Flávia de Souza Bastos

Analytical and numerical analysis of human dental occlusal contact

The knowledge of contact forces in teeth surfaces during mastication or para-functional movements can help to understand processes related to friction and wear of human dental enamel. The development of a numerical model for analysis of the occlusal contact between two antagonistic teeth is proposed, which includes three basic steps: the characterisation of the surface roughness, its homogenisation using an assumed distribution function and the numerical determination of the resulting forces. Finite element strain results for the main different asperities are statistically combined, deriving the predicted macroscopic behaviour of the interface. Axisymmetric and 3D numerical models with an elasto-plastic constitutive law are used to simulate micro-indentations and micro-contacts, respectively. The contact is allowed to occur locally in planes not necessarily parallel to the surfaces mean plane, a problem for which there is no analytical solution. The three identified parameters, homogenised surface hardness (3.68 GPa), surface yield stress (3.08 GPa) and static friction coefficient (0.23), agree with the experimental values reported in the literature.

Dental wear estimation using a digital intra-oral optical scanner and an automated 3D computer vision method

The objective of this work was to propose an automated and direct process to grade tooth wear intra-orally. Eight extracted teeth were etched with acid for different times to produce wear and scanned with an intra-oral optical scanner. Computer vision algorithms were used for alignment and comparison among models. Wear volume was estimated and visual scoring was achieved to determine reliability. Results demonstrated that it is possible to directly detect submillimeter differences in teeth surfaces with an automated method with results similar to those obtained by direct visual inspection. The investigated method proved to be reliable for comparison of measurements over time.

A FEM-based study on the influence of skewness and kurtosis surface texture parameters in human dental occlusal contact

Tooth wear, which manifests with a great variety of degree or level, is one of the dental abnormalities commonly found in diverse populations. The computational modeling of occlusal contact problem can help comprehension of any interaction between teeth generating stress concentration. The approach used to simulate contact between rough surfaces, given the probability density functions, consists in discretizing them into several intervals, so that each one represents a main asperity. The deformations of the main asperities are analyzed and, using homogenization techniques, it is possible to establish the relationship among the responses occurred in micro-scale and the predicted responses in macro-scale. In this work we create parameterized scripts in Python language for the Abaqus CAE software in order to analyze the influence of the surface topography on contact of human dental occlusal surfaces. The texture parameters influence their tribological behavior. As the mean roughness or mean curvature increases, the nature of the contact changes from elastic to plastic and the friction coefficient increases and becomes saturated. For negative skewness, the higher the skewness, the lower the contact area. For positive skewness, the opposite is observed. The higher the kurtosis, greater the area, except for kurtosis less than 3. The surface hardness is not affected by any of the surface texture parameters tested. Further verification using experimental data can encourage dentists to become more familiar with computer simulation.

Numerical analysis of human dental occlusal contact

The purpose of this study was to obtain real contact areas, forces, and pressures acting on human dental enamel as a function of the nominal pressure during dental occlusal contact. The described development consisted of three steps: characterization of the surface roughness by 3D contact profilometry test, finite element analysis of micro responses for each pair of main asperities in contact, and homogenization of macro responses using an assumed probability density function. The inelastic deformation of enamel was considered, adjusting the stress-strain relationship of sound enamel to that obtained from instrumented indentation tests conducted with spherical tip. A mechanical part of the static friction coefficient was estimated as the ratio between tangential and normal components of the overall resistive force, resulting in ?d = 0.057. Less than 1% of contact pairs reached the yield stress of enamel, indicating that the occlusal contact is essentially elastic. The micro-models indicated an average hardness of 6.25GPa, and the homogenized result for macroscopic interface was around 9GPa. Further refinements of the methodology and verification using experimental data can provide a better understanding of processes related to contact, friction and wear of human tooth enamel.