Centric relation is a foundational concept in dentistry, describing a specific, repeatable position of the lower jaw relative to the upper jaw. It represents a stable and reproducible orientation of the jaw joints, independent of how the teeth fit together. This distinct jaw relationship provides a consistent reference point for diagnosing issues, planning comprehensive care, and assessing the entire chewing system.
Understanding Centric Relation
Centric relation refers to the maxillomandibular relationship where the condyles, the rounded ends of the lower jawbone, are situated in their most superior and anterior position within the glenoid fossae of the temporal bone. In this position, the articular disc, a small cushion of cartilage, is properly interposed between the condyle and the fossa. This anatomical alignment allows the mandible to perform a purely rotary movement around a transverse horizontal axis, without any forward or backward sliding.
This jaw position is considered “skeletal” or “joint-based” because it is determined by the anatomy of the temporomandibular joints (TMJs) and surrounding ligaments and muscles, rather than by how the teeth interlock. Relaxed mastication muscles guide the condyles into this seated position. This distinguishes centric relation from maximum intercuspation, the habitual biting position where upper and lower teeth achieve their most interlocked contact.
Maximum intercuspation is primarily guided by the teeth and muscle memory, and it may not always align with centric relation. In fact, centric relation and maximum intercuspation coincide in only about 10% of the population. For the majority, there is a slight discrepancy or “slide” from centric relation to maximum intercuspation, which can range from approximately 0.5 to 2 millimeters.
Why Centric Relation Matters in Dentistry
Centric relation provides dentists with a stable and reproducible reference point for diagnosing and planning complex dental treatments. This consistent jaw position allows for a thorough assessment of the relationship between the jaw joints, muscles, and teeth, especially in cases requiring extensive changes to the bite or multiple dental restorations.
A precise centric relation contributes to the longevity and success of dental restorations. When restorations are built to this stable joint position, forces are distributed properly during chewing, which helps prevent excessive wear on teeth and restorations. This promotes a balanced and functional bite.
Centric relation also aids in the diagnosis and management of temporomandibular disorders (TMD). Discrepancies between the joint’s position and the habitual bite can contribute to muscle fatigue, pain, and accelerated tooth wear. By identifying these discrepancies, dentists can develop treatment strategies aimed at achieving a more stable and comfortable jaw position.
How Dentists Determine Centric Relation
Dentists employ various techniques and tools to accurately determine and record a patient’s centric relation. The goal is to guide the lower jaw into its most superior-anterior position within the TMJ, ensuring muscle tension and tooth contacts do not influence the recording. This process often begins with relaxing the jaw muscles to eliminate learned biting patterns.
One common method is bimanual manipulation, where the dentist gently guides the patient’s jaw with both hands. Fingers are placed along the lower border of the jaw, with thumbs positioned on the chin, applying light upward pressure. This technique aims to seat the condyles fully into their fossae, allowing the jaw to hinge purely in rotation without muscular interference.
Deprogramming devices are also used to help relax jaw muscles and eliminate tooth interference. Examples include the leaf gauge, Lucia jig, or anterior bite stops. A leaf gauge consists of a series of thin, calibrated plastic strips placed between the front teeth, gradually separating the back teeth until no posterior contact is felt. This allows jaw muscles to relax and the condyles to seat naturally. The Lucia jig functions similarly, made of acrylic and placed on the upper front teeth, creating a single point of contact that disengages the posterior teeth and encourages muscle relaxation.
Once centric relation is determined, dentists use articulators to replicate the patient’s jaw movements and relationships outside the mouth. These mechanical devices hold models of the patient’s teeth, allowing the dentist to analyze the bite and plan restorations with precision. Recording materials, such as wax or silicone, capture the centric relation bite, which is then transferred to the articulator.
Applications in Dental Treatment
Centric relation is applied in various dental scenarios, particularly those involving extensive reconstruction or significant changes to the bite. In full mouth rehabilitations, establishing centric relation provides a stable foundation for the new occlusion. This ensures newly restored teeth align harmoniously with the jaw joints and muscles, promoting long-term stability.
For patients receiving complete dentures, centric relation is a foundational reference point for fabricating prostheses. Since no natural teeth guide the bite, recording this bone-to-bone relationship ensures dentures function efficiently and comfortably. Accurate determination of centric relation helps prevent instability and discomfort often associated with poorly fitting dentures.
Orthodontic treatment planning also benefits from considering centric relation. Understanding the jaw’s position in centric relation helps orthodontists create a bite that is not only aesthetically pleasing but also stable and harmonious with the jaw joints. This can minimize the risk of occlusal issues or relapse after treatment.
In the diagnosis and treatment of temporomandibular joint (TMJ) disorders, centric relation helps identify discrepancies between the joint position and the habitual bite. Dentists use this information to determine if an occlusal appliance or other interventions are needed to alleviate pain and restore proper jaw function. Treatment based on centric relation aims to achieve a balanced and healthy chewing system by aligning the teeth, muscles, and joints.