For many dentists the direct composite restoration is the most commonly placed posterior restoration. The placement of a direct posterior composite is much more difficult and technique-sensitive as compared to an amalgam restoration. As opposed to the forgiving nature of amalgam, creation of a composite restoration is a multistep process, and each step must be meticulously performed with the appropriate materials in order to obtain an ideal result.
Understanding proper techniques and the advantages and limitations of composite resin as a posterior restorative material are critical for long-term success of these restorations. Current adhesive systems include total-etch, self-etch, and all-in-one, and recommendations concerning management of the tooth preparation differ for each system.1 Should the tooth be wet, dry, or moist? Should the clinician use desensitizers and/or cavity cleansers? Do caries detector dyes affect the bond strength of the restoration? Does contamination with saliva, blood, or astringents lead to failure of the final restoration?
This article will review results from research studies and offer clinical suggestions for managing the tooth preparation during the placement of posterior composite restorations. A clinical technique for management of the tooth preparation is also presented.
There have been many reports in the literature concerning the optimum moisture level when bonding with different types of adhesives. Optimum dentin moisture is important for successful bonding of composite to dentin. If too much moisture is present, water blisters can form at the dentin-adhesive interface, which cause an incompletely hybridized interface.2-4 On the other hand, if the dentin is too dry prior to placement of the primer, the collagen fibers will collapse, which prohibits the hydrophilic resin from penetrating the fibers to form a dense hybrid layer.5,6 Studies indicate that the primer solvent determines the moisture tolerance of the adhesive.7-9
For the hydrophilic resin primer to fully penetrate demineralized dentin, the solvent that carries the primer must also be evaporated. Alcohol and acetone solvents evaporate more quickly than water solvents. Therefore, water-based systems can tolerate drier dentin and should be dried longer than non-water-based systems after the primer is placed to evaporate the water solvent. Alcohol and acetone solvents should be used in more moist environments but are also more susceptible to the water blister phenomenon.7-9 Water-based adhesives are less sensitive to variations in surface moisture than ethanol-based or acetone-based adhesive systems.9
|Figure 1. Proper moisture level for successful adhesive application.|
Self-etching adhesives are water-based systems because of the acidic chemistry of their primers. Therefore, if using a self-etching system, the dentist should not overwet the dentin prior to bonding and also should thoroughly dry the primer to evaporate the water solvent. An advantage of self-etching adhesives is that they do not remove the smear layer. Therefore, in deep dentin, which has many large, fluid-filled tubules, the tubules are never completely exposed, and the dentist can maintain a consistent moisture level during the bonding process regardless of the type of dentin substrate.10 Figure 1 illustrates an optimal moisture level prior to placement of a self-etching adhesive. The preparation does not appear desiccated nor is there obvious pooling of water.
CARIES ELIMINATION'S THE BEST APPROACH FOR BONDING
Superficial dentin is relatively dry, has fewer and smaller diameter dentinal tubules than deep dentin, and is the ideal substrate for dentin bonding. However, there often is no superficial dentin when restoring a tooth that has previously been restored with an amalgam restoration or a tooth with a large carious lesion. In most cases the dentist must remove caries, which is a task requiring clinical judgment, and then restore the tooth considering the type of dentin that is available. The carious process has been described in 2 layers; the outer layer is infected with bacteria and is irreversibly demineralized. The inner layer, or the caries- affected layer, is infected with bacteria but can be remineralized again if disinfected and adequately sealed.11,12 Most studies have shown that bonding to caries-affected and sclerotic dentin provides about half of the bond strength of bonding to superficial dentin.13-15 Studies have also shown that microleakage can be much more pronounced with caries-infected dentin than with normal and caries-affected dentin.16,17
Caries detection dyes are useful for visualizing infected dentin. Many dentists use them as an aid in caries removal.18,19 Research has shown that these dyes aid in the complete removal of caries-infected dentin, which is important considering the results of the permeability and bonding studies described above.
Dentin desensitizers have been developed to decrease sensitivity resulting from cut dentinal tubules after tooth preparation. Desensitizers have become popular as an alternative to cavity varnishes, which were traditionally used to seal dentin prior to restoration with amalgam. Typically, desensitizers contain HEMA (unfilled resin), glutaraldehyde or benzalkonium chloride, and in some cases fluoride.20 The mechanism of action is thought to be that HEMA penetrates the tubules, and the combination of HEMA and glutaraldehyde or benzalkonium chloride occlude the dentinal tubules, making them impervious to fluid flow and bacterial contamination.21
Postoperative sensitivity may be due to 2 different mechanisms. Insult to the pulp can occur by exposing dentinal tubules during tooth preparation, thus subjecting them to fluid flow and osmotic pressure changes.22 The total-etch bonding technique will expose more tubules than self-etch systems due to phosphoric acid-induced dentin demineralization that occurs prior to penetration of the adhesive primer. Self-etching adhesive systems demineralize and dissolve the dentinal smear layer without the use of phosphoric acid. Therefore, tubules are not opened during the bonding process, which will mean less postoperative sensitivity.23
Sensitivity can also occur because of microleakage after restoration with composite. This occurs if the bond strength of the adhesive to the tooth is not adequate to counter the composite contraction shrinkage upon curing.24 Therefore, if patients are experiencing postoperative sensitivity, then tubules are open, the adhesive is not strong enough to withstand contraction forces, or a combination of both processes is occurring.
