Inhibition of Molar Eruption and Root Elongation by Cyclophosphamide in Young Mice

Abstract

Recently, outcomes of treatments for childhood cancer have improved, with a greater than 70% survival rate currently noted for affected individuals. On the other hand, late effects of antineoplastic treatment (i.e., dental disturbances such as microdontia, atypical root formation, and tooth aplasia) are frequently observed in these patients. Cyclophosphamide (Cy) is a cytostatic drug often present in chemotherapeutic cocktails commonly used for cancer treatment in children. However, to the best of our knowledge, no studies have reported the effects of cancer chemotherapy on cells that initiate growth of the tooth root. Here, we aimed to evaluate the effects of Cy on dental development in mice.We treated 12-day-old ICR mice with Cy (100 mg/kg, i.p.) and control mice with saline, then dissected the mandibles of mice in both groups at 14, 16, 20, 24, and 27 days of age. The mandibular right molars were scanned using micro-computed tomography and the distal root length of the first molar was measured, while the other side mandibular molars were fixed, then demineralized, dehydrated, and embedded in wax. Serial sagittal sections were prepared from the first molars and histomorphological (hematoxylin and eosin staining) and immunohistochemical (cytokeratin) examinations were performed.At 27 days, the root length in the experimental group was approximately 60% of that in the control group. Although all roots continued to develop after Cy injection, microscopic examinations showed that the roots of the first molars of mice in the experimental group developed more slowly and were shorter than those seen in the control group. Furthermore, Hertwig's epithelial root sheath (HERS) in the experimental group disappeared from 20 days of age and periodontal ligament fibers became more sparse than those observed in the control group. In the experimental group, a lower volume of alveolar bone was formed in the interalveolar septa and the first molars tended to show slower eruption.Our results indicate that Cy can induce defects in and alter the function of HERS. Since HERS plays an important role in tooth root formation, disruption of the epithelial sheath inhibits proliferation and root formation. Furthermore, Cy also affects periodontal tissue modeling. Our results suggest that Cy administration may cause delayed eruption of teeth.