JADA Continuing Education
The effect of saliva contamination on enamel and dentin using a self-etching adhesive
RICHARD D. TOWNSEND, D.M.D. and
WILLIAM J. DUNN, D.D.S.
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ABSTRACT
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Background. The authors conducted a study to evaluate the effect of saliva contamination on enamel and dentin before or after application of a self-etching adhesive.
Methods. The authors divided 120 extracted molars into enamel and dentin groups of 60 specimens each, and then further divided each group into three groups of 20 specimens each. Resin-based composite cylinders were bonded to tooth specimens that were uncontaminated (control) or were contaminated with saliva either before or after application of the adhesive and then loaded to the failure point. The authors calculated the mean shear bond strength for each group and subjected data to a one-way analysis of variance, or ANOVA, to test for differences among groups.
Results. Mean shear bond strength was 16.7 megapascals (± 3.0 standard deviation, or SD) for the dentin control group, 14.8 MPa (± 2.3 SD) for dentin contaminated with saliva before adhesive application, 15.9 MPa (± 3.8 SD) for dentin contaminated with saliva after adhesive application, 19.1 MPa (± 4.8 SD) for the enamel control group, 12.3 MPa (± 4.4 SD) for enamel contaminated with saliva before adhesive application, and 13.1 MPa (± 5.5 SD) for enamel contaminated with saliva after adhesive application. One-way ANOVA detected no difference in the dentin groups, but the authors found a significant difference among enamel groups. Uncontaminated enamel had higher bond strengths than either of the contaminated enamel groups.
Conclusions. Saliva contamination did not affect the dentin shear bond strength of the self-etching adhesive. Saliva did have a detrimental effect on enamel bond strength.
Clinical Implications. Newer generations of adhesives appear to be more tolerant of saliva contamination, but proper isolation still should be accomplished until further research proves otherwise.
Almost 50 years ago, Buonocore1,2 observed how phosphoric acid improved adhesion of paint to metal surfaces in industry and applied this concept to the dental profession. That discovery and the development of bisphenol glycidyldemethacrylate resin by Bowen3 in the early 1960s led to the evolution of the first dentin adhesive systems. Failure rates for the early dentin adhesive systems were high.4–6 It was not until the early 1990s that significant advances in dentin bonding were made with the development of multistep dentin adhesive systems. These fourth-generation adhesive systems typically used conditioners, primers or both to pretreat dentin to make the hydrophilic dentin substrate more receptive to bonding. The final step in this complicated bonding scheme was the application of a low-viscosity adhesive resin that copolymerized with the primed dentin surface, creating a hybrid layer that was amenable to bonding with the restorative composite material.7
Self-etching adhesives are not as tolerant of contamination of enamel surfaces as they are of contamination of dentin surfaces.
To reduce the number of steps involved in fourth-generation bonding, researchers and manufacturers developed more simplified systems by combining the etchant and primer, or the primer and adhesive. These fifth-generation adhesive systems demonstrated similar bond strengths to dentin in vitro8,9 and in vivo,10,11 but their claims of significantly reduced application times may have been premature. Self-etching primer systems generally were regarded as the "sixth" generation, but these systems still required the separate application of an adhesive.
To simplify things further, researchers developed all-inclusive adhesive systems. These dentin-bonding agents incorporate etchant, primer and adhesive into one bottle. There is some disagreement on the classification of these adhesive systems, and it should be noted that the nomenclature is dictated by the manufacturer who releases the products to the dental market and not by scientific categorization. A better classification system would separate adhesives into total-etch and self-etch categories. Total-etch systems then would be subdivided into separate-bottle systems, in which the primer and adhesive are separate, and one-bottle systems that combine the primer and adhesive. These total-etch systems require that both the enamel and dentin be etched with acid before placement of the adhesive. Self-etching adhesives would be subdivided into self-etching primers that require a separate application of adhesive and all-in-one self-etching adhesives that combine etchant, primer and adhesive.
