Spatial and Temporal Assessment of Orofacial Somatosensory Sensitivity: A Methodological Study

Aims: To evaluate the sensitivity and reproducibility of a multimodal psychophysical technique for the assessment of both spatial and temporal changes in somatosensory function after an infraorbital nerve block. Methods: Sixteen healthy volunteers with a mean (± SD) age of 22.5 ± 3.4 years participated in 2 identical experimental sessions separated by 2 weeks. The subjects rated the perceived intensity of standardized nonpainful tactile, painful pin-prick, warm, and cold stimuli applied to 25 points in 5 3 5 matrices in the infraorbital region of each side. The reproducibility of single points was tested, and a mean difference of 1.4 ± 0.5 was found. A 0-50-100 numerical rating scale (NRS) with 50 denoting "just barely painful" was used. A modified ice hockey mask with adjustable settings was developed as a template to allow stimulation of the same points in the 2 sessions. Assessment of somatosensory function was carried out before the injection (baseline) and after 30 and 60 minutes on both the anesthetized and contralateral (control) side. In addition, the applicability of the psychophysical techniques was tested in pilot experiments in 2 patients before maxillary osteotomy and 3 months afterward. Results: The overall analysis of mean NRS scores, number of points, and center-of-gravity coordinates for all stimulus modalities showed no significant main effects of session. Post-hoc tests for all stimulus modalities demonstrated significantly lower mean NRS scores and significantly more points (hyposensitivity) at 30 and 60 minutes postinjection compared to baseline values on the injection side (Tukey tests: P .002). In the 2 maxillary osteotomy patients, the psychophysical techniques could successfully be applied, and bilateral hyposensitivity to all stimulus modalities was demonstrated at the 3-month follow-up. Conclusion: The present findings indicate that the psychophysical method is sufficiently reproducible, with no major differences between sessions in healthy subjects. All stimulus modalities demonstrated adequate sensitivity. Furthermore, measurement of points in 5 3 5 matrices allowed a spatial description of somatosensory sensitivity. This method may be valuable for studies on changes in somatosensory sensitivity following trauma or orthognathic surgery on the maxilla. Parole chiave: local anesthesia, orthognathic surgery, psychophysics, somatosensory sensitivity, trigeminal physiology