The third point of reference and its effect on the protrusive condylar guidance angles obtained in semi-adjustable articulator

Abstract

Context: Clinicians have questioned the transferability of occlusal plane relationship from the patient to the articulator when Orbitale was used as anterior point of reference for the facebow transfer. Aims: The aim of this study was to evaluate the effect of 4 different anterior reference points on the protrusive condylar guidance angles in using an articulator. Settings and Design: Twelve dentate patients were selected for the study. Hanau Wide Vue (No. 183, Teledyne Water Pik, Fort Collins, Colorado, USA) and corresponding SpringBow (Teledyne Water Pik, Fort Collins, Colorado, USA) were used in the study. Materials and Methods: Four maxillary casts were obtained for each patient and mounted on a Hanau Wide Vue articulator with the help of a SpringBow using Orbitale, Orbitale minus 7 mm, and the inferior and superior annular notches of the articulator incisal guide pin as four points of references. The mandibular casts were hand articulated in the maximum intercuspal position. Protrusive records were made using Polyether Bite Registration material (Ramitec, 3M ESPE, St. Paul, MN), and the articulator was programmed for all the 4 mountings in each patient. The protrusive condylar path angles to Frankfort plane were obtained from lateral cephalometric tracings made in maximum intercuspation and protrusive position for comparison. Statistical Analysis Used: Statistical analysis was done using paired t test and Wilcoxon's signed rank test ( P < 0.05) to make a comparison between the protrusive condylar guidance angles obtained from the interocclusal records with the mountings using 4 different third points of references and those of radiographic tracings. Results: The protrusive condylar guidance values obtained on the casts related to the third point of reference with the superior annular notch and Orbitale minus 7 mm reference points differed significantly from the radiographic values ( P < 0.05). The mean protrusive condylar guidance angles differed from the mean radiographic values in an ascending order: inferior annular notch (-2.4 degrees), Orbitale (5.2 degrees), Orbitale minus 7 mm (13.1 degrees), and superior annular notch (17.0 degrees) respectively ( P < 0.05). The protrusive condylar guidance registrations for the right and the left sides on the casts related to the third point of reference with Orbitale (R = 41.8 degrees and L = 36.9 degrees) and inferior annular notch (R = 49.4 degrees and L = 44.8 degrees) were found to be closer to radiographic values (R = 47.0 degrees and L = 41.0 degrees) ( P < 0.05). Conclusions: Within the limitations of this study, the Orbitale and inferior annular notches were found to be more accurate anterior points of references than the superior annular notch and Orbitale minus 7 mm reference points to mount the casts in Hanau Wide Vue articulator using Hanau SpringBow.