Centric relation mysteries, Part 1: what is it and how do we find it?

By Chris Salierno, DDSQuick: What’s the definition of centric relation?If you’re having difficulty coming up with an answer, you’re not alone.According to Wikipedia, there have been 26 definitions of centric relation since the term first came into use in the 1930s. Pick up a book on occlusion and you will often see entire chapters dedicated to the subject. Attempts at definitions call for the condyles to be in their most retruded, most superior, or most medial position within the glenoid fossae, or some combination thereof. Authors argue about anatomical positions that are fractions of a millimeter apart. It makes me wonder if the whole exercise isn’t just purely academic. I’d like to know what would make a difference in how I treat my patients.Having reviewed my rather large collection of books and articles on the subject, I don’t feel any closer to offering a single definition of centric relation that would appease the many fine dentists who have tried to define the term themselves.But what seems to be fairly consistent in the literature is the belief that there is a certain position of the mandible that should be respected by dentists. That position is special for two main reasons:1. It does not induce stress in the condyle-disc assembly and associated structures.All pressure on the condyle is directed through the avascular, noninnervated disc straight through to the glenoid fossa on the other side. The muscles of mastication are allowed to rest, and we are given a healthy foundation on which to build our restorations. 2. It can be found consistently, regardless of the presence or position of teeth.Numerous authors provide techniques for guiding the mandible into centric relation. Patients may be instructed to lift their tongues to their soft palates or their mandibles may be gently pushed and rotated by the dentist. No favorite method has emerged among the many. But whichever approach is used, there is a consistency to the dentist’s technique and the dentition is not allowed to interfere.There lies the clinical significance of a term that is academically obscure. Put simply, it is a jaw position that is comfortable and easily located on anyone.Great. Now how do we find it? First, let’s define a border position as opposed to a functional position. If we trace the routine movements of the mandible during mastication, swallowing, and other daily activities, we will have found the functional positions. On the other hand, border positions denote the outer limits of movement that can be achieved. These have been famously outlined by Posselt (Fig. 1). If our goal is to find a jaw relationship that is practical, then we will want to find centric relation to be a functional position.