The objective of this study was to verify whether loss of posterior occlusal support induced displacement of the mandibular condyles from a physiological point of view. Stabilization-type splints were fabricated for 12 healthy dentulous individuals. Each splint was designed to cover the bilateral maxillary teeth up to the second molars. To reproduce loss of posterior occlusal support, the extent of the splint was reduced one tooth at a time, bilaterally, starting from the back and moving forward sequentially. Tapping movement and lateral excursions were performed with each splint and a jaw movement tracking device with 6-degrees of freedom used to observe condylar displacement. Evaluation of 3-dimensional (3-D) displacement of the kinematic axis of the condyle during experimental jaw movement was performed under each occlusal condition with occlusal contact on all teeth, including the maxillary second molars. The habitual closing position was used as the reference. An increase was observed in 3-D displacement of the kinematic axis at the terminal point of the tapping movement with loss of occlusal support, and significant differences were observed in both condyles. An increase was also observed in 3-D displacement of the kinematic axis on the working side during lateral excursion with loss of occlusal support, and a statistically significant difference was observed in the left condyle. A small increase was observed in 3-D displacement of the kinematic axis on the non-working side during lateral excursion with loss of occlusal support. The results of this study suggest that loss of posterior occlusal support induces displacement of the mandibular condyles, suggesting that occlusal support in the molar region is an important factor in stabilization of the condylar position.

Change in soft tissue in relation to that in hard tissue following orthognathic surgery was evaluated. Twenty-five patients were enrolled in the study. The diagnosis in all was jaw deformity (maxillary retrusion and mandibular protrusion) and all underwent a Le Fort I osteotomy and bilateral sagittal splitting ramus osteotomy. Three-dimensional (3D) computer-aided design (CAD) models (polygon models) of the hard and soft tissue of the maxilla and mandible were constructed and superimposed. Reference points were established on the pre- and postoperative hard and soft tissues. Specific elements of each reference point were divided into X, Y, and Z components, respectively, and the distances in each direction and 3D distance (normal distance) measured. The Wilcoxon signed-rank test was used to determine differences in the mean values for the distance moved of each element as the error between pre- and postoperatively. The results revealed statistically significant differences in the Y-direction in the maxilla and the X- and Z-directions in the mandible. A significant difference was also observed in the 3D distances of the maxilla and mandible. Little evidence was found of linearity between the amount of hard and soft tissue movement in the X- and Z-directions in the maxilla. This means that 3D movement in the maxilla was masked more by changes in the morphology of the soft tissue than in the mandible, making it less evident. The results of this study suggest that the 3D analysis method used enables changes in hard and soft tissues to be understood qualitatively, and that it can be used in diagnosis and treatment in orthognathic surgery. It may also be useful in simulation of morphological change in soft tissue.

Lip-seal strength is important for articulating bilabials, capturing food during eating, maintaining fluid within the oral cavity before swallowing, and achieving swallowing pressure. The objective of this study was to investigate the effect of lip-seal resistance training on lip-seal strength in young adults. The participants comprised 15 young healthy adults aged 26–34 years, all with complete dentition. Each was required to perform lip-seal resistance training 5 weekdays a week for 4 weeks with a commercially available instrument for that purpose. The instrument was placed on the midline, left corner, and right corner of the mouth, and pulled forward, leftward, and rightward, respectively. The participants were required to pull the training instrument forcefully while resisting by closing the lips together as strongly as possible until the instrument exited the lips. Lip-seal strength was measured at before and after training using a measurement device. Change in lip-seal strength between before and after training was analyzed using the Wilcoxon signed rank test. The mean lip-seal strength was 8.9±1.5 N before training and 10.4±1.8 N after. A significant difference was observed in lip-seal strength between before and after training (p=0.003), and the mean increase during the training period was 18.1±17.6%. The results showed that lip-seal resistance training for 4 weeks increased lip-seal strength in young adults. These findings suggest that training that involves pulling not only in a forward direction, but also in bilateral directions strongly stimulates the orbicularis oris muscle, resulting in an increase in lip-seal strength.

Bone marrow is the principal site of hematopoiesis in mammals. Amphibians were the first phylogenetic group in vertebrates to acquire bone marrow, but the distribution of hematopoietic cells in the bone marrow of the primitive frog, Xenopus laevis (X. laevis) has not been well documented. The purpose of this study was to perform a histological investigation of the distribution of hematopoietic cells in femoral bone marrow at various stages of development in X. laevis. Hematopoietic cells showed preferential distribution on the endosteal surface of cortical bone throughout all stages of development, from tadpole to aged frog. In mature frogs, hematopoietic cells appeared at the boundary between the epiphysis and the bone marrow. The distribution of hematopoietic cells around the blood vessels was limited to a small number of vessels in the bone marrow. Abundant adipose tissue was observed in the bone marrow cavity from the tadpole stage to the mature frog stage. Hematopoietic cells showed preferential distribution in a belt-like fashion on the surface of newly-formed bones in a bone regeneration model in the diaphysis of X. laevis. These results indicate that the distribution of hematopoietic cells in bone marrow in X. laevis differs from that in mammals, and that the bone marrow of X. laevis constitutes a useful model for exploring the mechanism underlying the phylogenetic differentiation of bone marrow hematopoiesis.

Aggressive periodontitis mostly affects young people, causing rapid destruction of periodontal tissue and loss of supporting alveolar bone. The destruction of periodontal tissue induces pathological tooth movement, resulting in various types of malocclusion such as crowding or spacing in the dentition. This report describes orthodontic treatment for malocclusion due to generalized aggressive periodontitis. The patient was a 31-year-old woman who presented with the chief complaint of displacement in the anterior teeth. An oral examination revealed pathological tooth mobility throughout the entire oral cavity due to severe loss of periodontal support. Many gaps in the displaced maxillary anterior teeth and crowding in the mandibular anterior teeth were also observed. The goal of subsequent treatment was to achieve ideal overjet and overbite by aligning the teeth and closing the spaces via non-extraction orthodontic treatment with stripping. The periodontal disease was managed by a periodontist who provided guidance on oral hygiene and periodontal disease control throughout the course of orthodontic treatment. Appropriate occlusion and a good oral environment were achieved. The condition of the periodontal tissue stabilized during and after orthodontic treatment, and favourable occlusal stability was observed at the 2-year follow-up examination.

One serious complication in implant surgery is displacement of the implant body into the surrounding tissue. This occurs only rarely in the mandible, however. This report describes a case of an implant body displacing into the medullary cavity of the mandible and discusses this in reference to the literature. The patient was a 72-year-old woman who was referred to our department at Tokyo Dental College Chiba Hospital (now Chiba Dental Center) by her regular dentist after an implant inserted in the left mandible in 2010 showed loosening in October 2016. Panoramic X-rays obtained at the initial examination revealed that 2 implants had been inserted into the left mandible, one on top of the other. Removal of both was recommended to prevent infection at the implant site and any potential effects on the alveolar nerve. In the absence of subjective symptoms other than implant loosening, however, the patient did not consent to this proposal. Therefore, only the broken abutment was removed. The patient was instructed to contact us immediately should infection or any other symptoms appear once the mucosa had healed, and the dental clinic that had referred her to us was requested to make her a set of dentures. To our knowledge, only 11 reports have been published to date describing displacement of an implant body into the mandible, and these address a total of just 20 cases. The possibility that an implant body in the mandible may become displaced must be kept in mind during treatment.