Effects of Lasers and Fluoride on the Acid Resistance of Human Enamel with Incipient Carious Lesions

Objectives In order to preserve the maximum amount of healthy enamel and increase the acid resistance of an incipient carious lesion, CO2 laser, Nd: YAG laser and APF were used to treat incipient carious lesions, then their effects were compared. Materials and Methods One hundred and twenty samples from human caries-free premolars were immersed in pH-cycling solution for 2 days for incipient carious lesion formation. Then all the samples, were divided into 4 groups randomly; control group, CO2 laser group, Nd: YAG laser group and APF group, and the lesions were treated by CO2 laser, Nd: YAG laser irradiation or APF application respectively. All the samples were immersed in pH-cycling solution a second time for 2 days. As for the acid-resistance evaluation, the calcium concentration dissolved from the enamel, surface was analyzed by ISE-trol. Scanning electron microscopy with energy dispersive X-ray analysis system was also used to assay the geographic change and the components of the enamel surface structures. Results According to the acid-resistance evaluation, the control group showed a statistically significant (P＜0.05) higher calcium concentration compared with the APF group and the other Mo laser groups. Moreover, the APF group showed a statistically significant higher calcium concentration compared with the Nd: YAG laser and CO2 laser groups (P＜0.05). However, there was no substantial statistical difference in the two laser groups (P＞0.05). From the SEM, the melting and re-crystallization surfaces and crater-like holes, 1-20µm in diameter, were found on the CO2 laser and Nd: YAG laser treated enamel surfaces. Finally, in the aspect of the EDS, there was no evidence of new components on the enamel surfaces after lasers and APF were applied. Conclusions The app1ication of CO2 laser, Nd: YAG laser and APF on enamel incipient carious increase acid resistance. Furthermore, the effect of laser irradiation is better than that application.