The interaction of pulsed Nd:YAG laser irradiation with human enamel
The aim of the work presented in this thesis was to investigate the interaction of pulsed Nd:YAG laser irradiation with both sound and artificially carious human enamel. More specifically, the aims were to characterise the effect of Nd:YAG laser irradiation on artificially created white spot enamel lesions (to simulate the effect of lasing carious enamel); to quantify the effects of pulsed Nd:YAG laser irradiation on enamel demineralisation; to investigate whether there is synergy between the action of pulsed Nd:YAG laser irradiation and fluoride in terms of impairing acid resistance to enamel; and finally to clarify the mechanism by which pulsed Nd:YAG laser irradiation physically interacts with enamel to induce acid resistance. Laser irradiation of artificial white spot lesions, at 50 mJ and 100 mJ (10 pps, 2 or 5 sec), was found to ablate tissue, causing crater formation. Ablation depth, as determined by microdensitometry, was correlated only with the power used, being greater at 100 mJ than at 50 mJ. SEM examination of the surface morphology of lased enamel, and the surrounding unlased area, was consistent with a process of melting and recrystallisation. It is evident, from this investigation, that in order to remove carious enamel selectively, while leaving sound enamel intact, successive applications of low power irradiation (50 mJ) are the most suitable. The work presented in this thesis has indicated the versatility of the Nd:YAG laser as a dental instrument. The laser can be used to ablate carious enamel and has potential as a prophylactic treatment for caries. The most significant aspect of the laser as a strategy to prevent caries, is that it seems to physically alter the structure of enamel so may, therefore, be a method of permanently increasing tooth resistance to decay.