Master Model Research Articles

Multi-method Coal Seam Floor Water Inrush Risk Evaluation Based on Variable Weight Theory

Frequent water inrush disasters in deep coal seam mining pose a significant threat to the safety of coal extraction operations. Due to the complexity and non-linearity of water inrush factors, evaluating the risk of water inrush in coal seam floor is challenging and the results can vary significantly. To achieve more accurate evaluations, the weighted rank-sum method and Grey-TOPSIS method were employed, alongside a master control indicator variable-weight model, for assessing the risk of water inrush in coal seam floor. Validation of the evaluation zoning map against actual conditions revealed that both methods produced accurate assessment results, thus affirming the reliability of the new evaluation approach. Compared with the water inrush coefficient method, the diversification of index factors weakened the absolute control effect of the water inrush threshold. The evaluation outcomes were more systematic and comprehensive, providing a new methodology and perspective for deep coal seam mining.

Effect of prefabricated auxiliary devices in different optical properties and shapes on the accuracy of intraoral scanning of the edentulous arch with multiple implants: An in-vitro study

ObjectivesThis study aimed to evaluate the impact of prefabricated auxiliary devices (PADs) in different optical properties and shapes on the accuracy of digital implant impressions. MethodsAn edentulous maxillary all-on-4 master model was fabricated. PADs were 3D-printed in different resin materials (Grey, Translucent, White, Yellow) and shapes (Cuboid, Cylinder, Sphere) using a 3D printer (AccuFab-C1s, 3DShining, Hangzhou, China). The master model was digitalized using a dental laboratory scanner (D2000, 3Shape, Copenhagen, Denmark) 4 times as the reference models. Test models were obtained without (control group) or with PADs by an intraoral scanner (Aoralscan 3, Shining3D, Hangzhou, China) for ten repetitions of each group using the scanning pattern recommended by the manufacturer. The related files were imported into inspection software to assess Root Mean Square (RMS), linear and angular accuracy. Aligned Ranks Transformation ANOVA, Kruskal-Wallis and Mann-Whitney tests were used to evaluate the differences in these values. The level of significance was set at α=0.05. ResultsPADs in different optical properties and shapes demonstrated accuracy enhancement to different extents depending on their combinations. The PADs in combinations of white-cuboid, grey-sphere and yellow-sphere demonstrated the optimal trueness enhancement. The Aligned Ranks Transformation ANOVA indicated that the optical properties of the PADs significantly influenced the RMS, linear and angular accuracy. The main effect of optical properties indicated that translucent PADs generally generated more deviations than the others. The shapes of the PADs significantly influenced the angular accuracy. The main effect of shapes indicated that cylinder resulted in lower angular trueness on YZ plane than cuboid (p = 0.006) and sphere (p < 0.001). ConclusionThe optical properties and shapes of the PADs significantly influenced the scanning accuracy. Translucent PADs demonstrated more deviations than the others. Lower angular trueness on the YZ plane was seen in cylinder design compared to the others. Clinical significanceThe optical properties and shapes of prefabricated auxiliary devices should be critically considered to optimize the scanning accuracy. Prefabricated auxiliary devices in translucent optical properties and cylinder shape should be avoided.

Effect of different sintering procedures on marginal and internal fit, color, and fracture load of monolithic zirconia fixed partial prostheses.

The aim of the present in vitro study was to investigate the effects of different sintering procedures on the fit, color parameters, and fracture load of monolithic fixed partial prostheses (FPPs). A metal master model was scanned and FPPs were designed. Groups were created by fabricating FPPs using four different sintering procedures (n &#61; 10): Prettau-Standard (PST); Prettau-Slow (PSL); Ice-Speed (ISP); Ice-Standard (IST). PST-PSL (Group P; N &#61; 20) and ISP-IST (Group I; N &#61; 20) were colored with different coloring liquids. The marginal and internal fit were measured using the silicone replica method. CIELAB values of the samples were measured using a spectrophotometer. Then, for each sample, the die was obtained from polymethyl methacrylate. The specimens were cemented into dies and tested in a universal testing machine for fracture load. One-way ANOVA was performed to assess the effect of the sintering procedure on the marginal and internal fit; fracture load; and ∆E00, ∆L', ∆C', and ∆H' values of the FPPs. The PSL and PST groups showed significantly smaller internal and marginal fit values compared with the ISP group. Additionally, the internal fit values of the IST group were significantly higher than those of Group P. Sintering time reduction led to a decrease in ∆E00 values. Fracture load values were not statistically significantly affected by the different sintering procedures for both brands. Different sintering procedures did not have a clinically significant effect on fit and fracture load. Different sintering procedures were found to have an impact on the color change of monolithic zirconia restorations.

