الفهرس 
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Abstract
Orthodontic treatment is based upon the principle that if prolonged pressure is applied to a tooth, tooth movement will occur as the bone around the tooth remodels (Pro/fit et al, 2007). The typical 2 to 3 years treatment period is burdensome for patients, so it is very important to accelerate alveolar bone remodelling during treatment to abbreviate the time required (Kawasaki and Shimizu, 2000). A long period of retention IS necessary to prevent early relapse. Although the reason for the early relapse is not fully clear, bone regeneration after orthodontic treatment may affect the post treatment relapse. It would be potentially beneficial therefore to accelerate bone formation to prevent relapse and abbreviate the retention period (Saito and Shimizu, 1997). The use of Ga-As diode laser has grown increasingly during the last 10 years. This kind of laser is known to have a high depth of penetration in comparison with other types and thus offers the clinician a penetrative tool of great efficiency (Nissan et al., 2006).Scientific findings indicate good healing of soft tissues, stimulation of DNA and RNA synthesis in the cell nucleus (Laru et al, 1983), and transformation of fibroblasts to myofibroblasts (Pourreau-Schneider et al., 1990). The effect of low energy laser on the alveolar bone after tooth extraction showed increase in the deposition of bone (Takeda, 1988). Radiological analysis after tooth extraction demonstrates that low intensity laser can activate repair of damaged bone tissue in patients (Nagazawa et aL., 1991). Lasing also results in new bone formation around hydroxyapatite implants in rabbits and a significant increase in the total bone area Asanami et al., 1993). In addition, low power laser irradiation significantly increased the number of viable osteocytes in the irradiated bone by a positive effect on bone matrix production to produce highly reactive and vital implant bone tissue (Dortbudak et al., 2002). Moreover, it is effective on the bone healing process in artificially created osseous cavities by affecting calcium transport during new bone formation (Nissan et al., 2006). Sun et al., in (2001) reported that the irradiation of low energy laser promotes tooth movement and remodeling of alveolar bone in rabbits. In addition, MiLoro et aL., in (2007) reported that low level laser therapy (LLL T) accelerates the process of bone regeneration during the consolidation phase after distraction osteogenesis. The adjunctive use of LLL T may allow a shortened period of consolidation and therefore permit earlier device removal, with the avoidance of morbidity associated with prolonged device retention. Therefore, if laser irradiation can cause the acceleration of bone remodeling, it may also have great potential benefit In abbreviating the orthodontic treatment period. This study was conducted in an attempt to evaluate the effect of low level laser therapy (LLL T) on alveolar bone remodeling and rate of tooth movement secondary to application of orthodontic force.