CAD/CAM supported production process of standardized enamel and dentin tooth discs with different thicknesses for in vitro material testing
Introduction
It is very important for in vitro experiments to produce standardized specimens for material testing in order to limit the influence of deviations in both the dimension of the specimen and its position in the testing machine on the results. Thus, it is mandatory to produce specimens with a correct dimension and position in the testing machines. Also, the whole production process has great influence on the final results.
These factors were listed by Pashley et al. [1] in a review paper divided into the categories of bonding variables, etching variables, priming variables, storage substrate variables and testing variables. This review has focused on the issues relating to the differences induced by the material properties and the process used in sample preparation. The effect of specimen size and geometry were studied by other researchers [[2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]]. Phrukkanon et al. [2] for example have investigated different specimens with round and rectangular cross sections and reported higher bond strength for the circular cross section compared to the rectangular cross section. Another part of their investigation was the cross-sectional area of the samples. They tested three different cross sections and estimated lower bond strength for larger cross sections.
With the help of new affordable and very precise desktop SLA 3D printers for the production of small parts it is possible to design and produce individual devices to create very precise and uniform specimens. In this study a new standardized method for the production of enamel and dentin tooth discs was described. All steps were performed by individual designed and produced devices. The production of these devices was described and tested with natural teeth.
Section snippets
Exemption by institutional review board
The study was proved by the Institutional Review Board and received an exemption.
CAD design of the models
Autodesk Inventor 2019 (Autodesk Corporation, San Rafael, USA) was used for the creation of our CAD models. All construction elements were displayed in different colors for a better description of the disc creation method. The devices were designed to be used together with a fixed dental contra-angel handpiece for a realistic preparation of natural teeth. The printed parts were optimized for 3D printing. The layer
Results
The results of the 40 milled discs are displayed in a boxplot diagram in Fig. 5. Furthermore, an example of the surface deviation of a milled disc with a diameter of 5 mm and a thickness of 2 mm is displayed in this figure on the right side. The very precise surface can be seen as an example of the production process. The lower and the upper quartile of the diameter and thickness were all under +/-0.06 mm and the median was under +/−0.05 mm. For the group with the 2 mm thickness the mean value
Discussion
With the method described above, it was possible to generate very precise tools for the standardized fabrication of round tooth discs of different dimensions in diameter and thickness. The precision of the milled discs can even be enhanced by a selection of the discs after the production. The selection can be done by the described control method in 2.4. With this method two outliers were detected for a thickness of 2.5 and 3 mm (Fig. 5). These discs can be removed for more precise results. Even
Conclusion
The whole process for the fabrication of standardized tooth disc were described and the usefulness and precision were shown. With this innovative method it is possible to generate tooth discs with different dimensions in thickness and diameter for in vitro material testing. Even the creation of discs with and without enamel is possible.
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