A Study On Acquired Acid Resistance Of Enamel And Dentine Irradiated By Er, Cr: YSGG Laser

This investigation was performed to evaluate the acid resistance of sound enamel and dentin treated by Er, Cr; YSGG laser or the combined use of fluoride with Er, Cr: YSGG laser to artificial caries formation in vitro .MethodsThe enamel or dentin samples from twenty extracted non - caries human molars were randomly divided into four groups and prepared by different methods as follows; Control group: no preparation; NaF group: treated with 2% NaF solution at 37@ for 30 minutes; laser group: enamel samples were irradiated with Er, Cr; YSGG laser at 6 W for 6 second, at the distance of 1 - 2mm, dentin samples were irradiated with Er, Cr; YSGG laser at 4 W for 6 second at the distance of 1 -2mm; laser and NaF group: first irradiated with laser then treated with 2% NaF. Then all the samples were washed with distilled water for one minute. Every sample was immersed in 3ml of lactic deminer-alization solution at pH 4. 8 and incubated at 37℃ for 24 hours. The parts per million of calcium ion of each 3 ml solution was measured by atomic absorption spectrophotometry. Another enamel and dentin samples were made, the method was similar to above. They were dehydrated and coated with platinum. The quantities of calcium, phosphate and fluoride on the surface of enamel and dentin sample were examined by SED - X and the ultrastructure was investigated by SEM. The data were analyzed statistically among group using ANOVA test. Result were expressed as a mean ±standard deviation, a value of p <0. 05 was considered significant.ResultIn the enamel and dentin samples, the dissolved Ca2 + concentration in the NaF, laser, NaF and laser - treated group were significant decreased compared with that of the control group (P < 0. 05). But no significant difference was observed between the NaF or laser group and NaF and laser - treated group (P >0. 05). In enamel and dentin samples, the quantities of Ca ( weight % ) in the laser or NaF and laser - treated group were increased significantly compared with that of the control group ( P < 0. 05). The content of P was increased in dentin and enamel samples, but only the increase in enamel sample was significant (P < 0.05). In both sample, no significant changes on Ca/p weight ratio were showed between the groups. Only in the NaF group, the F peak appeared. In the enamel sample, the content of F ( weight% ) was 14.78 ±2.17, in the dentin sample was 15.72 ±2. 26. SEM observation showed; the control group surface was cover with a smear layer; The lased enamel and dentin surface lacked a smearlayer and showed various patters of microirregulation with a scaly appearance , the openings of dentinal tubules were clearly visible, but no melting or carbonization; there were lots of calcium fluoride particles attached to the NaF group surface; the ultrastructure of the NaF and laser - treated group was similar to that of the laser group.ConclusionEr, Cr: YSGG laser irradiation is effective for increasing acquired resistance of dental hard tissue and dose not cause thermal side effect. The combined use of Er, Cr: YSGG laser with fluoride has no combined effect, the concrete mechanism is further needed to be studied.