Mandibular Movements PDF

BDS, MSc, PhD Lecturer of Prosthodontics, College of dentistry , AASTM During most normal movements of the mandible, both rotation and translation occur simultaneously (i.e., while the mandible is rotating around one or more of the axes, each of the axes is translating, or changing its orientatio...

BDS, MSc, PhD Lecturer of Prosthodontics, College of dentistry , AASTM During most normal movements of the mandible, both rotation and translation occur simultaneously (i.e., while the mandible is rotating around one or more of the axes, each of the axes is translating, or changing its orientation in space). This results in movements that are extremely complex in nature.  Reference planes Three-dimensional description of the Mandibular & Maxillary positioning  Axes of Rotation Centers of rotation  Frontal Plane: Best described by facing the patient. Frontal Axis  Horizontal Plane: Parallel to the Occlusal Plane or the floor.  Horizontal Axis: Imaginary line through both condyles  Sagittal Plane: Also known as a side view.  Sagittal Plane: Also known as a side view. Sagittal Axis   Basic mandibular movements Classified according to the direction of movement Opening and closing Forwards (Protrusive) Backwards (Retrusive) Sideways (Lateral)  Mandibular movements 1-Opening and closing: (depression and elevation of the mandible): Mandibular movement around the horizontal axis is an opening and closing motion. It is referred to as a hinge movement, and the horizontal axis around which it occurs is therefore referred to as the hinge axis.  Mandibular movements 1-Opening and closing: (depression and elevation of the mandible): This movement starts from the rest position to the maximum opening position. At the beginning of the opening movement, there is a rotation in the lower compartment of the TMJ The mandible can make pure rotational movements through an arc of 10-20 mm with further opening a gliding movement occurs in the upper compartment. For the closing movement, the mandible moves from the maximum opening position with a reverse movement back to the rest position. 10-20mm Mandibular movements 2- Forward (protrusive movement) The condyles together with their articular discs move as one unit downwards and forwards along the glenoid fossa and the articular eminence.  Mandibular movements 2- Forward (protrusive movement) Protrusive movements are brought about by the contraction of the external pterygoid muscles on each side.(both lateral pterygoids work )  2- Forward (protrusive movement) The incisal guidance Is the path performed by the forward glide of the incisal point from the intercuspal position towards the edge to edge position  2- Forward (protrusive movement) Condylar Path Protrusive condylar path (sagittal condylar path) Is the path traveled by the condyle in the protrusive movement. It varies in individuals and also in the same individual from the left to the right side. It ranges between 30°-40°  Reverse direction of protrusive movements Brought about by contraction of Temporalis Muscles. Similar to protrusive movement but in a reverse direction (Upward and backward) Mandibular movements 4- Lateral movement (sideways) The right and left lateral movements of the mandible from the intercuspal position and back again to the same position are asymmetric Mandibular movements 4- Lateral movement (sideways) When the mandible moves towards the right side, the condyle on this side rotates mainly with a very slight bodily lateral translation ( working side ), the condyle on the left side moves forward, downward and medially ( balancing or non-working side).  Working & nonworking side The side toward which the mandible moves in a lateral excursion is called working side And The nonworking side is that side of mandible that moves toward median line in a lateral excursion Working (Rotating) Condyle: It moves slightly in lateral direction, this movement is called (Bennett Shift, or Bennett Movement). Non Working (Orbiting) Condyle: 1. It moves forward, downward, and medial 2. It moves forward and downward like in protrusion (but not exact sagittal angle). 3. It moves medially, with an angle called lateral condylar angle or Bennett angle (about 15°). Importance of studying mandibular movements 1-Designing, selection, and adjustment of articulator. 2-Developing tooth form for dental restorations. 3-Diagnosis and treatment of TMJ disturbances. 4-Understanding the basic principles of occlusion. 5-Proper selection of teeth. 6-Arrangement of artificial teeth