Twenty-four hour microtensile bond strength of four adhesives to dentin

Objectives: To measure and compare the 24-hour microtensile bond strength of four self etching adhesives (Table) to dentin.  Methods: Freshly extracted human molars were wet-ground with a series of silica carbide paper ending with 320 grit to obtain flat intermediate level dentin surfaces and a uniform smear layer using a rotational polishing device (Buehler/Evanston/IL). The teeth were randomly assigned to one of four groups and the adhesives for each group was applied following manufacturers' instructions. Resin composite (Z100/3M ESPE) was placed in 2mm increments over the cured adhesive and light-cured (Elipar S10/3M ESPE/1100mW/cm²) until a 10mm thickness was obtained. Specimens were stored (distilled water/37°C/24h) then sectioned into approximately 1x1mm thick beams comprised of dentin, adhesive and composite build-up using a slow-speed cutting device (Isomet) and a 0.004” thick blade with water-cooling. Before testing, the dimensions of each beam was measured with a digital micrometer to calculate the bonded surface area at the adhesive-dentin interface. The beams were attached horizontally to the microtensile testing machine fixture, attached to Instron (5565) and loaded in tension until failure using a 1mm/min cross head speed. Tested samples were examined with a digital microscope (Keyence/VHX-600) at 100X to determine failure mode. Failure mode was classified as adhesive to the dentin or composite, cohesive to the dentin or composite or mixed (a combination of adhesive and cohesive).  Data was analyzed with ANOVA and Tukey/Kramer tests (p=0.05).

 Results: (Mean±SD).

	Bond Strength (MPa)
MTB 200/Kuraray	40.2±17
iBond/Heraeus Kulzer	29.9±15
OptiBond All-In-One/Kerr	40.7±14
Xeno IV/L.D. Caulk	34.5±12

Conclusions: OptiBond All-In-One and MTB 200 had higher microtensile bond strengths to dentin compared to iBond (p=0.0004). No other differences were found between the tested materials. Supported in part by a grant from Kuraray.