| ObjectiveTo observe the dental pulpal response and its biological effect to cut dental hard tissues in dog incisors by the Er:YAG laser and conventional high-speed handpiece.Get the best parameters of cutting dental hard tissues with Er:YAG laser,which caused minimal damage to dental pulp. Confirmed the safety and feasibility of Er:YAG laser for cutting dental hard tissues.Methods1,129 dog maxillary incisors and 76 human maxillary central incisors with their roots and lingual surface amputated ,had their enamel/dentin thickness at buccal surface measured with a caliper. The differences of dog maxillary incisors were tested by oneway ANOVA and LSD-t test (p=0.05) with SPSS 17.0. Compared with buccal surface thickness in cervical of human incisors,calculated the cutting thickness according to the corresponding proportions.2,A total of thirty two incisors of eight healthy dogs for the cutting of dental hard tissues by the Er:YAG laser with three different parameters and conventional high-speed handpiece were divided into four equal groups randomly (n=8): Group A(control group)- high-speed handpiece; Group B- noncontact Er:YAG laser (350 mJ/20Hz); Group C- noncontact Er:YAG laser (500 mJ/15Hz); Group D- noncontact Er:YAG laser (400 mJ/20Hz).All devices were used with water cooling. The cavities were cutted to a depth of 0.56 mm, measured with a marked periodontal probe,and covered with calcium hydroxide.3,After 72 hours post-operation,all experimental dogs were anesthetized at subcutaneous cephalic vein of forelimb with 3% sodium pentobarbital and perfusion fixation at external jugular vein with 4% paraformaldehyde. The teeth were extracted immediately and fixed in 4% paraformaldehyde for a week,then 10%EDTA for 3 months. Then embed with paraffin and sliced continuously for 5 micron. The dental pulpal morphological and histological changes for TGF-β1 were evaluated.4,Average optical density(OD)values of all immunohistochemical images and results of HE staining were measured with Image-Pro Plus 6.0 image analysis software.The data were analyzed statistically by oneway ANOVA and LSD-t test (p=0.05) with SPSS 17.0.Results1,There was no statistically significant difference in dog maxillary incisors when the thickness of buccal surface measured.2,The average thickness of buccal surface in dog maxillary incisors was 1.70mm and the average thickness of human maxillary central incisors was 3.01mm.3,The cutting thickness of buccal surface in cervical of dog maxillary incisors was 0.56mm.4,The subsequent morphological examination of the experimental teeth showed that odontoblast hyperplasia and telangiectasia mildly in the group of 7.0W output; odontoblast hyperplasia and telangiectasia in dental pulp could be seen when 7.5W output and conventional high-speed handpiece were used;Odontoblast proliferate obviously and there was large of telangiectasia and inflammatory cells in pulp tissue in the group of 8.0W output.5,Immunohistochemistric examination showed that TGF-β1 located in the cytoplasm of odontoblast and pulp cells. There was no statistically significant difference in expression of TGF-β1 between the group of 7.5W output and conventional high-speed handpiece. Compared with other groups,the expression of TGF-β1 in dental pulpal tissue was fewest pronounced in the group of 7.0W,and the expression of TGF-β1 in odontoblast was significantly more pronounced in the group of 8.0W output,and there was statistically significant difference with other groups.Conclusion1,Histologic evaluation revealed that Er:YAG laser with 7.5W output and conventional high-speed handpiece causes no visible pulpal damage to the dental pulpal tissue,but 8.0W output may cause obvious pulpal damage to the dental pulpal tissue.2,The results of immunohistochemical staining would allow a conclusion to be drawn that Er:YAG laser with 7.0W and 7.5W output may hold the potential for dental pulpal tissue repair.3,Er:YAG laser with 7.0W output causes no pulpal damage and appears to be a safe method for cutting dental hard tissues.4,Er:YAG laser with 7.5W output and conventional high-speed handpiece cause the same pulpal damage to the dental pulpal tissue for cutting dental hard tissues.5,If set appropriate parameters, Er:YAG laser could used for cutting dental hard tissues with high efficiency and minimal injury to dental pulpal tissue.
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