The prevalence and morphological types of non-carious cervical lesions (NCCL) in a contemporary sample of people.

Non-carious cervical lesions (NCCLs) were examined in 6541 extracted human teeth and classified based on the morphology of the lesions. As a result, NCCLs were found on 38.7% of teeth (41.6% on maxillary teeth and 36.0% on mandibular teeth), and were most frequent on canines and first premolars. According to the new method of classification, the morphology of NCCLs was classified both by the surface contour (SC) and by the cross-sectional contour (CC). Three types of NCCLs appeared to be dominant. The causes of these NCCLs were discussed based on their morphologies, positions where these NCCLs were frequently found, and the results of previous studies. NCCLs with a horizontal oval SC and a round CC (Type I), which were frequent on the labial surfaces of maxillary canines and buccal surfaces of maxillary first premolars, may be associated with wear by friction and chemical degradation. NCCLs with a vertical oval SC and a round CC (Type II), which were frequent on the lingual surfaces of mandibular incisors and canines, might be mainly related to chemical degradation. NCCLs with a horizontal oval SC and a wedge shape CC (Type III), which were extensively found on the buccal surfaces of maxillary premolars, had formed most probably due to wear by friction and microstructural loss by stress. This new method can classify the morphology of NCCLs more precisely and deduce the mechanisms of the formation of NCCLs more clearly than former methods.

Fluctuating asymmetry of the permanent mandibular molars in a Japanese population.

The purpose of the present study is to investigate the pattern of fluctuating odontometric asymmetry of permanent mandibular first and second molars in a Japanese population. Dental plaster casts of 112 (57 males and 55 females) Japanese undergraduate dental students were used. The mesiodistal and buccolingual diameters of the whole crown and trigonid and talonid crown components were taken on the left and right sides of the mandibular permanent first and second molars. Crown areas were also calculated. The fluctuating asymmetry (FA) value was obtained by dividing the absolute side difference by the absolute mean size of the left and right teeth: FA = abs (R-L)/((R + L)/2). Fluctuating asymmetry between mandibular first and second molars was significantly different with the mandibular second molar showing higher asymmetry in both males and females. Meanwhile, fluctuating asymmetry between males and females in the first and second molars was not significantly different in all measured dimensions. With regard to trigonid and talonid components, fluctuating asymmetry of the distal talonid area was significantly larger than the mesial trigonid area in the mandibular permanent first molar of males (P < 0.01), and asymmetry of buccolingual diameter of the talonid was also larger than that of the trigonid in the mandibular permanent second molar of males (P < 0.05). In conclusion, these findings suggest that the crown dimensions of later developing teeth in the mandibular molar tooth class and crown component in the same molar tooth show more asymmetry and, therefore, are more affected by external factors.

Samurai in Japan: Class System-Related Morphological Differences in Maxillofacial Regions in the Edo Period.

Previous studies have reported that compared to commoners in Japan's Edo period, samurai had long heads, more dental irregularities, and slightly worn teeth. However, these studies did not measure the mandible or only measured length. Angular analysis is essential to evaluate the maxillofacial morphology, but there are no comparative studies of samurai and commoners. This study explored the differences in maxillofacial morphology between samurai and commoners in the Edo period. Thirty male skeletons (samurai) and thirty-eight male skeletons (commoners) were used as materials from the National Museum of Nature and Science. The selected specimens were adults aged between 20 and 59 years without serious skeletal damage and with stable occlusion of the molars. We used three-dimensional scanning to measure the specimens' skeletal, alveolar, and facial widths. The mandibular plane angle and the gonial angle were significantly larger in the samurai than in the commoners. The ratio of the intermandibular first molars, interzygomatic arch, and mandibular width was significantly shorter in the samurai than in the commoners. The samurai had a high angle tendency and smaller mandibular width than the commoners, reflecting the class system.

Variability in cusp size of human maxillary molars, with particular reference to the hypocone.

OBJECTIVE: The purpose of this study was to investigate cusp size variability in the human permanent maxillary first and second molars, with particular reference to the hypocone. DESIGN: Data were obtained from dental casts collected during a longitudinal growth study of Australian Aboriginals (148 males and 119 females), living at Yuendumu in Australia. Categorical data described the expression of the hypocone and quantitative data described the areas of the molar cusps, mesiodistal and buccolingual crown diameters, and overall crown areas. Several hypotheses relating to cuspal variation within and between M1 and M2 were tested using Chi-square tests, t-tests and ANOVA. RESULTS: The pattern of relative variation in maxillary molar cusp areas reflected the ontogeny of crown development, with earlier-forming cusps showing less variation than later-forming cusps. Sex differences in hypocone area were larger in M2s than in M1s and there was evidence of an interaction during development between the protocone and the hypocone in M2s. Those M2s with larger hypocones displayed larger crown areas and the hypocone of M1s tended to be smaller in individuals who displayed hypocone reduction in their M2s. CONCLUSIONS: Our findings are consistent with the view that phenotypic variability within maxillary molar crowns is generated by dynamic interactions between developing cusps that form at different times and grow at different rates for different durations. Observed variation in cusp areas and hypocone expression between the maxillary M1 and M2 can also be explained in terms of differences in timing and duration of development of these teeth.

