Gingival Display in “Forced” Smile Evaluated by Sex and Age

The smile is an important standard by which individuals judge themselves and others.^1-8 Positive and negative personality traits have been attributed to certain smile features.^4-8 For example, a bright smile with well-proportioned teeth that are clearly displayed has been associated with the qualities of maturity, strength, and social competence.⁵ Thus, the smile can have a social impact on an individual.

Elements of an attractive smile include tooth size, shade, and alignment, diastemas, symmetry, buccal corridor, and gingival display (GD).^9-13 Laypeople and dental professionals have different sensitivities toward and perceptions of smile esthetics.^14-18 For example, orthodontists, general dentists, and laypeople were found to have detected specific dental esthetic discrepancies, such as maxillary midline, at varying levels of deviation.¹⁴ In addition, patients were found to have a significantly higher opinion of their own smiles than evaluating clinicians.¹⁶ Good communication between the patient and dental professional, therefore, is critical to successful treatment outcomes.

Maxillary GD is a key component to consider when evaluating the smile.^19,20 Perception regarding the esthetic impact of GD varies between the sexes and between laypeople and dental professionals.^21-23 GD in the esthetic zone of ≥4 mm has been considered excessive and unattractive.^14,15GD has been considered increasingly less esthetic as it progresses from 3 mm to 7 mm.²⁴ Examples of smiles that demonstrate various amounts of gingival display are shown in Figure 1 through Figure 5.

The smile can be characterized as being either emotional or posed.²⁵ The emotional smile is involuntary and may vary with the emotion being experienced.²⁶ The Duchenne smile, an early smile classification, is defined as an involuntary and emotional smile.^26,27 In contrast, the posed or non-Duchenne smile is voluntary.^26-28 If the voluntary smile is routinely presented, it could be considered the individual's natural smile.²⁶ The emotional or Duchenne smile can be mimicked.^29,30 Peck's classification described a stage II smile as a forced or strained smile resulting in maximal upper lip elevation.²⁸

When a dental patient is asked to smile, the clinician may be uncertain of the type of smile the patient is presenting. It may be a natural smile that the patient normally poses, or it may be less than the person's natural smile due to a cautious attitude that the patient may have in the office. Alternatively, the patient may show a forced smile that maximizes tooth and gingival display and which mimics their emotional smile. The differences in tooth and gingival display between the posed and emotional smiles can have important implications for diagnostics and treatment planning.³⁰

Tjan et al's article discussing GD in the smile is a frequently cited study.³¹ It evaluated only natural smiles in full-face photographs. All subjects were between the ages of 20 and 30 years. Smile types were divided into low (Figure 1), average (Figure 2), and high (Figure 3 through Figure 5) based on the amount of maxillary anterior tooth and gingival display. Their investigation provides important preliminary information into the prevalence of GD in the smile. However, Tjan et al's study design creates areas of uncertainty with regard to the authors' findings. Since subjects were asked to smile without instructions, the normalcy of the lip position, interocclusal clearance, and GD provided is unknown. Because no objective measurements of the GD were made, it cannot be determined how many of the study subjects with a high smile type actually had excessive (≥4 mm) GD. Also, since all subjects were between the ages of 20 and 30 years, the prevalence of smile types in older age groups was not determined.

The purpose of this prospective observational investigation was to document the smile type, GD, and upper lip movement (ULM) of male and female subjects in different age groups.

A prospective observational investigation of GD during smiling was conducted on patients seen consecutively in two private practices over approximately 2 years (2017-2019). These patients presented to the practices as part of their regularly scheduled appointments. Subject inclusion requirements were that all patients were between 20 and 79 years of age. Due to the small number of non-white patients of different ethnic backgrounds seen in these practices, only white patients were included in this investigation. Subjects with severe plaque/drug-induced gingival enlargement were excluded. A history of orthodontic treatment, orthognathic surgery, periodontal surgery, or restorative rehabilitation did not exclude a patient. All patients had intact maxillary dentitions, with at least bilateral first molar occlusion.

Measurement-taking was standardized between examiners in the two offices. All measurements were obtained using periodontal probes with millimeter markings. GD was measured as the distance from the gingival margin or cementoenamel junction of the maxillary central incisors to the inferior border of the upper lip when the patient was exhibiting a forced smile with the maximum ULM and with the posterior teeth touching. If measurement levels of the central incisors were not symmetrical, the central incisor that the examiner thought looked most harmonious with the appearance of teeth Nos. 6 through 11 was chosen. The ULM was measured by first determining the lip border at rest; the patient was then asked to smile with maximum ULM. The ULM was measured as the difference between these two points.

The smile type was determined by asking the patient to smile with maximum ULM and with their posterior teeth in full occlusion. Following Tjan et al's protocol,³¹ the smile was divided into three categories. A high smile type (S1) revealed the total cervicoincisal length of the maxillary anterior teeth (teeth Nos. 6 through 11) and a contiguous band of gingiva. An average smile type (S2) revealed 75% to 100% of the maxillary anterior teeth and the interproximal gingival only; a contiguous band of gingiva of the maxillary anterior teeth was not present in the S2 category. A low smile type (S3) revealed less than 75% of the anterior teeth.

Results were categorized by sex and age. Age categories were made in 10-year increments starting with 20 years of age. Age categories included: A (20-29), B (30-39), C (40-49), D (50-59), E (60-69), and F (70-79). A T (20-30) category was added to facilitate better comparison to the study performed by Tjan et al.³¹

A total of 736 subjects were included in the study; 463 were females and 273 were males, representing 62.9% and 37.1%, respectively. Table 1 shows the number of subjects divided by sex and age categories.

