Localized damage to the periodontal ligament and its effect on the eruptive process of the rat incisor

Localized thermal injury was produced in the coronal part of the rat incisor periodontal ligament (PDL). The tooth was cut off at the gingival margin and its pulp removed to a depth of 9 mm from the cut edge. An electrocautery needle was then inserted into the pulp cavity, and a current of two seconds duration was applied. The thermal injury affects primarily PDL vitality, and this is manifested by an eruption slow‐down accompanied by typical histological changes. Specimens for histological examination were obtained one, three, and seven days following treatment and compared with the sections prepared from sham operated and control incisors. The mean eruption rate of the cauterized teeth was slower by about 70 % than that in the other two groups. Histological sections of the former incisors revealed well demarcated coagulation necrosis, which was especially pronounced on the first and third post treatment days. Signs of repair in the damaged areas were observed on the seventh day following treatment. The lingual periodontal lesions were infiltrated with fibroblasts and vascular tissue. In some incisors, hard tissue deposits appeared in the tooth‐related part of the PDL. The PDL of sham operated or control animals did not exhibit any changes. These experiments demonstrate that isolated damage to the PDL retards tooth eruption, supporting the hypothesis which views the PDL as the prime motor pulling the erupting incisor outward.