Centric relation
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Centric relation is the maxillomandibular relationship where the condyles articulate with the thinnest avascular portion of the disks in their anterior-superior position against the articular eminences. It is used as a repeatable reference position for mounting dental casts. There are several methods for recording centric relation including static, graphic, physiological/functional, and cephalometric techniques. The bimanual manipulation technique described by Dawson, where the examiner applies downward and upward pressure on the chin and mandible respectively while cradling the patient's head, is recommended as it can be reliably learned and ensures the condyles are properly located in the mandibular fossae.
Centric relation
- 1. Centric relation : - An anteriorly superiorly braced position along the articular eminence of the glenoid fossa , with the articular disc interposed between the condyle and eminence . - the maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the condyle-disk complex in the anterior-superior position against the articular eminences. It is used as a repeatable reference position for mounting casts in an articulator , ideally the condylar position is also coincident with maximum intercuspation of the teeth . Centric Relation Record. provides the orientation of mandibular to maxillary teeth in CR in the terminal hinge position, where opening and closing are purely rotational movements. Systems for recording centric relation : 1- Static recording ( interocclusal checkout ). 2- Graphic recording ( intraoral or extraoral Gothic arch tracings ). 3- Physiological / functional on wax rims or wax cones during unguided / unassisted patient movement. 4- Cephalometric recording cephalometric radiography to determine optimal position of the condyles. Recording technique : Bimanual technique (Dawson) Single-handed technique Accurately mounted casts depend on precise manipulation of the patient's mandible by the dentist. The condyles should remain in the same place throughout the opening-closing arc. Trying to force the mandible backward will lead to downward translation of the condyles, and restorations made to such a mandibular position will be in supraclusion at the try-in stage . the load-bearing surfaces of the condylar processes, which face anteriorly, should be manipulated
- 2. into apposition with the mandibular fossae of the temporal bones, with the disk properly interposed. The ease with which this can be accomplished depends on the degree of the patient's neuromuscular relaxation and on sound technique. The latter, in turn, depends on the patient permitting the dentist to control the mandible. Attempts to force or shake the mandible will lead to a protective muscle response by the patient. The bimanual manipulation technique described by Dawson is recommended as a reproducible technique that can be reliably learned . In this technique, the dental chair is reclined and the patient's head is cradled by the examiner. With both thumbs on the chin and the fingers resting firmly on the inferior border of the mandible , the examiner exerts gentle downward pressure on the thumbs and upward pressure on the fingers, manipulating the condyle-disk assemblies into their fully seated positions in the mandibular fossae. Next, the mandible is carefully hinged along the arc of terminal hinge closure. Note: It is more difficult to ensure that the condyles will be properly located when the single- handed approach is used with the fingers exerting upward pressure, although this technique does allow the other hand to hold the record.
- 3. References : 1- Fundamentals of fixed prosthodontics by Herbert T.Shillingburg .. third edition. 2- Contemporary fixed prosthodontics by Rosenstiel.Land.Fujimoto ..third edition. 3- From a website : Section 10 - Centric Relation www.wrnmmc.capmed.mil/.../Section_010_Centric%20Relation.doc