Abstract
Laboratory tests are routinely used to test bonding properties of dental adhesives. Various aging methods that simulate the oral environment are used to complement these tests for assessment of adhesive bond durability. However, most of these methods challenge hydrolytic and mechanical stability of the adhesive- enamel/dentin interface, and not the biostability of dental adhesives. Objective To compare resin-dentin microtensile bond strength (μTBS) after a 15-day Streptococcus mutans (SM) or Streptococcus sobrinus (SS) bacterial exposure to the 6-month water storage (WS) ISO 11405 type 3 test.Methodology A total of 31 molars were flattened and their exposed dentin was restored with Optibond-FL adhesive system and Z-100 dental composite. Each restored molar was sectioned and trimmed into four dumbbell-shaped specimens, and randomly distributed based on the following aging conditions: A) 6 months of WS (n=31), B) 5.5 months of WS + 15 days of a SM-biofilm challenge (n=31), C) 15 days of a SM-biofilm challenge (n=31) and D) 15 days of a SS-biofilm challenge (n=31). μTBS were determined and the failure modes were classified using light microscopy.Results Statistical analyses showed that each type of aging condition affected μTBS (p<0.0001). For Group A (49.7±15.5MPa), the mean μTBS was significantly greater than in Groups B (19.3±6.3MPa), C (19.9±5.9MPa) and D (23.6±7.9MPa). For Group D, the mean μTBS was also significantly greater than for Groups B and C, but no difference was observed between Groups B and C.Conclusion A Streptococcus mutans- or Streptococcus sobrinus-based biofilm challenge for 15 days resulted in a significantly lower μTBS than did the ISO 11405 recommended 6 months of water storage. This type of biofilm-based aging model seems to be a practical method for testing biostability of resin-dentin bonding.
Highlights
A Streptococcus mutans- or Streptococcus sobrinus-based biofilm challenge for 15 days resulted in a significantly lower μTBS than did the International Standards Organization (ISO) 11405 recommended 6 months of water storage. This type of biofilm-based aging model seems to be a practical method for testing biostability of resin-dentin bonding
This study aims to determine whether the resin-dentin microtensile bond strength after a biofilm challenge using one of two cariogenic bacterial species, either Streptococcus mutans or Streptococcus sobrinus for 15 days was comparable or possibly even lower than that adhesive μTBS after an ISO 11405 type 3 test of 6 months of water storage
Mean μTBS of specimens subjected to 15 days of S. sobrinus challenge was significantly greater than that following 5.5 months of water storage + 15 days of S. mutans challenge, or 15 days of S. mutans challenge, whereas no difference was found between the latter two groups (Figure 2)
Summary
Dental composite restorations demonstrate favorable immediate bonding properties, failures occur over clinical service due to secondary caries, marginal defects or staining, chipping, and fractures. The degradation of the resin-dentin interface is considered the weak link and it is cited as one of the main reasons for failure of composite restorations. These facts, as well as newer dental adhesives claiming improved bonding effectiveness with simplified application techniques, emphasize the relevance of testing the resin-dentin interface integrity before dental bonding agents are marketed.Clinical trials provide an accurate and effective determination of the long-term bond effectiveness for new materials, and they constitute the highest standard for testing them. due to time and cost limitations, testing bond strength and conducting margin analysis in a laboratory are popular substitutes for clinical trials. The International Standards Organization (ISO) created the ‘ISO/TS 11405:2015 Dental Materials to standardize testing for these materials – testing of adhesion to tooth structure guideline which includes information about selecting substrates, storing and handling samples, the essential features of the various laboratory tests, including tests of microleakage, tensile bond strength, and marginal gaps. ISO 11405 (test type 3) recommends a water storage time of 6 months at 37oC to “show durability of the adhesive bond.” Additional in vitro techniques for simulated aging including thermocycling and mechanical loading are commonly reported in the literature. The degradation of the resin-dentin interface is considered the weak link and it is cited as one of the main reasons for failure of composite restorations.2 These facts, as well as newer dental adhesives claiming improved bonding effectiveness with simplified application techniques, emphasize the relevance of testing the resin-dentin interface integrity before dental bonding agents are marketed. In vitro bond strengths, when involving an aging method, have been correlated with the results of clinical trials.3,4,7 These techniques present disadvantages to simulated aging, which limits their use. It would be desirable to adopt a more relevant method for simulated aging in a laboratory that can simultaneously speed the aging process for resin-dentin interfaces and help evaluate an adhesive long-term bonding properties
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