iDentistry The Journal Volume 14 No.1 | 页面 7

The Journal According to the study of Kravitz (et al.), only 13 of the 64 teeth that protruded was greater than 1 mm and none protruded more than 2 mm. It was interesting that the accuracy of posterior extrusion was 52%, which is higher than the 5 prediction . The alignment of the marginal tooth edges that requires vertical control of tooth movement in the Invisalign group and fixed braces was equivalent. This suggests that Invisalign can actually level arches as successfully as fixed braces. But Invisalign can not create a proper occlusion compared to fixed braces. Perhaps this is due to the fact that aligner has a limitation to extrude the teeth, unless there is a significant undercut. Besides, Invisalign covered occlusal surfaces of teeth preventing the settling of the occlusion 4 . D. Tipping In Pavoni‟s study, Invisalign showed the ability to tip crowns easily . Invisalign can easily tip crowns but cannot tip roots because of the lack 10 of control of teeth movement . The tipping movement can be done with Invisalign readily 1. The removable aligners showed the ability to move teeth up to 6mm by tipping incrementally into the spaces 4 . The role of uncontrolled tipping and loss of anchorage complicate the progression of programmed aligners. The accuracy of tipping for Invisalign was found to be range from 40.5% to 55%. AUTHOR INTRUSION Nguyen and Cheng[5] Canine tipping 44% Premolar tipping 55% Kravitz et al.2009 6 According to Nguyen and Cheng„s study, the mean accuracy of premolar tip was 55% and of 5 canine tip was 44% . Clear Aligner is not effective in controlling mesiodistal tipping unless being used with special attachments. There are two types of attachments: Clear Aligner power grip 2 (MDI- mesial / distal inclination) to help move the crowns mesially and move the roots distally; and power grip 3 (DMI - distal / mesial inclination) to move the crowns distally and move the roots mesially . The average accuracy of anterior mesialdistal tip was 40.5%. The highest accuracy was achieved by the maxillary lateral incisors (43.1%) and the lowest was achieved by the mandibular canines (26.9%) 9. Boyd reported a case of distalization more than 3 mm in Class II division 2 patient (Boyd), but Djeu (et al) and Clements (et al) concluded that it was difficult to use invisalign to correct anteroposterior discrepancies (4, 2). The accuracy of labiolingual tip was evaluated according to two groups: labial crown tip and lingual crown tip. Only the labial crown tip of the mandibular canines had a higher accuracy (44.8) than lingual crown tip (42.5%), while the other anterior labial crown tips were was less accurate than the lingual crown tip. The average accuracy of anterior lingual crown tip was 53.1%, while labial crown tip was only 37.6%. The pretreatment malocclusion affected the accuracy of the labiolingual crown tip 9. Mesiodistal tip Anterior 40.5% Labiolingual tip Anterior 44.7% Vol. 14 No. 1 Jan-Apr 2018