A New Laser-Processing Strategy for Improving Enamel Erosion Resistance.

In the present study, a new automatic laser-processing strategy allowing standardized irradiation of natural tooth areas was investigated. The objective was to find a combination of laser parameters that could cause over a 600 degrees C temperature increase at the enamel surface while not damaging enamel, avoiding temperature change above 5.5 degrees C in the pulp and increasing enamel erosion resistance. Seventy-seven bovine enamel samples were randomly divided into 6 laser groups and 1 negative control (C/no treatment/ n = 11). A scanning strategy (7 x 3 mm) was used for the CO(2) laser treatment (lambda = 10.6 microm, 0.1-18 J/cm(2)) with different pulse durations-namely, 20 micros (G20), 30 micros (G30), 55 micros (G55), and 490 micros (G490), as well as 2 modified pulse distances (G33d, G40d). Measurements of temperature change were performed at the surface (thermal camera/50 Hz), at the underside (thermocouples), and at the pulp chamber using a thermobath and human molars ( n = 10). In addition, histology and X-ray diffraction (XRD/ n = 10) were performed. Erosion was tested using an erosive cycling over 6 d, including immersion in citric acid (2 min/0.05 M/pH = 2.3) 6 times daily. Surface loss was measured using a profilometer and statistical analysis with a 2-way repeated-measures analysis of variance (alpha = 0.05). Only G20 fulfilled the temperature requirements at the surface (619 +/- 21.8 degrees C), at the underside (5.3 +/- 1.4 degrees C), and at the pulp (2.0 +/- 1.0 degrees C), and it caused no mineral phase change and significant reduction of enamel surface loss (-13.2 +/- 4.0 microm) compared to C (-37.0 +/- 10.1 microm, P < 0.05). A laser-scanning strategy (20 micros/2 kHz/1.25 J/cm(2), 3.4 mm/s) has been established that fulfilled the criteria for biological safety and significantly increased enamel erosion resistance (64%) in vitro.