The question of whether sensory retraining exercises could be used effectively with patients with altered orofacial sensation was first raised in the 1992 literature by Gregg [32]. In 2001, Meyer and Rath presented a retrospective review of 372 patients who had had a microsurgical repair for a nerve injury after 1981 and for whom at least an 18-month postsurgical follow-up was available. A nonrandom sample of patients had been given facial sensory exercise instructions that incorporated some of the early-stage components of sensory retraining with the expectation that sensory retraining would help patients with altered orofacial sensation following nerve injury by (1) improving patients’ ability to interpret lip/chin sensations and movements, (2) improving perioral motor function subjectively and objectively, and (3) lessening the objectionable impression of numb/paresthetic sensations in the lip and chin by decreasing the subjective differences between affected and unaffected skin areas [55]. The percentage of patients who achieved a useful sensory recovery on the Medical Research Council Scale (MRCS), a clinical assessment, did not differ for those who did and did not receive instructions regarding facial sensory exercises. However, those patients who received instructions reached their final level of sensory recovery much sooner, on average 3 months earlier [55].

In order to assess the efficacy of sensory retraining for facial altered sensation, a multicenter double-blind parallel two-arm stratified block randomized clinical trial (RCT) was conducted at an academic center and a community-based center with enrollment of 191 subjects [61]. The intent was to assess whether the magnitude and duration of patient-reported burden from altered sensation was lessened when facial sensory retraining exercises were performed in conjunction with standard opening exercises than when the opening exercises were performed alone. The subjects were patients with a developmental disharmony who were scheduled for bilateral sagittal split osteotomy with or without maxillary osteotomy.

The emphasis in the RCT on patient-report was motivated by two factors: (1) the assumption that sensory retraining would not affect actual nerve recovery including objective sensory testing measures of nerve function and (2) the recognition of the difference in function of the sensory innervations to the facial as compared to skin in other anatomic areas like the fingers. The terminal distribution of the inferior alveolar nerve, i.e., the mental nerve, innervates skin functionally more like the back of the hand (radial nerve) than the palm side of the hand (median and ulnar nerves) [16, 84]. Thus, the receptors in the skin of the hairy lower lip/chin of the face deform in response to movements during function, and as such, the evoked neural discharge serves a proprioceptive role including a conscious awareness of facial expressions [16, 30].

The sensory retraining protocol in the RCT had three time-dependent levels of instructions that were given to patients at 1 week, 1 month (4–6 weeks), and 3 months after surgery. The time points were selected based on their use in clinical studies of the impact of sensory reeducation in patients with an injured median or ulnar nerve [94] and in clinical studies of sensory impairment in patients following orthognathic surgery [29, 48, 85, 96]. The three levels of sensory retraining were designed to increasingly challenge patients congruent with the early and late phases of sensory education used for the hand: constant versus moving touch, orientation of moving touch, and direction of moving touch (Table 18.2). (Three videos demonstrating each exercise at each level are available online at http://www.oralmaxsurgeryatlas.theclinics.com/article/S1061-3315(10)00065-X/abstract, March 2011 issue. The videos were produced by Video Services of the Center for Instructional Technology at the University of North Carolina. Written instructions provided to subjects and copies of the instructional tapes are available from the corresponding author upon request.)

Consistent with the anecdotal reports, the patients in this clinical trial who received the sensory retraining exercise instruction were less likely to report a problem related to unusual feelings on the face, loss of lip sensitivity, or numbness at 3 and 6 months after surgery than subjects who received standard opening exercises only [61]. At 6 months, subjects in the opening-only exercise group were almost twice as likely as those in the sensory retraining group to report a problem with altered sensation [61]. In addition to patient-reported outcomes, two-point perception, two-point discrimination, and contact detection thresholds were measured as secondary outcomes. The sensory retraining patients were more adept at discerning touch, indicating accommodation, even though there was no improvement in the ability to discriminate two distinct points of contact from one or to detect the presence of tactile stimulation (nerve recovery) [22].

The positive effect of the sensory retraining persisted even after the exercise protocol was completed (Fig. 18.1). Although the likelihood that a subject would report altered sensation steadily decreased in both groups over a 2-year follow-up protocol, the difference between the groups was relatively constant. Even at 2 years after surgery, patients who received only the opening exercises were about two times more likely to report an altered sensation than patients who used the sensory retraining exercises after surgery (Fig. 18.1) [62]. And patients in the sensory retraining group were less likely to report interference in daily life activities from numbness or loss of lip sensitivity (Fig. 18.2a, b) [63]. This difference between the two exercise groups appears to be related to the difference in how the “retrained” individual experienced or interpreted tactile stimuli rather than any difference in nerve recovery or repair [22, 23]. Two years after surgery, patients who received sensory training during the initial 3-month period still exhibited greater sensitivity on tests of two-point perception, i.e., sensory retraining subjects reported perceiving two-point contact from a one-point contact at a shorter separation between the points (Fig. 18.3) [23].

The results at 6 months and the longer-term analyses at 24 months suggest that for patients who experience an acute nerve injury, as is highly likely during a mandibular osteotomy, the simple, noninvasive sensory retraining facial exercises, which require only an inexpensive cosmetic brush and a mirror, are an effective therapy to promote accommodation to a sensory deficit on the face. Perhaps the desired outcome for “retrained” patients was best stated by Callahan, “If sensory re-education results in a person’s increased ability to better enjoy the tactile sensations of everyday living, then reeducation has been meaningful and successful” [9].

For orofacial sensory retraining, an important component of the retraining is the visual feedback provided by performing the exercises in front of a mirror. This elicits two different sensory events, the sensation of the brush on the facial skin and the sight of the brush on the face. Recent experimental studies have shown that viewing a body surface can directly enhance tactile perception and detection [27, 79] even when the “touch” is not physical but a mirrored reflection [71, 74]. The frequency of the ­repetitiveness with which the exercises are performed each day is much more important than the length of time spent at any given point in time. It may be that encouraging patients to perform orofacial sensory retraining exercises with a small handheld mirror for a short period of time, perhaps 1–2 min, four to six times per day would be more effective than a longer time in a less frequent protocol.