Influence of Light Energy on Bonding Performance

Objectives: Resin-ceramic hybrid materials for computer-aided design/computer-aided manufacturing (CAD/CAM) resins have recently been developed. The aim of this study was to examine the effects of the amount of light energy transmitted through CAD/CAM resin blocks on the bond performance of resin cement adhesive systems consisting of an adhesive and a dual-curable resin cement.
Methods: Four types of CAD/CAM resin blocks and corresponding resin cement adhesive systems (Kuraray Noritake, GC, Shofu and Tokuyama) were used. The amount of light energy at 468 nm passing through those four types of 1.5-mm-thick CAD/CAM resin blocks and the shear bond strengths of four types of dual-curable resin cements to the respective resin blocks were measured by varying the distance of the exit window for the LED light from the upper surface of the resin block at 0 and at 2 mm. All statistical analysis was performed using the SPSS 12.0 package, with a significance level of P<0.05.
Results: When the amount of light energy reaching the resin cement adhesive system decreases by increasing the distance of the exit window for the LED light from the upper surface of the resin block at 0 and at 2 mm, adhesives containing a dimethacrylate monomer (resin primers) provided shear bond strengths of 10.5 to 14.5 MPa, which were significantly greater than the values (3.1 to 7.2 MPa) for adhesives containing γ-methacryloxypropyltrimethoxysilane (silane primers) (P<0.05). However, when the amount of light energy reaching the resin cement adhesive system became zero, the shear bond strengths were significantly different for the two resin primers, being 1.1 and 11.7 MPa, respectively (P<0.05). Thus, the type of initiator system to polymerize the resin primer strongly affected the bonding performance.
Conclusions: Resin primer containing redox-initiators increase the bond performance of resin cement adhesive systems more than primer containing photo-initiators.