October 12, 2023

Dr Tim Pearce aesthetics expert BOTOX fillers

Having recently covered the best botulinum toxin or Botox® injection depths for the upper face, many aesthetic clinicians asked Dr Tim for more guidance on the lower face to avoid complications like a crooked smile. Some of the strangest side effects that you get from botulinum toxin treatments are related to injecting at the wrong depth; if you understand how the depth of your injections will affect the result, you can interpret and solve side effects much better.

In this blog, Dr Tim Pearce explains the injection depths you need to stay safe and create the best results when treating the lower face with botulinum toxin.

For a quick recap, learn facial muscle anatomy for Botox in 10 minutes with another great blog from Dr Tim.

How deeply should you inject Botox into the masseter muscles?

The crucial factor to understanding the depth of your injections when placing botulinum toxin is that it is a relative term. It is relative to the total size of the structures involved, therefore, in the case of the masseter muscle, a deep injection probably means having the needle tip in the lower third of the muscle, notes Dr Tim. But if it is a significantly large muscle, that will be a different depth compared to a very small muscle. Therefore, actual depth will vary, and you will need to gauge this by examining your patient. Every procedure you perform must be based on the patient in front of you and their anatomy, and not on a training guide or academic literature with a millimetre-by-millimetre depth for treating areas of the face.

lower face anatomyDr Tim’s advice is to examine the patient first – ask them to bite down to reveal their masseter muscle’s size and thickness as it is contracting. Then, you can aim to place the botulinum toxin into that muscle in the area that is least likely to cause undesirable side effects.

You should aim to inject deeper when treating the masseter muscle because the risorius originates from the surface of the masseter muscle and plugs into the modiolus as part of the function of the smile. If you inadvertently relax the risorius muscle, you will get an awful side effect where the patient cannot smile properly. Therefore, you want to place the botulinum toxin underneath the origin of the risorius muscle whilst relaxing as much of the masseter as possible. However, if you inject very deep, and there is a lot of contracting muscle on top of the masseter, it will result in a strange side effect that manifests as a bulge or protrusion at the side of the jaw as the surface fibres contract or pinch in an odd way without the balance normally created by the deeper fibres.

If you have a thinner muscle, you must be deeper. If you consider what we are trying to achieve in terms of safety, the aim is to avoid the surface of the muscle, whilst also trying to relax the bulk of the muscle, therefore there is a compromise. With a thinner muscle, you must be further away from the surface, or as far away as possible, which means in relation to the periosteum you are closer. It would be more appropriate to be nearer the bone in a very thin muscle than if you have a very thick muscle, where you may be further away, this is the concept of depth being relative.

Read more on how to avoid mistakes when injecting masseter muscles with Botox and avoid this Botox injection pattern when treating the masseter.

How deeply should you inject Botox into the DAO?

Treating the Depressor Anguli Oris or DAO is one of the most popular lower face treatments because it lifts the oral commission to make patients look happier. The DAO muscle is involved in pulling on the modiolus and depressing the mouth, therefore, if you relax it, you get the opposite effect.

The downside with this treatment comes when an aesthetic clinician inadvertently hits the depressor labii muscle which is next to and deep to the DAO. The depressor labii is an important muscle involved in smiling. When we smile, a true genuine, broad smile, the depressor labii pulls the lower lip downwards and out. If you relax the muscle by accident, typically only doing so on one side, the lip will not pull down on that side and the result is an asymmetrical smile which is very upsetting for the patient. Often, the appearance of their smile leads others to react as if something is wrong, like the look of someone having a stroke, and they become very self-conscious of the smile until the side effect resolves.

The solution to avoid this is depth and positioning. As you are sliding the needle in to inject the DAO, if you go deep enough, you are likely to get closer to the fibres that are pulling on the lip medially from the depressor labii, warns Dr Tim.

Another way to reduce the risk of hitting this muscle is to move more superior. Dr Tim does not inject on the jawline, a common injection point often used by aesthetic clinicians, because if you inject deeply, you are very close to the overlapping fibres of the depressor labii. He believes that the neurotoxin can diffuse more easily here and affect the lip. His approach is to slide up from the jawline, feeling for the lateral border of the DAO for positioning, thus aiming to be as far away from the lip depressors as possible. The only other muscle in this location is a little bit of the buccinator muscle, and potentially the risorius, but that is usually located a little more superior. The intention is to find the space where you are far enough away from other key muscles, and you can relax the down pull without relaxing any of the other vectors in the face.

Get more insight from Dr Tim when he asks which product do I use for the depressor anguli oris (DAO)?

