Mechanical properties and molecular structure analysis of subsurface dentin after Er:YAG laser irradiation

The purpose of this study was to evaluate the chemical and mechanical modifications in subsurface dentin layer after Er: YAG (Erbium-Yttrium Aluminium Garnet) laser irradiation, as the guidance of new dental restorative materials specific for laser irradiated dentin. Materials and Methods Dentin disks obtained from extracted human molars were prepared and exposed to a single pulse Er:YAG laser irradiation at 80 mJ/pulse. After laser irradiation the mechanical and chemical characteristics of intertubular dentin in subsurface layer were studied using nanoindentation tester and micro-Raman spectromy (μ-RS). The dentin 5–50 µm depth beneath the lased surface was determined as testing area. Two-way analysis of variance (ANOVA) were used to compare the mechanical values between lased and untreated subsurface dentin (P = 0.05). Results A laser affected subsurface dentin layer after Er:YAG laser treatment is present. The laser irradiation is considered to decrease the mechanical properties in the superficial subsurface layer (<15 µm deep). There was no significant difference in nanohardness and Young's modulus between lased subsurface dentin and untreated dentin (p > 0.05) under the depth of 15 µm. However, the dentin at 5 µm and 10 µm depth beneath the lased surface exhibited significantly lower (~ 47.8% and ~ 33.6% respectively) hardness (p < 0.05). Er:YAG laser irradiation affected both mineral and organic components in subsurface dentin layer, a higher degree of crystallinity and reduced organic compounds occurred in the lased subsurface dentin. Conclusion Under the tested laser parameters, Er:YAG laser irradiation causes lower mechanical values and reduction of organic components in subsurface dentin, which has deleterious effects on resin adhesion to this area.