Full Contour Research Articles

Direct measurement and compensation of contour errors for profile grinding

Profile grinding is widely used for precision machining of curved parts, such as tools and molds. Traditional methods are manual-dependent and struggle with autonomous measurement and compensation of contour errors. This paper introduces a novel method for the direct measurement and compensation of contour errors in large-size profile grinding. A new image stitching algorithm for complex smooth curves is proposed, enabling robust image registration in low-feature regions. Furthermore, an approach for on-machine sub-pixel detection of contour errors is investigated, and an in-situ compensation algorithm for contour errors is designed. Experimental results show that the proposed method achieves high-precision stitching with minimal overlap, significantly improving contour error measurement. The compensation algorithm optimizes the tool path and implement the online compensation of the full contour errors during secondary machining, effectively improving the machining accuracy of curve parts. Additionally, a negative correlation between the number of image stitches and machining accuracy is revealed, and the possible explanations are discussed. The impact of various factors on machining accuracy will be further investigated in future studies.

Comparing Zirconium Crown Marginal Adaptation in Preparations with Two Different Occlusal Reductions.

This study aimed to assess and contrast the effects on the vertical marginal fit of full contour CAD/CAM-generated monolithic zirconia crowns at pre- and post-cementation levels with various occlusal reduction schemes (planar and flat) and cements. Forty sound human maxillary first premolars were sampled for this study. The samples were divided into two main groups with twenty samples in each group according to the occlusal reduction scheme as follows: Group A included a chamfer finishing line design with a planar occlusal reduction scheme and Group B included a chamfer finishing line design with a flat occlusal reduction scheme. Each group was sampled into two subgroups (n = 10) based on the type of cement as follows: resin-modified glass ionomer cement (Fuji Plus) for subgroups A1 and B1, and a universal adhesive system (Duo Estecem II) for subgroups A2 and B2. Marginal gaps were tested in four indentations using a Dino light stereomicroscope (230×). Paired T-tests and Student's t-tests were used to analyze the data. Before cementation, subgroup A1 scored the lowest mean of vertical marginal gap values, while subgroup B2 scored the highest mean; following cementation, subgroup A1 scored the lowest mean of vertical marginal gap values, and subgroup B2 scored the highest mean of vertical marginal gap values. A chamfer finishing line design with a planar occlusal reduction scheme could be a preferable occlusal reduction scheme.

Efficient Search for New Physics Using Active Learning in the ATLAS Experiment

Searches for new physics set exclusion limits in parameter spaces of typically up to 2 dimensions. However, the relevant theory parameter space is usually of a higher dimension but only a subspace is covered due to the computing time requirements of signal process simulations. An Active Learning approach is presented to address this limitation. Compared to the usual grid sampling, it reduces the number of parameter space points for which exclusion limits need to be determined. Hence it allows to extend interpretations of searches to higher dimensional parameter spaces and therefore to raise their value, e.g. via the identification of barely excluded subspaces which motivate dedicated new searches. In an iterative procedure, a Gaussian Process is fit to excluded signal cross-sections. Within the region close to the exclusion contour predicted by the Gaussian Process, Poisson disc sampling is used to determine further parameter space points for which the cross-section limits are determined. The procedure is aided by a warm-start phase based on computationally inexpensive, approximate limit estimates such as total signal cross-sections. The procedure is applied to a dark matter search on data collected by the ATLAS detector at the LHC, extending its interpretation from a 2 to a 4-dimensional parameter space while keeping the computational effort at a low level. The result is published in two formats: on one hand there is a publication of the Gaussian Process model. On the other hand, a visualization of the full 4-dimensional contour is presented as a collection of 2-dimensional exclusion contours where the 2 remaining parameters are chosen by the user.

Fatigue behavior of three thin CAD/CAM all-ceramic crown materials

ABSTRACT The purpose of this study was to study the effect of crown thickness on the fatigue life of CAD/CAM ceramic materials. CAD/CAM ceramic materials for the crown were virtually designed with three thickness designs of (a) ultra-thin occlusal crown average 0.7 mm thick (group A), (b) thin occlusal crown 1.1 mm average thick (group B), (c) thick occlusal crown 1.5 mm thick. The materials are: zirconia Cercon ZC and IPS e.max CAD (LD). Finite Element Analysis (FEA) simulations were carried out to estimate the fatigue lives of restorative materials. The lives for groups B and C under fatigue load were not significantly different from each other for Zirconia. The predicted lives for group A zirconia crowns, under fatigue load 50 N, 100 N, 120 N is 24 years, 4.3 years, 1.9 years, respectively. Results for crowns made of LD can be summarized as follows: under load 50 N, all groups have survived longer than 5 respectively, while under the load of 100 N, only group C survived longer than 5 years. 0.7 mm thick full contour Zirconia crowns possessed adequate endurance strength to survive under physiologic conditions. On the other hand, the crown made of LD should have at least 1.5 mm thickness to survive longer than 5 years.

