POSTERIOR COMPOSITES: THE FUTURE FOR RESTORING POSTERIOR TEETH? CHRISTOPHER D LYNCH1, ROBERT J MCCONNELL1, NAIRN HF WILSON1
W
hile amalgam has had a long service history in dentistry, it is the opinion of the authors that its time has passed. We are now entering an era in dentistry, following the Minamata Treaty,1-3 in which we must prepare for clinical practice without amalgam. Therefore, the focus of this article is on the use of resin composites for restoration of posterior teeth.
As always, the authors are keen to emphasise that they are not antiamalgam. However, we are unashamed advocates and proponents of minimally invasive dentistry. In the opinion of the authors, minimally invasive management of posterior teeth can be achieved only when using resin composites, rather than amalgam, which requires mechanical retention and cannot be fully condensed in small preparations. In saying this, the authors readily acknowledge some of the challenges facing clinicians, particularly in UK dental practice, including the following: Posterior resin composites have a dubious past, with much concern being expressed about their longevity. This has been allayed by many recent studies, including practice-based studies, which illustrate that the longevity of posterior resin composites matches (if not exceeds) that of amalgam.4-6
Posterior resin composites are more technique-sensitive than amalgam. While the authors agree with this statement, we offer the view that with appropriate training, this difficulty can be largely overcome. It should be remembered that in the late 1990s, fewer than one in ten dental students graduated with clinical experience of placing posterior composites.7,8 In 2009, dental students in the UK and Ireland placed more posterior resin composites than amalgams (55% posterior resin composite: 45% amalgam).9 It is our experience that most recent graduates have had extensive exposure to posterior resin composite teaching at dental school, and have the competence and confidence to use resin composites in the restoration of posterior teeth in their subsequent clinical practice. Placing posterior resin composites is more costly, in terms of materials, associated equipment such as light-curing units, matrices, and chairside time, than placing restorations of dental amalgam. This tends to cause problems for those with NHS contracts, as current remuneration approaches (UDA values, etc.) do not encourage clinicians to place posterior resin composites, particularly when a patient has multiple teeth that require restoration. The authors understand these problems and suggest that they are issues that the representatives of the UK dental profession need to address as a priority with funders of dental care.
The Minamata Treaty has committed the world to a reduction in the use of mercury, with the aim of reducing mercury environmental pollution. It is not an unrealistic notion that in a world of reduced mercury use, political and public interests in 5-10 years’ time will no longer tolerate the availability of amalgam as a dental filling material. The danger to UK dental practice, if it does not move with the times, is significant – immediate withdrawal of amalgam from service, say, 10 years from now, would render an external shock to UK dental services that could be cataclysmic. Neither will the next generation of dentists thank us, their forebears, for dragging our feet in this important area. We, as a profession, need to move with the times and show leadership, rather than wait to be forced to change. In particular: • Dental schools need to phase-out amalgam teaching – the class of dental students entering clinical skills (phantom head) training in 2015, and subsequent classes, should no longer be taught amalgam placement, with the exception of amalgam repair and replacement therapy. Rather, the time saved should be distributed to increased teaching of posterior resin composites, the more accurate diagnosis of primary and secondary caries, techniques for refurbishing and repairing existing restorations that are still serviceable but feature signs of deterioration, and the use of ceramics
1
We, as a profession, should not be complacent about a prolonged “phasedown” period for dental amalgam, with the UK lagging behind other western countries with its adherence to amalgam. UK dental services, and their associated remuneration structures, must adapt to the reality of an ever-increasing use and demand for posterior resin composites.
V O L 3 N O 2 M AY 2 0 1 4
Christopher D Lynch
Christopher D Lynch, Reader/consultant in Restorative Dentistry, School of Dentistry, Cardiff University 2
Robert J McConnell
Professor of Restorative Dentistry, Centre for Dentistry, Queens University Belfast 3
Nairn HF Wilson
Professor of Dentistry, King’s College London
49
POSTERIOR COMPOSITES: THE FUTURE FOR RESTORING POSTERIOR TEETH?