The Effects of Different Restoration Materials on the Trueness of Intraoral Scanners

Aim: This study aimed to assess how different restoration materials affect the trueness of intraoral scanners. Materials and Methods: Artificial teeth on a typodont model were prepared for crowns and fixed partial dentures (FPDs) using full metal, monolithic zirconia, and porcelain-fused-to-metal (PFM) materials. Each group underwent 10 scans with a Trios intraoral scanner, generating 60 STL files. A reference scanner created a master model using scanning spray to reduce reflection errors. The STL files were aligned with reverse engineering software for comparison and were analyzed in micrometers (μm) using Root Mean Square (RMS) and Mean Distance measurements. The Levene test and two-way ANOVA with Post Hoc analysis were used for statistical evaluation. Results: The RMS deviations for the FPDs were 77.9 ± 15.2 μm (full metal), 84.6 ± 6.9 μm (monolithic zirconia), and 130 ± 19.7 μm (PFM). For the crowns, the RMS values were 76.9 ± 6.5 μm (metal), 71 ± 8.2 μm (monolithic zirconia), and 153 ± 22.4 μm (PFM). The mean distance deviations for the FPDs were 11.4 ± 4.8 μm (metal), 11.2 ± 3.4 μm (monolithic zirconia), and 18.3 ± 2.6 μm (PFM). For the crowns, the mean distances were 8.6 ± 3.4 μm (metal), 10.2 ± 3 μm (monolithic zirconia), and 24.7 ± 3.3 μm (PFM). Significant differences were noted in the PFM groups. Conclusion: Restoration materials notably affected intraoral scanner trueness, especially PFM restorations. The restoration length did not significantly affect the accuracy.

Effect of Implant Analog Design and Additively Manufactured Casts' Printing Layer Thickness on the Linear and Angular Accuracy of Analogs for Direct Digital Workflow: An In Vitro Study.

To evaluate how implant analog design and printing layer thickness affect the linear and angular accuracy of implant analogs in additively manufactured casts, comparing with conventional implant analogs in stone casts. A reference cobalt chromium mandibular model with a single implant was digitized with an industrial optical scanner and scan bodies compatible with a pressure/friction fit (S) or a screw-retained (N) implant analog for direct digital workflow. These scans were used to fabricate casts with 50 μm (S-50 and N-50) and 100 μm (S-100 and N-100) layer thickness (n&#61;10). Ten stone casts were made after single-step closed-tray polyvinylsiloxane impressions of the model (CNV). All casts were digitized with the same metal scan body and scanner used to digitize the master model, and these scans were superimposed over the scan of the master model to measure the linear (x, y, and z-axes) and angular (XY and YZ planes) deviations (Geomagic Control X). The precision of measured deviations was defined with the average deviation values. Generalized linear model analysis was used to compare the deviations within implant analogs for direct digital workflow, while 1-way analysis of variance and Dunnett's test were used to compare these analogs and conventional analogs (α &#61; .05) Results. The analog design affected the linear deviations (y-axis), while the interaction between the analog design and the layer thickness, and the analog design affected the angular deviations (XY plane, P ≤ .030). S analogs had lower linear and angular deviations than N analogs, and S-50 led to lower angular deviations than N-50 (P ≤ .030). CNV led to higher linear accuracy (y-axis) than N-50, N-100, and S-100 and led to lower angular deviations than all test groups (XY plane) (P ≤ .025). The analogs in S-50 casts had positional trueness similar to or higher than those in other test groups and their accuracy was mostly similar to those in CNV casts. Implant analogs for direct digital workflow deviated more towards lingual and gingival, and conventional analogs deviated more towards buccal, occlusal, and distal. All analogs had a tendency to tilt towards lingual and distal.