Depending on the adhesive system used, bonding resin-based composite to tooth structure can involve multiple steps, and the operative field could become contaminated during any of these steps.
With the addition of a glutaraldehyde disinfectant, a "seventh" generation surfaced in 2003. However, Settembrini and colleagues12 demonstrated that acid etching alone appears to suffice as a disinfectant.
Before the introduction of hydrophilic primers, the bonding of resin-based composite to etched enamel involved the application of a hydrophobic resin, which required meticulous attention to the operative field. Proper isolation was necessary to prevent unwanted contamination of the tooth surface that could significantly decrease the bonding efficacy of resin to enamel.13,14 As early as 1963, Buonocore2 concluded that a dry tooth surface was essential for achieving good adhesion because etched tooth surfaces readily absorb salivary constituents, thus reducing their surface energy and rendering them less favorable to bonding. This finding has been supported by other researchers.14–18
The concept of salivary contamination’s decreasing bond strength is not universally accepted, however. Fritz and colleagues,19 el-Kalla and Garcia-Godoy,20 Vargas and colleagues21 and Hitmi and colleagues22 were unable to demonstrate statistically significant decreases in shear bond strength to tooth surfaces contaminated with saliva when testing modern adhesive systems that incorporated a primer in the adhesive. el-Kalla23 also reported that salivary contamination did not affect the formation of the hybrid layer. These in vitro results suggest that modern adhesive systems may be more forgiving of contamination on dentin and enamel than were earlier separate-bottle systems.
The dental profession uses all of the adhesive system categories. Depending on the adhesive system used, bonding resin-based composite to tooth structure can involve multiple steps, and the operative field could become contaminated during any of these steps. Some studies have reported that salivary contamination could adversely affect the bond strength to dentin, but only when contamination occurred after adhesive application23 or light curing.20 Because self-etching adhesives incorporate etchant, primer and adhesive into one application, the time points at which salivary contamination could occur are reduced. There are few studies evaluating whether saliva contamination affects the enamel and dentin bond strength of self-etching adhesive systems.
We conducted this study to investigate whether saliva contamination at various time points has an effect on the shear bond strength of an all-in-one self-etching adhesive system used on enamel and dentin.
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MATERIALS AND METHODS
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We collected 120 recently extracted human molars that were free from restorations or caries, and we stored them in a solution of 0.5 percent chloramine-T and refrigerated them until we used them in the study. No more than six months elapsed between the extraction of the molars and their use in the study.
We randomly divided the teeth into two groups for enamel and dentin specimen preparation. For the dentin group, we ground the occlusal surfaces of the teeth serially with 180-, 320- and 600-grit silicon carbide paper on a polishing lathe under running water until all islands of enamel were just removed. We then embedded the specimens in dental mounting stone inside acrylic molds to expose a flat dentin surface for bonding.
For the enamel group, we ground the teeth serially with 180-, 320- and 600-grit silicon carbide paper until a flat enamel surface of at least 10 square millimeters was prepared. We embedded the specimens in dental mounting stone inside acrylic molds to expose a flat enamel surface for bonding. We kept all specimens moist before bonding.
We further separated the dentin and enamel groups into three additional subgroups each. The experimental groups were as follows:
- – dentin group 1: no saliva contamination (control);
- – dentin group 2: saliva contamination before application of self-etching adhesive system;
- – dentin group 3: saliva contamination after application of self-etching adhesive
- – system, but before light curing;
- – enamel group 1: no saliva contamination (control);
- – enamel group 2: saliva contamination before application of self-etching adhesive system;
- – enamel group 3: saliva contamination after application of self-etching adhesive system, but before light curing.
The noncontaminated enamel control group demonstrated higher bond strengths than either of the groups that were contaminated with saliva.
The principal investigator (R.T.) collected his fresh whole saliva. After contaminating each tooth specimen, he gently air-thinned the saliva with an air-water syringe, leaving the specimens visibly moist with saliva. He did not rinse or blot dry the specimens.
