Page 100 - Read Online

Page 4 of 14 Gossett et al. Plast Aesthet Res 2021;8:60 https://dx.doi.org/10.20517/2347-9264.2021.69

have an additional lag time between the first stage and second stage, when the GFMT is actually performed.

The main disadvantage to utilizing the masseteric nerve is its lack of spontaneity and synchronicity with the
unaffected side of the face when smiling. Under normal circumstances, the activation of facial muscles to
create an emotive smile is generally involuntary and spontaneous. However, in cases of GFMT powered by a
masseteric nerve, smiling is typically achieved by voluntarily clenching one’s jaw on the affected side, which
stimulates muscle contraction. As a result, when an emotive smile is involuntarily elicited on the unaffected
side, in response to humor, for instance, achieving a natural-appearing smile on the GFMT side to match
synchronously can be challenging and requires training and effort. Several studies have shown that patients
undergoing facial reanimation with the masseteric nerve can develop a spontaneous appearing smile with
[9]
motor re-education [9,19] . Manktelow et al. reported 45 GFMTs innervated by the masseteric nerve in adults
and found that 89% of patients reported achieving a spontaneous smile. However, only 37% of these patients
reported a spontaneous smile a majority of the time. When they divided their cohort into younger patients
(age 16-32) and older patients (age 34-61), they did not find a significant difference (64% of the younger
cohort routinely achieved a spontaneous smile compared to 54% of the older cohort) . Hontanilla and
[9]
[19]
Cabello reported 36 GFMTs innervated by the masseteric nerve and found that 55.6% were able to achieve
spontaneity, with a larger percentage of women achieving spontaneity (70.6%) compared to men (42.1%).

One explanation for the development of spontaneity in GFMT with masseteric nerve innervation as
opposed to other non-facial cranial nerves is that the masseteric nerve is commonly activated during a
normal smile; EMG activation of the masseter muscle is seen in 40% of healthy individuals during smile
[27]
production . Additionally, the cortical areas responsible for chewing and smiling are in very close
proximity. Buendia et al. assessed patients who underwent facial reanimation using masseteric nerve and
[28]
demonstrated overlap on functional MRI in the smile and jaw-clench areas of the motor cortex.

It is difficult to evaluate spontaneity in a smile, and a majority of studies rely on patient reports or clinician
evaluations. Some clinicians advocate a “tickle test” to stimulate a spontaneous smile and evaluate symmetry
in the office. To better evaluate the spontaneity in a smile, Dusseldorp et al. created the Spontaneous
[14]
Smile Assay (SSA), in which video clips are obtained from patients viewing humorous video clips and rated
by blinded observers for symmetry and spontaneity. Using this SSA assay to compare the spontaneity of
smile in GFMT innervated by masseteric nerve, CFNG, or both, 20% of GFMT innervated by masseteric
[14]
nerve were deemed spontaneous, compared to 75% for CFNG and 33% for dual innervation . Interestingly,
spontaneity was underestimated by clinician ratings in this study. When the SSA was compared to clinician
ratings in the office, spontaneity was rated as absent in 40% of patients and trace in 33.3% of patients who
were noted to have spontaneous smiles on the SSA, highlighting the challenges in evaluating spontaneity in
smiles.

CROSS FACIAL NERVE GRAFT
[29]
[30]
CFNG was first described by Scaramella and Smith in 1971. The original technique, in which a sural
nerve graft was coapted between facial nerves on the unaffected and paralyzed sides of the face, produced
limited facial movement. It was not popularized until 1976 when Harii modified the procedure by coapting
[2]
the nerve graft to a GFMT in a two-stage procedure . The primary advantage of the two-stage technique is
that time is allowed for axonal growth to occur through the CFNG prior to GFMT, such that viable axons
have reached the free distal end of the nerve graft by the time of coaptation. This leads to less time to
innervation of the GFMT and reduced wasting from denervation atrophy.