New forest fire assessment model based on artificial neural network and analytic hierarchy process or fuzzy-analytic hierarchy process methodology for fire vulnerability map

Forest fires significantly disrupt global ecosystems. Many forecasting techniques predict fire activity and allocate prevention resources, but various factors are missing from the assessments, and multi-criteria decision approaches alone are insufficient. This work introduced a novel methodology combining artificial neural networks (ANN) with the analytical hierarchy process (AHP), fuzzy AHP multi-criteria methods, and spatial data to detect potential forest fire vulnerability areas using twenty variables. The results from AHP or fuzzy AHP, were processed using a multilayer perceptron with a backpropagation algorithm. The final ANN model has two objectives: first, to create a forest fire vulnerability with four classes (low, moderate, high, and very high), and second, to classify burned area sizes in regions highly or very highly vulnerable to fire. Evaluation metrics were also applied for validation. The fire model was tested using both literature review data and in situ observations. Comparative analysis showed that the burned area size model performed better than other machine learning methods, achieving an accuracy score of 89%. Meanwhile, the fire vulnerability model scored 82%. The study addresses the problem of prediction and provides an algorithm for classifying fire risk based on historical data in the Czech Republic, offering a master model for future forest management. Therefore, the ANN model, once trained, validated, and tested, does not require resetting and is effective for estimating forest fire vulnerability. Moreover, it produces results quickly, providing rapid insights into complex forest ecosystems, saving time and enhancing understanding for decision-makers.

Scan accuracy of wireless intraoral scanners while digitizing a combined scan body-healing abutment system

ObjectivesTo investigate the accuracy (trueness and precision) of wireless and wired intraoral scanners (IOSs) when scanning an implant with the combined healing abutment-scan body (CHA-SB) system. MethodsA partially edentulous mandibular model with a CHA-SB at the right first molar site was digitized with 2 wireless (NeoScan 2000 (NW) and TRIOS 4 wireless (T4 W)) and 2 wired (NeoScan 1000 (N) and TRIOS 4 wired (T4)) IOSs 44 times in total (n = 11). The reference scan file was generated by digitizing the same master model and CHA-SB with an industrial-grade optical scanner. All files were imported into a metrology-grade analysis software program to evaluate the surface (root mean square, RMS), linear, and angular deviations of the top part of the SB. The average deviation values defined the precision of the scans. The data were statistically analyzed (α = 0.05). ResultsIOS type affected the surface and angular deviations and the precision (linear deviations on the x-axis) of the scans (p ≤ 0.043). T4 W had lower RMS than N and T4 (p ≤ 0.031). T4 had higher angular deviations than N on the XZ plane and had the lowest angular deviations on the YZ plane (p ≤ 0.011). T4 W scans had higher precision than N scans (p = 0.024). ConclusionDespite some differences in the trueness or precision of scans, tested IOSs mostly enabled similar scan accuracy. Regardless of the IOS, the implant scans had a tendency to tilt mesiobuccally, which can be considered clinically small. Clinical SignificanceTested wireless intraoral scanners may be suitable alternatives to their wired counterparts while digitizing an implant with a combined healing abutment-scan body system in the posterior region. However, the crowns fabricated from tested scans might require buccal, mesial, and occlusal surface veneering and distal surface adjustments.

Current applications of three-dimensional (3D) printing in pediatric dentistry: a literature review.

Advancements in 3D printing technology are providing a new direction in pediatric dentistry by offering innovative solutions to traditional challenges. The remarkable expansion of 3D printing necessitates a comprehensive examination of its status and applications in the dental field, particularly in the pediatric dentistry. This review provides a comprehensive exploration of the applications of 3D printing in pediatric dental practices by drawing from a systematic search across databases, including PubMed/MEDLINE, Scopus, Web of Science, Scielo and the Cochrane Library. The search strategy employed a combination of keywords: "Digital dentistry and 3D printing", "3D printing technology in dentistry", "3D printing in pediatric dentistry" and "3D printing in pediatric dental procedures". The review encompasses a wide array of studies, including original research, cross-sectional analyses, case reports and reviews. A detailed overview is presented in regard to the use of 3D printing for master and educational models, space maintainers, prosthetic restorations, surgical guide, splint design and fracture treatment, fluoride application, autogenous dental transplantation, anterior teeth restoration, and pediatric endodontics and regenerative treatments. This review shows that 3D printing improves clinical outcomes through personalized and precise treatment options and enhances dental students' educational landscape. Areas lacking extensive research were also identified, which warrent further investigation to optimize the integration of 3D printing in pediatric dentistry. By mapping out the current landscape and future directions, the aim of this paper is to support pediatric dentists in recognizing the broad implications of 3D printing for improving patient care and advancing dental education.

