What the injection weakens, and what it does not touch
- Botox for bruxism weakens the muscle that clenches the teeth, and it does not reach the mechanism that makes it clench. It does not replace establishing the form of bruxism, nor the protection of the teeth that an occlusal splint provides.
- One thing is measured and reproducible: a fall in bite force and a reduction in the thickness of the masseter, both of them passing off within a few months.
- The effect on bruxism itself, that is on the number of clenching and grinding episodes, remains unresolved; reviews of the research call the evidence conflicting.
- In bruxism the procedure is an off-label use, that is use outside the approved indications of the preparation, and there is no established protocol: the doses described differ several-fold.
- The procedure has described adverse effects, among them mild discomfort on chewing in close to four patients out of five in one study, and thinning of the outer, hard layer of the bone of the mandible.
“A friend of mine had the injections and says she has stopped grinding. Does it really work?” That question comes up more and more often, usually with before-and-after photographs of the face on the patient's phone.
The photograph, though, shows a muscle, and the patient is usually asking about grinding. Separate those two different things and the rest of the answer arranges itself. This text concerns the injection into the masseter alone: how to recognise the form of bruxism and how to select a protective device we have described separately.
What botulinum toxin does in the masseter muscle
Botox in the masseter, that is botulinum toxin type A delivered into that muscle, partially and reversibly weakens it. In the studies the effect was clear for about three months, and after six it stopped being significant. It has not been shown, on the other hand, that the procedure touches the central mechanism which triggers bruxism.
The masseter is a thick muscle running from the zygomatic arch to the angle of the mandible; you can feel it under your fingers when you clench your teeth. In it the toxin blocks the release of acetylcholine, the transmitter by which the nerve tells the muscle to contract. The signal from the brain still arises and still reaches the nerve ending. Beyond that it no longer passes.
The muscle weakens, but it is not paralysed. Chewing is possible, though it can be less efficient. And a weakened muscle that the patient uses less often shrinks as well, in the same way as any other muscle that stops working. It is precisely this loss of volume that is visible in the before-and-after photographs of the face which patients exchange between themselves. Strength does not come back in a single moment but over weeks, and a slimmer outline of the face can still be visible when the muscle has already regained its capacity.
The procedure changes one thing: how much force the muscle is able to generate. It does not touch the signal that flows to the muscle, nor the reason why that signal arises during sleep or in the tension of the day.
What botox for bruxism actually works on
Bite force. In a one-year study with a comparison group, twenty people were given 25 units of the preparation into each masseter, 50 units in total. A unit is a conventional measure of the activity of the preparation. It corresponds neither to volume nor to milligrams, and it does not convert between the products of different manufacturers. Maximum voluntary bite force fell significantly and stayed reduced for three months; after six the difference stopped being significant. The study, however, covered people presenting for an aesthetic procedure, not patients with diagnosed bruxism, and they were not allocated to the groups at random, so the result is weaker evidence than in studies which randomise.
Muscle thickness. A study with random allocation to groups covered forty-eight people with bruxism and masseter hypertrophy, and the thickness of the muscle measured by ultrasound decreased in them after a month, with the difference persisting at three months. The participants were mostly women, on average thirty years old, admitted to the study on the basis of tooth wear, pain on chewing and morning stiffness of the temporomandibular joint, that is the joint of the jaw. After six months the values in all the groups levelled out.
Muscle pain (disputed evidence). A meta-analysis of fifteen studies with random allocation to groups, covering 504 participants in total, showed that after the toxin pain fell more than after placebo by about two points on a scale from zero to ten, both at one month and at six months. Those works concerned the muscular form of temporomandibular disorders, that is pain in the muscles of mastication, and not bruxism as such. In promotional materials that distinction is sometimes blurred.
That leaves headache - and it is with headache that the patient with bruxism often comes in. The works cited measured pain in the muscles of mastication. Headache was not an endpoint of their own in them, that is a separately measured outcome. In the study comparing the toxin with biofeedback, that is with training in relaxing the muscles while watching them work, it was diagnosed in twenty-five of the forty participants, but no one checked whether the procedure changes it.
