Tissue alteration and thermal characteristics of excimer laser interaction with dentin

The interaction of two short pulse excimer lasers with dentin has been evaluated using 193 nm radiation from a 15 ns ArF and 308 nm pulses from a 15 ns XeCl. Temperature changes of the ablated surfaces were monitored and correlated to scanning electron microscope studies. While surface temperatures during irradiation with the XeCl laser rose significantly higher than those due to exposure to the ArF pulses, heat penetration into the tooth was minimal in both systems and did not perturb the vicinity of the root canal. The dependence of the dentin thermal response on changes in the beam spot size was investigated as well. Surface temperatures were found to be linearly dependent on spot size in both lasers. Scanning electron microscopic observations of the ablated surface showed that although temperature changes at low pulse repetition rates and at low fluence were minimal in both lasers, localized melting of dentin was observed in both lasers. In the case of the XeCl laser, sufficient amount of melted dentin was generated to induce flow and partial sealing of existing cracks in the dentin structure. Only minimal amount of dentin melting was generated by the ArF laser, but a very thin (approximately equals 1 micrometers ) coating of exposed tubules was observed at lower fluences. Surface morphology was found to depend strongly on the fluence levels used but was relatively insensitive to the laser pulse repetition rates.