A truly outstanding line-up of top speakers will headline the Scientific Program of IDEM Singapore 2012, themed Advances and Controversies.
In addition to the plenary sessions in one hall, intensive full day programmes will run concurrently in another.
On Sunday, April 22, Urs Belser, Pascal Magne and Michel Magne will deliver a full day programme on restorative dentistry.
Since 1983, Professor Belser has headed the Department of Fixed Prosthodontics and Occlusion at the University of Geneva School of Dental Medicine.
Pascal Magne graduated from the University of Geneva, Switzerland in 1989 and since 2004 has been the tenured Associated Professor at the University of Southern California, Los Angeles where he received the Chair of Esthetic Dentistry.
Michel Magne was certified as Dental Technician in Switzerland in 1979 and in 2005 became Associate Professor of Clinical Dentistry and Director of the Center of Dental Technology at the University of Southern California, Los Angeles.
Good morning gentlemen and thank you for your time.
We're excited about your upcoming program in Singapore in April and have prepared some questions for you about your programme and the latest advances in restorative dentistry.
Q: Do you think conventional porcelain/metal crowns have reached the end of their usefulness for single tooth restorations?
Urs Belser: Mostly, but not completely. In fact, adhesive technologies, implementing biomimetic principles, have drastically reduced the spectrum of indications for conventional (i.e. cemented), full coverage single crowns. One of the remaining indications, for example, is the remake of a pre-existing full crowns that needs replacement due to secondary caries, fracture of the porcelain veneering or exposure of an unsightly crown margin after a gingival recession in the aesthetic zone. Finally, when it comes to predictability and clinical documentation, one should not forget that some of the most novel alternative concepts still need scientific confirmation.
Michel Magne: Certainly in my practice, the use of bonded porcelain restorations has essentially replaced the use of PFMs. In order to bio-emulate nature, full bonded porcelain restorations can better mimic enamel and dentin in regards to biology, mechanics, function and especially aesthetics. Also, from an aesthetics perspective, the undesired opacity created by the metal coping has been overcome by using full ceramic crowns.
Pascal Magne: I don't see a future for PFMs long term but I don't believe that their time is quite at an end just yet. The alternatives have yet to prove their ability to replace PFM in all situations. For instance, many researchers are still in the process of understanding zirconia, which is a very technical material. The use of polymers and advances in bonding compete with zirconia in this race to replace PFM but bonding is more "biomimetic".
Q: Can bonded porcelain restorations last a lifetime or do they have greater limitations than PFMs?
UB: Would "last a lifetime" mean 50 years and more? In this context, we must be aware that there is no scientifically solid documentation (randomized clinical trials/systematic reviews) available to date that would reach so far ahead and allow us to conclusively answer this question. Besides predictability and longevity, bonded porcelain restorations primarily aim at being bio-mimetic, as minimally invasive as possible and cost-effective. Finally, it is inherent to many recent concepts and techniques that long-term data has still to be constituted.
MM: Bonded porcelain restorations do preserve more dental structure allowing better biological response and longevity.
PM: Whether a restoration should last a lifetime is a more relevant question. Natural teeth, their function, mechanics and aesthetic undergo significant changes during this period called a "lifetime". Even if bonded porcelain would last a lifetime from a mechanical perspective, changes in form, function and aesthetics of the natural teeth next to the restoration would require some adjustments. New robust polymers might be more attractive than porcelain in the future, especially on the posterior dentition. On implants, polymers have the advantage of flexibility and compliance as a substitute for the missing periodontal ligament according to recent works we published in Clinical Oral Implants Research.
Q: What do you see as the place for direct adhesive restorations?
UB: There are numerous indications for direct adhesive restorations. They refer to anterior class IV and V lesions as well as to small to moderate lesions in the posterior segments of the jaws.
MM: I still believe that direct adhesive restorations can be used for small restorations with limited extension.
PM: Direct composite resins represent an essential socio-economic tool. They are the "daily bread" of private practice and allow many patients to be treated conservatively and at lower cost than traditional prosthodontic approaches. According to a recent study by N. Opdam in The Netherlands, their survival rate is outstanding even in large restorations (3, 4 and 5 surfaces).
Q: Do you see a role for immediate ceramics such as CEREC and E4D?
UB: Yes, definitely. I believe more extended lesions in the posterior part of the mouth can be effectively treated chairside by these systems during single appointments, not requiring impressions and temporary restorations.
MM: I agree with that. In my opinion, the use of CAD/CAM systems will increase mostly for posterior teeth where aesthetics is not an issue. For anterior teeth, there are still some limitations, but these systems have been improving their software, milling systems and restorative materials.
PM: realy the main factor preventing these systems from being more prevalent is that they are still too expensive to acquire but hopefully, their growing success will result in more accessibility. Most of our simulated fatigue tests are made with these systems because they have the advantage of producing a restoration with more predictability (less confounding variables from the manufacturing process) and because their limited aesthetics is not critical in such tests.
Q: With the increasing emphasis on CAD/CAM, what will happen to dental technicians?
UB: One can currently hear the widespread opinion that dental technicians may lose a significant part of their daily activity due to the ever-growing volume of CAD/CAM generated restorations. This may be partly true, as some of the restorative spectrum, including the restorative work-piece itself, can now be accomplished entirely by the clinician. However, I am convinced that dental technicians and ceramists have a major role to play when it comes to virtually designing optimal restorations on the screen, finalizing milled frameworks/veneers and stratifying demanding cosmetic veneers for the aesthetic zone. Particularly in the context of complex and extended restorations, most clinicians probably still prefer to delegate this time consuming process to an IT competent specialist with a dental technician background. In other terms, the profile of competencies of the dental technician is rapidly changing, ultimately making this profession even more attractive, challenging and indispensible.
