Numerical identification of teeth in Japanese shrew-moles, Urotrichus talpoides and Dymecodon pilirostris.

Numerical determination of the teeth of two species of Japanese shrew moles, Urotrichus talpoides and Dymecodon pilirostris (Talpidae, Insectivora), was based on the position of the premaxillo-maxillary suture, comparison of the dentitions of the two species with those of their relatives and the supernumerary tooth. The premaxillo-maxillary suture is situated between the fifth and sixth tooth anterior to the M1, and the fifth tooth anterior to the M1 was determined to be C both in the two species. The supernumerary tooth which appears in the gap between the third and fourth anterior to the M1 of the lower jaw of Urotrichus talpoides was considered as a relic of pdl which seems to have been lost relatively recently in the evolution of this species. It was also shown that the first premolar of the upper jaw of the Urotrichus talpoides and the first premolars of the Dymecodon pilirostris are dihyodont. Retention of the dihyodont first premolars in these species seems to be a primitive character and is significant in determining the phylogenetical positions of these species.     

Inhibitory effect of synthetic histatin 5 on leukotoxin from Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a gram-negative bacterium strongly implicated in the pathogenesis of juvenile periodontitis. This periodontal pathogen synthesizes a leukotoxin that destroys human polymorphonuclear leukocytes (PMNs), and this toxin is thought to be responsible for the virulence of A. actinomycetemcomitans. It was therefore of interest to assess whether major virulence factors of periodontal pathogens were neutralized by salivary components. This study focuses on the effect of histatins, components of the nonimmune oral defense system, on leukotoxin activity. Leukotoxin was extracted with polymyxin B from freshly grown anaerobic cultures of A. actinomycetemcomitans strain Y4. PMNs isolated from blood of healthy human volunteers were incubated in a cytotoxicity assay containing PMNs (10(7) cells/ml) and leukotoxin preparation (0-500 microg/ml) in Hanks' balanced salt solution at 37 degrees C for 0-120 min with or without synthetic histatin 5 (0-500 microM). Cytotoxicity was measured by release of lactate dehydrogenase (LDH) at different time intervals. Histatin 5 neutralized the toxic effect of the leukotoxin preparation in a concentration-dependent manner, with an IC(50) value of 150 microM. When PMNs were preincubated with histatin 5 (300 microM), washed and subsequently exposed to leukotoxin, no protective effect was observed. This observation suggests a mechanism of inhibition whereby histatin 5 either directly neutralizes the leukotoxin or interferes with the leukotoxin-PMN interaction. The inhibitory effect of histatin 5 on leukotoxic activity may suggest a new biological function of histatins in the oral cavity as a naturally occurring secondary antibiotic.     

Clinical application of a new compact CT system to assess 3-D images for the preoperative treatment planning of implants in the posterior mandible A case report

When treatment planning before placing dental implants in the posterior region of the mandible, the locations of the inferior alveolar nerve and mental foramen need to be ascertained, as they determine the bone height available and the implant length selected. The purpose of this study was to introduce the clinical application of a newly developed compact computed tomography system (Ortho-CT) to assess three-dimensional (3-D) images for the preoperative treatment planning of implants in the posterior region of the mandible. To evaluate the 3-D images, we scanned using the Ortho-CT system the mandible with a radiopaque template placed in the posterior region. The Ortho-CT images provided excellent information for evaluating the morphology of the mandible, and for showing the location of the inferior alveolar nerve, mental foramen and the relationship of the template to the bone. We consider that Ortho-CT is a useful aid to preoperative treatment planning of implant therapy in the mandible.     

Effect of occlusal trauma on healing of periapical pathoses: report of two cases

AIM: To present two clinical cases and demonstrate that occlusal trauma may affect healing of periapical pathoses. SUMMARY: Two teeth with periradicular disease did not respond successfully to conventional root canal treatment or endodontic surgery. Occlusal adjustment was finally performed on both cases. After occlusal adjustment, uncomplicated healing and periapical repair occurred in both cases. The findings in these two cases suggest that occlusal trauma may play a role in the healing of periapical pathoses. KEY LEARNING POINTS: Occlusal trauma is positively correlated with changes in periodontal tissues. Although experiments in animals have shown that application of forces to teeth will not induce further periodontal destruction, we believe that some failures of root canal treatment may be due to the presence of occlusal trauma modulating the responses of inflamed periapical tissues or apical pathoses with persistent infection.     

Changes in mechanical properties of poly-l-lactic acid mini-plate under functional load simulating sagittal splitting ramus osteotomy

The purpose of this study was to investigate how the characteristics of a poly-l-lactic acid mini-plate changed with dynamic loading in an environment with hydrolytic degradation. A mandible osteosynthesis model was prepared with specimen poly-l-lactic acid mini-plates to simulate sagittal splitting ramus osteotomy. The model was then subjected to dynamic loading, and changes in specimen shape and surface quality were observed. Specimen bending strength was then measured, and degree of hydrolytic degradation estimated. Neither dynamic loading nor degree of load clearly affected degree of hydrolytic degradation. The specimens maintained their original shape and bending strength for up to 4 weeks with dynamic loading of 40 N or less in an environment with hydrolytic degradation. At 8 weeks, under the same conditions, the specimens showed cracks or fractures, or both, together with a clear decrease in bending strength. The results suggest that dynamic loading causes cracking in a poly-l-lactic acid mini-plate, and that growth of these cracks decreases bending strength over time, leading to fatigue fracture.     

Infant ectopic cervical thymus in submandibular region

Sporadic cases have been reported of ectopic thymic tissue formed along the path of embryologic descent from the mandibular region to the mediastinum, usually manifesting as an asymptomatic mass. Here is reported the case of an 8-month-old boy with a tender palpable mass in the right upper lateral neck. Preoperative posteroanterior chest radiograph revealed normal structures in the mediastinum superior including the thymus. Magnetic resonance imaging showed a 4-cm x 4-cm soft-tissue mass in the left submandibular region. Surgical resection was performed and histopathologic examination showed that the mass was composed of thymic lymphoid tissue and epithelial cells. Immunohistochemical features included positive expression of LCA, CKpan, EMA, CD20 and CD43 antibodies. The clinical 14-month follow up was negative and the child was growing normally after operation. Ectopic thymus in the submandibular region is uncommon; surgical treatment is the definitive means of pathological diagnosis. Prior to surgery, the presence of a mediastinal thymus should be confirmed to prevent the risk of a total thymectomy.     

Epithelial fibroblast growth factor receptor 1 regulates enamel formation

The interaction between epithelial and mesenchymal tissues plays a critical role in the development of organs such as teeth, lungs, and hair. During tooth development, fibroblast growth factor (FGF) signaling is critical for regulating reciprocal epithelial and mesenchymal interactions. FGF signaling requires FGF ligands and their receptors (FGFRs). In this study, we investigated the role of epithelial FGF signaling in tooth development, using the Cre-loxp system to create tissue-specific inactivation of Fgfr1 in mice. In K14-Cre;Fgfr1(fl/fl) mice, the apical sides of enamel-secreting ameloblasts failed to adhere properly to each other, although ameloblast differentiation was unaffected at early stages. Prior to eruption, enamel structure was compromised in the K14-Cre;Fgfr1(fl/fl) mice and displayed severe enamel defects that mimic amelogenesis imperfecta (AI), with a rough, irregular enamel surface. These results suggest that there is a cell-autonomous requirement for FGF signaling in the dental epithelium during enamel formation. Loss of Fgfr1 affects ameloblast organization at the enamel-secretory stage and, hence, the formation of enamel.