SEM analysis of dentin treated with the Er:YAG laser: a pilot study of the consequences resulting from laser use on adhesion mechanisms.

Objectives: The purpose of this study was to compare the morphological characteristics of lased dentinal surfaces obtained by chemical etching, which was applied either before or after laser treatment. The adhesive interface after the application of an adhesive-composite system on the above mentioned dentinal surfaces was also evaluated.

Materials and methods: Eighteen caries-free permanent molars were transversally cut to obtain the dentinal surfaces. Ten of these surfaces were divided into three main groups according to their preparation modality: laser only, laser followed by chemical etching, and chemical etching before laser. The Er:YAG laser was used with two different energy outputs: 200 and 400 mJ at 1 Hz. The eight remaining surfaces were divided into two groups and followed the same preparation as the first three groups. The only difference was a change in frequency: 4 Hz was used for treating these surfaces. An adhesive system (Scotchbond 1, 3M), a thin layer of flowable composite (Tetric Flow, Vivadent), and a regular composite (Z250, 3M) were applied to each dentinal surface and then separately light cured. In order to evaluate the dentine-restoration interface, the samples were cut longitudinally and prepared for SEM observation.

Results: The dentinal surfaces that were etched by the laser treatment did not demonstrate the characteristics necessary for guaranteeing a good bond with the adhesive materials. A closer observation of the dentine-restoration interface revealed some micro-fractures located just below the lased dentinal surface.

Conclusion: The decision to use the Er:YAG laser as an alternative to conventional techniques of acid etching is currently arguable. Given that the available adhesive systems require acid conditioning, it would not be advisable to skip this operative step.