When the teeth normally close in CO, the maxillary arch overlaps horizontally with the mandibular arch, a position called overjet (Figure 20-2). This normal horizontal overlap, usually 1 to 3 mm, between the anterior segment of the two jet-connected arches extends the range of motion (ROM) movement of the lower jaw and helps keep the soft tissues of the oral cavity out of the way during chewing. ROM is a normal physiological and functional reciprocal ROM for opening or closing the lower jaw. When we discuss an optimal condylar position for recovery, we often hear clinicians say they are restoring in CR. However, if you choose this position and look in the glossary of prosthetic terms, you need to decide which variant of the seven definitions you want to use. I believe that the simplest and most comprehensible definition was that synthesized by Peter Dawson from the Seven: the relationship of the lower jaw to the upper jaw, when the arrangements of correctly aligned condylar discs are completely in the highest position against the eminent, regardless of the vertical dimension or the position of the teeth. Centered occlusion refers to a position of maximum, bilateral and balanced contact between the cusps of the maxillary and mandibular arches. Several definitions of the centric relationship have evolved. For this reason, members of the Academy of Prosthodontics were interviewed to determine how they define the centered relationship in order to reach consensus. A report published in the Journal of Prosthetic Dentistry analyzed the results of this survey and found that the centric relationship is a “spatial relationship,” that is, although the previous and current glossary of prosthetic definitions is diametrically opposed, the methods used to capture CR have remained the same. [14,15] A common error is to assume that occlusive forces act on square and flat teeth in straight lines or planes, and that the axes of the teeth are perpendicular to their chewing surfaces. Many dental curvatures and angulations are present with normal occlusion and must be taken into account. The only caveat to this definition, which also exists in other definitions, is: What constitutes an assembly of properly aligned condylar discs? In its pure form, this would indicate that the disc tissue is intact in its entirety and is not deformed or displaced.

But what about the large number of discs damaged laterally but with the medial part intact? Does that disqualify them from the definition of CR? More importantly, is it clinically relevant? Of course, the answer here is, “It depends.” If the condylar disc is simply not intact but can be fully sedentary and functional in a reproducible state, the definition of adapted centered posture (ACP) may apply. When the teeth of a normal occlusion are in the CO position, each tooth in an arc is in occlusion with two others in the opposite arch, except for the central mandibular incisors and maxillary molars. This structure serves to compensate for impact forces during occlusion. Another advantage of this arrangement is that if a tooth is lost in one jaw, the alignment of the opposite jaw is not immediately disturbed or altered. An antagonist persists until appropriate restorative treatment can be performed. The centered relationship (CR) is a central topic in dentistry in general and prosthetics in particular. The term CR has become completely confusing due to many conflicting definitions. Unfortunately, the definition of CR has changed over the past decade. All existing definitions in the dental literature of the last 81 years are divided into definitions from 1929 to 1970, 1970-1980 and 1980-2010 and critically analyzed. PubMed (keywords: centered relationship/jaw-centered relationship) and handsearching were used from 1956 to 2010 to identify relevant articles in PubMed`s English-language peer-reviewed journals; Although the journal dates from 1929. Many definitions of CR have been given, but there is no consensus and the definition in a current glossary of prosthetic terms is confusing. It connects CR to many clinically invisible parts and cannot get a dentist to record CR as described.

The purpose of this article is not only to critically review all definitions, but also to propose an explicit definition in order to minimize confusion in the minds of dentists and students in order to better understand the concept of CR. The centered relationship is clinically significant because it is the only clinically reproducible jaw relationship and logical position for prosthetic manufacturing. One impetus for the redesign was the introduction of the more sophisticated temporomandibular joint (TMJ) imaging, which shows the temporomandibular joint and led to the change in the definition of CR from a posterior-superior position to a front position [1]. The argument in favor of anterior-superior positioned condyles was the belief that distal displaced condyles can cause anterior and medial displacement of temporomandibular discs. Dawson argued that the RC is neither the most refuted of the condyles nor an unencumbered position. It is not unloaded, as it is obtained by firm contraction of the elevator muscles. It is not the most retrus because it is possible to force the condyles distally to centered relationships, but such a distal displacement occurs only with a downward movement away from CR [15].