The effect of composition and holding time on glaze production using basalt rock as a base

This research studied the potential use of local basalt and feldspar from Lampung Province, Indonesia, as glaze materials. Frit(s) are composed of changing basalt-to-feldspar weight ratios of A (30:70), B (50:50), C (70:30), and D (100:0) w/w%. The added 20% boric acid to the total weight reduces the process temperature to 1,000oC with holding times of 1, 4, and 8 hr(s). Based on the chemical composition test of the specimen, the four variations of the sample have SiO2 content above 40%, and the average SiO2/Al2O3 ratio is 4 and 5, which is usually a low-alumina glaze that will cause a glossy effect and have an amorphous structure. At point 2theta 29o, amorphous forms. Quartz (SiO2), albite (NaAlSi3O8), anorthite (CaAl2Si2O8), and coesite (SiO2) phases were discovered in the glaze specimens. The anorthite phase in glass-ceramic glaze gives a transparent glaze color due to the amorphous glassy phase formed during heat treatment. The findings of this study suggest that local materials based on basalt and feldspar may be used as glaze materials to provide a smooth texture and surface; the glaze layer is evenly distributed, can follow the full surface contour of the test specimen, and has low porosity.

Survival of Partial Laminate Veneers and Categorical Covariates Affecting the Survival: A Systematic Review

Background: Partial laminate veneers (PLV) have been accepted widely among both clinicians and patients with their favorable specifications, such as conservativeness, superior esthetics, bond strength and durability, for three decades. Various esthetic and functional impairments spreading in a wide range may be restored with veneers instead of full contour crowns. Objective: Although advantages, partial laminate veneers are not free from complications and various factors can influence the service duration of these restorations. Methods: An electronic Pubmed/Medline and Google Academic search was conducted without time restriction, providing information on porcelain laminate veneer’s failure rate and survival. Assessment of the identified studies was performed by two independent reviewers. Clinical service durations and various types of failures were evaluated. Results: Debonding, fracture, discoloration of the porcelain; staining or disintegration of tooth-porcelain margin; hypersensitivity, secondary caries, pulp necrosis and the periodontal responses were the more frequently studied failures. The mean CFR was found as 8,22% per study. Enamel substrate, incisal overlapping and lithium disilicate veneers presented lower failure rates in comparison with dentine substrate, non-overlapping and feldspathic veneers. Conclusion: PLV’s have high survival rates. The overall survival of PLV restorations can be affected by several prognostic variables.

Multi-stage finite element modeling of the deformation behavior during ultrasonic-assisted incremental sheet forming

The incremental sheet forming (ISF) has the characteristics of high flexibility, short lead time and enhanced formability. However, it still needs to be further improved in the aspect of forming quality (e.g. geometric accuracy and surface finish). The introduction of ultrasonic energy field may improve the deformability of sheets and the performance of parts, and reduce the load during sheet metal forming. The present work aims to meticulously investigate the influence of ultrasonic vibration on the deformation mechanism of material in several periods. First, based on an improved material constitutive model which considers both the thermal activation and dislocation density evolution process, a multi-stage finite element model of UISF was established. In particular, the multi-stage finite element model of UISF is divided into two stages, the full contour forming stage and the local forming stage, in which a transient simulation with high frequency output was realized. The influence of vibration parameters on the forming force as well as the distribution of stress and strain field in the forming process was comprehensively analyzed. The results show that the ultrasonic vibration reduces the forming force obviously (53% at amplitude of 10 µm), which is due to the dynamic impact effect and acoustic softening effect. Four distinct stages, approaching, loading, unloading and departing, are observed in a single vibration period. The dynamic impact effect of ultrasonic vibration changes the contact state between sheet and forming tool and causes the continuous propagation of dynamic oscillatory stress wave inside the material (propagate to the entire plate at 0.002 s), which leads to the significant change of stress and strain field. At the same time, the maximum stress is significantly reduced (73% at amplitude of 10 µm). By applying ultrasonic vibration on the stress-strain field, it is found that these vibrations mainly act on the contact region between the sheet and forming tool. The high frequency vibration makes smooth stress distribution along the path as well as spread over the whole sheet area to create a uniform distribution. Benefitting from the smooth stress distribution, the vibration also promotes greater formability with good forming quality and the plastic deformation mainly occurs in the side wall deformed area. The present work provides a practical simulation approach to study the transient deformation behavior of materials under the ultrasonic field.

