Factors for Successful Composite Restorations
Operator technique remains key even with today’s advanced materials
Many steps go into the placement of a successful and long-lasting composite restoration. When a restoration fails, understanding the cause of the failure is an important first step in preventing a similar problem from occurring in the future.
It is easy for a dentist to put the blame for a failed restoration on the manufacturer of the material. In some instances, the manufacturer is the one to blame, as materials are often sent to the market based on laboratory testing without the proper clinical testing. Generally, this is not the case, however. When faced with a failed restoration, the dentist must look at his/her technique and the way the material is being used before placing all the blame for failure on the manufacturer.
Reasons for Failure
The principal reasons for failure are secondary caries, fracture, marginal deficiencies, wear, and postoperative sensitivity.1 Many of these things can be controlled by the operator; however, the patient also has a great deal to do with the long-term success of any restoration. In a recent prospective cohort study,2 it was found that patient age, patient ethnicity, number of surfaces restored, dentist sex, and dentist practice workload were significant predictors of early restoration failure, whereas the restorative material used was not significant. Therefore, before assuming that failure stems from a problem with a material, it is important to consider other relevant factors that may contribute to the failure of a restoration.
When analyzing a failure, one of the first questions one should ask is, “Were the manufacturers’ instructions read and followed for the product?” Many dentists assume that all bonding and composites systems are the same, and if they are familiar with one, then they can use any system on the market. With some bonding systems, the manufacturer’s instructions say to scrub the product into the dentin for a certain period of time, whereas others say to leave it undisturbed for a different period of time. Do you etch with phosphoric acid prior to use, and if so, for how long? Some composites require more curing time or smaller layers, whereas others need less light and can be bulk filled. Unless the instructions are read before use, the incorrect technique may lead to an inferior restoration, which leads to both an unhappy patient and dentist.
Effectiveness of Moisture Control
Excellent moisture control of the operating field is extremely important for a successful restoration. The use of a properly placed rubber dam during placement of the composite material is ideal. Restorations that were placed with a rubber dam have showed significantly fewer material fractures that needed replacement; this also had a significant effect on overall longevity.3 Wet bonding is recommended for most adhesive systems; however, the optimal amount of wetness varies depending upon the adhesive system (etch & rinse or self-etch) used and the primer (acetone or ethanol) in the system. No system includes blood or saliva as part of the bonding technique.
Recently, alternative systems for isolation, including Isolite/Isodry (Isolite Systems) and the Optragate (Ivoclar) have been introduced, and seem to work well. These systems can be a valuable addition when placing technique-sensitive materials and should be considered when help is needed placing hydrophobic resin materials and use of the rubber dam is not possible.
Typical resin composites applied in restorative dentistry exhibit volumetric shrinkage values from less than 1% up to 6%, depending on the formulation and the curing conditions.4 The result of this shrinkage can be the restorative material pulling away from the tooth, leaving a gap that eventually lead to postoperative sensitivity, marginal staining, recurrent caries, and eventual loss of the restoration.4 Different methods have been suggested to overcome this problem, including incremental layering,5 placement of flowable composite as stress breaker,6 and different light applications (pulse or ramp curing).7 The newest approach has been with the development of low-shrinkage stress composites that can be bulk filled because of their reported reduction in shrinkage stress. These seem to be very interesting for future consideration.
Each composite requires a certain amount of energy (joules) for complete curing. This may vary by the manufacturer, by the type of composite material, and the shade of the composite. It is a function of the power of the curing light (mW/cm2) and the amount of time that the light is delivered. Unfortunately, the amount of delivered energy can vary due to the improper placement of the light tip, movement of the light tip during curing, distance of the light tip from the resin, shade and type of the resin material, condition of the light curing unit, or thickness of the resin. Even the most powerful curing light will not cure a composite if it is not properly placed. Just because the top layer of the composite is hard, that does not mean that the composite is cured at the bottom.
In general, not enough attention is given to proper placement of the curing light or the condition of the light. The proper amount of irradiance is determined by the manufacturer and the shade of the composite. Incomplete or insufficient curing adversely affects the resin’s physical properties, reduces the bond strength to the tooth, decreases the biocompatibility of the restoration, increases marginal wear and breakdown, and increases bacterial colonization of the restoration.8
Several surveys have shown that many QTH (quartz-tungsten-halogen) curing lights in dental offices do not deliver enough light energy to completely cure composites.9
Size and Location of Restoration
The position of the tooth in the arch and the size of the cavity have been shown to be a factor in the success of a restoration. One study found the risk of failure in the molar area to be twice as high as for premolars,10 while another study placed the failure rate in lower molars as three times that of the upper premolars.11 Multi-surfaced restorations are also more prone to failure than single surface restorations. A study calculated that for every surface added to the restoration, a 40% increase in the failure rate resulted.10
Proper Placement Technique
Many experts recommend incremental placement of the composite because of the decrease in the “C” factor and the resultant decrease in the shrinkage stress.6 This has been the recommended technique; however, with the introduction of the low shrinkage stress composite materials, bulk filling has become more popular. Because of their low stress and good depth of cure, these composites may be the future.
