CO2 Laser Irradiation Enhances Interaction of 45S5 Bioglass with Dentin

Objectives: Dentin hypersensitivity is a problem affecting a growing sector of the population worldwide.  This study was designed to examine the interface between dentin and 45S5 bioglass mixed with phosphoric acid and irradiated by CO₂ laser and its ability to seal the dentinal tubules, moreover the chemical changes induced by the aforementioned method on the 45S5 bioglass was detected. Methods: Dentin discs were obtained from the mid coronal part of 40 extracted human non-carious third molars.  The dentin surfaces were ground using 600-grit silicon carbide abrasive paper under wet conditions. The dentin discs were treated as follows; 45S5 bioglass application with/without CO₂ laser operating in super-pulse mode, with the laser power set at 1 W, or without application of bioglass with/without CO₂ laser irradiation using the aforementioned parameters on dentin. The surface and cross-cut surfaces of these specimens were observed by FE-SEM/EDS (S-4500, Hitachi, Japan).  On an isolated test the chemical changes induced by the CO₂ laser irradiation on 45S5 bioglass mixed with phosphoric acid were analyzed using the X-ray diffraction spectroscopy (RAD II A, Rigaka Denki, Tokyo, Japan). Results: The interface and the surface examination showed the formation of a layer rich in phosphate and calcium on the dentin surface that penetrated the dentinal tubules when the 45S5 bioglass was mixed with phosphoric acid and irradiated by CO₂ laser.  However, when the bioglass mixture was not irradiated by CO₂ laser partial coverage of the dentin was observed.  XRD patterns showed crystal formation when 45S5 bioglass was mixed with phosphoric acid and irradiated by CO₂ laser. Conclusion: A crystallized phosphate-calcium rich layer was formed when 45S5 bioglass was mixed with phosphoric acid and irradiated by CO₂ laser on dentin surface. This study was partially funded by the COE Program, FRMDRTB at Tokyo Medical and Dental University.