Influence of canine vertical position on smile esthetic perceptions by orthodontists and laypersons


Our objectives were to verify the impact of alterations in the vertical position of the maxillary canines in smile esthetic perceptions and to determine whether exposure of the gingival margins directly affects laypersons’ and orthodontists’ perceptions.


A smile photograph of a male subject showing gingival zeniths was selected, and the canine vertical positions were symmetrically modified in increments of 0.5 mm, creating 4 new images varying from 1.0 mm of intrusion to 1.0 mm of extrusion, with and without gingival exposure. The total of 10 images were evaluated by 60 orthodontists and 60 laypersons, who determined the level of attractiveness of each smile on a visual analog scale.


For both orthodontists and laypersons, the canine vertical position modifications had a statistically significant influence ( P <0.0001), and the gingival exposure had no significant influence on the smile esthetic evaluations.


For both groups of evaluators, the most attractive smiles were the standard smile and the smiles with 0.5 mm of intrusion. The less attractive smiles were those with 1.0 mm of extrusion and 1.0 mm of intrusion. Orthodontists were more critical in their assessments. There were no differences in the esthetic evaluations of smiles with and without gingival margin exposure for both groups of evaluators.


  • Promoting lateral guidance by changing canine position may disfavor esthetics.

  • The most attractive smiles were the standard and the one with 0.5 mm of intrusion.

  • Smiles with 1 mm of extrusion or intrusion (extreme changes) were less attractive.

  • Orthodontists were more critical in their assessments.

  • Gingival margin exposure did not alter the perception.

The pursuit of excellence in smile and facial esthetics has become, in recent years, the main objective of patients consulting dental clinics. However, since the concept of beauty is subjective and wide, it is difficult to establish ideal standards.

According to recent literature, an esthetically pleasing smile should present some aspects such as proportion and symmetry between the central incisors, minimal gingival display, buccal corridor width from minimal to moderate, and anterior teeth with adequate gingival margins.

Several studies have indicated that, ideally, the gingival margins of the maxillary canines should be positioned on the same level as the central incisors and slightly above the margins of the lateral incisors. It is not uncommon that, in an attempt to make the gingival contours harmonious or improve the functional aspect, orthodontists tend to change the vertical position of the maxillary canines; this inevitably alters the relationship of the incisal edges and gingival margins of anterior teeth and may create unattractive steps.

From a clinical standpoint, it is often cited that the closer to the dental midline, the greater the perception of any alterations in smiles; this justifies the many studies investigating the relationship between vertical position of the central incisors and a pleasant smile. Nevertheless, in relation to these changes in canines, the literature is still seldom explored. There are no articles evaluating the variables of incisal edges and gingival margins together considering a change in the canines’ vertical position without modification of the dental crown size.

In this study, we aimed to evaluate, by observation of the symmetrical changes in the vertical position of the maxillary canines in a frontal smile, the canine positions that were more and less accepted, whether there was a statistically significant difference between the evaluations of laypeople and orthodontists, and the influence of gingival display in these perceptions.

Material and methods

This study was approved by the research ethics committee of the University Hospital Antonio Pedro, Universidade Federal Fluminense, Niteroi, Brazil.

A male volunteer had his smile photographed, with exposure of gingival zeniths of the maxillary incisors and canines: ie, a “high smile.” This subject had no previous orthodontic treatment, no restorations in anterior teeth, and healthy teeth and periodontal tissues. The photograph was taken with the subject at rest position, standing with the Frankfort horizontal plane and the bipupilar line parallel to the ground. In addition, his mouth was slightly open to minimize the display of mandibular incisors and to promote the contrast of the maxillary teeth with a darker background. He signed a release form authorizing the use of his image in scientific research.

This photograph was digitally manipulated with Adobe Photoshop (version CS5; Adobe Systems, San Jose, Calif) to remove the stains and adjust color changes. In the resulting image, 1 side was mirrored to ensure smile symmetry. This image was defined as the standard smile, and considering a straight line touching the incisal edges of the maxillary central incisors, it showed the canine incisal edges positioned 0.5 mm above this line, the gingival margins of the canines and central incisors at the same level, and the lateral incisor gingival margins 0.5 mm below the central incisors and canines. The smile was considered harmonious in relation to the smile curve. This standard smile was the same as that used by Machado et al.

Starting from the standard smile, new manipulations were made in the smile by changing the canine vertical positions symmetrically, making them more extruded or intruded in increments of 0.5 mm in relation to the line tangent to the central incisors’ edges. Variations were made by movements of 1 canine in the cervical or occlusal direction in relation to this line, without changing the length or the proportion between width and height; moreover, this image was mirrored to ensure perfectly symmetrical changes. The images obtained were 0.5 mm of extrusion, 1 mm of extrusion, 0.5 mm of intrusion, and 1 mm of intrusion. For movement graduation, the volunteer’s maxillary central incisors were measured directly in the mouth with a digital caliper (Lotus, Serra, Espírito Santo, Brazil), and the measurements were used as a reference for the calibration of a ruler in the software, from which the increments of 0.5 mm were made. Furthermore, an upper lip displacement was performed creating a low smile, which was reproduced for all the previously described images to hide the gingival margins. The same vertical changes in the maxillary canines were maintained, resulting in 5 new images with a low smile (standard smile, 2 intrusion smiles, and 2 extrusion smiles). The manipulations were performed by the same operator (R.M.M.). Finally, a set of 10 images composed the sample to be assessed ( Fig ).

