Ultrasonic jaw tracking device - accuracy of two different sensors

Objectives: For prosthodontic rehabilitation as well as for diagnosis and therapy of TMJ jaw tracking devices are useful tools. Aim of this study was to compare the accuracy of two different sensors of CMS20JMA (Zebris/Germany) – mounted close to (S1) or distant (S2) the temporomandibular joint (S1). S1 is expected to be more precise than S2.

Methods: For detecting also little differences a testing device (Dentatus ARH articulator) was used gauging the cephalometric points TMJ right/left (JR, JL), Incisal (IN). Discrepancies of the static coordinates as well as protrusion distances (3,6,9mm) were measured with different incisal guidance angles (IGA; 0-40°) and statistically analyzed.

Results: The median discrepancies of coordinates are spreading from -1.8mm to +0.6mm (max. SD=2.0) for S1 and -1.1mm to +0.4mm (max. SD=0.5) for S2 (p<0.0001). In protrusion no correlation could be found with different IGA. Measuring distances both sensors show median deviations up to 0.3mm (max. SD=0.2) JR/JL/IN. For 3mm distance the measured angles show substantial SD (max. 3.7) with maximum discrepancies up to 8.2° in JL and 6.3° in JR. Prolonging the distance to 9mm SD decreases near IN (SD<1,0) with maximum discrepancies up to 4.6° in JR and 2,7° in JL (p<0.0001).

Conclusion: S1 is more accurate in detecting cephalometric points (p<0.0001). This could be explained by the sensor geometry near to the points of interest as well as the special calibrating process which S2 does not allow. Both sensors measure also short distances with only little discrepancy. The most precise region for measuring angles is the fixation point of the sensor near IN. Especially discrepancies for angles in JR and JL can result in an extensive need for chair-side corrections of static and dynamic occlusion while using this jaw tracking device for oral rehabilitation.