Effects of Q-switched Nd:YAG Laser on Calcified Tissues

. This study evaluated the effects of the Q-switched Nd:YAG (1064 nm) laser on four types of calcified tissues (dentine, enamel, bone and cementum) at frequencies of 1, 5 and 10 Hz for irradiation times of 100, 100 and 50 s, respectively. Laser fluences per pulse ranged from 30 to 50 J/cm², and pulse duration was 15 ns. To evaluate morphological modifications after laser irradiation, specimens were examined by scanning electron microscopy. Chemical modifications in residual tissues were studied by Raman spectroscopy, and the depth of craters produced by laser impact was analysed as a function of laser fluences. The results showed that tissues were ablated essentially by a photoacoustic mechanism which produced no carbonisation or high melting zone in residual tissues, even though cracks and fractures appeared around craters. Crater depth per pulse was 1–5 μm/pulse depending on the frequency used. Statistical analysis showed that increasing the number of pulses, thereby increasing crater depth led to a decrease in the ablation rate. Raman spectroscopy showed none of the chemical modifications in residual tissues known to occur in heat-treated enamel, dentine and bone after laser irradiation. Paper received 5 June 1997; accepted following revision 11 February 1999.