Occlusal plane orientation: a statistical and clinical analysis in different clinical situations

Orientation of the occlusal plane is important in a number of clinical situations. Using the reported soft and hard tissue landmarks is difficult and requires experience, as the landmarks are located on the face or by use of a cephalometric radiograph. Improper use of these landmarks may compromise the functional and esthetic result of prosthetic restorations. This study evaluated the reliability of the hamular notch/incisive papilla plane (HIP) in establishing the occlusal plane.

Ninety healthy, Indian adults (60 dentate, 30 edentulous) participated in this study. The occlusal plane of the subjects was compared with their HIPs. In dentate subjects, the maxillary stone cast was mounted on the Wills surveyor with HIP, which was made parallel to the horizontal plane using the tripoding method. The vertical distance between the occlusal plane and floor of the surveyor was measured at four points. When the measured values were equal, the two planes were confirmed to be parallel for that situation. In turn, this relation confirmed the parallelism between the occlusal plane and HIP. In the edentulous subjects, the occlusal plane, established clinically using the ala tragal line, was compared with the HIP radiographically using lateral cephalograms. Paired t-test was used to test the equality of the mean differences at a 0.05 significance level.

The mean differences from the right canine were: 0.055 cm at the left canine, 0.05 cm at the right molar, and 0.065 cm at the left molar in dentate subjects and 0.001 cm between the incisive papilla and hamular notch in edentulous subjects. The HIP appeared parallel to the occlusal plane as the paired t-test showed no statistically significant difference (p > 0.05).

In the population tested, the HIP was parallel to the occlusal plane. Therefore, this may be a viable reference in complete denture prosthodontics.