Pathological Study of Experimental Luxation Injuries in Immature Rat Teeth

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School children have a relatively high incidence of luxation injuries to the immature permanent teeth. The luxated teeth often develop necrosis of the pulp, obliteration of the pulp cavity, and internal and external root resorption as a long-term reaction to the injury. The pathology and the degenerative processes of the complications, however, are not well understood. The influence of the fixation procedure to the prognosis of the luxated tooth also remains unclear.In this study, we histologically examined the long-term reactions of immature rat teeth after standardized luxation injuries delivered in our previously developed experimental model.Soon after the trauma, the periodontium at the pressure site had irregular fibers, degenerated cells and hemorrhage. The periodontium at the tension site suffered hemorrhage. The periodontal fibers on the tension side were elongated and, in some areas, torn. After 12 hours, a cell free area appeared in the periodontium on' the compression side. In the alveolar bone and on the surface of the root, resorption occurred one day and 5-7 days after injury respectively. Although the damage in the periodontium and alveolar bone was gradually repaired, the root resorption, especially in the cervical region on the compression side, continued throughout the experimental period. In the most cases, the dental pulp did not seem to be damaged immediately after the trauma. By the 7th day after injury, however, formation of irregular dentin was observed in some teeth. These changes of the pulp tended to disappear in the later stages of the experiment.The present data suggested that even with mild traumatic injury, the damage to the periodontal tissues locally will be severe. Also, the pulp cells were somehow disturbed in their function. Therefore, it is considered that the long-term follow-up is needed to the luxated immature permanent teeth.