Document Type

Thesis

Date of Degree

Spring 2016

Degree Name

MS (Master of Science)

Degree In

Operative Dentistry

First Advisor

Steven R. Armstrong

Second Advisor

Jeffrey A. Banas

Abstract

The objective of this work was to develop a short-term, clinically simulative, biofilm-based aging/storage model for lab testing of newer dental adhesives in order to predict their long-term performance. To do this we tested the hypothesis that 15 days of biofilm challenge with cariogenic bacterial species, Streptococcus mutans (SM) and Streptococcus sobrinus (SS), would produce similar or a greater reduction in microtensile bond strength (μTBS) of dental adhesives as compared to a standard 6 months of water storage (WS).

Thirty-one molars were flattened to dentin, restored using Optibond-FL adhesive and Z-100 dental composite, sectioned and trimmed into four dumbbell-shaped specimens and randomly distributed according to aging conditions (n=31): A) Water storage for 6 months, B) Water storage for 5.5 months + S. mutans-biofilm challenge for 15 days, C) S. mutans-biofilm challenge for 15 days and D) S. sobrinus-biofilm challenge for 15 days. Specimens were gripped centrally with respect to the test axis with a non-gluing passive gripping device. Microtensile bond strength testing was performed using a Zwick Material Testing Machine at a crosshead speed of 1 mm/min and failure modes were classified using light microscopy.

Mixed model ANOVA and Weibull regression analysis revealed that the type of storage condition significantly affected the microtensile bond strength (p<0.0001). Mean microtensile bond strength observed within group A (49.69 ± 15.53MPa) was significantly higher than those in groups B (19.26 ± 6.26MPa), C (19.92 ± 5.86MPa) and D (23.58 ± 7.88MPa). Also, microtensile bond strength obtained with group D was significantly greater than that with groups B and C, while no difference was seen between the latter two groups. Chi-square statistical analysis indicated that specimens from groups B (74.2%), C (83.9%) and D (80.6%) were more likely to have cohesive failures in dentin than specimens from group A (54.8%).

Within the limitations of the study, it can be concluded that 15 days of Streptococcus mutans- and Streptococcus sobrinus- based biofilm challenge produced more reduction in microtensile bond strength of dental adhesive than 6 months of water storage and appear to be a promising in vitro accelerated aging model.

Public Abstract

In order to evaluate the effectiveness of dental adhesives used in tooth restorations, one must mimic the usage of the adhesive material under conditions that simulate the oral environment. Of the many such aging conditions that are available, a 6-month water storage (WS) protocol is the most recommended. The objective of the present study was to see if a much shorter, clinically simulative bacterial challenge could be used as an effective aging method. Two bacterial species commonly associated with dental decay and restoration failure were tested, namely, Streptococcus mutans (SM) and Streptococcus sobrinus (SS). The study compared the effect of 6-month WS to that of a 15-day SM or SS challenge on the bond strength values of dental adhesive. Bond strengths were calculated at the end of the aging period by measuring the force required to separate the adhesive-tooth (dentin substrate) bonded specimens. The broken specimens were then evaluated under higher magnification to determine the location of failure.

Statistical analysis of the data indicated that 15-day SM or SS bacterial challenge produced more degradation of resin-dentin bonds resulting in lower bond strength values of the adhesive than 6-month WS. It was also observed that specimens exposed to bacteria were more likely to fail within the dentin substrate indicating greater dentin demineralization following the bacterial exposure.

Within the limitations of the study it was concluded that 15-day SM or SS bacterial challenge produced more degradation of dental adhesive than 6-month WS and appear to be a promising laboratory aging model.

Keywords

publicabstract, adhesion, aging, biofilms, dentin bonding agents, microtensile bond test

Pages

xii, 66 pages

Bibliography

Includes bibliographical references (pages 57-66).

Copyright

Copyright 2016 Aditi Jain

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