Is Botulinum Neurotoxin the Best Treatment for a Gummy Smile?
July 1, 2021
By Lisa Germain, DDS, MScD
Excessive gingival display also known as “gummy smile” can present some significant and unique treatment planning challenges for the clinician. The patient can have multiple etiological factors and deciding how to treat this condition can be a formidable task. Some of the most common causes of a gummy smile are insufficient length of the maxillary lip and or hypermobility of the maxillary lip, short clinical crowns, dentoalveolar extrusion and vertical maxillary excess. Botulinum neurotoxin injections continue to have a lot of attention in the expanding field of medical esthetics and its use is often a recommended treatment for this condition. However, before BoNT injections are used for the purposes of depressing lip elevator muscles to compensate for this concern, it is essential to do a differential diagnosis on each patient to determine the cause of the problem so that an appropriate treatment plan can be developed to address the aesthetic as well as the functional needs of the patient.
When the patient smiles, the lip should ideally move to the tooth/gingival interface of the maxillary central incisors and the canines. If more than 1.5 -2 mm of gingiva is exposed above this landmark, it begins to compromise the aesthetics of the patient’s smile. If the patient has healthy gingiva and pretty teeth, they may not feel that this is unattractive. However if there is any discrepancy in the height of the gingival margins, dental work that shows dark shadowing below the gum line, black triangles, discoloration with lack of translucency from injury or anything else that draws undue attention to the area, patients will invariable be conscious of this variable. Often they will ask for veneers or crowns to cover any imperfections that show above the gum line. However, in the absence of true pathology it might not be appropriate to do invasive cosmetic procedures. In addition, the end result may not live up to the patient’s expectations because prosthetics around the gingival margins has its share of challenges.
When a patient presents with a gummy smile, a complete evaluation of the etiology should be established. When the cause of the problem is orthodontic or orthognathic, this needs to be addressed, or at least presented to the patient, when discussing treatment options. Many patients are not aware if they have these issues especially if they are not having pain and are completely focused on how their teeth and smile look. While these problems may currently be incipient, the long-term consequences of these issues can create lifelong occlusal problems and the sequelae that accompany them such as broken restorations, TMD, and excessive tooth wear to name just a few.
The best candidate for treatment of a gummy smile with Botulinum Neurotoxin is when the etiology is hypermobility of the lip or insufficient lip length. In truth it might be the best solution for this particular etiology of excessive gingival display in the absence of other pathology. The bad news is that Botulinum Neurotoxin therapy is temporary and only lasts about 3 months. The good news is that it is Botulinum Neurotoxin therapy is temporary so no invasive permanent procedures limit your ability to go back to square one and re-evaluate the problem. In addition, if there are other etiologies involved, BoNT can be used in conjunction with them to enhance the results. Sometimes, tweaking the lip down even 1 mm can make all the difference in the world to the young adult who is reticent to take a “selfie” (perish the thought) because they are too self conscious to smile.
While there are many ways to assess the face for the purposes of medical esthetics, one way to quickly determine if the problem is inadequate length or hypermobility of the lip is to divide the face into three sections: upper, middle and lower. The middle and lower parts of the face should be equal in length. To determine the length of the mid face, a measurement is taken from the most prominent point on the forehead in the glabellar region between the eyebrows to the point just below the tip of the nose. To determine the length of the lower face, a measurement should be taken from just below the tip of the nose to the inferior border of the chin. The lip length is then determined by measuring from the area just below the tip of the nose to the inferior border of the upper lip known as the tubercle.
The average length of the maxillary lip is between 22 and 24 mm in young adult females and 24 and 26 mm in young adult males. At rest, 3-4 mm of the maxillary incisors should be visualized. In older adults, the tissue becomes elongated due to loss of elasticity hence there is an increase in the lip length due to the aging process making the maxillary incisors less visible at rest and the lower incisors more visible. For patients with a gummy smile this might be a welcome part of aging, however when this affects the smile of a younger person, they sometimes seek invasive dental procedures to improve the cosmetic appearance of their smile frequently in the absence of underlying dental pathology.
Botulinum Neurotoxin is a purified protein of the bacterium, Clostridium botulinum that is widely used in both cosmetic and therapeutics in medicine and dentistry to selectively relax muscles to improve both function and appearance. When determining where to inject, it is imperative to have a thorough understanding of the relevant neuromuscular anatomy of the area involved and any alterations to the anatomy due to prior surgical procedures. This is particularly important when injecting in the mid face area because diffusion of the toxin to adjacent antagonistic muscles can cause both adverse cosmetic results as well as functional deficits.
The muscle that is targeted to relax the maxillary lip is called the levator labii superioris alaeque nasi. This muscle belongs to the Buccolabial group of facial muscles. It originates on the upper frontal process of the maxilla and inserts into the skin of the upper lip as well as the skin on the lateral portion of the nostril. It has the longest name of any muscle in the mammalian species. When this muscle is activated, it dilates the nostril and elevates the lateral portion of the nose and the upper lip. It is often called the “snarl” muscle or the “Elvis” muscle since he activated this muscle to create a “snarling” facial expression when performing.
The muscle is injected at the Yonsei point, which is where the levator labii superioris, the levator labii superioris alaeque nasi), and the zygomaticus minor muscles converge.
This point is located 3 cm up from the oral commissure of the lip with the mouth at rest, and 1 cm away from the alar of the nose (Fig 1). The dose is dependent on how much relaxation of the lip is desired and averages between 1-2 units per side of Botox or Xeomin and 2-4 units of Dysport. It is better to underdose the patient to see how their muscles react. You can always add more, but you can’t remove it or reverse the effects.
The goal for treatment is relaxation of the maxillary lip with reduction of the gummy smile (Fig 2). The full effects of treatment should be evaluated 2 weeks after injections and the dosage can be enhanced if necessary if more relaxation is desired.
The Botulinum Neurotoxin effects should last about 3 months. However, because there is so much movement in this area, it may start to wear off sooner. Like most cosmetic procedures, managing the patient’s expectations is of paramount importance. However, in most cases, this small non-invasive procedure yields great results. Now that is something to smile about.
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