犬の下顎管内神経の発育と成長に関する研究

Abstract

The author studied the morphological change of the mandibular canal together with the growth change of the neural elements in the canal during the postnatal life of dog. A total of 46 dogs consisting of mixed breed ranging in age from 1 day to estimated 2-3 years was used as material. Histological methods such as nerve staining by silver nitrate and hematoxylin-eosin double staining were chiefly used and dissection, radiographical measurement, and tracing methods were supplementarily employed. Growth and development of the mandible were studied on the following groups of dog. Preeruptive stage of deciduous teeth Eruptive stage of deciduous teeth Shedding stage of teeth Eruptive stage of permanent teeth The following results were obtained. 1. Mandibular foramen shifts from the posterior upper position to the posterior lower position with growth of the mandible and eruption of teeth. At birth, the innervation of the inferior alveolar nerve through the canal takes place in various shapes according to the regions innervated. That is, in the region from i_1 to m_4, the nerve branched either in oblique frontal straight course, frontal curved course, or vertical and sometimes radial courses, and in the region behind M_1, it branched in oblique backward course and sometimes in hairpin-like or Y shapes. After the eruption of M_3, all branches of nerve except a few that run obliquely backward from lower margin of the main trunk assume a variety of shapes in their distribution such as frontal oblique projection, frontally bent curve, vertical projection or radial projection. These variations of shape was interpreted as an adaptation of the nerve tissue to the development and differentiation of jaw, teeth and their surrounding soft tissues. 2. The mandibular canal was consisted of a single tube at birth principally made up of osseous but in part of membranous tissues, with its upper wall showing porosity. The cross sectional view of the canal was either flattened or displaced sidewise with progressive growth of roots of deciduous and permanent teeth, but it turned roundish or ovoid at the time of permanent eruption. At later stage of this time, a part of the root was seen to appear within the canal. 3. Through entire length of the canal the main trunks of the nerve, artery and vein generally maintained respective position in their courses, the nerve always running uppermost, the artery in the middle and the vein lowest. Some exceptional cases may be seen with relation to the deciduous tooth eruption and tooth exchange taking place in the jaws. 4. The retromolar canal (Dieck & Fujita, Ono) and the incisal canal (Yamamoto) were always seen here too to branch from the canal. The neurovascular branches coming from the main trunks passed through the retromolar canal and supplied the temporal muscle, and buccinator, and also the gingiva and periodontal membrane around M_3 tooth. The incisal canal that runs through the lingual side of canine region contained the neurovascular bundles supplying i_1, i_2, I_1, I_2. The bundles were sometimes seen to emerge from the mandible and communicate with soft tissues. 5. The nerve fibers that distributed to the deciduous and permanent dentitions are derived from the subdental arch (Homma), the bundle which in turn was originated from the mandibular canal. By the time of tooth exchange the nerve bundles supplying the deciduous teeth suffered degeneration as far as to the main trunk and partially disappeared. From the same bundles of nerve, however, regenerated nerve fibers were seen to grow to distribute to the permanent dentition. This may be interpreted as an adaptation of the peripheral nerve corresponding to the progressive growth of jaw and teeth.