Histopathological changes in dental pulp in rats after irradiation of Nd:YAG laser

Abstract

The long-term effects of irradiation with the continuous wave Nd: YAG laser on the dental pulp of the rats were examined histopathologically. The rat mandibular first molar with or without the coating of laser absorption black material (Indian ink) was irradiated by the Nd: YAG laser, and the histopathological changes of the dental pulp were examined immediately, 1 week, 1 month, 4 months, 6 months and 12 months after the irradiation. The pulp of the lased teeth with Indian ink coating showed a marked formation of the secondary dentin following prominent cellular dynamics. Immediately after irradiation, the pulp showed exudative inflammatory changes with hyperemia and focal degeneration of the odontoblasts. One week after irradiation, these changes improved with the proliferation of the differentiated mesenchymal cells. Subsequently, the odontoblastic layer became thickened with differentiation of new odontoblasts. After 4 months, the pulp space gradually became reduced in size with the continuous formation of the secondary dentin. On the contrary, the pulp of the lased teeth without the Indian ink coating did not show any cellular dynamics and formation of the secondary dentin. These results suggested that the irradiation of the rat molar with the continuous wave Nd: YAG laser would have some kind of prolonged biological effects on the dental pulp tissue when the teeth are coated with laser absorption black material.