Shear bond strength of porcelain bonded to Er:YAG laser prepared dentin with self-etch and total-etch resin cements

The objective of this study was an in vitro investigation of the shear strength of the bonding where porcelain blocks are cemented using three different resin cements on dentine surfaces subjected to laser applications with different densities.Investigation was carried out using 45 extracted, unerupted human wisdom teeth. Following the removal of the periodontal residue using a curette, the crown of each tooth was separated from its roots and then each tooth was cut into two equal parts providing total of 90 test specimens. Each specimen was then embedded into acyrilic resin housed in a brass cylinder (diameter 20 mm, height 16 mm). Buccal and lingual surfaces of each specimen were ground under water using using 600 grid silicon carbide grinding paper to ensure 4-5 mm dentin thickness. After complete exposing of the dentin surfaces, three groups of specimens were applied Er:YAG laser of 30Hz/70mJ density and another three groups of specimens were applied Er:YAG laser of 30Hz/160mJ density. The remaining three groups of specimens were not subjected to any laser application since these groups were intended as reference (control) groups.A cylinder shaped porcelain block (diamater 4mm, height 2 mm) was cemented to each one of 90 specimens using three different resin cements in accordance with their manufacturers? recommendations; Kuraray Clearfil Esthetic Cement (Self-Etch), Ivoclar Multilink Automix (Self-Etch) and Ivoclar Variolink II (Total-Etch). Then, the specimens were randomly selected and grouped into 9 groups where each group contained 10 specimens. All the specimens were then subjected to an accelerated aging process in a thermo-cycle unit for 1,000 cycles between 5 and 55 degrees Celcius. The specimens were then tested in a Universal Testing Machine (Instron, USA) subjecting them to a shear force applied at 1 mm / second rate until the shear failure occured. A level of shear force at the instant of failure of each specimen was recorded in MPa. The statistical analysis was performed using Dunn?s multiple variable and Kruskal Wallis tests.The specimens bonded using Variolink II and Multilink Automix resin cements showed statistically meaningful differences with respect to the specimens bonded using Clearfil Esthetics Cement and thus giving better results.