Dental dolorimetry for the evaluation of an analgesic agent in the horse.

The researchers in this study developed and tested a method, dental dolorimetry, to measure pain thresholds in horses by stimulating a nerve in a tooth using a surgically implanted electrode. They found that this procedure was easily performed and that the results were consistent over time, with pain thresholds increasing after the administration of a pain-relieving drug.

Methodology of Dental Dolorimetry

• A constant-current stimulator was used to deliver a known amount of electrical current to the pulp nerve of the tooth of a horse. This was done using a surgically implanted monopolar electrode in the dentine layer of a canine tooth. An electrical current was used because it’s easily controlled and quantifiable, which helps to measure the pain threshold more accurately.
• A single stimulus lasting for 2-ms duration was used, and it was repeated at intervals of 20 seconds or more. This stimulation was performed to provoke a specific response from the horse – a head lift. The researchers monitored the horse for this reaction as an indication of the horse experiencing discomfort.

Testing Procedure and Base-line Thresholds

• The lowest current level that induced three positive head lift responses was recorded as the pain threshold of the horse. This was done in order to make sure the reaction was consistent, and not a random movement.
• Initial tooth pulp pain thresholds (TPPT) were established on eight adult male horses that were not under any medication. This was to make sure that the pain thresholds measured were not influenced by any substances influencing the perception of pain.

Stability of the Technique and Analgesic Evaluation

• The electrodes implanted were nonreactive and remained functional for up to 98 days. This shows that the dental dolorimetry process was not overly harmful or distressing for the horse, and that measurements over time could be taken with a minimal risk of complications.
• Base-line TPPT values were consistent with repeated measurements on the same day and subsequent test days. This ensured the reliability of the method.
• The quantity of electrical current necessary to elicit the TPPT increased after the administration of xylazine HCl, a test analgesic. This demonstrated that the technique could be used to effectively measure the effectiveness of pain relief medications.