The variability of centric jaw relations in the process chain of prosthetic restorations and their neuromuscular effects

Objective: A key factor for successful prosthetic rehabilitation is the reconstruction and/or stabilization of a physiological jaw relation. The bite registration technique of choice should here exhibit a high degree of reproducibility. The objective of this study was to determine how precisely the initially recorded jaw relation can be transferred to a prosthetic reconstruction, and how these two positions influence the bilateral activity of the masticatory muscles. Materials and methods: In 41 healthy subjects, 41 examiners incorporated simulated prosthetic restorations (SPRs) that were fabricated according to the procedures commonly used during prosthetic reconstructions. With the aid of the Zebris (WinJaw, Zebris Medical, Isny, Germany) jaw measurement analysis (JMA) system, the positions of the mandible were compared in intercuspation, with an incorporated centric bite record and an incorporated SPR at designated measuring locations of both condyles, the first molars on each side and at the incisal point. At the same time, the electromyographical activities of the masseter muscles and anterior temporal muscles were examined bilaterally under controlled isometric conditions. Results: The positions of the mandible with the centric bite record and the SPR differed significantly (P 0.05). A difference of approximately 0.3 mm in the absolute shift of the spatial position was determined at all five measuring points between both positions; this essentially corresponded to a caudal shift of the mandible. The electromyographical (EMG) activities in these positions showed significant differences (P 0.05) for the temporal muscles. Conclusions: In summary, the findings reveal that a centric jaw relation recorded using this technique can be transferred to a prosthetic reconstruction with the differences described in this article. Keywords: accuracy of the recording of the centric jaw relation, centric bite record, centric jaw relation, electromyography, prosthetic reconstruction