Table 2 shows the averages of all measurements and smile classifications for females and males of all ages. Females of all age groups had an average of 1.5 mm GD. The percentage with ≥4 mm of GD was 14.9 %, and their average ULM was 7.1 mm. The percentages of their smile types were: S1 = 33%, S2 = 51.4%, and S3 = 15.6%. Males of all ages had an average of 1 mm GD. The percentage with ≥4 mm of GD was 7.7%, and their average ULM was 6.6 mm. The percentage of their smile types was: S1 = 19%, S2 = 50.9%, and S3 = 30%.

Table 3 shows average GD above the central incisors in millimeters by sex and age category. In all age categories, females had a higher average GD than males. Both females and males were found to have a downward trend of average GD from category A (20-29) to category F (70-79) of 2.6 mm to 1 mm and 1.9 mm to 0.5 mm, respectively.

Table 4 shows the percentage of subjects with ≥4 mm of GD by sex and age category. In all age categories, females had a higher percentage of subjects with ≥4 mm of GD than males. Both females and males were found to have a downward trend from category A (20-29) to category F (70-79) of 33.3% to 9.8% and 22.9% to 0%, respectively.

Table 5 shows the percentage of subjects with smile types S1-S3 by sex and age category. In all age categories, females had a higher percentage of S1 than males. Males had a higher percentage of S3 than females in all age categories except category C (40-49).

Finally, Table 6 shows the average ULM by sex and age category. In all age categories, females had a higher average ULM than males. Both females and males were found to have a downward trend from category A (20-29) to category F (70-79) of 7.6 mm to 7 mm and 7.2 mm to 6.3 mm, respectively.

In the Tjan et al study, all of the subjects were between the ages of 20 and 30 years.³¹ The authors found 13.8% of women and 6.8% of men had a high smile type. These findings do not match well with the findings in the present study. In the T category (ages 20-30 years) in the present study, 54.9% of women and 31.6% of men were determined to have a high smile type. The findings are approximately four times the amount found in the Tjan et al study.³¹ Similarly, a higher percentage of females and males were determined to have a low smile type in the Tjan et al study as compared to this study.

An explanation for the difference between the findings could be the smile instructions given to the subjects. In the Tjan et al study, no specific smile instructions were given to the subjects.³¹ It could be anticipated that if subjects were not asked to smile with their maximum ULM, they may not have done so voluntarily. In the present study, subjects were specifically instructed to give a forced smile with maximum ULM. As a result, this study would record a greater percentage of subjects with high smile type.

The Tjan et al study was a survey based on full-face photographs.³¹ Their definition of a high smile was an open smile revealing the total cervicoincisal length of the maxillary anterior teeth and a contiguous band of gingiva. No minimum measurement of GD was required to fit into the high smile category. Later studies deemed ≥4 mm of GD to be excessive.^14,15 Considering Tjan et al's definition of a high smile type³¹ and that the definition of excess GD has been ≥4 mm, it is possible to have a high smile type without having excessive GD.

In the present study, the percentage of subjects with ≥4 mm of GD was determined. In the T category, 29.4% of females and 21.4% of men had ≥4 mm of GD. Subtracting these percentages from percentage of subjects determined to have a high smile type, this study found 25.5% of females and 10.2% of males had a high smile type but not excessive GD. Given the differences found in this study, it seems unlikely that Tjan et al's findings³¹ necessarily represent excessive GD.

Definite trends can be seen with regard to GD and smile category (Table 3, Table 4, and Table 5). In all age categories, females had higher GD than men. Both males and females had decreasing GD with increasing age. The average amount of GD decreased about 1.5 mm from age category A to F. The decrease in subjects with ≥4 mm of GD appeared to be more dramatic. Females went from 33.3% to 9.8%. Men went from 22.9% to 0%. An inverse relationship of percentage of patients of both sexes with smile type 1 and smile type 3 was seen with increasing age. With increasing age the percentage of subjects with smile type 1 decreased, while smile type 3 increased.

As a group and in all age categories, females had greater GD than males. Despite the decrease in GD with increasing age for females and males, a notable percentage of females show excessive GD in all age groups. These findings are consistent with studies evaluating tooth and gingival display in subjects from 20 to 60+ years of age.^32-34 Especially for females, therefore, including measurements of GD could be considered a necessary part of a smile evaluation protocol.

Normal ULM has been reported to be 6 mm to 8 mm, from the repose position to the position achieved at a full smile.^35,36 A recent study investigating excessive GD used 8 mm of ULM as the threshold for a hypermobile lip.³⁷ The present study found the average of all females and all men to have average ULM of 7.1 mm and 6.6 mm, respectively. This study found females and males had less ULM with increasing age. The reduction in ULM from age category A to F was 0.6 mm for females and 0.9 mm for males. It is interesting to compare these changes to that of changes in average GD. The reduction in GD from age category A to F was 1.6 mm for females and 1.1 mm for males. It could be surmised that some of the reduction in GD could be due to reduction in ULM.

Upper lip length was not measured in this study. It has been reported that upper lip length increases with age.^38,39 This may be another factor that contributes to decreasing GD with increasing age.

Based on the findings in this study, gingival display and the percentage of persons with a high smile type diminishes with increasing age. In all age groups, females have greater GD and a high smile type as compared to males. The percentage of females with excessive GD (≥4 mm) was also greater than with men in all age groups. ULM decreases with increasing age.

Douglas H. Mahn, DDS
Private Practice limited to Periodontics and Implantology, Manassas, Virginia

Sina Reangber, DDS
Private Practice, Haymarket, Virginia