In Practice materials

clinical brief | tech profile

The Search for a Low-Shrinkage Direct Composite Decreasing polymerization shrinkage stress is a critical determinant on the affects of composite curing on the adhesive interface.

By Robert A. Lowe, DDS

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ince the advent of lightcured direct composite restorations in the early 1980s, the search for the “tooth-colored amalgam replacement” has continued. Every dentist who places posterior composite resins has at the top of his or her “wish list” a composite material that can be placed using a bulk-fill technique similar to that of dental amalgam. Two primary reasons this has not occurred are polymerization shrinkage stress during the curing process and a limited depth of cure for composite materials. Traditional placement techniques for composite resins include incremental placement mainly for these reasons. The effect of polymerization shrinkage stress is greater on larger increments of composites than on smaller increments. Most clinicians recommend placing composites in 2-mm increments. Depth of cure is also critical. If the curing light does not cure the material in the deeper areas of a cavity because of the proximity to the light source or the inability of the light to penetrate the restorative material, the resultant uncured material can adversely affect the bond to tooth structure and, hence, the quality and longevity of the restoration. Robert A. Lowe, DDS

Diplomat, American Board of Aesthetic Dentistry Private Practice Charlotte, North Carolina

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Material science has been focused on creating a low-shrinkage composite (most of the current composites on the market shrink about 2.5% to 3.5%) to increase the durability of the composite bond to tooth structure and reduce the possibility of microleakage, one of the main causes of recurrent decay and ultimate restoration failure. While progress has been made in this area, as evidenced by the introduction of composite materials with lower shrinkage values, lower shrinkage alone cannot justify bulk placement. It is the stress created at bonded interfaces that must be lowered and stress can be independent of shrinkage. That is to say, two materials with the same amount of shrinkage can create different levels of stress on bonded interfaces depending on their polymerization dynamics.1-11 Two of the approaches that have been looked at as a potential solution to this problem are the development of a lowstress composite filling material using a different monomer system other than bis-GMA, and development of a lowshrinkage flowable material to use as a dentin replacement under conventional posterior composite resins.

com) is a silorane-based composite material that has been developed out of this research. As an alternative to conventional composite resins, the main advantage of silorane is its low shrinkage. Filtek LS also requires a dedicated adhesive bonding resin, LS Bond (3M ESPE) to achieve similar bond strengths to enamel and dentin as seen in conventional adhesive systems using bisGMA-based composite resins. The volumetric shrinkage of Filtek LS has been reported at 1.7%. Most conventional composites shrink between 3% and 5% during polymerization when volumetric shrinkage is measured. Conventional composites such as Aelite™ LS (Bisco, www.bisco.com), Kalore™ (GC America, www.gcamerica.com), N’Durance™ (Septodont, www.septodontusa.com), and Grandio® (VOCO America, www. vocoamerica.com) are advertised as

“low-shrinkage composites” and have volumetric shrinkages of less than 3% (Aelite LS: 1.39%, Kalore: 1.72%, N’Durance: 1.4%, and Grandio: 2.4%, respectively).13-16 It has been shown that these low-shrinkage composite materials do tend to have significantly less microleakage after mechanical load cycling.17 Some clinical studies do, however, raise the question on whether this translates into a clinically significant difference as to the long-term durability of the restoration.18

Bulk Fill Flowable Base for Posterior Restorations

Recently, a unique type of flowable composite resin has been developed that is intended to be used as a base beneath posterior composite resin restorations. Certainly, the use of a flowable composite as a liner or base beneath posterior composite restorations is not a new concept. Such use has been claimed to increase marginal adaptation in the gingival marginal area of Class II composite restorations, thereby reducing microleakage. It has also been claimed to counter the polymerization shrinkage stress of overlying composite resins because of the more elastic nature of flowable composites. Neither of these perceived advantages has been validated, but there is relatively broad consensus that the use of flowable composites

Low-Shrinkage Direct Composites

A new monomer system described by Weinmann et al,12 called silorane, is obtained from the reaction of oxirane and siloxane molecules. The mechanism of compensating stress in this system is achieved by opening the oxirane ring during the polymerization process. Filtek™ LS (3M ESPE, www.3mespe.

inside dentistry | January 2010 | insidedentistry.net

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PREOPERATIVE VIEW (1.) A preoperative occlusal view of tooth No. 12. Recurrent decay and marginal leakage existed, requiring that the defective restoration be replaced. (2.) The defective restoration was removed and decay excavated.

