To study a smile beyond static pictures, capturing a dynamic smile [2, 7, 10] was used, thus avoiding the inherent error of a single snapshot. The variables of smile were significantly affected by the facial growth pattern in this study.
Upper incisor exposure
The upper incisor exposure was less in females when compared with males in all three groups and this difference was significant in vertical facial growth pattern group. This is contrary to the findings of Vig and Brundo [11], Peck et al. [12, 13], and Balani et al [14], whereas the above finding is supported by a study done by Weeden et al. [15], where the results demonstrated that males exhibited greater amount of facial movements than females thus increasing the incisal display on smiling.
Incisal display
The incisal display significantly increased from horizontal to average to vertical facial growth pattern, with least incisal display in horizontal facial growth pattern subjects and maximum in vertical facial growth pattern subjects for both males and females. Contrary to this, Mc Namara et al. [16] found that the vertical display on smile of the maxillary right central incisor could not be correlated with the skeletal vertical dimension, as measured from nasion to menton and from anterior nasal spine to menton.
On correlating upper incisor exposure with cephalometric parameters, it was found that the upper incisor display was negatively correlated with posterior facial height and Jaraback’s ratio of males in horizontal facial growth pattern group but not in females and it was positively correlated with overjet, Y-axis, and palatal plane angle of males in vertical facial growth pattern group.
Incisal edge to lower lip distance
The incisal edge to lower lip distance was less in females when compared with males in all three groups and this difference was significant in average facial growth pattern group. This is supported by the findings of Vig and Brundo [11] and Peck et al. [12, 13] who found less mandibular tooth exposure in females than males at all ages.
The distance between incisal edge of the maxillary incisor and lower lip was least in horizontal growers and the maximum in vertical growers in both male and female.
No correlations of distance between incisal edge of the maxillary incisor and lower lip were found with cephalomteric measurements in the vertical facial growth pattern group.
Interlabial gap
The interlabial gap was significantly more in males when compared to that in females in average and vertical facial growth pattern group. This was contrary to Rigsbee et al. [17], Tjan et al. [1], and Jensen et al [18] and is supported by a study done by Weeden et al. [15], where the results demonstrated that males exhibited greater amount of facial movements than females thus increasing the interlabial gap on smiling.
Interlabial gap was significantly found to be maximum in vertical growers, followed by average and least in horizontal growers in both male and female.
Intercanine width
The intercanine width was more in males when compared to that in females in all groups but this difference was statistically significant only in the vertical facial growth pattern group.
Intercanine width was positively correlated with total width of visible maxillary teeth on smile of males in average and vertical facial growth pattern groups but not of males in horizontal growth pattern group. In males and females of vertical growth pattern group, the intercanine width was positively correlated with smile width and total width of visible maxillary teeth on smile.
The intercanine width was found to be least in vertical growers when compared with horizontal and average growers in both male a females. Similar results were found in a study done by Grippaudo et al. [19], in skeletal class II subjects. Changes in upper arch shape with intercanine diameter were proportionately smaller in patients with high angles and larger in low-angle patients.
Total width of all visible maxillary teeth
The total width of all visible maxillary teeth was significantly more in males when compared to that in females in all groups.
The total width of all visible maxillary teeth was negatively correlated with posterior corridor (left and right side) in all the groups indicating that in case of increased visible teeth during smile, the posterior corridor decreased. Due to the same reason, the total width of all visible maxillary teeth was negatively correlated with posterior corridor ratio in all the groups.
Smile width
The smile width was more in males when compared to that in females in all groups, but this difference was statistically significant only in the horizontal facial growth pattern group. This was contrary to the results of Rigsbee et al. [17] and Chetan et al. [20] who found that females exhibited more animation as compared to men resulting from a greater degree of upper lip elevation and increased width resulting in an increased display of teeth.
On comparing smile width separately in horizontal and vertical facial growth pattern group with average facial growth pattern group, statistically insignificant difference was found in both males and females in both the facial growth pattern groups.
Buccal corridor
With regard to the buccal corridor of males when compared with females, the mean value was found to be more in case of males in all groups but was significantly more only in males in horizontal facial growth pattern group. A similar finding was reported by Maulik and Nanda [21]who found that females had less buccal corridor space than males.
As regards buccal corridor of the left side when compared with the right side, statistically significant difference was found which demonstrates that the buccal corridor was greater on the left side than on the right side. This finding is supported by the study done by Okamoto et al. [22] where it was found that the displacements of the right and left corners of the mouth during voluntary smile were asymmetric and the left-sided laterality was found.
Buccal corridor of the left side when compared with the right side, in vertical facial growth pattern group with average facial growth pattern group, was found to be significantly less in vertical facial growth pattern group in males but not in females. The above findings are supported by the results of Yang et al. [23] who found that FMA and LAFH were negatively correlated with buccal corridor.
The buccal corridors (left and right) were positively correlated to each other indicating that if the buccal corridor was increased on the left side, it would increase on the right side as well, in all the groups irrespective of the age. A similar finding was observed by Krishnan et al. [6] showing a high correlation between the right and left buccal corridor spaces in both men and women. It was also positively correlated with posterior corridor (left and right) indicating that in case of increased buccal corridor, the posterior corridor also increased. No correlation was found between the total anterior facial height and the buccal corridor space similar to the findings of Yang et al [23].
Posterior corridor
Posterior corridor of males, when compared with females, was found to be less in case of males in horizontal and average facial growth pattern groups but was statistically significantly less in males in vertical facial growth pattern group. On comparing posterior corridor of the left and right sides, statistically significant difference was found which indicate that the posterior corridor was greater on the left side than on the right side. This finding is supported by the study done by Okamoto et al. [22] where it was found that the displacements of the right and left corners of the mouth during voluntary smile were asymmetric, and the left-sided laterality was found.
Posterior corridor in vertical facial growth pattern group, when compared with average facial growth pattern group, was found to be significantly less in vertical facial growth pattern group in both males and females. On comparing buccal corridor of left and right sides in horizontal facial growth pattern group with average facial growth pattern group, it was found to be insignificantly different in both males and females.
The posterior corridors (left and right) were positively correlated to each other indicating that if the posterior corridor was increased on the left side, it would increase on the right side as well, in all the groups irrespective of the age.
Upper lip vertical
Upper lip vertical length in males and females demonstrated an insignificant difference in all the groups.
Upper lip vertical length of horizontal facial growth pattern group, when compared with average facial growth pattern group, indicated that upper lip vertical length was more in horizontal and vertical growth pattern group in both males and females and least in average growers.
Lower lip vertical
For lower lip vertical length in males when compared with females, statistically significant difference was found showing increased lower vertical lip length in males in all the three groups.
With regard to the lower lip vertical length in horizontal and vertical facial growth pattern group when compared with average facial growth pattern group, no significant difference was found between the two groups in both males and females. In a study done by Joshi et al. [24], the lip position in relation to various malocclusions was studied which showed a significant difference in the sagittal lip positions in different skeletal malocclusions. Thus, it can be inferred vertical as well as the sagittal skeletal features influence the overall soft tissue drape.
To homogenize the sample, only class I subjects were selected. Increasing the sample size randomly followed by categorizing them based on Angle’s classification and using regression model to compute additional variables could further improve the study. The use of a three-dimensional methodology [25] can be used for analyzing anthropometric characteristics of soft tissue of face.