An immunohistochemical study of the effects of pulsed neodymium:yttrium–aluminium–garnet laser irradiation in root canals on the eruption of rat incisors

The incisors of 21 Wistar rats were transected, pulp tissue was extirpated for 10 mm from the level of the gingival margin and each canal was prepared with files. The fibre tip of a pulsed neodymium:yttrium–aluminium–garnet laser was inserted into the root canal for 10 mm and laser irradiation delivered at 2 W and 20 pulses/s for 10 s. After 6 weeks the mandibles were removed and sectioned. Sections were stained either with haematoxylin and eosin or immunohistochemically using polyclonal antibodies against keratin/cytokeratin, amelogenin and type I collagen. The inner epithelial cells on the labial side differentiated into ameloblasts in animals where eruption had recovered. The pulp cells differentiated into odontoblast-like cells and staining for type I collagen was evident in pulp cells, odontoblast-like cells and inside dentinal tubules. In animals where eruption had ceased, the inner epithelial cells on the labial side did not differentiate into ameloblasts. Staining for type I collagen was observed in the mineralized nodules and tubules of dentine-like hard tissues in the pulp cavity. These results suggest that differentiation of epithelial cells on the labial side into ameloblasts is involved in the re-eruption process.