Nowadays, orthodontic treatment has become increasingly popular. However, the biological mechanisms of orthodontic tooth movement (OTM) have not been fully elucidated. We were aiming to summarize the evidences regarding the mechanisms of OTM. Firstly, we introduced the research models as a basis for further discussion of mechanisms. Secondly, we proposed a new hypothesis regarding the primary roles of periodontal ligament cells (PDLCs) and osteocytes involved in OTM mechanisms and summarized the biomechanical and biological responses of the periodontium in OTM through four steps, basically in OTM temporal sequences, as follows: (1) Extracellular mechanobiology of periodontium: biological, mechanical, and material changes of acellular components in periodontium under orthodontic forces were introduced. (2) Cell strain: the sensing, transduction, and regulation of mechanical stimuli in PDLCs and osteocytes. (3) Cell activation and differentiation: the activation and differentiation mechanisms of osteoblast and osteoclast, the force-induced sterile inflammation, and the communication networks consisting of sensors and effectors. (4) Tissue remodeling: the remodeling of bone and periodontal ligament (PDL) in the compression side and tension side responding to mechanical stimuli and root resorption. Lastly, we talked about the clinical implications of the updated OTM mechanisms, regarding optimal orthodontic force (OOF), acceleration of OTM, and prevention of root resorption.

Objectives To analyze the biomechanical system of anterior retraction with clear aligner therapy (CAT) with and without an anterior mini-screw and elastics. Materials and Methods Models including a maxillary dentition (without first premolars), maxilla, periodontal ligaments (PDLs), attachments, and aligners were constructed and imported to finite element software. Three model groups were created: (1) control (CAT alone), (2) labial elastics (CAT with elastics between the anterior mini-screw and buttons on central incisors), and (3) linguoincisal elastics (CAT with elastics between the anterior mini-screw and precision cuts on the lingual sides of the aligner). Elastic forces (0–300 g, in 50 g increments) were applied. Results CAT alone caused lingual tipping and extrusion of the incisors. Labial elastics caused palatal root torquing and intrusion and mesial tipping of the central incisors, while linguoincisal elastics produced palatal root torquing and intrusion of both central and lateral incisors. Second premolars were intruded in all three groups, with less intrusion in the linguoincisal elastics group. For the control group, stress was concentrated on both labial and lingual root surfaces, alveolar ridge, and cervical and apical PDLs. Stress was more concentrated in the labial elastics group and less concentrated in the linguoincisal elastics group. Conclusions CAT produced lingual tipping and extrusion of incisors during anterior retraction. Anterior mini-screws and elastics can achieve incisor intrusion and palatal root torquing. Linguoincisal elastics are superior to labial elastics with a lower likelihood of buccal open bite. Root resorption and alveolar defects may occur in CAT, more likely for labial elastics and less likely for linguoincisal elastics.

Objectives To compare the effects of Forsus appliances with and without temporary anchorage devices (TADs) for patients with skeletal Class II malocclusion. Materials and Methods Through a predefined search strategy, electronic searching was conducted in PubMed, Embase, Web of Science, CENTRAL, ProQuest Dissertations & Theses, and SIGLE with no language restrictions. Eligible study selection, data extraction, and evaluation of risk of bias (Cochrane Collaboration tool) were conducted by two authors independently and in duplicate. Any disagreement was solved by discussion or judged by a third reviewer. Statistical pooling, sensitivity analysis, subgroup analysis, and assessment of small-study effects were conducted by using Comprehensive Meta-Analysis and Stata 12.0. Heterogeneity was analyzed for different types of study designs, TADs, and radiographic examinations. Results Electronic search yielded a total of 256 studies after removing duplicates. Among them, six studies were finally included. All articles were of high quality. The pooled mean differences were –0.27 (95% confidence interval [CI]: –0.59, 0.05) for SNA, 0.58 (95% CI: –0.07, 1.23) for SNB, –0.86 (95% CI: –1.74, –0.03) for ANB, 1.63 (95% CI: 0.46, 2.80) for Co-Po, 0.75 (95% CI: 0.28, 1.23) for SN-MP, –7.56 (95% CI: –11.37, –3.76) for L1-MP, 0.47 (95% CI: –0.98, 1.91) for overjet, 0.39 (95% CI: –0.57, 1.35) for overbite, –1.84 (95% CI: −5.15, 1.47) for SN-OP, and 4.97 (95% CI: –1.22, 11.17) for nasolabial angle. Conclusions TADs (especially miniplates) were able to eliminate dental adverse effects of Forsus appliances for correction of skeletal Class II malocclusion.