Crown dimensions of the maxillary molars in Tupaia glis.

The crown dimensions of the maxillary molars in Tupaia glis were measured, and the most common molar size sequence was M1 > M2 > M3. The M2 and M3 molars were smaller than the M1 in the mesiodistal crown diameters. With regard to the buccolingual diameters, the distal part of M1 and mesial part of M2 were relatively larger and less variable in size. This stable area corresponded to the inflection point of the maxillary arch curve. These results could be explained from a functional morphological standpoint.

A morphological study on the crown dimensions of the mandibular molars in Tupaia glis.

The crown dimensions of the mandibular molars in Tupaia glis were measured. All the mean values of crown diameters and areas were larger for the M1 molar than for the M2 and M3. The last two molars were more reduced in the talonid component than in the trigonid compared to the M1, and were more reduced in the buccolingual than in the mesiodistal direction. The most common molar size sequence (MSS) was M1 > M2 > M3, and this pattern was more frequently observed in the talonid component than in the trigonid. In the canonical discriminant analysis, all the cases of the M3 were discriminated correctly, but some cases of the first two molars were confused with each other. The molars size of the mandible was closely related to that of the maxilla.

A facial growth analysis based on FEM employing three dimensional surface measurement by a rapid laser device.

Although there have been several studies of finite element method (FEM) analysis on two dimensional (2D) facial growth with cephalometric X-rays, there has been little FEM analysis on three dimensional (3D) facial growth of long term observation. Therefore the objective of our study is to use FEM model by 3D surface measurement of rapid laser device from human dried skull and to analyze the changes of facial growth based on FEM by the volume and the direction of strain in each stage. Samples were taken from each human dried skull for 5 stages; about 0, 3, 6, 9, 12 and 18 years of age, a total of 6 normal human dried skulls. (No abnormal skeletal growth patterns were selected and age was supposed by tooth development and eruption.) After measuring each human dried skull by 3D rapid device, we selected the clearest 16 anatomical reference points from about 70,000 points on face image to form accurate FEM shells. The study utilized Cosmos/M (SRAC) for FEM analysis, on a PC(NEC). From the strain analyses, it was revealed that (1) The vale of growth strain from 0 to 3 years of age and from 3 to 6 years of age gradually increased from condylar area toward mental area and the most vale of growth strain was showed at mental area. The vale of growth strain of corpus area was bigger than other areas. (2) As a whole the vale of growth strain of other areas except mental, corpus and nasal area were almost equal. The results indicate especially the growth change of mandible were predominantly showed in the early stages, and the direction of growth strain changed backward and above from mental area to condylar area.

A somatometric study of the head and face in Japanese adolescents.

We studied somatometric measurements of the head and face in Japanese adolescents. We obtained craniofacial measurements of 164 children (82 males and 82 females, from 12 to 14 years of age) from the junior high school in Ayase City (Kanagawa prefecture). In order to have adult data with which to compare, we measured 56 dental students (28 males and 29 females, 20 years of age) from Showa University in Tokyo. We found that head breadth reached adult size at 14 years of age, but, in males, head length increased continuously after 14 years of age. Bizigomatic breadth increased from 12 to 20 years of age. Bigonial breadth had almost completed its growth during adolescence. Face depth grew more slowly than face breadth. From these results, it was clear that craniofacial breadth increased earlier than length. Sexual dimorphism in craniofacial size increased according to age, while sexual difference in the index decreased according to age. A comparison of 3 different generations (40 years ago, 20 years ago, and today) showed brachycephalization and secular change of head breadth and facial measurements. These findings were more evident in females than in males.

Crown structure of the maxillary molars in the Japanese shrew mole, Urotrichus talpoides (Insectivora, Talpidae).

The maxillary first and second molars (M1 and M2) in the Japanese shrew mole, Urotrichus talpoides, were investigated using an odontometrical approach. The mesiodistal crown diameter was larger in M1 than in M2, while the buccolingual diameter of M1 was nearly equal to that of M2. M2 was more compressed mesiodistally than M1. M1 had a large distal triangle on the stylar shelf. The mesial triangle of M2 was slightly larger than the distal triangle. Despite being smaller than M1, M2 was less variable than M1 in terms of size. The distal triangle of M1 and the mesial triangle of M2 were well developed, and thus this area, which corresponds to the inflection point of the maxillary dental arch, was most likely the center of an occlusal function.

An odontometrical difference in the mandibular molars of two laboratory strains of the musk shrew, Suncus murinus, derived from Bangladesh and Tokunoshima Island of Japan.

