Maxillary Incisors of the Horse before and at the Beginning of the Teeth Shedding: Radiographic and CT Study.

To gain insight into the radiographic appearance of maxillary deciduous incisors and dental germs of maxillary permanent incisors in the period prior to teeth shedding, radiographs and computed tomography (CT) of 25 horse skulls, with an estimated age of between 12 and 42 months, were studied. Data regarding morphology and development were obtained. Dental germs of first maxillary permanent incisors were identified radiographically as rounded radiolucent areas at the level of the apical parts of the first deciduous incisors, in skulls with an estimated age of twelve months. The first sign of crown mineralization of these dental germs appeared in skulls supposedly a few months older. Before teeth shedding, the unerupted, mineralized crowns of the first permanent incisor could be identified radiographically relatively caudal to the corresponding first deciduous incisors. The results of the present study indicate that radiographic intraoral images are suitable to identify the grade of development of the dental germs of maxillary permanent incisors. A detailed description of the radiographic appearance of deciduous incisors and dental germs of permanent incisors will help clinicians to expand their knowledge for diagnostic or treatment purposes.

Intracranial portion of the trochlear nerve and dorsal oblique muscle composition in dog: a structural and ultrastructural study.

In the present investigation the right intracranial portion of the trochlear nerves and dorsal oblique muscle of the right ocular globe were removed from six adult dogs and analyzed by light and electron microscopy. Unmyelinated fibers were observed in the analyzed nerves. The number, diameter, area, and density of myelinated fibers were determined, as were corresponding axon area and diameter and myelin sheath thickness. Frequency histograms of myelin sheath thickness and fiber size show a bimodal distribution with a similar proportion of large and small fibers. Muscle samples were taken from the central portion of the muscle belly, subsequently frozen, cut, and stained with m-ATPase at pH 4.6. Fibers were classified as Type 1 or Type 2 according to their reaction to the m-ATPase and detailed morphologic and morphometric studies were made. The muscles showed two clearly distinct layers, a central layer and a peripheral layer, chiefly composed of Type 2 fibers. The fibers in the central layer were larger in size than those in the peripheral layer.