Pure rotation in the temporomandibular joint during jaw opening? A digital motion analysis.

OBJECTIVE: In the temporomandibular joint two separate movements of rotation and translation occur in two articular spaces during mouth opening. Over the years, the approach has changed considerably, but it is still subject to controversy as to which of these movement is involved in the initial stage of mouth opening. In the present study, the extent of rotation and translation was investigated in the first 5 mm of mouth opening. MATERIALS AND METHODS: The study was carried out on 46 volunteers. Anamnesis was taken and patients were examined. For the investigation, an ultrasonic digital motion analyser (KaVo Arcus Digma 2) was applied. The measurements were made after calibration to an arbitrary axis. Each participant performed three open-close movements in succession, starting from maximum intercuspal position. RESULTS: Data were statistically processed using cubic spline interpolation. Linear regression was then used. The resulting line is significantly (p < 0.0001) different from the horizontal that represents only rotational movement. CONCLUSION: The results show that during mouth opening from maximum intercuspal position, translation is present continuously in addition to rotation. Therefore, it might be time to re-evaluate the principle of a pure rotational approach.

Different methods of determining centric relation - comparison with a digital mandibular motion analyser.

BACKGROUND: Finding and registering the maxillary-mandibular jaw relation is crucial in dental practice. Several comparative studies have been conducted to investigate the reproducibility and accuracy of techniques for determining the centric relation (CR) position of the mandible. The aim of our study was to determine which of seven different CR determination methods had the smallest deviation from the theoretical zero with the help of a digital mandibular motion analyser. The chosen theoretical zero position, the maximal intercuspal position (MIP), is the most reproducible and widely used position. METHODS: Thirty-four volunteers (24 females and 10 males) with a mean (SD) age of 29.1 (± 7.3) years with a negative history of temporomandibular disorder (TMD) participated in the study. A digital mandibular motion analyser was used to register the condylar position after the use of each technique for the determination of CR. The calibration was performed to the maximal intercuspal position (MIP) for each volunteer. The investigated techniques were (A) the gothic arch tracer, (B) the adduction field method, (C) Dawson's bimanual manipulation, (D) the patient placing the tongue tip on the palatal rugae, (E) the patient placing the tongue tip to the border of the hard and soft palate, (F) the patient actively pulling the chin backwards, and (G) the examiner pushing the patient's chin back. RESULTS: The position of the mandibular condyle was illustrated in a three-dimensional coordinate system, where the origin represented the MIP. Among the seven methods examined, five showed significant deviations compared to the MIP. Among these, two methods resulted in posterior deviation of the condyles. Methods C and E coincided with the MIP in all directions. CONCLUSIONS: Within the limitations of our study, we found that the smallest deviations from our theoretical zero (MIP) among the investigated centric relation determining methods were obtained with the bimanual mandibular manipulation technique derived from Dawson and the placement of the tongue tip on the border of the hard and soft palate (linguomandibular homotrophy theory).

Evaluation of the effect of vitamin D3 on mandibular condyles in an ovariectomized mouse model: a micro-CT study.

BACKGROUND: This study aimed to investigate the effect of ovariectomy and vitamin D3 on bone microstructure; this effect was examined in three regions of interest at one femoral and two mandibular sampling sites bone in an ovariectomized mouse model. METHODS: Thirty-six week-old female mice were randomly divided into three groups: 10 subjects were given oral cholecalciferol (vitamin D3) daily for 6 weeks after undergoing bilateral ovariectomy (D3 group), while 10 ovariectomized subjects (OVX) and 10 subjects who underwent a sham operation (SHAM) received peanut oil daily during the investigation. After extermination, the left hemimandible and femur were removed and scanned by micro-CT. The bone micromorphology parameters were analyzed and the BMD was calculated. RESULTS: The bone volume fraction (BV/TV) was significantly lower in the trabecular bone of the mandibular condyle in the OVX group than in the SHAM and D3 groups. Also there was a significant difference between the SHAM and D3 groups. The specific bone surface (BS/BV) was significantly higher in the OVX and D3 groups than in the SHAM group. Trabecular thickness (Tb.Th) was significantly higher in the SHAM group, and the trabecular bone pattern factor (Tb.Pf) was significantly higher in the OVX group than in the other two groups. Bone mineral density (BMD) of the femur and the mandible was significantly lower in the OVX group than in the SHAM and D3 groups. CONCLUSIONS: Our results show that ovariectomy causes a significantly weaker bone microstructure in the mandibular condyle, where the protective effect of vitamin D3 resulted in a partial resorption.

