Assessment of the Dentin Bond Strength Values of Resin Modified Glass Ionomer Restorative Material using Different In Vitro Test Methods

Abstract

Objective: To assess whether the in vitro dentin bond strength values of a resin modified glass ionomer restorative material (RMGI) are affected by different in vitro test methods. Methods: Mid-depth occlusal dentin of 36-extracted human third molars free of defects was exposed and finished with wet 600-grit silicon carbide paper for 10s. A commercially-available RMGI (Fuji II LC, GC America) was applied to all specimens according to manufacturer’s instructions, after which specimens were stored in 100% humidity at 37 °C for 24 h. Specimens were then randomly divided into three different test groups (n=12): shear bond strength (SBS), microtensile bond strength (μTBS), and four-point bending bond strength (4PBBS). Specimens were loaded to failure using universal testing machines and test-specific parameters: Instron for SBS and 4PBBS tests, EZ-Test for the μTBS test. The mode of bond failure (adhesive, cohesive or mixed) was qualitatively assessed with optical stereomicroscopy. Data were analyzed using one-way ANOVA and descriptive statistics. Results: There was a statistically significant difference between bond strength values for the different test methods (p<0.05). The mean bond strength values (± SD, in MPa) were 15.7 (±7.1) for SBS, 9.7 (±5.3) for μTBS and 37.3 (±12.8) for 4PBBS. With respect to the mode of failure, most SBS failures were adhesive in nature (83%), while the majority of μTBS and 4PBBS failures were mixed (69% and 47% respectively). Several μTBS and 4PBBS specimens failed during processing (before testing). Conclusion: The in vitro dentin bond strength values of a resin-modified glass ionomer material are greatly affected by the test method. The mode of bond failure is also affected by test method. The SBS test method demonstrated the highest percentage of adhesive failure and proved to be less technique sensitive. The majority of μTBS and 4PBBS failures were mixed. Use of the μTBS and 4PBBS may not be optimal laboratory test methods for comparison of the relative bond strength of RMGI materials to dentin. Use of the SBS test may allow more controlled comparison of the adhesive dentin bond among various RMGI formulations, whether already commercially available or under development.