STANDARDIZED ELECTROMYOGRAPHIC INDEXES ALLOW A RELIABLE MEASUREMENT OF MASTICATORY MUSCLES FUNCTION
recruitment. This performance alteration hesitated in a torque effect during maximal voluntary clenching( Torque index-20 %). The Impact index confirmed that the occlusal condition needed muscular adaptation( while clenching in maximal intercuspation, the muscles performed only 51 % of electrical activity developed while clenching with cotton rolls). After a detailed explanation of the clinical and instrumental conditions, the patient agreed to rehabilitate her first and second right mandibular molars with overlays, changing her right posterior occlusal support. During the final impression taking appointment, a stiff flat resin jig was set on reduced tooth substance to slightly increase the posterior vertical dimension. A sEMG acquisition was made, and the patient was invited to perform two maximal voluntary clench: the first one with cotton rolls between the dental arches and the second one wearing the jig( Fig. 4). Figure 5 shows that the torque effect was reduced; muscular total work and Masseter coordination increased but did not reach physiologic values( Impact index from 51 to 71 % and POC Masseter 78 %). The jig was then slightly reduced and retested obtaining a muscular recruitment very similar to those recorded in healthy young subjects with sound dentition( Fig. 6) 24, 41-42. The new EMG tested mandibular position( wearing the modified jig) was used as occlusal posterior vertical index to produce the final indirect overlays.
During the subsequent appointment, the overlays were bonded in a dry setting and the function verified again acquiring muscle performance with the same standardized protocol. The new posterior occlusal morphology well integrated in the patient stomatognathic structures, and she had a good masticatory muscles coordination: her performance with the new dental surfaces well overlapped the“ occlusion-free” reference test( clench on cotton rolls)( Fig. 7). The functional test was satisfactory so reconstructions were accurately polished( Fig. 8).
5. Conclusions
Standardized sEMG indexes allow the evaluation of occlusal-induced proprioceptive mediated muscular recruitment in a reliable way. Merging biomechanical concepts with sEMG standardized indexes, occlusal devices and prosthesis adapting procedures could be clinically performed in order to reduce the muscular adaption to the new occlusal conditions or to reestablish physiological muscular coordination 45.
Acknowledgments
The authors declare no conflict of interest related to this study. There are no conflicts of interest and no financial interests to be disclosed.
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