The Experts below are selected from a list of 1620 Experts worldwide ranked by ideXlab platform
Michael E Razzoog - One of the best experts on this subject based on the ideXlab platform.
-
influence of Screw Channel angulation on the fracture resistance of zirconia abutments an in vitro study
2021Co-Authors: Sabrina S Garciahammaker, Berna Saglik, Marianella Sierraalta, Michael E RazzoogAbstract:Purpose The aim of this study was to investigate the effect of implant Screw Channel angulation on the fracture resistance of zirconia abutments without artificial aging. Materials and methods Ten implant replicas were embedded in a jig of autopolymerizing acrylic resin. Using a surveyor and a metallic platform, the implant replicas were mounted centrally and with an angulation of 30°. A maxillary left central incisor crown was fabricated from pattern resin and scanned. The digital design of a monolithic zirconia implant abutment-crown was completed using a 3D imaging software. For all specimens of this group (ASC25 ), the Screw Channel was positioned at 25° to the lingual. Following fabrication, the samples were attached onto the embedded implant replicas and manually torqued to 35 Ncm as recommended by the manufacturer. The monolithic zirconia implant abutment-crowns were mounted in a metallic platform, positioned perpendicular to the indenter, and subjected to loading until failure. Crosshead speed was set at 0.5 mm/min for the universal testing machine. Data from a similar in vitro study where straight zirconia custom abutments (ASC0 ) were subjected to static load until failure was used as a control group. An unpaired Student's t-test was used to determine if fracture resistance based on load at failure and maximum load in each group were significantly different from each other (ASC25 vs ASC0 ). Statistical significance level was inferred at p ≤ 0.05 RESULTS: Group ASC25 fractured at a mean (SD) load of 215.49 (47.10) N and a mean (SD) maximum load of 420.50 (17.18) N. Group ASC0 fractured at a mean (SD) load of 534.04 (133.77) N and a mean (SD) maximum load of 762.69 (109.59) N. The difference was statistically significant for both mean load and mean maximum load at failure (p ≤ 0.05). The survival rate of 0° zirconia abutments was significantly higher than that of 25° ASC zirconia abutments. Conclusions Within the limitations of this in vitro study the mean fracture load was significantly higher in the group with a straight Channel angulation.
Henny J A Meijer - One of the best experts on this subject based on the ideXlab platform.
-
full zirconia single tooth molar implant supported restorations with angulated Screw Channel abutments a 1 year prospective case series study
2020Co-Authors: Gerry M Raghoebar, Zakelina Maragkou, Marco S Cune, Henny J A MeijerAbstract:BACKGROUND: Implant-supported restorations in the posterior region are subjected to various complications that could be prevented by changing either the design or the material. PURPOSE: The aim of this prospective case series study was to evaluate full-zirconia implant-supported restorations with angulated Screw Channel abutments in the molar region of the maxilla and mandible and their effect on hard and soft peri-implant tissues, during a 1-year follow-up period. MATERIALS AND METHODS: Thirty consecutive patients with a single missing molar, sufficient bone height, and implant site free of infection were included. Each patient was to receive a parallel-walled implant with conical connection according to a two-staged surgical protocol. After 3 months, a full-contour Screw-retained zirconia restoration with angulated Screw Channel abutment was provided. Clinical and radiographic examinations were performed 1 and 12 months after placement of the restoration. Patients' satisfaction was scored prior to treatment and after 12 months with the restoration in function. Primary outcome measure was success of the restoration. RESULTS: All patients could be evaluated after 12 months. Success of the restorations was 100%. From loading to the 12-month follow-up, the mean marginal bone loss was 0.16 mm (SD: 0.26). Mean scores for plaque, calculus, peri-implant mucosa, bleeding, and pocket probing depth were low, depicting healthy peri-implant conditions. Patients' satisfaction was high and had improved after treatment. CONCLUSION: Full-contour zirconia implant-supported restorations with angulated Screw Channel abutments in the molar region have an excellent clinical performance after 1 year of function.
Krzysztof Wilczynski - One of the best experts on this subject based on the ideXlab platform.
