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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.