Centric relation is misunderstood. No other dental term generates a more emotional response than “centric relation,” but ironically, the term is usually misused.

While the Glossary of Prosthodontic Terms provides several definitions of centric relation,1 let’s simplify the discussion and assume centric relation is defined as “normal joints fitting in normal joint sockets,” which would require an intact condyle–disc assembly (Fig. 1).

A normal condyle–disc assembly helps foster normal bone growth, reduces stress in the condyle during articulation, and ensures occlusal stability
Figure 1: A normal condyle–disc assembly helps foster normal bone growth, reduces stress in the condyle during articulation, and ensures occlusal stability.

Why a Normal Condyle-Disc Assembly is Important

There are three main advantages of a normal condyle–disc assembly. The first relates to the growing patient: An intact condyle–disc assembly fosters normal growth at both the mandibular and maxillary levels.

If the joint is injured during the growing years and there is a displacement, the superior surface of the condyle is unprotected. Forces applied to growing bone that is not protected by the soft-tissue disc can increase the likelihood of diminished growth and the development of a Class II occlusion.2–11

The second advantage of an intact disc is load distribution in the temporomandibular joint (TMJ). An intact soft-tissue disc helps dissipate the loading forces that can have a negative effect on the condyle. Condyles without disc coverage have an increased risk for eroded cortical plates, osteophyte formation, decreased condylar volume, inflamed marrow space, and increased pain. Before 3D imaging with MRI and CBCT was available, we assumed muscle was the primary source of pain; today, we believe structural changes in the TMJ cause more pain than previously suspected.12–15

The third advantage of an intact disc is occlusal stability. The disc acts as a three-dimensional positioning tool that aligns the condyle in a repeatable position in the joint socket upon closure. The gasket-like effect of the disc allows for a consistent condylar position, which increases the predictability of occlusal, orthodontic, restorative, orthognathic, and airway treatment.16–17

We mistakenly assumed that most joints have normal anatomy and temporomandibular-disordered (TMD) patients were pain patients, with masticatory muscle contraction being the most common pain source in clinical practice. As a result, the challenge when trying to achieve centric relation was obtaining a superior condylar position. This position can be achieved using bimanual manipulation, a leaf gauge, or an anterior deprogrammer. If the disc is in a normal position, obtaining a superior condylar position is relatively easy.

Considerations for Using Centric Relation

So, the question becomes: When do we consider using centric relation? Let’s think about two times it may be beneficial to consider using centric relation and the factor that must be present to gain the benefits of centric relation.

That factor is an intact condyle–disc assembly. If the disc is displaced, it’s not possible to have “normal joints fitting in normal joint sockets.” It may be more detrimental to use a superior condylar position in the type of patient seen in Fig. 2, for example, because there is no soft-tissue protection at the joint level.

This patient's lack of a soft-tissue disc means there is no soft-tissue protection at the joint level, so a superior condylar position could be harmful
Figure 2: This patient’s lack of a soft-tissue disc means there is no soft-tissue protection at the joint level, so a superior condylar position could be harmful.

If the patient does have “normal joints fitting in normal joint sockets,” it may be advisable to consider using centric relation when:

  • Maximum force distribution is required at the tooth and joint levels. Cases such as wear cases, implant cases, or restoring the initial point of contact in a superior condylar position might be cases to consider using centric relation to take advantage of the anatomy to dissipate the loading forces of the muscles.

  • Maximum occlusal stability is required. Cases such as multiple teeth being restored at the same time or orthodontic treatment can have very successful treatment outcomes when centric relation is used.

Symptoms of an Abnormal Condyle–Disc Assembly

The clinical question becomes how we recognize patients who don’t have “normal joints fitting in normal joint sockets.”

Much of the confusion around centric relation occurred because dentists thought the soft-tissue disc was in the correct position when it wasn’t, which left the unprotected condyle being compressed. When the expected benefits of load distribution and occlusal stability didn’t occur, the assumption was that centric relation was not a viable condylar position. However, the clinical reality is that the structurally altered TMJ wasn’t recognized, and therefore the benefits of centric relation weren’t possible.

Recognizing patients who don’t have normal joints fitting in normal joint sockets occurs primarily through analyzing the case history and assessing the occlusal relationship of the teeth in a fully seated condylar position. Any history such as clicking joints, locking joints, headaches, painful joints, Class II occlusion, open bites, deep bites, canted occlusal planes, facial asymmetries, or orthodontic treatment for any of the abovementioned malocclusions, increases the risk of structurally altered joints that may not respond well to superior positioning.18–20

Rethinking Centric Relation

I hope this article has given you a new perspective on centric relation. The longstanding reports of success using centric relation as a condylar position can be explained through understanding the joint condition rather than achieving a superior joint position.

Structurally intact TMJs, or “normal joints fitting in normal joint sockets,” tend to distribute force efficiently without significant tooth wear, breakage, or mobility, assuming even intensity, simultaneous contact in vertical mandibular movements, and nonrestrictive anterior guidance in horizontal mandibular movements. Structurally intact TMJs also tend to maintain occlusal stability because of intact holding contacts at the joint level (back end of the system) and the tooth level (front end of the system).

If the joints are structurally altered, it may be better to build the occlusion in maximum intercuspation to avoid compressing injured hard and soft tissue. MRI and CBCT imaging can give a greater insight into the anatomy of structurally altered joints and help influence the treatment plan and the prognosis discussion with the patient.

References

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