Figure 1: Discussions at the Minamata Convention on Mercury
in the restoration of badly brokendown posterior teeth. • It has to be recognised that, through no fault of their own, there are significant cohorts of dentists who have little or no formal instruction in the placement of posterior resin composites. Such clinicians require supportive training, which in itself is costly, whether provided by postgraduate deaneries, dental organisations or private companies. This training must, however, be undertaken to allow a safe lead-in to a phase-out of amalgam. • The leaders of the dental profession need to engage with funders of dental treatment to seek enhanced payments for the placement of posterior resin composites rather than amalgam restorations. While further reductions in the incidence of caries and the increasing use of refurbishment and repair procedures should contain and possibly reduce the cost of initial restoration placement, the population is anticipated to grow by several million people, with tens of millions more teeth at risk of disease. • We need to actively encourage the use of materials other than amalgam. Many dental schools now teach their students that posterior resin
50
composites are the material of choice for restoring posterior teeth,10 and established practitioners need to adopt a similar change in approach. In other words, consider posterior resin composites first, and then, where not indicated, use an alternative material, possibly amalgam. This is especially important when treating children: resin composite should be used rather than amalgam, if for no other reason than to avoid creating another “amalgam generation” – once restored with amalgam, the restorative destiny of a tooth tends to be determined. All change is difficult; however, a change in the use of restorative materials for posterior teeth is now inevitable, and the longer it is ignored, the more difficult it will become. It is never constructive to put off until tomorrow something which should be done today. The evidence shows that where placed appropriately, using state-of-the-art techniques, posterior resin composites show comparable, if not enhanced, survival when compared to amalgam restorations.4-6 Coupled with this, posterior resin composites offer effective restoration of posterior teeth without without sacrificing intact, healthy tooth tissue to gain mechanical retention –
amalgam bonding offers no such apparent benefits. It is recognised that posterior resin composites are not indicated in every situation. Contraindications are shared with other restorative materials, such as an oral environment where restorations are prone to failure (eg. because of high caries rate or poor compliance). Problems specific to posterior resin composites include inability to achieve moisture control and conditions in which normal dentine or enamel structure is altered (eg. dentinogenesis imperfecta or amelogenesis imperfecta, but more commonly fluorosis and hypocalcification); in these situations bonding may not always be successful, and a trial restoration is indicated in the first instance. Another commonly encountered problem is that of the subgingival margin: in these circumstances, the use of gingival margin retraction techniques using cords, rubber dam or matrices can be attempted, or crown lengthening procedures can be undertaken. Alternately ‘sandwich’ techniques can be used, wherein a resinmodified glass-ionomer cement is used to restore the subgingival portion of the preparation to the level of the gingival margin prior to application of the resin composite.
P R I M A R Y D E N TA L J O U R N A L
The purpose of the remainder of this article is to provide helpful guidance, based on the best available evidence, on placement of posterior resin composite restorations. Readers are also referred to more detailed considerations of the evidence behind posterior resin composite placement techniques, such as guidance from the European Section of the Academy of Operative Dentistry.11
Cavity design – to bevel or not to bevel? One of the greatest attributes of resin composite placement is that it is possible to avoid the needless sacrifice of healthy, intact tooth tissue to gain retention for the restoration being placed. Minimal intervention dentistry techniques can be implemented to best advantage: beyond smoothing of sharp or rough enamel, it is enough to excise the lesion of caries and then apply a resin composite. In so doing, the patient’s journey along the downward cycle of restoration placement and replacement with ever increasing cavity sizes (the so-called “restorative death spiral”) is much slower than if amalgam had been placed instead. When dealing with cavity designs for posterior teeth, an often-asked question is whether or not there is a need to bevel the cavosurface margin. Such bevelling is thought advantageous in anterior restorations, where a gradual blend between the restoration and tooth helps to enhance the aesthetic outcome. In posterior teeth, bevelling of the cavosurface margin should be avoided. Should bevels be included on the occlusal surface, this can give the (false) impression that the restoration is larger than it really is – remember that another dentist may have to replace the restoration in the future. While some laboratory testing suggests that bevels may be helpful on the proximal surfaces,12,13 such bevels should be avoided, in the opinion of the authors, as they invariably lead to loss of enamel from regions where enamel thickness is already compromised.14
V O L 3 N O 2 M AY 2 0 1 4
The best bond/adhesion is achieved to enamel – at all costs, enamel should be preserved in the proximal regions.
Management of operatively exposed dentine – to bond or to base? The vexed issue of treatment of operatively exposed dentine continues to challenge clinicians. Over the course of many postgraduate lectures, common questions asked of the authors include: • How can the best bond be achieved? • Will etchant irritate the pulp? • How can we prevent against postoperative sensitivity? To understand the protection of operatively exposed dentine, the following considerations must be kept in mind: • The use of bases is traditionally associated with amalgam, mainly because bases were necessary to provide thermal insulation for (heatconducting) amalgam restorations. Resin composite is an insulator in its own right – it does not transmit heat in the same way as amalgam, and therefore the need for a base can be avoided. • Predictable adhesion of resin composite restorations to dentine can be achieved using modern dentine bonding systems. Using a base therefore limits the available surface area for bonding. In addition,
reducing the thickness of resin composite by placing an effective thickness (>1.5mm) of a base material reduces the physical properties of the completed restoration. • There is evidence that the incidence of post-operative sensitivity is unaffected by the choice of (etching and) bonding or basing with a cement. In a randomised control trial of 103 young patients (average age 22 years, and therefore not likely to have sclerosed dentine), the incidence of postoperative sensitivity after one month was independent of technique used.15 It would appear, therefore, that there is no longer an indication for placing a base under a posterior resin composite, and bonding a restoration in place instead should suffice. The authors recommend one exception to this – where materials are applied to manage pulpal healing (eg. calcium hydroxide or MTA), it would be sensible to place a layer of glass-ionomer cement over this material so that it is not affected by the acidity of the etchant. In terms of dentine bonding, there does not appear to be a clinically significant difference in the performance of fourthgeneration (three-bottle etch-and-rinse), fifth-generation (two-bottle etch-and-rinse)
51
POSTERIOR COMPOSITES: THE FUTURE FOR RESTORING POSTERIOR TEETH?
or sixth-generation (self-etch) adhesives.16 Self-etch systems offer obvious attractions in terms of ease of use and reduced technique sensitivity. That said, self-etch adhesives lightly dissolve and infiltrate the smear layer, while the etch-and-rinse systems remove it. As such, the use of etchand-rinse systems should be considered when restorations placed using self-etch systems fail. There is also some concern about the degree of staining which can occur with self-etch adhesive systems. So-called ‘selective etching’ techniques have been recommended in aesthetic areas where an additional etching step with phosphoric acid is completed before using the self-etch system.17 In all probability, effective clinical technique with meticulous attention to detail may be found to be more important than which of the current bonding systems is selected for use.