We investigated an odontometrical difference in the mandibular molars (M1, M2, and M3) of two laboratory strains of the musk shrew (Suncus murinus) originating in Bangladesh (BAN strain) and Tokunoshima Island of Japan (TKU strain). We used skulls from two strains of shrews that were maintained under identical laboratory conditions. Mesiodistal and buccolingual crown diameters in the trigonid and talonid of the mandibular molars were measured with a measuring microscope, calibrated to 0.001 mm. The crown proportion was expressed by the crown indices calculated from the measurements. Size reduction was analyzed quantitatively according to the reduction index. All crown dimensions were significantly larger in BAN shrews than in TKU shrews (P < 0.01). Sexual differences were noted in the talonid dimensions, while interstrain differences were clearly evident in the trigonid dimensions. The crown indices in M1 showed the least interstrain difference of the three molars. The crown indices showed that TKU shrews had relatively larger buccolingual diameters and talonid diameters than BAN shrews, and the reduction indices showed that TKU shrews had relatively larger M2 and M3 than BAN shrews. To extract the variance components of tooth shape, a principal component analysis was performed after the variables were standardized. After Varimax rotation, each factor was interpreted. The first three factors accounted for 79.9% of all variances. The first component represented the mesiodistal crown proportion of the trigonid-to-talonid crown component. The second and third components represented the relative size of buccolingual diameters in the distal molars for M1. The principal component scores showed that TKU shrews had relatively larger talonids and distal molars than BAN shrews.

Comparison of the crown dimensions between the maxillary second deciduous molar and the first permanent molar.

The morphologic relationship of the crown structures of the maxillary second deciduous molar (m2) and the first permanent molar (M1) was investigated with odontometric methods. Materials used were 124 male dental casts taken from Chinese living in Kaohsiung (Taiwan). The mesiodistal and buccolingual diameters, cusp sizes, and intercusp distances were measured. The mean crown diameters were larger in M1 than in m2. The tooth crown proportions were similar in m2 and M1. The intercusp distance was compressed buccolingually in m2. With respect to the relative cusp size, the paracone was not significantly different between m2 and M1. The metacone was relatively larger in m2 than M1, while lingual cusps (protocone and hypocone) were relatively smaller in m2 than in M1. Principal component analysis was performed to investigate factors influencing the variation in crown dimensions of the two teeth. Four components were extracted: (1) buccolingual intercusp distances, (2) crown proportion (mesiodistal and buccolingual diameters), (3) mesiobuccal and distolingual compression, and (4) protocone and mesiodistal intercusp distance. Analysis of principal component scores indicated that the crown proportions of m2 and M1 were similar. The m2 had a smaller protocone and more buccolingually compressed intercusp distances than did M1. The morphologic characteristics of the crown of m2 indicate that it is more primitive and has developed less than M1.

Sexual dimorphism in the tooth crown dimensions of the second deciduous and first permanent molars of Taiwan Chinese.

Sexual dimorphism in the crown components in the second deciduous molar (dm2) and the first permanent molar (M1) of the dental casts taken from Chinese living in Kaohsiung (Taiwan) was investigated. Mesiodistal and buccolingual crown diameters, and 4 main-cusp sizes in the maxillary molars and mesiodistal diameters of the trigonid and talonid in the mandibular molars were measured using a digital caliper (0.01 mm). Percentage sexual differences were calculated. With the exception of trigonid mesiodistal diameters, the mean values of males were larger than females. In both of dm2 and M1 the mean values of the trigonid mesiodistal diameters were slightly larger in females than in males, but the differences were not significant. Percentage sexual dimorphism was smaller in the mesiodistal diameters than in the buccolingual in both dm2 and M1. The crown components showed larger sexual difference in dm2 than in M1, while in the maxilla the external crown size showed larger sexual difference in M1 than in dm2. The buccal cusps showed larger sexual difference than the lingual in the maxillary molars and the talonid showed larger sexual difference than the trigonid in the mandibular. Sexual dimorphism of dm2 and M1 in their crown components displayed similar pattern, although the different degree was noted. This result is thought to relate to the fact these molars belong to the first dentition embryologically.

Studies on the reduction indices of the deciduous teeth of Chinese living in Taiwan.

The reduction index of deciduous teeth was investigated statistically. Materials used were plaster casts of the deciduous dentition taken from Chinese children living in Taiwan. The reduction indices showed no sexual differences. In the maxillary teeth, reduction indices of the bucco-lingual diameters (BL) had the largest values, followed by those of the mesio-distal diameters (MD), and those of the crown area (AREA) which were the least. In contrast to the maxillary teeth, in the mandibular teeth, the reduction indices of MD and those of BL had nearly the same values although the reduction indices of MD were slightly larger than those of BL in females (p < 0.05). With respect to the difference between the maxilla and the mandible, in deciduous incisors the reduction index of MD in the mandible was larger than that in the maxilla (p < 0.01). While in BL the reverse relation was noted. In the deciduous molars the reduction indices of BL and AREA in the maxilla were larger than those in the mandible (p < 0.01). The reduction indices showed no significant difference among the Mongoloid populations sampled. This result may be explained by the primitiveness of deciduous teeth.