Centric Relation: A Survey Study to Determine Whether a Consensus Exists Between Prosthodontists and Orthodontists

Purpose: The purpose of this study was to evaluate whether there is a consensus among prosthodontists and orthodontists as to the definition of centric relation.
Materials and Methods: A survey constructed from five definitions of centric relation (CR) as provided from the “Glossary of Prosthodontic Terms” was sent to the chairpersons of every prosthodontist and orthodontist program in Tunisia.  The different responses were analyzed statistically by: chi square analysis and examined by use of 95% confidence intervals.
Results: We obtained 80 responses from prosthodontists and 67 from the orthodontists, representing 54% and 45% of the total responses, respectively. The survey study showed a significant difference between Orthodontists and prosthodontists responses regarding the definition of centric relation. Orthodontists and prosthodontists had no significantly different response regarding definition of centric occlusion. Regarding the definition of maximum intercuspation, there was a significant difference between orthodontists and prosthodontists.
On another hand, there was a significant difference between the two groups on the need for mounting models in centric relation   or in CO. Concerning the direction in which the mandible and the condyle move   If the patient has a CR/CO slide, there was no significant difference between the 2 groups respectively.
Conclusion: The results of this survey highlight a lack of consensus and   inconsistency regarding the CR definition among prosthodontists and orthodontists, which lead more likely to confusion among practitioners.

Communication between different dental specialists must be clear and used terms should be well defined.  There are still some ambiguities between dental practitioners regarding the definition of the centric relation (CR).  Orthodontic treatment ensures   the management of cross bite, open bite, collapsed occlusion plane (due to over erupted teeth), and tilted teeth and it is usually   performed prior to prosthetic treatment. After orthodontic treatment, the management of remaining spacing among teeth is frequently carried out using fixed denture prosthesis to ensure esthetic and function. In fixed denture prosthesis, many clinic cases require, after orthodontic treatment, the use of CR   as reference for occlusion record and for the mountain of the cast on articulator. Nevertheless, other clinic cases   need   MI for occlusion registration and to mounting the models in the same position. In 1930, based on observation of dry skulls, the National Society of Denture Prosthetics gives the first definition:  The first definition of the National Society of Denture Prosthetics was published in 1930. Centric relation position, when the condyles are in the most posterior position and lateral movements of the mandible are still possible [1]. The definition of CR has evolved over the past half-century from being a posterior and superior position of the condyle in relation to the glenoid fossa to an anterior superior position [2-4]. Multiple definitions of centric relation (CR) have evolved over time that may have created confusion or impeded understanding. A recent attempt to achieve a singular definition by surveying the members of the Academy of Prosthodontics (AP) did not achieve majority consensus [5]. The purpose of this study was to determine   whether there is a consensus among orthodontists and prosthodontists related to the definition of CR.

To evaluate differences between prosthodontists and orthodontists related to condylar position, an electronic survey was constructed. The definition of CR was limited to the five most commonly used definitions as provided by the Academy of Denture Prosthetics’ “Glossary of Prosthodontic Terms” (GPT) (table 1). Furthermore, there were questions relating to centric occlusion (CO), (table 3;5) and the reference used to mountain The casts on articulator. The questionnaire of the survey was sent to 85 Orthodontists programs, (70% male and 30

We acquired   80 responses from prosthodontists and 67 from the orthodontists, representing 54% and 45% of the total responses, respectively. According to this study there is a significant difference between prosthodontists and orthodontists regarding the question related to definition of CR relation, (chi-square =45, df=4, p<0>0.3). 

Table 3: questions and responses: Count Cross tab

Table 4: Chi-Square Tests

(Table 3&4), a. 0 cells (0, 0%) have expected count less than 5. The minimum expected count is 10.03. b. Computed only for a 2x2 table

On another hand and regarding the definition of MI there is a significant difference between orthodontists and prosthodontists (table 5&6) chi-square =5, df=2, p<0 chi-square =31, df=2,>

Table 5: questions and responses cross tab count

Table 6: Chi-Square Tests

Ɨ: 0 cells (0,0%) have expected count less than 5. The minimum expected count is 12.31.

