also RF-degree (Fig. 1), RF-quality and restoration had a significant influence on the failure rates. The highest failure frequency could have been observed after overfilling. Adequately filled teeth had a risk of failure of 63.6 % versus underfilled teeth; overfilled teeth had a 1.8-fold higher risk in comparison to underfilled teeth. Extraction rates of adequately and underfilled teeth featured nearly the same extraction frequency, whereas overfilled teeth showed an extraction risk of 18 % less. 25 % of all front teeth and premolar RFs as well as 52.6 % of all molar RFs showed a poor RF-quality which ended in a twofold failure risk versus a good RF quality and thus a 16 % higher risk of extraction (Fig. 2).
Root-filled teeth provided with one filling only had a higher tendency to failures and extractions. Cox regression proved a failure rate of 28 % less after crowning with build-up pins versus filling therapy. Without build-up pin insertion, crown provision was the reason for a 57 % lower failure rate. Crowning reduced the extraction risk to 31 % of teeth provided with a filling.
Three hundred and eighty-two (4.4 %) of fractured canal instruments were registered—1.83 % in front teeth and premolars, 10.29 % in molars. A failure was diagnosed in 72 cases (18.8 %) resulting in a 2.2-fold higher failure risk for teeth with fractured canal instrument. During observation period, 108 (23.8 %) teeth were extracted with a fractured canal instrument. The statistic relevance determined by the log-rank test was confirmed in theCox regression by finding a 32 % higher extraction risk (Fig. 3).
The process-related accident of a via falsa with perforation increased failure risk (75.2 % failure-rate after 8 years) to the 8.4-fold, extraction risk to the 2.5-fold.
Extractions represented the main contingent of re-interventions with another 299 treatments (RER, RTR, TR, HEM). Nearly 30 % of re-interventions were needed due to failure. The relation of re intervention and failure can be learned from Table 5. Table 6 gives a survey about reasons for extraction and their relation to failures. Figure 4 shows the chance of survival of cases which were not subject to extraction, further re-interventions or failure (clinically, radiologically) in a survival curve according to Kaplan Meier. After 20 years, 82.3 % (CI 80.5–84.2) of RCTs were not affected by radiological and/or clinical failure with n = 381 remaining under risk. Within the first year after RCT the incidents were: 183 of the 199 (92 %) acute exacerbations, 22 of the 514 (4.3 %) failures with follow- up X-ray, 159 of the 1,883 (8.4 %) extractions and 140 of the 299 (46.8 %) further re-interventions.
‘Presence or absence of the tooth is not subject to interpretation as would be subjective measurement of radiographic change, clinical signs and symptoms, patient history, etc’. With this statement, Alley et al. pointed out the advantages of survival studies, whereas Torabinejad et al.14 limited these advantages by calling survival studies as being ‘less biased’ as well as less informative. They further noted that endodontic studies come up with another variability making comparability more complicated.
The cases of the present study were treated in the authors office and evaluated by the author himself. Whereas extraction and thus the relevant survival represent a hard, non-discussible fact, success/failure evaluations are subject to bias. According to literature6, 7 the survival rate regarding tooth extractions is higher than the failure rate. Analysis of the practice data showed the opposite: after 20 years, 51.5 % of the teeth were still in situ and 82 % were still saved from failure.
Comparison with some studies can partly not be made, as survival data refer to the initial case numbers and are not in reference to the remaining cases getting less over the years. So the survival dates referring to extractions gained from the insurance registers have to be seen critically. Lazarski et al. indicated that 94.4 % remained in the mouth functionally after an average of 3.5 years. Salehrabi and Rotstein16 calculated a remaining in situ of 97.1 % after 8 years and Chen et al.17 a remaining in situ of 93.3 % after 5 years. Drop-outs are not mentioned in these studies. The fact is that only data known to the insurance are evaluated in those studies, which is rather unlikely in non-treated pathology, non-treated radiographical failure or goodwill treatments. In 914 cases, Stoll et al. noticed 105 (11.5 %) losses (extractions, RER, RTR) after 106 months, which can be interpreted as a cumulative survival rate of 74 %. De Chevigny et al. report about 70–73 % of drop-outs. They judged the remaining cases as being in function (95 %) and as healed radiographically (86 %).
The present study includes a drop-out rate of 40.6 % after 5 years, of 58.5 % after 10 years. As a recall never took place it can be supposed that the drop-out rates would have been more favorable in case of recall management.
The long observation period of up to 25 years may have supported the low failure rate. The later lower failure rate can be led back to the fact that the radiographical failure diagnosis averaged from 9.9 % to 8.3 % after the fourth year. It has to be mentioned that 9.5 % of the failures accompanied by X-ray could not have been verified radiographically. This may be due to the fact that the apical osteitis has not yet rounded the corticalis with sufficient mineral loss what is, according to Bender20, the pre condition for a radiographical AP presentation. Also anatomic features may superimpose an AP. The declining development of apical lesions over time conforms to literature data indicating a better RCT success result[4,21] although Eckerbom et al. noted an increase of apical lesions from 17.3 % to 21.4 % within 20 years. The own, relatively high success rate might be based on a bias with a too positive evaluation of the cases or an over-representation of the VitEs. It might also be due to the used RCT method as observed in epidemiological studies23 in countries with extensive application of formaldehyde-containing materials despite poor technical RF-quality.
