A weighted fusion method with multi-system for improving measurement accuracy of structured light 3D profilometry

It is a challenge to improve the accuracy of 3D profile measurement based on binary coded structured light for complex surfaces. A new method of weighted fusion with multi-system is presented to reduce the measurement errors due to the stripe grayscale asymmetry, which is based on the analysis of stripe center deviation related to surface normal and the directions of incident and reflected rays. First, the stripe center deviation model is established according to the geometric relationship between the stripe center deviation, the incident and reflected angles at any measured point. The influence of each variable on stripe center deviation is analyzed, and three subsystems are formed by a binocular structured light framework to achieve multiple measurements based on the influence regularity. Then in order to improve the measurement accuracy, different weights are assigned to the measured point in different subsystems according to the stripe center deviation model and its relationship with measurement error, and the weighted data from different subsystems are fused. Experiments are carried out to validate the presented method, and the experimental results demonstrate that it effectively improves the measurement accuracy of complex surfaces and measurement accuracy is improved by about 27% compared with the conventional method.

Monolith Dental Bridge by Soft Machining of Dried Ceramic Dough

All-ceramic fixed restorations are gaining popularity because of increased esthetic consciousness in the younger population. Monolith ceramic crowns and bridges are preferred to withstand masticatory loads where the availability of occlusal height is limited. Machining green blanks of ceramic with organic binders have been studied to reduce loss of final strength, cost, and wastage associated with milling partial sintered and sintered blanks. Notches on the surface/edge associated with green milling will disappear after sintering in contrast to sintered state machining where diamond polishing is essential. In this study, we explored a novel ceramic dough process to form a green body of alumina or 3 Mol% yttria-stabilized zirconium oxide (YSZ), and computer numerical control (CNC) machining was performed on the dried dough. Micro Computer Tomography analysis of the bridges after sintering revealed a negligible void volume, 0.06–0.08% of the total volume, with randomly dispersed voids. Precision analysis of the sintered bridges with respect to the reference file resulted in a deviation range of +0.56 to −0.79 mm, with negligible deviation on the cementation surface. The green machined surface had a roughness profile of 1.2–1.7 μm after machining and 2.2–2.4 μm after sintering, as revealed by 3D profilometry.

Bacterial Adhesion to Grade 4 and Grade 5 Turned and Mildly Acid-Etched Titanium Implant Surfaces: An In Vitro and Ex Vivo Study

The aim of the present study was to investigate the bacterial adhesion to titanium (Ti) implant surfaces, different for composition and topographic features. Grade 4 and 5 turned (T-4, T-5,) and mildly acid-etched (MA-4, MA-5) Ti 6 × 1 mm disks were topographically analyzed by scanning electronic microscopy and 3D profilometry. Bacterial cultures (Streptococcus sanguinis) were in vitro seeded and, after two and six hours, adherent bacteria were quantified by colony-forming unit (CFU) counting. Ti samples were also exposed to the oral environment of six periodontally healthy volunteers and, after 12 h, the formed biofilm was evaluated by CFU counting. Inter-group differences were tested by the Mann–Whitney U-Test (α = 0.05). MA surfaces were significantly rougher than T ones, whereas no difference between grade 4 and grade 5 disks was detected. Significantly higher in vitro bacterial adhesion for MA than T disks was shown at two and six hours. Significantly higher values of CFU counting for MA than T surfaces and for grade 5 than grade 4 disks were found at the 12 h-ex vivo test. Bacterial adhesion showed to be sensitive to both Ti surface topography and composition, with possible implications on peri-implant tissue health maintenance.

Mechanical Strength and Fatigue Fracture Analysis on Al-Zn-Mg Alloy with the Influence of Creep Aging Process

The Al-Zn-Mg alloy comes under the aluminium alloy; it possesses good capability of age hardening and superior strength in contrast to other alloys. The numbers of creep aging experiments are conducted with the support of different temperature levels such as 180, 200, and 2000°C. The effects of tests are reflected on the tensile test and fatigue tests; the temperature and stress directly affects the creep characteristics, mechanical strength, and fatigue performance of the Al-Zn-Mg alloy. The time period of the creep test is maintained as 15 hrs with constant load of 200 MPa and 220 MPa. The increasing temperature increases the tensile strength and fatigue life of the Al-Zn-Mg alloy under initial condition; furthermore, continuous increment reduces the strength and fatigue existence. In the fatigue test, the fatigue span of the Al-Zn-Mg is extremely enhanced by the application of creep aging at a particular temperature. The 3D profilometry image visibly shows the influence of temperature in forming a fracture in fatigue analysis through microstructure analysis.

A Fast Shape-from-Focus-Based Surface Topography Measurement Method

Shape from focus is an accurate, but relatively time-consuming, 3D profilometry technique (compared to e.g., laser triangulation or fringe projection). This is the case because a large amount of data that needs to be captured and processed to obtain 3D measurements. In this paper, we propose a two-step shape-from-focus measurement approach that can improve the speed with 40%. By using a faster profilometry technique to create a coarse measurement of an unknown target, this coarse measurement can be used to limit the data capture to only the required frames. This method can significantly improve the measurement and processing speed. The method was tested on a 40 mm by 40 mm custom target and resulted in an overall 46% reduction of measurement time. The accuracy of the proposed method was compared against the conventional shape from focus method by comparing both methods with a more accurate reference.