We placed the self-etching adhesive system on the tooth specimens according to the manufacturer’s recommendations. To bond a cylinder of resin-based composite to each specimen, we secured a circular, split polyethylene mold (inner diameter: 3.0 mm; height: 3.0 mm) to the flat tooth surface. We filled the mold with a light-curable resin-based composite in two equal increments. We polymerized each increment separately for 40 seconds with a curing light. To ensure a minimum intensity of at least 500 milliwatts per square centimeter, we used a hand-held curing radiometer to test the light output after each specimen was handled. After storing the tooth specimens in water at 37 C for 48 hours, we subjected them to shear force in a universal testing machine (model 1541s, Instron, Canton, Mass.) with a crosshead speed of 0.5 mm per minute until we noted failure. We calculated mean shear bond strength for all groups and subjected the data to a one-way analysis of variance, or ANOVA, to determine if a difference existed among the groups. We used Tukey’s Honestly Significant Difference post hoc test to identify the differences. We considered all statistical analyses to be significant at the P < .05 level.
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RESULTS
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Results of the one-way ANOVA comparing the shear bond strength of resin-based composite to dentin and enamel are presented in Tables 1
and 2. We found no evidence to suggest a difference among any of the three dentin groups (P = .16). Among the enamel groups, we found that the non-contaminated enamel control group demonstrated higher bond strengths than either of the groups that were contaminated with saliva. This difference was significant (P < .05).
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DISCUSSION
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The advantage of self-etching adhesive systems is that all three basic steps (etching, priming and applying adhesive) occur simultaneously. The benefits of simplicity and time savings are intuitive, but an added advantage is that there are fewer time points during placement when contamination can occur. Self-etching adhesive systems simultaneously demineralize dentin while infiltrating it with monomers to the same depth, and they then are polymerized in situ.24 Simultaneous demineralization-infiltration might improve the marginal seal and adhesion to dentin; when etching and priming are accomplished in separate steps, some regions of demineralized dentin may not be penetrated by the resin primer. Self-etching primer systems do not require the primer to be rinsed off after application. What happens to the acid still is not understood completely, but it is thought to be neutralized at some point by hydroxyl ions that are released from the hydroxyapatite during demineralization.24 The high buffering ability of the dentin should limit further demineralization of hydroxyapatite.
The components of the adhesive system we used in our study are listed in Table 3. Bonding agent A contains phosphoric acid and methacrylate monomers. Bonding agent B contains more methacrylate monomers, water and filler particles. This particular self-etching adhesive system incorporates a bifunctional acid monomer (MAC-10, J. Morita USA, Irvine, Calif.) into the adhesive (Figure). This bifunctional molecule essentially is a hydrophilic acid monomer with a methacrylate group on the hydrophobic portion of the molecule and two carboxylic acid groups on the hydrophilic portion. The carboxylic acid portion of the molecule aids in dentin bonding. The methacrylate portion of the molecule copolymerizes with other methacrylic resin monomers in establishing the bond between the adhesive and the resin-based composite restorative material. An additional phosphoric acid monomer was added to facilitate self-etching.
The results of our study on salivary contamination—which agree with the findings of Hitmi and colleagues,22 Fritz and colleagues,19 Vargas and colleagues21 and el-Kalla and Garcia-Godoy20—demonstrated that the newer generations of adhesive systems that use hydrophilic primers may be less sensitive to salivary contamination of prepared tooth surfaces than previous generations of adhesive systems. Ideal operative dentistry still mandates the use of rubber dams, but certain instances may preclude their use. Unfortunately, an increasing number of dental adhesive manufacturers state in their instructions that the operating field routinely may be isolated with cotton rolls.19 The results of our study suggest that self-etching adhesive systems are more tolerant of salivary contamination on dentin surfaces. This, however, does not imply that proper isolation is unnecessary, as there will be instances in which saliva has contaminated the field despite the operator’s best efforts and observations. Previous investigators have examined the effect of saliva after it was blotted dry or rinsed off.19–21,23,25 This implies that the operators were aware of saliva contamination. Because modern adhesive dentistry uses a wet, total-etch approach, salivary contamination may go unnoticed because the tooth surface already is wet. In our study, we examined saliva-contaminated specimens that were neither blotted dry nor rinsed to investigate the effects of an "unnoticed" saliva-contaminated surface.