Seating accuracy of removable partial denture frameworks fabricated by different digital workflows in comparison to conventional workflow.

To evaluate the seating accuracy of removable partial denture (RPD) frameworks fabricated by two digital workflows involving selective laser melting (SLM) in comparison to the conventional workflow. A Kennedy class III modification 1 partially edentulous mandibular arch was used as a master model. Three RPD framework groups were included: (1) a conventional workflow group with conventional impression and casting (CC), (2) a partial digital workflow group with conventional impression and digital fabrication (CD), and (3) a complete digital workflow group with digital impression and digital fabrication (DD). A total of 10 frameworks were produced for each group. The marginal gaps at the occlusal rests, retention arms, and reciprocating arms were measured by a traveling microscope. The data were analyzed with the one-way analysis of variance test. At the framework level, the most superior fit was observed for the CD group (79.5µm) followed by DD (85.3µm) and CC (114.2µm) groups. The CD and DD groups were significantly superior to CC (p<0.001). This fit pattern was consistent for the retention and reciprocating arms, while the occlusal rest fit was similar among all the groups. The SLM frameworks had a promising seating accuracy in comparison to conventional frameworks. The type of impression, conventional or digital, did not affect the accuracy of SLM frameworks. The differences observed in the present study are likely to be of minimal clinical significance.

Trueness of Intraoral Scanners in Different Scan Patterns for Full-Arch Digital Implant Impressions.

The optimal scan pattern for full-arch digital implant impressions remains to be determined. This study aimed to analyze the effects of different scan patterns on the trueness of intraoral scanners for full-arch digital implant impressions. A maxillary plaster model with 4 implant analogs was employed as the master model. Scan bodies were attached to the master model and scanned with a laboratory scanner to obtain reference data. Test scans were obtained using 3 different scan patterns with Cerec Primescan and Trios 3. Each test datum was superimposed onto the reference data. The trueness was assessed by determining the 3D distance and angular deviations between the test and reference data. Significant differences in 3D distance deviation were detected among the scan patterns for both scanners. Significant differences in angle deviation were detected among the scan patterns for the Cerec Primescan, whereas it was not substantial for the Trios 3. Cerec Primescan exhibited superior trueness across all scan patterns compared with Trios 3. The zigzag pattern resulted in more accurate scans for the Cerec Primescan, whereas both the zigzag and occlusal-palatal-buccal patterns showed higher accuracy for the Trios 3.

Evaluation of fracture resistance and marginal fit of implant-supported interim crowns fabricated by conventional, additive and subtractive methods

BackgroundInterim crowns are utilized for restoring implants during and after the process of osseointegration. However, studies on adaptation and fracture strength of implant-supported interim crowns are rare.Aim of the studyThe aim of this in vitro study is evaluating marginal fit and fracture resistance of conventional, subtractive, and additive methods of fabricating implant-supported interim crowns.Materials and methodsAn implant was placed in an epoxy resin model with a missing first molar. A scan body was attached, and scanned with an intraoral scanner (IOS), the STL file was used to fabricate eighteen master models with standardized implant digital analogue spaces. The digital analogues and their corresponding abutments were attached to the master models and scanned with the IOS, the STL files were used to fabricate eighteen crowns using three different techniques (n = 6): conventional (CR); from Autopolymerizing composite resin, subtractive (SM); milled from PMMA resin blanks, and additive (AM); from 3D printed resin material. The crowns were fitted and cemented on their corresponding abutments and subjected to cyclic loading and thermocycling. The marginal fit was evaluated using a stereomicroscope. The crowns were then loaded until fractured in a universal testing machine. The Shapiro–Wilk and the Kolmogorov-Smirnov tests revealed that data of Marginal gap was non-parametric. Kruskal-Wallis test followed by the Dunn test was used (α = 0.05). While data of Fracture resistance test was parametric. ANOVA (F-test) was used followed by the Tukey test (α = 0.05).ResultsFor marginal gap, a significant difference was shown between the study groups (P = .001) according to Kruskal–Wallis test. Groups SM and AM had significantly lower marginal gap values compared to group CR (P = .003). No significant difference was found between groups SM and AM (P = .994). For fracture resistance, One-way ANOVA revealed a significant difference in fracture resistance between study groups (P < .001). Group SM had significantly higher fracture strength followed by group AM and group CR (P = .001).ConclusionsGroup SM and AM showed better marginal adaptation than group CR. Group SM showed superior fracture resistance compared to other groups. All study groups showed acceptable marginal gap and fracture resistance.

