Double-sided Microtensile Test for Simultaneous Evaluation of Adhesives Bond Strength

Objectives: To compare the conventional mTBS test with an alternative double-sided mTBS test using self-etch adhesives.
Methods: Sixty non-carious human molars and four current self-etch adhesives were used: Clearfil^TM SE Bond2 (SE), Clearfil^TM Universal Bond (CU), Scotchbond^TM Universal (SB) and G-Premio Bond (GP). The adhesives were applied to flat dentin surfaces according to manufacturer’s instructions. In EXP-1: Teeth were sectioned in the middle portion of dentin and bonded with self-etch adhesives: SE, CU, SB and GP for conventional mTBS test. In EXP-2: Teeth were sectioned into dentin discs with varied thicknesses (0.5, 1.0, 1.5, 2.0-mm). One side of each disc was bonded with SE and the opposing side with CU. In EXP-3: 1-mm dentin discs were used for double-sided (EXP-2) mTBS test and bonded with CU, SB and GP (in six combinations of 2 adhesives) either on coronal or pulpal side of dentin disc. Bonded surfaces received resin build-ups, stored in distilled water (24h, 37°C), cut into beams (1mm²) and tested with mTBS. Failure mode was observed using stereoscope and SEM. Data were statistically analyzed by ANOVA and post hoc tests (p<0.05).
Results: EXP-1: Differences were found on mTBS of all adhesives. SE showed the highest mTBS (63.98MPa) than SB (48.70MPa), CU (44.52MPa) and GP (40.56MPa). EXP-2: Dentin thickness of 1 mm (41.54MPa) showed no significant difference with other thickness.
Failure occurred on CU side in all groups. EXP-3: Differences on mTBS were found for adhesive’s combinations. SB-CU combinations showed the highest and no significant different mTBS between their intra-combination (43.86 and 41.20MPa). CU-GP combinations showed the lowest mTBS values (29.94 and 29.63MPa). Most failures occurred on GP side followed by CU and SB sides.
Conclusions: Double sided technique seems to be adequate to compare two different self-etch adhesives simultaneously.