There are several explanations for the tolerance of self-etching adhesives to salivary contamination. If contamination occurs after etching but before adhesive application, the tooth surface already should be moist with water to prevent collagen collapse in the demineralized dentin. This moist tooth surface may be an important factor in preventing salivary proteins from penetrating and blocking openings in the collagen mesh in dentin and pores in enamel. Further, the hydrophilicity of the self-etching products may allow for their diffusion through the salivary film.20
Similarly, if the tooth surface is contaminated with saliva after the application of the adhesive, but before light curing, there appears to be no significant effect on bond strength. There is, however, evidence that if salivary contamination occurs after light curing, significant decreases in bond strength may occur.19 Fritz and colleagues19 hypothesized that if saliva contamination occurred after the adhesive already was polymerized and the operator intervened by rinsing and air drying the preparation or by applying additional adhesive after rinsing, a collapsed zone of resin-deprived collagen could result. They assumed that not all of the resin in the interstices of the collagen mesh will be polymerized. The addition of more resin likely would not penetrate this altered collagen surface completely. This assumes that some adhesive would not fill the collagen mesh completely, permitting its collapse after subsequent rinsing, drying or application of additional resin. Theoretically, a self-etching primer system would demineralize dentin and infiltrate it simultaneously with monomers that are polymerized in situ so that no gaps would be left between the primed surface and the organic dentin surface.26 Another theory for decreased bond strength that occurs when surfaces are contaminated with saliva after light curing is the adsorption of glycoproteins to the poorly polymerized, air-inhibited adhesive surface. These glycoproteins may act as a barrier that prevents complete wetting with the next increment of resin, preventing adequate copolymerization.19
Results from our study suggest that self-etching adhesives are not as tolerant of contamination of enamel surfaces as they are of contamination of dentin surfaces. Enamel consists primarily of an inorganic mineral matrix that contains little moisture, whereas dentin consists of a mineral-impregnated organic matrix and fluid-filled tubules. Because of the high mineral content of enamel, acid etching results in the formation of micropores, which increases the enamel’s surface energy for bonding and allows for micromechanical retention.27 In dentin, dissolution of the inorganic constituents results in exposure of the organic collagen matrix, which must be kept moist to prevent collapse.7
These inherent differences in enamel and dentin led to the understanding and development of the total-etch, wet-bonding technique. Some research has indicated that newer, hydrophilic adhesives are tolerant of saliva contamination on enamel,19,20 but our results demonstrated that the bond strength still was significantly higher in uncontaminated enamel specimens than in the contaminated enamel specimens (Table 2
). In similar fashion, Powers and colleagues25 determined that in vitro bond strengths to enamel were sensitive to the effects of saliva. Re-etching improved the bond strength, except for enamel contaminated by plasma. In contrast, Fritz and colleagues19 determined that the adverse effects of salivary contamination of etched enamel were reduced greatly if the saliva was rinsed off or blotted dry. They also determined that any contamination of the already cured adhesive layer seriously compromised the bond—regardless of how the contaminant was removed or altered—and that the entire bonding procedure should be repeated to ensure adequate adhesion.
