The Predictability of Transverse Changes in Patients Treated with Clear Aligners

Abstract

Arch expansion might be used to correct buccal corridors, improve smile aesthetics, resolve dental cross bite, and gain space to resolve crowding. In clear aligner treatment, the predictability of the expansion is still unclear. The purpose of this study was to evaluate the predictability of dentoalveolar expansion and molar inclination with clear aligners. In the study, 30 adult patients (27 ± 6.1 years old) treated with clear aligners were selected (treatment time: 8.8 ± 2.2 months). The upper and lower arch transverse diameters were measured for canines, first and second premolars, and first molars on two different sides (gingival margins and cusp tips); moreover, molar inclination was measured. A paired t-test and Wilcoxon test were used to compare prescription (planned movement) and achieved movement. In all cases, except for molar inclination, a statistically significant difference was found between achieved movement and prescription (p < 0.05). Our findings showed a total accuracy of 64% for the lower arch, 67% at the cusp level, and 59% at the gingival level, with a total accuracy of 67% for the upper arch, 71% at the cusp level, and 60% at the gingival level. The mean accuracy for molar inclination was 40%. Average expansion was greater at cusps of canines than for premolars, and it was lowest for molars. The expansion achieved with aligners is mainly due to the tipping of the crown rather than bodily movement of the tooth. The virtual plan overestimates the expansion of the teeth; thus, it is reasonable to plan an overcorrection when the arches are highly contracted.

Keywords: accuracy; aligner treatment; expansion; predictability.

Figure 1

Tooth segmentation.

Figure 2

Molar inclination.

Figure 3

Landmarks and transverse parameters on the buccal and gingival side. (a) Upper arch transverse diameters. Upper canine gingival width (UCGW); upper first premolar gingival width (U1PmGW); upper second premolar gingival width (U2PmGW); upper first molar gingival width (UMGW); upper canine cusp width (UCCW); upper first premolar cusp width (U1PmCW); upper second premolar cusp width (U2PmCW); upper first molar mesiobuccal cusp width (UMMCW); upper first molar distobuccal cusp width (UMDCW). (b) Lower arch transverse diameters. Lower canine gingival width (LCGW); lower first premolar gingival width (L1PmGW); lower second premolar gingival width (L2PmGW); lower first molar gingival width (LMGW); lower canine cusp width (LCCW); lower first premolar cusp width (L1PmCW); lower second premolar cusp width (L2PmCW); lower first molar mesiobuccal cusp width (LMMCW); lower first molar distobuccal cusp width (LMDCW).

Figure 3

Landmarks and transverse parameters on the buccal and gingival side. (a) Upper arch transverse diameters. Upper canine gingival width (UCGW); upper first premolar gingival width (U1PmGW); upper second premolar gingival width (U2PmGW); upper first molar gingival width (UMGW); upper canine cusp width (UCCW); upper first premolar cusp width (U1PmCW); upper second premolar cusp width (U2PmCW); upper first molar mesiobuccal cusp width (UMMCW); upper first molar distobuccal cusp width (UMDCW). (b) Lower arch transverse diameters. Lower canine gingival width (LCGW); lower first premolar gingival width (L1PmGW); lower second premolar gingival width (L2PmGW); lower first molar gingival width (LMGW); lower canine cusp width (LCCW); lower first premolar cusp width (L1PmCW); lower second premolar cusp width (L2PmCW); lower first molar mesiobuccal cusp width (LMMCW); lower first molar distobuccal cusp width (LMDCW).

Figure 4

Superimposition example. (a) Superimposition of T0 (blue scan) and T1 (green scan). (b) Superimposition of T0 (blue scan) and T2 (yellow scan).