Three-dimensionally printed and milled polyphenylene sulfone materials in dentistry: Tensile bond strength to veneering composite resin and surface properties after different pretreatments.

STATEMENT OF PROBLEM: Polyphenylene sulfone (PPSU) is a thermoplastic that can be processed using 3-dimensional printing. PPSU is new to dentistry, and scientific data on its properties are lacking. PURPOSE: The purpose of this in vitro study was to test the surface properties and the tensile bond strength (TBS) between PPSU and a veneering composite resin in comparison with a polyetheretherketone (PEEK). MATERIAL AND METHODS: Gehr PPSU (PPSU-B1), Radel R-5000 NT (PPSU-B2), and Juvora Dental Disc (PEEK-CG) substrates were cut from bulk material, while FIL-A-GEHR PPSU (PPSU-3D) was 3-dimensionally printed (N=504, n=126/material). TBS to veneering composite resin (CeramageUp) was tested initially and after 5000 and 10 000 thermocycles, and fracture types were analyzed. Surface free energy (SFE) and surface roughness (Ra) were determined after pretreatment with aluminum oxide (Al2O3) of different grain sizes (50 and 110 µm) applied with different pressures (0.1, 0.2, 0.4 MPa), silicon dioxide (SiO2)-coated Al2O3 (0.28 MPa), sulfuric acid, or polished. Qualitative surface characterization was performed by using a scanning electron microscope (SEM). One-way ANOVA, the Kruskal-Wallis, Mann-Whitney U, and the Spearman correlation tests were computed (α=.05). RESULTS: PPSU-3D and PEEK-CG presented higher TBS results than PPSU-B1 and PPSU-B2. Initial TBS values were higher than after 10 000 thermocycles. Adhesive fractures between substrate and veneering composite resin occurred most frequently. With a few exceptions, PEEK-CG presented higher SFE values than all other materials within a pretreatment group, while PPSU-3D and PEEK-CG showed consistently high Ra values. An increase in pressure and particle size increased SFE and Ra. CONCLUSIONS: FFF-printed PPSU-3D showed similar TBS values with the veneering composite resin to the more established PEEK. Pretreatment methods devised for PEEK represent valid strategies for increasing both the SFE and Ra of the high-performance polymer PPSU.

3D printing of dental restorations: Mechanical properties of thermoplastic polymer materials.

In the seminal field of 3D printing of dental restorations, the time and cost saving manufacturing of removable and fixed dental prostheses from thermoplastic polymer materials employing fused filament fabrication (FFF) is gaining momentum. As of today, the additive manufacturing of the established semi-crystalline polyetheretherketone (PEEK) requires extensive post-processing and lacks precision. In this context, the amorphous polyphenylene sulfone (PPSU) may provide a higher predictability and reliability of the results. The aim of this study was to investigate the mechanical properties of PPSU and PEEK processed by FFF (PPSU1-3D (PPSU Radel) and PPSU2-3D (Ultrason P 3010 NAT)) or extrusion (PPSU1-EX (Radel R-5000 NT) and PEEK-CG (PEEK Juvora)). Three-point flexural strength, two-body wear, and Martens hardness (HM) and indentation modulus (EIT) were tested after aging. One-way ANOVA, the Kruskal-Wallis and the Pearson's and Spearman's correlation tests were computed (α = 0.05). PPSU1-3D and PPSU2-3D showed lower flexural strength values than PPSU1-EX and PEEK-CG. PPSU1-3D showed the highest, and PEEK-CG and PPSU1-EX the lowest height loss. The highest HM and EIT results were observed for PEEK-CG and the lowest for PPSU1-3D. Correlations were observed between all parameters except for the application height. In conclusion, the manufacturing process affected the flexural strength of PPSU, with 3D printed specimens presenting lower values than specimens cut from prefabricated molded material. This finding indicates that the 3D printing parameters employed for the additive manufacturing of PPSU specimens in the present investigation require further optimization. For 3D printed specimens, the quality of the filament showed an impact on the mechanical properties, underlining the importance of adhering to high quality standards during filament fabrication. Extruded PPSU led to comparable results with PEEK for flexural strength and two-body wear, indicating this novel dental restorative material to be a suitable alternative to the established PEEK for the manufacturing of both removable and fixed dental prostheses.