Materials selection – hybrid, bulk-fill or flowable? Many new resin composite systems have been introduced over the past years with the aim of simplifying the restoration of posterior teeth. In the main, these materials are based on traditional methyl methacrylate chemistry. Until recently, the most commonly used materials were socalled hybrid resin composites: those which included smaller filler particles associated with microfilled resins as well as larger filler particles associated with macrofilled resins. As such, these materials featured
REFERENCES 4 1
2
3
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United Nations Environment Programme. Minamata Convention Agreed by Nations. UNEP website. Available at: http://tinyurl.com/bkkekac. Accessed: 14 April 2014. Lynch CD, Wilson NHF. Managing the phase-down of amalgam (Part I): educational and training issues. Br Dent J 2013;215:109–113. Lynch CD, Wilson NHF. Managing the phase-down of amalgam (Part II): implications for practising arrangements and lessons from Norway. Br Dent J
5
6
enhanced wear resistance and compressive strength, along with improved polishability. Such materials have a long service history and still have much to offer the profession.
This approach offers many advantages, including increased speed of placement and reduction of the need to place many increments. Early evidence suggests that this material shows promise.18
However, newer formulations of materials exist to help manage specific situations. Low-shrinkage set resin composites have been developed to reduce the deleterious effects of contraction of resin composite increments on polymerisation. One example of a low-shrink resin is Silorane (3M). This features 1% shrinkage, in comparison to the 2% experienced by traditional hybrids. Silorane includes a different setting chemistry to traditional resin composites – it is not based on methyl methacrylate – and therefore clinicians must use its own bonding system. This material has also drawn criticism for being stiff and tacky to handle, and for its limited depth of cure.
Clearly, developments in materials will improve the application of posterior resin composites in years to come. However, as always, clinicians should continue to be mindful of the principles of placement and follow manufacturers’ guidelines as necessary.
More recent developments include the introduction of Smart Dentin Replacement (Dentsply). This material has gained significant traction in the market and allows placement of a bulk-fill (4mm) flowable base. The material, which is still methyl methacrylate-based, includes a polymerisation modulator which slows the development of polymerisation stresses, particularly at the restoration-tooth interface. A ‘traditional’ composite is then placed over the flowable base.
2013;215:159–162. Opdam NJ, Bronkhurst EM, Roeters JM, Loomans BA. A retrospective study clinical study on longevity of posterior resin composite and amalgam restorations. Dent Mater 2007;23:2-8. Opdam NJM, Bronkhorst EM, Loomans BAC, Huysmans MC. 12year survival of resin composite vs amalgam restorations. J Dent Res 2010;89:1063–1067. Pallesen U, van Dijken JW, Halken J, Hallonsten A-L, Höigaard R. Longevity of posterior resin composite restorations in
7
8
9
Light-curing – who cares? Light-curing is often an under-appreciated stage in placing resin composites. Given the challenges in achieving suitable conditions for bonding, and applying the various steps in bonding systems, let alone resin composite increments, the risk is that clinicians will adopt a more relaxed approach to this stage in resin composite placement, as it is perceived as an opportunity to take a break. Light-curing is a critical stage to resin composite placement, and failure to pay sufficient attention can lead to an under-polymerised restoration which is susceptible to fracture. Some important considerations should be remembered: • For traditional resin composites, based on methyl methacrylate chemistry, increments of thickness less than 2mm need to be cured for 30 seconds. • The efficiency of curing depends on
permanent teeth in Public Dental Health Service: A prospective 8 years follow up. J Dent 2013;41:297–306. Mjör I, Wilson NHF. Teaching of Class I and Class II direct resin composite resin restorations: results of a survey of dental schools. J Am Dent Assoc 1998;129:1415– 1419. Wilson NHF, Mjör I. The teaching of class I and class II direct resin composite restorations in European dental schools. J Dent 2000;28:15-21. Lynch CD, Frazier KB, McConnell RJ, Blum IR, Wilson NHF. State-of-
the-art techniques in Operative Dentistry: contemporary teaching of posterior resin composites in UK and Irish dental schools. Br Dent J 2010;209:129–136. 10 Lynch CD, Shortall AC, Stewardson D, Tomson PL Burke FJT. Teaching posterior composite resin restorations in the United Kingdom and Ireland: consensus views of teachers. Br Dent J 2007;203:183-187. 11 Lynch CD et al. Guidance on the use of resin composites for direct restoration of posterior teeth: Academy of Operative Dentistry European Section. J Dent
P R I M A R Y D E N TA L J O U R N A L
the proximity of the light-curing tip – if held far away from the surface of the increment (eg. if curing resin composite at the base of a deep cavity or gingival/proximal box), the energy applied will be reduced. Thinner increments will be required in such situations. • Newer LED light-curing units offer many advantages. However, care is needed with some newer narrower-emission lights when curing highly bleached shades in specialised aesthetic resin composites – such bleached resins do not always use camphorquinone (the ‘traditional’ photoactivator molecule, which adds a yellow tinge). Therefore, the LED and resin composite may not match each other. This is a discussion to have with your supplier before purchasing either newer LED lights or bleached/aesthetic resins. • If using traditional quartz halogen lightcuring units, please remember that the bulbs in these units lose power output and should be monitored for output and replaced as a matter of routine, possibly after around six months of use. The power output should be checked using a radiometer.
