Electrognathographic Evaluation of Mandibular Movement during Speech: A Preliminary Evaluation

Objectives: In Prosthodontic treatment speech is used to establish tooth position and occlusal vertical dimension. The oral cavity is an essential part of speech production with the tongue and mandible as functional components. During speech production, maxillary dental prostheses structurally perturb the oral cavity requiring compensatory motor control strategies, such as mandibular movement. The purpose of this study was to measure vertical and horizontal mandibular displacement in response to oral-articulatory perturbation during speech. We hypothesize that vertical jaw displacement will be dependent upon the word spoken, the type of prostheses, and oral morphology. Methods: This preliminary evaluation of mandibular movement during speech used a within subject evaluation crossover model of three subjects. Mandibular displacement was measured during speech on two subjects wearing two Experimental Palatal Prostheses (EPP) with a 5 mm increased thickness in the anterior palate(EPP-A), or the posterior palate (EPP-B). Electrognathography and ultrasound measurements were recorded during three repetitions of five English vowels /i/, /e/, /a/, /o/, /u/ and five repetitions of two fricatives /s/ and /sh/. Recordings were made with no prosthesis (NP), immediately after insertion (P), fifteen minutes after insertion (P15) and after 2 weeks of adaptation (P2wk). Results: Results show a trend for increased vertical jaw opening upon initial insertion. Adaptation back to baseline occurred over the two week period. Additionally, there was compensatory anterior movement of the mandible during the two week adaptation period; there was a trend towards a greater magnitude of mandibular movement in low palatal vault subjects. Conclusions: This study suggests insertion of a maxillary prosthesis produces increased vertical jaw opening initially with adaptation occurring over time. This is accompanied with an increased anterior jaw movement as a long-term compensatory strategy. Therefore, patients should be given a period of adaptation when using speech to evaluate tooth position and occlusal vertical dimension.