Artifacts in recording immediate mandibular translation: A laboratory investigation

Statement of problem. Even though immediate mandibular translation has been extensively studied and analyzed, and its clinical significance emphasized, there is controversy as to whether it actually exists or whether it is just an artifact of the pantograph. Purpose. The aim of this study was to determine whether what appears to be pantographic evidence of immediate mandibular translation can actually be an artifact and, if so, to find a method to avoid it. Material and methods. The first part of this article explains geometrically with computer vector graphics how pure rotation can produce a pantographic tracing on the horizontal plate that is identical to what would be seen for immediate mandibular translation. The second part of the article presents a technique that uses a modified pantograph that eliminates the rotational artifact and thus permits proper interpretation of true immediate mandibular translation. Results. This study shows that pure rotation about the sagittal axis mimics immediate mandibular translation on a pantographic tracing when the plates are inferior to the transverse horizontal axis, produces scribings in an opposite direction for plates in a superior position, and produces no scribing when the plates are level with it. By modifying the pantograph so the tip of the scribing pin of the horizontal plate is level with the transverse horizontal axis, true immediate mandibular translation can most easily be differentiated from rotational artifact. Conclusions and Clinical Significance. Rotation can cause artifacts that mimic immediate mandibular translation. A technique to avoid this problem is presented. This technique provides the foundation for a valid evaluation of patients to determine whether true immediate mandibular translation exists and whether it is clinically important. (J Prosthet Dent 1997;78:172-8.).