Protuberance or fossa on the lateral surface of the mandible in primates.

In order to clarify the morphological characteristics and function of the protuberance and/or fossa on the lateral surface of the mandible, we examined 778 mandibles of 9 genera, 19 species of non-human primates. Both protuberance and fossa were found in Macaca, Chlorocebus, and Cercocebus at frequencies ranging from 0% to 60%. The protuberance was composed of compact bone and was similar to the mandibular torus in humans. A well-developed protuberance extended from the fourth premolar to third molar region, and was situated at the central part of the mandibular body, or continued on the oblique line. Sometimes the protuberance localized on the mandibular base. A deep and large fossa was found in all individuals of Papio, Theropithecus, and Mandrillus, and the bone width was thin in the center of the fossa. The fossa extended from the third premolar to the second molar region, and the deepest area was the first molar region. In Macaca, Chlorocebus, and Cercocebus, the curvature of the external table of the mandible created a fossa. In Colobus, and Hylobates, the external surface of the mandible looked concave because of the thickened mandibular base. These concavo-convex structures have some biological functions and represent an adaptive change for mastication.

Comparative study of craniofacial morphology and bite force in Fijians and Japanese.

An anthropological survey was conducted in Fiji in 1994 and 1995 to study dental arch form, craniofacial morphology, and bite force of Fijians. Measurements were obtained from dental casts, cephalograms, and thin pressure-sensitive sheets (Dental Prescale®) for bite force analysis. Results were compared with those of Japanese. In every direction, the size of the dental arch in Fijians was larger than in Japanese. Fijians displayed longer palates, longer mandibles, and bimaxillary protrusion. There was no significant difference in upper and lower facial heights. FH to lower incisor angle in Fijians was significantly larger than in Japanese. Fijians were characterized by a small palatal plane angle, occlusal plane angle and mandibular plane angle, and were thus brachyfacial. The Japanese tended to be more dolichofacial. The distances from the Cd line to the pterygoid muscles, masseter muscles, and teeth in Fijians were significantly longer than in Japanese. Occlusal contact areas of Fijians were also greater than those of Japanese. The results indicate that the masticatory muscles and craniofacial morphologies supporting them would be better integrated in Fijians than in Japanese. Am. J. Hum. Biol. 10:63-72, 1998. © 1998 Wiley-Liss, Inc.

Associations among distributions of dental postgraduate residents, dentists and clinical training facilities in Japan.

The purpose of this study was to evaluate the correlation and distribution of dental postgraduate residents, dentists and clinical training facilities in each prefecture to analyze the regional distribution and supply of dentists in Japan. The results were also compared with referential data for medicine. The coefficient of correlation between the dentist index and dental postgraduate resident index was r = 0.76 (P < 0.001) in 2006. The distribution (coefficient of variation) was greatest for the dental postgraduate resident index. The numbers of dentists per 100,000 population in prefectures with dental colleges were significantly higher in 1986, 1996 and 2006 for each comparison (P < 0.001). Coefficients of correlation between dentist index and dental postgraduate resident index were r = 0.65 (P < 0.01) in prefectures with dental colleges and r = 0.11 in those without dental colleges in 2006. The prefectures with high level of numbers of cooperative-type clinical training facilities had dental colleges.

Mandibular permanent second molar with four roots and root canals: a case report.

Although four-rooted mandibular first molars have been observed on a few occasions in the literature, to the best of our knowledge, four-rooted second molars have not been reported. Here, we describe a mandibular second molar with four roots and canals: two mesial and two distal. Mesial roots were separated in the cervical one-third near the cervical margin, while distal roots were divided at a lower level in the middle one-third of the root. We discuss the possibility of different root and canal variations of the mandibular second molar from a developmental point of view.

Root and canal morphology of permanent mandibular molars in a Sri Lankan population.

