DYNAMIC OCCLUSION - Working vs. Non-working Movement & Occlusal Grid

Ryan introduces the concept of dynamic occlusion, which involves the movement of the jaw. He suggests watching a previous video on static occlusion before proceeding. The video revisits a drawing from the first video, illustrating the left and right sides of the mouth and the molars. It explains how the mandible's movement to the left results in working movement on the left side and non-working or balancing movement on the right. A simple rule of thumb is provided to remember which side is working based on the direction of movement. The video then delves into the Twin Peaks diagram, coloring it to represent the Centrex tops and explaining how surfaces will touch during leftward and rightward movements. The explanation continues with an axial or occlusal view, showing how the upper lingual cusps contact the central fossa and the lower marginal ridges, and vice versa for the buccal cusps. The video concludes with an introduction to the occlusal grid, which represents each tooth and contact point, and how it correlates with the visual representation of the mouth.

The video continues by discussing the difference between working and non-working movements from an occlusal view. It explains that when the patient moves to their left, the left side becomes the working side, and the right side becomes non-working. The condyle on the working side pivots, while the condyle on the non-working side slides down the articular eminence. The video emphasizes that the non-working side's condyle does more work due to the nature of the mandible's single bone with two joints. It then describes the direction of working and non-working movements, with working movements being more straight out towards the buccal, and non-working movements being oblique or diagonal. The video also introduces protrude movement, where the mandibular cusps move anteriorly as both condyles move forward. The occlusal grid is revisited with arrows indicating the directions of working and non-working movements for both the maxilla and mandible. Practice problems are presented to apply the concepts, with two methods suggested for solving them: converting to a word problem or solving directly on the picture.

The video provides a method for determining which cusps contact during static and dynamic occlusion. It emphasizes the importance of knowing the location within the mouth and the specific tooth in question. Using the picket fence concept from a previous video, the video demonstrates how to identify which cusps will contact at a given point. A shortcut is introduced for quickly determining the contacting cusp from a picture by moving disto-facial and in an oblique line. The video then practices using the occlusal grid to determine which cusps a mandibular second premolar's buccal cusp may contact during a leftward movement. It outlines a systematic approach to locate the cusps, find where they include in the opposing arch, and determine the type of movement (working or non-working). The video also addresses the limitations of the occlusal grid, noting the absence of distal cusps for the mandibular first molar and the unlikelihood of questions regarding them.

The video demonstrates how to use the occlusal grid to solve practice problems involving dynamic occlusion. It shows how to locate the cusps, determine the opposing arch, and draw in the appropriate arrow for the specified movement. The video explains that for a right-lateral excursion, the mesial-lingual cusp of the maxillary second molar would pass through the lingual groove of the mandibular second molar during a working movement. For a left non-working movement, the mesial buccal cusp of the right maxillary first premolar would pass through the mesial buccal groove of the first mandibular molar and the central fossa area. The video emphasizes the utility of the occlusal grid for exams and board situations, providing a method that can be easily memorized and reproduced on test papers.

The video concludes by summarizing the key tools covered: the twin peaks diagram for the coronal view, the picket-fence diagram for the sagittal view, and the occlusal grid diagram for the axial view. Ryan expresses confidence that with these tools, viewers can effectively tackle any occlusion question they encounter. He thanks the viewers for watching, encourages them to like, comment, and subscribe, and invites them to request additional topics for future videos.