Effects of ionic and non-ionic solutions on intradental nerve activity in the cat

Intradental nerve activity (INA) was recorded from cat canine teeth to determine whether solutions altering intradental nerve sensitivity were strongly correlated to the osmotic concentration of the solution or via a more direct action on intradental nerve excitability. The effects of various ionic and non-ionic solutions were tested in both deep and shallow dentinal cavities. With saline in the deep dentinal cavity a very low firing rate or resting nerve spike (action potentials) activity was recorded. When 3 M NaCl was placed in the same or similar cavity a high discharge rate of nerve spike activity was obtained. This 3 M NaCl elicited activity was utilized to determine the inhibitory or excitatory effects of various test agents on the intradental nerves. The following agents: MgCl₂, MgSO₄, and CaCl₂ were inhibitory to the INA response elicited by 3 M NaCl. Non-ionic solutions of urea or sucrose failed to evoke INA and they were also minimally effective in altering 3 M NaCl elicited activity. Shallow cavities were utilized to maintain the tubular structure of dentin relatively intact. In the shallow cavity preparations hypertonic sucrose or urea failed to evoke INA, even when dentin was etched with 50% citric acid for 2 min. The results suggest that the osmolarity of these solutions is a poor indicator of the INA.