Ajl Harrison

The chewing robot: A new biologically-inspired way to evaluate dental restorative materials

This paper presents a novel in vitro dental wear simulator based on 6-6 parallel kinematics to replicate mechanical wear formation on dental materials and components, such as individual teeth, crowns or bridges. The human mandible, guided by a range of passive structures moves with up to six degrees of freedom (DOF). Currently available wear simulators lack the ability to perform these complex chewing movements. In addition simulators are unable to replicate the normal range of chewing forces as they have no control system able to mimic the natural muscle function controlled by the human central nervous system. Such discrepancies between true in vivo and simulated in vitro movements will influence the outcome and reliability of wear studies using such approaches. This paper summarizes the development of a new dynamic jaw simulator based on the kinematics of the human jaw.

Improved single- and multi-contact life-time testing of dental restorative materials using key characteristics of the human masticatory system and a force/position-controlled robotic dental wear simulator

This paper presents a new in vitro wear simulator based on spatial parallel kinematics and a biologically inspired implicit force/position hybrid controller to replicate chewing movements and dental wear formations on dental components, such as crowns, bridges or a full set of teeth. The human mandible, guided by passive structures such as posterior teeth and the two temporomandibular joints, moves with up to 6 degrees of freedom (DOF) in Cartesian space. The currently available wear simulators lack the ability to perform these chewing movements. In many cases, their lack of sufficient DOF enables them only to replicate the sliding motion of a single occlusal contact point by neglecting rotational movements and the motion along one Cartesian axis. The motion and forces of more than one occlusal contact points cannot accurately be replicated by these instruments. Furthermore, the majority of wear simulators are unable to control simultaneously the main wear-affecting parameters, considering abrasive mechanical wear, which are the occlusal sliding motion and bite forces in the constraint contact phase of the human chewing cycle. It has been shown that such discrepancies between the true in vivo and the simulated in vitro condition influence the outcome and the quality of wear studies. This can be improved by implementing biological features of the human masticatory system such as tooth compliance realized through the passive action of the periodontal ligament and active bite force control realized though the central nervous system using feedback from periodontal preceptors. The simulator described in this paper can be used for single- and multi-occlusal contact testing due to its kinematics and ability to exactly replicate human translational and rotational mandibular movements with up to 6 DOF without neglecting movements along or around the three Cartesian axes. Recorded human mandibular motion and occlusal force data are the reference inputs of the simulator. Experimental studies of wear using this simulator demonstrate that integrating the biological feature of combined force/position hybrid control in dental material testing improves the linearity and reduces the variability of results. In addition, it has been shown that present biaxially operated dental wear simulators are likely to provide misleading results in comparative in vitro/in vivo one-contact studies due to neglecting the occlusal sliding motion in one plane which could introduce an error of up to 49% since occlusal sliding motion D and volumetric wear loss V(loss) are proportional.

A minimal controller synthesis algorithm for narrow-band applications

Abstract A common control problem is that of reducing a narrow-band error signal or a narrow-band component of a broad-band error signal. The particular application described in this paper is that of active vibration isolation for automotive vehicles. The error-driven minimal control synthesis (Er-MCSI) algorithm with integral action has been applied to this problem, but is known to exhibit gain windup. The nature of the gain windup phenomenon is investigated and methods to mitigate its effects are discussed. A new controller, the narrow-band MCS (NBMCS), is developed specifically for narrow-band applications. NBMCS is based upon Er-MCSI and exploits the deterministic nature of the system disturbance. The NBMCS algorithm is shown not to suffer from the gain windup problem. The properties and performance of the Er-MCSI and NBMCS controllers are compared analytically, via simulation and experimental application, to an automotive vehicle equipped with active engine mounts.

Capturing motions and forces of the human masticatory system to replicate chewing and to perform dental wear experiments

One way to evaluate the life-time performance of dental restorative materials is to use in vitro dental wear simulators, which generate accelerated artificial dental wear on dental restorative components outside of the human oral environment. However, the work of several researchers has questioned the reliability of these in vitro results as a consequence of significant result variations produced by different types of dental wear simulators testing identical dental specimens. Natural six degree of freedom (DOF) mandibular movements and other characteristics of the human masticatory system are not replicated by any of these available simulators. A simulator replicating and controlling 6 DOF mandibular movements and occlusal bite forces improves this situation. This paper presents a method by which accurate jaw motion data can be obtained using a conventional 6 DOF motion capturing system and a method of measuring occlusal bite forces. The data obtained have subsequently been used as input signals for a new 6 DOF dental wear simulator capable of generating single and multi-contact wear formations in dental wear studies.