Influence of the pulse duration of an Er:YAG laser system on the ablation threshold of dental enamel.

The present study examines the dependence of the ablation threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (lambda=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 micro m. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm(2), while the duration of the pulses applied was changed in four steps from 100 micro s to 700 micro s. The irradiated tooth surfaces were examined for visible signs of ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which ablation sets in is reduced by up to approx. 3 J/cm(2). This expands the ablation threshold range of Er:YAG laser radiation to between 6 and 10 J/cm(2). In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the ablation threshold (logistic regression, p<0.0001). Although the ablation threshold of the dental enamel can be changed by varying the pulse duration of the Er:YAG laser, no clinical consequences can be expected, as the shift is only slight.