MM: The great majority of lab technicians will have to adapt and learn how to be good with computer-based design. Unfortunately, I can see the lower level of technicians fading away, since in some cases the machine can do a better job. The number of dental technicians with artistic skills will increase though. These artists will still be requested for cases demanding high quality and high aesthetics.
PM: There are many benefits that dental laboratories can derive from the evolution of CAD/CAM if they adapt it to meet the needs of their dentists. According to my experience, intraoral use of CEREC and E4D is not as easy as it seems and I favour what I call the semi-indirect approach in which the laboratory or staff could play a role.
Q: Monolithic porcelain restorations are becoming more popular - do you think this trend is leading to a reduction in aesthetics?
UB: It depends in which area of the jaws they are applied. Full contour zirconia crowns, e.g. inserted in the posterior mandible, may be aesthetically acceptable in many instances. Furthermore, one should not forget the possibility to "customize" such monolithic porcelain restorations quite simply in the laboratory or directly chairside.
MM: I would say yes for some cases such as single units. However, this would not be the case for very thin veneers which are very adaptive. Also, the use of monolithic restorations is essentially indicated only for posterior teeth.
PM: I believe monolithic approaches represent a response to the problems encountered with bi-layered structures that failed. It is very likely that clinicians and demanding patients will not be satisfied with the aesthetic result of those monolithic restorations.
Q: What do you see as the main advantages of high strength ceramics?
UB: The term "high strength ceramics" usually refers to mechanical resistance in general and to flexural strength and fracture toughness, particularly when it comes to ceramic materials. It is well established that ceramics mostly fail in a mode termed "crack propagation". Toughness is the ability of a structural material to prevent or slow down the propagation of a crack. In the context of ceramics, latest generation zirconia has now reached a toughness level that permits its predictable clinical use, particularly in the form of single restorations located in the more anterior segments of the jaws. This has been confirmed by favorable 5-year data.
MM: One of the main advantages of using high strength ceramics is the replacement of metal frameworks for anterior bridges, both tooth-supported and implant-supported. Also, there is the possibility of using high strength ceramics in high load posterior teeth, even in cases where minimal reduction is required such as occlusal veneers.
PM: The main advantage of high strength ceramics is that their longevity does not depend so much on bonding to the substrate when retention and resistance form are used.
Q: What are the main problems that need to be overcome?
UB: As contemporary high strength ceramics still belong to the category of "brittle" materials, in contrast to so called "ductile" materials like dental alloys, they have to be applied with respective caution and in respect of strict design and fabrication guidelines, particularly in the load carrying part of the mouth. Connecting areas of multi-unit restorations, e.g., have to be designed with dimensions that are clearly superior to those advocated for metal-ceramic frameworks. This, in combination with the rather opaque intrinsic optical properties of zirconia, may lead to aesthetic shortcomings.
MM: The main problem with high strength ceramics in my opinion would be chipping of the feldspathic veneering porcelain. Also, dentists and dental technicians should understand better that the translucency/opacity of the material is related to its thickness in order to choose better the technique and material to be used.
PM: If you are talking about zirconia, I believe it is a very "technical" material (meaning "technique-sensitive") and it is difficult to bond to. We must bear in mind that "stronger and stiffer is not always better". I personally favour "bondability" to increase strength because none of the components of a natural tooth are strong like zirconia (enamel, dentin), yet they last for a lifetime. Remember that the God-made tooth is a veneer of super-brittle enamel perfectly bonded to super-flexible dentin. And it works!
Q: Do you think high strength ceramics will completely replace alloy-reinforced ceramics in the future?
UB: Clearly no! There will always be the odd but specific clinical situation, for example multi-unit tooth - or implant-supported FDPs in a reduced inter-arch distance and/or high occlusal stress environment, requiring the superior mechanical properties inherent to metal alloys. Finally, one should not forget the material category of the polymers that definitely hold a lot of future promise. Maybe the polymers will ultimately win the race for an optimal structural material?
MM: Absolutely!
PM: I believe replacement of alloy will eventually happen but not necessarily with ceramics but rather by bonding and by new materials other than pure ceramics.
Q: Finally, if your own upper lateral incisor was fractured at gingival level, what treatment would you want?
UB: The clinical situation described by this question refers to substantial pulp exposure on the one hand and to total absence of supra-gingival mineralized dental tissue on the other hand. Therefore, endodontic therapy appears inevitable, followed by adhesive insertion of a glass-fiber post, a composite core build-up, and a temporary resin crown. If the adjacent dentition permits from both an aesthetic and a periodontal point of view, a moderate crown-lengthening procedure would allow the biologic width to be respected and establish an acceptable ferrule height of 1.5-2 mm, both representing prognostic key factors. If such a procedure would not be feasible for aesthetic reasons, one may eventually accept this risk (particularly if the overbite is small to moderate and the patient has no bruxing habits, as myself) or one may consider a local orthodontic intervention called "forced eruption", followed by "crown-lengthening". The final restoration would be a zirconia-based all-ceramic crown using CAD/CAM technology and a thin, uniform layer of lithium-disilicate veneering porcelain. Under such precise circumstances, I would prefer to postpone root extraction and a single tooth implant restoration, despite its excellent predictability and scientific documentation. "Implants are supposed to replace missing teeth - they do not replace teeth"... Jan Lindhe.
MM: I would have it restored with a full ceramic restoration (feldspathic) directly bonded to remaining tooth structure.
PM: My choice would be for a bonded porcelain restoration with a composite resin core and if possible, without a post.
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