0065-1281/02/104/2-131 $ 15.00/0 A histochemical study of the regeneration process after injury by pulsed Nd:YAG laser irradiation of root canals Yoshiko Murakami 1 *, Arine Unno 1 , Yuichi Kimura 1 , Tomohiro Okano 2 , Mozammal Hossain 1 , Yukio Nakamura 1 , and Koukichi Matsumoto 1 1 Department of Endodontics, and 2 Department of Oral Radiology, Showa University School of Dentistry,Tokyo 145-8515, Japan Received 16 August 2001 and in revised version 2 November 2001 and 7 December 2001; accepted 10 December 2001 Summary Histological changes of rat dental pulp cells were followed after injury. The regeneration process after 3, 6 and 10 days was monitored. Mandibular incisors were irradiated with a pulsed Nd:YAG laser at 2 W and 20 pulses per sec (pps) for 5 sec and the pulp was examined histologically and immunohisto- chemically for TGF-β1. Eruption of the developing tooth was disturbed for a short period only. Rapid formation of osteodentin was observed. After 3 days, a zone of fibrodentin matrix as well as newly formed vessels were found. Afterwards, regenerative dentin formation was observed accompanied by the formation of a layer of odontoblast-like cells in the damaged area. Immunohistochemical staining of TGF-β1 showed that positivity was present in small tissue areas beneath the mantle dentin, the zone of fibrodentin matrix and odontoblast-like cells. These results indicate that pulsed Nd:YAG laser irradiation of rat incisor pulp induces formation of osteodentin, and TGF-β1 plays a role during regen- eration. Key words: immunohistochemistry – pulsed Nd:YAG laser – rat incisor – tooth eruption – TGF-β1 – osteodentin Introduction Rodent incisors are continuously growing teeth with an asymmetry between their labial and lingual sides. Enamel matrix formation is restricted to the labial side, whereas dentin is present on both sides. On the other hand, the epithelial root sheath is formed and consists of inner and outer dental epithelia of the lingual side. The inner epithelium of the root sheath induces dentin for- mation but lacks the ability to form enamel matrix (Warshawsky and Smith, 1974; Smith and Warshawsky, 1975, 1976). Hertwig’s root sheath (HRS) interacts with ectomesenchymal cells during proliferation and differ- entiation in the process of root formation. The enamel organ, which contains the cervical loop and HRS, is essential for continuous root growth. Dental pulp is unique in its ability to regenerate and to form new dentin, which results from successive and interrelated processes like chemotaxis, neovasculariza- tion, proliferation, and synthesis of extracellular matrix. Dentin repair is stimulated by caries, trauma and opera- tive procedures resulting in pulpal inflammation which *Correspondence to: Dr.Y. Murakami, Department of Endodontics, School of Dentistry, Showa University, 2-1-1, Kitasenzoku, Ohta-ku, Tokyo 145-8515, Japan; fax: +81-3-3787-1229; e-mail: mumingg@aol.com acta histochem. 104(2) 131–137 (2002) © Urban & Fischer Verlag http://www.urbanfischer.de/journals/actahist