The Journal of Osaka University Dental School最新文献

Stress patterns and levels were analyzed by use of the three-dimensional finite element method. Three-dimensional models were constructed for the human upper central incisor (1205 nodes and 920 elements) and the sheep metacarpus (240 nodes and 128 elements). Orthodontic and orthopedic forces were applied to the tooth and the bone, simulating orthodontic tooth movement and experimental loading test for the bone. Three principal stresses were determined in the alveolar bone and the sheep long bone. The following results were obtained. 1. Stress distributions in the lateral alveolar bone were similar to those with bone deformation from cantilever bending mode. On the medial surface of the alveolar bone, a bending stress was observed, however, remaining stresses exhibited changes corresponding to those in the PDL produced by tipping displacement of the tooth. 2. In the sheep long bone, tensile and compressive stresses were induced on the dorsal and volar sides, respectively. The magnitude of stresses was greatest at the mid-diaphyseal region. Compressive and tensile stresses were related with bone resorption and apposition. The magnitude of principal stresses was almost proportional to dimensional changes of the bone at the mid-diaphyseal region. Bone remodeling in the long bone is related with mechanical stress, principal stress in particular, indicating that remodeling of the alveolar bone may be induced by application of orthodontic force in addition to conventional change of the bone adjacent to the PDL. Thus, it is shown that mechanical stress in living structures may be a trigger to induce biological remodeling of bones.

Prevalences of malocclusions and dental caries in molars were investigated on a database of high school students collected between 1977 and 1986. A total of 6,665 schoolgirls were evaluated. The proportions of 54.1% in the seventh grade and 56.6% in the tenth grade students were judged as having malocclusions. The prevalences of dental caries for the lower first and the second molars were significantly higher (p less than 0.001) than those for the upper opponents during the observation period. The prevalence of dental caries increased linearly for all kinds of molars in accordance with age, but they were lower than those reported by the Ministry of Health and Welfare in Japan determined for the entire nation. The percent of dental caries for the second molars revealed abrupt increases from 10% at the seventh grade to 50% at the 12th grade. These changes were particularly noticeable between the eighth and the tenth grades. These results suggest the significance of oral health care education during the adolescent period based on a long-term cooperation made by dentists, school nurses, teachers through the participation of students into the oral health care programme.

The production of enkephalin (EK) in the rat dental pulp was studied in pharmacological and biochemical aspects of EK-producing enzyme, EK precursor protein and the regulation of EK production. The EK precursor protein was primarily distributed in the microsomal fraction, and a common precursor protein (Mr about 58,000) was partially purified by Sephadex G-100 chromatography. Since the EK-producing enzyme, however, was mainly localized in the lysosomal fraction, and was found to be a cysteine proteinase, the lysosomal cysteine proteinases, cathepsins H, B and L, were separated by CM Sephadex C-50 ion exchange chromatography, and identified in respects to substrate specificity, pH optimum and inhibitor sensitivity. The EK-producing activity of the cathepsin B was demonstrated using the partially purified EK precursor protein from the pulp tissue as a substrate. The cathepsin B was further purified by Sephadex G-75 gel filtration to a 400-fold purity, and SDS polyacrylamide gel electrophoresis of the enzyme showed a distinct homogeneity (Mr about 23,600). The purified enzyme cleaved BAM-12P, a met-EK-containing peptide from bovine adrenal medulla, to met-EK-Arg6, but did not convert met-EK-Arg6 to met-EK, suggesting an endopeptidase activity of the enzyme. On the other hand, a concentration-dependent activation of the enzyme by bradykinin (BK) and des-Arg9-BK was found to be mediated through B1 receptor in intact pulp tissue. It was also demonstrated that intact structure of lysosomes and Ca++ were necessary for the activation of the enzyme by BK.

A new type of ceramic bracket was prepared to minimize the destruction at the bracket-resin interface and to suppress resin remaining on the tooth surface in debonding. The brackets were of a chemical bonding type, and had a box-formed cavity in the bracket base to hold resin, a 0.018 inch slot, and twin-type wings. Impact strengths and debonding aspects of the residual resin were studied. The impact strengths of the brackets seemed to exceed the desired level, compared to other control ceramic brackets or metal brackets. A resin remaining ratio (RRR) was adopted as the quantitative evaluation for the residual resin condition. Mean RRR's of the brackets were about 10%, which was a very low value in comparison to the other brackets.

This paper describes the surgical treatment of six patients with internal derangement of the temporomandibular joint (nine joints). Meniscectomy was performed on all the patients, because severely advanced cases in which the articular disk could not be preserved or replaced were chosen. Our surgical technique and the results of short-term follow up are presented. Indications of meniscectomy and the criteria for postoperative evaluation are also described. The postoperative outcomes were assessed as "good" for seven joints in five patients and as "acceptable" for two joints in one patient.

A FRP denture base, which was made from visible light curing prepreg, was developed. The visible light cured FRP denture base had advantages with respect to an adequate strength, bonding strength of acrylic base resin, esthetic properties and ease to manipulation. The matrix resin of Bis-GMA/UDMA/3 G at 48/48/4 was determined from the results of the bending test and manipulation processing. The sateen weave's glasscloth was used for the reinforcement of the prepreg. The adaptability of the FRP plate denture was better than that of the resin base denture constructed with microwave heating.

The rotational path of insertion differs substantially from the conventional path or perpendicular path of insertion. With a rotational path, one segment of the partial denture is seated first, then the remainder of it is rotated into position. One segment of this system is the rigid retentive component with a long occlusal rest and the other is the conventional clasp. This study examined the influence of mesio-distal distance of the edentulous space, the point of the displacing force, the undercut of rigid retentive component and the inclination of the abutment tooth on the retention of this system. The following results were obtained: 1) Retention of the denture was the lowest when a displacing force was applied at the conventional clasp part under the conditions of mesio-distal distances with edentulous spaces of 10, 20 and 30 mm, respectively. 3) Retention showed a tendency to decrease progressively as the proximal undercut on the rigid retentive component was changed to 2.0, 1.5, 1.0 and 0.5 mm, respectively. The values of the decreasing ratio of retentive forces were almost the same regardless of the mesio-distal distance of the edentulous space. 4) Retention of the denture was improved when a tilted tooth was used as an abutment tooth on the rigid retentive component side.

Unilateral complete root resorption of the permanent central incisor was experienced in a boy with deaf and dumb. Transposition of tooth germ or abnormally directed eruption of the canine caused not only an entire root but a part of enamel resorption. The patient was diagnosed clinically and radiographically as an ectopic eruption of the right maxillary upper canine and then treatments were provided to improve esthetic and functional conditions in terms of eruption guidance. It should be emphasized that the early diagnosis and the subsequent eruption guidance is essential in the patient with these kinds of eruption disorder of the mixed dentition.

The long-term complications of dental implants are associated with loosening of the implant-bone interface, due to bone resorption and subsequent connective tissue interposing at the implant-bone interface. Mechanical stresses, which are induced in the surrounding bone, play a key role in the interface bone remodeling. In the present study, it is investigated how local stress patterns are associated with local bone structure. For identical geometry alumina, and titanium implants, the stress patterns, determined in the finite element models with boundary conditions, are compared with the local bone structure found in animal experiments. The results indicate that there appears to be relationship between the stress patterns and the bone remodeling at the implant-bone interface independently on the materials properties in alumina and titanium.