The influence of low-level laser on orthodontic relapse in rats.

SUMMARY OBJECTIVES This study evaluated the effect of low-level laser therapy (LLLT) on the tendency of rat molars to relapse following orthodontic tooth movement (OTM). MATERIAL AND METHODS Maxillary rat molars were moved mesially for 10 days. Animals were randomly assigned to group I (non-irradiated) or II (irradiation with LLLT). Appliances were removed, and the molars allowed to relapse for 1, 3, 5, 7, 14, or 21 days; rats in group II received LLLT according to a protocol. Bone density of periapical alveolar bone was measured using radiographs and Digora software. Dental supporting structures were examined histologically with haematoxylin and eosin and tartrate-resistant acid phosphatase. RESULTS In both groups, first molar relapse was rapid 1 day after the end of active treatment; by 21 days percentage relapse was measured as 86.11 per cent in group I, and 72.22 per cent in group II. Osteoclast number was highest at the end of active OTM, and thereafter successively decreased during the relapse phase in both groups. Decrease in number, and redistribution of osteoclasts occurred more rapidly in the non-irradiated than the LLLT group. Whilst molar relapse was generally less and osteoclast numbers generally higher in group II compared to group I, the differences were not significant. There was no significant difference in bone density between the two groups. CONCLUSIONS These results indicate that LLLT may reduce the relapse tendency, possibly due in part to bone formation in previous tension areas, and to redistribution of osteoclasts following removal of orthodontic force. The role of LLLT in the prevention of orthodontic relapse requires further study.