Evidence for chronic mechanical irritation as a causative factor in oral cancer: application of Bradford Hill criteria

Chronic mechanical irritation (CMI) of the oral mucosa has been proposed as a risk factor for oral cancer (OC), but the available evidence is limited and controversial. One of the main limitations is the lack of proper criteria to define and classify CMI. The objective of this narrative review is to apply the Bradford Hill causality criteria to assess such an association based on the published literature. The level of evidence is not conclusive, mainly due to methodological shortcomings. Hence, to systematize future CMI research, we recommend the following items should be included: a clear definition for CMI, ascertaining any temporal association, recording all types of CMI: dental, prosthetic, and functional. Finally, it is important to emphasize that studies dealing with risk factors for OC should not only be restricted to established factors such as tobacco, alcohol, and areca nut consumption but should also consider other factors including the patient’s dental condition. In this regard, CMI, tooth loss, periodontal disease, and many others could be included. The causality criteria set out by Bradford Hill could be used for studying different controversial risk factors for OC.