The placement of standard jaw angle implants or a custom wrap around jawline implant requires elevation of the masseter muscle and some or all of its ligamentous attachments. The goal is to elevate the muscle to fit the implant underneath while not losing its periosteal attachments along the inferior border and around the angle area. This is not as easy as its sounds and is a highly technical maneuver that is harder too accomplish in some patients than others (e.g., females elevated easier than males) as well as with certain styles of jaw angle implants. (vertical lengthening vs widening implants)
While successful in the majority of patients there are a certain percentage of patients in which the periostea attachments is lost and the muscle retracts superiorly over the implant as it heals. This is known as masseteric muscle dehiscence. While the loss of muscle length has no functional significance it does create a cosmetic soft tissue contour discrepancy between the location of the muscle bulge when chewing/clenching and the inferior location of the implant.
While there are various methods of surgically treating masseteric muscle dehiscence of varying effectiveness, the non-surgical options are to either add soft tissue volume over the implant (fillers or fat) or to decrease the abnormally high bulge of the muscle. (Botox injections) Each has their advantages and disadvantages and in some cases the combination of both mango be the most effective.
When performing Botox injections, which are not rare for the masseter muscle, it is important to recognize that there are anatomic differences and risks between injections for muscle size reduction over a normally placed muscle vs that of one that is torn and retracted. Botox injections for a normally positioned masseter muscle for size reduction has no risk of causing temporary facial nerve weakness as the jaw angle area is devoid of facial nerve branches. But in the higher positioned muscle it lies directly in the area where the buccal facial nerve branches run. The difference is why I call the facial equator which is a line that runs from the corner of the mouth to the attachment of the earlobe. Below this line there are no nerves while above it there are. Also above this line lies the main body of the parotid gland which is over the sideburn and non-beard area on front of the ear.
When injecting the high masseter muscle bulge it is imrportant to go deep using at least a 1″ 30 gauge needle.There is no danger in going too deep. only it being too superficial where the nerve branches may inadvertently be affected. The muscle bulge will always be in front of the parotid gland so it being effected its not usually an issue. The needle should be placed deep enough that the hub is near the skin before injecting. The muscle can usually be felt as it will feel ‘gritty’ as opposed so soft like fat. The usual dose would be 25 units per side.
The usual response time for the effects to be seen is 2 to 3 weeks before muscle reduction may start to be seen. Full effects will be seen in 4 to 6 weeks. The duration of the effects is 3 to 4 months before muscle size reappears.
Dr. Barry Eppley
World-Renowned Plastic Surgeon