Chapter 5. Biomechanics of the Masticatory Apparatus
6 topics with concise breakdowns: definitions, key facts, and class questions.
This chapter is dedicated to the complex mechanics of mandibular movements and the interaction of the elements of the dentognathic system. Understanding biomechanics is the absolute foundation without which it is impossible to correctly model the occlusal relief of teeth and design prostheses.
In this section, we will analyze in detail the trajectories of mandibular movements in the sagittal and transversal planes. You will study the key concepts of articulation and occlusion, and also get acquainted with devices that simulate these movements in laboratory conditions—occluders and articulators.
During practical classes and credit tests, examiners most often ask about the difference between central, anterior, and lateral occlusions, require you to draw and explain the condylar and incisal pathways, and name the main angles (Bennett angle, sagittal condylar path angle). Pay special attention to the design of the articulator—this knowledge will be useful to you as early as your first clinical practice.
Why does the mandible protrude forward in complete edentulism?
This phenomenon is called senile progenia. When teeth are lost (edentulism), the alveolar processes resorb, and the jaw relationship is then determined by the basal arches. Since the lower basal arch is wider than the upper one, the mandible visually protrudes forward significantly.
What is the fundamental difference between articulation and occlusion?
Articulation encompasses absolutely any movements of the mandible in the TMJ. Occlusion, on the other hand, is merely a specific case of articulation characterized by the mandatory physical contact of the teeth of the upper and lower jaws.
What is the difference between habitual occlusion and central occlusion?
With habitual occlusion, there is maximum intercuspation of the dental arches, but the condyles of the TMJ may not occupy a strictly central position in the articular fossae. For true central occlusion, the correct position in the joint is mandatory.
Which muscles provide anterior occlusion?
Forward movement of the mandible is carried out due to the simultaneous (bilateral) contraction of the lateral pterygoid muscles.
What is the Bennett angle and where is it formed?
This is the angle that occurs during lateral movement of the jaw on the balancing (non-working) side. It is projected in the horizontal plane and is formed between the sagittal plane and the trajectory of the condyle shifting medially.
What is the interocclusal clearance and what is its normal value?
This is the distance between antagonist teeth in the anterior region when the mandible is in the position of relative physiological rest. The average value is 2–4 mm.
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