Smile Enhancement

By Dr Rupert Critchley / 10 Nov 2016

Dr Rupert Critchley shares his techniques for improving a smile using botulinum toxin

Smile verb or noun

Form one’s features into a pleased, kind, or amused expression, typically with the corners of the mouth turned up and the front teeth exposed.

Psychology of the smile

A smile is universally acknowledged as one of our most powerful human attributes. Whether a social smile at six weeks old, or a smile at successes later in adult life, evidence of the importance of a smile has been well documented by evolutionary, cross-cultural and social psychological research for many decades.

Alongside the union of biological evolution and foundation of the Darwinian Theory, Charles Darwin was lesser-known for making important contributions to early experimental psychology of the smile. Studies published in Expression concluded that the smile is truly universal, unlike other physical actions such as body language or verbal communication, which differs from one culture to another.3 Other less-ethical experiments were carried out by French anatomist Guillaume Duchenne, who studied emotional expression by stimulating various facial muscles with electrical currents. The term ‘Duchenne Smile’ refers to what characterises a ‘true smile’ and is suggested as a predictor of marital happiness, personal wellbeing and even longevity.4 In contrast, a ‘false smile’ can be an indicator of negative emotional states such as grievance and misery. More recently, scientists have discovered a total of 14 different smile types ranging from broad and symmetrical to narrow and lopsided.5

Smiles are impactful in more than one way: internally, by helping build self-confidence and overall well-being, having a ‘self-medicating’ effect, i.e. the hormonal and physiological consequences of a smile that make us feel good and want to smile more, and externally, by allowing people to build rapport, trust and instill confidence.5

In essence, every human understands the meaning of a smile and the underlying associated emotions, thus making smiling an integral part of human interaction and behaviour. It is for this reason that an individual’s smile is so important, and why an aesthetically pleasing smile, including the teeth and lips, is so highly sought after in the aesthetics arena.

Smile science and aesthetics

Generally speaking, we recognise a smile as a behavioural expression indicating pleasure and happiness. Once the senses are aroused, neurotransmitters are released in the left anterior temporal region or limbic system in the brain. As a result, motor pathways are activated.6 Two key muscles – the zygomatic major and the orbicularis oculi – are roused into action. The entire event that results in a smile being formed is short, typically lasting from two-thirds of a second to four seconds. In this time, the zygomatic major pulls the lips upward and the orbicularis oculi squeezes the outside corners of the eyes into the shape of a crow’s foot.3 It is widely accepted that the known aesthetic characteristics of an attractive, or ‘perfect’ smile is one which is symmetrical, wide, displaying white, straight teeth which follow the lip line and gingival visibility of between 1-3mm.

Although dental assessment still plays an important role in the beautification of the smile, the development of advanced injection techniques using botulinum toxin type-A for correcting common smile imperfections is becoming increasingly popular in the aesthetics field and is an important skill for clinicians.

Injection techniques for smile improvement using botulinum toxin

The common causes of an ‘imperfect’ or un-aesthetically pleasing smile which can be safely treated with non-surgical injectables include: the ‘gummy smile’, smile asymmetry due to an overpowering unilateral depressor anguli oris (DAO) and down-slanting lip edge corners, and ‘long and sad’ face at rest due to a bilateral overpowering DAO.

Please note as per best practice, only a suitably trained clinician should carry out these advanced procedures. A thorough history and appropriate consent should be taken, target areas of injection marked, and before and after images obtained. The safest approach to treatment is to avoid over paralysation of the muscle by injecting smaller quantities of botulinum toxin, with a review and top up if required at the two-week point.

The ‘gummy smile’

A ‘gummy smile’ is a term used to describe the excessive display of gingival tissue in the maxilla when a person smiles. This common complaint can impact someone psychologically by affecting their self-esteem and confidence.

