The terms centric occlusion and centric relation are sometimes used interchangeably but are actually different.
Centric Occlusion & Relation
Let’s look at what centric occlusion is first. The term centric occlusion was introduced by Gysi in 1922. In most descriptions of centric occlusion, the maxillary and mandibular teeth contact simultaneously in multiple strong occlusal articulating contacts. This is with the masticatory muscles activated (maximum strained masticatory muscles) when the condylar processes are fully seated in the articular fossa at the base of the articular eminences.
In determining centric occlusion, priority is given to the interarch occlusal relationship of teeth. The mandibular buccal and maxillary lingual cusps of the posterior teeth are in evenly distributed and stable contact with the opposing occlusal fossae. These cusps are called the supporting cusps, or centric (functional) cusps, and are primarily responsible for the vertical facial height support and mastication. Centric occlusion is the most mesial central interarch occlusal relationship.
So, what about Centric relation and how does it differ from centric occlusion? Centric relations were coined by McCollum in 1926. This is an interarch occlusal relationship with minimally strained masticatory muscles. There is only a single or multiple light (slight) occlusal articulating contact when the condyles are in the most retruded unstrained position in the articulating fossae hence providing the possibility for unforced lateral sliding movements of the mandible. Priority is given to the TMJ when concerning the position of the condyles in the articular fossa.
Centric relation is considered the optimal mandibular position in which the bilateral condyle-disc assemblies are fully seated in their corresponding articular (glenoid) fossae with the condyles positioned along the anterior slope of the articular eminence. Centric relation is considered a reliable and reproducible reference position.
How Can We Correlate Centric Occlusion And Centric Relation During Clinical Dentistry?
In an optimum or ideal occlusion the intercuspal position (centric occlusion) coincides with the centric relation position but this occurs in only 23% to 43% of the population when there is the complete coincidence of CR and CO. In 60% of the population, centric relation is 0.46 mm on the average distal to centric occlusion. Under the influence of the minimum activated muscles, the mandible moves up (upwards) to the first slight interocclusal contact – this is CR.
The subsequent activation of the masticatory muscles forces the mandible to slide mesially to CO. This movement (sliding) of the mandible from a centric relation forward is called sliding in centric or freedom in centric. It is easily verified in a relaxed patient sitting upright in the dental chair.
In dental occlusion studies, this concept is known as the long centric. In healthy natural dentitions centric relation only rarely coincides with the maximum intercuspation position (CO). In such cases, allowing some freedom of movement in an anteroposterior direction is advantageous because it protects teeth and TMJ from overloading and occlusal trauma.
The term myocentric occlusion was introduced by Jankelson in the 1950’s. Priority is given to the neuromuscular system. This is a physiologic position regarding musculoskeletal relationships of the structures. It is not a forced position, but is gently guided by allowing natural muscle activity to place the condyle in a physiologically unstrained position.
Myocentric occlusion is a centric occlusal interarch relationship determined by bilateral, symmetric and uniform action of levator muscles and not with maximum strained muscles. Multiple slight occlusal articulating contacts of posterior teeth. The condyles are in their most superoanterior position in the articular fossa, assuming a position between CR and CO. In myocentric occlusion the condyles are in an intermediate position compared to centric occlusion and centric relation.
When seeing a patient for the first time, one should record centric occlusion and centric relation in their clinical notes.