Matrices – clear, metal, or circumferential? Restoring missing proximal contours can be a real challenge with resin composites,
2014;42:377–383. 12 Opdam NJ, Roeters JJ, Kuijs R, Burgersdijk RC. Necessity of bevels for box only Class II composite restorations. J Prosthet Dent 1998;80:274-279. 13 Hilton TJ, Ferricane JL. Cavity preparation factors and microleakage of Class II composite restorations filled at intraoral temperatures. Amer J Dent 1999;12:123-130. 14 Lynch CD, O’Sullivan VR, Dockery P, McGillycuddy CT, Sloan AJ. Hunter-Schreger Band patterns in human tooth enamel. J Anat 2010;217:106–115.
particularly since, in contrast to amalgam, the material shrinks on setting. It is also important to remember when restoring occlusoproximal cavities that one must think of restoring the contour, not just the contact point. For restoring proximal contours, the available occlusoproximal resin composite options available are: • Clear matrix bands and lighttransmitting wedges • Sectional metal matrix bands and wooden/flexible wedges • Circumferential metal matrix bands and wooden/flexible wedges. Clear matrix bands were introduced at a time when it was thought that resin composite shrank towards the light, and that specific problems could be encountered when increments placed at the floor of a proximal box would lift when the light was incident from the occlusal surface. It was recognised over 15 years ago that resin composite does not shrink towards the light,19 so the need for such techniques can no longer be justified. Furthermore, problems were identified with clear matrix bands and light-transmitting wedges over 10 years ago.20 Due to their stiff and inflexible nature, such systems are associated with open proximal contacts on completed restorations, as well as overhang formation. As such, these systems are discredited and should no longer be used.
15 Burrow MF, Banomyong D, Harnirattisai C, Messer HH. Effect of glass-ionomer cement lining on postoperative sensitivity in occlusal cavities restored with resin composite–a randomized clinical trial. Oper Dent 2009;34:648– 655. 16 Peumans M, Kanumilli P, De Munck J, Van Landuyt K, Lambrechts P, Van Meerbeek B. Clinical effectiveness of contemporary adhesives: a systematic review of current clinical trials. Dent Mater 2005;21: 864881. 17 Kubo S, Yokota H, Yokota H, Hayashi Y. Two-year clinical
V O L 3 N O 2 M AY 2 0 1 4
Sectional and circumferential systems can be used with ease to recreate missing proximal contours. Evidence shows that sectional systems allow tighter proximal contacts than circumferential systems, albeit with slightly greater evidence of flash formation.21,22 Whichever system is used, careful application techniques should be used. It is also suggested that whichever system is used, the ‘missing’ proximal wall should be replaced first, to ensure adaptation of the resin composite in the proximal area.
Concluding remarks In this post-Minamata age, the postamalgam era is upon us. As well as ensuring a minimally invasive approach to the restoration of posterior teeth (which can be achieved when resin composite rather than amalgam restoration techniques are used), practitioners should seek to improve their skills and confidence in the use of resin composite materials. This can be achieved by proactively taking the approach in clinical practice (as is the case in many dental schools) that resin composites are the material of choice for restoring posterior teeth. Once the mindset of posterior resin composite placement is embraced, the challenge of placing such materials becomes a lot easier. It is better to be ahead of the curve than run the risk of lagging behind and, at some time in the future, being forced to make a sudden change in everyday clinical practice.
evaluation of one-step self-etch systems in non-carious cervical lesions. J Dent 2009;37:149-155. 18 Roggendorf MJ, Krämer N, Appelt A, Naumann M, Frankenberger R. Marginal quality of flowable 4-mm base vs. conventionally layered resin composite. J Dent 2011;39:643-647. 19 Versluis A, Tantbirojn D, Douglas WH. Do dental resin composites always shrink toward the light? Journal of Dental Research 1998;77:1435-1445. 20 Mullejans R, Badawi MO, Raab WH, Lang H. An in vitro comparison of metal and
transparent matrices used for bonded Class II resin composite restorations. Operative Dentistry 2003;28:122-126. 21 Loomans BAC, Opdam NJM, Roeters JFM, et al. Influence of resin composite resin consistency and placement technique on proximal contact tightness of Class II restorations. J Adhes Dent 2006;8:305-310. 22 Loomans BAC, Opdam NJM, Roeters FJM, et al. Restoration techniques and marginal overhang in Class II resin composite resin restorations. J Dent 2009;37:712– 717.
