Tongue Volume, Function and Biomechanics

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DESCRIPTION: The role of tongue in craniofacial function, biomechanics and growth is more critical than the larger jaw muscles but receives less attention. Thus knowledge of tongue functional morphology and loading is very rudimentary. Reducing tongue volume is a valuable approach to treat various craniofacial deformities and disorders, but the efficacy, functional consequences and growth impact following this approach have not been evaluated. The current application is to use a well-established pig model to explore functional morphology of the tongue and how its volume influences function, mechanical loads and the consequences for craniofacial growth following tongue reduction surgery. We propose (Aim 1) to measure tongue deformation during function and relate these volume-constant shape changes to the patterns of contraction in tongue musculature and to the jaw movements. We will record 3D functional deformation of the tongue using the novel technology of digital microsonography, along with electromyography of tongue/jaw muscles and jaw/head movement tracking. The neuromuscular and vascular organization of the tongue will be depicted using whole-mount histology. Further, we propose (Aim 2) to understand how tongue functional deformation produces loads on hard tissues of the oral cavity and what role tongue volume plays. We will make direct measurements of strains and pressures on mandibular, premaxillary and maxillary bones during natural conditions and electrical stimulations to hypoglossal nerves and individual tongue and jaw muscles. Tongue volume will be reduced surgically to understand the relations of tongue volume with function and ensuing loads. Finally, to address the major concerns of recovery and growth effect following tongue volume reduction, we propose (Aim 3) to evaluate the functional consequences and growth impact following tongue volume reduction. We will use chronic electromyography and x-ray fluoroscopy to track functional recovery, and longitudinal measurements of tongue/dental casts, serial cephalometrics, dual energy x-ray absorptiometry and histomorphometry to analyze growth. Whole-mount and immunohistochemical histology will be used for evaluating neuromuscular and vascular reorganization of the tongue and osteogenic cellular replication of sutures and bones after the surgery. The unique contribution of this application is to characterize tongue internal deformation during function, to elucidate how tongue volume influences its biomechanical loads, and to correlate these loads to the parameters of function recovery and craniofacial growth. Application of this information will allow understanding of normal tongue functional morphology and to evaluate how tongue volume affects function and craniofacial growth.