What the procedure does not change
No effect on bruxism activity itself has been demonstrated. A systematic review gathered only studies measuring the electrical recording of the muscle or bite force, found four such works, and concluded that the available evidence is inconclusive. Studies with measurement during sleep did not show that the episodes became fewer; only the force of clenching performed on command decreased. In a study with random allocation to groups, comparing the toxin with biofeedback training in people with a painful temporomandibular disorder and frequent awake bruxism, the number of bruxism behaviours fell in the exercising group, and in the group after the injections it did not change at any of the three follow-up measurements. The dose given there was lower than the one typically used, and the authors list this among the limitations. When, however, the two groups were compared directly, no difference was demonstrated. The brain still tells the jaw to clench.
The brain still tells the jaw to clench.
The teeth still meet, only with less force.
In conversations with patients presenting to Modern Dental & Orthodontics (Klinika MDO), the question about before-and-after photographs of the face keeps returning, photographs taken with neither the form of bruxism established nor the teeth examined. The order is reversed in such cases: the decision about the procedure is taken before a diagnosis which the procedure will not replace in any case.
Damage that has already occurred is not undone by the injection. Worn cusps and cracks in the enamel stay where they were; repairing them belongs to prosthetic restoration with crowns and veneers, not to an injection. Whether the procedure protects the teeth against further wear remains an open question, because in the works cited the wear of the tissues was not an endpoint. The cautious conclusion therefore runs like this: less force probably means less loading, but there is no study which would confirm it. It is the splint that wears away instead of the teeth. Both methods stand side by side in the table below.
Botox or an occlusal splint - what each method actually does
| Botulinum toxin | Occlusal splint | Certainty of the evidence for the toxin | |
|---|---|---|---|
| Point of action | The muscle, that is the executor | The surface of the teeth, that is the site of the damage | Established |
| What it changes | The force of contraction and the thickness of the muscle | The distribution of forces and the contact of tooth with tooth | Established |
| Effect on pain in the muscles of mastication | The results of studies diverge | Comparable relief in a direct comparison with the toxin | Disputed |
| Effect on the number of episodes | Unresolved | Unresolved in the studies cited | Unresolved |
| Protection of the tissues of the tooth | Not measured in the studies cited | Direct; the material wears away | No one has measured it |
| Duration of action | A few months, then a return | For as long as the device is worn | Established |
| Reversibility | The effect on the muscle passes off; no one has followed the consequences of repeated administrations for bone | Full, after discontinuation | Established for the muscle |
Neither the toxin nor the splint is a causal treatment for bruxism. The splint protects against the consequence, the toxin weakens the tool. The cause, that is the mechanism which sets clenching in motion, is touched by neither of them. One row of this table is moreover not symmetrical, and it is that row which decides the most. “Protection of the tissues of the tooth” on the side of the splint means something literal. On the side of the toxin it does not mean “no protection”, but no one has measured it, because no work took the wear of the teeth as an endpoint.
Those are two different kinds of empty space.
Four groups at once were compared by one study: no treatment, a splint, an injection, and both of these together. A splint added to the injection gave nothing beyond the injection alone, and in the first months it was the injection that reduced the thickness of the masseter more clearly than the splint alone. That is one study and one endpoint, so it does not close the question of combining the two methods.
Work on the contributing factors and on the habit itself is a separate part of the plan, different for the sleep form than for the awake form. In the awake form it consists in catching the moments of clenching and relaxing the jaw during the day; in the study with biofeedback it was precisely the exercising group that reduced the frequency of bruxism behaviours. In the sleep form the consensus links stress, mood, caffeine, alcohol and smoking with evidence of moderate strength.
Botox for bruxism: what is established, what is disputed and what remains unresolved
Established. Botulinum toxin type A reversibly weakens the masseter and reduces its thickness; this is a pharmacological effect, reproducible across several independent works.
Disputed. The effect of the injection on pain in the muscles of mastication is described divergently across the studies. The meta-analysis comes out in favour of the procedure, but a study with random allocation to groups, in which it was compared directly with a splint in fifty-nine people with probable sleep bruxism, showed no advantage of either method in reducing pain. In that same study the group after the injections came out worse on the assessment of the function of the jaw and on the range of mouth opening. Those two results are not equivalent. The meta-analysis measured the advantage of the procedure over placebo. It answered, therefore, the question of whether it works better than nothing. The study with fifty-nine people compared it with a splint, that is with a method in actual use, so it answered the question of whether it is worth choosing instead of one. The first question is the easier one, and the answer to it comes out more favourably.