Before 1987, CR was considered as a detruded (posterior-superior) condylar position and in our study 68% of orthodontists agree with this definition [6]. In the 1970s, Roth, gnathological orthodontist, suggested that orthodontists should embrace the principles of gnathology that had long been held by eminent prosthodontists and restorative dentists [7,8,21-25]. He advocated that orthodontic treatment is analogous to doing full-mouth occlusal rehabilitation, with the difference being that orthodontics did not “cut” or modify the natural tooth structure. Although contemporary orthodontic graphologists believe in attaining an anterior-superiorcondyle position at the same time the teeth are in CR (CR-CO), there is little scientific evidence to support this view [9]. Gnathological oriented orthodontists advocate the use of the terminal hinge axis position, the need for pretreatment CR-MI–converted lateral cephalograms and the placement of gnathological positioners immediately after orthodontic appliances are removed Orthodontic graphologists believe that it is possible to locate a particular position of the condyles precisely in the glenoid fossa via CR recordings [10]. Nongnathologic orthodontists tend to use hand-held models and noninstrument-oriented CR techniques. Their aims   are to obtain the best occlusal relationship within the framework of optimal dentofacial esthetics, function and stability [11]. The latest edition of the Glossary of Prosthodontic Terms (GPT) defines CR as “a maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the anterior-superior position against the slopes of the articular eminences [7,4]. In our study 68% prosthodontists agree with this definition. Many prosthodontists use detruded CR only as a guide so that dentures can be fabricated a millimeter or so anterior to this position [11]. The argument for anterior-superior positioned condyles was the belief that distally displaced condyles can cause anterior and medial displacement of the TMJ disks would be prone to develop TMJ symptoms [12,13].  There is no one ideal position of the condyle in the glenoid fossa, but there is a range of normal position [14-22]. A study conducted by Jasinevicius TR and co related to Centric relation definitions taught in 7 dental schools suggested  that the controversy will continue, because there is no consensus regarding the definition of centric relation within the 7 dental schools surveyed [23]. Early studies found that CO usually was 0.1 to 1.8 mm anterior to CRO, depending on the population studied and the age of the subjects [24].
In 1995, Lindauer and colleagues studied the condylar movements and centers of rotation during jaw opening in eight subjects without TMD using a sonic digitizing system. They found that all of the subjects demonstrated both rotation and translation during the initial phase of jaw opening, and none had a center of rotation at the condylar head. Their findings support the theory of a constantly moving, instantaneous center of jaw rotation that is different for different people. This initial translator movement is not incorporated in the mechanic of articulator and thus, it does not replicate the patient’s mandibular movement with precision to localize the occlusal interferences [25]. To avoid some of the confusion about the term “CR-CO,” Recently, CO-CR (or CR-CO) and MI-CR (or CR-MI) in which MI is synonymous with CO, have been used interchangeably. Although CO and MI have been used synonymously in the past, the most recent editions of GPT6,7 have made a distinction between the two terms [4,26]. Maximum intercuspation (MI) has been defined as “the complete intercuspation of opposing teeth independent of condylar position [26]. CR is a position of the condyles independent of tooth contact, whereas centric occlusion (CO) is an interocclusal dental position of the maxillary teeth relative to the mandibular teeth.2 Maximum intercuspation (MI) has been defined as “the complete intercuspation of opposing teeth independent of condylar position [26]. The results of this study clearly show a significant lack of a consensus between prosthodontists and orthodontists as to the definition of CR

This survey study agrees with other studies that a lack of consensus exists between prosthdontists and orthodontists regarding the definition of centric relation. Although communication and therapeutic project between orthodontists and prosthodontics require certain precision, the disagreement and confusion continue.

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Conflict of interest
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