Smiles after manipulation of canine vertical positions with ( left column ) and without ( right column ) gingival exposure: A and B, 1.0 mm of intrusion; C and D, 0.5 mm of intrusion; E and F, standard smile; G and H, 0.5 mm of extrusion; I and J, 1.0 mm of extrusion. (E and F are used with permission ).

These 10 images were assembled into a presentation, using PowerPoint software (version 12.0; Microsoft, Redmond, Wash). An initial slide was displayed for 20 seconds with all smile images, grouped by the type of smile (with or without exposure of gingival margins) and in sequential order of vertical position of the canines. Moreover, the same pictures were presented one by one, in random order defined by sorting, with automatic transition and 15 seconds of display time for each image. The evaluators were not allowed to return to previous photos for revaluation, and they were not told that the model was male.

To assess the attractiveness of each smile, visual analog scales were used. The evaluators were given a sheet of paper containing 10 scales, with each scale measuring 100 mm and graded from 0 to 10, numbered according to the order of the pictures, but without identifying any characteristics. They were instructed to make a perpendicular line on the scale at any point, corresponding to the desired score, considering 0 as unattractive and 10 as very attractive. The evaluators were not aware of the subject of the research. A digital caliper (Starrett 779; Itu, São Paulo, Brazil) was used to measure the scores in millimeters and adjust for possible printing distortions.

Evaluators included laypeople and orthodontists. A sample size calculation was performed using the formula described by Pandis, considering an 80% test power, α = 0.05, standard deviation described by Machado et al, and a difference of 10 scores to be detected. The calculation showed that 57 subjects per group would be enough. Therefore, 60 laypeople and 60 orthodontists were selected for this research.

Inclusion criteria were age between 18 and 60 years, both men and women; lay people should have a university degree, no training in dentistry, and a 5-year gap from the last orthodontic treatment, if any; orthodontists should be specialists in orthodontics and work with the fixed orthodontic technique. Orthodontic patients, dental clinic staff, dentists who were not orthodontists, and dentistry students were excluded. Evaluations were made consecutively, regardless of sex or age distribution.

Statistical analysis

BioEstat software (version 5.0; Mamiraua Institute, Tefé, Amazonas, Brazil) was used for statistical analysis. The normality of the data was tested by the Lilliefors test. Because the sample data did not have a normal distribution, descriptive statistics were presented through medians, interquartile ranges, and confidence intervals. Two-way analysis of variance (ANOVA) was used to detect the influence on scores attributed to the factors of kind of smile and vertical changes of the canines. Intragroup differences were evaluated using the Kruskal-Wallis test along with the Dunn posttest, and the intergroup differences were evaluated using the Mann-Whitney test for each image.

Three evaluators from each group reassessed the 10 photos with a minimum interval of 2 months after the first evaluation. Reliability was tested using the intraclass correlation coefficient. A good correlation coefficient of 0.767 was obtained, ensuring reliability.


The sample of evaluators comprised 60 orthodontists (38 women, 22 men) with a mean age of 32.58 years (SD, 6.43) and 60 laypeople (46 women, 14 men) with a mean age of 30.26 years (SD, 8.73).

Based on the analysis of smiles with gingival display, the highest scores for both orthodontists and laypeople were given to the standard smiles (medians, 80.24 and 90, respectively) and the smile with a 0.5-mm intrusion (medians, 74.60 and 83.79, respectively). The lowest scores were given to the smiles with a 1-mm extrusion (medians, 32.13 and 50.00, respectively) and a 1-mm intrusion (medians, 39.93 and 57.46, respectively) for both groups ( Table ).

Descriptive statistics of orthodontists’ and laypersons’ scores and intragroup and intergroup comparisons
Orthodontists Laypersons Difference
Median IQR Intragroup comparison* Median IQR Intragroup comparison* Intergroup comparison ( P value)
Full smile
1 mm intrusion 39.93 29.01 A 57.46 35.32 AB <0.001†
0.5 mm intrusion 74.6 22.34 C 83.79 20.83 C 0.003†
Standard smile 80.24 21.88 C 90 20.85 C 0.009†
0.5 mm extrusion 59.67 27.66 B 68.21 29.92 B 0.023†
1 mm extrusion 32.13 29.58 A 50 29.85 A <0.001†
Smile without gingival display
1 mm intrusion 51.78 25.84 AB 75.21 27.26 B <0.001†
0.5 mm intrusion 70.12 24.22 C 88.58 19.24 C <0.001†
Standard smile 79.77 21.39 C 89.28 18.42 C 0.005†
0.5 mm extrusion 59.86 29.99 B 64.87 20.53 B 0.018†
1 mm extrusion 37.12 29.93 A 47.63 29.15 A <0.001†
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Dec 12, 2018 | Posted by in Orthodontics | Comments Off on Influence of canine vertical position on smile esthetic perceptions by orthodontists and laypersons
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