Mechanical behavior of different machinable ceramic crowns using vertical and horizontal preparations: an in-vitro study

Objective: the aim of this study was to compare the mechanical behavior of different ceramics when used in thinvertical preparations versus traditional horizontal preparation. Material and Methods: two stainless-steel dieswere milled to simulate a minimally invasive vertical preparation (VP) and a traditional horizontal preparation(HP) for an all-ceramic crown of a maxillary first premolar. The stainless-steel dies were duplicated using epoxyresin. Eighty monolithic crowns were milled and divided into 2 groups according to preparation design. Eachdesign group was subdivided into 4 sub-groups according to material (n=10): IPS e.max CAD (lithium disilicate),Bruxzir shaded zirconia (full contour zirconia), CeraSmart (resin nanoceramic) and CEREC Tessera (advancedlithium disilicate). The crowns were cemented on their relevant epoxy resin dies using self-adhesive resin cement.All specimens were subjected to 15,000 thermocycles and then loaded to fracture in a universal testing machine.Data were analyzed using two-way ANOVA and Tukey pair wise comparison test. Results: the fracture resistancemean values of the VP (1344 + 118 N) was significantly lower than the HP design (1646 + 191 N). Ceramiccrowns made of full contour zirconia had higher fracture resistance mean values (2842 + 380 N) than advancedlithium disilicate (1272 + 125 N) followed by lithium disilicate crowns (983 + 52 N) and resin nanoceramic(882 + 61 N). Conclusion: both vertical and horizontal preparations, regardless the different ceramic materials,showed clinically acceptable fracture resistance values. KEYWORDSDental crown; Prosthodontics; Zirconia; Lithium disilicate; Hybrid ceramics.

Comparison the marginal and internal fitness of veneered and anatomical zirconia crowns milled by two different CAD/CAM systems (An in Vitro Study)

Background: Accuracy of fit is considered a very important factor in a crown fabricating procedure. Zirconium oxide ceramic is gaining popularity because of its remarkable mechanical capabilities and the potential aesthetic results obtained by using its recommended veneering porcelain, this study aimed to determine the effect of porcelain veneering on the marginal and internal fitness of zirconium-oxide crowns milled with two different CAD/CAM systems ( Wet and dry milling).
 Materials and methods: An ideal prepared tooth #16 to receive an all-ceramic crown restoration with 0.8mm chamfer finishing line was used as a master die. It duplicated and poured to get thirty-two stone working dies. The stone dies divided into two major groups according to the CAD/CAM systems being used, then each group subdivided into two subgroups (n=8) either zirconia crowns milled to full contour or traditional veneered zirconia crowns. Each crown then cemented to it stone die and sectioned longitudinally into four pieces. Stereomicroscope with aid of (image J) was used to examine the sample at a magnification of (140X). Four points of measurement were selected at each of the four-sectioned parts.
 Results: The final internal gap value of each sample was the arithmetical mean of the selected points of the four-sectioned pieces The data was evaluated statistically, using One-way ANOVA and LSD tests which revealed highly significant differences (p<0.001) among groups.
 Conclusion: Full-contoured zirconia crowns have better marginal and internal fit than the traditionally veneered crown, (CEREC AC, Sirona) system showed the best internal fitness. The mean gap of all groups was within the clinically acceptance.

