Few studies have investigated the morphologic characteristics of teeth, dental arches and occlusion in elderly persons with many remaining teeth. The purpose of this study was to establish a method of measurement using 3-D imaging to investigate tooth angulation in the elderly from the orthodontic point of view. The dental casts of 20 elderly persons with many remaining teeth were digitized with a 3-D laser scanner (VMS-100F, UNISN INC., Osaka, Japan) to construct 3-D images. The mesio-distal angulation of each tooth was then measured with analytical software (SURFLACER, UNISN INC. and IMAGEWARE 12, UGS PLM Solutions, MO, USA). The occlusal plane formed by the incisal edge of the central incisor and distal buccal cusp tip of the first molar on either side was used as a reference plane for measurements. Mesio-distal tooth angulation (indicated in degrees) of maxillary teeth in this subjects averaged 1.26 for central incisors, 5.46 for lateral incisors, 7.84 for canines, 6.59 for first premolars, 5.78 for second premolars, 1.64 for first molars and -4.17 for second molars. Average values for mandibular teeth were 0.91 for central incisors, 2.35 for lateral incisors, 7.04 for canines, 8.76 for first premolars, 10.44 for second premolars, 7.33 for first molars and 12.67 for second molars. There was no statistical difference between the data in man and women except maxillary second molar (p<0.05). Mesial angulation in the mandibular arch showed a progressive increase from the anterior to the posterior. However, this tendency was not observed in the maxillary arch.

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The purpose of this study was to investigate differences between natural tooth color and that selected for artificial teeth in partial dentures at our department with a view to establishing criteria for obtaining greater harmonization between colors. The participants in this study comprised partial denture wearers visiting the Department of Prosthodontics, Tokyo Dental College Chiba Hospital, in whom both artificial teeth and natural teeth were present in the maxillary anterior tooth area. Natural tooth color was measured according to VITA classical shade guide number using a dental color measurement apparatus. Artificial tooth color in partial dentures produced at our department was investigated by referring to medical records. Color of 28 participants' natural teeth and 345 participants' artificial teeth was investigated. Differences in color distribution between the natural and artificial tooth were analyzed using the Fisher exact test. The most frequent color of natural tooth was C-type, accounting for 39%, followed by D- at 32%, A-at 22% and B-type at 7%. In terms of artificial tooth color, A-type was the most common (97%). The color distribution of natural teeth differed significantly from that of artificial teeth in partial dentures. These results suggest that artificial tooth color did not harmonize with the color of the natural teeth in partial denture wearers.

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Tooth inclination has been discussed many times in terms of esthetics and functionality, but reports related to aging are extremely rare. The purpose of this study was to evaluate tooth inclination in the elderly from the orthodontic point of view. The dental casts of twenty elderly persons with many remaining teeth were digitized with a 3-D laser scanner (VMS-100F,UNISN INC., Osaka, Japan) for reconstruction into 3-D images. Inclination of each tooth was then measured with an analytical software (SURFLACER, UNISN INC. and IMAGEWARE 12, UGS PLM Solutions, MO, USA). The occlusal plane formed by the incisal edge of the central incisor and distal buccal cusp tip of the first molar on either side was used as a reference plane to measure tooth inclination, and the complementary angle as tooth inclination was measured. The average tooth inclinations (degrees) of the maxillary teeth were 8.08 for central incisors, 8.10 for lateral incisors, 4.85 for canines, -6.68 for first premolars, -5.58 for second premolars, -5.15 for first molars, and -5.41 for second molars. The corresponding values for the mandibular teeth were 6.78 for central incisors, 4.87 for lateral incisors, -5.73 for canines, -13.74 for first premolars, -19.21 for second premolars, -23.76 for first molars, and -28.63 for second molars. There was no statistical difference between men and women, except for in the maxillary lateral incisors (p<0.05). Tooth inclination showed a progressive decrease from anterior to posterior. The decrease in the mandibular teeth was more regular than that of the maxillary teeth.

