Journal of the Korean Academy of Pediatric Dentistry 1996;23(3):640-658.
Published online August 31, 1996.
A STUDY OF THE MECHANISM OF IMPROVING ACID RESISTANCE OF BOVINE TOOTH ENAMEL AFTER PULSED Nd-YAG LASER IRRADIATION
 
펄스형 Nd-YAG 레이저 조사에 의한 법랑질 내산성 증가 기전에 관한 연구
이영순, 손흥규
연세대학교 치과대학 소아치과학교실
Abstract
The purpose of this study was to examine the mechanism of improving acid resistance of Nd-YAG laser irradiated tooth enamel and determine the most effective energy density for improving acid resistance. The bovine tooth enamel were lased with a pulsed Nd-YAG laser. The energy densities of exposed laser beam were varied from 10 to 70J/cm2. To investigate the degree of improving acid resistance by irradiation, all the samples were submerged to demineralize in 0.5 N HClO4 solution for 1 minute. After 1 minute, 0.05 % LaCl3 was added to the solution for interrupting the demineralization reaction. The amounts of dissolved calcium and phosphate in the solution were measured by using an atomic absorption spectrophotometer and the UV/VIS spectrophotometer, respectively. To examine the mechanism of improving acid resistance, X-ray diffraction analysis, infrared spectroscopy, and scanning electron microscopy were taken. The X-ray diffraction pattern of the samples were obtained in the 10˚~80˚2θ range with Cu-Kα radiation using M18HF(Mac Science Co.) with X-ray diffractometer operating at 40 KV and 300 mA. The infra-red spectra of the ground samples in 300 mg KBr pellets 10 mm diameter were obtained in the $4000cm-1 to 400cm-1 range using JASCO 300E spectrophotometer. The scanning electron microscopy was carried out using JSM6400(JEOL Co.) with 500~2000 times magnification. The results were as follow 1. The concentration of calcium dissolved from laser irradiated enamel with 50J/cm2 was significantly lesser than that of unlased control group (p<0.05) 2. From the result of the X-ray diffraction analysis,β-TCP, which increases acid solubility, was identified in lased enamel but the diffraction peaks of (002) and (004) became sharp with increasing energy density of laser irradiation. This means that the crystals in lased samples were grown through the c-axis and subsequently, the acid solubility of enamel decreased. 3. The a-axis parameter was slightly increased by laser irradiation, whereas the c-axis parameter was almost constant except for a little decrease at 50J/cm2. 4. In the infra-red spectra of lased enamels, phosphate bands (600~500cm-1), B-carbonate bands (870, 1415~1455cm-1), and A-carbonate band (1545cm-1) were observed. The amounts of phosphate bands and the B-carbonate bands were reduced, on the other hand, the amount of the A-carbonate band was increased by increase the energy density. 5. The SEM experiments reveal that the surface melting and recrystallization were appeared at 30J/cm2 and the cracks were observed at 70J/cm2. From above results, It may be suggested that the most effective energy density for improving acid resistance of tooth enamel with the irradiation of Nd-YAG laser was 50J/cm2. The mechanism of improving acid resistance were reduction of permeability due to surface melting and recrystallization of lased enamel and reduction of acid solubility of enamel due to decrease of carbonate content and growth of crystal.


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