Large-aperture two-dimensional x-ray refractive mosaic lenses.

Lenses with high numerical aperture are required for images with very high spatial resolution, which is difficult to realize in the x-ray range because of low-refraction-index decrement and relatively high absorption of x-rays in the material. However, such an aperture can be realized by means of a mosaic lens, as shown in this work.

Imaging of metastatic lymph nodes by X-ray phase-contrast micro-tomography.

Invasive cancer causes a change in density in the affected tissue, which can be visualized by x-ray phase-contrast tomography. However, the diagnostic value of this method has so far not been investigated in detail. Therefore, the purpose of this study was, in a blinded manner, to investigate whether malignancy could be revealed by non-invasive x-ray phase-contrast tomography in lymph nodes from breast cancer patients. Seventeen formalin-fixed paraffin-embedded lymph nodes from 10 female patients (age range 37-83 years) diagnosed with invasive ductal carcinomas were analyzed by X-ray phase-contrast tomography. Ten lymph nodes had metastatic deposits and 7 were benign. The phase-contrast images were analyzed according to standards for conventional CT images looking for characteristics usually only visible by pathological examinations. Histopathology was used as reference. The result of this study was that the diagnostic sensitivity of the image analysis for detecting malignancy was 100% and the specificity was 87%. The positive predictive value was 91% for detecting malignancy and the negative predictive value was 100%. We conclude that x-ray phase-contrast imaging can accurately detect density variations to obtain information regarding lymph node involvement previously inaccessible with standard absorption x-ray imaging.

X-ray phase-contrast tomography of porcine fat and rind.

X-ray computed tomography (CT) has recently received increased attention in the food science community. The aim of this paper is to demonstrate how grating based phase-contrast CT can provide contrast superior to standard absorption based CT. The method of phase-contrast CT is applied to two samples of porcine subcutaneous fat and rind. The additional contrast obtained may be used for quality testing, to investigate variations in fatty acid composition of the fat-fraction, and density variations in the meat-fraction. The possibility of integrating the method into an abattoir environment is discussed.

High-resolution tomographic imaging of a human cerebellum: comparison of absorption and grating-based phase contrast.

Human brain tissue belongs to the most impressive and delicate three-dimensional structures in nature. Its outstanding functional importance in the organism implies a strong need for brain imaging modalities. Although magnetic resonance imaging provides deep insights, its spatial resolution is insufficient to study the structure on the level of individual cells. Therefore, our knowledge of brain microstructure currently relies on two-dimensional techniques, optical and electron microscopy, which generally require severe preparation procedures including sectioning and staining. X-ray absorption microtomography yields the necessary spatial resolution, but since the composition of the different types of brain tissue is similar, the images show only marginal contrast. An alternative to absorption could be X-ray phase contrast, which is known for much better discrimination of soft tissues but requires more intricate machinery. In the present communication, we report an evaluation of the recently developed X-ray grating interferometry technique, applied to obtain phase-contrast as well as absorption-contrast synchrotron radiation-based microtomography of human cerebellum. The results are quantitatively compared with synchrotron radiation-based microtomography in optimized absorption-contrast mode. It is demonstrated that grating interferometry allows identifying besides the blood vessels, the stratum moleculare, the stratum granulosum and the white matter. Along the periphery of the stratum granulosum, we have detected microstructures about 40 µm in diameter, which we associate with the Purkinje cells because of their location, size, shape and density. The detection of individual Purkinje cells without the application of any stain or contrast agent is unique in the field of computed tomography and sets new standards in non-destructive three-dimensional imaging.