In Practice

materials

does help to achieve optimal adaptation of overlying composite to the intricacies of cavity preparations. A new flowable composite (SureFil® SDR Flow, DENTSPLY Caulk, www. caulk.com) is indicated for use as a bulkfill base beneath posterior composite restorations and can be bulk filled in layers up to 4 mm in depth. Being able to place that amount of material in a single increment is a significant time saver, and while the concept sounds quite simple, there are several important requirements a material must meet for this particular indication. According to the manufacturer, these include the following.

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Increased Depth of Cure

This is perhaps the most obvious requirement for the material. It is essential that the flowable composite cure from top to bottom to a minimal depth of 4 mm. The manufacturer reports that Surefil SDR meets this requirement because of its polymerization initiating process and its optical properties that enhance light transmission. It should be noted that while this material is radiopaque, it would appear more translucent in color than many composite “dentin replacements.” This is to allow for light penetration and a greater depth of cure. It is important to pay attention to what manufacturers claim regarding the depth of cure of their materials and to have an idea as to how those claims were substantiated. It may be possible to realize a certain depth of cure in the laboratory where the light can be positioned only a millimeter from the surface of the material being cured but not in a clinical situation where the light can be several millimeters removed.

Specialized Handling

This requirement is essential if the material is to offer true convenience and performance. Surefil SDR, being a flowable material, can be placed in bulk quantities very quickly because it readily adapts to the internal configuration of cavities without the need for manipulation after dispensing (Figure 1 through Figure 11). In addition, the material levels itself (self-leveling) after only seconds to form a uniform base for subsequent placement of composite, again obviating the need for further manipulation. Without the rheological properties this material possesses, it would not be possible to bulk-fill while

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RESTORATION STEPS (3.) The adhesive resin was placed into the preparation using a microbrush, then light-cured. (4.) A sectional matrix (Garrison 3D Sectional Matrix; Garrison Dental Solutions) was placed on the distal aspect to restore the contour and contact to the disto-proximal surface. Since there was a diastema present on the mesial aspect, this surface would be restored directly without a matrix. (5.) Surefil SDR was used to bulk-fill the cavity as a dentin replacement.

ensuring optimal adaptation to all aspects of the cavity preparation (Figure 12 through Figure 14).

Low Polymerization Shrinkage Stress

Composites resins all shrink to some extent upon photopolymerization. Flowable composites shrink to a greater extent because of a lower filler loading. If not allowed to shrink, as when bonded to tooth surfaces, stress will be created on the bonded surfaces which can lead to marginal defects, and is thought to lead to postoperative sensitivity. The challenges facing a bulk-fill base with respect to polymerization shrinkage

inside dentistry | January 2010 | insidedentistry.net

RESTORATION STEPS (6.) Note the self-leveling property of the dentin replacement prior to light-curing. The pulpal floor and proximal box were filled to the level of the proximal contact area and then light-cured. (7.) The facial cusp and marginal ridge were sculpted to contour using a microhybrid composite resin. (8.) Minor marginal adjustment and contouring was accomplished using an interproximal finishing diamond.

stress are large. The volume of material being placed can be relatively large, and the larger the volume of material, the greater the shrinkage stress. In addition, the C factor of posterior cavity preparations is large—a Class I restoration, in fact, has the largest C factor of all cavity classifications. The C factor is the ratio of bonded to non-bonded surfaces and would compute to a 5 for Class I restorations and a 2 for a Class II restoration. Reduction of polymerization shrinkage stress, as might be expected, is the most difficult requirement to meet for a bulk fill material. The manufacturer reports that Surefil SDR meets this requirement by incorporating a unique curing process

FINAL STEPS (9.) After final polishing with rubber abrasives, the occlusion was verified using articulation paper. (10.) After etching for 2 seconds and a thorough rinse with water spray, a surface sealant was placed on the restoration to seal any microscopic areas of imperfection that may be present at the margins, yet remain undetectable to an explorer. (11.) An occlusal view of the completed restoration of tooth No. 12 using a low-shrinkage flowable resin as a dentin replacement.

that builds very little stress as the material is forming the bonds of polymerization. The net effect of this is very little stress being created on bonded surfaces after the material has polymerized.19-28

