October 1, 2013
by Leendert (Len) Boksman, DDS, BSc, FADI, FICD; Brad Carson, BSc, DDS; Gildo Coelho Santos Jr., DDS, M
In his Meta-analysis of the clinical effectiveness of direct Class II restorations, Heintze states that, “more than five hundred million direct dental restorations are placed each year worldwide” and “in about 55 percent of the cases, resin composites or compomers are used.” When evaluating the clinical trials in the literature, he found that “restorations with hybrid and microfilled composites that were placed with enamel etching techniques and rubber dam showed the best overall performance, with resin restorations having no etching or self-etching adhesives demonstrating significant shortcomings and shorter longevity.”1 The dental research for the mean annual failure rate for Class I and Class II composite restorations ranges from 1-3 percent,2,3 while other reviews place the median failure rate after 10 years at about eight percent when compomers are excluded.1 This failure rate has been mostly attributed to secondary caries due to the inherent characteristic of composite resin polymerization shrinkage.4 This failure occurs especially in high C-factor restorations where either gap formation is induced due to the failure of the adhesive bond,5,6 or due to micro-crack development just outside of the cavo-surface margins.7,8
To help mitigate the effects of composite shrinkage, many insertion techniques for Class I and Class II composite resin restorations have been suggested. Variations utilizing composite placement in small 2 mm increments9 include horizontal layering,10 angled placement or oblique layering,11-13 the directed gingival shrinkage technique, also called the three-site technique,14 or individual cusp build-up.15 However, the use of these incremental insertion techniques to reduce polymerization shrinkage has been challenged, and in a study by Versluis et al. he has shown that no reduction in stress or improved marginal integrity is evident between small increments and bulk filling techniques.16 Of particular note in this study was the fact that oblique layering in increments showed higher stress concentration than a horizontal gingivo-occlusal incremental filling technique.
The reduction of stress with the use of a flowable low-viscosity composite resin has been documented and attributed to its low elastic modulus.17-19 The flowable composite, when used as a liner, is thought to have an ability to deform, thereby reducing the polymerization stress a resultant decrease in cuspal deflection.20 When evaluating lining with a flowable composite on the internal adaptation of the composite restorations using all-in-one adhesives, Yahag found void formation at the composite-adhesive-dentin interface in every all-in-one adhesive system.21 Percolation or water movement from the dentin through the adhesive layer causing adhesive degradation, has been shown by Tay when simplified adhesives are not covered by a hydrophobic resin layer.22 It may be that the addition of a flowable low viscosity hydrophobic resin over the dentin adhesive used, can play a role in reducing this “water tree” effect. In a clinical in-vivo setting, when using multiple step adhesives, even this lining technique can demonstrate inconsistent results.23
The disparity between the clinical in-vitro results of many of these studies (when looking at the effects of polymerization contraction, insertion technique and flowable lining), can be attributed to and explained by: the tooth type that is restored (premolar, molar, bovine, human), the position in the dental arch, the type (particle size and resin structure) and colour of composite used, the type and reactivity of photo initiator present in the composite, the size of the cavity preparation in width, depth and volume, the type of adhesive used, in-vivo versus in-vitro dentin characteristics, type and density of the light energy used, and by the realization that there is no standard testing methodology.
