Occlusion of the Teeth
The patient elevates the lower jaw to a position where the teeth are in contact and the relative position of the mandibular teeth in relation to the maxillary teeth is observed.
Depression of the Mandible
The patient is asked to open the mouth. On slow active opening of the mouth, the therapist observes for deviation of the mandible from the midline. In normal mouth opening, the mandible moves in a straight line. Deviation of the mandible to the left in the form of a C-type curve indicates hypomobility of the TMJ situated on the convex side of the C curve, or hypermobility of the joint on the concave side of the curve. Deviation in the shape of an S-type curve may indicate a muscular imbalance or displacement of the condyle. Functional ROM is determined by placing two or three flexed proximal interphalangeal joints between the upper and lower central incisor teeth. The fingers represent a distance of about 35 to 50 mm. Using a ruler and the edges of the upper and lower central incisor teeth for reference, a measure of opening can be obtained for recording change. Vernier calipers may also be used to measure the distance between the edges of the upper and lower central incisor teeth to establish the range of mandibular depression.
Protrusion of the Mandible
The patient protrudes the lower jaw. The lower jaw should protrude far enough for the patient to place the lower teeth beyond the upper teeth. A ruler measurement may be obtained by measuring the distance between the upper and lower central incisors. Normal protrusion from resting position is 3 to 7 mm.
Lateral Deviation of the Mandible
The patient deviates the lower jaw to one side and then the other. A measure can be obtained for recording purposes by measuring the distance between two selected points that are level, one on the upper teeth and one on the lower teeth, such as the space between the central incisors. The normal range of motion is 5 to 12 mm. Lateral deviation of the mandible should be symmetrical.