Conclusion

Composite shrinkage will continue to be a problem that is looked at by scientists and clinicians alike to see if it is possible to create a material that has no shrinkage, better marginal integrity, but yet has satisfactory physical properties and handling characteristics that make significant improvements in today’s available technologies. Decreasing the polymerization shrinkage stress seems

In Practice

materials to be a critical determinant on the affects of composite curing on the adhesive interface and does not necessarily translate to the volumetric shrinkage of the restorative material. References

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fig. 14 SECOND CASE EXAMPLE (12.) Two mandibular molars were excavated and prepared for restoration with composite resin. (13.) After etching and placement of adhesive resin, Surefil SDR was placed as a dentin replacement. (14.) An occlusal view of the completed restorations after placement of microhybrid composite completed the enamel layer of the restoration.

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1. He Z, Shimada Y, Sadr A, et al. The effects of cavity size and filling method on the bonding to Class I cavities. J Adhes Dent. 2008;10(6): 447-453. 2. Nayif MM, Nakajima M, Foxton RM, Tagami J. Bond strength and ultimate tensile strength of resin composite filled into dentine cavity; effect of bulk and incremental filling technique. J Dent. 2008;36(3):228-234. 3. Félix SA, González-López S, Mauricio PD, et al. Effects of filling techniques on the regional bond strength to lateral walls in Class I cavities. Oper Dent. 2007;32(6):602-609. 4. Ilie N, Hickel R. Quality of curing in relation to hardness, degree of cure and polymerization depth measured on a nano-hybrid composite. Am J Dent. 2007;20(4):263-268. 5. Lazarchik DA, Hammond BD, Sikes CL, et al. Hardness comparison of bulk-filled/ transtooth and incremental-filled/occlusally irradiated composite resins. J Prosthet Dent. 2007;98(2):129-140. 6. Chikawa H, Inai N, Cho E, et al. Effect of incremental filling technique on adhesion of light-cured resin composite to cavity floor. Dent Mater J. 2006;25(3):503-508. 7. Quellet D. Considerations and techniques for multiple bulk-fill direct posterior composites. Compend Contin Educ Dent. 1995;16(12): 1212-1216. 8. Hirabayashi S, Hood JA, Hirasawa T. The extent of polymerization of Class II lightcured composite resin restorations; effects of incremental placement technique, exposure time and heating for resin inlays. Dent Mater J. 1993;12(2):159-170. 9. Puckett A, Fitchie J, Hembree J Jr, Smith J. The effect of incremental versus bulk fill

characteristics, and microtensile bond strengths of a new low shrinkage composite to dentin after artificial aging. Dent Mater. 2009;25:589-600. 14. Simon JF, Waldemar G, de Rik BA. Lowshrink composites. Inside Dentistry. 2009; 5(3):56-58. 15. Radz G. New chemistry opening doors. Dental Products Report. September 2009. Available at: http://www.dentalproductsreport. com/articles/show/dpr0909_360_cosresto. Accessed Decmber 9, 2009. 16. Data on file. GC America Corporation R&D, Tokyo, Japan. 17. Yamazaki PCV, Bedran-Russo AKB, Pereira PNR, Swift EJ. Microleakage evaluation of a new low-shrinkage composite restorative material. Oper Dent. 2006;31(6):670-676. 18. van Dijken JWV, Lindberg A. Clinical ef­ fectiveness of a low shrinkage resin composite: a five-year evaluation. J Adhes Dent. 2009;11: 143-148. 19. Clifford SS, Roman-Alicea K, Tantbirojn D, Versluis A. Shrinkage and hardness of dental composites acquired with different curing lights. Quintessence Int. 2009;40(3):203-214. 20. Park J, Chang J, Ferracane J, Lee IB. How should composite be layered to reduce shrinkage stress: incremental or bulk filling? Dent Mater. 2008;24(11):1501-1505. 21. Muñoz CA, Bond PR, Sy-Muñoz J, et al. Effect of pre-heating on depth of cure and surface hardness of light-polymerized resin composites. Am J Dent. 2008;21(4):215-222. 22. Cunha LG, Alonso RC, de Souza-Junior EJ, et al. Influence of the curing method on the postpolymerization shrinkage stress of a composite resin. J Appl Oral Sci. 2008;16(4):266-270. 2 3. G e r d o l l e DA , Mo r t i e r E , D r oz D. Microleakage and polymerization shrinkage of various polymer restorative materials. J Dent Child. 2008;75(2):125-133. 24. Lopes LG, Franco EB, Pereira JC, Mondelli RF. Effect of light-curing units and activation mode on polymerization shrinkage and shrinkage stress of composite resins. J Appl Oral Sci. 2008;16(1):35-42.

