[Show abstract][Hide abstract] ABSTRACT: Centric relation (CR) is a core topic of dentistry in general and prosthodontics in particular. The term CR has become thoroughly confusing because of many conflicting definitions. Unfortunately definition of CR changed repeatedly over past ten decades. All the existing definitions in the dental literature, for the past 81 years, are segregated into definitions from 1929 to 1970, 1970–1980, and 1980–2010 and are critically analyzed. Both PubMed (key words: centric relation/centric jaw relation) and hand searches were employed, from citation in other publications, to identify relevant articles in English language peer reviewed PubMed journals from 1956 to 2010; although the review is from 1929. Numerous definitions for CR have been given, however, no consensus exists and the definition given by a current glossary of prosthodontic terms is confusing. It relates CR to many clinically invisible parts and cannot guide a dental surgeon to record the CR following its description. The purpose of this article is not only to review all the definitions critically but to propose a self explanatory definition to minimize the confusion in the minds of dental practitioners and students for better understanding of the concept of CR. Centric relation is clinically significant since it is the only clinically repeatable jaw relation and the logical position to fabricate prosthesis.
The Journal of Indian Prosthodontic Society 08/2013; 13(3):149-154.
[Show abstract][Hide abstract] ABSTRACT: OBJECTIVES: To determine if disc displacement (DD) can be a factor causing changes in condylar position in the glenoid fossa, using limited cone beam CT (LCBCT) images taken in the same time period as MRI that verified DD. METHODS: The study included 60 joints in 57 male and female subjects aged 12-20 years (mean age 14.8 years). Subjects fulfilling the inclusion criteria were enrolled from a pool of post-orthodontic patients, and divided into four groups according to their disc status confirmed by MRI: partial DD (PDD), total DD with reduction (TDDWR), lateral DD (LDD) and medial DD (MDD). Changes in joint space from previously reported norms were measured on LCBCT images. RESULTS: In PDD, the condyles were displaced posteriorly in the fossae with mean anterior space of 2.7 ± 0.5 mm (normal 1.3 ± 0.2 mm) and posterior space of 1.8 ± 0.4 mm (normal 2.1 ± 0.3 mm). In TDDWR, the condyles were displaced not only posteriorly as observed in PDD, but also vertically with reduced superior space of 1.9 ± 0.4 mm (normal 2.5 ± 0.5 mm). In LDD, lateral space was significantly increased to 2.5 ± 0.3 mm (normal 1.8 ± 0.4 mm), while central and medial spaces were significantly decreased to 2.2 ± 0.5 mm (normal 2.7 ± 0.5 mm) and 1.7 ± 0.4 mm (normal 2.4 ± 0.5 mm), respectively. In MDD, medial space was increased and lateral and central spaces were significantly decreased, respectively. CONCLUSIONS: These results indicate that DD in adolescents and young adults can cause the condyle to change its position in the fossa with alterations in joint space which depend on the direction and extent of DD.
[Show abstract][Hide abstract] ABSTRACT: Centric relation (CR) has been considered mainly as a position posterior to habitual occlusion or maximum intercuspation (MI). Awareness of the tooth contacts relationship in centric relation position of the mandible and diagnosing the case from this position is essential to consistently select treatment plans that will allow to treat to or very near to centric relation occlusion. Centric slide and other occlusal relationships are conceived of as positions, which can be studied in three dimensions. Clinically, the difference between the two occlusal positions namely CR and MI (centric slide) can easily be determined, but for a more precise evaluation of its length and directions, an occlusal analysis on articulator mounted casts is necessary. Study was under taken on the mounted casts of ten subjects on a semi adjustable articulator to which a stylus and recording table was devised and attached for measurement of CR-MI slide in the three planes namely anterior-posterior, medio-lateral and superior-inferior. It was found that there was a displacement from CR to MI (centric slide) in all the three planes and numerically the mean slide was 0.688 ± 0.623, 0.261 ± 0.627 and 0.127 ± 0.541 mm in the antero-posterior, medio- lateral and superior-inferior directions respectively. The stylus and table attachment may be an accurate indirect method to measure positional changes of the condyle in 3D.
The Journal of Indian Prosthodontic Society 12/2012; 12(4).
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