-
DRAFT IMECE2006-13074 SSEM-AG COMPUTER MODEL FOR OPTIMIZATION OF POLYMER EXTRUSION
2020Co-Authors: Krzysztof Wilczynski, A NastajAbstract:ABSTRACT The optimization of an extrusion process is a conflicting, multi-objective problem. It is complicated by the number of variables (Screw/die geometry, operating conditions, material data) and their non-linear relations, as well as by the opposing criteria, for example extrusion throughput and power consumption. It is difficult to find the global optimum for the process avoiding local optima. There are two approaches to solve the problem, experimental and using a mathematical model of extrusion. Optimization techniques based on an experimentation are time-consuming and very expensive. In this paper we present an optimization methodology based on the Genetic Algorithms (AG), where response surface is given by the extrusion model. A mathematical Single-Screw Extrusion Model SSEM developed at the Warsaw University of Technology is used to predict the extruder behavior, and AG approach is used for optimization. An integrated SSEM-AG system was developed to study optimization of the single-Screw extrusion process. Three design criteria (output variables) are selected for optimization: maximum extrusion throughput, minimum power consumption and low melt temperature. As input variables, Screw speed, barrel temperature and Screw Channel depth are chosen
-
experimental study for starve fed single Screw extrusion of thermoplastics
2012Co-Authors: Adrian Lewandowski, Krzysztof WilczynskiAbstract:An experimental study of the polymer behavior in a starve-fed single Screw extrusion is presented. Various polymeric materials, semicrystalline low density polyethylene (LDPE), polypropylene (PP), and (LDPE/PS) polyblends were investigated at various operating conditions. A “Screw pulling-out” technique was used to study polymer behavior along the Screw. The solid conveying, melting position, the extent of starvation, and the fully filled regions were observed. Polymer samples were stripped off from the Screw which was removed from the machine to investigate melting mechanism. It was seen that filling of the Screw Channel increases with the flow rate at a fixed Screw speed, and decreases with the Screw speed at a fixed flow rate. Contiguous solids melting mechanism was observed for flood fed extrusion, but it was not observed for starve-fed extrusion. A new two-stage physical model of polymer melting has been proposed with conductive mechanism for melting in the starve-fed region and dispersed melting mechanism in the fully filled region. Melting action seems to be faster for starve feeding than for flood feeding, since the pellets are not compacted into a dense solid bed. It was observed that the pressure and power consumption considerably decrease with starvation. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
-
ssem a computer model for a polymer single Screw extrusion
2001Co-Authors: Krzysztof WilczynskiAbstract:Abstract A fully predictive computer model SSEM (single-Screw extrusion model) has been developed for the single-Screw plasticating extruders (with conventional and non-conventional Screws of different geometry, and different dies as well). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, melt conveying) and the die, and describes an operation of the extruder–die system, making it possible to predict mass flow rate of the polymer, pressure and temperature profiles along the extruder Screw Channel and in the die, solid bed profile, and power consumption. The simulation parameters are the material and rheological properties of the polymer; the Screw, hopper and die geometry; and the extruder operating conditions (Screw speed and barrel temperature profile).
-
chemomechanical systems study of contraction and mechanical work of poly acrylonitrile gel fibers
1999Co-Authors: Krzysztof WilczynskiAbstract:Abstract A fully predictive computer model SSEM (Single-Screw Extrusion Model) has been developed for the single-Screw plasticating extruders (with conventional and mixing Screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, and melt conveying) and the die, and it describes an operation of the extruder-die system, making it possible to predict the mass flow rate of the polymer, the pressure and temperature profiles along the Screw Channel and in the die, the solid-bed profile, and power consumption. Moreover, the mixing degree, the temperature fluctuation, and the viscoelastic characteristic of the polymer are evaluated. The model also makes it possible to predict the morphological changes of the polymer blend during the compounding process in the single-Screw extruder. The simulation parameters are the material and rheological properties of the polymer, the Screw, hopper, and die geometry, and the operating conditions (Screw speed and barre...
-
a computer model for single Screw plasticating extrusion
1996Co-Authors: Krzysztof WilczynskiAbstract:Abstract A fully predictive computer model has been developed for a single-Screw plasticating extrusion (with conventional Screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, melt conveying) and the die, and describes an operation of the extruder-die system, making it possible to predict a mass flow rate of the polymer, pressure and temperature profiles along the Screw Channel and in the die, solid bed profile, and power consumption. Moreover, mixing degree, temperature fluctuation and viscoelastic properties of the polymer are estimated. The simulation parameters are the material and rheological properties of the polymer, the Screw, hopper and die geometry, and the operating conditions (Screw speed and barrel temperature profile). Such a comprehensive approach to the modeling of extrusion creates the possibility of optimizing the process, for example, from the point of view of the quality of extrusion. The model has been verified experimen...
Marco S Cune - One of the best experts on this subject based on the ideXlab platform.
-
full zirconia single tooth molar implant supported restorations with angulated Screw Channel abutments a 1 year prospective case series study
2020Co-Authors: Gerry M Raghoebar, Zakelina Maragkou, Marco S Cune, Henny J A MeijerAbstract:BACKGROUND: Implant-supported restorations in the posterior region are subjected to various complications that could be prevented by changing either the design or the material. PURPOSE: The aim of this prospective case series study was to evaluate full-zirconia implant-supported restorations with angulated Screw Channel abutments in the molar region of the maxilla and mandible and their effect on hard and soft peri-implant tissues, during a 1-year follow-up period. MATERIALS AND METHODS: Thirty consecutive patients with a single missing molar, sufficient bone height, and implant site free of infection were included. Each patient was to receive a parallel-walled implant with conical connection according to a two-staged surgical protocol. After 3 months, a full-contour Screw-retained zirconia restoration with angulated Screw Channel abutment was provided. Clinical and radiographic examinations were performed 1 and 12 months after placement of the restoration. Patients' satisfaction was scored prior to treatment and after 12 months with the restoration in function. Primary outcome measure was success of the restoration. RESULTS: All patients could be evaluated after 12 months. Success of the restorations was 100%. From loading to the 12-month follow-up, the mean marginal bone loss was 0.16 mm (SD: 0.26). Mean scores for plaque, calculus, peri-implant mucosa, bleeding, and pocket probing depth were low, depicting healthy peri-implant conditions. Patients' satisfaction was high and had improved after treatment. CONCLUSION: Full-contour zirconia implant-supported restorations with angulated Screw Channel abutments in the molar region have an excellent clinical performance after 1 year of function.
