The relationship between base dimensions, force to failure, and shear bond strengths of bondable molar tubes

OBJECTIVES: To compare forces versus failure and shear bond strengths, and to explore their association with the base dimensions of four currently available bondable molar tubes. MATERIALS AND METHODS: Tubes were bonded to hydroxyapatite discs using a conventional light-cured adhesive and were tested to shear failure with the Instron Universal testing machine. Results were analyzed using the Kruskal-Wallis test and regression and survival analyses. RESULTS: No statistical difference was observed between the four groups globally in terms of force to failure (P = .059) and bond strength (P = .179). However, regression analysis showed that each 1 mm(2) increase in base surface area required an additional force of 3.11 N to debond the tube. Survival analysis showed that the tube with the greatest base dimensions had the best survival with increasing force to failure. CONCLUSIONS: Although a relationship was demonstrated between force to failure and base surface area, it was not a simple one. No statistically significant relationship was found between bond strength and base surface area.