The main purpose of this study was to investigate the root and canal morphology of Sri Lankan mandibular molars and to determine the affinities of these morphological variations to those of people of European and Asian origin. Two hundred mandibular first and second molars were examined. The number of roots and the prevalence of C-shaped (gutter-shaped) roots in mandibular second molars were recorded. Root canal morphology was studied using a clearing technique. The examination of root canal systems of the teeth was based on Vertucci's classification. Among mandibular first molars, only 3% had three roots. Mesial roots of the first molar typically presented with two canals and two apical foramina with type IV, V, or VI canal configuration. Most distal roots of the first molar presented with a type I canal configuration. The remainder were distributed mainly between types III and V. Among mandibular second molars, 6% had single C-shaped roots, while C-shaped canals were found in only 2%. The majority of mesial roots of the second molar showed one or two canals, with one apical foramen with type I, II, or III canal morphology. In addition, the distal root commonly showed type I canal configuration. Intercanal communications and lateral canals were more frequently seen in the first molar than in the second. The root canal morphology in mandibular molars varies among population groups. Mandibular root and canal morphology of Sri Lankan people has closer affinities with that of people of European than of East Asian origin.

Size relationships among permanent mandibular molars in Aboriginal Australians and Papua New Guinea Highlanders.

Size relationships among crown units of permanent mandibular molars were investigated in two Sahul-Pacific samples: Aboriginal Australians (Yuendumu) and Papua New Guinea Highlanders (Wabag). Measurements of first, second, and third molars (M1, M2, and M3), including overall mesiodistal and buccolingual diameters as well as the mesiodistal and buccolingual diameters of the trigonid and talonid, were obtained from dental casts using a sliding caliper. Molar reduction was noted in talonid dimensions within both samples, but the trigonid mesiodistal diameter was not reduced in M2 or M3 compared with M1, indicating that the later-developing crown unit (talonid) was more reduced than the early-developing unit (trigonid). M2 was most reduced in size mesiodistally of the three molars, but its buccolingual diameter was not reduced. M3 was the most reduced tooth in trigonid buccolingual diameter. The percentage sexual dimorphism values were greater for the size of the talonid than for the trigonid, indicating that male values exceeded those for females by a greater amount in the later-developing crown unit. Crown dimensions were larger generally in the Aboriginal Australians from Yuendumu than in the Papua New Guinea Highlanders from Wabag, with differences being more evident in M2 and M3 than M1, especially in talonid dimensions. The trigonid, which develops early both phylogenetically and ontogenetically, tended to be relatively stable in size, whereas the later-forming talonid displayed size reduction when comparisons were made both within and between groups.

New method for estimation of adult skeletal age at death from the morphology of the auricular surface of the ilium.

A new method for estimating skeletal age at death from the morphology of the auricular surface of the ilium is presented. It uses a multiple regression analysis with dummy variables, and is based on the examination of 700 modern Japanese skeletal remains with age records. The observer using this method needs only to check for the presence or absence of nine (for a male) or seven (for a female) features on the auricular surface and to select the parameter estimates of each feature, calculated by multiple regression analysis with dummy variables. The observer can obtain an estimated age from the sum of parameter estimates. It is shown that a fine granular texture of the auricular surface is typical of younger individuals, whereas a heavily porous texture is characteristic of older individuals, and that both of these features are very useful for estimating age. Our method is shown here to be more accurate than other methods, especially in the older age ranges. Since the auricular surface allows more expedient observations than other parts of the skeleton, this new method can be expected to improve the overall accuracy of estimating skeletal age at death.

A quantitative approach for measuring crowding in the dental arch: Fourier descriptors.

Dental crowding is defined as a discrepancy between tooth size and jaw size that results in a misalignment of the tooth row. Proposed reasons for crowding include excessively large teeth, small jaws, and a combination of both. Nevertheless, the parameters that would allow the prediction of crowding have not been identified. This study compared the shape of crowded and uncrowded dental arches, matched for size and sex. The application of elliptical Fourier functions (EFFs) provided an accurate numeric description of the dental arch form. Dental casts from the Nihon University School of Dentistry at Matsudo, Chiba, Japan, were studied. Group I, the control group, consisted of 118 dental cast pairs (49 female, 69 male, aged 20.40 +/- 1.68 years [mean +/- SD]) with little or no crowding. Group II, which exhibited crowding, consisted of 78 dental cast pairs (64 female, 14 male, aged 19.67 +/- 4.95 years). From photographs, a set of 24 homologous points describing the tooth row was identified. These points were then fitted with EFFs. Each maxillary and mandibular outline was subsequently standardized for size by scaling the bounded area to a constant 10,000 mm(2). These "shape only" data were used to assess differences between arches in the 2 groups. By multivariate analysis of variance, statistically significant shape differences between groups I and II were obtained for both arches. Patients with crowding exhibited more variability than did the controls. This variability was illustrated with canonical axes derived from discriminant function analysis.