Reference points to evaluate changes in the upper lip after labial incisor movement between tipping and translation...

This study aimed to compare the changes of reference points on the labial surface of upper incisors (U1) to upper lip (UL) after U1 labial movement between a translation group (TSL) and tipping group (TIP). Correlations between changes in U1 and UL were determined.

Lateral cephalometric radiographs were selected and divided into TSL and TIP groups by pre- and post-treatment superimpositions. Skeletal, dental, and soft tissue of pre- and post-treatment and variables were evaluated. Independent t-test and Mann-Whitney U test were applied for the statistical analysis between TSL and TIP. Spearman's correlation coefficients and multiple linear regression analysis were used to verify the association between lip profile changes and other variables in TSL and TIP group separately.

After U1 labial movement, the incisal edge (LaU1e), middle (LaU1m), and cervical (LaU1c) points of TSL moved evenly labially, whereas the TIP group had incisal edge that moved greater labially than the middle and cervical points. UL moved more labially in TSL (0.87-1.05 mm) than the TIP (0.31-0.41 mm). UL changes to the E-line in TSL showed significant positive correlations to all three LaU1(e, m, c)-SnTV changes. In the TIP group, only a positive correlation presented for the LaU1m-SnTV and LaU1c-SnTV changes. Nevertheless, Multiple linear regression analysis indicated the unfeasibility of predicting the upper lip changing.

LaU1e in TSL and TIP moved almost equally labially but less labially in TIP at the middle and cervical points. The UL moved more labially in TSL than TIP. Rather than using the incisal edge to estimate upper lip changes, it would be better to use the middle and cervical points of U1, which coincide with Labrale superioris (Ls).