When looking at retrospective studies, it is important to remember that materials and techniques have evolved since the restorations in these studies were placed. To address the ever-present clinical challenge of polymerization contraction, new composite resin systems have been recently developed. A new low shrinkage composite with a silorane resin matrix containing oxirane and siloxane has recently been introduced to the marketplace which has a polymerization contraction of less than one percent (Filtek Silorane Low Shrink Posterior Restorative, 3M/Espe St. Paul MN).24 There are many current studies evaluating the newly introduced flowable bulk fill resin-based composites such as Venus Bulk Fill (Heraeus Kulzer Gmbh, Hanau, Germany) and Surefil SDR (Dentsply/Caulk, York, PA) which are recommended for bulk fill to expedite the restorative process and also to be used as liners in Class I and Class II restorations.25-27 When evaluating Surefil SDR, a dentin replacement product that contains a resin that has been modified by the addition of a polymerization modulator which reduces the polymerization contraction, these studies show: a reduced shrinkage stress on polymerization, lower shrinkage values than silorane composites, a reduction in cuspal deflection, and satisfactory bond strengths regardless of the filling technique and cavity depth. These bulk fill composites have a good depth of cure because of more potent initiators and a higher translucency, which means that clinically, a composite overlay is required for good esthetic results.28 As well Ilie and De Biasi have raised concerns about the physical properties such as micro-hardness when compared to other composite resin systems,29,30 with these systems being more prone to wear. As well, Miller has raised concerns that Surefil SDR might not be wear-resistant enough for contacts.31
Fortunately for clinicians, the one area where there is no current controversy, is the fact that the negative periodontal results of inflammation,32 bone loss33 and caries,34 created because of open contacts34 when Class II composite resins are placed, has been solved. The challenge and difficulty of creating tight inter-proximal contacts35 and proper anatomic profile, has been eliminated by advancements in matrix and separating ring systems. It is now possible to create tighter contacts intra-orally than those that existed prior to the restoration.36
It has always been obvious that, when tightening a Tofflemire retainer with a circumferential metal matrix band, even when the band is anatomically contoured, the band tends to flatten out interproximally due to tensioning, and an open contact is almost always the only possible outcome.37 Therefore, when possible, a sectional matrix which facilitates contact creation should be used. As well, when properly contoured occluso-gingivally, a sectional matrix will place the contact in its normal anatomic position rather than migrating the contact occlusally, which results in a weakened marginal ridge.38 It has been shown that a separating ring has a larger influence on the tightness of the new interproximal contact, than the physical consistency or flow of the material.36
The three matrix systems that have emerged as the market leaders for restoring class II restorations are the Garrison Composi-Tight 3D Sectional Matrix System, the Triodent Sectional Matrix System, and the Palodent Plus Sectional Matrix System.
The Composi-Tight Matrix System (Garrison/Clinical Research Dental) has evolved from the original Composi-Tight Silver Plus G-Rings which are made from circular stainless steel encased in plastic,39 and now feature a more anatomic soft silicone face. The ring penetrates the interproximal areas well to adapt the matrix band, minimizing proximal flash while giving good separation. The gingival contour is U-shaped to fit effortlessly over a gingival wedge. Recent improvements in the ring system include a better over-mould covering of the stainless steel, the introduction of the 3D Clear soft face ring (Fig. 1) which can be used with clear celluloid matrix bands (Composi-Tight 3D Clear Matrix bands)
for lateral and improved interproximal light penetration, and the recent introduction of the Composi-Tight 3DXR ring, which is designed to grab the infra-bulge better, thereby resisting slip off, especially in short teeth (Fig. 2). A recent addition to the matrix choice is the addition of slick bands, which are coated to facilitate removal due to the fact that they do not stick to the bonding agent (Fig. 3). The Composi-Tight system works well when the proximal box extent is minimal, but when the preparation is wide, this system tends to collapse the matrix band, indenting it to create poor anatomic form. Repeated heat cycles when autoclaving stainless steel can create metal fatigue and brittleness.
The Triodent V3 Ring Matrix System (Triodent/Clinical Research Dental) and the Palodent Plus Sectional Matrix System (Dentsply/Caulk, Milford DE) are similar in that they have a ring that is fabricated from high elastic memory nickel titanium. It was introduced in two sizes; one for premolar applications and the other for molars (Fig. 4). The V-shaped notch in the plastic tines allows placement over the wedge and hence the name of the product line, while the interproximal shape of the tines does not readily fall into wide embrasure preparations due to their rounded design. Since the tines do not go as deep interproximally, there may be more flash at the proximal margins when a “packable” type composite is placed. The matrix bands have an anatomic occlusal embrasure design, which fits into the occlusal tab’s perforations well as the small perforations placed laterally on the matrix wings. The matrix bands have good occluso-gingival contour, and are easily placed and removed with the accompanying pin-tweezer which fits into the occlusal tab which has a small perforation and the small perforations placed laterally on the matrix wings. The matrix system was recently expanded with the new Super Curve coated matrix with a deeper gingival design which accommodates deep class II restorations, has a better curvature, and has a non stick surface (Fig. 5). The new V4 ClearMetal Matrix System (Clinical Research Dental) incorporates three major changes. The rings have new transparent tips, allowing a cure-through option (Fig. 6). A new ClearMetal Matrix has been introduced with “micro-windows” to allow light to pass through. This design retains the rigidity of a metal matrix, but adds transparency (Fig. 7). The ClearMetal matrix is also non-stick as it is coated with PTFE. The plastic wedge has been updated, with the V4 wedge having a segmented design adapting the matrix well, and it better resists “backing out” as some plastic wedges have a tendency to do (Fig. 8).
