Chapter 1: Molar Distalization by Clear Aligners with Sequential Distalization Protocol Introduction: With the popularity of clear aligners, the sequential distalization protocol has been more commonly used for molar distalization. However, the amount of molar distalization that can be achieved, as well as the accompanying side effects on the sagittal dimension, are unclear. Methods: Registered with PROSPERO (CRD42023447211), relevant original studies were screened from seven databases (MEDLINE [PubMed], EBSCOhost, Web of Science, Elsevier [SCOPUS], Cochrane, LILACS [Latin American and Caribbean Health Sciences Literature], and Google Scholar) supplemented by a manual search of the references of the full-reading manuscripts by two investigators independently. A risk of bias assessment was conducted, relevant data were extracted, and meta-analysis was performed using RStudio. Results: After the screening, 13 articles (11 involving maxillary distalization, two involving mandibular distalization) met the inclusion criteria. All studies had a high or medium risk of bias. The meta-analysis revealed that the maxillary first molar (U6) mesiobuccal cusp was distalized 2.07 mm [1.38 mm, 2.77 mm] based on the post-distalization dental model superimposition, and the U6 crown was distalized 2.00 mm [0.77 mm, 3.24 mm] based on the post-treatment lateral cephalometric evaluation. However, the U6 mesiobuccal root showed less distalization of 1.13 mm [−1.34 mm, 3.60 mm], indicating crown distal tipping, which was validated by meta-analysis (U6-PP angle: 2.19° [1.06°, 3.33°]). In addition, intra-arch anchorage loss was observed at the post-distalization time point (U1 protrusion: 0.39 mm [0.27 mm, 0.51 mm]), which was corrected at the post-treatment time point (incisal edge-PTV distance: −1.50 mm [−2.61 mm, −0.39 mm]). Conclusion: About 2 mm maxillary molar distalization can be achieved with the sequential distalization protocol, accompanied by slight molar crown distal tipping. Additional studies on this topic are needed due to the high risk of bias in currently available studies.

Chapter 2: Vertical Control in Molar Distalization by Clear Aligners Background: Molar distalization is used to correct molar relationships or to create space for mild anterior crowding. However, whether clear aligners can provide proper vertical control with the sequential distalization strategy has been highly debated. Thus, the current study aimed to systematically review the amount of dentoskeletal changes in the vertical dimension that results from sequential molar distalization in clear aligner therapy without temporary anchorage devices (TADs). Methods: Registered with PROSPERO (CRD42023447211), relevant original studies were screened from seven databases and supplemented by a manual search by two investigators independently. Articles were screened against inclusion and exclusion criteria, and a risk of bias assessment was conducted for each included article. Relevant data were extracted from the included articles and meta-analysis was performed using RStudio. Results: Eleven articles (nine for maxillary distalization and two for mandibular distalization) were selected for the final review. All studies have a high or medium risk of bias. For maxillary molar distalization, the meta-analysis revealed 0.26 mm [0.23 mm, 0.29 mm] of maxillary first molar intrusion based on post-distalization dental model analysis, as well as 0.50 mm [−0.78 mm, 1.78 mm] of maxillary first molar intrusion and 0.60 mm [−0.42 mm, 1.62 mm] of maxillary second molar intrusion based on post-treatment lateral cephalometric analysis. Skeletally, there was a −0.33° [−0.67°, 0.02°] change in the SN-GoGn angle, −0.23° [−0.30°, 0.75°] change in the SN-MP angle, and 0.09° [−0.83°, 1.01°] change in the PP-GoGn angle based on post-treatment lateral cephalometric analysis. There was insufficient data for meta-analysis for mandibular molar distalization. Conclusions: No significant changes in vertical dimension were observed, both dentally and skeletally, after maxillary molar distalization with a sequential distalization strategy. However, further studies on this topic are needed due to the high risk of bias in the currently available studies.

Chapter 3: Maxillary Molar Distalization with Clear Aligner Therapy and Infrazygomatic Temporary Anchorage Devices System Introduction: Based on systematic reviews and meta- analyses, approximately 2 mm of maxillary molar distalization can be achieved with sequential molar distalization with clear aligner therapy (CAT) without skeletal anchorage. Distalization is accompanied by significant distal crown tipping and insignificant changes in the vertical dimension. Thus, combining CAT with temporary anchorage devices (TADs) has been proposed, but a detailed evaluation is lacking. Methods: This retrospective study evaluated pre-treatment (T1) and post-anterior retraction (T2) cone beam computed tomography (CBCT) images and digital models of adult patients treated with CAT + infrazygomatic TADs with at least 1 mm of programed maxillary first molar distalization. Achieved tooth movement shown on the CBCT and intraoral scan was compared to prescribed ClinCheck tooth movement. Results: The present study included 38 sides from 21 patients (17 females, 4 males; 28.71±4.16 years old at T1). At the crown level, about 1 mm of molar distalization was achieved (first molar (U6): 1.05 mm [-0.8, 3.6] based on digital models, 0.80 mm [-1.1, 3.4] based on CBCTs; second molar (U7): 0.95 mm [-1.8, 4.4] based on digital models, 1.25 mm [-1.9, 3.7] based on CBCTs), which is significantly lower than the prescribed ClinCheck movement (U6: 3.05 mm [1.0, 5.6]; U7: 3.05 mm [0.9, 6.1]). We observed limited crown distal tipping and mesial-out rotation but significant buccal expansion and intrusion of the maxillary molars. In addition, a negative correlation was detected between the amount of prescribed molar distal movement and the distalization efficacy. Measurements based on the CBCT and digital models were comparable for maxillary molar, rotation and tipping, as well as maxillary central incisor retraction and buccal crown torque. However, CBCT and digital model measurements showed discrepancies in vertical measurements. Conclusion: The CAT+TADs system did not significantly improve the efficacy of maxillary molar distalization when compared to existing clear aligner studies but provided more bodily movement and intrusion of the molars. As all patients in this study were treated with TADs, further studies with comparative designs are needed to isolate and evaluate the contribution of TADs to molar distalization.