Chronic mechanical irritation of the oral mucosa (CMI) has been proposed as a possible causative factor of oral cancer. However, the available scientific evidence is insufficient and controversial to determine this causal relationship, so more studies are needed to analyze it. Thus, it is essential to standardize the criteria to define CMI and consequently, for assessing its presence in each patient. In order to systematize CMI research, the following items should be included: (1) a clear definition for CMI; (2) a temporal association, (3) a record of all types of CMI, including dental, prosthetic, and functional; and (4) a notation of tumor size. Based on previously published CMI criteria, 5 cases of oral mucosal carcinomas T1 and T2 are presented. In each of them, the methodology to outline clinically the presence of CMI is shown, and compliance with the proposed CMI criteria is analyzed in detail. Chronic mechanical irritation of the oral mucosa (CMI) has been proposed as a possible causative factor of oral cancer. However, the available scientific evidence is insufficient and controversial to determine this causal relationship, so more studies are needed to analyze it. Thus, it is essential to standardize the criteria to define CMI and consequently, for assessing its presence in each patient. In order to systematize CMI research, the following items should be included: (1) a clear definition for CMI; (2) a temporal association, (3) a record of all types of CMI, including dental, prosthetic, and functional; and (4) a notation of tumor size. Based on previously published CMI criteria, 5 cases of oral mucosal carcinomas T1 and T2 are presented. In each of them, the methodology to outline clinically the presence of CMI is shown, and compliance with the proposed CMI criteria is analyzed in detail.