|Table 1. Bond Strength (MPa) of Composite to Superficial Dentin After Use of 3 Dentin Desensitizing Agents at 24 Hours, 7 Days, and Thermocycling.|
|Table 2. Bond Strength (MPa) of Composite to Deep Dentin After Use of 3 Dentin Desensitizing Agents at 24 Hours, 7 Days, and Thermocycling.|
Several studies have tested the bond strength of composite resin to dentin after treatment with dentin desensitizers. The data have indicated that bond strength of composite to dentin is not negatively affected by these HEMA-containing products, and in some cases, is actually increased after using desensitizers.22,25 At the Biomaterials Research Center at the University of Texas at Houston Health Science Center, similar results were observed26,27 (Tables 1 and 2). In this in vitro study, composite resin was bonded to both superficial and deep dentin. The control group was bonded to moist dentin, and desensitizers were placed on the dentin surface prior to bonding with the other groups. All groups were debonded under tension. None of the test groups demonstrated significantly lower bond strengths than the control groups, and in some cases (Gluma and Health Dent), bond strength significantly increased after 24 hours, 7 days, or after thermocycling.
Therefore, it can be concluded that if necessary, desensitizers can be used prior to bonding without decreasing the bond strength of the adhesive/composite to dentin. However, if using a self-etching adhesive, or an adhesive that is known to have high bond strength to dentin, dentin desensitizers may not be necessary.
CONTAMINATION WITH SALIVA, BLOOD, AND ASTRINGENTS
Considering the technique-sensitive nature of composite resin restorations, contamination is always a concern. However, studies have shown that saliva contamination during the bonding process is not always detrimental to the bond of composite to tooth structure.28,29 Fritz, et al28 studied saliva contamination to enamel and dentin at several different points in the bonding process using a total-etch, 1-bottle experimental adhesive. They found that with enamel and with dentin, air-dried saliva reduced bond strength significantly, but rinsing and blot drying either before or after the adhesive was placed did not significantly lower the bond strength.
Abdalla and Davidson29 showed that saliva contamination did not significantly influence the bond strength of Scotchbond 1, One-Step, Scotchbond Multi-Purpose (3M/ESPE), or Prime & Bond 2.1 (DENTSPLY Caulk) compared with the air-dried or wet dentin control groups. However, when all adhesives were applied to the blood-contaminated groups, bond strengths in all groups were significantly reduced. It has been shown in another study that the adverse effects of contamination with blood can be avoided if the preparation is rinsed and again etched with phosphoric acid prior to bonding.30
|Figure 2. Tensile bond strength of self-etching adhesives to blood-contaminated dentin.|
With self-etching systems, phosphoric acid is not generally used in the bonding process. The results of an in vitro study at the Univer-sity of Texas at Houston Biomaterials Research Center involving 2 self-etch adhesive systems (Clearfil SE Bond and Clearfil Protect Bond, Kuraray America) indicated that in general, the adhesives were not negatively affected by blood contamination (Figure 2).31 An adequate bond strength for the adhesive interface of composite restorations has been defined as being at least 18 MPa, the strength required to counteract the polymerization shrinkage forces of the composite during curing.32 The results of the above study demonstrated that rinsing with water after contamination (SE Bond), or water rinsing followed by reapplication of the adhesive (Protect Bond), restores bond strength to near control levels. Although contamination with blood is never desired, these results indicate that in the case of self-etch adhesive systems, if contamination occurs before the adhesive is placed, or if the preparation is rinsed well with water after the adhesive is placed, blood may not significantly affect the bond strength of the final restoration. However, it is advisable to reapply adhesive after blood contamination to ensure optimal adhesion.
|Figure 3. SEM micrograph (1,000x) of acid-etched dentin surface.|
|Figure 4. SEM micrograph (1,000x) of dentin surface after Hemodent placement, rinsing, and air drying. (Reprinted with permission from the American Journal of Dentistry, in press.)||Figure 5. SEM micrograph (1,000x) of dentin surface after Viscostat placement, rinsing, and air drying. (Reprinted with permission from the American Journal of Dentistry, in press.)|
Many practitioners use astringents to avoid blood contamination during the bonding process. Research has shown that astringent contamination may be more detrimental to bond strength than blood contamination.33,34 Scanning electron micrographs were obtained of a dentin surface after acid etching (Figure 3) and of the dentinal surfaces after applying Hemodent (Premier Dental) and Viscostat (Ultra-dent Products) astringents and then rinsing them from the surface. As seen in Figures 4 and 5, after astringent contamination the dentinal tubules can still be seen but are partially occluded with the astringent.
