Browsing by Subject "forces"

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    The effects of occlusion on single miniplate osteosyntheses of the mandible
    (2017-11) Katona, Thomas R.
    Aim: Miniplate osteosyntheses of a fractured mandible is a complex structural engineering problem that has been modeled experimentally, analytically and numerically. In general, the more realistic the model, the more difficult it is to appreciate its nuances. Thus, a purpose of this paper is to present a basic analytical model that illustrates the most fundamental principles of static equilibrium as it applies to the mechanics of single miniplate osteosynthesis designs. The second purpose is to use the model to demonstrate the effects of changes in occlusion on the loads experienced by the structures. Materials and methods: The 3 equations of static equilibrium were derived from the free-body-diagram of the distal segment of a vertically fractured reduced mandible. The equations were solved parametrically with variations in plate screw locations, anterior-posterior locations of occlusal contact, and occlusal contact force direction, including the simulation of sticky foods. Results: The results indicate a profound effect of occlusal contact force location and direction on the magnitudes and/or directions of the forces acting on the screw and the miniplate, and on the location and magnitude of the interfragmental bone-bone compression force. Conclusions: In some respects, this model is as barebones as is possible. Atypically however, it includes occlusal contact force direction. The results strongly suggest that all analyses of plating systems should account not only for occlusal contact force location and magnitude, but also its direction.
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    The roles of wedging and friction in the mechanics of dental occlusal contacts
    (2019-04) Katona, Thomas R.; Eckert, George J.
    Objective: The primary aim of this project is to elucidate the basic mechanical engineering principles that govern and explain unexpected and counter-intuitive occlusal contact force measurements. Methods: Forces were measured on matched pairs of first molar denture, ceramic and stainless steel crowns during occlusion and disclusion, with human saliva and dry (control). The weighted maxillary assembly, guided by a precision slide, was lowered onto, and raised from, the mandibular crown. The forces experienced by the mandibular tooth were continuously measured by the load cell that supported it. Statistical analyses included LOESS smoothing splines and generalized additive models. Principles of basic statics and classic friction were applied to explain and validate the results. Results: It was determined that within the span of a single chomp, the in-occlusal plane force component (Flateral) on the tooth is highly variable in direction and/or magnitude. The most salient observations were that Flateral was higher in disclusion than in occlusion, and the largest Flateral did not necessarily occur when the bite force was maximum. Furthermore, saliva significantly affected the results. Conclusions: The results demonstrated that contacting teeth experience complex transient mechanical environments that can be readily explained with elementary engineering principles involving wedging and friction at the occlusal contacts.