53
W
hile amalgam has had a long service history in dentistry, it is the opinion of the authors that its time has passed. We are now entering an era in dentistry, following the Minamata Treaty,1-3 in which we must prepare for clinical practice without amalgam. Therefore, the focus of this article is on the use of resin composites for restoration of posterior teeth.
As always, the authors are keen to emphasise that they are not antiamalgam. However, we are unashamed advocates and proponents of minimally invasive dentistry. In the opinion of the authors, minimally invasive management of posterior teeth can be achieved only when using resin composites, rather than amalgam, which requires mechanical retention and cannot be fully condensed in small preparations. In saying this, the authors readily acknowledge some of the challenges facing clinicians, particularly in UK dental practice, including the following: Posterior resin composites have a dubious past, with much concern being expressed about their longevity. This has been allayed by many recent studies, including practice-based studies, which illustrate that the longevity of posterior resin composites matches (if not exceeds) that of amalgam.4-6
Posterior resin composites are more technique-sensitive than amalgam. While the authors agree with this statement, we offer the view that with appropriate training, this difficulty can be largely overcome. It should be remembered that in the late 1990s, fewer than one in ten dental students graduated with clinical experience of placing posterior composites.7,8 In 2009, dental students in the UK and Ireland placed more posterior resin composites than amalgams (55% posterior resin composite: 45% amalgam).9 It is our experience that most recent graduates have had extensive exposure to posterior resin composite teaching at dental school, and have the competence and confidence to use resin composites in the restoration of posterior teeth in their subsequent clinical practice. Placing posterior resin composites is more costly, in terms of materials, associated equipment such as light-curing units, matrices, and chairside time, than placing restorations of dental amalgam. This tends to cause problems for those with NHS contracts, as current remuneration approaches (UDA values, etc.) do not encourage clinicians to place posterior resin composites, particularly when a patient has multiple teeth that require restoration. The authors understand these problems and suggest that they are issues that the representatives of the UK dental profession need to address as a priority with funders of dental care.
The Minamata Treaty has committed the world to a reduction in the use of mercury, with the aim of reducing mercury environmental pollution. It is not an unrealistic notion that in a world of reduced mercury use, political and public interests in 5-10 years’ time will no longer tolerate the availability of amalgam as a dental filling material. The danger to UK dental practice, if it does not move with the times, is significant – immediate withdrawal of amalgam from service, say, 10 years from now, would render an external shock to UK dental services that could be cataclysmic. Neither will the next generation of dentists thank us, their forebears, for dragging our feet in this important area. We, as a profession, need to move with the times and show leadership, rather than wait to be forced to change. In particular: • Dental schools need to phase-out amalgam teaching – the class of dental students entering clinical skills (phantom head) training in 2015, and subsequent classes, should no longer be taught amalgam placement, with the exception of amalgam repair and replacement therapy. Rather, the time saved should be distributed to increased teaching of posterior resin composites, the more accurate diagnosis of primary and secondary caries, techniques for refurbishing and repairing existing restorations that are still serviceable but feature signs of deterioration, and the use of ceramics
1
We, as a profession, should not be complacent about a prolonged “phasedown” period for dental amalgam, with the UK lagging behind other western countries with its adherence to amalgam. UK dental services, and their associated remuneration structures, must adapt to the reality of an ever-increasing use and demand for posterior resin composites.
V O L 3 N O 2 M AY 2 0 1 4
Christopher D Lynch
Christopher D Lynch, Reader/consultant in Restorative Dentistry, School of Dentistry, Cardiff University 2
Robert J McConnell
Professor of Restorative Dentistry, Centre for Dentistry, Queens University Belfast 3
Nairn HF Wilson
Professor of Dentistry, King’s College London
49
POSTERIOR COMPOSITES: THE FUTURE FOR RESTORING POSTERIOR TEETH?
