Effects of Nd: YAG Laser Irradiation on the Changes in the Microhardness. Ca/P Ratios and Morphology of Root Surface

Abstract

It has been reported that laser irradiation har-dened enamel. If laser irradiation could also harden cementum. then it would be beneficial in the prevention of root caries and periodontal disease. The purpose of this study was to compare the changes in microhardness of cementum after Nd: YAG laser irradiation : to measure Ca/P ratios after laser irradiation using XMA and to observe the cementum surface structure using SEM. Per-iodontally healthy single rooted teeth were used in this experiment. After extraction of the teeth. remaining remnants of soft tissue were removed useing collagenase. Seventy-five flat cementum surface sites (3× 3mm) selected for the experimet-nts. The roots were cut into 5× 5mm segments. Among them. 75 flat segments were selected for the experiment. Twenty-five segments served as the control (10 for microhardness. 10 for Ca/P. 5 for SEM observation). Fifty segments were used for laser irradiation at 30mJ 10 pps for 30secs (10 for microhardness. 10 for Ca/P. 5 for SEM) and 25 segments were lased at 50mJ 10 pps for 30secs (10 for microhardness. 10 for Ca/P. 5 for SEM). After irradiation. the roots were cut into 5× 5mm seg-ments for measurement of microhardness. Knoop hardness was measured with a 25-gram-load 3 times on each segment. The remaining roots were cut into 3× 3mm segments for analysis of Ca/P ratios and SEM observation. The Ca/P ratios of each segment was measured by XMA (JEOL. Tokyo) The average microhardness of cementum (control) was 24.95±6.59Hk. The average of microhard-ness after laser irradiation was 39.58±16.16Hk for the 30mJ group (p<0.01) and 51.42±20.93Hk for the 50mJ group (p<0.01). The average of the Ca/P ratio (control) was 1.76. The average of the Ca/P ratios for the 30mJ and 50mJ group 1.78 and 1.84 for the 50mJ group (p<0.05). There were no topographical differences between the con-trol and the 30mJ segments. Melting and resolidification of the cementum surface were ob-served on the 50mJ segments. These results sug-gested that laser irradiation at 30mJ 10pps made the cementum surface resistant to demineralization without topographical change on the cementum surface.