techniques on the microleakage of composite resin using a glass-ionomer liner. Oper Dent. 1992;17(5):186-191. 10. Tjan AH, Bergh BH, Lidner C. Effect of various incremental techniques on the marginal adaptation of class II composite resin restorations. J Prosthet Dent. 1992;67(1):62-66. 11. Wieczkowski G Jr, Joynt RB, Klockowski R, Davis EL. Effects of incremental versus bulk fill technique on resistance to cuspal fracture of teeth restored with posterior composites. J Prosthet Dent. 1988;60(3):283-287. 12. Weinmann W, Thalacker C, Guggenberger R. Siloranes in dental composites. Dent Mater. 2005;21:68-74. 13. Duarte S, Phark, JH, Varjao FM, Sadan

25. Pereira RA, Araujo PA, CastañedaEspinosa JC, Mondelli RF. Comparative analysis of the shrinkage stress of composite resins. J Appl Oral Sci. 2008;16(1):30-34. 26. Ilie N, Hickel R. Quality of curing in relation to hardness, degree of cure and polymerization depth measured on a nano-hybrid composite. Am J Dent. 2007;20(4):263-268. 27. Tanoue N, Murakami M, Koizumi H, et al. Depth of cure and hardness of an indirect composite polymerized with three laboratory curing units. J Oral Sci. 2007;49(1):25-29. 28. Ilie N, Kunzelmann KH, Visvanathan A, Hickel R. Curing behavior of a nanocomposite as a function of polymerization procedure.

A . Na n o l e a k a g e , u l t r a m o r p h o l o g i c a l

Dent Mater J. 2005;24(4):469-477.

materials | buyer’s guide

In Practice

Composite Resin Systems A sampling of composites available for the clinical armamentarium.

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hese featured composite systems offer many advantages and benefits, including ease of use, high strength properties, and more lifelike restorations. For more information about any of these products, visit any of the manufacturer Web sites listed.

Vertise Flow

Kerr introduces Vertise™ Flow, its first self-adhering flowable composite. Powered by Kerr’s renowned OptiBond® adhesive technology, this product will greatly simplify the direct restorative procedure for today’s time-challenged dentist by incorporating the bonding agent into the flowable. For more information, visit www.kerrdental.com. (Circle 69 on Reader Service Card)

EPIC®-TMPT

Parkell, Inc’s EPIC®-TMPT is a non-sticky, micro-filled composite resin that contains a reactive organic filler, producing a resilient and durable restoration. EPIC-TMPT polishes beautifully, leaving margins all but invisible, and blends in with its chameleon-like shades. For more information, visit www.parkell.com. (Circle 66 on Reader Service Card)

Tetric EvoCeram Grandio

Grandio is a new 87% by weight filled nanohybrid composite. The high filler degree leads to outstanding wear resistance due to a high surface hardness, enamel-like thermal expansion, and reduced shrinkage. Grandio has excellent translucency and a curing time of only 20 seconds. It outperforms the wear of hybrids, has the beauty of microfilled composites, and is available in pre-dosed standard compules or syringes. For more information, visit www.voco.com/usa. (Circle 67 on Reader Service Card)

Tetric EvoCeram features three types of nanoparticles; nano-fillers of different sizes for low wear and high polishability; nano-pigments that help better adjust the shade of the restoration to the surrounding teeth and impart a chameleon effect for single-shade, “universal” placement; and nano-modifiers for excellent handling properties and stability. For more information, visit www.ivoclarvivadent.us. (Circle 70 on Reader Service Card)

REFLEXIONS™

BISCO Dental Products introduces REFLEXIONS™, a simplified universal nanotechnology composite system. The system consists of 4 highly chromatic Low-Shrinking XLS Dentin and 4 translucent Highly Polishable XP Enamel shades. REFLEXIONS composites are indicated for use in all classes of anterior and posterior direct restorations. For more information, visit www.bisco.com. (Circle 71 on Reader Service Card)

