Determination of optimal incisor overtreatment and molar anchorage preparation for first-premolar extraction patients treated with clear aligners

OBJECTIVES: This study aimed to analyze the optimal incisor overtreatment and molar anchorage preparation in premolar-extraction cases with clear aligner therapy (CAT) and generate a formula to provide reference values in the digital setup. METHODS: Eligible patients who underwent upper first premolar extraction with CAT were recruited. Angular changes (buccolingual tipping of central incisors, mesiodistal tipping of upper first molars) and linear movements (incisor retraction, molar protraction) were measured. Target value was defined as the required value for the tooth to revert to its normal angulation. Excessive amount (overtreatment and anchorage preparation) beyond target values were designed in digitized setup. The differences between achieved and target values (DAT) for incisors and molars were analyzed. Associations between DAT and demographic, clinical, cephalometric, and anatomic factors were evaluated. RESULTS: Undesired lingual tipping (-5.5 ± 7.1º) of central incisors and mesial tipping (0.2 ± 2.5º) of first molars were observed. DAT of incisor proclination was significantly associated with incisor overtreatment, U1-SN, incisor retraction, incisor and canine attachment. DAT of molar inclination was significantly correlated with molar anchorage preparation, overbite, molar mesial displacement, incisor overtreatment, crowding, U1-SN, and cortical anchorage of canines. LIMITATIONS: Residual confounding may persist due to limitations inherent to observational studies. CONCLUSIONS: Optimal incisor overtreatment is influenced by incisor retraction, U1-SN, incisor and canine attachment. Molar anchorage preparation is influenced by molar mesial displacement, U1-SN, overbite, incisor overtreatment, crowding, and cortical anchorage of canines.