Physiology

As described earlier, the tissues of pulp and dentin are considered as one. The pulp is vascularized as are other organs of the body. A large arteriole passes through the root pulp to supply the coronal pulp. They branch as capillaries in the coronal sub-odontoblastic region. The blood capillaries have discontinuity in the endothelial walls. Such types of arrangements facilitate easy exchange of nutrients and the waste fluid. This exchange is important in case of pulp injury. The fluid flow from the pulp to exposed dentin is dependent on the hydraulic conductance of the dentinal fluid. Any reduction in this conductivity will reduce the dentin sensitivity.

Myelinated and un-myelinated nerves enter the pulp through apical foramen

Usually both the myelinated A fibers and un-myelinated C-fibers carry pain impulses. The sensory and the sympathetic nerve endings are activated at an early stage of the inflammatory process and are the initiator of vasodilatation. This is the start of the protective response to the injury by increasing blood volume and vascular permeability in the affected areas. Both the sympathetic and sensory nerve fibers have effect on the pulpal circulation. The number of nerve fibers decreases with age, which explains the reduced sensitivity in older adults.

Pulpal pain is characteristically pulsating, long lasting and of variable severity, very rarely excruciating. It is also affected by changes in blood pressure. The typical dentinal pain is short lasting, sharp and may be lancinating. The cold stimulus is considered more painful than the hot stimulus. In cold stimulus, there is outward fluid flow that results from shrinkage of the contents of the tubules. When heat is applied the contents of the tubules expand and an inward flow occurs, leading to comparatively less pain.