How deeply should you inject Botox into the mentalis muscle?

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The kidney bean chin side effect happens when treating the mentalis muscle to prevent the chin from being pulled upwards or to remove the textural indentations that sometimes appear on the skin when the muscle fibres are continuously contracted. Although the mentalis muscle has been injected and relaxed with a good aesthetic result, if you do not treat the complete depth of the muscle because you are trying to not inject too deeply, or trying to make sure that you inject at the right depth but are over-cautious of other nearby muscles like the depressor labii muscle, you can inadvertently inject more superficially. This will leave the top of the chin without movement, but underneath some strands of the mentalis muscle will continue to pull up causing bunching on the surface of the skin which is a kidney bean shape. The solution to managing this side effect is to look for the muscle fibres that are still contracting and directly treat them during the review appointment.

The mentalis muscle is quite difficult to understand in three dimensions. Most textbooks give you the idea that the muscle simply runs around your chin, but Dr Tim believes it is better to think of it as a muscle that almost projects out of your chin and then meets on the skin surface – its origin is near the mental crease, and it is projecting outwards.

This knowledge can influence your injection approach. If you aim perpendicular to the chin and inject deeply, you will go straight underneath the mentalis most of the time, which may place you close to the depressor labii muscle. If you approach the same way but superficially, there is a likelihood of only relaxing the surface fibres and causing the kidney bean chin. The preferential approach is one which is in parallel with the mentalis muscle fibres as they project, more at a 45-degree angle, to accurately place the needle in the bulk of the muscle at a middle depth layer.

Get further insight from Dr Tim Pearce on how to avoid mistakes when injecting masseter muscles with Botox.

Top tips for injecting Botox into the lower face

Precision is important when injecting botulinum toxin into the lower face, reiterates Dr Tim because there is often a balancing act going on between too deep and too superficial and aesthetic clinicians must have a clear understanding of how these muscles work, where the origin of the muscle is located, where the attachments are, and how to accurately stay within that muscle and not affect the nearby muscles.

Another top tip from Dr Tim is to avoid rushing to blame the depth or position of your injections if a patient complains about muscle movement and a potential side effect or undesirable result two or three days after treatment. Do not panic. Often, the act of waiting a week after treatment will see potential side effects resolve because, in those early days, the result is only ‘half-baked’ and some of the muscle fibres are reacting quicker than others to the botulinum toxin. Only after two weeks can you agree to review the outcome for your patient and assess if there is any undesirable muscle movement or consequential impact on other muscles. It might turn out a lot better than it appeared in those initial first days.

Check out this blog on Botox injections: common mistakes aesthetic clinicians make!

For more guidance on botulinum toxin treatments, download Dr Tim Pearce’s 26 essential injection patterns for botulinum toxin and learn more about how to manage and avoid Botox® complications with Dr Tim’s eLearning course for aesthetic practitioners.

If you have any additional questions for him, you can find Dr Tim Pearce on Instagram.

Botox® is a registered trademark of Allergan Aesthetics plc.

Aesthetics Mastery Show

The Best Botox Injection Depths | Botox Injection Depth Guide

Dr Tim says:

“It can be difficult to know the correct depths to be injecting and many injectors often worry about causing a crooked smile or other complications if they inject wrongly in the lower face. In this episode I break down the injection depths you need to stay safe and create the best results.”

Watch the full Aesthetics Mastery Show here.

The show has had thousands of views and 11 comments already, including:


“Once again a clear comprehensive video.”


“Excellent tips, thanks Doc”

Read comments and join in the debate on our YouTube channel.

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BOTOX (Botulinum Toxin) eLearning Courses

If you want to increase your confidence in botulinum toxin injections, or learn how to avoid and handle complications, Dr Tim Pearce offers two comprehensive courses that are highly rated by our delegates:

Both give CPD and certificates on completion.

In addition, browse our FREE downloadable resources on complications.

Dr Tim Pearce eLearning

Dr Tim Pearce MBChB BSc (Hons) MRCGP founded his eLearning concept in 2016 in order to provide readily accessible BOTOX® and dermal filler online courses for fellow Medical Aesthetics practitioners. His objective was to raise standards within the industry – a principle which remains just as relevant today.

Our exclusive video-led courses are designed to build confidence, knowledge and technique at every stage, working from foundation level to advanced treatments and management of complications.

Thousands of delegates have benefited from the courses and we’re highly rated on Trustpilot. For more information or to discuss which course is right for you, please get in touch with our friendly team.

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