Predictability of curve of Spee levelling and vertical tooth movements in the lower arch with clear aligners based on cone-beam computed tomography.

OBJECTIVE

This study aims to evaluate the predictability of Curve of Spee (COS) levelling and vertical tooth movements (VTMs) -- anterior intrusion and posterior extrusion– to determine optimal overtreatment ratios with clear aligners.

METHODS

This study included 464 teeth from 50 patients (mean age 24.3 ± 8.0; 68% female, 32% male) receiving clear aligner treatment. Pretreatment and posttreatment CBCT were superimposed with their corresponding dentition models using Geomagic Control X. The effectiveness of COS levelling and the achieved and predicted VTMs were measured.

RESULTS

The mean effectiveness for COS levelling was 52.9 ± 0.3%. The median effectiveness for VTMs ranged from 36.7% for mandibular first molar extrusion to 49.4% for mandibular premolar extrusion. No significant differences were observed across different tooth types (P > 0.05). The achieved changes in COS and VTM were significantly correlated with the predicted values (P < 0.001). Multivariate analysis revealed that predicted change in COS and VTM, age, pretreatment IMPA, MP-FH, COS depth, overbite, anterior intrusion staging, and extraction had differential impacts on the achieved change in COS and VTMs. Calibrated predictability values were derived, and the overtreatment ratios of 61%, 58%, 204%, and 79% were suggested for incisors, canines, premolars, and first molars, respectively.

CONCLUSIONS

Complete levelling of the COS in the lower arch is not fully achievable with clear aligners. The extent of COS levelling and VTMs is significantly correlated with predicted values, IMPA, MP-FH, intrusion staging, age, and overbite. Clinicians were recommended to overtreat incisors, canines, premolars, and first molars in the setup to achieve effective COS levelling.

CLINICAL RELEVANCE

Clear aligners exhibited suboptimal effectiveness in COS levelling. For effective levelling of the COS, a hybrid approach of incorporating attachments, vertical elastics, and aligners overtreatment is recommended.