Under pressure—mechanisms and risk factors for orthodontically induced inflammatory root resorption: a systematic review

BACKGROUND: The application of orthodontic forces causes root resorption of variable severity with potentially severe clinical ramifications. OBJECTIVE: To systematically review reports on the pathophysiological mechanisms of orthodontically induced inflammatory root resorption (OIIRR) and the associated risk factors based on in vitro, experimental, and in vivo studies. SEARCH METHODS: We undertook an electronic search of four databases and a separate hand-search. SELECTION CRITERIA: Studies reporting on the effect of orthodontic forces with/without the addition of potential risk factors on OIIRR, including (1) gene expression in in-vitro studies, the incidence root resorption in (2) animal studies, and (3) human studies. DATA COLLECTION AND ANALYSIS: Potential hits underwent a two-step selection, data extraction, quality assessment, and systematic appraisal performed by duplicate examiners. RESULTS: One hundred and eighteen articles met the eligibility criteria. Studies varied considerably in methodology, reporting of results, and variable risk of bias judgements.In summary, the variable evidence identified supports the notion that the application of orthodontic forces leads to (1) characteristic alterations of molecular expression profiles in vitro, (2) an increased rate of OIIRR in animal models, as well as (3) in human studies. Importantly, the additional presence of risk factors such as malocclusion, previous trauma, and medications like corticosteroids increased the severity of OIIRR, whilst other factors decreased its severity, including oral contraceptives, baicalin, and high caffeine. CONCLUSIONS: Based on the systematically reviewed evidence, OIIRR seems to be an inevitable consequence of the application of orthodontic forces-with different risk factors modifying its severity. Our review has identified several molecular mechanisms that can help explain this link between orthodontic forces and OIIRR. Nevertheless, it must be noted that the available eligible literature was in part significantly confounded by bias and was characterized by substantial methodological heterogeneity, suggesting that the results of this systematic review should be interpreted with caution. REGISTRATION: PROSPERO (CRD42021243431).