**4. Discussion**

Although the most common choice is use of gracilis muscle in reanimation of smiling muscles in facial paralysis [3], free muscle transfers such as serratus anterior muscle, latissimus dorsi muscle, extensor digitorum brevis muscle, and pedicled muscle transfers such as temporalis muscle transfers have been used.

In free muscle transfers, the contralateral facial nerve with use of nerve grafts, ipsilateral hypoglossal nerve (12th Cranial Nerve (CN)), ipsilateral accessory nerve

### *Reanimation of Mouth Corner with Free Gracilis Muscle Flap DOI: http://dx.doi.org/10.5772/intechopen.105909*

(11th CN), or the ipsilateral masseter nerve, which is one of the motor branches of fifth CN, can be used as the recipient nerves. In the cases where the contralateral facial nerve is used as the recipient nerve, when an impulse is generated toward the contralateral side, it passes on the nerve graft and causes contraction of the transferred muscle, which in the end causes a "spontaneous smile" on the effected side. This situation is not possible in cases where other cranial nerves except facial nerve on the same side are used as the recipient nerve. In the beginning of cases, which are used CV as recipient nerve, in order to generate smiling function on the operated side, the patient needs to think of an action, which will cause their chewing muscles to work. In the studies carried out, it has been shown that masticatory center and smiling center in the brain are located close to each other and with certain exercises accessory neural pathways will be generated between these two centers [4]. Therefore, it has been stated that smiling function will be performed with use of these pathways when patients want to smile. Some studies state that simultaneous stimulation of masticatory center causes action on transferred muscle to generate smiling action, during the stimulation of the smiling center. It has been stated that success of the operation is increased with younger patient. When transfer to the masseter nerve operations is performed on patients who were in childhood, spontaneous smiling is achieved at advanced ages approximately 80% of the patients, compared with 50–80% of the patients when the operation is done in older ages [5, 6]. There are important exercises that the patient and the physiotherapist need to perform in order the neural pathways to be created. Patients are advised to smile constantly in their social lives. This includes daily life advices from greeting everyone in the most appropriate way to social lives, to trying to use every opportunity throughout the day to smile. Patients are advised to watch a comedy movie on alternate days. Furthermore, one of the most important practices is exercises to be done in front of a mirror. The goal of these exercises is to increase patients' comprehension of the traction strength on the transferred side during smiling and to equalize their smile with the contralateral side. Therefore, patients are going to make their brains learn the traction power of the transferred muscle, and they are going to equalize the strength on both sides of their face during smiling. To start these exercises, it is necessary to wait until the maximum traction strength of the transferred muscle is achieved and revision operations regarding muscle traction and tension are completed. On my cases, I start external electrical stimulus by using TENS devices when patients feel the first contraction on the transferred muscle, although a clinically visible contraction has not been achieved. I suggest these external stimuli are given in 20 minute sessions every 3 hours. Therefore, I believe that the number of new neuromuscular junctions is increased and direct muscle stimulation is provided during muscle innervation period, which prevents muscle atrophy. There is a direct proportion between the number of neurons in the recipient nerve and contraction strength of transferred muscle. With increased number of neurons in the recipient nerve, the number of neurons, which reach the transferred muscle and cause contraction, is increased. In valuable studies carried out, it is stated that buccal branch of the facial nerve contains approximately 834+/−285 neurons. When these neurons are used at the paralyzed side with a sural nerve graft, the axons budded from the recipient nerve need to pass through two nerve coaptation sites through the nerve graft. In studies carried out, number of the neurons of buccal nerve is observed to be around 100–200 after these neurons pass through the nerve graft and reach the transferred muscle. This situation is because number of neurons of the recipient nerve is few and because neurons pass through two coaptation sites. The branch of the masseter nerve that is used as

the recipient nerve contains 1542+/−291 neurons [2, 7], which is much greater than buccal branch of the facial nerve. Other benefit of using the masseter nerve is, since neurons are going to pass through a single nerve coaptation site, the decrease in the number of neurons that reach the transferred muscle is going to be less compared with when buccal branch is used as the recipient nerve. In a study, it is shown that the number of neurons pass to the obturatory nerve from masseter nerve is 10–15 times greater than the neurons pass through sural nerve graft. In my clinical practice, in the beginning I used buccal branches as the recipient nerves. However, because I observed muscle traction strength was fairly weak and because a second session was needed, I have started to transfer partial thickness gracilis muscle to the masseter nerve as the recipient nerve with a single session operation. The second frequent complaint of patients who had free muscle transfer is the unaesthetic view of the patients' faces during contraction caused by excessive swelling, following the most common complaints, which are about traction strength [8]. This is the reason during removal of the flap from donor site, I use 1/3–2/3 of the muscle according to entrance site of the pedicle8. I use straight intestinal staplers to remove the muscle flap to be transferred from the main muscle. Therefore, ends of the muscle flap stay together preventing separation of fibers at the ends of the flap. These titanium staplers facilitate fixation of proximal end of the flap to zygomatic arch and by preventing fibers from scattering staplers facilitate division of the distal end to three parts, one for upper lip, one for lower lip, and one for mouth corner. Therefore, fixation of muscle fibers to sides of lips and mouth corner, which is among the most important parts of the operation, can easily be done with the help of staplers. I suggest that if a flap thinning operation is being planned, it should be performed at late stages after the operation. Because I believe in the long terms if the muscle is fixated to the recipient site properly and soundly, it adapts well and a thinning operation is not going to be necessary. I believe that most of the permanent swellings during muscle contraction are caused by poor fixation of the muscle to lip corner or to the zygomatic arch or detachment of the muscle from fixation sites because of poor wound healing or weak adhesion of the muscle. However, if none of the problems stated above exists and swelling during contraction is observable, a thinning operation to the nearest parts of the muscle to the skin can be performed very carefully. It has to be kept in mind that as a result of a careless procedure, contractions of the transferred muscle can be totally lost.
