Ultrastructure of terminal pulpal blood vessels in mouse molars.

The purpose of this investigation was to study the fine structure of pulpal capillaries located in the odontoblastic layer and immediate subjacent zone. The observations were from first molars of white mice sacrificed at five day intervals from 25-90 days. Both capillaries and small vessels with an incomplete smooth muscular coating appeared in the zone subjacent to the odontoblastic layer from 25-60 days. At the same time, capillaries which exhibited intracellular fenestrations in the endothelial wall were located within the odontoblastic layer. From 50-90 days, the capillaries among odontoblasts, especially at the pulpal horns, appeared close to the predentinal surface, and an isolated capillary appeared to extend into predentin and run parallel to the outer surface of the odontoblastic layer for a short distance. At these ages, the capillaries subjacent to the odontoblastic layer also exhibited fenestrations along the thin endothelial walls similar to those observed at earlier ages in capillaries among odontoblasts. The vascular supply of the odontogenic zone of the dental pulp is of interest, since it supplies those cells responsible for the development and reparative processes of the dentin. Knowledge to date regarding the arrangement and structure of the terminal capillaries among odontoblasts has been derived from histological observations of a wide variety of species studied at various stages of development (Kramer, '60; Bernick, '60; Adams, '59, '62; Provenza, '58; Jesson, '67 and James, '55), and some differences in the morphology of pulpal capillaries have appeared related to both species-to-species and stage of development variations. The vascular supply among the odontoblasts has also been described in the continuously growing rodent incisor (James, '55; Adams, '59) a phenomenon of dental growth without analogy in many mammalian species including human. The ultrastructure of pulpal capillaries has been reported in several species of mammal by Matthews, Dorman and Bishop ('59), Han and Avery ('63), Riedel, Fromme and Tallen ('66), and Kukletova ('70) who reported cellular specializations which appear to contribute to transendothelial transport. Although the ANAT. REC., 179: 527-542. pinocytotic microvesicles frequently have been reported present in capillary walls, only Riedel et al. ('66) reported three types of capillaries, one of which exhibited intracellular fenestrations or pores. The ultrastructural study of Takuma and Nag& ('71) revealed capillaries located among the odontoblast. Since there are wide variations in the organization and structure of capillaries from tissues in different regions of the body (Farquhar, '61; Majno, '65), it is the purpose of the present study to investigate the fine structure of capillaries located in the odontoblastic layer and immediate subjacent zones. Teeth which are in functional occlusion will be utilized for all such observations. METHODS AND MATERIALS Mandibular first molars were used from groups of five Swiss-Webster white mice sacrificed at five day intervals from 25-90 days. Fixation was carried out using 1.33% osmic acid buffered with s-collidine at pH 7.4 with 5% sucrose added to obtain Received Nov. 30, '73. Accepted Feb. 5, '74. I This project was supported by US.PHS Research Grant DE 01604 from the National Institute of Dental Research, National Institutes of Health, Bethesda. Maryland.