The advantages of the V4 system include:
• Two ring sizes to give consistent separation force for premolars and molars;
• Nickel titanium metal which resists metal fatigue better than stainless steel;
• A ring tip design that does not readily “fall into” the preparation when the proximal box is extended more than ideal;
• A new plastic clear ring tip design to facilitate interproximal curing;
• A new ClearMetal matrix with micro-windows allowing light penetration;
• Matrix designs which give better anatomic form occluso-gingivally and bucco-lingually;
• Matrix designs which facilitate deep proximal boxes.
Matrices that are easier to place and remove due to the holes allowing the pin tweezers to handle and grab the matrix
CLINICAL CASE PRESENTATIONS:
A female patient presented to the dental clinic with a defective DO amalgam restoration (Fig. 9). After colour selection, anaesthesia and precise rubber dam application to minimize moisture contamination (Fig. 10), the amalgam and all caries were removed resulting in a wider than ideal lingual box extension (Fig. 11). The non-stick ClearMetal Matrix with micro-windows was inserted using the pin-tweezers (Fig. 12) with the curvature bucco-lingually and occluso-gingivally obvious in Figure 13. The transparent V4 wedge was placed with pin tweezers from the widest embrasure to adapt the matrix to the gingival margin (Fig. 14), with the V4 ring applied over the gingival wedge adapting the matrix and creating separation. The angulation of the V4 ring allows for stacking when restoring MOD restorations and for better placement of the curing light close to the occlusal surface of the tooth structure (Fig. 15). Note that the gingival margin is completely closed and even in a preparation with a wide lingual embrasure, the V4 does not distort the contour of the matrix band (Fig. 16). The enamel margins were etched first by placing Ultra-Etch (Ultradent) phosphoric acid for five seconds and then the cavity preparation was etched for another ten seconds (Fig. 17). The cavity preparation was thoroughly rinsed for 15 seconds and lightly dried (Fig. 18). Application of G5 All Purpose Desensitizer (Clinician’s Choice) to the dentin coagulated the plasma proteins in the tubules, decontaminated the preparation (anti-microbial) and strengthened the collagen by cross-linking (Fig. 19). The excess was removed with dry air and suction, leaving the surface moist with no puddling. The MPa Maximum Performance Adhesive (Clinician’s Choice) was liberally applied, and the solvent evaporated with a dry air syringe for 10 seconds (Fig. 20). The MPa was fully polymerized with a Valo broad spectrum LED curing light (Ultradent) placed at 90 degrees to the surface for 10 seconds (Fig. 21). DeMark radiopaque flowable liner (Cosmedent) is teased into a fine layer over the dentin and over the gingival floor of the preparation (Fig. 22). This created a secondary hydrophobic layer, while closely adapting the composite to the gingival margin and, as well, introducing a “stress absorbing layer.” The DeMark was cured for 10 seconds with the Valo. Renamel Nano A2 (Cosmedent) was incrementally placed into the cavity preparation with the gingival layer cured for 20 seconds and the successive layers for 10 seconds each (Fig. 23). Upon removal of the V4 and ClearMetal Matrix the occlusal and interproximal embrasures were fully formed with minimal occlusal finishing required (Fig. 24). The lateral photograph Figure 25 shows minimal flash with proper anatomic contour immediately after matrix removal. The D-Fine Double Diamond primary polisher (Clinician’s Choice) was used with light pressure for pre-polishing the restoration (Fig. 26), followed by a D-Fine Double Diamond high shine polisher, which has a finer diamond polishing particle (Fig. 27). Figure 28 shows an occlusal view of the final restoration.
With the newly developed separating and matrix armamentarium that is available, it is now possible for the clinician to predictably create tight and anatomic Class II restorations.OH
Dr. Leendert (Len) Boksman is a paid part time consultant to Clinical Research Dental.
Dr. Brad Carson has no disclosures.
Dr. Gildo Coelho Santos Jr. has received materials support from Clinical Research Dental.
Dr. Leendert (Len) Boksman is a former tenured Associate Professor of Restorative Dentistry at the Schulich School of Medicine and Dentistry in London, Ontario.He has recently retired from private practice, and writes extensively and teaches nationally and internationally on topics related to Restorative. He currently consults part-time for several dental manufacturers including Clinical Research Dental and Clinician’s Choice. He is an Adjunct Clinical Professor at the University of Technology, School of Oral Health Sciences Dental Faculty in Jamaica where he donates his time.
Oral Health welcomes this original article.
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