| Objective:Cone-beam computed tomography(CBCT)3-dimensional measurement was used to evaluate the effect of anchorage control with indirect anchorage assisted clear aligner appliance on maxillary molar distalization,which was constructed by rigid connection between mini-implant and anchorage teeth,and to provide theoretical reference for the anchorage design of clear aligner appliance.Method:11 adult patients(3 males and 8 females,average age 27.6 years)were selected as the subjects in this study,which were designed to distalize upper molar with clear aligner appliance.At the stage of molar distalization,the mini-implants were implanted between the buccal roots of the maxillary first molar and the second premolar,then connected to the maxillary second premolar rigidly to assist strengthening anchorage of molar distalization.Until the first molar had distally moved to the designated position,the mini-implants were transferred to the buccal roots between the first molar and the second molar,followed by connected with the first molar rigidly to assist strengthening the anchorage of alignment and retraction of the anterior teeth.CBCT images were taken at the time before the treatment(T0),when the first maxillary molar were distally moved to the designated position(T1),and when the anterior teeth were aligned(T2).The CBCT data were imported into Mimics 20.0 software for three-dimensional reconstruction.After correcting the head position,each reference point was determined in the multi-plane reconstruction view.The bilateral Porion,the right Orbitale,the Nasion and the Anterior nasal spine were selected as reference points to construct the three dimensional space coordinate system,and the positions of the first molar,the second premolar and the incisor were analyzed by three dimensional measurement.SPSS 22.0 software was used to analyze the data.The three dimensional position changes of maxillary first molars andmaxillary second premolars during the stage of T0-T1,T1-T2,T0-T2,and the mesiodistal and vertical position changes of maxillary central incisors were studied.Result:During the stage of T0-T1,T1-T2 and T0-T2,the three dimensional changes of the maxillary first molar,maxillary second premolar and maxillary central incisor were as follows:1.T0-T1 stage: The first maxillary molar had moved distally significantly in the sagittal direction,while the crown presented 3.57 ± 0.95 mm of distalization,the root presented 2.57 ± 0.73 mm of distalization.In the vertical direction,maxillary first molar presented 1.28 ± 0.77 mm of intrusion,which the differences had statistical significance(P <0.05).While in the horizontal direction,the positon change of maxillary first molar has no statistical significance(P> 0.05).There was no statistical difference in the three dimensional position changes of the maxillary second premolar and maxillary central incisor(P> 0.05).2.T1-T2 stage: There was no significant difference in the three-dimensional position of the first maxillary molar(P > 0.05).The maxillary second premolar moved distally significantly,while the crown presented 2.50 ± 1.06 mm of distalization,the root presented 1.67±1.40 mm of distalization.The differences were statistically significant(P <0.05).There was no significant position change for the second premolar in the vertical and horizontal direction(P> 0.05).The crown and root of the maxillary central incisors were presented retraction,while the crown presented 1.20±1.33 mm of retraction,and the root presented 1.07±0.87 mm of retraction.The differences were statistically significant(P <0.05).In the vertical direction,there was no significant change in the position of the maxillary central incisor,(P> 0.05).3.T0-T2 stage: The first maxillary molar had distalized significantly in the sagittal direction,while the crown presented 3.46±0.88 mm of distalization,and the root presented 2.06±1.86 mm of distalization.And it showed 1.03±0.80 mm of intrusion,which had statistical significance(P <0.05).But there was no significant positon change of the first maxillary molar in the horizontal direction(P> 0.05).Thecrown and root of the maxillary second premolar had distalized significantly in the sagittal direction,while the crown presented 2.65±1.06 mm of distalization,and the root presented 2.33±2.09 mm of distalization.The differences were statistically significant(P <0.05).There was no significant position change of the second premolar in the vertical and horizontal direction(P> 0.05).There was a slight retraction for the crown and root of the maxillary central incisor in the sagittal direction,while the crown presented 1.10±1.29 mm of retraction,and the root presented 1.05±1.24 mm of retraction.The differences had statistically significant(P<0.05).In the vertical direction,the maxillary central incisors presented 0.40±1.60 mm of extrusion.But the difference had no statistically significant(P > 0.05).Conclusion:The using of the mini-implant and rigid connection of teeth as an indirect anchorage to assist the clear aligner appliance on molar distalization could effectively enhance the anchorage of the teeth.It is an appropriate method to enhance the anchorage of clear aligner for the maxillary molar distalization. |
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