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When Do You Restore in Centric Relation and When Do You Not?
Dean E. Kois, DMD, MSD | John C. Cranham, DDS | Michael Fling, DDS
Dean E. Kois, DMD, MSD maintains a private practice limited to restorative, esthetic, and implant dentistry in Seattle, Washington. In addition, he works with restorative dentists at the Kois Center, a didactic and clinical teaching program. He also lectures nationally and internationally, and publishes extensively on various topics in dentistry.
Dean E. Kois, DMD, MSD: I receive this question more often than you might imagine from other clinicians. The answer is relatively straightforward. Not to be overly simplistic, but centric relation is merely a therapeutic or treatment position. When a tooth-based determinant of occlusion is not and/or cannot be used, a joint-based determinant can and should be used (centric relation). Theoretically, centric relation aligns the condyle disc assembly. This directs pressure on the condyle through the avascular, non-innervated disc straight through to the glenoid fossa on the other side. This is considered the most orthopedic position of the mandible due to resultant skeletal and muscular harmony. A few points on when and why will help elucidate my feelings on how I manage the use of centric relation.
Clinically, I utilize centric relation when maximum intercuspal position is unhealthy (occlusal disease), unreliable (patient does not have stable tooth contacts), and when occlusal vertical dimension is being altered (all teeth in at least one arch are being treated).
There are also several indications when not to use centric relation, specifically when maximum intercuspal position is healthy and reliable, when there is active degenerative joint disease, when the mandible cannot accept load, and when appropriate, the clinician is using a “position of comfort” (positioning the jaw into centric relation can sometimes exacerbate joint symptoms when the joint is not healthy) or myocentric techniques.
Centric relation is a joint-based determinant of occlusion. It is a position that is repeatable and can be found consistently, regardless of the presence or position of teeth. This makes it popular for clinicians. There is no mystery—treatment goals and patient presentation will dictate whether to use centric relation or not.
John C. Cranham, DDS maintains a private practice in general dentistry, cosmetic dentistry, and restorative dentistry in Chesapeake, Virginia. He founded Cranham Dental Seminars, which provides lectures, mobile programs, and intensive hands-on experiences to dentists around the world. In 2008, Cranham Dental Seminars merged with The Dawson Academy.
John C. Cranham, DDS: In the Dawson philosophy, there are two reasons that we make a decision to fundamentally change the occlusion. The first is when there is evidence of “occlusal disease.” Wear, mobility, or migration of the teeth are the primary indicators. While there can be other causes of increased forces to the teeth, these conditions, known as “signs of instability,” should trigger us to study the patient’s occlusion to determine the cause. Mounting models in centric relation on an articulator is the way we do that.
The other time we would want to optimize the occlusal forces to centric relation is during esthetic, implant, or larger restorative cases.
Centric relation is about control. When the teeth occlude while the condyles are seated in centric relation, it distributes the forces throughout the entire system. When the occlusion is harmonized with the condyles down and forward of centric relation (on the articular eminence), the inferior lateral pterygoid is left to contract and hold that condylar position. The steepness of the slope, combined with the synovial fluid in the inferior and superior joint spaces on either side of the disc, make it very easy for the condyle to seat, should the lateral ptyerygoid release. Centric relation is a bone braced position that prevents the condyle from going higher.
This is important because one of the primary tenants of a stable occlusion is to prevent the back teeth from rubbing or interfering. Rubbing of back teeth dramatically increases muscle activity. Patients can have posterior interferences for two reasons:
They lack anterior guidance, causing posterior interferences in protrusion, mediotrusion, or laterotrusion.
The occlusion is not harmonized to centric relation. If the lateral pterygoid is overpowered by the elevator muscles that seat the joint (masseter, medial pterygoid, and temporalis), the condyle will seat, bringing the mandible with it. This causes posterior interferences on the medial inclines of the upper teeth and distal inclines of the lower teeth [mesial of uppers distal on lowers (MUDL) rule]. In either case, posterior interferences are the primary cause of muscular hyperactivity/incoordination.
To summarize, we use centric relation whenever we need to optimize and control the occlusal forces. Not using CR as a primary starting point will lead to increased forces, and far less predictability in our restorative endeavors.
Michael Fling, DDS is a cosmetic dentist in Oklahoma City, Oklahoma, and has been actively participating in dentistry since 1976 as a laboratory technician before entering dental school. His practice focuses on restorative and cosmetic dentistry, as well as TMJ treatment.
Michael Fling, DDS: There are many occlusal camps—Kois, Spear, LVI, Pankey, Dawson, centric occlusion, or centric “whatever.” The fact is that many occlusal schemes can be successful, so what is the big deal about CR? From an anatomical perspective, CR is a stable, repeatable physiologic position, which is by definition a superior, anterior braced position with a disc interposed, pain free when loaded, irrespective of tooth contact position.
To understand when someone should be restored in centric relation, an evaluation of restorative needs and evidence of occlusal disease must also be considered. Symptoms of occlusal disease may include wear, fractures, cracks, fremitus, mobility, dentin exposure, abfraction, tori, joint pain, muscle pain, recession, or loss of vertical dimension of occlusion. If occlusal disease exists in conjunction with healthy joints, then it is preferred to restore in CR. It is also optimal to create an occlusal scheme that doesn’t contribute to occlusal disease. Thus, it is ideal for teeth to touch simultaneously without deflection with the joint in a superior, anterior braced position and for back teeth to separate in lateral excursions.
Another consideration is the patient’s parafunctional pattern. The reality is that a patient’s pattern of mandibular movement “is what it is.” Some of these parafunctional patterns can be very destructive. If restorative material is put “in the way” of what “they do,” and if the muscle force is strong enough, they can destroy their teeth or the restorations.
At the end of the day, a patient is treated to CR in the presence of healthy joints when there is evidence of occlusal disease and/or when a repeatable restorative position is needed. CR optimizes the potential to effect ideal joint and tooth loading, and to reduce muscle activity. CR is a predictable and repeatable position that gives opportunity to minimize occlusal disease and parafunctional destruction.