Ask how long masseter Botox lasts and you'll usually be handed one figure, and one figure is the wrong shape of answer for this particular muscle. The jaw gives the question two answers, and the second is the one nearly everyone forgets to ask about.
Why the jaw answers this question twice
Masseter Botox® is an anti-wrinkle injection placed into the muscle you clench with, the thick pad at the corner of your jaw, rather than into a line on your forehead. How it takes the power out of a clench has a piece of its own. What matters here is that it hands you two separate changes. The clenching eases, and the morning ache goes with it. And a muscle that has stopped working all night gradually settles toward its natural size, so if years of grinding had squared off the corners of your face, those corners soften.
Those are two different things, and they don't keep the same time.
Think of a small milk pan and a big stockpot on the same hob. Turn both rings off together and the milk pan is cool enough to wash up by the time you've cleared the table, while the stockpot is still too hot to touch an hour later, because there's a great deal more in it holding the heat. Turn both rings back on and the same thing happens in reverse. The little pan is up in a minute, and the stockpot takes an age to come back to the boil.
A forehead muscle is the milk pan. It's small, and what it does to the skin above it follows the nerve signal fairly closely in both directions, which is why how long Botox lasts in general can be answered by the four things that decide that signal's timetable, and we won't go over those again here. The masseter is the stockpot. It's a big working muscle, for its size one of the strongest you own, and the bulk that clenching has built into it is the heat in the pot. Quieten the signal and the bulk doesn't vanish. It drains away slowly, over weeks, as the muscle rests. Let the signal return and the bulk doesn't spring back either. It has to be rebuilt, one night of clenching at a time.
So the honest answer comes in two parts. The relaxation lasts about as long as any anti-wrinkle treatment lasts, and the change in shape lasts longer, because it lags behind the signal at both ends.
How long the relaxation lasts
The easing of the clench is the part that arrives first, building over about ten days as the muscle properly relaxes, and it's the part that leaves first too.
Like any anti-wrinkle injection, it was never built to hold. The muscle steadily wins its strength back over the months that follow, and the clench returns with it if the habit is still there. People commonly report that stretch in months rather than weeks, and we'd rather not turn it into a figure on this page, for exactly the reason the general article gives: how long your muscle takes to win back its strength is a fact about your muscle, and nobody has felt it yet.
What's worth knowing is how it comes back, because it isn't in the mirror. The first sign is usually in the biting. There's a morning when the jaw feels tighter on waking than it has for a while, or a moment mid-afternoon when you catch your back teeth pressed together with the old force behind them. That's the signal returning and the clench getting its top end back. The ache tends to follow rather than lead, because the ache was always the result of a full night's work, and a muscle has to be back to full strength before it can put a full night in.
Why the slimming outlasts the relaxing
Here's where the stockpot earns its keep.
When the clench returns, it returns to a muscle that has spent months resting, and a rested muscle is smaller and weaker than the one you brought to your first appointment. So the shape of your jaw doesn't change on the day the signal comes back. The muscle has to be worked back up to its former size before the corners of your face square off again, and that's the same slow job that built it in the first place, only now starting from further back.
That's why the two things people notice sit so far apart. The clenching can be back for a good while before the jaw looks any different, and plenty of people arrive for a second round with the ache returning and the slimming still very much there. It isn't a trick and it isn't luck. It's what a large muscle does. The pot goes back on the ring having already gone cold.
We won't put a number on that either, because it depends on how much bulk your muscle had to lose in the first place, how hard and how often the clench comes back, and how much was placed, and every one of those belongs to you rather than to the syringe. What we can say plainly is the direction. The shape holds longer than the relaxation, and people commonly find it holds longer still with each round.
Why the gaps between rounds commonly grow
That last point deserves its own heading, because it's the thing people are most pleased to find out.
Each time the clench returns, it returns to a muscle that starts from lower than it did the time before. The first round meets a masseter at its fullest, built by years of nightly work. The second meets one that has spent months slimmer and weaker than that, and so on. So there's less muscle behind the clench when it comes back, and more ground for it to make up before it's back to the size that ached in the mornings. People commonly find their second stretch runs longer than their first, and that later rounds sit further apart than the early ones, and that's the plain reason behind it. The muscle isn't learning anything clever. The pot is simply colder each time the ring goes back on.