Figure 1: Discussions at the Minamata Convention on Mercury
in the restoration of badly brokendown posterior teeth. • It has to be recognised that, through no fault of their own, there are significant cohorts of dentists who have little or no formal instruction in the placement of posterior resin composites. Such clinicians require supportive training, which in itself is costly, whether provided by postgraduate deaneries, dental organisations or private companies. This training must, however, be undertaken to allow a safe lead-in to a phase-out of amalgam. • The leaders of the dental profession need to engage with funders of dental treatment to seek enhanced payments for the placement of posterior resin composites rather than amalgam restorations. While further reductions in the incidence of caries and the increasing use of refurbishment and repair procedures should contain and possibly reduce the cost of initial restoration placement, the population is anticipated to grow by several million people, with tens of millions more teeth at risk of disease. • We need to actively encourage the use of materials other than amalgam. Many dental schools now teach their students that posterior resin
50
composites are the material of choice for restoring posterior teeth,10 and established practitioners need to adopt a similar change in approach. In other words, consider posterior resin composites first, and then, where not indicated, use an alternative material, possibly amalgam. This is especially important when treating children: resin composite should be used rather than amalgam, if for no other reason than to avoid creating another “amalgam generation” – once restored with amalgam, the restorative destiny of a tooth tends to be determined. All change is difficult; however, a change in the use of restorative materials for posterior teeth is now inevitable, and the longer it is ignored, the more difficult it will become. It is never constructive to put off until tomorrow something which should be done today. The evidence shows that where placed appropriately, using state-of-the-art techniques, posterior resin composites show comparable, if not enhanced, survival when compared to amalgam restorations.4-6 Coupled with this, posterior resin composites offer effective restoration of posterior teeth without without sacrificing intact, healthy tooth tissue to gain mechanical retention –
amalgam bonding offers no such apparent benefits. It is recognised that posterior resin composites are not indicated in every situation. Contraindications are shared with other restorative materials, such as an oral environment where restorations are prone to failure (eg. because of high caries rate or poor compliance). Problems specific to posterior resin composites include inability to achieve moisture control and conditions in which normal dentine or enamel structure is altered (eg. dentinogenesis imperfecta or amelogenesis imperfecta, but more commonly fluorosis and hypocalcification); in these situations bonding may not always be successful, and a trial restoration is indicated in the first instance. Another commonly encountered problem is that of the subgingival margin: in these circumstances, the use of gingival margin retraction techniques using cords, rubber dam or matrices can be attempted, or crown lengthening procedures can be undertaken. Alternately ‘sandwich’ techniques can be used, wherein a resinmodified glass-ionomer cement is used to restore the subgingival portion of the preparation to the level of the gingival margin prior to application of the resin composite.
P R I M A R Y D E N TA L J O U R N A L
The purpose of the remainder of this article is to provide helpful guidance, based on the best available evidence, on placement of posterior resin composite restorations. Readers are also referred to more detailed considerations of the evidence behind posterior resin composite placement techniques, such as guidance from the European Section of the Academy of Operative Dentistry.11
Cavity design – to bevel or not to bevel? One of the greatest attributes of resin composite placement is that it is possible to avoid the needless sacrifice of healthy, intact tooth tissue to gain retention for the restoration being placed. Minimal intervention dentistry techniques can be implemented to best advantage: beyond smoothing of sharp or rough enamel, it is enough to excise the lesion of caries and then apply a resin composite. In so doing, the patient’s journey along the downward cycle of restoration placement and replacement with ever increasing cavity sizes (the so-called “restorative death spiral”) is much slower than if amalgam had been placed instead. When dealing with cavity designs for posterior teeth, an often-asked question is whether or not there is a need to bevel the cavosurface margin. Such bevelling is thought advantageous in anterior restorations, where a gradual blend between the restoration and tooth helps to enhance the aesthetic outcome. In posterior teeth, bevelling of the cavosurface margin should be avoided. Should bevels be included on the occlusal surface, this can give the (false) impression that the restoration is larger than it really is – remember that another dentist may have to replace the restoration in the future. While some laboratory testing suggests that bevels may be helpful on the proximal surfaces,12,13 such bevels should be avoided, in the opinion of the authors, as they invariably lead to loss of enamel from regions where enamel thickness is already compromised.14
V O L 3 N O 2 M AY 2 0 1 4
The best bond/adhesion is achieved to enamel – at all costs, enamel should be preserved in the proximal regions.
Management of operatively exposed dentine – to bond or to base? The vexed issue of treatment of operatively exposed dentine continues to challenge clinicians. Over the course of many postgraduate lectures, common questions asked of the authors include: • How can the best bond be achieved? • Will etchant irritate the pulp? • How can we prevent against postoperative sensitivity? To understand the protection of operatively exposed dentine, the following considerations must be kept in mind: • The use of bases is traditionally associated with amalgam, mainly because bases were necessary to provide thermal insulation for (heatconducting) amalgam restorations. Resin composite is an insulator in its own right – it does not transmit heat in the same way as amalgam, and therefore the need for a base can be avoided. • Predictable adhesion of resin composite restorations to dentine can be achieved using modern dentine bonding systems. Using a base therefore limits the available surface area for bonding. In addition,
reducing the thickness of resin composite by placing an effective thickness (>1.5mm) of a base material reduces the physical properties of the completed restoration. • There is evidence that the incidence of post-operative sensitivity is unaffected by the choice of (etching and) bonding or basing with a cement. In a randomised control trial of 103 young patients (average age 22 years, and therefore not likely to have sclerosed dentine), the incidence of postoperative sensitivity after one month was independent of technique used.15 It would appear, therefore, that there is no longer an indication for placing a base under a posterior resin composite, and bonding a restoration in place instead should suffice. The authors recommend one exception to this – where materials are applied to manage pulpal healing (eg. calcium hydroxide or MTA), it would be sensible to place a layer of glass-ionomer cement over this material so that it is not affected by the acidity of the etchant. In terms of dentine bonding, there does not appear to be a clinically significant difference in the performance of fourthgeneration (three-bottle etch-and-rinse), fifth-generation (two-bottle etch-and-rinse)
51
POSTERIOR COMPOSITES: THE FUTURE FOR RESTORING POSTERIOR TEETH?
or sixth-generation (self-etch) adhesives.16 Self-etch systems offer obvious attractions in terms of ease of use and reduced technique sensitivity. That said, self-etch adhesives lightly dissolve and infiltrate the smear layer, while the etch-and-rinse systems remove it. As such, the use of etchand-rinse systems should be considered when restorations placed using self-etch systems fail. There is also some concern about the degree of staining which can occur with self-etch adhesive systems. So-called ‘selective etching’ techniques have been recommended in aesthetic areas where an additional etching step with phosphoric acid is completed before using the self-etch system.17 In all probability, effective clinical technique with meticulous attention to detail may be found to be more important than which of the current bonding systems is selected for use.