Significance of the Tks4 scaffold protein in bone tissue homeostasis.

The main driver of osteoporosis is an imbalance between bone resorption and formation. The pathogenesis of osteoporosis has also been connected to genetic alterations in key osteogenic factors and dysfunction of bone marrow mesenchymal stem/stromal cells (BM-MSCs). Tks4 (encoded by the Sh3pxd2b gene) is a scaffold protein involved in podosome organization. Homozygous mutational inactivation of Sh3pxd2b causes Frank-ter Haar syndrome (FTHS), a genetic disease that affects bone tissue as well as eye, ear, and heart functions. To date, the role of Tks4 in adult bone homeostasis has not been investigated. Therefore, the aim of this study was to analyze the facial and femoral bone phenotypes of Sh3pxd2b knock-out (KO) mice using micro-CT methods. In addition to the analysis of the Sh3pxd2b-KO mice, the bone microstructure of an FTHS patient was also examined. Macro-examination of skulls from Tks4-deficient mice revealed craniofacial malformations that were very similar to symptoms of the FTHS patient. The femurs of the Sh3pxd2b-KO mice had alterations in the trabecular system and showed signs of osteoporosis, and, similarly, the FTHS patient also showed increased trabecular separation/porosity. The expression levels of the Runx2 and osteocalcin bone formation markers were reduced in the bone and bone marrow of the Sh3pxd2b-KO femurs, respectively. Our recent study demonstrated that Sh3pxd2b-KO BM-MSCs have a reduced ability to differentiate into osteoblast lineage cells; therefore, we concluded that the Tks4 scaffold protein is important for osteoblast formation, and that it likely plays a role in bone cell homeostasis.

Phospholipase Cγ2 is required for basal but not oestrogen deficiency-induced bone resorption.

BACKGROUND: Osteoclasts play a critical role in bone resorption under basal conditions, but they also contribute to pathological bone loss during diseases including postmenopausal osteoporosis. Phospholipase Cγ2 (PLCγ2) is an important signalling molecule in diverse haematopoietic lineages. Here, we tested the role of PLCγ2 in basal and ovariectomy-induced bone resorption, as well as in in vitro osteoclast cultures using PLCγ2-deficient (PLCγ2(-/-) ) mice. MATERIALS AND METHODS: The trabecular architecture of long bone metaphyses was tested by micro-CT and histomorphometric analyses. Postmenopausal osteoporosis was modelled by surgical ovariectomy. Osteoclast development and function, gene expression and PLCγ2 phosphorylation were tested on in vitro osteoclast and macrophage cultures. RESULTS: PLCγ2(-/-) mice had significantly higher trabecular bone mass under basal conditions than wild-type mice. PLCγ2 was required for in vitro development and resorptive function of osteoclasts, but not for upregulation of osteoclast-specific gene expression. PLCγ2 was phosphorylated in a Src-family-dependent manner upon macrophage adhesion but not upon stimulation by M-CSF or RANKL. Surprisingly, ovariectomy-induced bone resorption in PLCγ2(-/-) mice was similar to, or even more robust than, that in wild-type animals. CONCLUSIONS: Our results indicate that PLCγ2 participates in bone resorption under basal conditions, likely because of its role in adhesion receptor signalling during osteoclast development. In contrast, PLCγ2 does not appear to play a major role in ovariectomy-induced bone loss. These results suggest that basal and oestrogen deficiency-induced bone resorption utilizes different signalling pathways and that PLCγ2 may not be a suitable therapeutic target in postmenopausal osteoporosis.