Effects of CO2 Laser Irradiation in vivo on Rat Alveolar Bone and Incisor Enamel, Dentin, and Pulp

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Abstract
Previous studies have shown that a surgical 'window' can be drilled in alveolar bone for experimental manipulation of the underlying enamel organ and enamel. To determine whether similar and/or improved access could be obtained by use of the surgical capabilities of laser optics, and to note the effects of laser irradiation in vivo on the extracellular matrices and cells of bone, enamel, and dentin, tissue responses to laser-created lesions were examined histologically. Briefly, samples were prepared in which the alveolar bone along the inferior mandibular border of Wistar rats was exposed, and a continuous-wave CO2 laser equipped with a custom-made micromanipulator was used to penetrate the bone and to create lesions within the lower incisor. Animals were perfusion-fixed at either 10 min or 10 days post-treatment, and affected tissues were processed for light and transmission electron microscopy. At 10 min, all lesions consisted of a void of ablated tissue containing some organic debris. Tissues immediately surrounding the lesion were generally intact, but showed some damage, presumably resulting from elevated temperature effects. At 10 days, lesions in the bone, dentin, odontoblast layer, or pulp showed morphological evidence of tissue repair represented by the presence of cell infiltrates, new bone, or reparative dentin. In lesions that were created during the secretory stage of amelogenesis that had moved into the maturatiori stage, there was evidence of delayed or incomplete maturation of enamel ( i.e., retention of organic matrix normally lost during maturation) related to the enamel organ affected by the laser treatment. In the bone lesion at 10 days, new bone formation was observed, while bone fragments originally created at the time of lasing were surrounded by mononuclear and large multinucleated giant cells. It is thus concluded that the application of this laser system is an alternative method for exposing unerupted dental tissues for experimental manipulation, and that laser irradiation may also be useful for the study of mineralized tissue repair.