Numerical variation of teeth in the wild house musk shrew Suncus murinus captured from Nagasaki, Japan.

Wild populations of Suncus murinus from Nagasaki were thought to be extinct, although specimens from Nagasaki are kept at the National Science Museum, Tokyo. Variation in the number of teeth, including both congenital and postnatal absence, was observed in 25 of 85 individuals. All 25 abnormal individuals were checked using a micro-CT unit to document the presence or absence of embedded teeth and any traits of postnatal absence. Four of these had congenitally absent teeth, whereas the rest showed signs of postnatal absence. There was no significant difference in the ratio of length of tooth group P(4)M(3) against palatal length between individuals with congenital absent teeth and normal ones. Because S. murinus in captivity shows a high rate of periodontal disease, we suggest that the high rate of postnatal absence of teeth in the wild population is due to oral diseases such as periodontal disease or other traumatic factors.

Tooth size variability and relevance of numerical variation in the Japanese serow.

We analysed the variability of the lower cheek teeth of the Japanese serow, Capricornis crispus, from Aichi Prefecture, Japan, based on the coefficient of variation (CV), and examined tooth size variability. The mesiodistal (MD) and buccolingual (BL) crown diameters of permanent cheek teeth were measured, and an index of the crown surface (MDxBL) was calculated. As a result, the CV for MD measurements ranged from 3.6 to 6.3, and that for BL measurements ranged from 3.6 to 6.5. In males and females, the first molar (M(1)) was the least variable (3.6-4.1) and the second premolar (P(2)) was the most variable (5.0-6.5), except for the case of BL in females. The crown surface index showed a morphological gradient that increased from mesial to distal, and the values of P(2) in both sexes were extremely small. Overall, cheek tooth variability was not influenced by developmental factors, but appeared to be inversely related to functional factors. The highest coefficient of variation was observed for P(2), which was characterised by a simple shape with a single cusp, and an extremely small size compared to other teeth. Only P(2) showed congenital absence or impaction in the lower dentition. We also confirmed the relationship between tooth size variability and numerical variation.

Quest for the cause of oligodontia in Suncus murinus (Soricomorpha, Soricidae): Morphological re-examination.

Many mammal species, including humans, exhibit oligodontia, or a lack of certain teeth in their dentition. However, the causes of the condition remain controversial. In the house musk shrew, Suncus murinus, both osteological and odontogenetic factors, which are genetically determined, have been implicated as causes of oligodontia. We examined 350 dry cranial specimens of S. murinus, representing seven laboratory strains and two wild populations. Oligodontia was observed in the upper third incisor (I(3)) and upper third premolar (P(3)); no supernumerary teeth were observed. None of the specimens with oligodontia had embedded teeth, as determined by soft X-ray. Congenital oligodontia was observed on P(3) and I(3). Moreover, the type and frequency of missing teeth differed among strains/populations. We compared the ratio of P(4)M(3) to PL as a possible cause of oligodontia. For P(3), we compared normal individuals to those with missing teeth within populations/laboratory strains, but did not detect significant differences. I(3) was compared among three laboratory strains: NAG (I(3) absent in 97%), TESS, and RYU (normal strains). TESS and RYU individuals had a longer distance from the upper fourth premolar to the upper third molar (P(4)M(3)), relative to palate length (PL), than NAG individuals. Specimens with oligodontia at I(3) and P(3) showed no difference in the ratio of P(4)M(3) length to PL. These findings suggest that osteological factors do not account for the absence of P(3) and I(3). Therefore, we believe that oligodontia in S. murinus depends on odontogenetic factors. In addition, as for I(3) and P(3)-absent, possibility related to some genes was thought about.

Premolar and molar rotation in wild Japanese serow populations on Honshu Island, Japan.

The skulls of 1195 Japanese serow (Capricornis crispus) from six geographically distinct populations were examined for tooth rotation. Our objectives were to determine tooth rotation patterns in Japanese serows, investigate geographical variation in tooth rotation and examine whether space limitations in the jaw accounted for variations. We then sought to explain the origin of tooth rotation in the Japanese serow. Rotated teeth were found in 131 specimens (62 males, 57 females and 12 unknown gender), with no statistically significant difference between males and females (chi(2)=0.03, P=0.86, d.f.=1). Among the six populations, the frequency of tooth rotation varied from 3.7-32.1% (average 11.0%). Most tooth rotation occurred in the upper third and fourth premolars. The lingual cusp of anomalous teeth was rotated 30 degrees -90 degrees mesially or distally from the buccolingual tooth axis, and the rotation direction differed among populations. However, we found no difference in skull or tooth morphology between normal individuals and those with tooth rotation. Therefore, hereditary factors may be involved in Japanese serow tooth rotation. We concluded that genetic differentiation occurred in the past among local Japanese serow populations isolated in mountainous habitats. Gene frequencies were likely subject to random drift, especially during possible population bottlenecks, when genetic factors could most strongly affect the direction of rotation.

Analysis of dental anomalies in the Siberian mole, Talpa altaica (Insectivora, Talpidae).

