While oral appliances (OA) have demonstrated good efficacy in patients ranging from mild to severe levels of obstructive sleep apnea (OSA), this form of treatment is not completely effective in all patients. As a successful treatment response is not dependent solely on apnea hypopnea index severity, the prediction of OA treatment efficacy is of key importance for efficient disease management. This systematic review aims to investigate the accuracy of a variety of clinical and experimental tests for predicting OA treatment outcomes in OSA. A systematic literature review was conducted and the quality of the selected studies was assessed using the quality assessment of diagnostic accuracy studies (QUADAS-2) tool. Some 17 studies involving various prediction methods were included in this review. The predictive accuracy varied depending on the definitions of treatment success used as well as the type of index test. The studies with the best predictive accuracy and lowest risk of bias and concerns of applicability used a multisensor catheter. While a remotely controlled mandibular positioner study showed high accuracy, there was a high risk of bias. The available information on the validity of predictive index tests is very useful in clinical practice and allows for greater disease management efficiency.