Aims: To evaluate a method for self-registration of maximum mandibular opening capacity by means of a spatula and estimation of vertical overbite from photos. Methods: The study group consisted of 50 adults. Each participant received written instructions, photos, a measuring spatula, and a pencil. The first task was to register maximum interincisal distance. The participant opened up his or her mouth as wide as possible, looked in a mirror, and marked the distance on the spatula. The second task was to estimate the vertical overbite in the intercuspal position. A clinician then estimated the type of overbite and measured the maximum interincisal distance and the vertical overbite with a ruler in millimeters. Results: The normal overbites showed a mean value of 2.4 mm, and a standard value of 2 mm was set. The deep bites showed a mean value of 5.2 mm, and a standard value of 5 mm was set. The standard overbite value, added to the value measured on the spatula, was compared with the clinical values made by the clinician for maximum mandibular opening. The limits of agreement for 95% of the mean difference were -4.2 mm and 4.4 mm. Six people missed the correct diagnosis for the vertical overbite. Conclusion: The self-registration method of measuring maximum mandibular opening capacity seems valid for studying major differences in opening capacity when clinical measurements are not possible to perform. Keywords: craniomandibular disorders, mandibular opening, repeatability for measurements, self-registration, temporomandibular joint, vertical overbite