Pulpal Nerve Responses to Dentine Stimulation in Extracted Human Teeth

Objectives: We have previously attempted to maintain the function of the sensory units (receptors and nerve terminals) in human premolars following extraction by superfusing the pulp; but failed. At least 10 minutes were required to set up the teeth in vitro.
Aim: to determine for how long units continue to function following extraction without superfusion.
Methods: In 9 premolars due for extraction during orthodontic treatment in young adults (ages 20-25 years), 3 cavities (2.5 mm deep, 1 mm diameter) were cut without anaesthetic at the tips of the buccal and lingual cusps and occlusally. Electrodes were inserted into the cavities and action potentials recorded during hydrostatic pressure stimulation (5s, ±300-500 mm Hg) of the dentine. Each tooth was then anaesthetised (mandibular block or infiltration) and the recordings repeated then, in 7 cases, the tooth was extracted and its roots either immersed in oxygenated Ringer’s or replaced in the socket. Recordings were repeated at 1 minute intervals until no response was obtained.
Results: Initially, action potentials were recorded during stimulation from all the teeth. These responses were not abolished by the local anaesthetic although the number of impulses evoked tended to be reduced: for responses to negative pressure stimuli recorded from the buccal electrode the difference between the counts was significant (P<0.01, Wilcoxon Signed Rank test; median before 114; after, 71) . In the 5 teeth in which the electrodes survived the extraction, responses ceased within 5 minutes in 3, 8 minutes in one, and 14 minutes in the other. Before the responses failed, both the numbers and the amplitudes of the action potentials decreased.
Conclusions: To study the sensory mechanisms of human dentine in vitro, effective superfusion or perfusion of the pulp should begin within 5 minutes of extraction. Local anaesthetic used for the extraction can affect intradental nerves.