Letter to the editor regarding “Centric relation: From red giant to white dwarf,” published in the November 2021 issue of CRANIO

Centric relation (CR) is defined as “a maxillomandibular relationship, independent of tooth contact, in which the condyles articulate in the anterior-superior position against the posterior slopes of the articular eminences [1].” There is a clear anatomic-biomechanical rationale for using CR for occlusal analysis and predictable treatment with restorative dentistry, orthodontics, and orthognathic surgery. Accurate occlusal analysis requires that the condyles are fully seated in CR. With this information, the clinician can design treatment to function in harmony with the anatomic requirements of the masticatory system. All clinicians and researchers need a thorough understanding of the physical reality of the masticatory system in which they are tasked to diagnose and solve structural problems. 1. CR in the healthy temporomandibular joint (TMJ) is a precise anatomical position dictated by the elevator muscles vectors of force. The masseter and anterior temporalis muscles align the condyles in the most anterior-superior direction, and the medial pterygoid muscles align the medial pole of the condyles medially so the condyles are braced in three dimensions against the temporal bone [2]. This is a close packed position, as shown by the sagittal and coronal sections in dissection studies [3]. CR creates a transverse horizontal axis, which is consistently recorded by pantographic tracing, central bearing point devices, or an anterior deprogrammer marked by the opposing incisor [4]. These devices substitute a single mechanical point for teeth with occlusal interferences, allowing proper condylar seating. If CR was not a precise position, a consistent recording could not be achieved. 2. If teeth prevent the condyle from seating in CR, the condyle is positioned inferiorly away onto the incline of synovial fluid-lined articular cartilage, a completely unstable position. Constant lateral pterygoid muscle contraction must substitute for bony bracing. Ideal lateral pterygoid protrusive activity is reciprocal to elevator muscle closing activity [5]. When the lateral pterygoid cannot rest during closure, muscle hyperactivity may lead to pain and compromised chewing patterns. 3. Treatment planning from a tooth-dictated position like maximum intercuspation (MI) incorporates the error from the seated condylar position, precluding predictable treatment. Cordray found the mean dimension of this error in the condyles to be 0.86 mm horizontal and 1.8 mm vertical [6]. Chang showed that the error from CR to MI can profoundly detract from orthodontic results [7]. The mandible always closes with the same anatomicbiomechanical principles. Since the mandible is a Class III lever system with the elevator muscles positioned between the TMJ and teeth, elevator muscle contraction always seats the condyle in its 3-D braced position unless a tooth or restoration interferes. When the condyle loses dimension, the unchanged elevator muscle vectors seat the condyle toward its former braced position, causing retrognathia and anterior open bite [8]. 4. Accepting MI as a closing position ignores the interferences to the physiologic arc of closure. These are typically on cusp inclines that are also excursive interferences. They stimulate periodontal mechanoreceptors to induce protective mandibular movement, causing muscle hyperactivity. Traumatic occlusal interferences can cause dental pain, wear, mobility, microcracks, and fracture [9]. In his recent editorial, Türp [10,11] introduces his co-authored paper with these main points: 1. MI should dictate condylar position for healthy patients with posterior teeth. 2. “Goal is a reasonable condylar position in relation to the posterior slope of the eminence, keeping in mind that this relationship is variable in the general population.” 3. After “maximum intercuspation is established, both the new tooth and jaw relations are gradually ‘normalized’ by cellular remodeling.” 4. MI is stable and comfortable for the vast majority of patients. 5. “CR” is conceptually flawed because it is based upon the assumption that there is a place where condyles ”should be.” CRANIO®: THE JOURNAL OF CRANIOMANDIBULAR & SLEEP PRACTICE 2022, VOL. 40, NO. 2, 181–182 https://doi.org/10.1080/08869634.2022.2031170