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Laser Conditioning of Enamel with the Erbium YAG and the CO2 Laser.Bond Strength and Surface Structure

Lorenz M. Brauchli*,Andrea Schramm,Christiane Senn,Judith Ball,Andrea Wichelhaus

Introduction: Acid etching is the standard procedure for enamel conditioning. However it leaves a demineralized surface, which is prone to caries. This is a major disadvantage especially in combination with a fixed orthodontic appliance and reduced oral hygiene. Therefore it was the aim of this study to evaluate the effect of an Erbium:YAG laser as well as a CO2 laser on bond strength and enamel surface structure.
Material and methods: 90 freshly extracted bovine incisors were used as substitutes for human enamel. One group of 30 samples was bonded following conventional acid conditioning and served as the control group. The two other groups were conditioned with an Erbium:YAG laser or a CO2 laser. All samples were tested for shear forces with a universal testing machine (Instron 4444). PMMA (polymethylmethacrylate) cylinders were used as shear bodies. SEM (scanning electron microscope) images were taken to compare the effect of the conditioning methods on the enamel surface.
Results: There was a significant difference between the shear forces attained with conventional etching (16.5 MPa), the Erbium:YAG laser (6.2 MPa) and the CO2 laser (3.3 MPa). However due to large standard deviations in the groups conditioned with laser, no significant difference was observed between the Erbium:YAG laser and the CO2 laser. The SEM images revealed a micro-retentive relief for both lasers, but the surface treated with the Erbium:YAG laser showed cracks in the enamel.
Conclusion: Conventional acid etching showed a superior bond strength in comparison with both the laser conditioning methods. Of concern were the fissures observed in the enamel surface treated with the Erbium:YAG laser.