Effect of Different Sintering Cycles on the Flexural Strength of Full Contour Monolithic Zirconia – An In-Vitro Comparative Study

BACKGROUND
 Monolithic zirconia restorations are known to exhibit good mechanical properties and acceptable aesthetics. During the fabrication of zirconia prostheses, the sintering process is the most critical step which determines the performance of the final product. However, a lot of issues with zirconia restorations were related to sintering cycles which can affect the crystalline content and grain growth that can affect its mechanical properties. The purpose of this study was to evaluate and compare the effect of different sintering cycles on the flexural strength of full-contour monolithic zirconia.
 METHODS
 In this in-vitro study, a total of 44 bar-shaped zirconia samples (Amann Girrbach Ceramill® CAD/CAM Material – ZOLID HT+) of final dimensions 20 x 4 x 2 mm were fabricated using Amann Girrbach Ceramill mind – computer-aided designing software and Amann Girrbach Ceramill® motion2 – computer-aided milling unit. These samples were randomly allocated into four groups with 11 samples in each group namely, Group 1, 2, 3 and 4 (Group 1: Long sintering cycle, Group 2: Intermediate sintering cycle, Group 3: Short sintering cycle, Group 4: Ultra-short sintering cycle) and sintered under the respective sintering cycles. The Ceramill® therm (Amann Girrbach) sintering furnace provided 3 sintering cycles ranging from the longest group-1 (19 hours), to the short sintering cycle group-3 (8 hours), with an intermediate sintering cycle group-2 (15 hours). The zircon (KDS) sintering furnace provided an ultra-short sintering cycle group-4 (2 hours). The testing of flexural strength was performed using a three-point bend test on a universal testing machine. Statistical analysis of the collected data was performed by one-way ANOVA using SPSS software.
 RESULTS
 One-way ANOVA showed no statistically significant difference in the flexural strength of full-contour monolithic zirconia sintered under the four different sintering cycles. (P > 0.05).
 CONCLUSIONS
 The flexural strength of full-contour monolithic zirconia was influenced to some extent by various sintering cycles. The longest sintering cycle (Group 1) showed the least flexural strength whereas the intermediate sintering cycle (Group 2) showed the highest flexural strength. Also, the ultra-short sintering cycle (Group 4) of 2 hours exhibited flexural strength comparable to the rest of the groups with longer sintering cycles, thus making the cycle a viable alternative to the conventional sintering cycles, thereby making the ‘tooth-in-a-day‘ possible for the patients.

A Contouring Strategy and Reference Atlases for the Full Abdominopelvic Bowel Bag on Treatment Planning and Cone Beam Computed Tomography Images

PurposeTo establish a practical contouring strategy with reference atlases for the abdominopelvic bowel bag on treatment planning computed tomography (TPCT) and cone beam computed tomography (CBCT) images. Methods and MaterialsA scoping literature review was done to evaluate the existing definitions and contouring guidelines for bowel bag and small bowel planning-at-risk volume–like structures. A comprehensive definition was proposed for the abdominopelvic bowel bag that expanded the Radiation Therapy Oncology Group Pelvic Normal Tissue Consensus definition. Seven patients with TPCT and first-treatment-day CBCT images were selected from an institutional database to represent a range of normal anatomy and CBCT image quality. The TPCT and CBCT images were contoured using the proposed definition. During contouring, the Radiation Therapy Oncology Group definition's list of inclusion and exclusion structures was expanded. For areas with limited visibility of the bowel bag on either TPCT or CBCT, a set of operational definitions was developed based on consistently visible reference structures. ResultsA literature review showed that previously existing bowel bag definitions predominantly focused on the pelvic region and did not provide a complete and practical description of the full abdominopelvic contour relative to structures consistently visible in all radiation therapy images. The proposed contouring strategy had 4 components: a definition, a list of inclusion and exclusion structures, 15 tabulated operational definitions, and a set of atlases. The bowel bag was defined as the peritoneal cavity and retroperitoneal duodenum and ascending and descending colon, as visualized at the time of image acquisition. The operational definitions formalized the location of the peritoneal fascial planes through a simple look-up table. The proposed contouring strategy and reference atlases were successfully used on both TPCT and CBCT images. ConclusionsThis study produced a practical contouring strategy and reference atlases to enable reproducible delineation of the full bowel bag on TPCT and CBCT images. The strategy is a necessary first step toward consensus contouring with reduced observer variability, which is a prerequisite for evaluation of cumulative dose and its correlation with toxic effects, adaptive planning strategies, and automated contouring potential.

DNA in nanochannels: theory and applications.

