Lip-tooth relationships during smiling and speech: an evaluation of different malocclusion types

Few studies have focused on the impact of malocclusion on lip - tooth relationships during smiling and speech.

To evaluate the impact of different malocclusions on lip - tooth relationships during smiling and speech, using video images.

One hundred and three subjects with Class I (N = 31), Class II division 1 (N = 26), Class II division 2 (N = 16) and Class III malocclusions (N = 30) were asked to repeat the same sentence and then smile in front of a video camera. Nine frames were extracted from each subject's video clip: at rest, posed smile, unposed smile and during the pronunciation of the sounds: 'che', 'fa', 'se', 'chee', 'tee' and 'mee'. On each frame, up to 10 parameters describing the lip - tooth relationships were measured.

In all frames, there were no statistically significant differences in the upper central incisor display ratios among the malocclusion groups (p > 0.05). The buccal corridor ratio in the posed and unposed smiles did not differ significantly among the malocclusions (p > 0.05). The most frequently visible last maxillary tooth was the first premolar in the posed smile, and the second premolar in the unposed smile. In each malocclusion group, the upper central incisor display ratio varied significantly among the nine frames and the buccal corridor ratio during the unposed smile was less than the ratio during the posed smile; although this was only significant in the Class II division 2 subjects. The smile arc was similar in all malocclusions.

In each malocclusion the upper central incisor display ratio varied significantly among the nine frames. In each group, the buccal corridor ratio during the unposed smile was less than that during the posed smile, but only the Class II division 2 group was significantly different. The smile arc did not differ among the malocclusions.