None of that makes the treatment permanent, and it doesn't touch why you clench in the first place; stress, sleep and habit carry on being themselves. What it means is that the sensible timing of your next round is a signal from your own jaw rather than a date on a wall chart, which is the principle how often you can have Botox sets out for the face generally.
If your grinding has been going on long enough to be given its medical name, bruxism, or you've been told your jaw joint itself is involved, say so at your consultation. Whether these injections are the right answer for you, or one part of it, is a judgement made by the person examining your jaw, and it's a straightforward thing to ask.
Masseter Botox aftercare: the jaw's own list
The first hours after any anti-wrinkle injection are about leaving what was placed exactly where it was placed until it's been taken up, and every rule that follows from that is written out, with the reason for each, in Botox aftercare. The instructions you were given on the day come first, wherever they differ from anything here. What belongs on this page is the part that's different because the muscle is the jaw.
Keep your hands off the corner of your jaw. On a forehead, rubbing is mostly a hand propping the brow while you read. The jaw is a far busier place. It's where a chin rests in a palm at a desk, where a phone gets clamped between ear and shoulder, where a cheek settles onto a fist on the sofa, and where a face lands on the pillow if you sleep on your side. Every one of those presses on the exact muscle during the exact hours it matters, so notice them for an afternoon and an early night, and then forget about them.
Go easy on chewing for the rest of the day. This is the one rule the forehead never needs. Chewing is the treated muscle at work, and a hard chew works it hard: crusty bread, a steak, a whole packet of chewing gum, the tough end of a toffee. The advice commonly given is to keep the first day's meals soft and let the muscle sit still, for the same reason you keep your hands off it. Tomorrow you eat what you like.
Don't massage it, even when it aches. Anyone who has had a sore jaw for years has usually taught themselves to knead it, often without noticing. Hold off through the first hours, and after that ask us before booking a facial or a jaw massage in the early weeks, because those work by pressing and moving the very area we've treated.
The rest of the ordinary list stands: upright rather than lying flat for the first hours, the hard session and the hot bath and the glass of wine left until tomorrow, and the little bumps at each point settling within the hour. None of that belongs to the jaw alone, which is why it lives on the other page.
The first weeks: when a crusty roll feels like work
There's one thing to expect in the weeks after the ten days, and it's better heard now than discovered over dinner.
Some people find their jaw tires sooner than it used to on hard or lengthy chewing. A bagel takes more out of them than it did, a tough steak wants a rest halfway through, a piece of gum gets given up early. It can be a surprise, so it's worth knowing what it is.
Think of a bike that's lost its climbing gear. On the flat you'd never know, because you never used that gear on the flat. On the one steep hill on your route you still get to the top, but it takes more out of your legs than it used to, and you feel it sooner. The injections take the top end off the clench, the force you were only ever using against your own teeth at night, and ordinary chewing never needed that end. What needs it is the hard stuff, so the hard stuff is where you notice, and a muscle asked to do a job without its strongest gear takes a little longer over it and tires a little sooner.
People commonly find this settles as the weeks go on and the jaw finds its new working range, and it doesn't stop anyone eating. If it isn't settling, or it's more than a tired jaw at the end of a chewy meal, ring us on 0161 526 2232 and describe it. We have a record of what was placed and where, which is what makes that a short call.
Bring both clocks to your review
We recommend a post-treatment appointment so we can look at your result together, and with this muscle there are two things to look at rather than one.
The first is the clench, which we can feel while you bite, and which by then will have eased or will not have. The second is the shape, and at the review it will barely have started, which is exactly why a masseter before and after is so easy to misread and worth taking properly. The two run on different clocks, and the review is where we check that both have been set going.
Arrange a consultation and bring the ache with you. We'll feel the muscle while you clench, tell you plainly whether it's built up or not, and explain what the injections would change about your jaw and what they wouldn't. Every treatment at Broadway Retreat is delivered by experienced medical professionals at our CQC-registered clinic on Broadway in Manchester, and nothing goes ahead until you decide.
Turn the rings off and the milk pan is cold before the washing-up is done. The stockpot is still warm at bedtime, and that, in the end, is the whole answer to how long masseter Botox lasts. The shape outlasts the signal that made it.