Markus Dekiff

Simultaneous acquisition of 3D shape and deformation by combination of interferometric and correlation-based laser speckle metrology

A metrology system combining three laser speckle measurement techniques for simultaneous determination of 3D shape and micro- and macroscopic deformations is presented. While microscopic deformations are determined by a combination of Digital Holographic Interferometry (DHI) and Digital Speckle Photography (DSP), macroscopic 3D shape, position and deformation are retrieved by photogrammetry based on digital image correlation of a projected laser speckle pattern. The photogrammetrically obtained data extend the measurement range of the DHI-DSP system and also increase the accuracy of the calculation of the sensitivity vector. Furthermore, a precise assignment of microscopic displacements to the objects macroscopic shape for enhanced visualization is achieved. The approach allows for fast measurements with a simple setup. Key parameters of the system are optimized, and its precision and measurement range are demonstrated. As application examples, the deformation of a mandible model and the shrinkage of dental impression material are measured.

3D printed simulation models based on real patient situations for hands-on practice

During the last few years, the curriculum of many dentistry schools in Germany has been reorganised. Two key aspects of the applied changes are the integration of up-to-date teaching methods and the promotion of interdisciplinarity. To support these efforts, an approach to fabricating individualised simulation models for hands-on courses employing 3D printing is presented. The models are based on real patients, thus providing students a more realistic preparation for real clinical situations. As a wide variety of dental procedures can be implemented, the simulation models can also contribute to a more interdisciplinary dental education. The data used for the construction of the models were acquired by 3D surface scanning. The data were further processed with 3D modelling software. Afterwards, the models were fabricated by 3D printing with the PolyJet technique. Three models serve as examples: a prosthodontic model for training veneer preparation, a conservative model for practicing dental bonding and an interdisciplinary model featuring carious teeth and an insufficient crown. The third model was evaluated in a hands-on course with 22 fourth-year dental students. The students answered a questionnaire and gave their personal opinion. Whilst the concept of the model received very positive feedback, some aspects of the implementation were criticised. We discuss these observations and suggest ways for further improvement.

Quantitative analysis of dynamic behavior of osteoblasts during in vitro formation of micro-mass cell cultures.

Improvements in bone tissue engineering require an understanding of cellular and tissue level behavior of osteoblast-like cells. Experiments indicate that in the absence of an anchoring material, intercellular adhesion may be based on signals that promote cell activity resulting in the formation of a spheroid cell-matrix. The aim of the present study is to investigate the formation of scaffold-free three-dimensional micro-mass cell spheroids in vitro, and to characterize quantitatively the cell movement. A new correlation based automated tracking method is evaluated in order to optimize the processing parameters and to identify statistical parameters that characterize the cell behavior. Results suggest that the temporal development of the mean distance of the cells to the center of gravity may be described by an exponential function, thus providing a characteristic time constant as a quantitative measure of cell dynamics. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

Dynamic behavior of different quantities of osteoblasts during formation of micromass cultures: Dynamic Behavior of Different Quantities of Osteoblasts

Implantation of micromass cultures of osteoblastic cells offers the possibility of scaffold free tissue engineering for example, regeneration of bone defects. However, the details of cell dynamics during the formation of these micromasses are still not well understood. This study aims to investigate and clarify the extent to which cell quantity influences the dynamics of micromass formation of osteoblastic cell cultures. For this purpose, the migration and aggregation during this process are investigated by optical inspection employing image processing software that allows for automated tracking of cell groups using digital image correlation. An exponential time behavior is observed with respect to the velocity of the cells and the distance of the cells to their common center of gravity. Characteristic time constants are derived as quantitative measures of the cell dynamics. The results indicate that the time constants strongly depend on the quantity of cells, that is, will decrease with increasing cell quantity.

Holographic interferometric and correlation-based laser speckle metrology for 3D deformations in dentistry

The mechanical loading of dental restorations and hard tissue is often investigated numerically. For validation and optimization of such simulations, comparisons with measured deformations are essential. We combine digital holographic interferometry and digital speckle photography for the determination of microscopic deformations with a photogrammetric method that is based on digital image correlation of a projected laser speckle pattern. This multimodal workstation allows the simultaneous acquisition of the specimen’s macroscopic 3D shape and thus a quantitative comparison of measured deformations with simulation data. In order to demonstrate the feasibility of our system, two applications are presented: the quantitative determination of (1) the deformation of a mandible model due to mechanical loading of an inserted dental implant and of (2) the deformation of a (dental) bridge model under mechanical loading. The results were compared with data from finite element analyses of the investigated applications. The experimental results showed close agreement with those of the simulations.