Industrial and Management Systems Engineering


Date of this Version

Fall 12-2010


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering (Industrial and Management Systems Engineering), Under the Supervision of Professors Ram Bishu and Erick Jones. Lincoln, Nebraska: December, 2010
Copyright 2010 Vettrivel Gnaneswaran


Force exertion is critical in grasping and holding activities at sub-maximal levels. Exertion misjudgments lead to musculoskeletal disorders (MSDs) impairing performance and productivity. Published literatures on grasping have addressed the force balance and endurance issues for non-prehensile movements of hand. However, little information is available on the force exerted in precision gripping employed in health care. Professionals, especially dental hygienists, when treating patients adopt awkward postures for extended period leading to cumulative trauma. Literatures on cumulative trauma have identified force exertion to be an important risk factor. Lack of information on fatigue with precision gripping motivated this research to establish force-endurance relation for simulated dental task.

A preliminary study was performed to estimate the force exerted during sub-maximal three-jaw chuck pinch and maximal three-finger pencil-hold tasks. Exertions were recorded with force sensing resistors (FSR). The tasks were evaluated for four hand conditions: Bare hand, Vinyl, Latex and Nitryl gloves. Results from the preliminary study provided directions to investigate the fundamental research question of how long can dental professional exert and hold using modified pencil-hold before fatiguing. This research question was addressed by developing a mathematical relation between force exertions and time for a simulated dental task. Periodontal scaling was identified as the representative healthcare task and five participants performed the simulated scaling task on a typodont. The average scaling force was found to be 53.95% of maximum voluntary contraction (MVC). A limiting exertion level of 40%MVC was established for the development of force-endurance relation to accommodate the average scaling force exertion.

Mathematical prediction equations for endurance times were developed and validated using the data from a total of sixty participants that included 30 experts and 30 novices. Similarly, relation between perceived and actual force exertions were developed and validated. The force-endurance models and the relations between perceived and actual exertions were found to follow a third-order polynomial. This research is first of its kind on precision grasps used in dentistry whose implications and recommendations have been discussed.