Hypsodontia in Castor canadensis: an anatomical and histological study.

OBJECTIVES: The aim of this original study is to describe the dental morphology and anatomy of Castor canadensis and to compare results with existing data in the literature relating to this mammal. This will give us a better knowledge of its very distinctive dental system, representative of rodent typology. MATERIAL AND METHODS: The authors used an osteological sample that is rarely found in Europe. A series of horizontal histological sections of the labial and jugal dental organs were prepared at different coronal and radicular levels for study under the optic microscope. Coloration was applied for tissue differentiation. RESULTS: Observation of the histological sections reveals an enlargement of the space reserved for the pulp tissue which increases from the crown towards the widely open apex of the incisors. These characteristics are not found in the jugal teeth which, although they also have an open apex, present a different configuration. CONCLUSION: The dental organs of Rodents in general and Castorides in particular are subject to a constant eruptive force throughout their lifetime. This permanent dental growth occurs as the dental system undergoes intense abrasion, especially the incisors.

[Morphology and characteristics of the cingulum of the permanent maxillary central incisors]. / Morphologie et particularités du cingulum des incisives centrales maxillaires permanentes.

This study constitutes a synthesis of the main cingular morphologies of the permanent maxillary central incisors. The descriptions concern the teeth of one or other of the left or right hemi-dental arches. In complement was realised a statistical study on a sample of 102 people, between 16 and 38 years old, men and women belonging to diverse ethnic groups. The results are interesting, as indicative, of the proportions of the different cingular morphologies inside the diverse ethnic groups (west Europeans, Melano-africans, Maugrabins).

[Carabelli's tubercule in the Wolof ethnic group (Senegal)]. / Le tubercule de Carabelli dans l'Ethnie Wolof (Sénégal).

UNLABELLED: The authors study the Carabelli's trait in a Wolof population (Senegal). This morphologiest alteration is mainly present on the first permanent maxillary molar. MATERIAL AND METHODS: 195 left and right first molars of 102 individuals with one equal sex distribution were used. The morphological examination of 194 second maxillary molars (left and right) completed the study. RESULTS: They show a frequency of 11.8% traits, either individualized (6.7%), either hypertrophic (5.1%), with a predominance of attenuated (37.4%) or absent formations (50.8%), as well as a sexual dimorphism (19% of individualized or hypertrophic traits in the female population, versus 4.2% in the male). The presence of an attenuated trait (grooves and pits) on the second molars follows also a repartition in favor of the female population (24% versus 4.2%).

[Disappearance of the avian teeth or "when birds had teeth"]. / La disparition de la denture avienne ou "quand les poules avaient des dents".

Authors describe the evolution of the avian lineage since its origin to our days and in particular the characteristics of the Jurassic or Cretaceous periods. They evoke the mechanisms which explain the involution of birds' teeth, their complete disappearance, birds nowadays having a beak instead. They stress the importance of natural selection and heterochrony.

About a mandibular hyperostosis: the torus mandibularis.

The human skeleton sometimes shows some peculiarities: the torus mandibularis (TM) is one of them. It is not a pathological or tumoral formation but a rare anatomic peculiarity. It is an exostosis which appears on the medial side of the body of the mandible. This exostosis is neither embarassing nor dysfunctional. It is not a pathologic development nor does it cause any pathology but sometimes a removable dental plate may be a source of injury. The examination of 80 mandibles of individuals from South-West France has yielded one specimen presenting a TM.

[Topographical and spatial anatomy of the mandibular alveolar nerve]. / Anatomie topographique et spatiale du nerf alveolaire mandibulaire.

After reviewing the origin and the anatomical path of the mandibular alveolar nerve, the author describes the study techniques used on dry bone: serial frontal sections laid out sagittaly; catheterism prior to standard radiographs; and, fenestration of the external osseous wall. These techniques demonstrate the precise topographical and spatial anatomy of this branch of the trigeminal nerve (V3).