An in vitro study into the accuracy of a novel method for recording the mandibular transverse horizontal axis.

OBJECTIVES To assess the accuracy of a novel, non-invasive method for determining the axis of rotation of articulated dental study casts. METHOD A 3D structured light scanner was constructed using a projector and two CMOS cameras. Dental stone casts were arbitrarily mounted on an average value articulator. With the teeth together, sets of 10 scans were taken from three different viewpoints. Each scan captured approximately six upper teeth and six lower teeth. The teeth were then propped open, creating 10mm of incisal separation, and the three sets of 10 scans were repeated. From each pair of scans an axis of rotation was calculated using custom software. A total of 900 axes were created this way. The locations of these axes were plotted in sagittal planes located 57.5mm left and right of the midline to represent the position of the temporo-mandibular joints (TMJs). The accuracy of axis location was then assessed. RESULTS The average radius of error of the individual axes, compared to the real axis, was 2.65 ± 1.01 mm. 61.3% of the axes lay within 3mm of the true axis, and 99.2% of the axes lay within 5mm of the true axis. CONCLUSIONS The accuracy of this method is clinically acceptable. Further studies are required to confirm the accuracy of the virtual inter-occlusal records at the level of the dentition. Clinical studies are then indicated to determine whether the transverse horizontal axis on a patient can similarly be determined.