No matter which technique that is used, proper matrix placement is extremely important for the restoration success. A restoration that has an open contact or a gingival overhang is not an acceptable restoration. Food impaction from an open contact does not lead to good gingival health and an open or rough margin may lead to bacterial growth and eventual recurrent decay. Sectional matrix systems and separating rings may lead better contours, contacts, and marginal seal.
Proximal Box Placement
Bonding failures have been commonly attributed to the gingival margin of Class II composite restorations.12 In the proximal box of most Class II restorations, there is little or no enamel at the margin for bonding. Gaps at the gingival margins have been attributed to the potential for poor bonding at this margin.13 The discrepancy between etching depth and adhesive infiltration leads to a large area of exposed collagen at the gingival margin.14
Another variable that may interfere with the bonding in the gingival area is water content. Increased water content leads to reduced adhesive infiltration and lower monomer/polymer conversion of the adhesive at the gingival margin as compared to the proximal wall.15 Sometimes, the placement of a glass ionomer as the first layer for these deep margins may be considered because of some of the favorable qualities of this material.16
Correct color matching of the restoration and the tooth is an important aspect of the esthetic restoration. Many things can complicate making the correct shade selection, such as the lighting system in the operatory, the fact that teeth lighten when dehydrated, the color of the operatory or the patient’s clothing, and the experience of the person doing the shade selection. Shade selection requires knowledge of physics and the physiology of color; therefore, it is both an art and a science requiring in depth knowledge, accurate clinical judgment, and perception on the part of the dentist.17 Unfortunately, the limitations of shade guides are significant factors that compromise shade matching procedures in dentistry and contribute to the dissatisfaction of clinicians, technicians, and patients.18
Finishing and Polishing
High-quality finishing and polishing improve both the esthetics and the longevity of composite restorations, whereas rough, poorly polished surfaces contribute to staining, plaque accumulation, gingival irritation, recurrent caries, and discoloration of the restoration.19 There are many systems available for the finishing and polishing process, including carbide or fine diamond burs, disks, rubber or silicone points or wheels, bristle brushes, and polishing pastes. It is important to use each correctly and in the proper sequence to achieve the best polish. Skipping steps may shorten the appointment time, but also shortens the useful life of the restoration. Discoloration of composite resins was found to be related to surface treatments as well as resin composition.20
There are many variables that go into the success or failure of a resin composite restoration. Although it is easy to blame the manufacturer for a failure and ask them for a better material, an improved material used incorrectly will not make for a better restoration. Every so often, it is necessary to step back and review the way the material is being used to make sure that all the basics are covered before looking for that better material. Manufacturers can—and should—be held accountable if a material in the market does not perform as claimed; however, most manufacturers endeavor to give the profession the best materials possible. As dental professionals, it is our responsibility to follow best clinical practices and ensure that we are using these materials correctly for the benefit of our patients and our practices.
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2. McCracken MS, Gordan VV, Litaker MS, et al; National Dental Practice-Based Research Network Collaborative Group. A 24-month evaluation of amalgam and resin-based composite restorations: Findings from The National Dental Practice-Based Research Network. J Am Dent Assoc. 2013;144(6):583-593.
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7. Feilzer AJ, Dooren LH, de Gee AJ, Davidson CL. Influence of light intensity on polymerization shrinkage and integrity of restoration-cavity interface. Eur J Oral Sci. 1995;103(5):322-326.
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9. Martin FE. A survey of the efficiency of visible light curing units. J Dent. 1998;26(3):239-243.
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13. Roulet JF. Benefits and disadvantages of tooth-coloured alternatives to amalgam. J Dent. 1997;25(6):459-473.
14. Bohaty BS, Ye Q, Misra A, et al. Posterior composite restoration update: focus on factors influencing form and function. Clin Cosmet Investig Dent. 2013;5:33-42. doi: 10.2147/CCIDE.S42044.
15. Wang Y, Spencer P. Interfacial chemistry of class II composite restoration: structure analysis. J Biomed Mater Res A. 2005;75(3):580-587.
16. Hagge MS, Lindemuth JS, Mason JF, Simon JF. Effect of four intermediate layer treatments on microleakage of Class II composite restorations. Gen Dent. 2001;49(5):489-95; quiz 496-497.
17. Judd DB, Wyszecki G. Color in Business, Science, and Industry. 3rd ed. New York: Wiley-Interscience;
18. Rodrigues S, Shetty SR, Prithviraj DR. An evaluation of shade differences between natural anterior teeth in different age groups and gender using commercially available shade guides. J Indian Prosthodont Soc. 2012;12(4):222-30. doi: 10.1007/s13191-012-0134-9.
19. Lopes GC, Vieira LC, Araujo E. Direct composite resin restorations: a review of some clinical procedures to achieve predictable results in posterior teeth. J Esthet Restor Dent. 2004;16(1):19-31; discussion 32.
20. Gönülol N, Yilmaz F. The effects of finishing and polishing techniques on surface roughness and color stability of nanocomposites. J Dent. 2012;40(suppl 2):e64-e70. doi: 10.1016/j.jdent.2012.07.005.
ABOUT THE AUTHORS
James F. Simon, DDS, Med
Professor & Director, Esthetic Dentistry
University of Tennessee Health Science Center
Lloyd A. George, DDS, MED, JD
Professor & Associate Dean of Clinical Affairs
University of Tennessee Health Science Center