Fine Structures of the Dental Pulp

1NTERRELATIONSHIPS of nerves and blood vessels can be studied in the dental pulp with little interference from other tissue elements. Pulp tissue contains numerous nerves and vessels of varying size suspended in a fibrous and sparsely cellular gelatinous matrix. Graf' made a quantitative study of the types of nerves in the human dental pulp and reported that a pulp cross section contains approximately one thousand separate nerve fibers, varying between 1 and 10 t in diameter. The maximum size of arterioles in dental pulp has been measured by Provenza,2 who reported diameters ranging up to 100 /. The adventitia of the arterioles, metarterioles, and precapillaries were obliterated by dense bundles of nerve fibers and by the adjacent interstitial tissue. Smooth muscle innervation by autonomic fibers is generally described by light microscopists3 as a plexus of unmyelinated nerves that terminate on the surface or within the sarcoplasm of the muscle fibers. Connections between the nervous and muscular elements in mammalian urinary bladder and in the ureters were examined with the electron microscope by Ceasar.4 These neuromuscular structures consisted of simple contacts between the cytolemma of the smooth muscle and the lemnoblast of autonomic fibers. Smooth muscle tissue in these preparations was seen to be cellular and no evidence was obtained in support of a syncytial arrangement. Electrophysiologic and pharmacologic data indicate the vasomotor role of the autonomic fibers,5 but they do not indicate the morphologic basis for the vasodilator and vasoconstrictor mechanisms. Data have been collected in this laboratory which indicate the presence of sympathetic vasoconstrictor fibers in the mandibular nerves 7 The present investigation utilizes the electron microscope for the study of structures in the dental pulp and particularly emphasizes the blood vessel nerve complex. The fine structure of all vessel and nerve types was examined in an attempt to define the structures which mediate vasomotor tone.