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A Definition That Has Been Quietly Changing for Decades

Most dentists learned centric relation as a fixed anatomical concept — the most superior anterior position of the condyle in the glenoid fossa. They were taught it as if it were settled science. A reference point. A border position. Something reliable and unchanging.

What most dentists were never taught is that the profession’s own definition of centric relation has changed — significantly and repeatedly — over the course of dental history.

Understanding how CR has evolved is not merely an academic exercise. It reveals something important about where the profession has been heading — and why the language of physiologic occlusion has been quietly gaining ground even within the most traditional corners of dental scholarship.

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The Evolution of the CR Definition — GPT-1 Through GPT-9

The Glossary of Prosthodontic Terms has been the authoritative reference for dental terminology since its first edition. The definition of centric relation has changed with nearly every edition — each revision moving further from a purely mechanical border position and closer to a physiologic and functional concept.

GPT-1 through GPT-4 (1956–1977): Centric relation was defined as the most retruded position of the mandible — a posterior border position. The condyles were to be seated as far back as possible in the fossa. Treatment was built around this retruded reference.

GPT-5 through GPT-8 (1987–2005): The definition shifted significantly. The word retruded was progressively de-emphasized. CR was redefined as the relationship of the mandible to the maxilla when the condyles are in the most superior anterior position in the glenoid fossa — in contact with the posterior slope of the articular eminence — with the disc properly interposed. The posterior border concept was largely abandoned.

GPT-9 (May 2017): The most significant revision in the history of the definition. For the first time two words appeared that had never been part of any previous CR definition:

Physiologic. Unstrained.

GPT-9 defined centric relation as the relationship of the mandible to the maxilla when the condyles are in the most superior position in the fossae — physiologic and unstrained — against the posterior slopes of the articular eminences.

The word retruded — which had defined CR for the first thirty years of the GPT — was fully and permanently abandoned.

This progressive migration of the field’s own standard terminology toward a physiologic, unstrained position is itself a form of evidence — a documented convergence toward what GNM has measured and treated to since the 1970s. That convergence, alongside the instrumentation validation and clinical record, is examined in The Evidence Behind GNM: Objective Measurement and Clinical Outcomes..

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What GPT-9 Actually Means — And Why It Matters

The addition of physiologic and unstrained to the GPT-9 definition was not a minor editorial change. It was a fundamental shift in how the profession understands what CR is supposed to be.

Physiologic means the position must be compatible with the normal function of the biological system — not merely a border position that can be mechanically reproduced.

Unstrained means the musculature must not be under tension or compensation to hold the mandible in that position.

These two words — physiologic and unstrained — are the language of neuromuscular science. They are the language Bernard Jankelson used to describe Myocentric position decades before GPT-9 was written. They are the language GNM has been built on since its inception.

GPT-9 did not explicitly validate GNM. But it moved the profession’s own authoritative definition closer to the GNM position than any previous edition had ever been. 

The critical question GPT-9 raises but does not answer:

How do you verify that a condylar position is physiologic and unstrained — without objective measurement of the musculature?

Bimanual manipulation cannot answer that question. A Lucia jig cannot answer that question. Articulating paper cannot answer that question. None of these methods can address what the lateral pterygoid muscle is doing during closure — and the lateral pterygoid is the single muscle whose superior and inferior heads must be in physiologic balance for the condyle-disc complex to occupy a truly unstrained position.

Only objective EMG measurement — combined with jaw tracking and the J5 Dental TENS deprogramming protocol — can confirm that the musculature is genuinely relaxed and that the position the mandible finds is both physiologic and unstrained.

This is precisely what the K7 Evaluation System and the OC Optimized Bite Protocol are designed to do.

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The Honest Implication of This Evolution

If CR meant one thing in 1956 and something meaningfully different in 2017 — if the profession itself has progressively moved away from a retruded border position toward a physiologic unstrained position — then the question every serious clinician should ask is:

What does the next evolution look like?

The trajectory is clear. Each revision of the GPT definition has moved closer to what neuromuscular and gneuromuscular science has been measuring and documenting objectively for decades. The language of physiology — unstrained, physiologic, functional — has replaced the language of mechanics — retruded, border, manipulated.

GNM is not ahead of dentistry. GNM is where dentistry is heading.

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Written by Clayton A. Chan, D.D.S. — Founder and Director, Occlusion Connections | Las Vegas, Nevada

6170 W. Desert Inn Road, Las Vegas, Nevada 89146 | Telephone: (702) 271-2950

www.occlusionconnections.com

Leader in Gneuromuscular Dentistry