We evaluate the ablation thresholds of Er：YAG and Er,Cr：YSGG laser for enamel and dentin. A total of 140 dental slices is evenly divided into two groups： the dentin group and the enamel group. Dental tissues are irradiated with either an Er：YAG laser or an Er, Cr：YSGG laser with pulse widths in the order of 100 μs. The laser fluence is increased gradually until the ablation crater is formed. The laser ablation threshold is calculated using probit analysis. The ablation thresholds of the Er：YAG laser for dentin and enamel range from 2.88 to 3.36 J/cm^2 and from 2.94 to 3.8 J/cm^2, respectively, and the ablation thresholds of the Er,Cr：YSGG laser for dentin and enamel range from 2.92 to 4.2 J/cm^2 and from 4.93 to 5.66 J/cm^2, respectivelv.
The influence of scanning speed on hard bone tissue ablation is studied with a 10.6-μm laser. The groove morphology and the thermal damage created in bovine shank bone by pulsed CO2 laser are examined as a function of incident fluence by optical microscope following standard histological processing. The results show that ablation groove width, depth and ablation volume, as well as the zone of thermal injury, increase gradually with incident fluence. As compared to the result for high scanning speed, the lower scanning speed always produces larger ablation volume but thicker zone of thermal injury. It is evident that scanning speed plays an important role in the ablation process. In clinical applications, it is important to select appropriate scanning speed to obtain both high ablation rates and minimal thermal injury.
