Jeffrey Nickel, D.M.D., M.Sc., Ph.D.
Numerical modeling of central nervous system control of the human mandible. Efforts to define normal TMJ loading directions and magnitudes are compromised because available methods for recording physical events within and around the functioning articulation are too invasive. While data from animal models have demonstrated that the mandibular condyle is exposed to compressive loads as a consequence of masticatory muscle contraction, the peculiarities of hominid musculoskeletal and dental morphology are linked to local biomechanics in ways that cannot be extrapolated readily from experiments on other species. Computer-assisted modeling of the human craniomandibular apparatus is an alternative method of studying the control of the mandible during static loading. The approach used in our Biomechanics Laboratory employs computer based numerical methods that render solutions for static biting based on an objective that is of biological importance. The objective thus represents a theory of underlying neuromuscular control. Various neuromuscular objectives governing the muscle force mix in the craniomandibular apparatus have been proposed, including maximization of bite force, minimization of muscle force, minimization of joint loads, minimization of muscle effort, and minimization of muscle stress. Our work continues to test in human subjects which objective is most often employed to control muscle recruitment during static biting.
Biomechanics of the temporomandibular joint disc. Long-term goals of this research is to gain knowledge of the role of dynamic contact mechanics in degenerative joint disease (DJD) of the temporomandibular joint and the reason for the predilection of DJD for certain individuals, the majority of whom are women. Our central hypothesis is that there is greater localization of mechanical work densities (joules per cubic mm, J/mm3) in the TMJ disc during function in women and in individuals with DJD. Our published work to date demonstrates that among healthy individuals, the mechanical work imposed on TMJ cartilages during movement of the loaded mandible can differ by a factor of 100 to 1. It is hoped that our work will improve understanding of the observed sex-bias in DJD of the TMJ, will improve identification of susceptible individuals, and will provide biophysical guidelines for future development of engineered tissues for the TMJ.
Biomechanics and cytokine function during orthodontically induced tooth movement. Fundamental information about variables that affect oral bone remodeling and tooth movement in humans is lacking. Mechanical, biological, and genetic factors have been proposed but not established based on quantitative data. This lack of fundamental information is a barrier to improved understanding of oral bone remodeling and efficiency of orthodontic treatment. To date, our work has shown that for equivalent mechanical conditions, velocity of tooth translation differs by more than 5-fold between individuals. Furthermore, the ratio of 2 inflammatory mediators involved in bone remodeling, interleukin-1β (IL-1β) and its naturally-occurring competitive receptor antagonist, IL-1RA, measured in GCF during tooth movement accounted for up to 60% of the inter-subject variation. Genetic differences are likely to account, in part, for these differences in cytokine secretion and rate of tooth movement for equivalent stresses. Select IL-1 gene cluster polymorphisms modulate the levels of IL-1β. Similarly, specific polymorphisms impact IL-1RA secretion. Our continued efforts in this area of translational research is to investigate specific factors that impact oral bone remodeling and result in predictable effects on the speed of human tooth movement. Of specific interest are the effect of magnitude of stress, and IL-1 gene cluster polymorphisms, on velocity of tooth movement.
Static and Dynamic mechanical analysis of orthodontic hardware. The efficiency of tooth movement associated with orthodontic mechanics can be compromised by friction between arch wire and bracket. In the Biomechanics Laboratory, we measure the apparent coefficient of static friction during “stick-slip” sliding of a bracket along an archwire. Tests include variation in the methods of ligation of a wire into an orthodontic bracket, whether or not energy in the form of vibration like that produced during chewing reduces the apparent coefficient of friction. To date, the results suggest that vibration introduced by mastication does not eliminate friction caused by traditional methods of ligation. There does seem to be some effects on self-ligating brackets, but is not consistent among different methods of self-ligation. Tipping moments and ligation forces were equally significant in determining frictional forces. As well, there was considerable intra-operator variation in ligation forces. Variations in clinical ligation forces are likely to be equal or greater than these experimental data and have the potential to affect treatment efficiency.