Quality of Alveolar Bone - Structure Dependant Material Properties and Design of a Novel Measurement Technique

摘要

In a first part, the aim of this paper is to describe the biomechanical background which can be used as a basis for determining bone quality by measuring elastic properties of bone. Applying material mechanical equations for porous and cellular structured models, the elastic material properties (modulus of elasticity) of cellular and cortical bone as porous structures were approximated over the whole range of relative bone mineral density 0 < rBMD < 1 with a specific equation. Proper approximation of experimentally determined values for mechanical properties of bone could be achieved based on this equation, which can not only be used for the description of cellular bone but also for cortical bone with values for rBMD greater than 0.35. As clinically applicable measurement systems for the objective classification of bone quality are missing, in a second part the design of a novel measurement technique is presented. Based on a circular disc with a central hole reflecting a horizontal cross-section of an implant socket, the mechanical effects of expanding the central hole were studied. Subsequently, the clinical situation of a loading device prepared for the placement of a dental implant (depth: 10mm; diameter 3.5mm) was simulated using 3D finite element analysis. Both cortical and trabecular areas of bone were modelled allowing for elastic properties to be varied independently. Finite element analysis revealed that it was possible to estimate bone quality applying the measurement technique proposed. Maximum deviations of 6% of experimentally determined elastic modulus from setpoint elastic modulus were found. Measuring internal pressure in a drill hole e.g. in an implant socket caused by a defined expansion of a rotational symmetric loading device could be used for establishing a clinically meaningful test system for the objective classification of alveolar bone.