Objective:The aim of this research was to study the transverse changes during molar distalization with clear aligner treatment,and to evaluate the predictability.Methods:This retrospective study included the following two parts:(1)20 patients treated with Invisalign system were selected.Their digital models were measured with OrthoCAD(Align Technology)and then com-pared with the initial ClinCheck arch width to verify the consistency between them;(2)34 patients whose maxillary molars were dis-talized,and 12 patients whose maxillary and mandibular molars were both distalized,were involved.The widths between canines,premolars and molars were recorded from Clincheck software at T0(initial),T1(Invisalign-predicted),and T2(pretreatment,from the refinement ClinCheck plan)and then compared.Results:The measured value of dental arch width of OrthoCAD and ClinCheck were consistent.After wearing the first stage appliance,the width between maxillary and mandibular teeth at T2 ranges from 1.63 to 3.45 mm.In the maxilla,the width at T1 differed from that at T2 and the predictability ranged from 80.43％to 82.29％,while the predictability ranged from 88.88％to 93.08％in the mandible.Conclusion:(1)The arches were expanded during molar distaliza-tion with clear aligners;(2)The predictability ranged from 80.43％to 93.08％.It can be considered that the actual width change is close to the target change.

Objective:The aim of this research was to study the transverse changes during molar distalization with clear aligner treatment,and to evaluate the predictability.Methods:This retrospective study included the following two parts:(1)20 patients treated with Invisalign system were selected.Their digital models were measured with OrthoCAD(Align Technology)and then com-pared with the initial ClinCheck arch width to verify the consistency between them;(2)34 patients whose maxillary molars were dis-talized,and 12 patients whose maxillary and mandibular molars were both distalized,were involved.The widths between canines,premolars and molars were recorded from Clincheck software at T0(initial),T1(Invisalign-predicted),and T2(pretreatment,from the refinement ClinCheck plan)and then compared.Results:The measured value of dental arch width of OrthoCAD and ClinCheck were consistent.After wearing the first stage appliance,the width between maxillary and mandibular teeth at T2 ranges from 1.63 to 3.45 mm.In the maxilla,the width at T1 differed from that at T2 and the predictability ranged from 80.43％to 82.29％,while the predictability ranged from 88.88％to 93.08％in the mandible.Conclusion:(1)The arches were expanded during molar distaliza-tion with clear aligners;(2)The predictability ranged from 80.43％to 93.08％.It can be considered that the actual width change is close to the target change.