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Dental erosion, and specifically its symptoms, has long been studied in Japan as an occupational dental disease. However, in recent years, few studies have investigated the development of this disease or labor hygiene management aimed at its prevention. As a result, interest in dental erosion is comparatively low, even among dental professionals. Our investigation at a lead storage battery factory in 1991 found that the work environmental sulfuric acid density was above the tolerable range (1.0mg/m³) and that longterm workers had dental erosion. Therefore, workers handling sulfuric acid were given an oral examination and rates of dental erosion by tooth type, rates of erosion by number of working years and rates of erosion by sulfuric acid density in the work environment investigated. Where dental erosion was diagnosed, degree of erosion was identified according to a diagnostic criterion. No development of dental erosion was detected in the maxillary teeth, and erosion was concentrated in the anterior mandibular teeth. Its prevalence was as high as 20%. Rates of dental erosion rose precipitously after 10 working years. The percentages of workers with dental erosion were 42.9% for 10-14 years, 57.1% for 15-19 years and 66.7% for over 20 years with 22.5% for total number of workers. The percentages of workers with dental erosion rose in proportion to work environmental sulfuric acid density: 17.9% at 0.5-1.0, 25.0% at 1.0-4.0 and 50.0% at 4.0-8.0mg/m³. This suggests that it is necessary to evaluate not only years of exposure to sulfuric acid but also sulfuric acid density in the air in factory workers.

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The aim of this retrospective clinical study was to evaluate the treatment of intrabony periodontal defects with enamel matrix derivative (EMD) during the early stages of healing. Sixteen patients aged 38-77 years with a clinical diagnosis of chronic periodontitis were subjected to data analysis. A total of 25 teeth with various osseous defects received regenerative therapy with EMD, and were followed for a minimum of 6 months. Post-operative healing was uneventful in the majority of cases. Treatment of the intrabony defects with EMD led to a statistically significant improvement in the mean value of probing depth at 3 months compared with that at baseline (p<0.001). Mean values of attachment gain at 3 and 6 months were of clinical significance: 3.6±1.8mm and 3.2±1.5mm, respectively. Reduction in probing depth was achieved with minimal recession of gingival margin and was sustained over a time course of 6 months. A progressive increase in radiopacity, suggestive of initial signs of bone-fill, was observed by 6 months. In summary, the results suggest that treatment of intrabony defect with EMD induces favorable periodontal healing with a high level of predictability.

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The occurrence of accidental ingestion/aspiration and preventive measures were investigated at Tokyo Dental College Chiba Hospital. In addition, the characteristics of accidents at our hospital were analyzed by surveying the awareness of accidental ingestion/aspiration to utilize the data for prevention. Accidental ingestion accounted for about 30% of accidents that occurred at our hospital in fiscal 2008, but all ingested items were naturally excreted, and no accidental aspiration occurred. Accidental ingestion most frequently occurred when dental restorations were removed. Inlays and crowns were most frequently ingested, and dentists with 5 to less than 10 years of clinical experience tended to be involved in these accidents. According to the results of the questionnaire, removal of restorations was perceived as the treatment least likely to cause accidental ingestion/aspiration. Moreover, dentists who always took preventive measures against accidental ingestion/aspiration accounted for only 40% or less on average. To avoid accidental ingestion/aspiration, repeated courses and individual instruction for repeaters and the establishment of a surveillance system along with manuals to manage the violation should be emphasized.

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Since clinical dental training became mandatory in April 2006, Tokyo Dental College Chiba Hospital has been offering the following two types of training system: 1. a single system, and 2. a clinical training facilities group system. The clinical training facilities group system consists of program B, in which residents are trained in a cooperation-type clinical training facility for 3-4 months, and program C, in which residents are trained in two cooperation-type clinical training facilities for 7-8 months. A matching system within the clinical training facilities group is applied to select and decide on the cooperation-type clinical training facility for residents. In this system, the ranking of resident candidates that a cooperation-type clinical training facility would like to accept, and the ranking of training facilities that candidates choose are matched. The present study investigated the matching system within the clinical training facilities group in 2006, 2007, and 2008. The rate of matching to their third choice was more than 90% in program B and about 80% in program C in each year, suggesting a high matching rate. The percentage of cooperation-type clinical training facilities accepting dental residents dropped due to a decrease in the number of such residents. The distribution of accepted cooperation-type clinical training facilities is concentrated in Chiba Prefecture where our hospital, the management-type clinical training facility, is located, and the neighboring prefectures.

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