Determination of the Transverse Horizontal Axis and Interocclusal Registration Using a Novel Optical Technique

Motivation: Dental treatments sometimes require the recording and reproduction of the patient’s transverse horizontal axis (THA). This is the axis about which the mandible will rotate, when the condyles are fully seated in their glenoid fossae. However, methods for recording this axis are rarely used in general practice, due to expense and perceived lack of efficacy.
Problem Statement: A simplified method for accurately recording the THA, and interocclusal records (IORs), is needed for general dentistry.
Approach: An optical 3D scanning method is proposed to kinematically record the THA. A simulation determines the required hardware specifications to build the scanner at minimal cost. The ability to record the hinge axis of a dental articulator is explored. High quality interocclusal optical records are essential, and these are investigated in subsequent experiments. Areas for improvements are identified and efforts are made to enhance the system speed and calibration.
Results: Simulation results indicated that all 6 upper and lower anterior teeth, including 2mm of gingivae should be captured, with an accuracy of 50µm.
The THA on a dental articulator could be located with a radial accuracy of 2.65±1.01mm.
The repeatability (precision) of IORs showed a standard deviation of 22µm anteriorly, and a mean of 43µm posteriorly in vitro.
The accuracy (trueness and precision) of the IORs was -15±22µm anteriorly, and up to -93±121µm posteriorly in vitro.
A faster scanning protocol enabled in vivo testing. 29 IORs of a single subject took <2s to perform. The registrations showed a repeatability of 31µm anteriorly and 70µm posteriorly.
A novel calibration process produced significantly reduced stereo reprojection errors compared to traditional methods (0.22 vs 0.27 pixels), offering a potential future system enhancement.
Conclusions: The proposed method shows potential to improve the speed, accuracy and simplicity with which the THA, and interocclusal registration, can be recorded. Further developments have been suggested prior to embarking on clinical trials.