Dimensional Accuracy of Different Three-Dimensional Printing Models as a Function of Varying the Printing Parameters.

Even in digital workflows, models are required for fitting during the fabrication of dental prostheses. This study examined the influence of different parameters on the dimensional accuracy of three-dimensionally printed models. A stereolithographic data record was generated from a master model (SOLL). With digital light processing (DLP) and stereolithography (SLA) printing systems, 126 models were produced in several printing runs-SolFlex350 (S) (DLP, n = 24), CaraPrint 4.0 (C) (DLP, n = 48) and Form2 (F) (SLA, n = 54)-and their accuracy was compared with plaster and milled polyurethane models. In addition to the positioning on the build platform, a distinction was made between parallel and across arrangement of the models to the printer's front, solid and hollow models, and printing with and without support structures. For accuracy assessment, five measurement sections were defined on the model (A-E) and measured using a calibrated digital calliper and digital scans in combination with the GOM Inspect Professional software 2021. The mean deviation between the measurement methods for all distances was 79 µm. The mean deviation of the models from the digital SOLL model were 207.1 µm for the S series, 25.1 µm for the C series and 141.8 µm for the F series. While positioning did not have an influence, there were clinically relevant differences mainly regarding the choice of printer, but also individually in alignment, model structure and support structures.

An approach for mitigating cognitive load in password management by integrating QR codes and steganography

AbstractThe proliferation of digital services and the imperative for secure authentication have necessitated the management of an expanding array of passwords, imposing a significant cognitive burden on users. The predominant method for authentication remains the use of passwords. However, a critical issue with this approach is that individuals frequently forget their passwords, particularly when managing multiple accounts. This often results in users creating similar or easily guessable passwords for different accounts or writing them down, compromising security. This article investigates an innovative method to mitigate cognitive burden using steganography‐embedded quick response (QR) codes for streamlined password management. The proposed model, named MASTER (Multi‐device‐based Authentication using STEgged QR Codes), was evaluated for usability using the system usability scale (SUS) and the subjective mental effort scale. The security of the model is evaluated using attack analysis and comparative analysis with image visibility and robustness. The evaluation results indicate that the MASTER model achieved a SUS score of 75.94, with the majority of participants agreeing that the system reduces cognitive effort.

Master equation modeling of water dissociation in small ionic water clusters: Ag+(H2O) n , n = 4-6.

We model temperature-dependent blackbody infrared radiative dissociation (BIRD) rate coefficients of Ag+(H2O) n , n = 4-6, a system with loosely bound water molecules. We employ a master equation modeling (MEM) approach with consideration of absorption and emission of blackbody radiation, comparing single and multiple-well descriptions. The unimolecular dissociation rate coefficients are obtained using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory, employing two approaches to model the sum of states in the transition state, the rigid activated complex (RAC) and the phase space limit (PSL) approach. A genetic algorithm is used to find structures of low-lying isomers for the kinetic modeling. We show that the multiple-well MEM approach with PSL RRKM in the All Wells and Transition States Are Relevant (AWATAR) variant provides a reliable description of Ag+(H2O) n BIRD, in agreement with previously published experimental data. Higher-lying isomers contribute significantly to the overall dissociation rate coefficient, underlying the importance of the multiple-well ansatz in which all isomers are treated on the same footing.

Comparative Analysis of Four Different Intraoral Scanners: An In Vitro Study.

