Adhesive Properties of Resin Bonding System to Er: YAG or CO₂ Lased Dentin

Does the resin bonding system exhibit its full adhesive performance to lased dentin?

Abstract

Laser ablation [Er: YAG (Erwin Adverl®, 60mJ/10pps), CO₂ (Topal®, 1W/0.3sec)] of dentin reduces the adhesive properties of resin bonding systems. The so-called “laser-etching” might not be effective in promoting adhesion. By TEM observations of non-decalcified specimens, such morphological changes as observed in the acid-etched dentin surface could not be detected in the subsurface layer of the lased dentin. It was mechanically weakened due to the formation of structural defects and heat-denatured layer, leading to considerably lower adhesive properties. Significantly lower bond strength was obtained in the wedge-shaped defects compared with the flat surfaces. The configuration factor (C-factor) might be an important factor especially for the adhesion to lased dentin.
However, high-energy laser ablation of dentin (Er: YAG: 250mJ/lOpps, CO₂: 3W/0.3sec) hardly reduced the bond strength. In the subsurface layer of low-power lased dentin (Er: YAG: 60mJ/1 pps, CO₂: 1W/0.3sec), TEM observations of decalcified specimens revealed that amorphous matrix substances containing denatured collagen fibers were generated (Er: YAG: 3-4μm, CO₂: 1-2μm). On the other hand, in the high power-lased dentin (Er: YAG: 250mJ/1pps, CO₂: 3w/0.3sec), such morphological structure that could hardly be distinguished from sound dentin (Er: YAG) or the subsurface dentin layer having both little amorphous matrix and torn collagen fibers with cross-striation (CO₂) was observed. The effects of high-energy laser ablation might be limited to the superficial layer.
It was concluded that laser-etching might not be effective in promoting adhesion, and that the amount of irradiation energy should be considered when evaluating the adhesive properties of resin bonding systems.