title: Occlusion regulates tooth-root elongation during root development in rat molars.
abstract: Occlusion is commenced by contact of a tooth with an opposing tooth and is the mechanical force working against the periodontal ligament (PDL). However, the influences of occlusion during root development remain uncertain. By extracting the unerupted counterpart molars of rats, we established a non-occlusal model that directly examined the effects of the absence of occlusion in developing molars using micro-computed tomography (μ-CT) and histological procedures. The μ-CT data for experimental molars confirmed no attrition and hypogenesis of the alveolar bone. Root lengths in experimental groups increased more than in control groups. Histological findings of experimental molars showed a wide crown pulp, a long and narrow root, immature Sharpey's fibers, and hypogenesis of cementum. Proliferating cells localized in Hertwig's epithelial root sheath (HERS), the apical pulp, and the PDL of experimental teeth. Furthermore, cell-proliferative activity in experimental roots exceeded that in normal roots. These data indicate that cell proliferation is decreased by occlusion during root formation. Thus, occlusion is one factor that regulates root elongation.
authors: Division of Periodontology, Department of Oral Biological Science, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan. nakasone@dent.niigata-u.ac.jp
authors: Naohiro
authors: N
authors: Nakasone
authors: Hiromasa
authors: H
authors: Yoshie
mesh_terms: D000367:Age Factors; D000539:Alveolar Process / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development*; D000818:Animals; D003766:Dental Occlusion; D008137:Longitudinal Studies; D008963:Molar / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development*; D010519:Periodontium / Q000033:anatomy & histology / Q000254:growth & development; D051381:Rats; D017208:Rats, Wistar; D014070:Tooth / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development*; D014078:Tooth Eruption; D014092:Tooth Root / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development*; D055114:X-Ray Microtomography