N’Durance Composite

CLEARFIL MAJESTY Posterior

A light-cure, nano-superfilled, radiopaque restorative composite resin, CLEARFIL MAJESTY Posterior is composed of nano- and micro-inorganic filler treated with a proprietary new surface coating technology. The new surface technology permits a larger quantity of nanofiller to be dispersed in the resin matrix, which consists of monomer and microfiller. The resulting resin matrix is reinforced with a filler loading of 92wt% (82vol%). For more information, visit www.kuraraydental.com. (Circle 68 on Reader Service Card)

The unique nano dimer conversion technology created by Septodont changes the shrinkage dynamic. With over 75% conversion and as little as 1.4% shrinkage, N’Durance restorations provide great wear resistance, biocompatibility, and color stability as well as exhibiting no postoperative sensitivity. N’Durance is available through the dental supply dealer. For more information, visit www. septodontusa.com. (Circle 72 on Reader Service Card) insidedentistry.net | January 2010 | inside dentistry

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In Practice

materials | buyer’s guide

Vit-l-escence

Vit-l-escence is a Bis-GMA-based, radiopaque microhybrid system with an average particle size of 0.7 μm. The all-composite shade guide contains uniquely shaded tabs to assist in the most refined layering and shade selection possible. Low-translucency, highly fluorescent dentin shades combined with high-translucency, opalescent/translucent enamel shades facilitate superior reproduction of natural teeth. For more information, visit www.ultradent.com. (Circle 73 on Reader Service Card)

Venus Diamond®

Venus Diamond®, a universal nano-hybrid composite, is the newest product to join the Venus® Esthetic System which offers dentists and laboratories a unified, integrated, and simplified approach to esthetic restorations, with unprecedented and unique handling, exceptional strength and durability, low shrinkage, long lasting polishability, and perfect color adaptation. For more information, visit www.smilebyvenus.com. (Circle 77 on Reader Service Card)

Kalore™

Formulated with exclusive, new monomer technology from DuPont, Kalore offers superior handling. Patented HDR prepolymerized fillers offer exceptional and easy polishability that is sustainable and flawless beauty is achieved from the optimization of matrix and filler refractive indices. For more information, visit www.kalore.net. (Circle 78 on Reader Service Card)

8 Filtek™ LS

Virtuoso Flowable

The Filtek™ LS Low Shrink Posterior Restorative System from 3M ESPE combines the lowest-shrinking silorane-based composite with a dedicated, two-step, self-etching bonding system: 3M™ ESPE™ LS System Adhesive Self-Etch Primer and Bond. It offers excellent bond strength to enamel and dentin, and is the one and only adhesive formulated to provide optimal bonding with such an extraordinarily low-shrinking composite. For more information, visit solutions.3m.com. (Circle 74 on Reader Service Card)

Virtuoso Flowable composite is intended for use with small restorations that present difficult access. The light-cure, lowviscosity, flowable composite has characteristics designed for fast, easy techniques. Its precision needle tip dispensing allows the material to flow quickly for precise placement. For more information, visit www.denmat.com. (Circle 79 on Reader Service Card)

SureFil® SDR™ flow

SureFil® SDR™ flow material is the first ever bulk fill flowable base that allows you to place posterior composites in 40% less time. The new stress decreasing resin (SDR™) system allows for bulk placements up to 4 mm with a 20-second cure time. For more information, www.surefilsdrflow.com. (Circle 75 on Reader Service Card)

Accolade SRO Super Radiopaque Flowable

With a radiopacity of 320% of aluminum (similar to titanium), radiographs were never easier to read! Available in A5, A2, & Extra Light. For more information, visit www.danvillematerials.com. (Circle 76 on Reader Service Card)

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Luxatemp Fluorescence

Luxatemp Fluorescence reacts to light more like natural teeth, so it makes provisionals look more lifelike than ever before. All Luxatemp formulations offer low shrinkage during polymerization, high flexural strength, and can be fabricated directly in the patient’s mouth without concern for temperature. Luxatemp Fluorescence is available in six shades, in 76-gm cartridges and dispensed through the 10:1 Automix dispensing gun. For more information, visit www.dmg-america.com. (Circle 80 on Reader Service Card)