Retention phase is fundamental in orthodontic treatment. Around 70% of patients are subjected to relapse postorthodontic treatment. The risk of relapse can be minimized by prescribing a retainer suitable to a patient’s pre-treatment clinical condition and based on retention characteristics of retainers. When removable retainers are prescribed, responsibility of maintaining tooth stability lies on patients. Recent idea has been proposed that removable retainer should be worn indefinitely in order to maintain the treatment result. Therefore, the understanding of retention characteristics of removable retainers is important for promoting patient compliance and satisfaction. This article focuses on reviewing the use of removable retainers in relation to preferences among clinicians, patient acceptability, effectiveness, compliance, as well as retention regimes. An electronic search was conducted in the PubMed/MEDLINE, ScienceDirect and Scopus database. The search was performed up to June 2020 using a variety of keywords including orthodontic retainers, Hawley, vacuum formed and retention. Among the 248 publications that were initially searched, total of 56 publications were finally included. Twenty-seven were observational (6 prospective; 16 cross-sectional, 4 retrospective, and 1 case series), fourteen experimental, fourteen review articles, and one opinion piece. Although quite a number of reviews on removable retainers were available, several significant papers have been published recently. Furthermore, a guideline on retention regime is warranted.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can cause acute respiratory distress syndrome, hypercoagulability, hypertension, and multiorgan dysfunction. Effective antivirals with safe clinical profile are urgently needed to improve the overall prognosis. In an analysis of a randomly collected cohort of 124 patients with COVID-19, we found that hypercoagulability as indicated by elevated concentrations of D-dimers was associated with disease severity. By virtual screening of a U.S. FDA approved drug library, we identified an anticoagulation agent dipyridamole (DIP) , which suppressed SARS-CoV-2 replication . In a proof-of-concept trial involving 31 patients with COVID-19, DIP supplementation was associated with significantly decreased concentrations of D-dimers ( < 0.05), increased lymphocyte and platelet recovery in the circulation, and markedly improved clinical outcomes in comparison to the control patients. In particular, all 8 of the DIP-treated severely ill patients showed remarkable improvement: 7 patients (87.5%) achieved clinical cure and were discharged from the hospitals while the remaining 1 patient (12.5%) was in clinical remission.