Answer:
Anatomic studies have shown that the SMAS layer becomes thin and attenuated as it crosses the nasolabial fold but nevertheless connects with the superficial portion of the orbicularis oris muscle on the upper lip. This anchoring effect of the upper lip muscle on the SMAS means that lateral traction on the SMAS in the medial cheek has little effect on the overlying skin and may actually deepen the fold. Therefore, it is recommended that after performing the initial dissection deep to the SMAS layer, once the area of the medial cheek is reached just lateral to the nasolabial fold, the dissection should then become more superficial, breaking through the fascia to continue medially in the subcutaneous plane. Traction on such a flap will be transmitted more directly to the medial cheek skin and consequently result in a smoothing of the nasolabial fold.