Study Of Structure And Composition Of Human Dentine After Er,Cr:YSGG Laser Irradiation

Objective:Multiple bio-technologies were employed to investigate the alternations of Er,Cr:YSGG lased human dentine in composition, micro-structure and morphology. The clinical applicability of this kind of laser for removing dental hard tissues was also studied.Method:Extracted human third molars were used in this study. Crowns with caries, restoration, and fractures were excluded. X-ray Diffraction (XRD) analysis was used to identify the crystal structures, average particle sizes and lattice parameters of HA crystals before and after Er,Cr:YSGG laser irradiation. Several teeth were randomly chosen and analyzed by phase imaging, Energy-dispersive Spectroscope (EDS), Environmental Scanning Electron Microscope (ESEM) and Atomic Force Microscopy (AFM). By EDS, we were able to analyze the changes of the major elements of dentine samples; AFM phase imaging technology was applied to detect the proportional changes of the organic component on dentine surface before and after Er,Cr:YSGG laser irradiation. By ESEM and AFM, we were able to observe the morphological changes of dentine surface and HA crystals before and after Er,Cr:YSGG laser irradiation.Result:1. XRD patterns revealed that all the inorganic phase of the dentin samples could be identified as Hydroxyapatite (HA) structure according to the standard calculated pattern of HA structure. The thermal effects of Er,Cr:YSGG laser with water-cooling spray system on the dentin surface was not intense enough to induce the mineral phase change. The average particle sizes before laser irradiation were 29.1±1.7nm at the (002) position and 9.9±4.1nm at the (130) position, whereas after laser irradiation they were respectively 28.9±2.6nm at the (002) position and 8.3±3.0nm at the (130) position, no obvious changes in the HA nanoparticle size within the error range according to Scherrer formula. By using the Popa model, HA nano-particles appeared as a prolate spheroid in which the polar diameter is greater than the equatorial diameter.2. After laser irradiation, the proportion of the collagens with low contrast was reduced remarkably in the phase images. Accordingly, the proportion of inorganic phase significantly increased. EDS results showed that dentine was composed of Ca, P, O, C and some trace elements of Na, Mg and Cl. The content of C, O, Na as well as the C/Ca ratio declined significantly (p<0.05) after Er,Cr:YSGG laser irradiation, yet that of Ca, P and Ca/P ratio obviously increased (p<0.05). However, no statistical significance was obtained in the content of Ca, P, O, C, Na, Mg and Cl between different energy densities.3. SEM appearance of dentine before laser irradiation showed a relatively flat and smooth topography. In contrast, the dentine appearance after the laser irradiation presented rough surface morphology. The ablated surface was clean and dentinal tubules were completely open at all power settings. With the laser energy density increased, ablation in the peritubular dentine became more serious, peritubular and intertubular dentine showed a partial glassy molten appearance, but no obvious alternations occurred in the general characteristic of dentine surface. In further analysis, the boundary between the treated dentine and untreated dentine was clear but irregular.4. In nano-scale, the particles arranged closely packed to one another, the top of them was hemispherical and the size was similar to each other. Irradiation with Er,Cr:YSGG laser at energy densities range from 6.18 J/cm2 to 11.1 J/cm2 would cause agglomeration and mildly affect the appearance of nano-particles, but no fusion of particles took place. Conclusion:Irradiating human dentine with Er,Cr:YSGG laser at varying energy densities from 6.18 J/cm2 to 11.1 J/cm2 will not significantly influence the inorganic phase structure of the surface dentine layer, however, thermal ablation occurs in organic component. The ablated surface becomes rough and clean, minor alternations of nano-particles can be observed but no obvious crack, fracture, carbonization or fusion can be observed. This study thoroughly evaluated the composition, micro-structure and morphology alternations of human dentine irradiated by Er,Cr:YSGG laser. The potential influence of the changes on the consequent bonding outcome was also completely discussed. It provides a theoretical basis for using Er,Cr:YSGG laser in clinical treatment in the future.