Microleakage and Microtensile Bond Strength of Loaded Composite MOD Restorations

Objectives: To investigate the effect of mechanical loading on the microleakage and microtensile bond strength of MOD direct composite restorations bonded with either a self-etch or total-etch adhesive.

Methods: Class II MOD cavities were prepared into dentine in 28 extracted molar teeth. 14 teeth were bonded with a self-etch adhesive (G Bond, GC Corporation) and 14 with a total-etch adhesive (Optibond Solo Plus, Kerr) then restored with resin composite (Gradia, GC Corporation). For each adhesive, 7 teeth were loaded and 7 unloaded (controls). Mechanical loading was achieved with an axial force of 80 N at 2.5 cycles/second for 250,000 cycles. All the teeth were then stored in 0.25% Rhodamine solution for 24 hours and sectioned in a bucco-lingual direction at the proximal boxes to examine microleakage using a tandem scanning confocal microscope. The restorations were further sliced mesiodistally to obtain two 1.0 mm-thick slabs, which were sectioned into 1.0 mm² beams for the µTBS test. Analysis of variance was performed to assess the effect of loading on the microleakage and bond strength of the two adhesives.

Results: There were no differences in microleakage between the two adhesives when unloaded. However, after loading, the self-etch bonded restorations exhibited greater microleakage (90%) compared to total-etch bonded restorations (70%, p<0.001). When unloaded, the mean µTBS of the self-etch bonded restorations was lower at 23.7 MPa than total-etch bonded restorations at 37.5 MPa, but not statistically significant (p=0.146). Loading affected the µTBS of the total-etch adhesive, which reduced to 20.2 MPa (p<0.001), whereas it had no effect on the µTBS (22.8 MPa, p=0.153) of the self-etch adhesive.

Conclusions: Although restorations bonded with the self-etch adhesive exhibited greater microleakage after loading, their µTBS did not reduce. On the other hand, the µTBS of the restorations bonded with the total-etch adhesive reduced after loading.