| The main purpose of this study was to evaluate, through a in vitro experiment , the effects of Er, Cr: YSGG laser irradiation for the removal of subgingival calculus, and make a comparison between impacts of different methods applied to the planing of periodontal - diseased root surfaces, so as to determine the feasibility and effectiveness of Er, Cr: YSGG laser in the treatment of periodontal diseases.Materials and Methods36 periodontal - diseased in vitro teeth from middle to old aged people and 12 healthy wisdom teeth were collected. As the first step of this study, 6 teeth with evident subgingival calculus were selected from the 36 periodontal - diseased samples, and Er,Cr:YSGG laser was applied with an energy output of 2. 0W. The irradiation was performed with the working tip held at angles between 15 ~ 20o to the areas with subgingival calculus in a quasi - contact scanning mode. A stereomicroscope was then used to observe the calculus on the root surfaces both before and after irradiation and photos were taken. After that, a SEM was used to observe the morphology of the irradiated and un - irradiated areas and photos were taken. In the second step, 12 of the 36 periodontal - diseased teeth were selected and divided randomly into 2 groups. The first group was the non - laser treatment control group, and only root planing was performed. The second group was the laser treatment group. Samples in this group were root planed and then irradiated in a scanning manner for 5 seconds with Er,Cr; YSGG laser at an energy output of 1. 5W. The working tip was held about 1mmfrom, and at angles between 15 ~20o to, the root surfaces. A third group of 6 randomly selected wisdom teeth was the healthy control group which did not receive any treatment. Subsequently came the preparation of specimens. After de-calcification , embedment, cutting sections and dyeing, the histological morphologies of the root surfaces in each group were observed under an optical microscope. In step three, 12 teeth were randomly selected from the other 18 of the 36 periodontal - diseased teeth, and Er, Cr: YSGG laser irradiation was performed after root planing with the same parameters as used in the second step. This was the laser treatment group of periodontal - diseased teeth. The remaining 6 were covered for 2 minutes with saturated citron acid ( PH = 1) soaked sponges after root planing, and this was the acid treatment group. The last 6 wisdom teeth constituting the laser treatment group of healthy teeth received Er, Cr:YSGG laser irradiation with the same parameters as used in step 2. Then, specimens were prepared. After dehydration, desiccation, fixing and gold spraying, the specimens were observed under a SEM to evaluate the root surface morphology changes produced by different treatment approaches, and a comparative study was performed. Meanwhile, an energy spectrum analyzer was used to analyze the root surface Ca/p ratio in each group and a statistical comparative study was performed ( P = 0.05 ).ResultsIn the first step, it could be seen under a stereomicroscope that the 6 teeth with evident subgingival calculus were free of calculus after laser irradiation. A SEM examination of the irradiated areas showed clean surfaces and equal roughness with no signs of melting, carbonization and cracking, obviously different from the un - irradiated areas covered with calculus and smear layers. In the second step, irradiation on planed root surfaces of the laser treatment group produced totally different results from the other 2 groups. An optical microscope examination showed craters on the irradiated root surfaces, which were limited to the cementum, not so deep as to reach the dentin. Root surfaces of the healthy wisdom teeth were more smooth and even than those planed root surfaces of theperiodontal - diseased teeth. A SEM examination of the teeth treated in step 3 showed that 58. 33% of the irradiated root surfaces of the periodontal - diseased teeth was clean and smooth, and 41. 67% was uneven with residues attached.
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