Various study designs were used in this dissertation to assess the defining, seeking, and reporting of adverse effects in systematic reviews of orthodontic interventions. Distorted presentation (spin) of these effects in the abstracts of these reviews was also assessed. For the cross-sectional studies, The Cochrane Database of Systematic Reviews and five leading orthodontic journals were searched for eligible reviews. Study selection and data extraction were conducted by two researchers independently. 98 eligible systematic reviews of orthodontic interventions were identified of which 35 (36%) defined seeking of adverse as a research objective, 84 (86%) sought findings related to adverse effects, 83 (85%) reported them and 89 (91%) considered or discussed potential adverse effects. 77% (75/98) of the abstracts of these reviews reported or considered potential adverse effects of orthodontic interventions. Spin regarding these effects was present in 41% (40/98) of abstracts and misleading reporting was the predominant type (90% (36/40). Univariable logistic regression models (95% CI) showed no associations between the presence of spin in the abstracts of the reviews and any of the variables explored. The 195 adverse effects identified in the reviews were used for a new framework for categorizing and defining adverse effects of orthodontic interventions. Having included only leading orthodontic journals could have implied an underestimation of the problems. In conclusion, most systematic reviews of orthodontic interventions assessed and reported adverse effects but these actions were not systematic, incomplete, and selective. These findings and the risk of spin in the pertinent abstracts require caution when making clinical decisions
