Blink reflex with stimulation of the mental nerve. Methodology, reference values, and some clinical vignettes

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Abstract
In order to develop an objective electrophysiological method for detecting and grading lesions in the inferior alveolar nerve (IAN) and its terminal branch, the mental nerve (MN), the normal physiology of the blink reflex (BR) with stimulation of the distribution of the MN was evaluated and reference values for the MN BR test obtained. The BR responses to electrical stimulation of the distribution of the MN on each side were recorded in all 44 healthy adults. The onset latencies and peak-to-peak amplitudes were measured and analysed. The effects of the stimulation site, the size of the stimulating electrode, and facilitation by eye closure and mathematical task on the MN BR responses were tested. A small paediatric stimulating electrode was found to be efficient for dermatomal stimulation of the MN distribution. The MN BR responses consisted of an ipsilateral late component (R2i) on the side of the stimulation and a contralateral component (R2c) with similar latency. The latencies were longer and the stimulation thresholds needed to evoke a reflex response were higher with stimulation of the MN, when compared with the BRs with supraorbital nerve stimulation. Eye closure resulted in facilitation of the MN BR in the form of latency shortening, while mathematical task did not have any significant effect on the responses. In addition, the test was found useful in the diagnosis of iatrogenic IAN lesions after extraction of third molars in two patients, and after an orthognathic operation in one patient. Contrary to some previous reports, constant MN BR responses can be elicited in healthy adults, which enables further clinical application of this test.