Analysis of dynamic smile and upper lip curvature in young Chinese

Abstract

During smile evaluation and anterior esthetic construction, the anatomic and racial variations should be considered in order to achieve better matching results. The aims of this study were to validate an objective method for recording spontaneous smile process and to categorize the smile and upper lip curvature of Chinese Han-nationality youth. One hundred and eighty-eight Chinese Han-nationality youths (88 males and 100 females) ranged from 20 to 35 years of age were selected. Spontaneous smiles were elicited by watching comical movies and the dynamics of the spontaneous smile were captured continuously with a digital video camera. All subjects' smiles were categorized into three types: commissure, cuspid and gummy smile based on video editing software and final images. Subjects' upper lip curvatures were also measured and divided into three groups: upward, straight and downward. Reliability analysis was conducted to obtain intra-rater reliabilities on twice measurements. The Pearson Chi-square test was used to compare differences for each parameters (α=0.05). In smile classification, 60.6% commissure smile, 33.5% cuspid smile and 5.9% gummy smile were obtained. In upper lip measurement, 26.1% upward, 39.9% straight and 34.0% downward upper lip curvature were determined. The commissure smile group showed statistically significant higher percentage of straight (46.5%) and upward (40.4%) in upper lip curvatures (P<0.05), while cuspid smile group (65.1%) and gummy smile group (72.7%) showed statistically significant higher frequency in downward upper lip curvature (P<0.05). It is evident that differences in upper lip curvature and smile classification exist based on race, when comparing Chinese subjects with those of Caucasian descent, and gender.

Esthetics and smile‐related characteristics assessed by laypersons

“… Upper lip Curvature : This specifies the horizontal morphology of the inferior border of the upper lip and is based on the positional relationship of the corner of the mouth and the center of the inferior border of the upper lip. Three categories were classified as follows: upward lip curvature means that the corner of the mouth is at 1 mm higher than a horizontal line drawn through the center of the inferior border of the upper lip; straight lip curvature means that the corner of the mouth is at or within 1 mm above or below a horizontal line drawn through the center of the lower border of the upper lip; downward lip curvature means that the corner of the mouth is at more than 1mm lower than a horizontal line drawn through the center of the lower border of the upper lip (Figure ) Smile pattern of Rubin classification : Rubin classification was adapted to categorize smile patterns of the subjects.…”

Evaluation of the maxillary midline, curve of the upper lip, smile line and tooth shape: a prospective study of 140 Caucasian patients

“…The arc of the smile can be defined as the relationship between the curve of the incisal margins of the upper incisors and canines and the curve of the lower lip in a posed smile, and may be consonant or non-consonant [12]. The curve of the upper lip can be divided into three categories according to the position of the corners of the mouth in relation to the center of the lower margin of the lip: upward, straight or downward [21]. The smile line in turn is classified as high if it exposes the entire clinical crown together with a continuous gingival band of variable size; medium if it exposes 75-100% of the clinical crown and only the interdental papilla; or low when the smile exposes less than 75% (three-quarters) of the clinical crown [22].…”

A Comparison of Facial Proportions in Pleasing and Unpleasing Smile Photographs from Nepalese Population

“…21 But videographic analyses are superior to static photographs as suggested by many authors. [38][39][40] This is one of the limitations of current study. Schabel et al 41 however, argued Journal of Nepalese Prosthodontic Society (JNPS) that videography provided more information about dynamic character of smile, photography was an equally useful alternative when used in social smile.…”