Bonding auto-polymerising acrylic resin to acrylic denture teeth
Objectives: To investigate the effect of surface treatments on the shear bond strengths of an auto-polymerising acrylic resin cured to acrylic denture teeth. The hypotheses to be tested were that two particular surface treatments would increase shear bond strengths compared with no treatment. Methods: The occlusal surface of acrylic molar denture teeth, Replica Delphic [Davis, Schottlander and Davis], were ground to a flat finish (tungsten carbide bur) and divided into 3 groups (n = 3 x 20): Group 1 (control) - no surface treatment; Group 2 - grit-blasted with 110 micron aluminium oxide, Korox [Bego]; Group 3 - grit-blasted and wetted with the monomer component of an auto-polymerising acrylic resin, Snap [Parkell], for 180 sec. A quantity of the same acrylic resin was immediately cured to the surface in a commercial jig, Multi-T [Bencor], placed in a pressure pot (2 atm), to yield a cylindrical button for shear testing. After storage in water 37 ±2oC for 30 days each assembly was tested in a tensometer, H10KS [Tinius Olsen], with a crosshead speed of (0.75 +/-0.2)mm/min. As the data did not meet the assumption of constant variability, a Kruskal-Wallis test was performed to compare the results between the groups. Post hoc comparisons were performed using Mann-Whitney U tests and employing the Bonferroni correction. Results: Median (interquartile range) shear bond strengths were (MPa): Group 1, 4.5 (4.1-5.8); Group 2, 13.0 (9.8-16.4); Group 3, 11.7 (8.8-16.0). Groups 2 & 3 had significantly greater mean shear bond strengths compared to Group 1 (P<0.001). The treatment groups did not differ significantly (P=1.000). Conclusion:Grit-blasting acrylic denture tooth surfaces may significantly increase shear bond strength of subsequently-bonded auto-polymerising acrylic resin compared to no surface treatment.