Acute and chronic reactions of dental sensory nerve fibers to cavities and desiccation in rat molars

Abstract

We have studied the effects of air drying of exposed, acid etched dentin on the sensory innervation of rat molars. In the acute series of experiments, trigeminal nerve fibers were labeled by axonal transport of radioactive protein prior to the dentin exposure and desiccation, the anesthetized rats were fixed by aldehyde perfusion 10 min later, and the teeth were prepared for autoradiography. The results confirmed the hydrodynamic theory by showing outward movement of labeled nerve material in response to dentinal drilling and desiccation. It also showed that some odontoblasts could be separated from the dentinal nerve fibers. In the chronic series, teeth were injured 25 h, 5-7 days, or 21 days prior to fixation and nerves were labeled during the last 24 hours; the surviving vital nerve fibers were evident because of their axonal transport of the radioactive label. In that series, sensory nerve fibers were found to have been lost from areas with newly-formed reparative dentin, or from dentinal tubules that had lost their odontoblasts. In the teeth injured 25 h, 5-7 days, or 21 days earlier, an abnormal nonneuronal labeling occurred 0.2-0.3 mm into injured dentin. Our results are discussed in relation to the hydrodynamic theory, nerve-odontoblast interactions, differences between shallow and deep cavity injuries, altered nerve location in response to pulpal or dentinal injury, and characteristics of the pulp-dentin border.

Response of Pulp Sensibility Test Is Strongly Influenced by Periodontal Attachment Loss and Gingival Recession

“…Changes in temperature tend to influence dentinal fluid flow and, subsequently, the mechanical stimulation of pulp nerves (15)(16)(17)(18)(19). Enamel and dentin are thermal insulators (20) known to interfere with the passage of cold temperatures; therefore, teeth with closed dentinal tubules and substantial secondary dentin formation may yield false-negative results when the PST is used with cold stimuli (21).…”

Early Odontoblastic Layer Response to Cavity Preparation and Acid Etching in Rats

“…The cavity and the burr were constantly cooled with sterile saline solution. The second molar in the same quadrant, intact and left without any restorative procedure, served as a control (BYERS et al 1988).…”

“…The animals were killed in a CO 2 chamber at different post-operative time intervals and were divided into four time groups: 5 min, 6, 24 and 72 hours (BYERS et al 1988), each including 7 animals. The blocks of three molars with surrounding soft and hard tissues were dissected and fixed in 4% neutral buffered formalin for 24 hours.…”

“…The predentine is thinned directly beneath the cavity, demonstrating the reduction of odontoblastic activity (MJÖR 1983). Hyperaemia (MJÖR 1983), temporarily increased blood flow in the dental pulp (MJÖR 2001), inflammatory cell infiltrates (ZACH 1972), necrosis and apoptosis of cells in the odontoblastic layer beneath the cavity (BRONCKERS et al 1996), disruption and rarefaction of Korff's fibrils (ZACH 1972), sprouting of nerve endings (BYERS et al 1988) and diminished protein synthesis of odontoblasts (SEARLS 1975) are also observed among early dental pulp responses to cavity preparation.…”

Twenty-Four Months Of Follow-Up After Partial Removal Of Carious Dentin: A Preliminary Study

“…This diagnosis implied that the pulp was vital, but had some areas of inflamed tissue that would heal after conservative vital pulp therapy [27]. Mild trauma with subsequent inflammation can cause small regions of neurogenic inflammation and sufficient mechanical damage to stimulate a nerve sprouting reaction [28] and thereby possibly cause exaggerated response to vitality tests, indicating more severe inflammation than is actually present.…”