Date of Degree
MS (Master of Science)
Objectives: This study evaluated the effects of extended acid etching on microtensile bond strength (µTBS) of a etch and rinse adhesive system to sound vital dentin. Etching times of 5, 20 and 80 seconds was used to evaluate the µTBS on vital dentin with resin bonded composite [RBC] restoration (Esthet-XTM) which used a two step etch and rinse adhesive system(Prime Bond NTTM) for bonding.
Methods: 26 premolars which were going to be extracted for orthodontic treatment were used for this experiment. The teeth were randomly divided into 3 groups based on the etch times and restored with RBC using two step adhesive and extracted in `Guarulhos University' Brazil. After extraction, these teeth were sectioned ( Microtome) in such a way to obtain 2 testing beams of 2mm diameter from each tooth were obtained which were trimmed (CNC specimen former, University of Iowa, IA, USA) to a dumb bell shape and tested for the microtensile bond strength in University of Iowa. Out of 26 teeth, 46 beams were obtained. For statistical analysis, One-way ANOVA with post-hoc Tukey-Kramer's test was used to determine whether there were significant differences in micro-tensile bond strength among three etching times under each condition. All tests had a 0.05 level of statistical significance. SAS for Windows (v9.1, SAS Institute Inc, Cary, NC, USA) was used for the data analysis. Fracture mode was analyzed using scanning electron microscopy.
Results: Bond strengths in 20 seconds and 5 seconds groups were significantly greater than that observed in 80 seconds group, while there was no significant difference between 20 and 5 etching times.SEM showed majority of the failure was adhesive/ joint failure.
Significance: The results in this In-vivo study are consistent with other in-vitro studies and thus bring an insight on the importance of duration of phosphoric acid application on dentin and extended etch times could compromise the bond strength of the restorations.
Copyright 2009 Aadarsh Gopalakrishna