From the very start of their use until today, processes in Additive Manufacturing (AM) have found a way to grow from prototype production to individual and small-series production. Improvements in machinery, materials and other challenges in AM development have improved product quality, its mechanical properties and dimensional accuracy. Research in the field of dimensional accuracy must be focused on achieving better tolerances. From the beginning of AM, there has been a big issue in assuring dimensional repeatability and reproducibility of a part being printed over the course of several days. In order to examine that, a test plate was designed and built repeatedly with PolyJet technology over the course of several weeks. Measurements of dimensional accuracy and shape deviations of several typical features were carried out using X-ray Computed Tomography. Measurement results were analysed and presented in order to indicate the repeatability and reproducibility of PolyJet AM technology. Results show that PolyJet technology consistently produces parts within ±100 μm, at a 95% confidence interval, under reproducibility conditions of over a 1-month period. Accuracy for measurands (distance) in the x and y axis was significantly better than it was for the z axis which was from 56 to 197 µm, i.e., in the x and y axis, it was from −8 to 76 µm. Shape errors (i.e., cylindricity) were larger than positional or dimensional errors; this can be attributed to relatively large surface roughness and small feature sizes on the test plate that was used.

The removal of filling material is important for successful root canal retreatment. The aim of the study was to compare the efficiency of two activated irrigation techniques, the shock wave-enhanced emission photoacoustic streaming (SWEEPS) mode of the Er:YAG laser and ultrasonically activated irrigation (UAI) and a conventional syringe-needle technique (SNI), in the removal of bioceramic sealer/gutta-percha during conventional retreatment in oval root canals. The study sample consisted of distal root canals of 42 extracted human mandibular molars, which were prepared using a ProTaper Next system up to size 40/0.06 and filled with bioceramic sealer using a single-cone obturation technique. The teeth were then re-treated with a Reciproc Blue RB40 file and 3% sodium hypochlorite solution. The prepared teeth were randomly divided into three groups (n = 14 per group) and subjected to one of the three irrigation methods. Micro-CT scans were performed at different stages to assess the amount of filling material after each retreatment phase. The results of the study showed that all the tested irrigation techniques reduced a statistically significant amount of the remnant filling material at retreatment (p < 0.05), and there were no statistically significant differences in efficacy between the three methods. All tested techniques had similar efficacy in the removal of the remaining filling remnants.

X-Ray Computed tomography (XCT) has become an important non-destructive quality assurance technique in industry. Consequently, standards for quality insurance of XCT and on its performance are required to support industrial XCT users for reliable production. This performance is determined by analysis of the quality of the images produced and by the dimensional measurement accuracy achieved for a given XCT parameter setting. Until recently, standards assessed image quality solely in terms of contrast sensitivity and spatial resolution. Detection limits could not be predicted until now. A new term is introduced: The Detail Detection Sensitivity (DDS). It depends on the contrast sensitivity as a function of contrast and noise, and on the spatial resolution. The spatial frequency needs to be implemented into the analysis to consider sensitivity as a function of the size of an indication. The contrast sensitivity is quantified by the Contrast Discrimination Function (CDF) and the spatial resolution by the Modulation Transfer Function (MTF). The numerical DDS is determined for air flaws from the Contrast Detection Diagram (CDD) at 100% contrast. However, some XCT operators prefer visual determinations rather than numerical ones. To face this need, the SensMonCTII project proposes a new Image Quality Indicator (IQI), consisting of a disk with holes of different sizes for visual DDS determination. The project aims to produce a new ISO standard draft providing a practice to evaluate numerically the XCT image quality via MTF, CDF, CDD and DDS, as well as to evaluate visually the DDS from the hole visibility of a disk IQI. The paper does not address the performance of XCT in terms of dimensional measurement accuracy, but focuses on the performance of XCT in terms of image quality. It describes the methodology to evaluate the image quality, including DDS for the first time.

Following a shift in the industry to solid-state lasers during the past decade, resonator tubes which can be used in iodine-stabilized helium-neon (He-Ne) lasers are being discontinued by most manufacturers. After installing a...

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