Root and Eruption Defects in c-Fos Mice Are Driven by Loss of Osteoclasts.

c-Fos homozygous mice lack osteoclasts with a failure of the teeth to erupt and with an arrest of root development. Here, we characterize the defects associated with the failure in root development and the loss of the tooth-bone interface, and we investigate the underlying causes. We show that, while homozygous c-Fos mice have no multinucleated osteoclasts, heterozygous mice have a reduction in the number of osteoclasts with a reduction in the tooth-bone interface during development and subtle skeletal defects postnatally. In the homozygous mutants bone is found to penetrate the tooth, particularly at the apical end, physically disrupting the root forming HERS (Hertwig's epithelial root sheath) cells. The cells of the HERS continue to proliferate but cannot extend downward due to the presence of bone, leading to a loss of root formation. Tooth germ culture showed that the developing tooth invaded the static bone in mutant tissue, rather than the bone encroaching on the tooth. Although c-Fos has been shown to be expressed in developing teeth, the defect in maintenance of the tooth-bone interface appears to be driven solely by the lack of osteoclasts, as this defect can be rescued in the presence of donor osteoclasts. The rescue suggests that signals from the tooth recruit osteoclasts to clear the bone from around the tooth, allowing the tooth to grow, form roots, and later erupt.

Gingival crevicular fluid flow rate and alkaline phosphatase level as potential marker of active tooth movement.

BACKGROUND: Gingival Crevicular Fluid (GCF) changes occur during orthodontic tooth movement and this could serve as a potential indicator to the response to active treatment. AIM: The objective of the study is to assess the changes in the GCF volume and the levels of Alkaline Phosphatase (ALP) during early phase of tooth movement. METHODS: 20 patients requiring all first premolar extractions were selected and treated with conventional straight wire mechanotherapy. Canine retraction was done using Nitinol closed coil springs. Maxillary canine on one side acted as experimental site while the contralateral canine acted as control. GCF was collected from around the canines before initiation of retraction, 1 hour after initiating canine retraction, 1 day, 7 days, 14 days and 21 days. GCF volume and the ALP levels were estimated and compared with the control side. RESULTS: The results showed statistically significant changes in the GCF volume and ALP levels on the 7th, 14th and 21st days at the experimental sides. The peak in the activity occurred on the 14th day of initiation of retraction. The GCF volume and ALP levels did not show any significant variations at the control sites where no retraction was done. CONCLUSIONS: It can be concluded that GCF volume and ALP levels may serve as an indicator to assess tooth movement dynamics in orthodontic therapy. Based on the available data and further studies, ALP levels in GCF may aid in developing a reliable non-invasive chair side test for assessing the prognosis and progress of orthodontic therapy.

Interactions of the tooth and bone during development.

The tooth works as a functional unit with its surrounding bony socket, the alveolar bone. The growth of the tooth and alveolar bone is co-ordinated so that a studied distance always separates the 2, known as the tooth-bone interface (TBI). Lack of mineralization, a crucial feature of the TBI, creates the space for the developing tooth to grow and the soft tissues of the periodontium to develop. We have investigated the interactions between the tooth and its surrounding bone during development, focusing on the impact of the developing alveolar bone on the development of the mouse first molar (M1). During development, TRAP-positive osteoclasts are found to line the TBI as bone starts to be deposited around the tooth, removing the bone as the tooth expands. An enhancement of osteoclastogenesis through RANK-RANKL signaling results in an expansion of the TBI, showing that osteoclasts are essential for defining the size of this region. Isolation of the M1 from the surrounding mesenchyme and alveolar bone leads to an expansion of the tooth germ, driven by increased proliferation, indicating that, during normal development, the growth of the tooth germ is constrained by the surrounding tissues.