The long-term effects of saliva contamination are not known. It is conceivable that contamination could result in nanoleakage in the hybrid layer itself. Nanoleakage is thought to be the result of incomplete resin infiltration of demineralized dentin, which leaves exposed collagen fibers and results in nanopores in the hybrid layer.28 These nanopores are large enough to allow fluid entry into the hybrid layer, but small enough to prevent invasion by microorganisms. Nanoleakage is a laboratory discovery, and its long-term effects on the longevity of the bond are unknown.29 There is, however, concern that the exposed collagen fibrils will hydrolyze over time, leading to microleakage and failure of the restoration in the long term.Traditionally, tooth structure has been re-etched to compensate for contamination of tooth structure. Research by Perdigão and Lopes30 demonstrated that reapplication of acid etchant on tooth structure demineralizes deeper into dentin than a single application for the same amount of time. This suggests that re-etching dentin could result in increased risks of nanoleakage in the hybrid layer or poor hybridization due to the collapse of the collagen fibers.
Although a simple-to-use, all-in-one adhesive system is appealing, no long-term data exist on the clinical performance of self-etching adhesive systems or the effects of salivary contamination. Therefore, we recommend caution in interpreting these in vitro results, as they cannot necessarily be extrapolated to the clinical situation. Further clinical studies are required, and use of proper isolation techniques still is highly encouraged.
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CONCLUSIONS
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In this in vitro investigation, we did not find any evidence to suggest a difference in mean shear bond strength between dentin specimens contaminated with saliva before or after application of a self-etching adhesive system and uncontaminated dentin specimens. However, enamel specimens contaminated with saliva displayed a significant decrease in mean shear bond strength compared with uncontaminated enamel specimens. Although the shear bond strength to dentin was not significantly affected, the long-term effects of saliva contamination on the integrity of the hybrid layer are not known. Incomplete hybridization between the resin adhesive and dentin likely will lead to future failure of the restoration. Therefore, routine use of isolation techniques still is highly encouraged.
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Dr. Dunn is the director of research and biomaterials, Lackland Air Force Base, Texas. Address reprint requests to Dr. Dunn at 9406 Tranquil Park Dr., San Antonio, Texas, e-mail "William.dunn{at}lackland.af.mil".
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FOOTNOTES
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The views expressed in this article are those of the authors and do not reflect the official policy of the Department of Defense or other departments of the United States government.
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REFERENCES
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- Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34:849–53.[Free Full Text]
- Buonocore MG. Principles of adhesive retention and adhesive restorative materials. JADA 1963;67:383–91.
- Bowen RL, inventor. Dental filling material comprising vinyl silane treated fused silica and a binder consisting of the reaction product of bispenol and glycidyl acrylate. U.S. patent 3 066 112. Nov. 27, 1962.
- Buonocore M, Wileman W, Brudevold F. A report on a resin composition capable of bonding to human dentin surfaces. J Dent Res 1956; 35:846–51.[Free Full Text]
- Bowen RL. Adhesive bonding of various materials to hard tooth tissues, II: bonding to dentin promoted by a surface-active comonomer. J Dent Res 1965;44:895–905.[Free Full Text]
- Asmussen E, Hansen EK. Dentine bonding agents. In: Vanherle G, Degrange M, Willems G, ed. State of the art on direct posterior filling materials and dentine bonding: Proceedings of the International Symposium Euro Disney. 2nd ed. Leuven, Belgium: Van der Poorten; 1994:33.
- Nakabayashi N, Pashley DH. Hybridization of dental hard tissues. Tokyo: Quintessence; 1998.
