Expressing a smile is one of the most natural and important of human emotions, but the slight asymmetry or weakness about the lip may impose a severe psychologic burden and restrict the personal relations and social life.
Damage to the mandibular branch of facial nerve may be encountered following direct iniury or parotid surgery, radial neck dissection, rhytidectomy and tumor of the surrounding muscles, Bell´s palsy, ctc, and result in a drooping of corner of mounth and pull up, flattening and inward rotation of lower lip when a patient smiles. Although there are considerable literatures on the treatment of facial paralysis, there is little specific information on the management of paralysis of the marginal mandibular branch. Section of mandibular branch of opposite facial nerve or myotomy of ipsilateral elevator group may achieve some increase in lip symmetry but they produce unpleasent results such as mask like appearance and difficulty in pronouncing labial consonants. The plication of orbicularis oris muscle or the wedge resection do not provide a natural apperance during smile because they use the paralysed muscle. But the transfer of anterior belly of digastric muscle can provide not only acceptable balance at rest, but also a relative degree of symmetry upon smiling and opening the mouth. In addition, operative technique is simple. So the transfer of anterior belly of digastric muscle is excellent method of treatment for the unilateral paralysis of lower lip.
We treated two cases of unilateral pralysis of lower lip by transfer of anterior belly of digastric muscle and obtained a satisfactory results. We report them with review of articles.
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