Dentin ablation with three infrared lasers.

Abstract

BACKGROUND AND OBJECTIVE: Lasers are used for caries removal in enamel and dentin, but are currently limited in their ability to remove sound tooth structure. In this study plasma interaction regimes are investigated as the principal factor determining the ablation characteristics. STUDY DESIGN/MATERIALS AND METHODS: Three ablation parameters are considered: ablation rates (AR), surface temperatures (ST), and surface morphological characteristics. The three lasers investigated were Er:YSGG with wavelength (WL) of 2.94 mu m and pulse duration (PD) of 250 mu s, Ho:YSGG at 2.1 mu m and 250 mu s and an Nd:YAG with WL of 1.06 mu M and PD of 15ns. RESULTS: The highest surface temperatures were observed during Er:YSGG treatment (> 300 degrees C), moderate temperatures with the Ho:YSGG (150 degrees C), and lowest with the Nd:YAG (with highest surface temperature generally lower than 80 degrees C). Ablation rates were also compared and were shown to be highest with the Er:YSGG and Ho:YSGG, and lower with the Nd:YAG (< 3 mu m). In all systems, efficient ablation was observed only in the presence of plasma. In spite of their different wavelengths, for similar spot sizes, energy, and pulse duration, ablation rates of Ho:YSGG and Er:YSGG were found to be comparable. These were an order of magnitude larger than the ablation rates observed with the nanosecond system. CONCLUSION: Possible explanation for these observations is given in terms of plasma characteristics.