• The korean journal of orthodontics
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• v.35 no.4 s.111
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• pp.262-274
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• 2005

Tooth movement is a result of mutual physiologic responses between the periodontal ligament and alveolar bone stimulated by mechanical strain. The PDL cell and osteoblast are known to have an influence on bone formation by controlling collagen synthesis and alkaline phosphatase activation. Moreover. recent studies have shown that the PDL cell and osteoblast release osteoprotegerin (OPG) and the receptor activator of nuclear factor ぉ ligand (RANKL) to control the level of osteoclast differentiation and activation which in turn influences bone resorption. In this study. progressively increased, continuous tensional force was applied to PDL cells. The objective was to find out which kind of biochemical reactions occur after tensional force application and to illuminate the alveolar bone resorption and apposition mechanism. Continuous and progressively increased tensile force was applied to PDL cells cultured on a petriperm dish with a flexible membrane The amount of $PGE_2$ and ALP synthesis were measured after 1, 3, 0 and 12 hours of force application. Secondly RT-PCR analysis was carried out for OPG and RANKL which control osteoclast differentiation and MMP-1 -8, -9, -13 aud TIMP-1 which regulate the resolution of collagen and resorption of the osteoid layer According to the results. we concluded that progressively increased, concluded force application to human PDL cells reduces $PGE_2$ synthesis, and increases OPG mRNA expression.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.348-353
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• 2003

Early detection and prudent management of mesiodens or supernumerary tooth should be considered essential in reducing disturbance in the eruption and position of the adjacent permanent incisor. While it is true that the presence of diastema may be regarded as normal at the early mixed dentition stage, the early detection and removal of the mesiodens is a prerequisite to facilitate spontaneous alignment or subsequent approximation of the permanent central incisors. In many cases, diastema due to mesiodens can be physiologically corrected spontaneously after the extraction of mesiodens. The best choice of treatment of diastema may be observation. Orthodontic intervention is required only spontaneous closing of diastema does not occur within observation period. In orthodontic intervention, careful treatment plan should be established. Clinician gives considerations to angulation of central and lateral incisor, proximity of lateral incisor, developmental stage and position of canine, pattern and extent of anterior crowding. Orthodontic movement should be done slowly with light force. In addition, periodic radiographic observation are needed to monitor the root development and root resorption. Case 1, 2 and 3 showed physiologic closures after the extraction of mesiodens. In these cases, acceptable alignment of central and lateral incisors was obtained. In case 4, orthodontic correction for diastema was performed successfully after the extraction of mesiodens. After the orthodontic closure of the diastema, it was decided that a retainer was not needed, because the dentition was under a dynamic stage in exchanging teeth and also developing arches.