Streptococcus sobrinus and Streptococcus downei are closely related cariogenic species. A pair of polymerase chain reaction (PCR) primers for dextranase gene of S. sobrinus NIDR6715 was designed for differentiation of S. sobrinus and S. downei. The primers amplified a single PCR product from S. sobrinus and S. downei but none of the other mutans streptococci nor other gram-positive cocci. To differentiate S. sobrinus and S. downei, a restriction analysis of the amplified products was carried out. These two species were effectively differentiated by digestion with either BamHI, BstPI, EcoRI, HaeIII, PvuII, or SalI. These results suggest that PCR amplification followed by restriction digestion is a useful method for simple and rapid differentiation of S. sobrinus and S. downei.

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Tooth measurements by dental students were investigated to evaluate their understanding of the tooth axis. Ninety-six students of Showa University School of Dentistry in 1996 made two-time measurements of the resin models of maxillary incisors (Nissin Dental Products Inc., B2-TA.2). The first measurement was made at the first lecture on Dental Anatomy, and the second was made after they studied a chapter on the incisors. The tooth models were measured by Fujita's method, using a sliding caliper to the nearest 0.05 mm, and the measurements were made of crown height, root length, mesiodistal crown diameter, and labiolingual crown diameter. The instructor, who taught the students to measure the tooth, measured five times for each tooth measurement as control data. The results were as follows : The mistakes of the measurements were decreased from first to second measurements. The range of the measurements and coefficients of variation were also decreased. The minimum of the measurements was smaller in the second than in the first measurement, and the mean value was also decreased. A lateral incisor was more difficult to measure than a central incisor. A labiolingual diameter was more difficult to measure than a mesiodistal diameter, and the crown height was more difficult to measure than the root length. Tooth measurements by the students indicated their understanding of tooth morphology, and also evaluated the effect of education in dental anatomy.

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We have been developing a new system to fabricate crown restorations automatically by using a CAD/CAM process. The newly developed laser displacemeter was composed in the CAD/CAM device to digitize the surface of the stone model to obtain the morphological information of the abutment. Even a laser digitizer has merit to measure the object quickly, we afraid the accuracy of the digitizing, especially on the axial wall and the margin of the crown abutment. Therefore in this study, the digitizing accuracy of the stone model was investigated by using a simplified abutment model, which has a perpendicular axial wall and a shoulder margin with a different width. The developed laser digitizer could recognize both the axial wall and shoulder with a digitizing pith of 20 μm. However, since the sharp corner of the original model was recognized as a round corner, the width of the shoulder was recognized as being smaller than that of the original width. This discrepancy became smaller as the width of the shoulder enlarged. Furthermore, the digitized height of the shoulder was slightly elevated when the model was digitized along the medial-distal direction because of the secondary reflect of the irradiated laser beam on the stone model. These results suggest that the developed laser digitizer was useful, but we need more investigation on the digitizing conditions to increase the digitizing accuracy.

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This histological study was designed to clarify the relapse processes of rat molars following orthodontic tooth movement by the Waldo method. An elastic band was inserted between the upper first and second molars and removed either 7 or 21 days later. The relapse processes of first molars were examined at 1 or 4 days after the 7-day insertion was completed and at 5 or 10 days after the end of the 21-day insertion. At the end of the 7-day insertion period, the mean interdental space was 158μm, but it decreased rapidly, reaching 44μm by 1 day after removal and 16μm by day 4. In the periodontal ligament (PDL) compressed by elastic band insertion, partial hyalinization and/or mineralization occurred. The stretched PDL consisted of irregularly distributed, thin principal fibers, approximately 2.4μm in diameter. On days 1 and 4 after removal, osteoclasts, macrophage-like cells, and fibroblastic-like cells were localized around hyalinized tissues, but thick principal fibers, approximately 3.8μm in diameter, were regularly distributed throughout the PDL proper. The mean interdental space after the 21-day insertion was 526μm, but this had decreased to 108μm by day 5, and to 71μm by day 10. On day 5 after removal, numerous osteoclasts were evenly distributed in the compressed PDL, and thick principal fibers, approximately 3.5μm, were present in the stretched PDL. These results suggest that during a relapse of experimentally moved rat molars, 1) rapid remodeling of the PDL and surrounding alveolar bones is the main cause of tooth relapse, and 2) hyalinized and/or mineralized tissues occurred by compression are rapidly resorbed by osteoclasts, macrophage-like cells, and fibroblast-like cells.

