Orthomicrotribometer

Abstract

This paper presents a novel concept for a test rig specially developed for reciprocating sliding wear tests in a controlled environment. The developed device, known as an orthomicrotribometer, was used to characterise the tribology of orthodontic appliances. It consists of a reciprocating movement system that drives the sample horizontally while the counter-body is moved vertically by a slider. Moreover, a piezoelectric translator is used to control the counter-body movement while a 3D load cell controls the normal load during the test. The sample position was monitored using a displacement sensor that enabled the construction of triboscopic maps (e.g., the evolution of the tribo-parameters being measured in relation to the number of cycles and the position of the counter body within each cycle). The tests were parameterised in order to represent the mouth environment and movement. The orthodontic components, namely the bracket and wire, were used as the sample and counter-body, respectively, and the samples were immersed in artificial saliva. According to the literature, low speeds and high amplitudes represent the movements of the orthodontic parts. The test parameters were: 1: normal load (0.5; 1.0 and 1.5 N), 2: frequency (0.1; 0.5 and 1.0 Hz) and 3: environment (dry and immersed in artificial saliva). The friction coefficient and wear rate were monitored to evaluate the reactions and interactions between the bracket and wire. The wear scar and formed tribolayer were also characterised using scanning electron microscopy and optical microscopy. The increase in the normal load and frequency induced a reduction in the friction coefficient and wear rate. This indicates that the main mechanism governing the tribosystem is the tribolayer formation. Artificial saliva acted as a lubricant in the system. This new methodology enables tribological characterisation of the orthodontic appliance reproducing the oral cavity environment, and provides a powerful tool for the development of new materials for wires and brackets.