Vertical Tooth Movement Research Articles

Development of a novel mouse osteoclast culture system including cells of mandibular body and erupting teeth

Osteoclasts are multinucleated cells with the specialized function of resorbing calcified tissues. These cells develop from hemopoietic cells of the monocyte–macrophage lineage with the support of osteoblasts/stromal cells. Tooth eruption is a vertical movement of teeth via creation of an eruption pathway in and through the alveolar bone. The precise cellular and molecular determinants of tooth eruption are not yet clear, and a cell culture system that can reproduce the activity of osteoclast formation during tooth eruption is expected to be a useful tool to clarify the mechanism of eruption pathway formation. To this end, mandibular bodies, including incisors and molars, were isolated from 9- to 11-day-old mice undergoing active tooth eruption. Primary cells were obtained from mandibular bodies by enzymatic digestion and cultured in αMEM containing 15% FBS without any cytokine or growth factor or hormone in the culture (AFT culture, for alveolar bone, dental follicle, and tooth). A progressive increase in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclastic cells was observed in AFT culture. The osteoclastic cells generated were immunopositive for cathepsin K and calcitonin receptor, and formed resorption pits when cultured on dentine slices. Parathyroid hormone-related protein (PTHrP), expressed by the enamel organ of tooth, is reported to be an essential factor in creation of the eruption pathway. To verify this point, cells were isolated from mandibular bodies from which all teeth and dental follicles had been removed and cultured similarly (A culture, for alveolar bone). Osteoclastic cells were not formed and PTHrP production was hardly detected in the medium of A culture, in contrast to the high level of PTHrP in AFT culture. Since our previous study demonstrated that neonatal homozygous PTHrP-knockout mice show impaired osteoclastogenesis around tooth germs, AFT culture was performed by using this sample to examine whether this culture system can reproduce the status of osteoclastogenesis observed in vivo. The result showed that none of the osteoclastic cells were generated from cells of homozygous mice. We here report a novel mouse osteoclast culture system that reproduces the activity of osteoclast formation around erupting teeth without addition of any cytokine or growth factor or hormone to the medium. Histological examination of various transgenic and mutant mice now offers valuable findings on studies of tooth eruption and the present culture system using these animals would be a powerful tool in clarifying the cellular and molecular mechanisms of eruption pathway formation.

Alveolar bone loss of maxillary anterior teeth in adult orthodontic patients

The purpose of this study was to evaluate prevalence and severity of alveolar bone loss in adult orthodontic patients, and to identify risk factors for such bone loss. Standardized periapical radiographs of maxillary anterior teeth and cephalograms made before (T-1) and after (T-2) treatment and treatment charts of 343 adults aged 20.0 to 70.1 years (mean 34.5, SD 9.0) before treatment, representing groups of consecutively treated patients from four orthodontic practices, were examined. Alveolar bone loss was calculated by subtracting the distance from the cementoenamel junction (CEJ) to the alveolar crest (AC) at each interproximal tooth surface from the mesial of one maxillary canine to the mesial of the other. Changes in bone level were calculated by subtracting the distance CEJ-AC at T-1 from the corresponding distance at T-2. Tooth movement was calculated from measurements of superimposed tracings of pretreatment and posttreatment cephalograms. Hygiene level was scored subjectively as adequate or inadequate on the basis of gingival appearance on posttreatment intraoral color slides. Sample means of averaged bone loss of all six anterior teeth and of the surface with the most severe bone loss per patient were 0.54 mm (SD 0.62) and 1.82 mm (SD 1.01), respectively. Only 2.5% of the patients had averaged bone loss of > or = 2 mm, whereas 36% of the patients had one or more surfaces with bone loss of > or = 2 mm. Multiple linear regression analyses revealed a positive relationship between age and bone loss, and a negative relationship between initial bone level and subsequent bone loss. No association was found between bone loss and length of treatment, posttreatment gingival appearance, amount of horizontal or vertical tooth movement, or treatment with maxillary osteotomy.

The finite element analysis of stress in the periodontal ligament when subject to vertical orthodontic forces.

In the past, vertical intrusive movement of teeth has been considered difficult and most routine clinical vertical movement of teeth has been confined to extrusion. It has been suggested that attempts at intrusion may result in an increased incidence of root resorption and also in occasional devitalization. The displacement and resulting stress fields associated with such treatment can be successfully studied using the finite element method. In the case being considered initial movements are known to be small; therefore, the assumption in the study that the material behaves linear-elastically is considered to be reasonable. This study of vertical tooth movement demonstrated that the maximum cervical margin stress in the periodontal ligament was 0.0046 N/mm2, whilst the highest apical stress was 0.00205 N/mm2 when intrusive and extrusive forces of 1 Newton were applied to the buccal surface of the crown of a tooth model. These stresses were evaluated in the light of previous studies and found to be within the suggested clinical optimum level. However, the periodontal stress distribution following orthodontic loading within this three-dimensional finite element model was found to be highly complex.

Brief communication: interproximal tooth wear: a new observation.

Microscopic observations were made of wear on the proximal surfaces of tooth crowns of Australian Aboriginals and whites. Typical wear facets displayed well-defined borders within which vertical or near vertical furrows, ranging from about 0.1 to 0.5 mm in width, were noted. Furrows on the interproximal surface of one tooth seemed to "interdigitate" with those on the proximal surface of the adjacent tooth. These observations are not consistent with the commonly-held view that interproximal tooth wear results from a buccolingual movement of adjacent teeth that maintain contact through mesial migration. Vertical or near vertical movement of teeth, possibly including a tipping action, must be an important factor, although the precise nature of the movement requires further investigation.

Periodontal changes after experimentally induced intrusion of the upper incisors in Macaca fuscata monkeys

We are studying the biologic aspects of vertical movement of teeth, which are often used in orthodontic treatment involving variations in alveolar tissue. In the present study, the four upper incisors of five infant Macaca fuscata monkeys were intruded vertically from 1.1 to 5.5 mm. The following effects were examined: (1) movement of the gingiva, (2) change in the depth of the gingival sulcus, and (3) microscopic effects on the alveolar tissue. The results were as follows. (1) The gingiva moved in the same direction that the teeth were intruded, but only about 60% as far. (2) The clinical crown shortened and the gingival sulcus deepened. The shortening of the crown and the deepening of the sulcus were both approximately 40% as much as the tooth intrusion. (3) There was no inflammation or swelling microscopically in the gingiva of either the experimental animals or the controls. (4) The epithelium was always attached in the cementoenamel junction, even when the tooth was intruded. As the tooth intrusion was increased, the dentoperiosteal fiber (DPF) and the dentogingival fiber (DGF) terminating in the cementum gradually parted from it; when the tooth was intruded more than 5.0 mm, few fibers terminated in the cementum. It was concluded that the gingival sulcus deepened with horizontal tooth intrusion because of an accumulation of gingival tissue applied with good oral hygiene—not because of swelling around the gingival margin or apical movement of the gingival pocket—and the DPF and the DGF were parted from the cementum gradually as the tooth intrusion increased.