Assessment of dynamic smile and gingival contour in young Chinese people

This study aimed to classify the dynamic smile and to quantify the gingival line (GL), as well as apico-coronal displacement of the gingival zenith (GZ), in the maxillary anterior dentition in a young Chinese population.

Two-hundred young Chinese subjects (100 men and 100 women; 20-35 years of age) with healthy dentogingival tissue were recruited. The dynamic smile process was captured using a digital camera. The smile type, GL type, the vertical distance of the GZ between the canine and the central incisor on the same side and the GZ of the lateral incisor-GL relationship were measured using a self-developed smile-analysis method. The kappa statistics was used to examine the reliability of the data recorded by the rater. The Pearson chi-square test was used to analyse the differences between subjects regarding the frequencies of smile type and GL type at α = 0.05.

Data revealed that 45.5% of subjects had a high smile and 45.5% had an average smile; 58.2% of the subjects presented an upwards GL. The GZ of canine teeth was 0.33 mm apical to the corresponding central incisor and no significant difference between both sides of the GZ was observed. The GZ of the lateral incisor was located coronal to the GL in 87.9% of samples. The vertical distance between the GZ of the lateral incisor and the GL was 0.59 mm and no statistically significant difference was detected.

The most common findings were a high or average smile type, combined with an upward GL. In the majority of subjects, the GZ of the lateral incisor is coronal to the GL. The apico-coronal displacement of the GZ showed bilateral symmetry.