Objective:The purpose of this studywas to evaluate the effects of the pulsed Nd:YAG laserirradiation in root canals on tem- perature changes on the root surface in vitro and optimize the parameters of laser irradiation in root canal treatment.Methods:A total of 108 extracted single-root human teeth were divided into A, B and C groups, after the preparation of root canals and re- moval of their crowns. GroupAwas evaluated the surface temperature changes of differentteeth irradiatedwith the same outputen- ergy. The teeth inGroup B and Cwere irradiated respectivelywith the frequencies of 15 Hz and 20 Hz, and 7 differentoutput en- ergy, and the inner root canal surface inGroup Bwas coatedwith a layerof ink, whichworked as the initiator.Results:The tooth surface temperature of the mandibular incisor increased more obviously than that of the maxillary incisor, canine and premolar, during root canal irradiation treatment (P
