Local anaesthesia produces a transient loss of sensitivity at the level of a limited cutaneous or mucosal area. The drug induces depression of nerve endings and/or inhibits the conduction of peripheral fibers.
The somatosensory variation can be evaluated through the method of quantitative sensory testing (QST), which can also be used to assess the results of a traumatic event, affecting the nerve, typically as a complication of oral or maxillofacial surgery.
In 2006, the German Research Network on Neuropathic Pain (DFNS) proposed a comprehensive QST protocol capable of discriminating negative (hypoesthesia, hypoalgesia) and positive (hyperalgesia, allodynia) symptoms, as well as the involvement of different fibers (Aδ, Aβ, C).
Recently, a study recently conducted and published by Scandinavian and Japanese researchers has applied the QST protocol to the oro-facial region in order to test the effect of local anaesthetic.
The objective was to verify, in quantitative (QST) and qualitative (QualST) terms, the degree of sensory alteration at the level of 2 different branches of the trigeminal nerve, undergoing nerve blockage.
The study involved a total of 30 patients and consisted of a double placebo-controlled trial conducted on two separate samples from 15 subjects; one group was treated at the level of the infraorbital nerve, terminal branch of the maxillary nerve (II branch of the V pair of cranial nerves), and the other at the level of the mental nerve, terminal branch of the mandibular nerve (III branch).
Each experiment consisted of a double session, in which the patient was treated with either local anaesthetic or saline solution.
The QST and QualST evaluations were carried out immediately before administration, then at 10-minute, and then two- hour apart during each session. In fact, when the two-hour was measured, due to the degree of recovery, the sensitivity was significantly closer to the baseline state than the 10-minute for most of the QST and QualST parameters.
The degree of perceived numbness, temperature variation, and perceptual distortion were also evaluated.
The collected data were processed through variance analysis and McNemar’s tests.
A significant decrease in sensitivity was detected with respect to both baseline and control. The blockage, partial or complete, affected mechanical and even thermal fibers. QST and QualST are, therefore, to be considered reliable and repeatable tests even in the study of local anesthesia in the oro-facial region. The qualitative protocol alone is able to discriminate the condition of complete blockage.