Abstract: Centric relation is the accepted term for defining the condylar axis position of intact, completely seated, properly aligned condyle-disk assemblies. However, some structurally deformed temporomandibular joints may function comfortably, even though they do not fulfill the requirements for centric relation. A wide range of temporomandibular disorders from partial to complete disk derangements with or without reduction may adapt to a conformation that permits the joints to comfortably accept maximal compressive loading by the elevator muscles. There has been no accepted terminology to define the condition or position of such joints. The purpose of this article is to define a new term, adapted centric posture, and to explain its rationale and how it is determined. Verification of successful adaptation is an important step in diagnosis, because it rules out structural intracapsular disorders as a source of orofacial pain and establishes responsible guidelines for initiation of occlusal treatment or prosthetic dentistry. It also establishes a much needed terminology for more specific description of temporomandibular joint position and condition for clinical research on the relationship between occlusion and the temporomandibular joints.

Abstract: Clinical studies have confirmed the adequate reproducibility of both centric occlusion and centric relation when used as reference positions during treatment; however, the reproducibility of the neuromuscular position has been found inadequate. This study evaluated the location and reproducibility of these three mandibular positions in relation to body posture, sitting and supine, and bilateral muscle activity before and after the insertion of a flat mandibular positioning device equilibrated to balance the muscle functions, as shown by two electromyography biofeedback instruments. Intraoral recordings were made in 11 young subjects with complete natural dentition. Acrylic resin clutches that supported a screw point in the maxillary arch and painted glass in the mandibular arch were used and positioned not to interfere with the occlusion. The distances of the screw scratch from two of the edges of the painted glass were used to measure the anteroposterior and mediolateral locations with a micrometer. The reproducibility was evaluated by measuring the scratch surface by measuring the weight of the print cutouts made from photographs of the scratches taken with a stereoscope. The location and reproducibility of centric occlusion and centric relation were not affected by body posture. A more precise posterior neuromuscular position was obtained in the supine position. The insertion of a mandibular positioning device did not affect centric occlusion but gave a more precise centric relation. Neuromuscular position became as precise as centric occlusion and was located anteroposteriorly between centric occlusion and centric relation.