We re-examined tooth variation in specimens of the Siberian mole, Talpa altaica, from the collection of the Siberian Zoological Museum and discuss the mechanisms of dental evolution. The number of teeth counted in 1789 specimens ranged from 34 to 47, and supernumerary, absent, and connate teeth were observed. The most frequent tooth anomaly was an absent tooth in the premolar region (200 maxillary first premolars and 190 mandibular third premolars), which does not support Fujita and Kirino's terminal reduction hypothesis in the mandible [Fujita T, Kirino T. Ha No Kaibougaku. 21st ed. Tokyo: Kanehara Publishers Inc.; 1976 (in Japanese)]. Supernumerary teeth were found in premolar rows and in the incisor and molar regions. An maxillary fourth molar, positioned distal to the normal third molar, was thought to result from a genetically programmed atavistic event during the natal stages. Connate teeth were observed only in the premolar rows and were thought to have developed with the fusion of two independent tooth germs. Connate premolars appeared to result from an expression of an incomplete division of tooth germ at an early developmental stage or a reunion of independent tooth germs, based on the morphological similarity of the normal and supernumerary premolars. These extraordinarily frequent tooth anomalies of T. altaica are of much interest both in terms of tooth development and classification.

A model of spontaneous periodontitis in the miniature goat.

BACKGROUND: The pathogenesis and progression of periodontal disease have been extensively studied through the use of animal models. However, no animal model has yet been established that is precisely similar to periodontitis in humans. In the present study, we examined the use of Shiba goats as a model for spontaneous periodontitis. METHODS: Thirty-four Shiba goats (seven males and 27 females, aged 10 to 98 months) were used. We examined periodontitis in Shiba goats clinically, histopathologically, and microbiologically. RESULTS: The mean probing depth (PD) of the 68 teeth examined was 2.7 +/- 0.8 mm. The incidences of PD > or =3 and 4 mm were 46.4% and 22.1%, respectively. The incidence of bleeding on probing in 68 sites and in 34 animals was 60.7% and 73.5%, respectively. The formation of vertical alveolar bone defects and downgrowth of gingival epithelial cells were found in the areas of periodontitis. The prevalence of Tannerella forsythensis, Campylobacter rectus, Fusobacterium necrophorum, Fusobacterium nucleatum, and Actinobacillus actinomycetemcomitans in subgingival plaque by polymerase chain reaction was 46.4%, 28.5%, 28.5%, 17.8%, and 3.5%, respectively. These percentages were increased in subgingival plaque from PD > or =3 mm. CONCLUSIONS: The clinical, histopathological, and microbiological features of spontaneous periodontitis in Shiba goats were somewhat similar to those in human periodontitis. Moreover, there are some advantages of using the Shiba goat; the size of the oral cavity is suitable for periodontal treatment, and handling and housing are relatively easy. Therefore, these results suggest that the Shiba goat is a useful animal model for human periodontitis.

Variations in the number of teeth in wild Japanese serow (Naemorhedus crispus).

Skulls of 755 Japanese serow (Naemorhedus crispus) were examined for numerical anomalies of teeth, and these were found in 30 (4.0%) specimens. In addition to supernumerary and congenital missing teeth, embedded teeth were also identified. Supernumerary teeth were found in 10 (1.3%) specimens, congenital missing teeth were found in nine (1.2%) specimens, and embedded teeth were found in 11 (1.5%) specimens. Supernumerary teeth were found among the incisors, the upper and lower premolars, and the lower molars. Based on the appearance of certain tooth classes, their size, and their form, atavism was considered to be a possible cause of the occurrence of some of these teeth. Congenital missing teeth were found at the loci of the lower incisors, canines and P(2). In Japanese serow, there appeared to be a tendency for congenitally missing P(2) as well as P(1). All embedded teeth were found at the locus of P(2). These teeth may have occurred as an intermediate state between normal and congenital missing teeth. Variations in the number of teeth in Japanese serow were concordant with their phylogenetic background. Moreover, although variations in the number of cheek teeth tended to be concentrated in the mesial region of the premolars, the tendency in the incisive region was for teeth to appear mesial as well as distal within an incisor-tooth sequence. These results, which are not in accordance with terminal reduction theory, indicate that the phenomenon of tooth degeneration does not only occur at the end of a tooth row.

Effects of diet on the incidence of dental pathology in free living caviomorph rodents.

Examinations of dental pathology in five genera of caviomorph rodents found caries and periodontal disease in both grazers and frugivores, although the prevalence differed between the two groups. Caries was more prevalent in the frugivores (10.5-19.8%) than in the grazers (1.1-8.7%); mild periodontal disease occurred occasionally in the grazers (5.6-8.7%), but was almost absent in the frugivores (0.0-1.3%). The consistent findings of caries and periodontal disease suggest that ecological differences between the two related groups, and the subsequent dietary differences, are important in determining the incidence of dental pathology.

Dental and skull anomalies in feral coypu, Myocastor coypus.

The study of dental and skull abnormalities of wild animals can provide useful information for comparative studies. Although studies of captive and laboratory rodents have been published, there are few reports on wild populations. We examined anomalous and pathological conditions in the skulls of feral coypus, Myocastor coypus, from Aichi Prefecture, Japan, and identified the types of abnormality. Of the 203 coypu skulls of various ages examined, 19 specimens (9.4%) had abnormalities. A total of 23 anomalies were divisible into three categories: dental diseases, dental injuries and skull injuries. Seven specimens (3.4%) had evidence of periodontal disease in the cheek teeth, and one specimen (0.5%) had caries. Seven specimens (3.4%) had broken upper or lower incisors. Four specimens (2.0%) had injured cranial bones and three (1.4%) had fractures near the zygomatic arch. A single specimen (0.5%) had a deformed rostrum. No statistically significant differences between the genders were found in any category (chi2 test: P < 0.05). The incidence of dental disease appeared to be related to the biological characteristics of this species, i.e., long lifespan, herbivorous diet and molar crown morphology. By contrast, dental and skull injuries appeared to be due to trauma caused when farmers attacked feral coypus.