Unresolved. It is not known whether the procedure changes bruxism itself, whether it protects the teeth, and whether administrations repeated over years are safe. The consensus statement of the prosthodontic society from 2021 describes the evidence for botulinum toxin outright as conflicting, and it recalls that there is no established method of curing bruxism. The same document notes that there is also no agreement as to which symptoms of bruxism require treatment at all. Without such a threshold every assessment of effectiveness measures something different - botox for bruxism is assessed once by pain, once by the appearance of the face, once by the recording of the muscle at work.
Practice diverges here from the literature. To a survey sent out to 906 German oral and maxillofacial surgeons, 107 replied. Among those who use the procedure, six in ten regarded it as an evidence-based method, and almost all declared themselves ready to recommend it to colleagues. With a response rate that low it is hard to rule out that those replying were mainly the ones who use the method. The survey measures the convictions of the profession, not effectiveness.
For the patient this means one thing: the conviction with which she hears about this procedure in the surgery says nothing about the strength of the evidence standing behind it.
Botox in bruxism: side effects and the limits of the method
The commonest side effects of botox in the masseter are mild and passing: soreness at the site of the injection, a sense of weakness when biting hard foods, transient asymmetry of the smile when the injection is placed too superficially. In the study comparing the procedure with a splint, mild discomfort during chewing was reported by twenty-three out of twenty-nine patients, that is close to four in five.
Bone stands apart. A meta-analysis of works in humans and in animals showed in humans a thinning of the outer, hard layer of the bone of the mandible, that is of the cortical layer, by about six per cent after administration of the toxin. The volume and the density of the bone remained without appreciable change. In animals the loss was more pronounced and took in the region of the condylar process, that is the part of the mandible which forms the temporomandibular joint. What this change means for the strength of the bone is not known: the work measured cortical bone thickness, bone volume and bone density. The authors note that most of the works did not take into account the realities of repeated injections or of inflated doses. The mechanism of the change has not been established; the simplest explanation says that a muscle which does not work stops loading the bone to which it attaches. A single administration in an adult is a different situation from series repeated every few months over many years, and it is precisely such series that are the rule in this indication.
No one has established a protocol either. One review describes a symptomatic effect at doses below 25 units given into the masseters alone, the meta-analysis on muscle pain points to 60 to 100 units bilaterally as the more favourable range, and the German surgeons administered on average 29 units per side. The works report the dose once as a total for both sides, once per one side - and that alone makes them harder to compare. The spread is several-fold - and use in bruxism is still an off-label use. The practical conclusion for the patient is a single one: the dose and the number of injection sites do not follow from a guideline but from the decision of the person performing the procedure. That is a question worth asking before administration, together with the question of how many administrations are planned over the course of a year.
Who may consider the procedure, and who rather not
A sensible candidate is a person with marked masseter hypertrophy in the course of bruxism and persisting muscle pain, in whom a splint and work on the habit have been tried and did not suffice. The procedure is then sometimes a supplement to the plan.
Administration of the toxin into the masseters must be held off in several situations, and some of them are absolute contraindications:
- diseases of the neuromuscular junction, for example myasthenia, and treatment with aminoglycoside antibiotics;
- pregnancy and breastfeeding;
- hypersensitivity to botulinum toxin or to the components of the preparation;
- infection of the skin at the site of the planned injection;
- the expectation that the procedure will stop the grinding or replace protection of the teeth.
Every medicine being taken and every chronic illness must be reported to the doctor who qualifies the patient for the procedure.
Ask outright, too, who performs the procedure. Administration into the masseter calls for knowledge of the anatomy of the muscles of mastication and of the right depth of the injection: nearer the surface lie the muscles of facial expression, and it is their accidental weakening that gives transient asymmetry of the smile. Qualification calls for a clinical examination, for establishing the form of bruxism and for examining the teeth - none of these things can be done from a photograph of the face.
Botox for bruxism is sometimes proposed as a first step, though in the order of management it stands far behind diagnosis and behind protection of the teeth.