- Fortin D, Swift EJ Jr., Denehy GE, Reinhardt JW. Bond strength and microleakage of current dentin adhesives. Dent Mater 1994; 10:253–8.[Medline]
- Swift EJ Jr, Triolo PT Jr, Barkmeier WW, Bird JL, Bounds SJ. Effect of low-viscosity resins on the performance of dental adhesives. Am J Dent 1996;9:100–4.[Medline]
- Van Meerbeek B, Peumans M, Verschueren M, et al. Clinical status of ten dentin adhesive systems. J Dent Res 1994;73:1690–702.[Abstract/Free Full Text]
- Van Meerbeek B, Peumans M, Gladys S, Braem M, Lambrechts P, Vanherle G. Three-year clinical effectiveness of four total-etch dentinal adhesive systems in cervical lesions. Quintessence Int 1996;27:775–84.[Medline]
- Settembrini L, Boylan R, Strassler H, Scherer W. A comparison of antimicrobial activity of etchants used for a total-etch technique. Oper Dent 1997;22:84–8.[Medline]
- Tagami J, Hosoda H, Fusayama T. Optimal technique of etching enamel. Oper Dent 1988;13:181–4.[Medline]
- Barghi N, Knight GT, Berry TG. Comparing two methods of moisture control in bonding to enamel: a clinical study. Oper Dent 1991; 16:130–5.[Medline]
- Silverstone LM. State of the art on sealant research and priorities for further research. J Dent Edu 1984;48:107–18.[Medline]
- Thomson JL, Main C, Gillespie FC, Stephen KW. The effect of salivary contamination on fissure sealant: enamel bond strength. J Oral Rehabil 1981;8:11–8.[Medline]
- Hormati AA, Fuller JL, Denehy GE. Effects of contamination and mechanical disturbance on the quality of acid-etched enamel. JADA 1980;100:34–8.[Medline]
- Xie J, Powers JM, McGuckin RS. In vitro bond strength of two adhesives to enamel and dentin under normal and contaminated conditions. Dent Mater 1993;9:295–9.[Medline]
- Fritz UB, Finger WJ, Stean H. Salivary contamination during bonding procedures with a one-bottle adhesive system. Quintessence Int 1998;29:567–72.[Medline]
- el-Kalla IH, Garcia-Godoy F. Effect of saliva contamination on micromorphological adaptation of single-bottle adhesives to etched enamel. J Clin Pediatr Dent 1999;24:69–74.[Medline]
- Vargas MA, Denehy GE, Silberman JJ. Bond strength to etched enamel and dentin contaminated with saliva. Am J Dent 1994;7:325–7.
- Hitmi L, Attal JP, Degrange M. Influence of the time-point of salivary contamination on dentin shear bond strength of 3 dentin adhesive systems. J Adhes Dent 1999;1:219–32.[Medline]
- el-Kalla IH. Saliva contamination and resin micromorphological adaptation to cavity walls using single-bottle adhesives. Am J Dent 1999;12:172–6.[Medline]
- Watanabe I, Nakabayashi N, Pashley DH. Bonding to ground dentin by a phenyl-P self-etching primer. J Dent Res 1994;73:1212–20.[Abstract/Free Full Text]
- Powers JM, Finger WJ, Xie J. Bonding of composite resin to contaminated human enamel and dentin. J Prosthodont 1995;4:28–32.[Medline]
- Gordan VV, Vargas MA, Cobb DS, Denehy GE. Evaluation of adhesive systems using acidic primers. Am J Dent 1997;10:219–23.[Medline]
- Van Meerbeek B, Inoue S, Perdigao J, Lambrechts P, Vanherle G. Enamel and dentin adhesion. In: Summitt JB, Robbins JW, Schwartz RS, eds. Fundamentals of operative dentistry: A contemporary approach. 2nd ed. Carol Stream, Ill.: Quintessence; 2001:181.
- Sano H, Takatsu T, Ciucchi B, Horner JA, Pashley DH. Nanoleakage: leakage within the hybrid layer. Oper Dent 1995;20: 18–25.[Medline]
- Sano H, Uno S, Inoue S, eds. Modern trends in adhesive dentistry: Proceedings of the adhesive dentistry forum, Sapporo, Japan, Feb. 21, 1998. Tokyo: Dental Materials Department, Medical Products Division, Kuraray; 1998:6–10.
- Perdigão J, Lopes M. The effect of etching time on dentin demineralization. Quintessence Int 2001;32:19–26.[Medline]
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ABSTRACT
MATERIALS AND METHODS