Materials selection – hybrid, bulk-fill or flowable? Many new resin composite systems have been introduced over the past years with the aim of simplifying the restoration of posterior teeth. In the main, these materials are based on traditional methyl methacrylate chemistry. Until recently, the most commonly used materials were socalled hybrid resin composites: those which included smaller filler particles associated with microfilled resins as well as larger filler particles associated with macrofilled resins. As such, these materials featured
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United Nations Environment Programme. Minamata Convention Agreed by Nations. UNEP website. Available at: http://tinyurl.com/bkkekac. Accessed: 14 April 2014. Lynch CD, Wilson NHF. Managing the phase-down of amalgam (Part I): educational and training issues. Br Dent J 2013;215:109–113. Lynch CD, Wilson NHF. Managing the phase-down of amalgam (Part II): implications for practising arrangements and lessons from Norway. Br Dent J
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enhanced wear resistance and compressive strength, along with improved polishability. Such materials have a long service history and still have much to offer the profession.
This approach offers many advantages, including increased speed of placement and reduction of the need to place many increments. Early evidence suggests that this material shows promise.18
However, newer formulations of materials exist to help manage specific situations. Low-shrinkage set resin composites have been developed to reduce the deleterious effects of contraction of resin composite increments on polymerisation. One example of a low-shrink resin is Silorane (3M). This features 1% shrinkage, in comparison to the 2% experienced by traditional hybrids. Silorane includes a different setting chemistry to traditional resin composites – it is not based on methyl methacrylate – and therefore clinicians must use its own bonding system. This material has also drawn criticism for being stiff and tacky to handle, and for its limited depth of cure.
Clearly, developments in materials will improve the application of posterior resin composites in years to come. However, as always, clinicians should continue to be mindful of the principles of placement and follow manufacturers’ guidelines as necessary.
More recent developments include the introduction of Smart Dentin Replacement (Dentsply). This material has gained significant traction in the market and allows placement of a bulk-fill (4mm) flowable base. The material, which is still methyl methacrylate-based, includes a polymerisation modulator which slows the development of polymerisation stresses, particularly at the restoration-tooth interface. A ‘traditional’ composite is then placed over the flowable base.
2013;215:159–162. Opdam NJ, Bronkhurst EM, Roeters JM, Loomans BA. A retrospective study clinical study on longevity of posterior resin composite and amalgam restorations. Dent Mater 2007;23:2-8. Opdam NJM, Bronkhorst EM, Loomans BAC, Huysmans MC. 12year survival of resin composite vs amalgam restorations. J Dent Res 2010;89:1063–1067. Pallesen U, van Dijken JW, Halken J, Hallonsten A-L, Höigaard R. Longevity of posterior resin composite restorations in
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Light-curing – who cares? Light-curing is often an under-appreciated stage in placing resin composites. Given the challenges in achieving suitable conditions for bonding, and applying the various steps in bonding systems, let alone resin composite increments, the risk is that clinicians will adopt a more relaxed approach to this stage in resin composite placement, as it is perceived as an opportunity to take a break. Light-curing is a critical stage to resin composite placement, and failure to pay sufficient attention can lead to an under-polymerised restoration which is susceptible to fracture. Some important considerations should be remembered: • For traditional resin composites, based on methyl methacrylate chemistry, increments of thickness less than 2mm need to be cured for 30 seconds. • The efficiency of curing depends on
permanent teeth in Public Dental Health Service: A prospective 8 years follow up. J Dent 2013;41:297–306. Mjör I, Wilson NHF. Teaching of Class I and Class II direct resin composite resin restorations: results of a survey of dental schools. J Am Dent Assoc 1998;129:1415– 1419. Wilson NHF, Mjör I. The teaching of class I and class II direct resin composite restorations in European dental schools. J Dent 2000;28:15-21. Lynch CD, Frazier KB, McConnell RJ, Blum IR, Wilson NHF. State-of-
the-art techniques in Operative Dentistry: contemporary teaching of posterior resin composites in UK and Irish dental schools. Br Dent J 2010;209:129–136. 10 Lynch CD, Shortall AC, Stewardson D, Tomson PL Burke FJT. Teaching posterior composite resin restorations in the United Kingdom and Ireland: consensus views of teachers. Br Dent J 2007;203:183-187. 11 Lynch CD et al. Guidance on the use of resin composites for direct restoration of posterior teeth: Academy of Operative Dentistry European Section. J Dent
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the proximity of the light-curing tip – if held far away from the surface of the increment (eg. if curing resin composite at the base of a deep cavity or gingival/proximal box), the energy applied will be reduced. Thinner increments will be required in such situations. • Newer LED light-curing units offer many advantages. However, care is needed with some newer narrower-emission lights when curing highly bleached shades in specialised aesthetic resin composites – such bleached resins do not always use camphorquinone (the ‘traditional’ photoactivator molecule, which adds a yellow tinge). Therefore, the LED and resin composite may not match each other. This is a discussion to have with your supplier before purchasing either newer LED lights or bleached/aesthetic resins. • If using traditional quartz halogen lightcuring units, please remember that the bulbs in these units lose power output and should be monitored for output and replaced as a matter of routine, possibly after around six months of use. The power output should be checked using a radiometer.
