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Features / July 15, 2015

Clinical tips: smile line assessment

by Guy Hiscott

Photo – Figure 3: Average smile line

Emily Clarke discusses smile and gingival display assessment

Assessment of the ‘smile line’ or amount of gingiva displayed when smiling is essential for the diagnosis of aesthetic dentofacial problems and for restorative treatment planning in the aesthetic zone – and only takes a few seconds.

An average smile line, showing 100% of the tooth length, and a high smile line require careful consideration when treatment planning in order to avoid, minimise or warn a patient in advance of potential asymmetry. A full range of gingival tissue and tooth display can be observed among individuals from no gingival display to a ‘gummy smile’ possibly extending as far back as posterior teeth. The extent of the smile will depend on the length and mobility of the upper lip and the length of the alveolar process.

It is useful to at least attempt to categorise an individual’s smile to provide an objective basis for interpretation and verbalisation of dentofacial problems (Figures 1-3).

Fig 1 low
Figure 1: Low smile line


In a study population of 454, ranging from 20 to 30 years of age, and based on the above classification, researchers found that 20.5% had a low smile line, 69% had an average smile line and 10.5% had a high smile line (Tjan and Miller, 1984). High smile lines are also more common in younger patients.

Smile assessment

It is important to remember that when assessing the smile line a patient is unlikely to produce a natural smile on demand when seated in the dental chair. In addition, a patient conscious of a particular aesthetic problem may have trained themselves to restrain their natural smile.

Figure 2: High smile line
Figure 2: High smile line

It is often more useful to simply observe the patient during a light-hearted conversation. Making a humorous comment to your patient is often enough to trigger a demonstration of their true smile line.
Photographing the patient during a normal conversation is also a very useful tool for future diagnosis and treatment planning, although a natural smile may not be fully demonstrated.

The ideal smile

The aesthetically ideal smile is one in which roughly 0-1mm of marginal gingiva is revealed during a natural smile and the interdental papillae are visible. Exposure of more than 3mm of gingiva when smiling is perceived as unattractive in the majority of patients. There are always exceptions to the rule, however, and in some individuals a gummy smile can be very attractive! In addition, individual opinion on what is an attractive smile varies, especially between different cultures.

Figure 3: Average smile line
Figure 3: Average smile line

Screen Shot 2015-06-29 at 10.46.11

Tjan A, Miller G (1984) Some esthetic factors in a smile. J Prosthetic Dentistry 51:24-28

Dr Emily Clarke works in practice limited to periodontology and implant dentistry in the Riverpoint Specialist Dental Clinic in Limerick and at Galway Periodontics and Implant Dentistry, Clybaun Road, Galway. She can be contacted via or