D2 Mechanical Diagnosis

Topic

Mechanical diagnosis evaluates the biomechanical behavior of the masticatory system based on four aspects: the distribution of occlusal loads across the teeth, tooth mobility, the muscular forces generated by the masticatory system, and the pressures exerted within the temporomandibular joint. To assess these four aspects, mechanical diagnosis employs various instruments, each targeting one or more of them.

To evaluate the distribution of occlusal loads, the simplest tool is the occlusal record made using articulating paper; the patient bites down on the paper, which leaves a mark at every point of contact between the teeth. The greater the occlusal force applied at a contact point, the more distinct and larger the resulting mark on the articulating paper.

Unlike articulating paper, which provides only a static record of the contact, a digital system also exists that measures the relative force of each occlusal contact and how that force is distributed over time as the patient closes their mouth; this provides not only the distribution of occlusal loads but also the temporal sequence in which each occlusal contact engages.

To assess tooth mobility, a periodontometer is used; this instrument applies a standard force to the tooth and quantitatively measures the extent of the tooth's displacement in response to that force, thereby yielding a numerical value for tooth mobility rather than a subjective clinical assessment.

To evaluate the muscular forces of the masticatory system, electromyography of the masticatory muscles is employed; this records the electrical activity of these muscles during chewing, clenching, and grinding, allowing for a comparison of muscle activation levels across these three different situations. Bite analysis using force sensors directly measures the bite force the masticatory system can generate; this recorded force, combined with each patient's muscle geometry, informs a biomechanical model that treats the mandible as a lever. Based on bite force and muscle geometry, this mandibular lever model calculates the reaction force borne by the temporomandibular joint and the distribution of loads across the various teeth involved in the bite.

Together, these instruments provide a consistent set of measured variables for the masticatory system: bite force, tooth mobility, and the electromyographic signal of the masticatory muscles. From these measured variables, the mechanical diagnosis determines derived values—such as occlusal distribution among the teeth, torques borne by the temporomandibular joint, and a mechanical safety factor—that summarize how far the masticatory system's biomechanical behavior is from a point of failure.

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