iDentistry The Journal Volume 14 No.1 | Page 5

The Journal Material and Methods Used Pubmed to search electronic databases in English, with keywords such as "Invisalign", "Clear aligners", "Thermoplastic appliances", "Clear plastic appliances", "Sequential removable orthodontic appliances ", “ Clear aligners tooth movement” and using filters “Clinical trial” . After reading through the abstracts, articles in English that related to the effectiveness of clear aligners, the accuracy of clear aligners and the factors related to the effectiveness of clear aligners were selected. Finally, the articles of the clinical studies including prospective, retrospective, randomized studies were chosen. Results Optimum force levels for orthodontic tooth movement should be just high enough to stimulate cellular activity without completely occluding blood vessels in the PDL. Both the amount of force delivered to a tooth and the area of the PDL over which that force is distributed are important in determining the tooth movement. There are many different forces that can be used for tooth movement; like translation [70- 120gms], uprighting [50-100gms], rotation [35- 60gms], extrusion [35-60gms, tipping [35- 60gms], and intrusion which needs lighter amount of force [10-20gms]. Tipping needs only a single force, while bodily movement needs two or more force systems. The use of plastic, transparent polyurethane aligners as a solution to replace fixed orthodontic therapy raises questions about its effectiveness in moving the teeth as well as the accuracy of the software that simulates and predicts the tooth movements. The Clear aligner therapy is complicated by the uncertainty of where the exact point the forces reach and its coverage over all surfaces of the 4 teeth, so the point of force application depends on the tooth geometry, the materials‟ properties, the fit over the teeth and programmed activation. 1. How accurate is the prediction. In these three clinical studies[ 5,8,9 ] the accuracy of tooth movements was measured by comparing predicted with actual achieved outcomes. While the ClinCheck software program predicts the movements of the teeth, achieved outcomes could not be exactly the same. The average accuracy of tooth movements for anteriors was found to range from 41% 9 to 56% 5 . The amount of concordance was only 14.3% when comparing the predicted outcomes with the achieved outcomes 11 . 2. Types of tooth movement A. Expansion Expansion is used to create the space needed for orthodontic treatment. Sometimes transverse maxillary expansion and protrusion on the anteriors can create enough space for orthodontic treatment without the need of extraction. The change of transverse dento- alveolar width by self- ligating braces was found to be statistically better results than Invisalign in the study of Pavoni et al. In the Invisalign group, the first intermolar widths (lingual and cusp), the second intermolar widths (lingual) and the intercanine widths (lingual and cusp) showed no statistically significant change. In general, no significant expansions in maxillary arches in all of the measurements were shown in Invisalign group 11 . On the contrary, the Invisalign treatment of crowded anteriors showed satisfactory success in all subjects by protrusion on the anteriors, distalization, and IPR in the study by Krieger et al.2012. Noteworthy finding was that 47% of the mandibular crowding subjects were treated successfully by a combination of IPR and protrusion 13 . Vol. 14 No. 1 Jan-Apr 2018