[The study of root resorption of human deciduous teeth. I. Histological observation by light microscope]

Sixty-four human non-carious deciduous teeth were used to observe the root resorption of deciduous teeth by means of light microscope. The extent of root resorption was classified into 6 grades: Res. O, Res. i, Res. 1/4, Res. 1/2, Res. 3/4, Res. Co. In the physiological root resorption of deciduous tooth, there are numerous, large multinucleated odontoclasts and mononuclear fibroblasts or macrophages residing at the Howship's lacunae. The odontoclasts resorbed hard dental tissues, including cementum, dentin. A characteristic of active or "resorbing" odontoclasts, but not in free or inactive odontoclasts is cytoplasmic projections, or brush borders, which were found near the underlying hard dental tissues. The deciduous root resorption was found to be most advanced in the apical areas. Because of the different eruption path of the permanent successors, the position of deciduous root resorption varied. Generally, the lingual surface was resorbed more extensively than the labial surface in the deciduous anterior teeth; the resorption of the furcal area and interradicular cementum surface of the roots were more advanced in the deciduous molars. Predentin can be resorbed by odontoclasts, too. However, it seems more resistant to resorption than dentin. Resorption lacunae could be observed in the root canal and pulp chamber. This means that the internal root resorption probably occur simultaneously. Periodontal fiber attachment was observed in some Howship's lacunae of the root surface. Inflammatory changes occurred in the pulp of deciduous teeth during the shedding process, especially when the deciduous root was resorbed more than one half way. The appearance of the repairing cellular cementum and periodontal fiber attachment was clearly observed in some deciduous roots.