Martin Rosentritt - One of the best experts on this subject based on the ideXlab platform.
-
laboratory performance and fracture resistance of cad cam implant supported tooth coloured anterior fdps
2020Co-Authors: Julian Zacher, Robert Bauer, Thomas Strasser, Martin RosentrittAbstract:Abstract Objectives This study investigated the in-vitro performance and fracture force of anterior implant-supported tooth-coloured fixed dental prosthesis (FDPs). Different material types with varying flexural strength and modulus of elasticity were compared with Screw-retained or bonded application. Materials and methods Identical anterior FDPs (tooth 11–13; n = 80) from materials (flexural strength 240−1150 MPa, modulus 7.6−210 GPa; 1x lithiumdisilicate ceramic, 2x zirconia (4Y-TZP, 5Y-FSZ), 3x resin-based composites (with different flexural strength and modulus)) were milled. FDPs were grouped into chairside (bonded) and labside (Screw-retained) procedure. To simulate a 5-year clinical application, thermal cycling with mechanical loading (TCML) was accomplished. TCML-performance and fracture force were evaluated and failure patterns were analysed. Data were statistically investigated (Kolmogorov-Smirnov-test, one-way-ANOVA; post-hoc-Bonferroni, α = 0.05). Results TCML did not lead to any cracks, fractures or chipping on all tested FDPs. Fracture values varied between 1208.9 ± 354.6 N (experimental resin-based composite) and 2094.3 ± 293.4 N (4Y-TZP) for FDPs without Screw Channel. With Screw Channel the results ranged between 1297.9 ± 268.3 N (5Y-FSZ) and 2129.3 ± 321.7 N (4Y-TZP). The influence of the Screw Channel was not significant for all materials (p ≥ 0.218). Modulus of elasticity and flexural strength had influence on the fracture force only in the individual material groups. Fractures at the connector were predominant for ceramic and zirconia. Resin-based composites primarily showed radial fractures in abutment region or mixed failure types. FDPs with/without Screw-Channel showed comparable types of failure. Conclusions TCML did not lead to drop-outs or failures for all FDPs. Individual materials showed no different in-vitro performance, but varying fracture force after TCML. Independent from material, Screw Channels did not weaken the FDPs. All tested systems showed sufficient properties for an anterior implant application.
-
in vitro fatigue and fracture testing of cad cam materials in implant supported molar crowns
2017Co-Authors: Verena Preis, Sebastian Hahnel, Michael Behr, Laila Bein, Martin RosentrittAbstract:Abstract Objective To investigate the fatigue and fracture resistance of different CAD/CAM-materials as implant- or tooth-supported molar crowns with respect to the clinical procedure (Screwed/bonded restoration). Methods 168 crowns were fabricated from different CAD/CAM-materials (n = 8/material): ZLS (zirconia-reinforced lithium silicate ceramic; Suprinity, Vita-Zahnfabrik), COB (composite; Brilliant Crios, Coltene), COL (composite; Lava Ultimate, 3M Espe), PMV/PPV (polyether ether ketone (PEEK) + milled composite veneer/composite paste veneer; BioHPP + HIPC veneer/Crealign veneer, Bredent), COH (composite; Block HC, Shofu), and ZIR (zirconia; IPS e.max ZirCAD, Ivoclar-Vivadent) as reference. Three groups were designed simulating the following clinical procedures: (a) chairside procedure ([CHAIR] implant crown bonded to abutment), (b) labside procedure ([LAB] abutment and implant crown bonded in laboratory, Screwed chairside), and (c) reference ([TOOTH] crowns bonded on human teeth). Combined thermal cycling and mechanical loading (TCML) were performed simulating a 5-year clinical situation. Fracture force was determined and failures were documented. Data were statistically analyzed (Kolmogorov–Smirnov-test, one-way-ANOVA; post-hoc-Bonferroni, α = 0.05). Results All crowns of group LAB-PPV showed cracks after TCML. The other groups survived fatigue testing without failures. Fracture forces varied between 921.3 N (PPV) and 4817.8 N (ZIR) [CHAIR], 978.0 N (COH) and 5081.4 N (ZIR) [LAB], 746.7 N (PPV) and 3313.5 N (ZIR) [TOOTH]. Significantly (p 0.05) differences between the individual groups. Significance Different ceramic and resin-based materials partly performed differently in implant or tooth situations. Individual resin-based materials (PPV, COB, COH) were weakened by inserting a Screw Channel. Most CAD/CAM-materials may be clinically applied in implant-supported crowns without restrictions.