Socially advantaged patients were represented with approx. 40 % in the examined patient population. They carried a 24 % lower extraction risk than social weak patients. A different failure risk did not exist between the individual social statuses of the patients. According to Hujoel et al., decision for extraction is determined by sociodemographic factors. A low income status and a low level of education favor the decision for extraction. The authors Jafarian and Etebarian concluded from an analysis of 2,620 extracted teeth that the level of education is of significant importance for tooth preservation. In a company health insurance study representing the working class, 8.3 % of the endodontic cases were extracted within 2 years. After 5 years, 28 % of reinterventions in the form of extractions and RTRs became necessary. In my own practice, the cumulative survival quote of all reinterventions increased to 16 % after 5 years.
According to Lee et al., the median survival limit regarding extraction had been reached after 21 years, thus approximately corresponding to my own. The median failure limit of Lee et al. was after 119 months (about 10 years). It has to be added that the authors scheduled their study 2 weeks after RCT only, so very early extractions and failures might have been skipped from the study.
Torabinejad et al. pointed out that in their study they categorically assigned pain after RCT to the failures. The same principle is valid for the present study. All acute exacerbations (clinical failures) were treated. 10.5 % of the failures accompanied by X-ray did not undergo therapy. The postoperative pain sensations amounted to 1.7 % after vital, after completion of a non-vital treatment to 11 %. A little more than a third could be contributed to overfilling: 30.9 % after overfilling of vital and 41.7 % after overfilling of non-vital teeth. The Gesi et al.27 study on vitally extracted teeth mentions a pain rate of 13.3 % within the first week after VitE. 30.7 % of the pain arose in overfilled teeth. In the own study, 69 overfillings (34.2 %) were responsible for 199 postoperative pain sensations.
Neither the sex, nor the preoperative pathology or the number of appointments were decisive for extractions or failure. However, the failure risk of vital teeth only amounted to 30.9 % of non-vital teeth. The multivariate analysis emphasised the results of the univariate analysis regarding the extraction risk subject to age and kind of tooth. The two older age classes attained higher extraction rates compared to the age class of <30. With increasing age, tooth loss rises even in non-root canal treated teeth by carious destruction and periodontal diseases. According to
Eriksen et al., epidemiologic studies reflect the endodontic performance of general dentists with success rates of 60–75 %. In his own practice, the author achieved a failure rate of 10.3 % in vital and 28.7 % in non-vital teeth.
It is also to be expected that different levels of experience are responsible for different success rates. The cases treated by assistant doctors had a statistically significantly higher failure rate compared to the practice senior while the extraction rates of assistants and practice senior were on the same level. Cox regression proved that RF-degree and RF-quality do hardly play a role for the extraction risk the more however for the failure risk. An RF with ‘voids’ and incomplete canal wall adhesion allows a bacterial augmentation/ invasion, an overfilling at least a periapical irritation caused by canal content flowing over the apex and root canal filling material.
According to Ng et al., the most significant criteria for survival were: crown, two proximal contacts, no use as prosthetic post and non-molar. In their studies, crowned teeth with or without build-up pin showed the lowest extraction risk versus all other researched variables, crowned teeth without build up pin simultaneously featured the lowest failure risk. Crowns offer a high fracture protection and are an expensive investment, where the patient does not like to separate from. It has to be considered though that crowning of teeth is preceded by an estimation of the survival prognosis and the better case material will be considered first when it comes to crowning.
Regarding the incidents of perforation and fractured canal instrument, the author found evidence from Ng et al. in the survival literature, where 76 (4.7 %) of 1,617 cases were subject to perforation and 105 cases (12.2 %) out of 858 secondary root canal treatments subject to fracture of a canal instrument. The Cox regression proves a 3.7-fold extraction risk for perforations, for the cases with fractured canal instrument a 3.1-fold extraction risk. Marquis et al. added 11 fractured canal instruments and 18 perforations in 369 endodontic cases to the intraoperative complications which affect the success result. Their own study proved a 2.5-fold extraction and a 8.4-fold failure risk for via falsa perforations. In case of fractured canal instruments the risk of extraction increased 1.3 times and the risk of failure to 2.2 times.
More than 8,000 endodontic primary cases had been observed for up to 25 years. Quality and length of RF, the type of restoration, the fracture of root canal instruments and the incident of perforation were responsible for the failure and extraction risk. The position of the tooth, age and social status had an influence on extraction frequency, the pulp state and the operator on the failure frequency. A symptom-free tooth remaining in situ of 73.2 % after 10 years and 51.5 % after 20 years speaks for a successful endodontic treatment therapy under practice conditions.
Acknowledgment: The author would like to thank Dr rer. nat. Monika Kriner for performing the statistics.
Editorial note: A list of references is available from the publisher.
This article was published in roots – international magazine of endodontology No. 3, 2016.