A limitation of the maximal mouth opening (MMO) is a frequent complication of oral (cancer) surgery. The measurement between the right central incisors is considered the golden standard for assessing MMO, although it has been noted to overestimate MMO in edentulous patients. This study aims to evaluate the reproducibility and validity of four MMO techniques and to determine the extent to which they are dependent on the remaining dentition.

Four methods for capturing the MMO were recorded in consecutive patients with mixed dentition. The degree of agreement between the different measurement methods was compared using Bland-Altman plots. To investigate the reproducibility of each method, intersession, interobserver and intraobserver reliability were calculated for measurements performed by two clinicians across two sessions. Two subgroups were created based on dentition: (A) cases missing at least one right central incisor, and (B) patients with both right central incisors present.

All but one intraclass correlation coefficient (ICC) demonstrated excellent reproducibility (ICC > 0.9). The highest ICC values were found for the intraoral MMO(iMMO) and corrected intraoral MMO(ciMMO) method. A significant relationship between the MMO in both subgroups was identified only for the intraoral Range of Motion (iROM) method (p=.010*).

The findings suggest that the current golden standard for measuring MMO does not adequately account for the absence of the right central incisor(s). Two of the proposed methods, which include corrections for missing incisors, should be incorporated into future clinical trials on MMO.