Effect of composite thickness and curing units on bond strength

It has been recommended that a composite should be filled in increments in deep cavities. New generation curing units have been introduced to facilitate the clinical practice as well as to improve the material’s properties, i.e., depth of cure, hardness and bond strength. Objective; To test the effects of the thickness of composite cured with 4 light sources on the shear bond strength to dentin. Methods; Flat coronal dentin surfaces of bovine incisors were prepared and Clearfil SE Bond (Kuraray) was applied. Discs of resin composite (Clearfil AP-X, Kuraray) were built-up using metal matrix with an internal diameter of 5.4 mm and either 2 or 4 mm in thickness. Each of the following curing units were used for polymerization: Halogen lamp (Candelux, Morita)/40 sec, LED (Lux-O-Max, Akeda Dental)/40 sec, Xenon (Arc-light, Air Techniques)/10 sec and Metal Halide (Rayblaze, Moritex)/10 sec. The shear bond tests were performed after 24h of storage in water, with a crosshead speed of 2mm/min. Results; Values are MPa(SD), N=10 for all groups.

Two-way ANOVA showed statistical differences for both factors (p<0.05) and interactions between them (p<0.05). Increasing thickness of composite, decreased bond strength for xenon and metal halide lamps. The bond strength was not affected by composite thickness when halogen lamp was used. Conclusion; Bond strengths to dentin were affected by both, thickness of composite and light sources.