Centric Relation (CR) is a foundational concept in reconstructive and restorative dentistry, serving as a reliable starting point for complex treatment planning. Understanding this specific jaw position is important for diagnosing and treating various dental health issues. Unlike a simple bite, Centric Relation describes a repeatable, stable alignment of the jaw joint that is independent of how the teeth fit together. This makes it a powerful reference for dentists when a patient’s natural bite has become compromised or is unstable.
Defining Centric Relation
Centric Relation is a specific bone-to-bone relationship between the mandible (lower jaw) and the maxilla (upper jaw). The accepted definition describes CR as the maxillomandibular relationship where the mandibular condyles are positioned in their most anterior-superior position within the glenoid fossa. The mandibular condyles are the rounded ends of the lower jawbone, and the glenoid fossa is the concave socket in the skull where the condyles articulate to form the temporomandibular joint (TMJ).
In this position, the condyles are braced against the posterior slopes of the articular eminences, which is a bony prominence in the skull. Crucially, the condyles articulate with the thinnest, most central, and least vascular portion of the joint’s disc. This anatomical alignment allows the jaw to perform a pure, hinge-like, rotational movement without any forward or backward sliding. This joint-guided position provides a stable reference that is consistent throughout a person’s life, barring injury or disease.
Centric Relation Compared to Bite Position
Centric Relation (CR) is fundamentally different from a patient’s habitual “bite,” which dentists refer to as Maximum Intercuspation (MIP). MIP is the position where the upper and lower teeth achieve their tightest, most complete mesh of cusps, regardless of the condyle’s position in the joint. This MIP is the position people naturally close into when chewing or swallowing.
In most individuals, CR and MIP do not perfectly align, meaning the ideal joint position is not the same as the tightest tooth position. This discrepancy is often referred to as a “slide in centric.” When closing from the joint-guided CR position, the first tooth contact often acts like a ramp, forcing the jaw to shift slightly forward or sideways into the MIP position.
The habitual MIP bite is guided by the teeth and can change over time due to wear, movement, or poor alignment. If the teeth are not in harmony with the joint, the jaw muscles and the TMJ may be placed under undue stress as the body attempts to find the most comfortable closure. Centric Occlusion (CO) is the occlusion of the opposing teeth when the jaw is in the CR position. The distinction is important because the MIP bite, while comfortable for the patient, may not be the healthiest position for the jaw joints over the long term.
Why Dentists Use Centric Relation
CR serves as a foundational reference point for extensive dental reconstruction and diagnosis because of its stability and repeatability. When a patient’s existing bite is severely compromised due to worn or missing teeth, the habitual bite (MIP) is unreliable for new dental work. Using CR ensures that any new restorations, such as crowns or fillings, are built upon a stable, joint-friendly framework.
Dentists utilize CR in several key areas:
- Full mouth reconstruction: Establishing the jaw in CR allows the dentist to design a new occlusion that harmonizes the teeth with the optimal position of the jaw joints, minimizing stress on the joints and surrounding muscles.
- Complete denture fabrication: Without any natural teeth to guide the bite, the dentist relies solely on the CR joint position to determine where artificial teeth should meet. Accurately recording CR is essential, as denture failure can result if the prosthetic teeth are not in harmony with this joint position.
- TMJ disorder diagnosis: Guiding the condyles into their unstrained, most superior position allows the dentist to evaluate the health and function of the joint complex without the influence of a disruptive tooth-guided bite. This evaluation helps determine if the joint is healthy enough to serve as the reference for treatment.
Methods for Recording Centric Relation
Recording the Centric Relation position involves various techniques designed to relax the jaw muscles and physically guide the condyles into their anterior-superior position. The primary goal of these methods is to deprogram the muscles, removing the patient’s learned habit of closing into their tooth-guided bite (MIP).
One common method is Bimanual Manipulation, where the dentist gently guides the patient’s jaw with both hands, allowing the condyles to seat passively into the glenoid fossa. Other techniques use deprogramming devices to prevent teeth from touching, which helps eliminate muscle memory. Examples include a Leaf Gauge, which uses plastic strips between the front teeth to gradually separate the back teeth, and an Anterior Jig, a custom acrylic device providing a single point of contact for the lower front teeth.
Once CR is established, the dentist uses a stable recording material, such as wax, plaster, or specialized impression paste, to capture the space between the upper and lower arches. This record is then used to mount the patient’s dental casts onto an articulator. The articulator is a mechanical device that mimics the movements of the jaw, allowing the dentist and lab technician to plan and execute the necessary restorative work in a stable, repeatable joint position.