Nanofluidic structures have over the last two decades emerged as a powerful platform for detailed analysis of DNA on the kilobase pair length scale. When DNA is confined to a nanochannel, the combination of excluded volume and DNA stiffness leads to the DNA being stretched to near its full contour length. Importantly, this stretching takes place at equilibrium, without any chemical modifications to the DNA. As a result, any DNA can be analyzed, such as DNA extracted from cells or circular DNA, and it is straight-forward to study reactions on the ends of linear DNA. In this comprehensive review, we first give a thorough description of the current understanding of the polymer physics of DNA and how that leads to stretching in nanochannels. We then describe how the versatility of nanofabrication can be used to design devices specifically tailored for the problem at hand, either by controlling the degree of confinement or enabling facile exchange of reagents to measure DNA-protein reaction kinetics. The remainder of the review focuses on two important applications of confining DNA in nanochannels. The first is optical DNA mapping, which provides the genomic sequence of intact DNA molecules in excess of 100 kilobase pairs in size, with kilobase pair resolution, through labeling strategies that are suitable for fluorescence microscopy. In this section, we highlight solutions to the technical aspects of genomic mapping, including the use of enzyme-based labeling and affinity-based labeling to produce the genomic maps, rather than recent applications in human genetics. The second is DNA-protein interactions, and several recent examples of such studies on DNA compaction, filamentous protein complexes, and reactions with DNA ends are presented. Taken together, these two applications demonstrate the power of DNA confinement and nanofluidics in genomics, molecular biology, and biophysics.

English

BACKGROUND A smooth zirconia surface is necessary to protect the opposing natural dentition, to prevent plaque accumulation and to increase the survival rate of restoration by reducing the chances of failure by crack propagation. Surface roughness can be incorporated by routine dental procedures done in labs and clinics to adjust the restoration. It is unclear which surface treatment is most appropriate to achieve clinically acceptable zirconia surface. The purpose of this study was to evaluate the effect of grinding and subsequent various surface treatments on the surface roughness of full contour monolithic zirconia. METHODS In this invitro study 10 zirconia bars of final dimensions 20 x 4 x 2 mm & 40 zirconia bars of final dimensions 20 x 4 x 2.2 mm were milled and sintered. The zirconia bars with final dimensions 20 x 4 x 2mm were glazed and selected as samples for control group (Group C) (n = 10). Forty zirconia bars with dimensions of 20 x 4 x 2.2 mm were grounded using a standard straight cylindrical diamond point (105 – 125 µm) by placing them in a customized grinding apparatus till the dimensions became similar to that of control group i.e. 20 x 4 x 2 mm. After grinding and confirming the dimensions of each full contour monolithic zirconia bar using digital vernier caliper, zirconia bars were randomly allocated into 4 groups with 10 samples in each group (n = 10), namely (Group G: Grinding only, Group G+R: Grinding & Reheating, Group G+G: Grinding & Glazing, Group G+P: Grinding & Polishing) respectively. Surface roughness values were measured using a profilometer. Differences between groups were examined using one-way analysis of variance (ANOVA) (P ≤ 0.05) and Post hoc Tukey HSD test was done for multiple comparisons of surface roughness in between the groups using Statistical Package for Social Sciences (SPSS) software. RESULTS Group C showed the least surface roughness values. The maximum surface roughness values were seen in Group G. Surface roughness of Group G, Group G + H and Group G + G were statistically significant from Group C and Group G + P. There was no statistically significant difference in surface roughness values between Group C and Group G + P. CONCLUSIONS It can be concluded that polishing after grinding significantly reduced the surface roughness and re-established the surface smoothness of full-contour monolithic zirconia bars. KEY WORDS Surface Roughness, Zirconia, Monolithic, Full Contour, Profilometer

English

BACKGROUND This in-vitro study was conducted to compare the effect of different sintering cycles on the surface hardness of full contour monolithic Zirconia. METHODS In this in-vitro study, a total of 28 bar shaped Zirconia samples of final dimensions 20 x 4 x 2 mm were fabricated using Amann Girrbach CAD - CAM unit. These samples were randomly allocated into four groups with 7 samples in each group namely, Group 1, 2, 3 and 4 (Group 1: Long sintering cycle, Group 2: Intermediate sintering cycle, Group 3: Short sintering cycle, Group 4: Ultra-short sintering cycle) and sintered under the respective sintering cycles. The Ceramill® Therm sintering furnace provided 3 sintering cycles ranging from the longest Group - 1 (19 hours), to the short sintering cycle Group - 3 (8 hours), with an intermediate sintering cycle Group - 2 (15hours). The Zircom sintering furnace provided an ultra-short sintering cycle Group - 4 (2 hours). The testing of surface hardness was performed using TECSOL hardness tester. Statistical analysis of the collected data was performed by one - way ANOVA using SPSS software. Multiple comparison was done using post-hoc Tukey’s test. RESULTS One - way ANOVA showed statistically significant difference in the surface hardness of different samples (P < 0.05). The highest mean hardness was observed in Group 3 with 2713.757 + 233.89 VHN, followed by Group 2 with 2595.714 + 62.35 VHN, followed by Group 4 with 2518.600 + 103.65 VHN and Group 1 with the least, 1734.300 + 460.20 VHN. CONCLUSIONS The surface hardness of full contour monolithic Zirconia was influenced to some extent by various sintering cycles. The longest sintering cycle showed the least surface hardness whereas, the short sintering cycle showed the highest surface hardness. Also the ultra-short sintering cycle of 2 hours exhibited surface hardness comparable to the other sintering cycles with longer duration, making it a viable alternative to the conventional sintering cycles. KEY WORDS Monolithic Zirconia, CAD - CAM, Sintering, Hardness

