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What’s in a gummy smile? What do I need to know | part 1

This blog looks at the topic of gummy smiles, an area of increasing interest in orthodontics and dentistry. The occurrence of gummy smiles is 1-in-10 to 1-in-3 patients, with a myriad of presentations, causes and treatments, adding to a topic considered unclear in both aetiology and therapy. This blog is based on our paper, recently published in Seminars in Orthodontics, led by Adith Venugopal, and the excellent review paper by Dalya El-Bokle in the AJODO Clinical companion, both papers seeking to inform readers of a structured approach to a topic. Part 1 will explore the aetiology of the condition and how as clinicians we can effectively and accurately diagnose. Part 2 (coming soon) with discuss both orthodontic and non-orthodontic treatment options, with a contemporary review.


What does a gummy smile look like?

 

A gummy smile is an excessive gingival display on smiling greater than 2mm. it has been classified as mild (2-4mm), moderate (4-8mm) and severe (8mm+) Tjan 1984. For most patients there is equal anterior and posterior excess (88%), however, it can be isolated to either anterior or posterior areas Graber 2000

The difficulty in assessment is that there is not one smile, but two, full smile (posed smile) and a maximum smile (spontaneous smile). There are several muscles involved in smiling, the full smile involves contraction of the levator muscles raising the upper lip to the nasolabial fold, whereas a maximum smile involves further raising superiorly of the lip by the levator labii superior muscles, with accompanied flaring of the nostrils and squinting of the eyes. The full smile has been considered the more reliable smile (0.1-0.9mm), with video assessment of a video (cropped to the mouth only) offering the most reliable method of assessment Walder 2013.

 

How to measure a gummy smile?

The formal assessment of a gingival smile is a vertical measurement from the zenith of the maxillary dentition to the lower border of the upper lip during a full smile, it is recommended to repeat measurements to ensure consistency. However, this measurement does not indicate any aetiology nor the appropriate treatment. For aetiology each of the three potential causes requires evaluation soft tissue, dental and skeletal.

Soft tissue assessment

There are two distinctively different aspects to soft tissue assessment; the static measurements of the upper lip and gingiva, and the dynamic mobility of the upper lip.

The static measurement of the upper lip length is measured from subnasale to the inferior border of the upper lip. The average length of adults is 23mm in males and 21mm in females Peck 1993. The gingival position is assessed via proportions of crown width-to-length ratio of 80% and an assessment of altered passive eruption through periodontal probing. The altered passive eruption is the failure of the gingival tissues to recede to the cementoenamel junction, resulting in excessive gingiva on the enamel of the tooth and increased periodontal probing depths.

Dynamic mobility of the upper lip assesses the upper lip levator muscles, with an increase in muscle activity resulting in a gummy smile. The assessment involves calculating a ratio of upper lip mobility. It is calculated by measuring the distance between the upper lip in full smile, subtracted from the upper lip length at rest, and divided by the upper lip length at rest. The average ratio is 27%, with an increased ratio indicating  a gummy smile Peck 1993.

Upper lip length in full smile – upper lip length in repose / upper lip length in repose   x 100 = upper lip mobility ratio (27% average)

Dental

Excessive eruption of maxillary anterior also known as passive dental eruption results in the periodontium also moving inferiorly, and a gummy smile. The reason for excessive eruption can relate to a lack of an occlusal stop anteriorly, caused by discrepancies in the antero-posterior plane or vertical plane. Bimaxillary proclination can result in the upper lip retracting to an inferior position, resulting in a gummy smile.  

Skeletal

The last factor is the skeletal aetiology, avoided until this point in the blog as it is an area of significant variation. The premise is that the maxilla is positioned inferiorly and therefore the dentition and gingiva are also inferior relative to the lips, resulting in greater exposure on smiling. To assess the maxillary skeletal position there have been two proposed methods; 1/ linear measurement, and 2/ angular-based measurement.

Linear measurements assess the vertical height from the maxillary plane to the incisal tip, with an average of 29.7mm (SD 2.9mm), and vertical maxillary excess at 32.0mm (SD 3.0mm), however the sample was based on patients aged 14 years old Peck 1992.

2/ Angular measurement of the maxillary height angle N-CF-A (nope, I too could not remember it). The angle is constructed from Nasion to CF (pterygoid root vertical to the Frankfort horizontal plane) to A point, with an average value of 56° (SD 3°) Gutierrez 2014. The greater the angle the further inferior the maxilla is from the cranial base.

 

However, with patients unlikely to be forged from textbooks, there tends to be a multifactorial aetiology, with the skeletal relationship the least robust method of assessment. An insightful comment by Dalya El-Bokle regarding this was; “increase in GD that is not accounted for by the (other) variables will be due to VME”, or it is a diagnosis by elimination.

Verdict

Gummy smiles are an area of increasing interest within dental, aesthetic and orthodontic clinical practice. With part 1 we have explored the aetiology, as well as a structured method of analysis, part 2 will detail treatment options for the gummy smile, those within orthodontics and that which we need to dial a friend for.

The excellent structured method described by Dalia ElBokle is below:

 

Link to papers used for this blog:

Gummy smiles: Etiologies, diagnoses & formulating a clinically effective treatment protocol. Venugopal.  Manzano Ahmed Vaid Bowmane https://doi.org/10.1053/j.sodo.2023.11.014

Conflict of interest – i was an author of the above publication

  

Contributions

 

Edited/contents: Farooq Ahmed

 

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1 comment
  • ‘Gummy smile’ is also known as vertical maxillary excess. Simple measurements are OK but to fully appreciate it, allometric techniques such as geometric morphometrics (GM) that capture size-related shape change are also useful. The gummy smile is a bit of an optical illusion since size-related shape-changes of the maxilla appear as a positional change clinically. GM is preferable since it also illustrates anisotropy (direction of change). Given this approach, clinical techniques for correction can be formulated. Surprisingly perhaps, maxillary ‘expansion’ (even in adults) is useful since it reshapes the dysmorphic maxilla. This approach is supported by other clinical features of gummy smile, which include a narrowed maxilla, a high palatal vault sometimes with anterior open bite and mandibular retrognathia. In these cases, the tongue needs to be retrained thru oral myofunctional therapy to add stability to the clinical treatment,
    Harris WG, Singh GD. Resolution of ‘gummy smile’ and anterior open bite: Case Report. J Amer Orthod Soc. 2013: 30-34.