March 04, 2015
The mandibular movements have borders that can be recorded and displayed on a horizontal plane. If we imagine that we are looking down through the head from above we can draw the borders of the lateral and anterior-posterior movements of the jaw. These tracings can be made on an intraoral plate, or extraorally using a pantographic tracing device. The borders of the mandibular movement drawn on a piece of paper are known as Gothic arch tracings.
The Gothic arch tracing begin with the mandible at the terminal hinge position. The hinge position (point A) is achieved when the mandible is retruded maximally. The central occlusion point (point CO) is located 1mm anterior to the hinge position. If we keep protruding the lower jaw we will get to the fully protruded position of the mandible (point C). In this position both condyles have translated onto their eminences.
The lateral movements of the jaw are connected to condyle repositioning in the temporomandibular joints (TMJ). The incisal point moves left and anteriorly as the right condyle translates anteriorly and inward. The right lateral border tracing is made as the incisal point moves right laterally and anteriorly while the left condyle translates anteriorly and lingually.
There are great individual differences in the characteristics of the Gothic arch tracings. These differences are due to individual variability in the shape and size of the condyle and fossa forming the TMJ and to muscular and ligament characteristics.