(1) Background: Intraoral scanners undergo rapid advancements in hardware and software, prompting frequent updates by manufacturers. (2) Aim: This study aimed to quantitatively assess the precision of full dental arch digital impressions obtained from four different intraoral scanners: Trios 5-3SHAPE, Copenhagen, Denmark, CEREC Primescan- Dentsply Sirona, New York, NY, USA, Planmeca Emerald S-Planmeca Oy, Helsinki, Finland, and Medit i700-Medit Corp, Seoul, Republic of Korea. (3) Methods: A maxillary virtual dental model (digital master model) was created in accordance with ISO standard 20896-1. Subsequently, a 3D-printed model was obtained from the master model's STL file and scanned 15 times consecutively with each scanner. STL files were aligned with the master model's STL using Medit Link-Medit Design software v.3.1.0. The accuracy was evaluated by measuring deviations in micrometers between each scanner's scans and the master model. (4) Results: The study revealed variations in accuracy ranging from 23 to 32 µm across scans of the same dental arch, irrespective of the scanner used and scanning strategy employed. The anterior regions exhibited higher precision (Mean Absolute Deviation of 112 µm) compared to the posterior regions (Mean Absolute Deviation of 127 µm). Trios 5 demonstrated the smallest deviation (average 112 µm), indicating superior accuracy among the scanners tested. Emerald S and Medit i700 exhibited balanced performance (average 117 µm and 114 µm, respectively), while Primescan consistently displayed high deviation (average 127 µm). (5) Conclusions: Based on clinically accepted thresholds for accuracy in intraoral scanning, which are typically 200 µm for full arch scans, Trios 5 surpasses these benchmarks with its average deviation falling within the 200 µm range. Emerald S and Medit i700 also meet these standards, while Primescan, although showing high overall deviation, approaches the upper limit of clinical acceptability. Considering the limitations of an in vitro investigation, the findings demonstrate that each intraoral scanner under evaluation is capable of reliably and consistently capturing a full arch scan for dentate patients.

CROSS-WORLD NARRATIVES AND TRAVELS: RECONSTRUCTING THE HISTORY OF EARLY SYRIAN-AMERICAN IMMIGRANTS

Narratives of travel are part of world literature and cultural history. Scholarly research on migrant narratives and literature is a subfield of intercultural studies and comparative literature which allow cultures to bond and interact. Written histories of Arab Americans start with the Foundational Period (1880-1920) which revolves around the early immigrants from Historical Syria. This period is one of the least documented eras which is still difficult to reconstruct due to its many gaps and various obstacles. This paper examines the strategies and approaches used by Philip Hitti, the founder of Arabic Studies in the United States, who established the master models and approaches for the study of the Syro-Lebanese immigrant community. This model is based on locating alternative sources that include ̶ in addition to official sources and written accounts ̶ folksongs, literary texts, popular stories, and personal memories. It makes use of them to reconstruct the history of this community, which is characterized by its rich popular culture and long tradition of story-telling. There may be polemics and prejudices in presenting the wealth of the oral and cultural tradition of Historical Syria’s communities in the mainstream popular and official narratives about Arabs and Muslims. When presented with scholarly research and comparative perspectives, immigrants’ narratives can have a valuable contribution to world literature on immigration.

Development Of Economic Mathematics Learning System Through Master Model For Students Of Economic Education Study Program

The purpose of this study is 1) to identify the need for the development of an Economic Mathematics Learning System through the MASTER Model for students of the Economic Education Study Program in participating in the learning process, 2) to develop a tool for making Economic Mathematics Learning System Development through the MASTER Model for students of the Economic Education Study Program in following the process learning, and 3) measuring or knowing the validity of the Economic Mathematics Learning System through the MASTER Model for students of the Economic Education Study Program in participating in the lesson. The study results found that the validation of material experts and learning system experts (learning models), it can be seen that results of the validation of material experts are 4,44 or good and the results of validation by media experts are 4.33 or good. The results of interviews with lecturers and students as a whole showed good responses to the use of the MASTER learning model in the learning process.

Fracture Resistance of Posterior Milled Nanoceramic Crowns after Thermomechanical Aging.

