| Objective:To study the effect of different energy density of low level laser irradiation (LLLI)on orthodontic tooth movement, we establish the tooth movement model of rat and observe periodontal tissue remolding. This will provide a theoretical basis for LLL applications in fixed orthodontic treatment.Methods:1. Forty-five healthy male Wistar rats of6-week-old were obtained and used for the experiments (mean weight,220+15g). Both sides of rats were randomly divided into control group(non-irradiation, n=30),experimental groupl (irradiated5s, energy density15.92J/cm2,n=30), and experimental group2(irradiated20s,energy density63.68J/cm2,n=30,).Both sides are different in every rat. Nine rats were killed on day1,3,5,7and14.2. Establish tooth movement model Under general anesthesia, the0.2mm stainless steel ligation was used to fix0.008inch nickel titanium tension coil spring between the front teeth and the first molars of maxillary in both sides.40g of orthodontic force was applied to the maxillary first molars. In order to prevent tension spring off, ligation wire of first molars and two incisors was reinforced by light-cured resin.The two incisors were fixed as a whole to secure anchorage.3. Low level laser irradiation was applied by placing the optical tip from buccal, palatal, mesial of mucosa, located in the area of experimental maxillary first molar. Irradiation was performed once a day from day0-6. To measure the amount of tooth movement, plaster models were made using silicone impression material before (day0) and after tooth movement (day1,3,5,7,14). Using Photoshop CS4software, we measured the distance between the mesial groove point of the first molar and distal tip of the second molar. Taking the including maxillary first molar tissue blocks on day1,3,5,7and14, they were sliced, stained with HE, then observed periodontal histological changes under the microscope.Results:1. The movement of rat upper first molar, the control side, groups were different in day (1,3,5,7,14),5s>20s> control side. The result of One-Way ANOVA indicated that the tooth movement among groups was statistically significant differences on day7and14. When Means of tooth movement distance were compared with each other in every period, the difference of Means between the control side and5s side was statistically significant (P<0.05) in the14th day. Low level laser irradiation (5s,15.92J/cm2) accelerate orthodontic tooth movement of rats.2. In pressure area, in the first day, osteoclasts were visible in5s group, and rare in0s&20s group. In the3rd and5th day, number of osteoclasts in5s group increased significantly; osteoclasts were more active compared with0s&20s group. In the7th,14th day, number of osteoclasts in5s group tended to decrease and is less than0s&20s group. Number of osteoclasts continued to increase as time prolonging in0s&20s group. But the number of osteoclast in20s group is more than0s group on day (3,5,7). The finding showed that low level laser irradiation accelerates osteoclast generation.In tension area, we fond osteoclasts and pit-like absorption of alveolar bone each group in the1st and3rd day. With time extending, osteoclasts reduced, osteoblasts gradually increased. In the7th day, number of osteoblasts on the alveolar bone surface in5s group was significantly higher than0s&20s group,and the number in20s group was more than0s group.Osteoblasts of5s group decreased, while it increased in0s&20s group on day14. This suggests that low level laser irradiation accelerates osteoblast generation.Conclusions:1. The findings suggest that low level laser irradiation accelerates orthodontic tooth movement.2. Low level laser irradiation promotes periodontal tissue remodeling and accelerates expression of osteoblast and osteoclast. 3. Low level laser irradiation(irradiated5s/point, energy density15.92J/cm2) will more significantly accelerate orthodontic tooth movement and periodontal bone remodeling in rats. |
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