|Figure 6. Tensile bond strength of Clearfil SE Bond to astringent-contaminated dentin.||Figure 7. Tensile bond strength of Adper Prompt L-Pop to astringent-contaminated dentin.|
In a bond strength study at the University of Texas at Houston Biomaterials Research Center, the bond of composite to dentin using 2 self-etching adhesives was tested after contaminating the dentin with 3 types of astringents (Expasyl [Kerr] [ES], Hemodent [HD], and Viscostat [VS]). In an attempt to restore bond strength, in the last 2 groups after astringent contamination the dentin surface was rubbed with one of 2 types of cavity cleansers (Consepsis or Prep-Quick, Ultradent Products) and then rinsed. As shown in Figures 6 and 7, for both adhesives ES (which is a paste form of aluminum chloride injected into the sulcus) reduced bond strength the least of the 3 astringents. For SE Bond (Figure 6), Viscostat (ferric sulfate) was most det-rimental, but bond strength was restored to control levels using both types of cavity cleansers. For Adper Prompt L-Pop (3M ESPE, Figure 7), both Hemodent (aluminum chloride) and Viscostat lowered the bond strength to about half of the control level, but Consepsis restored the bond strength of the Hemodent group to the control level.
The results of this study indicate that astringents should be used with caution prior to bonding. The tooth preparation should be rinsed well and cleaned with a cavity cleanser prior to bonding with a self-etching adhesive.
As demonstrated, restoring posterior teeth with composite resin requires attention to detail and knowledge of the materials involved. In the clinical technique that follows, the adhesive system used was Clearfil Protect Bond, a self-etching adhesive system.
|Figure 8. Amalgam restoration with recurrent caries.||Figure 9. Shade match to existing tooth.|
|Figure 10. Preparation complete.||Figure 11. Matrix placed.|
Figure 8 shows a leaky amalgam restoration with recurrent caries. In Figure 9, a shade was taken to determine the composite to be used. Note the gray appearance of the distal half of the tooth. A rubber dam was placed to minimize the possibility of contamination during restoration. The old restoration and recurrent caries were removed (Figure 10). Even with rubber dam isolation, it is almost impossible to maintain a completely contaminant-free environment in a restoration that is this large and that extends to the gingival tissue. A sectional matrix was placed (Composi-Tight, Garrison Dental Solutions), which aids greatly in isolation (Figure 11). If needed, a cavity cleanser and/or desensitizing agent can be used at this time. (Protect Bond cleanses and disinfects the preparation, therefore additional products to achieve these objectives are not necessary.)
|Figure 12. Protect Bond Primer being placed.||Figure 13. Primer is dried gently for several seconds to evaporate the solvent.|
|Figure 14. Bond is then brushed into the primed preparation.||Figure 15. Unfilled resin "bond" is air-thinned.|
|Figure 16. The adhesive is light-cured for 10 seconds.|
The preparation is now ready for bonding. Figures 12 to 16 demonstrate the application of the adhesive. First, the primer is brushed into the preparation and left in place for 20 seconds. Agitation of the adhesive has been advocated by some manufacturers to increase bond strength for some adhesives. Therefore, dentists may elect to agitate the adhesive on the surface of the preparation during that 20 seconds. Next, the primer solvent is evaporated with a mild stream of air for approximately 5 seconds. Protect Bond (the resin component of the system) is then brushed into the preparation and gently air-blown to create a thin, uniform thickness. The adhesive is light-cured for 10 seconds.
|Figure 17. Syringing shade A2 Clearfil AP-X PLT into the preparation.||Figure 18. First layer of composite placed and light-cured.|
|Figure 19. Second layer (Clearfil AP-X PLT shade XL) in place after light curing for 20 seconds.||Figure 20. The completed and polished restoration.|
The first layer of composite is placed into the deepest areas of the preparation. Clearfil AP-X PLT (Kuraray America) was used as the restorative composite. This composite can be purchased in syringes or in individual PLT (preloaded tip) ampules and placed with a syringing gun. It is a universal micro-hybrid composite with 85% filler by weight. In this case, shade A2 is used to match the dentin shade of the tooth (Figure 17). The first 2-mm layer is light-cured for 20 seconds (Figure 18). The next layer is shade XL to simulate the high value of the tooth enamel, and this is placed and light-cured for an additional 20 seconds (Figure 19). The completed and polished restoration is seen in Figure 20.
Composite resin restorations are now requested by dental patients. Fortunately, adhesive technology has improved dramatically during the last decade. Understanding key components of the bonding process, such as the nature and composition of dentin, moisture levels needed for different adhesive systems, the importance of caries identification techniques, the use of products to cleanse/desensitize teeth, and the issue of contamination can improve the quality of care provided to patients.
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Dr. O´Keefe received her dental degree from the University of Texas at Houston Dental Branch in 1985 and her master´s degree in oral biomaterials in 2000. She has been a member of the faculty of the University of Texas at Houston Dental Branch for 19 years and also practices dentistry 2 days a week in Houston. Dr. O´Keefe cond