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To study the dynamic arrangement of matrix fibrils of the compact bone and the bone trabeculae of the spongy bone of the attaching region of the masticatory muscles on the mandible and the stress against the tensile by the masticatory muscles to the mandible, we examined with a scanning electron microscope mainly the arrangement of matrix fibrils of the compact bone of the mandible with all teeth dissected from male anatomy cadavers.
The superficial bone matrix of the external basic lamellae attached by the masticatory muscles was formed by collagen fibril bundles. Matrix fibril bundles were arranged suitably for the stress of the tensile with the masticatory muscles. At Tuberositas masseterica and Tuberositas pterygoidea, matrix fibril bundles ran from under-anterior to over-posterior. Matrix fibril bundles ran downward at the central region of the coronoid process. At the pterygoid fovea, matrix fibril bundles ran from under-anterior to over-posterior.
The external basic lamellae of the attaching region of the masticatory muscles were composed of bone lamella about 3μum thick, which ran in the same direction as the superficial matrix fibrils, and the bone lamella about 1μm thick, which crossed diagonally to the adjacent lamella. In the osteons of the Haversian lamellae, the lamellae about 5μm thick, which ran in the same direction as the superficial matrix fibrils, and the lamellae about 1μm thick, which ran concentrically, were arranged alternately. The bone trabeculae had the dynamic arrangement suitable for the tensile of the masticatory muscles. The bone trabeculae of the angle of the mandible were arranged from under-anterior to over-posterior. The bone trabeculae of the pterygoid fovea were arranged from front-inferior to back-posterior.

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It is essential to treat cleft lip and palate in close conjunction with specialists in related fields.
A patient with right cleft lip and palate accompanied by severe growth retardation of the maxilla was treated by a team approach. This patient has been followed up for more than 10 years since orthodontic intervention.
The case was a female patient who was 13y 8m old when she first visited. She had received lip and palate closure by plastic surgery at a university hospital. Various examinations revealed vertical and anteroposterior growth retardation of the maxilla and the associated anticlockwise rotation of the mandible. Dental caries was observed in many of the teeth. Orthodontists, oral surgeons, and prosthodontists discussed the case, and this team made a plan that she would first wear an overlay denture in the upper jaw to improve vertical and anteroposterior retardation of the maxilla, then mandibular osteotomy was to be performed to improve occlusion after presurgical orthodontics.
The patient began to wear an overlay denture at 17y 3m to initiate presurgical orthodontics. Mandibular osteotomy (SSRO) was performed at 19y 2m. Following 8-month postsurgical orthodontics, retention was initiated. After a 1-year retention, a telescopic denture was applied to the maxillary dentition.
At the present time, 12 years having passed since the patient began to wear the telescopic denture, she has shown stable occlusion and is satisfied with the therapeutic results. However, if treatment and management with a team approach would have been initiated earlier, it would have been possible to improve occlusion without the use of a large prosthesis. This case indicates the importance of a team approach for the treatment of cleft lip and palate.

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This report presents the results of a long-term orthodontic care of an individual with right cleft of the lip and alveolus after autogenous bone grafting for the alveolar cleft.
Primary lip repair was performed at 3 months of age. Orthodontic care was started at the age of 6 years. A maxillary protractor was used from the age of 6 years and 6 months to the age of 8 years and 2 months. At the age of 13 years and 2 months, bone grafting of the alveolar cleft was performed, using autogenous particulate marrow and cancellous bone harvested from the iliac crest. A multibracket system was used from the age of 13 years and 6 months to the age of 15 years and 9 months. The occlusion of the permanent teeth was found to have stabilized at the retention stage.
An orthodonticaly moved lateral incisor to the site treated with autogenous bone grafting can effectively substitute for the prosthodontic reconstruction.

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A lymphoepithelial cyst usually occurs in the lateral cervical areas. It is characterized histopathologically as the lymphoid tissue below the lining of the stratified squamous epithelium of the cyst, but the similar cyst occurs in the oral cavity. This report includes one case of this cyst on the left side of the ventral surface of the tongue of a 34-year-old woman. The tumor was observed to be approximately 7-8 mm in diameter. It was histopathologically observed with the parakeratinizing stratified squamous epithelium and consisted of lymphoid tissue.

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[in Japanese]

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