Extended application of deep learning combined with 2DCOS: Study on origin identification in the medicinal plant of Paris polyphylla var. yunnanensis.

Medicinal plants are very important to human health, and ensuring their quality and rapid evaluation are the current research concerns. Deep learning has a strong ability in recognition. This study extended it to the identification of medicinal plants from the perspective of spectrum. In order to realise the rapid identification and provide a reference for the selection of high-quality resources of medicinal plants, a combination of deep learning and two-dimensional correlation spectroscopy (2DCOS) was proposed. For the first time, Fourier transform mid-infrared (FT-MIR) and near-infrared (NIR) spectroscopy 2DCOS images combined with residual neural network (ResNet) was used for the origin identification of Paris polyphylla var. yunnanensis. In total 1593 samples were collected and 12821 2DCOS images were drawn. The climate of different origins was briefly analysed. The xishuangbanna, puer, lincang, honghe and wenshan are the five regions with more ecological advantages. The synchronous 2DCOS models of FT-MIR and NIR could realise origin identification with the accuracy of 100%. The synchronous images were suitable for the identification of medicinal plants with complex systems. The full band, feature band and different contour models had no big difference in distinguishing ability, so they were not the key factors affecting the discrimination results. The ResNet models established were stable, reliable, and robust, which not only solved the problem of origin identification, expanded the application field of deep learning, but also provided practical reference for the related research of other medicinal plants.

Material Thickness Influence on Fracture Load of Polymer Infiltrated Ceramic Network CAD/CAM Restorations

Polymer infiltrated ceramics are hybrid materials that combine the strength of ceramics and the flexibility of polymers. The aim of this study was to compare the fracture load capacity of monolithic CAD/CAM crowns with different occlusal thicknesses, made from polymer infiltrated ceramic network. Fifteen full contour CAD/CAM crowns made of Vita Enamic with occlusal thicknesses of 0.5 mm, 1.0 mm and 1.5 mm were fabricated with a wet milling machine. Restorations were cemented on human molars with adhesive cement. Samples were loaded along the long axis until fracture, with a single static compressive force. A scanning electron microscope (SEM) was used to examine the fracture surface of specimens after the fracture. The results of this study reveals that the fracture load of the samples increased progressively with the occlusal thickness. The highest fracture value was recorded for1.5 mm occlusal thickness of the crown. No statistically significant difference was reported between the three experimental groups. It can be concluded that hybrid monolithic CAD-CAM crowns showed sufficient fracture strength to be used for single restorations in the posterior area, even with a reduced occlusal thickness.

INFLUENCE OF PORCELAIN FIRING AND CORE THICKNESS ON MARGINAL GAP OF CAD/CAM AND PRESSABLE ALL-CERAMIC CROWNS (IN-VITRO STUDY)