Until recently, corrective procedures involving invasive orthognathic surgery or orthodontic appliances were the most common treatment options for patients suffering from a gummy smile.7 Now, however, the scalpel is increasingly being laid to rest and non-surgical techniques using botulinum toxin are often favoured. This treatment is less costly, less painful and requires less patient downtime, whilst achieving the same standard of results. Techniques of this treatment vary but ultimately the aim is to target and weaken only those muscles around the mouth that are causing the excess retraction of the lip upon smiling. Typically, there are four injection points that can be used to depress the lip at different locations (Figure 1).

Injection points 1 and 4: 1cm directly lateral from the most superior point of nasolabial sulcus (levator anguli oris) dropping the lateral aspects of the lip.

Injection points 2 and 3: a vertical line is drawn between the nose and the lip border – injection point is two-thirds above the lip on the ridge of the philtrum (orbicularis oris) dropping the middle one-third of the lip downwards.

Smile asymmetry due to unilateral overpowered depressor anguli oris

Botulinum toxin injections can be used to correct smile symmetry as a result of a unilateral overpowered DAO. Patients are rarely aware of potential correction using botulinum toxin and a thorough history should be obtained to ensure there is no underlying neurological pathology.

Injection points: 1-1.5cm below the angle of the mouth – unilateral injection in the DAO (arrow on Figure 2 marks the direction of pull of stronger DAO).

Downturned lip corners due to bilateral overpowered depressor anguli oris

This common complaint mostly occurs due to the imbalance between lip elevator and stronger DAO function (Figure 3). The dentition and orthodontic status of the patient may also play a role in development of this pathology.

Injection points: 1-1.5cm below the angle of the mouth (deep into the DAO) several injections can be made on either side running down towards the mandible.

Treatment results

Treatment results vary from patient to patient but providing the practitioner has appropriate anatomical understanding and training, patients are generally very satisfied with results (Figure 4). The results last four to six months depending on administration. Potential side effects and management

Figure 4: Gummy smile before and after administration of botulinum toxin 

The risk of complications depends on both the clinician’s competence and experience, as well as the post-procedure advice given. Generally, the risk of complications can be minimised by cautious measures of product, anatomical awareness and injection technique. The depth of administration should be intramuscular with the needle perpendicular to the skin surface and bevel facing upwards.

The clinician must have appropriate training in advanced non-surgical injectables and be mindful of facial anatomy, avoiding the key vessels in the perioral area, in particular, the superior and inferior labial arteries, the facial artery/angular branch. Toxin quantity depends on the choice of product. Under no circumstances do you want to impact the general movement and function of the facial muscles, which could affect the patient’s ability to smile altogether, or could cause difficulties with speech, chewing and/or drinking. Over-administration can result in drooping or ptosis of the lip below the gingival margin causing obstruction of visible teeth on full smile. In addition, it is of utmost importance that the clinician manages patient expectations prior to treatment, as well as discusses the immediate effects such as temporary redness, swelling and potential bruising. Spreading of the treatment to the muscle nearby can easily be prevented by avoiding rubbing or massaging the treated areas for approximately four hours post treatment.8


The smile plays a key role in the expression of happiness, confidence and social interaction on many psychosocial levels. The aesthetics of a person’s smile not only alters their physical appearance but is also proven to impact their psychological and emotional well-being. Someone who feels that they suffer from a ‘gummy smile’, where more than 3mm of gingival tissue is displayed when they smile, may try to hide this by not smiling fully, or not smiling at all. This can make them feel uneasy and unable to connect as well with others in social environments, as well as potentially impacting how they are perceived by others. It’s therefore understandable why people seek treatment for this condition. The use of botulinum toxin type-A injections to relax key muscles around the mouth can greatly improve smile aesthetics by incapacitating the muscle’s ability to elevate above the gingival tissue to the same extent as before. In comparison to other treatments, botulinum toxin injections are a quick and minimally-invasive alternative with less chance of complications, available at a lower cost and requiring less patient downtime than many surgical alternatives. 

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