Matrices – clear, metal, or circumferential? Restoring missing proximal contours can be a real challenge with resin composites,
2014;42:377–383. 12 Opdam NJ, Roeters JJ, Kuijs R, Burgersdijk RC. Necessity of bevels for box only Class II composite restorations. J Prosthet Dent 1998;80:274-279. 13 Hilton TJ, Ferricane JL. Cavity preparation factors and microleakage of Class II composite restorations filled at intraoral temperatures. Amer J Dent 1999;12:123-130. 14 Lynch CD, O’Sullivan VR, Dockery P, McGillycuddy CT, Sloan AJ. Hunter-Schreger Band patterns in human tooth enamel. J Anat 2010;217:106–115.
particularly since, in contrast to amalgam, the material shrinks on setting. It is also important to remember when restoring occlusoproximal cavities that one must think of restoring the contour, not just the contact point. For restoring proximal contours, the available occlusoproximal resin composite options available are: • Clear matrix bands and lighttransmitting wedges • Sectional metal matrix bands and wooden/flexible wedges • Circumferential metal matrix bands and wooden/flexible wedges. Clear matrix bands were introduced at a time when it was thought that resin composite shrank towards the light, and that specific problems could be encountered when increments placed at the floor of a proximal box would lift when the light was incident from the occlusal surface. It was recognised over 15 years ago that resin composite does not shrink towards the light,19 so the need for such techniques can no longer be justified. Furthermore, problems were identified with clear matrix bands and light-transmitting wedges over 10 years ago.20 Due to their stiff and inflexible nature, such systems are associated with open proximal contacts on completed restorations, as well as overhang formation. As such, these systems are discredited and should no longer be used.
15 Burrow MF, Banomyong D, Harnirattisai C, Messer HH. Effect of glass-ionomer cement lining on postoperative sensitivity in occlusal cavities restored with resin composite–a randomized clinical trial. Oper Dent 2009;34:648– 655. 16 Peumans M, Kanumilli P, De Munck J, Van Landuyt K, Lambrechts P, Van Meerbeek B. Clinical effectiveness of contemporary adhesives: a systematic review of current clinical trials. Dent Mater 2005;21: 864881. 17 Kubo S, Yokota H, Yokota H, Hayashi Y. Two-year clinical
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Sectional and circumferential systems can be used with ease to recreate missing proximal contours. Evidence shows that sectional systems allow tighter proximal contacts than circumferential systems, albeit with slightly greater evidence of flash formation.21,22 Whichever system is used, careful application techniques should be used. It is also suggested that whichever system is used, the ‘missing’ proximal wall should be replaced first, to ensure adaptation of the resin composite in the proximal area.
Concluding remarks In this post-Minamata age, the postamalgam era is upon us. As well as ensuring a minimally invasive approach to the restoration of posterior teeth (which can be achieved when resin composite rather than amalgam restoration techniques are used), practitioners should seek to improve their skills and confidence in the use of resin composite materials. This can be achieved by proactively taking the approach in clinical practice (as is the case in many dental schools) that resin composites are the material of choice for restoring posterior teeth. Once the mindset of posterior resin composite placement is embraced, the challenge of placing such materials becomes a lot easier. It is better to be ahead of the curve than run the risk of lagging behind and, at some time in the future, being forced to make a sudden change in everyday clinical practice.
evaluation of one-step self-etch systems in non-carious cervical lesions. J Dent 2009;37:149-155. 18 Roggendorf MJ, Krämer N, Appelt A, Naumann M, Frankenberger R. Marginal quality of flowable 4-mm base vs. conventionally layered resin composite. J Dent 2011;39:643-647. 19 Versluis A, Tantbirojn D, Douglas WH. Do dental resin composites always shrink toward the light? Journal of Dental Research 1998;77:1435-1445. 20 Mullejans R, Badawi MO, Raab WH, Lang H. An in vitro comparison of metal and
transparent matrices used for bonded Class II resin composite restorations. Operative Dentistry 2003;28:122-126. 21 Loomans BAC, Opdam NJM, Roeters JFM, et al. Influence of resin composite resin consistency and placement technique on proximal contact tightness of Class II restorations. J Adhes Dent 2006;8:305-310. 22 Loomans BAC, Opdam NJM, Roeters FJM, et al. Restoration techniques and marginal overhang in Class II resin composite resin restorations. J Dent 2009;37:712– 717.
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