Infundibula of equine maxillary cheek teeth. Part 1: Development, blood supply and infundibular cementogenesis.

There is increasing interest in diseases of infundibula of equine maxillary cheek teeth. Imperfect infundibular cementogenesis has been recognized as an aetiopathological factor for the onset of infundibular necrosis. In this article, infundibular development was examined with particular attention to infundibular blood vessels and cementogenesis. Forty-one deciduous maxillary premolars prior to eruption were investigated using routine histological and immunohistological methods to visualize blood vessels and the enamel organ. Selected specimens were scanned by micro-computed tomography to analyze the three-dimensional configuration of the developing infundibulum. Before eruption, the infundibula are supplied by a central infundibular artery entering the infundibulum from an occlusal direction and by arteries entering the mesial infundibulum from the mesial aspect, and the distal infundibulum from the distal aspect. The central infundibular artery is destroyed shortly after tooth eruption but the lateral arteries remain vital for a time after eruption. As the arteries of the distal infundibulum are located in a more apical position, blood is received for a longer period compared with the mesial infundibulum. Cementogenesis starts first at distinct enamel in-foldings in the occlusal part of the infundibula, advancing in an apical direction. The results suggest a distinct asymmetry between the infundibula with the mesial infundibulum prone to incomplete cementogenesis due to early blood supply cessation.

Ultrastructural observation of capillary sprouts in the dental organs of rat molars.

The morphological events associated with the formation of capillary sprouts were examined in the dental organs to elucidate the morphological processes of angiogenesis in epithelial tissues. Mandibular first molars of 2-day-old male rats were processed for routine observation by transmission electron microscopy. In angiogenic regions, capillaries were located in the caves delineated by outer enamel epithelium, and extravasated erythrocytes were often observed in the stellate reticulum. At the capillary sprout, endothelial cells were amoeboidal in shape, and extended their filopodia to the fluffy extracellular matrix. On the other hand, each endothelial cell interdigitated with each process to form a tubule, and bulbous cell processes filled the luminal side of capillaries. Coated vesicles or pits 50-90 nm in diameter lined the luminal plasma membrane and that comprising the base of filopodial processes. Some endothelial sprouting tips (30 of 47 sprouts) were associated with pericyte-like cells. However, pericyte-like cells were observed in most of the caves where capillaries were located or destined to be located. We investigated the dynamic status of endothelial cells via parameters such as cell elongation and spreading which were supported by the additional observation of membranous components such as coated vesicles at the capillary sprouting region. It was also suggested that pericyte-like cells participated in angiogenesis of epithelial tissues by guiding the sprouts and sealing labile junctions between endothelial cells.

Blood supply of the rat periodontal space during amelogenesis as studied by the injection replica SEM method.

Distribution of blood vessels at the labial periodontal space of the rat lower incisor teeth was studied, using Mercox-resin vascular casts, which were coated with gold-palladium and observed in a scanning electron microscope (SEM). Three different layers were identified in the vascular bed of the periodontium. In the inner layer the enamel organ was supplied by a blood capillary network that changed from a circular mesh to a ladder-like pattern during amelogenesis. The middle layer was supplied by small arteries and arterioles. Small arteries originated from the inferior alveolar artery; arterioles, arising from them, became blood capillaries. In the outer layer, the sinusoid veins continued with the blood capillaries which ran into the proximal and the distal sites of the inner layer. This venous layer is located near the alveolar bones. As capillary networks change in pattern during amelogenesis, the circular mesh is considered convenient to provide the required materials for the proliferation and differentiation of inner enamel epithelial cells as well as for early enamel matrix formation, whereas the ladder pattern seems suitable to supply numerous organic or inorganic materials for the advanced enamel matrix formation and calcification.