• A clinically relevant viscoelastic FEA model of the mandible simulating the effect of a Herbst appliance

      Heidari Zadi, Zahra; Pae, Eung-Kwon (2018)
      As a powerful numerical solution to partial differential equations with sophisticated boundary conditions, Finite element analysis (FEA) has been vastly used to solve engineering problems. This tool also found to be useful in predicting load-strain patterns and biological failures in mechanics of dental applications as well. In orthodontics field, several studies addressed the benefits in use of FEM models to predict stresses and strains in jaws. These studies mostly considered only the linear elastic phase which corresponds to the immediate response of the bone to the loading during functions. On the other hand, it is the prediction of long-term stress and strain distributions that are useful for clinical purposes. Therefore, it is suggested in this study that the viscoelastic properties of the bone need to be incorporated in the analysis to render long-term stress and displacement patterns. In this research, for the first time to our knowledge, effects of viscoelasticity of the mandibular bone are incorporated into finite element analyses of force distribution and displacement of anatomical structures in response to a Herbst appliance. Our models clearly demonstrate how displacements of the mandible occur in accordance with distributions of force vectors.
    • Compensatory tongue-jaw strategies during speech in response to intra-oral perturbation

      Mays, Keith; Stone, Maureen L. (2010)
      When normal speech production is disrupted by perturbing devices, such as dental prosthesis or appliances, a compensatory motor strategy must emerge using unaffected speech articulators. The purpose of this study was to use a unique methodology to measure compensatory oral motor function in response to oral articulatory perturbation. Compensatory speech was evaluated for the fricative "s" in three different vowel contexts, while the oral cavity was perturbed using two different five millimeter thickened devices. Measurements were made of the acoustical spectral properties, ultrasonographic images of mid-sagittal tongue movement, and electrognathographic jaw displacement during speech. Recordings were made at baseline, immediately upon insertion, after 15 minutes, and after two weeks and upon removal of the perturbing device. A Within-Subject 2-way Repeated Measures ANOVA was performed to statistical evaluate the significance of the mean acoustical output, mandibular displacement, and change in tongue height at four time intervals and between each type device with a significance level of p < 0.05. The results revealed that compensatory motor control of speech organs is time and task dependent, and that for /s/ the acoustic output and jaw displacement sensitive. However, the tongue was used to create long-term compensation in response to oral perturbation. Therefore, changes in the oral cavity, such as prosthesis, appliances, and surgery may initially impact speech function. However, the tongue and the jaw movement is altered to compensate for perturbation resulting in new motor control strategies.
    • The Effects of Glossectomy on Airway to Tongue Ratio and Mandibular Morphology Using MRI

      Kim, Eric J.; Stone, Maureen L. (2019)
      Purpose: This study asked if glossectomy surgery causes anatomical changes of the surrounding structures and the airway by altering the balance of forces in the oral cavity. We predict that glossectomy patients will have proportionately larger pharyngeal air spaces than controls relative to the hard and soft structures around the mandible. Materials and Methods: Twenty subjects were studied, ten T1 or T2 SCC glossectomies and ten controls. The gathered MRI data sets were reconstructed into 3D volumes. Results: Mid-sagittal transpalatal airway lengths were significantly shorter for the glossectomy subjects. All other measurements were not statistically significant between the two groups. Discussion: A person may compensate for the reduction of tongue size following glossectomy, which may contribute to a shorter A-P airway distance at the transpalatal level. However, all other tests were not statistically significant, including the transpalatal area inidicating that objects in the oral cavity adapt to the reduction in tongue size and does not affect the established equilibrium. The overall transpalatal airway size may be maintained in post-glossectomy speakers by lateral expansion of the airway at the transpalatal level. Conclusion: This study concluded that the spatial relationships between airway and oral structures may change in dimension, but not in balance of forces following glossectomy. Second conclusion was that a 3-dimensional imaging is required for evaluation of the airway.
    • Variation in Accessory Branches of the Mylohyoid Nerve in the Posterior Mandible: An Anatomic Study

      Ottey, Elizabeth Alston; Stone, Maureen L. (2020)
      Purpose: To examine the courses and branching patterns of the mylohyoid nerve in adult cadavers in order to determine if there are accessory branches, which insert on the posterior mandible. Materials and Methods: 25 cadavers preserved in 10% formalin were dissected in the gross anatomy dissection lab. The mylohyoid and any varying branches were dissected and preserved as far as possible. The dissected cadaver’s data sets were analyzed using Image J software. Results: 12 out 25 (48%) cadavers had at least one accessory branch present that attached to the posterior mandible. The accessory branch identified was located an average of 2.3 cm from the posterior mandible. Conclusion: Accessory branches of the mylohyoid exist in the posterior mandible. Our next step is testing the identified branches to confirm if they are nerve fibers.