Maxillary Expansion Efficiency And Possible Influence Factors With Clear Aligner

Objective: To evaluate the efficiency of maxillary expansion with Invisalign clear aligners and to analyze the possible influence factors.Methods: 25 Invisalign cases with maxillary expansion were enrolled in this study.The 3D digital models of pre-treatment,Clincheck planned and post-treatment were collected.Upper dental arch width,buccal-lingual inclination of posterior teeth,and the expansion efficiency(expansion acquired/expansion planned)were measured and calculated.The CBCT images of 4 cases before and after the treatment were measured,and superimposed on the planned 3D models.SPSS 19.0 software was used to analyze the data.Factors such as planned buccal-lingual inclination,expansion amount,attachment,and the mode of expansion affecting the expansion efficiency were evaluated.Results:(1)The increases of upper inter-canines,premolars,first molars and second molars arch width were 2.10±1.49 mm,2.88±1.42 mm,1.76±0.90 mm and 0.39±0.45 mm,with their efficiency of 69.86%,68.10%,55.13% and 17.61% respectively.(2)The posterior teeth showed significantly more buccal inclination than the planned position(P<0.05).(3)CBCT measurements showed little changes on the width of maxillary base after the treatment.The heights and widths of buccal alveolar bone were reduced with significant increase in the buccal inclinat ions of the alveolar bone.(4)When the increase in planned inter-molar width was less than 2.5mm(n=9),the expansion efficiency of the other teeth were higher compared with those cases with the planned inter-molar width increase more than 2.5mm(n=16,P<0.05).(5)When the buccal-lingual inclination change of first molar was less than 0°(n=11),its expansion efficiency were higher than those with the inclination changes more than 0°(n=14,P<0.05).(6)Premolars and first molar with attachments showed more expansion than those without attachment(P<0.05).(7)No significant difference was observed between the groups of en-mass expansion and step-by-step expansion(P>0.05).Conclusion: The expansion of maxillary arch with clear aligners was achieved by the buccal movement and buccal inclination of the posterior teeth,along with the significant buccal inclination of the alveolar bone.The efficiency of expansion declines from canines to second molars.The planned inter-molar width has a significant influence on the efficiency of expansion.Attachment has positive influence on the expansion amount.Planned buccal-lingual inclination of posterior teeth and the mode of expansion have no significant influence on the expansion efficiency.