Predictability Of Curve Of Spee Levelling With Clear Aligners

This study aims to evaluate the predictability of Curve of Spee(COS) levelling and that of its mechanics, vertical tooth movement(VTM) – anterior intrusion and posterior extrusion– to determine optimal overtreatment ratios with clear aligners. This study included 464 teeth from 50 patients receiving clear aligner treatment and ethical approval was obtained. Pretreatment and posttreatment CBCT were superimposed with its corresponding dentition models using Geomagic Control X. The effectiveness of COS levelling and the achieved and predicted VTMs were measured. The mean effectiveness for COS levelling was 52.9±0.3%. The median effectiveness for VTM 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 overtreatment ratios of 61%, 58%, 204%, 79% were suggested for incisors, canines, premolars and first molars, respectively. Complete levelling of the COS in the lower arch is not fully achievable. The achieved COS levelling and VTMs are 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.