3D-printed Surgical Training Model Based on Real Patient Situations for Dental Education.

Background: Most simulation models used at university dental clinics are typodonts. Usually, models show idealized eugnathic situations, which are rarely encountered in everyday practice. The aim of this study was to use 3D printing technology to manufacture individualized surgical training models for root tip resection (apicoectomy) on the basis of real patient data and to compare their suitability for dental education against a commercial typodont model. Methods: The training model was designed using CAD/CAM (computer-aided design/computer-aided manufacturing) technology. The printer used to manufacture the models employed the PolyJet technique. Dental students, about one year before their final examinations, acted as test persons and evaluated the simulation models on a visual analogue scale (VAS) with four questions (Q1-Q4). Results: A training model for root tip resection was constructed and printed employing two different materials (hard and soft) to differentiate anatomical structures within the model. The exercise was rated by 35 participants for the typodont model and 33 students for the 3D-printed model. Wilcoxon rank sum tests were carried out to identify differences in the assessments of the two model types. The alternative hypothesis for each test was: "The rating for the typodont model is higher than that for the 3D-printed model". As the p-values reveal, the alternative hypothesis has to be rejected in all cases. For both models, the gingiva mask was criticized. Conclusions: Individual 3D-printed surgical training models based on real patient data offer a realistic alternative to industrially manufactured typodont models. However, there is still room for improvement with respect to the gingiva mask for learning surgical incision and flap formation.

Dynamic behavior of different quantities of osteoblasts during formation of micromass cultures.

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. © 2018 International Society for Advancement of Cytometry.

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 object's 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.

In vitro comparison of instrumental and visual tooth shade determination under different illuminants.

STATEMENT OF PROBLEM: While a considerable body of literature deals with the comparison between visual and instrumental tooth color determination, in most of these studies either the number of color specimens or the number of examiners is too small to allow for a general statement about such a subjective method as visual color determination. Furthermore, perceptual aspects like perceptible or acceptable color differences are often not considered. PURPOSE: The purpose of this study was to investigate the precision of a spectrophotometer in tooth shade determination compared with visual color matching using a shade guide in vitro. Moreover, the influence of different illuminants as well as of sex and professional experience of the examiners on visual color matching was analyzed. MATERIAL AND METHODS: Fifty examiners (13 men, 37 women; without dyschromatopsia), grouped by professional experience, determined the shades of 10 prosthetic teeth with the Vitapan classical shade guide under 4 illuminants (daylight, halogen, fluorescent [5000 K], fluorescent [nonspecific ceiling light]) and with a spectrophotometer (Shadepilot). Reproducibility (precision) of color determination was characterized by the average of the highest percentages of interexaminer agreement for each specimen. Additionally, color differences (ΔE) were calculated based on CIELab values. RESULTS: The mean reproducibility of the spectrophotometer was 92.2%, while for visual examination it was 43.7%. The corresponding differences in CIELab color space amounted to ΔEinstr=2.6 and ΔEvis=5.2. Illuminants and professional experience showed a significant influence, while sex did not. CONCLUSION: While the spectrophotometer provided higher reproducibility, considering the color differences, the results obtained by visual inspection were still satisfactory. The differences due to type of illuminant, degree of experience, and sex of the examiners are of little practical relevance.

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).