Finite element analysis (FEA) is a powerful and effective tool for analyzing the mechanical behaviors of dental implants. The objective of this study was to investigate the influence of taper angle on the dynamic stability of tapered abutments in a dental implant system, using dynamic FEA. The Ankylos implant system (Degussa Dental, DENTSPLY, Friadent, Germany) was selected as a dental implant with a tapered abutment. The finite element model consisted of a titanium alloy abutment and a pure titanium implant. Dynamic FEA was performed on dental implants with six different taper angles : 1°, 3°, 5°, 6°, 7°, and 9°. Both the movement corresponding to the micromotion of the tapered abutment obtained from the point at the bottom of abutment and the von Mises equivalent stress within the abutment-implant complex were analyzed when impulsive loads as external loads were loaded at the top of the abutment. The results showed that the movement corresponding to the micromotion of the tapered abutment decreased with increasing taper angle of the abutment. Additionally, maximum von Mises equivalent stress decreased with increasing taper angle. Within the limitations of this study, it was confirmed that the dynamic stability of a tapered abutment in a dental implant system was sensitive to the taper angle ; abutment stability increased with increasing taper angle. Furthermore, it was concluded that dynamic FEA is a useful technique for evaluating the dynamic stability of taper implant-abutment joints in dental implant systems.

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Mutans streptococci has been implicated as a primary causative agent of dental caries in animal. Two kinds of mutans streptococci, Streptococcus orisuis serovar strains were identified previously. New gram-positive streptococcal mutans-like strains from the oral flora of pigs were characterized. The distribution of three kinds of the mutans streptococci was studied. A third strain was newly identified as Streptococcus ferus based on 16S rRNA gene sequencing, G+C content, DNA-DNA homology, and extensive biochemical testing, and serologically grouped into serotype c of mutans streptococci. The distribution of three strains revealed that S. ferus was the predominant species. S. orisuis serovar strains made up 4∼13% of all the streptococci in young pigs. These results suggest that the detection rate of these mutans streptococci corelates with feed containing sucrose and S. ferus is the outlived strain among the three mutans streptococci in pig oral cavity.

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To describe signal characteristics of normal structures in the mandibular region using spectral attenuated inversion recovery (SPAIR) magnetic resonance (MR) imaging and evaluate the usefulness of SPAIR MR images in mandibular osteomyelitis compared with T1- and T2-weighted spin echo (SE) images. SPAIR MR images of 212 normal subjects and T1- and T2-weighted SE images of 21 subjects of mandibular osteomyelitis were evaluated. T1- and T2-weighted images were obtained in all patients. MR images were evaluated in terms of signal characteristics of normal and abnormal mandibular bone marrow, and surrounding soft tissue. In normal subjects, the mandibular bone marrow demonstrated low signal intensities (100%) and cortical bone showed no signal intensities (100%) on SPAIR images. In surrounding soft tissue of normal subjects, the submandibular glands demonstrated high signal intensities (100%), the parotid glands showed intermediate to high signal intensities (100%), the sublingual glands showed high (92%) and intermediate to high (8%) signal intensities, the lymph nodes showed high signal intensities (100%), and the masseter muscles showed intermediate signal intensities (100%) on SPAIR images. The lesions in mandibular bone marrow were low (86%) and low to intermediate (14%) signal intensities on T1-weighted images and high (52%), intermediate to high (33%), and intermediate (15%) signal intensities on T2-weighted images. On SPAIR images, the signal intensities resulted in high (86%), and intermediate to high (14%). The use of SPAIR imaging is useful for evaluating normal mandibular bone marrow and detecting osteomyelitis in the mandible and identifying the spread of inflammation to soft tissue.

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The present study attempts to evaluate the flexural properties of a denture base material relined with three different soft lining materials and investigate the effects of the thickness of the soft lining materials on the flexural properties of the relined denture base materials. Three commercially available soft lining materials (GC Reline Soft, S ; GC Reline Extra Soft, ES ; and GC Reline Ultra Soft, US) were evaluated. Acrylic resin (GC Acron) was used as the denture base material. The relined denture base specimens were prepared with four different thickness ratios of the soft lining material (mm)/denture base material (mm) : 0.5/2.5, 1/2, 1.5/1.5, and 2/1. Thus, the thickness ratios were set to 0.2, 0.5, 1, and 2. The flexural strengths and moduli of the relined denture base specimens were obtained from the three-point bending test. As a result, the flexural strengths and moduli of the relined denture base specimens tended to decrease in the order of US, ES, an S. For all relined denture base specimens, flexural strength and modulus decreased with increasing thickness ratio. The predicted values obtained by the Euler-Bernoulli composite beam theory showed that the normalized bending rigidity decreased with increasing thickness and elastic modulus ratio of the soft lining material/denture base material, in agreement with the experimental results of the three-point bending test. It was concluded that the flexural properties of the relined denture bases depend on the soft lining material properties such as the lining thickness and lining material type.