Statement of Problem: Marginal gap is important for the long-term success of all-ceramic restorations, the marginal accuracy of different manufacturing techniques and core thicknesses must be considered. Purpose: This study compared marginal gap of CAD/CAM and heat-pressed ceramic cores with different thicknesses before and after veneering porcelain application. Materials and Methods: A standard die was prepared. Sixty resin dies were duplicated. Samples were divided into two groups, Group I: samples were fabricated by CAD/CAM, Group II: samples were fabricated by heat pressing. Each group was divided into three subgroups: Subgroup 1: cores of 0.3 mm. thickness, Subgroup 2: cores of 0.5 mm. thickness, Subgroup 3: full contoured crowns were manufactured by characterization technique. marginal gap was measured at core stageand after veneering porcelain firings using a microscope . Results: Marginal gaps of CAD/CAM samples in all subgroups were higher than pressable(P˂0.05), A significant increase in the marginal gap was observed after porcelain firing, Full contour crowns recorded the lowest marginal gap(58.54±9.1, 32.76±8.5) followed by 0.5mm.( 66.7±8.4, 40.06±4.1) while 0.3mm. thickness recorded the highest value (81.14±12.3, 47.96±7.15). Significant difference in pre-firing and post firing gap values in 0.3mm. thickness(P=0.001), while in 0.5mm. thickness and full contour there were no significant difference (P=0.657 and 0.88 respectively). no statistically significant difference in mean marginal gap between 0.5 mm. and 0.3mm. at both pre-firing and post-firing. Conclusion: Marginal gap were all within the clinically acceptable range. Marginal gap increased after porcelain firing. for esthetic reasons, 0.3mm core thickness can be used instead of 0.5mm.

Induction Heating of Gear Wheels in Consecutive Contour Hardening Process

Induction contour hardening of gear wheels belongs to effective heat treatment technologies especially recommended for high-tech applications in machinery, automotive and aerospace industries. In comparison with long term, energy consuming conventional heat treatment (carburizing and consequent quenching), its main positive features are characterized by high total efficiency, short duration and relatively low energy consumption. However, modeling of the process is relatively complicated. The numerical model should contain both multi-physic and non-linear formulation of the problem. The paper concentrates on the modeling of rapid induction heating being the first stage of the contour induction hardening process which is the time consuming part of the computations. It is taken into consideration that critical temperatures and consequently the hardening temperature are dependent on the velocity of the induction heating. Numerical modeling of coupled non-linear electromagnetic and temperature fields are shortly presented. Investigations are provided for gear wheels made of a special quality steel AISI 300M. In order to evaluate the accuracy of the proposed approach, exemplary computations of the full induction contour hardening process are provided. The exemplary results are compared with the measurements and a satisfactory accordance between them is achieved.

A machine vision method for measurement of machining tool wear

Tool wears directly affect the quality of product and service life of tool. This paper proposes a machine vision-based measurement method for chisel edge wear of drills. Firstly, the full contour of a drill is extracted by local variance threshold segmentation. Secondly, the image is enhanced by using an adaptive contrast enhancement algorithm based on bidimensional local mean decomposition (BLMD). A threshold segmentation method is proposed to extract contour of the non-worn area. After the above two contours are superimposed, the centroid of each region in the binary image is calculated as the starting point to fill in the overflow water for tool wear extraction. Finally, the chisel edge wear can be measured directly by counting the number of pixels. The experiment in the process of drilling is performed to verify the effectiveness of the proposed method. The experimental results show that the proposed method effectively implements the measurement of tool wear.

Evaluation of a commercial synthetic computed tomography generation solution for magnetic resonance imaging-only radiotherapy.

PurposeTo evaluate the Siemens solution generating Synthetic computed tomography (sCT) for magnetic resonance imaging (MRI)‐only radiotherapy (RT).MethodA retrospective study was conducted on 47 patients treated with external beam RT for brain or prostate cancer who underwent both MRI and CT for treatment planning. sCT images were generated from MRI using automatic bulk densities segmentation. The geometric accuracy of the sCT was assessed by comparing the Hounsfield Units (HU) difference between sCT and CT for bone structures, soft‐tissue, and full body contour. VMAT plans were computed on the CT for treatment preparation and then copied and recalculated with the same monitor units on the sCT using the AcurosXB algorithm. A 1%‐1mm gamma analysis was performed and DVH metrics for the Planning Target Volume (PTV) like the Dmean and the D98% were compared. In addition, we evaluate the usability of sCT for daily position verification with cone beam computed tomography (CBCT) for 14 prostate patients by comparing sCT/CBCT registration results to CT/CBCT.ResultsMean HU differences were small except for the skull (207 HU) and right femoral head of four patients where significant aberrations were found. The mean gamma pass rate was 73.2% for the brain and 84.7% for the prostate and Dmean were smaller than 0.5%. Large differences for the D98% of the prostate group could be correlated to low Dice index of the PTV. The mean difference of translations and rotations were inferior to 3.5 mm and 0.2° in all directions with a major difference in the anterior‐posterior direction.ConclusionThe performances of the software were shown to be similar to other sCT generation algorithms in terms of HU difference, dose comparison and daily image localization.