Artificial caries removal and inhibition of artificial secondary caries bypulsed CO2 laser irradiation

Purpose: To investigate the inhibition of artificial secondary caries aroun d restorations placed after removal of artificial caries by pulsed CO2 lase r irradiation and by mechanical means. Materials & Methods: Beveled cavitie s were prepared mechanically on the facial surfaces of extracted human mola rs. Each cavity was subsequently exposed to an artificial caries (demineral izing) solution (pH 5.0) for 7 d to generate a demineralized zone approxima tely 100-200 mu m thick on the cavity surface. The artificial carious/demin eralized zones of the cavities were kremoved by a pulsed CO2 laser operatin g at a wavelength of 9.3 mu m with pulse duration of 100 mu s and an irradi ation intensity of 5 J/cm(2). Artificial control caries were removed mechan ically with a carbide bur in a slow speed handpiece. The cavities were slig htly undercut and restored with a resin-based composite without etching and bonding and the restored teeth were subjected to pH cycling solutions for 10 d as follows: Demineralization solution, pH 4.5 for 6 hrs, followed by r emineralization solution, pH 7.0 for 18 hrs. Cycled teeth were sectioned th rough the restorations and the resulting lesions were analyzed in thin sect ion using polarized light and Knoop microhardness. Results: Mean microhardn ess Delta Z values, indicating mineral loss were: 549 (SD 191) for control, and 140 (SD 127) N = 11. This difference is significant with t = 5.543 and P = 0.000 (Paired t-test). Caries penetration: Control side - 231 mu m (SD 71), Laser treated side: 123 mu m (SD 79) N = 6. This difference is signif icant with t = 5.198 and P = 0.003 (Paired t-test). The results show that t he laser treatment not only removed artificial caries, but also inhibited d ecalcification of the cavity wall in a subsequent artificial caries challen ge by as much as 81% compared to control samples. No etching and bonding wa s used in this pilot study, which might have influenced the results. Future studies should address the inhibition effect of the laser treatment as com pared to adhesive techniques, fluoride treatments and fluoride release rest orative materials. Conclusion: Caries removal by a pulsed lambda = 9.3 mu m CO2 laser produces a cavity surface morphology with marked resistance to a rtificial secondary caries as compared to mechanical removal.