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Yours sincerely,
Paul R. Lambert, M.D.
Professor and Department Chair

When the proximal facial nerve is not available but distal nerve fibers remain, an alternative neural input can be transferred to the intact distal facial nerve. Traditionally, a separate cranial nerve such as the hypoglossal or accessory nerve have been used for this purpose. Recently there has been increased interest in transferring the masseteric nerve to restore oral commissure and smile movement. The masseteric nerve is a terminal motor branch of the third division of the trigeminal nerve (V3) that supplies the masseter muscle. This nerve passes through the sigmoid notch of the mandible to run within the substance of the masseter muscle and can consistently be found in a triangle formed by the zygomatic arch, mandibular condyle and frontal branch of the facial nerve. ² The masseteric nerve can be transected distally enough to reliably reach individual branches of the facial nerve for direct neural coaptation without the need for an interposition graft. Typically the largest buccal branch of the facial nerve that drives smile production is targeted for coaptation with the masseteric nerve, in some cases this selection can be aided intraoperative by direct electrical stimulation of the facial nerve branches. This targeted nerve transfer focuses all the axons of the masseteric nerve toward smile production and limits the development of synkinesis and mass movement that can be seen with coaptation to the main facial nerve trunk. Once neural ingrowth is complete, a smile can be produced when the patient clenches his or her jaw. The resulting smile can have quite strong excursion and with training can become very natural for patients to produce without consciously biting down, although it is never truly spontaneous. There is little to no morbidity or functional deficit seen with sacrifice of the masseteric nerve.

When denervation exists for a period of over two years, there is considerable motor endplate fibrosis that occurs and re-innervation via nerve grafting or nerve transfer is much less successful. In these cases, smile restoration is best accomplished via dynamic muscle or tendon transfer. Temporalis muscle transfer has been utilized for facial reanimation for decades, but more recently has undergone progressive changes and is now accomplished through a less invasive, orthodromic, temporalis tendon transfer without need for muscle mobilization. ³ In this procedure, the temporalis tendon is released from the mandibular ramus and mobilized along with the coronoid process. This can be accomplished via an intraoral incision or a direct incision in the nasolabial fold. Once mobilized, the tendon is transposed to dynamically suspend the oral commissure and inset directly with sutures or with an intervening fascia lata extension depending on available reach. The location of inset can be optimized intraoperatively with direct stimulation of the temporalis muscle to assure optimal tension of the muscle tendon unit. ⁴ This procedure allows for suspension of the paralyzed oral commissure along with a method of immediate dynamic movement produced with jaw clench.  Post surgical re-training is very beneficial to allow patients to achieve a more natural smile without the need to consciously clench the jaw.