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Transplantation experiments are a common method in tooth developmental research. Many organs have been previously selected as hosts ; however, there is little information comparing developmental differences in the transplanted tooth among these host organs. In the present study, the authors examined the effect of transplantation into the subcutaneous tissue and the kidney capsule for 4 weeks using E13.5 mandibular first molar tooth germs from mice. The shape and size of the tooth crown of the tooth transplanted into the subcutaneous tissue are smaller than those of the tooth transplanted into the kidney capsule and a normal tooth in vivo. However, the number and arrangement of cusps of the transplanted tooth were similar to those of a normal tooth. Compared with those of the tooth transplanted into the kidney capsule, development and calcification of the transplanted tooth progressed slowly in the subcutaneous tissue. These differences may cause movement of the transplanted tooth ; the subcutaneous tissue is composed of loose connective tissue and the transplanted tooth moves easily in the subcutaneous tissue, although the tooth transplanted into the kidney capsule is maintained tightly between the kidney capsule and kidney cortex. However, cell differentiation and cell function were not affected by movement of the tooth germ ; enamel and dentin were formed in the transplanted tooth in both the subcutaneous tissue and the kidney capsule. These findings suggest that development of the transplanted tooth may be affected by the host organ.

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Relaxin (RLX) is a hormone in the insulin/RLX family of structurally related hormones. It has been shown to bind to receptors LGR7 and LGR8 in the leucine-rich repeat-containing G-protein-coupled receptor family. Furthermore, RLX influences many other physiologic processes such as collagen turnover, angiogenesis, and antifibrosis. Immunohistochemical studies have reported that RLX was localized in ovarian and other tissues. The present study focused on the localization of RLX in rat periodontal ligaments, midpalatal suture, and dental pulp tissue. To determine the localization of RLX proteins, an immunohistochemical study was performed. Positive immunoreactivity for RLX was identified in osteoblasts, osteoclasts, fibroblasts, collagen fibers, odontoblasts, and predentin in the periodontal ligaments, dental pulp, and midpalatal suture. Therefore, RLX may be involved in the process of collagen metabolism in the oral tissues.

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The purpose of this study was to isolate and identify of yeast-form fungi from the oral cavity of dogs. Oral samples from 38 dogs were cultured on Brucella-blood agar for total organisms, and selective media for fungi. The distribution and characterization of the isolates were studied. The fungi were present in 52.6% of the examined dogs. The average detection rate against total cultivable bacteria was 0.0018% (0∼0.013%). Most yeast-form fungi could grow on CHROMagar Candida medium for 5 days and formed small, smooth colonies. Malassezia spp. was detected from 52.6% of the tested subjects. The genera Candida, Trichosporon and Cryptococcus were identified at a low percentage. However, Candida albicans was not detected in any of the dogs. The conclusions of this study are that dog inherent C. albicans was absent, and the predominant fungus was Malassezia spp. These results suggest that the composition of yeast-form fungi in oral cavities of human and dogs differs.

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Conformational analysis of three types of pamidronate/calcium (Ca) complex model was performed using a molecular mechanics method with a standard MM3 force field. Three types of pamidronate/Ca-complexes were designed. Namely, one calcium atom was connected to two oxygen atoms of different P-O bonds [Ca-complex (I)], one calcium atom was connected to two oxygen atoms of the same P-O bond at one end of the molecule [Ca-complex (II)], and one calcium atom was connected to two oxygen atoms of the same P-O bond at both ends of the molecule [Ca-complex (III)]. Three-dimensional imaging clearly showed the steric conformation of each compound. Ca-complex (I) showed the lowest steric energy and Ca-complex (III) showed the highest steric energy among the three types of Ca-complexes. The Ca-O bond lengths of Ca-complexes (II) and (III) were shorter than that of Ca-complex (I). The P-O bond lengths of Ca-complexes (II) and (III) were longer than that of Ca-complex (I). The O-Ca-O dihedral angles of Ca-complexes (II) and (III) decreased approximately 30% from that of Ca-complex (I). These data suggested that the Ca-complex (I) was most stable and that the structure of Ca-complex (I) had the highest possibility when pamidronate reacted with a calcium atom. The structure of Ca-complex (III) has the lowest possibility. The present results revealed the stable structures of Ca-complexes using molecular mechanics calculations, a useful tool for obtaining geometrical information about molecules.

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Central odontogenic fibroma is a rare odontogenic neoplasm whose classification has been actively discussed, although few cases have been described in the literature. This article presents a case report of a central odontogenic fibroma discovered in a routine radiographic examination of the jaws of a female patient, 45 years old. The lesion was enucleated and the site was followed for 5 years without any sign of lesion recurrence.

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