Immediate microshear bond strength of a universal adhesive to dentin

Methods: Twenty-four intact, human, third molars were randomly allocated to three groups of 8 teeth. Mid-coronal flat dentin of each tooth was exposed and each tooth was further sectioned in two halves. Single bond universal (SBU; 3M ESPE) adhesive was applied to one half following the ‘total-etch’ (TE) and the other half following the ‘self-etch’ (SE) approach. In the TE protocol, dentin was first etched with 37% phosphoric acid, rinsed and blot-dried. SBU was applied to dentin according to manufacturer’s instructions. Each sample was light-cured for 10 s using a high-intensity LED light-curing unit (bluephase, Ivoclar Vivadent) maintaining the following positions between the light tip and the adhesive surface:

Group 1: 1 mm 90° (control);

Group 2: 8 mm 90°;

Group 3: 8 mm 60°

Composite build-ups (Filtek Z250, 3M ESPE), 2 mm high and 1.7 mm thick, were prepared and light-cured for 20 s at 1 mm distance. Following 24 h storage, μSBS was measured in a universal testing machine at 1 mm/min speed until fracture. Fracture types were analyzed under a stereomicroscope.

Results: μSBS values ranged from 12.66±4.76 MPa in Group 1-SE to 15.08±5.68 MPa in Group 2-TE. No statistically significant differences in μSBS were observed between TE and SE subgroups within each group (p>0.05, paired t-tests). No differences were found between groups for either TE or SE protocol (p>0.05, two-way ANOVA). Group 1 showed predominantly ‘adhesive’ fractures, whereas similar occurrence of ‘adhesive’ and ‘mixed’ fractures was found in Groups 2 and 3.

Conclusions: TE and SE application protocols gave comparable results for SBU adhesive. A high-intensity LED unit allows some departure from an ideal curing position without jeopardizing adhesive bond strength to dentin.