Incisor inclination and perceived tooth colour changes

Social attractiveness is influenced by a variety of different smile-related factors. We evaluated whether the degree of upper central incisor proclination can result in tooth colour change.

Forty young adult subjects (20-25 years) in good health with a complete sound dentition were selected. The subjects were seated in standardized light conditions with an above-directed light source. Their natural head position was stated as 0 degrees. To mimic the range of possible anterior torque movements they were asked to tilt their heads upward +15 degrees (upward tilting) and downward -15 degrees (downward tilting). Frontal macro photographs, parallel to the Frankfort plane of the patient's natural head position were taken at the three head angulations (+15, 0, and -15 degrees ). Photographs were analysed for colour differences at the centre of the incisor clinical crowns with a CIE L*a*b* colour model based software. A paired t-test was used to test for significance between each value for each inclination.

Differences were found between the CIE L*a*b* colour values for: upward tilting, downward tilting, and -15 to +15 degrees (total tilting) except for b* values for downward tilting. As the inclination of the subject's head changed downward, the upper incisors were retroclined and the CIE L*a*b* values indicated a darker and less green but redder colour component. As the inclination of the subject's head changed upwards the upper incisors were proclined and the L*a*b* values indicated a lighter and less green and yellow but redder and bluer colour component.

Proclination of upper incisors caused lighter tooth colour parameters compared to retroclined incisors and colour changes. Orthodontic change of upper incisor inclination may induce alterations on how tooth colour is perceived.