Smile surgery or smile reconstruction is a surgical procedure that restores the smile for people with facial nerve paralysis. Facial nerve paralysis is a relatively common condition with a yearly incidence of 0.25% leading to function loss of the mimic muscles. The facial nerve gives off several branches in the face. If one or more facial nerve branches are paralysed, the corresponding mimetic muscles lose their ability to contract. This may lead to several symptoms such as incomplete eye closure with or without exposure keratitis, oral incompetence, poor articulation, dental caries, drooling, and a low self-esteem. This is because the different branches innervate the frontalis muscle, orbicularis oculi and oris muscles, lip elevators and depressors, and the platysma. The elevators of the upper lip and corner of the mouth are innervated by the zygomatic and buccal branches. When these branches are paralysed, there is an inability to create a symmetric smile. Smile surgery is performed as a static or dynamic reconstruction. An example of static reconstruction is upper and lower lip shortening or thickening with commissure preservation. Dynamic smile reconstruction procedures restore the facial nerve activity.
Historical background The first known surgical repair of an injured facial nerve was performed by Drobnick in 1879, who connected the proximal spinal accessory nerve (innervates trapezius and sternocleidomastoid muscles) to the paralysed facial nerve. More symmetrical features were the result. In 1971 a new technique for facial nerve reconstruction was introduced, as Scaramella and Smith reported on the technique of cross facial nerve grafting (CFNG) for reconstruction of a coordinated smile in unilateral facial paralysis cases. Harii et al. for the first time used a free muscle transfer in combination with a nerve transfer in 1976. Eight years later, Terzis introduced the "babysitter" procedure, which consists of a combination of CFNGs and a simultaneous partial hypoglossal to facial nerve transfer. In 1989, Zuker et al. suggested the use of the masseteric nerve as possible donor nerve for innervation of the transplanted muscle in patients with Moebius syndrome.
Indications The main indications for dynamic smile reconstruction are unilateral or bilateral facial paralysis due to acquired and congenital causes. Trauma, Bell's palsy and tumour extirpation are examples of secondary or acquired facial paralysis. Bell's palsy or idiopathic facial paralysis is a condition which leads to facial paralysis, however, without a known cause. It has an acute onset and is mostly self-limiting. But if spontaneous recurrence of (near) normal function does not take place, surgical reanimation may be indicated. Some head and neck tumours invade or compress the facial nerve leading to facial paresis or paralysis. Examples of such tumours are facial neuromas, cholesteatomas, hemangiomas, acoustic neuromas, parotid gland neoplasms or metastases. Sometimes, the facial nerve cannot be preserved during resection of these tumours. Congenital facial paralysis occurs usually unilaterally and may be complete or incomplete. The most common congenital cause is the Moebius syndrome. Moebius syndrome is a congenital neurological disorder with bilateral paralysis of both the facial and abducens nerves. Therefore, lateral eye movement and facial animation are absent. In Moebius-like syndrome, only one side of the face is affected, but with additional nerve palsies of the affected facial and abducens nerve.
Surgical techniques
Selection of the type of nerve transfer is based on the individualised needs and condition of the patient. Individual factors can be patient age, type of paralysis (partial or complete, uni- or bilateral), denervation time of the mimetic muscles, availability of nerve grafts and medical condition of the patient. If facial paralysis is caused by trauma or tumour surgery, direct reinnervation of the facial muscles (ideally within 72 hours after facial nerve damage) can be achieved by neurorrhaphy, with or without an interposition nerve graft. (Algorithm 1) Neurorrhaphy is a primary end-to-end reconnection of the facial nerve stumps. However, tension-free reconnection is needed, otherwise scar formation can occur and axons will regenerate outside the facial nerve. If a tension-free reconnection is not possible, interposition nerve grafts are an option. Mostly the great auricular nerve or sural nerve is used as a graft between the two facial nerve stumps.
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