Frequently asked questions
How long does the effect of the procedure last?
A clear fall in bite force lasted about three months, and after six the difference stopped being significant; with the thickness of the muscle the same thing happened. Slimmer features of the face are sometimes perceived as more lasting than the measured effect, because volume comes back more slowly than strength does. The return is a process, not a moment.
Does the procedure have to be repeated, and how often?
The effect is transient by its nature, so maintaining it calls for repetitions, usually every few months, and the intervals have not been established by anyone in studies, because there is no protocol for this indication. The safety of repeated administrations over years remains poorly investigated, particularly as regards the bone of the mandible.
Is the effect weaker with each successive procedure?
It is not known. None of the works cited measured the response to successive administrations, and the authors of the meta-analysis concerning bone write outright that most of the studies did not take into account the realities of repeated injections or of inflated doses. The absence of an answer is here an answer in itself: in planning a series of administrations, no one is relying on data from studies.
Does botox for bruxism replace an occlusal splint?
It does not replace it. A splint separates the teeth and takes over the wear, which the injection does not do in any degree. In the comparative study both methods gave comparable relief in pain, but the function of the jaw and the range of mouth opening improved more clearly after the splint. Protection of the tissues of the tooth remains the task of the device.
What can be seen in before-and-after photographs, and what cannot?
What can be seen is a narrower lower part of the face, because a weakened masseter loses volume, and that is sometimes the aim of the procedure rather than a side effect of it; about grinding, on the other hand, the photograph says nothing, because it measures a muscle and not the number of clenching episodes. The change is transient and it recedes together with the return of the muscle's strength. Where administration is asymmetrical or too superficial, transient asymmetry of the smile may appear.
What happens when I stop repeating the procedure?
The strength of the muscle and its volume come back to the state from before the procedure, and the studies do not describe them deteriorating below the starting point. The bone of the mandible, however, is another story, described in the section on adverse effects. Bruxism went on uninterrupted throughout all that time. The procedure was not treating it. What comes back, then, is exactly the same problem the patient arrived with, together with the full force of clenching.
Is it safe with crowns, veneers and implants?
The toxin itself does not act on the materials of a restoration or on an implant, and reduced bite force is sometimes described as favourable for prosthetic work. Studies measuring the durability of crowns and veneers after the procedure are, however, lacking. That is an expectation, not a result. Where a restoration is planned, the order is settled by the doctor conducting the prosthetic treatment.
Does the procedure hurt, and how long does it take?
Administration takes a dozen or so minutes and consists of several injections into each masseter, usually without anaesthesia. The sensation is sometimes compared to the prick of having blood taken. Soreness and tenderness of the area usually pass off within a few days. The weakening of the muscle is not felt at once: it builds up gradually over the first weeks.
The injection works on the muscle, not on the habit
Botox for bruxism weakens the tool with which the patient destroys their own teeth, and it does so effectively and reversibly. It touches neither the mechanism which sets clenching in motion nor the damage already done, and its effect on the number of episodes remains unresolved to this day. The sensible order is therefore a fixed one: first establishing the form of bruxism, then protection of the teeth and work on the contributing factors, and only at the end, where muscle pain persists, a conversation about the injection as a supplement.
Read more:
- Modern Dental Prosthetics in Warsaw
- Night guard types — hard, soft or repositioning splint. How the type is selected
- Bruxism - symptoms: eight signs your dentist spots before you do
- Teeth grinding at night or clenching during the day — two different problems, two different treatments
Content and liability disclaimer
This article is informational and educational in nature and does not constitute medical advice, a diagnosis or a therapeutic recommendation — it does not replace a consultation with a specialist. If you are experiencing symptoms, have doubts or are facing a decision about treatment, consult a dentist. The methods described and the data cited are general in nature. The results of scientific studies relate to populations, not to an individual patient. The course and outcome of therapy depend on the individual clinical situation and may vary between patients. No information contained in this article constitutes a guarantee of result. The content has been prepared with due care, based on publicly available medical knowledge and the scientific publications indicated in the Sources section. We do not advise taking or refraining from any health-related action solely on the basis of the content of this article, without prior consultation with a doctor.
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