OBJECTIVE: To evaluate the bonding performance of two different dentin bonding adhesives to dentin, after application of three different air thinning protocols for adhesive materials in dry (D) and aged (A) conditions.
METHODS: Occlusal surfaces of 48 human molar teeth were ground with #600 SiC paper below the enamel and were sectioned longitudinally in 4 pieces. Each test group was comprised of 32 dentin specimens. A self-etch (FL-Bond II, FLB) and an etch-and-rinse bonding agent (Scotchbond Multipurpose, SMP) were evaluated. After primer application, an adhesive layer was applied in one coat (NA), thinned with air for 5 s (T5) or for 10 s (T10). Composite cylinders were built on the surfaces with plastic matrices and cured. Half of the specimens from each group were tested immediately after preparation or exposed to 10,000 thermal cycles (5-60 ºC±1, 60s dwell time). Shear bond strength was tested at a cross head speed of 1 mm/minute. Data [MPa] were analyzed with ANOVA & Tukey's HSD tests.
RESULTS: There were no significant differences between bond strength of two adhesives regardless of adhesive thinning and aging. After thermal aging, bond strengths in the NA groups were not significantly different from each other. However, in the air thinned groups, bond strengths significantly decreased for both adhesives (p < 0.05).
Materials | Bond strength(MPa)±SD | |||
NA | T5 | T10 | ||
FLB | D | 21.3 ± 4.2 a | 18.9 ± 3.4 b | 16.0 ± 3.4 b |
A | 18.8 ± 5.1 ab | 10.2 ± 3.4 c | 9.7 ± 2.7 c | |
SMP | D | 20.6 ± 6.2 a | 17.7 ± 5.3 b | 16.7 ± 4.8 b |
A | 18.7 ± 4.7 ab | 13.8 ± 4.2 c | 13.4 ± 4.6 c | |
CONCLUSIONS: Bond strengths for both dentin adhesives remained stable after thermal aging when they were not thinned with air. Conversely, air thinning decreased bond strengths after thermal aging.