Fracture resistance is an important parameter used to predict the performance of indirect dental restorations. The purpose of this in vitro study was to assess the fracture load of posterior milled nanoceramic crowns, in comparison with the lithium disilicate crowns, after fatigue loading, for two different restoration occlusal thicknesses. Forty test metal dies were fabricated by duplicating a master metal model consisting of an anatomic abutment preparation of the maxillary first premolar for a single crown. The dies were divided into two groups of 20 each for the fabrication of nanoceramic (Lava Ultimate) and lithium disilicate (IPS e.max CAD) single crowns. Each material group was further divided into two sub-groups of 10 dies each, based on crown occlusal thickness, of 0.5-mm and 0.75-mm (n = 10). Dental Type V stone dies poured from polyvinyl siloxane impressions of the test metal dies were laboratory scanned in order to design and mill 40 ceramic crowns. The crowns were cemented on to the test metal dies with a self-adhesive resin luting cement. All crowns were thermocycled (2500 cycles) and mechanically loaded (250,000 cycles) in a chewing simulator followed by static loading until failure, and the values noted. The data were statistically analyzed by 2-way ANOVA and Tukey HSD post-hoc multiple comparison tests (α = 0.05). The mean fracture loads ranged from 1022 to 1322 N for nanoceramic crowns and from 1145 to 1441 N for the lithium disilicate crowns. Two-way ANOVA revealed insignificant differences between the nanoceramic and lithium disilicate crowns (p > 0.05) in terms of fracture load. Significant differences were noted in the fracture resistance of crowns based on occlusal thickness (303 N; p = 0.013) regardless of the material used. Multiple comparisons by Tukey HSD post-hoc test showed insignificant differences between the four material-occlusal thickness groups (p > 0.05). The nanoceramic crowns were found to be comparable with lithium disilicate crowns in terms of fracture load. The mean fracture loads of all of the tested crowns were within the normal physiological masticatory load limits. Based on the fracture-resistance results, nanoceramic crowns seem to be suitable for clinical use for the tested occlusal thicknesses.

Parametric Analysis of “Zollinger Type” Ribbed Timber Shells

The following article presents the study and further development of the roof system developed and patented by Friedrich Zollinger in 1920. The so-called Zollinger construction system is based on short timber components ‐ lamellae, connected by a bolt and a form of decking only for covering purpose. By developing the micro step joint, an increase in joint stiffness can be achieved. In addition, by applying and activating a load-bearing roof covering, a further increase in system stiffness can be achieved and demonstrated. Especially with regard to large spans, the increase of the stiffness and reduction of the deflection becomes inevitable against the background of an economic feasibility. Based on the analysis of the historic Zollinger system, it is possible to evaluate potential for improvements in terms of system stiffness as well as contemporary design, development and manufacturing. Due to the large number of different influencing factors, the system was modeled as a parametric master model. In this, a closed process cycle can be developed from the geometric definition, to the static analysis and to the derivation of the computer-aided manufacturing data. In the present study especially the exact recording, description and modeling of the stiffness and feasibility of the connection details “lamella‐lamella” and “lamella‐planking” was investigated. A parametric finite element model can be used to determine the stiffness parameters as a function of the fasteners used and the spacing of the fasteners. Staple connections are used as the main means of connection between the lamella and the planking. The implementation of the staple connections in the finite element analysis was carried out using spring parameters, which are determined in the course of the development. The analysis and optimization of the connection stiffnesses is presented against the background of an economical structure development. By using digital planning methods and interfaces, a contemporary way of working is presented. In addition, a contribution is made to digitalization in the construction industry.

Dimensional Accuracy of Two-Step Impressions Relined with Extra-Light Addition Silicone Material.

Objectives: Some small defects may remain in the impression after making a two-step putty-light body impression. The aim of this study was to evaluate and compare the dimensional accuracy of 2-step and relined 2-step (3-step) putty-light body impressions. Materials and Methods: In this in vitro study, 30 impressions were made with putty, light body, and extra-light body addition silicone materials using the 2-step and 3-step impression techniques (N=15). An epoxy resin master model was made duplicating a maxillary typodont with left first premolar and first molar teeth prepared with a shoulder finish line and truncated pyramidal-shaped indices in the mid-palate and third molar sites. In addition to creating a reference digital model by scanning the master model, 30 master casts were scanned to produce digital models. The anteroposterior (AP) and cross-sectional (CS) dimensional accuracy of the models were compared with the master model using linear measurements. Moreover, tooth size measurements were made and compared using the root mean square (RMS). Two-sample t-test was applied to analyze the data (α=0.05). Results: The mean AP and RMS differences between the two study groups were not significant (P>0.05). However, the CS difference between the two groups was significant (P<0.001), and the 3-step impression technique showed smaller discrepancies in comparison to the master model. Conclusion: There was no significant difference in accuracy of the two techniques for single-unit and multiple-unit preparations. The 3-step impression technique had a higher CS dimensional accuracy.