Background: The clinical success of large class II resin-modified glass-ionomer cement/composite resin (RMGIC/CR) 'open-sandwich' restorations in permanent or primary molars may be influenced by certain bonding parameters.
Aim: To examine in vitro the effect of placing/curing mode on the RMGIC/CR bond strength.
Design: Two restoratives, a CR (Z250), a RMGIC (Vitremer) and a bonding agent (Adper Single Bond 2), all of 3M ESPE, were used for preparing five groups of seven specimen sticks each. The bond between the two restorative materials at the stick centre was created in the three test groups by: (A) 1-step placing RMGIC in contact with CR, then photocuring; (B) 2-step RMGIC placing/curing, then CR placement/curing; (C) 3-step RMGIC placing/curing, bonding agent placing/curing, CR placing/curing. Control groups consisted of sticks made of CR alone (D, positive) and RMGIC alone (E, negative). The specimens were subjected to tensile stress measurements in an Instron dynamometer and examined by scanning electron microscope for type of failure.
Statistics: Tensile bond strength, tensile strain and elastic modulus differences were examined with one-way ANOVA and Tukey test.
Results: Among experimental groups, Group C exhibited significantly higher tensile strength (MPa) means (A = 12.11 ± 4.72, B = 15.69 ± 5.18, C = 19.08 ± 4.05) and significantly higher tensile strain (%) means (A = 0.50 ± 0.11, B = 0.64 ± 0.19, C = 0.98 ± 0.24), compared to Group A, at p = 0.05. Group D had significantly higher tensile strength and strain than all other groups. No statistically significant differences were observed in the elastic modulus. The use of bonding agent (Group C) resulted in absence of adhesive failures as seen by SEM.
Conclusion: The use of bonding agent improved the CR/RMGIC bond by tensile strength and strain tests.