Diametral tensile strength of dual-curing resin cements submitted exclusively to autopolymerization.

OBJECTIVES: To evaluate, at different times, the diametral tensile strength (DTS) of dual-curing resin cements that were not photopolymerized. METHOD AND MATERIALS: Equal amounts of base and catalyst pastes of Panavia F (Kuraray), Variolink II (Vivadent), Rely X (3M ESPE), and Enforce (Dentsply) were mixed and inserted into cylindrical molds (4 x 2 mm) (n = 10). Cements were not photopolymerized. DTS test was performed in a testing machine at 30 minutes, 1 hour, 24 hours, and 7 days. The specimens were stored in light-proof containers with distilled water at 37 degrees C until the time of assay. An autopolymerizing resin cement (Cement-It, Jeneric Pentron) and a zinc phosphate cement served as controls. One-way analysis of variance (ANOVA) and Tukey test were performed separately for each cement and for each time (P <.05). RESULTS: All cements showed an increase in DTS when tested at 1 and 24 hours. Tests at 24 hours and 7 days revealed no statistically significant differences. In all groups, the zinc phosphate cement had the lowest DTS mean values (2.1 MPa, 3.6 MPa, 6.5 MPa, and 6.9 MPa), while Cement-It (35.1 MPa, 33.6 MPa, 46.9 MPa, and 46.3 MPa) and Enforce (31.9 MPa, 31.7 MPa, 43.4 MPa, and 47.6 MPa) presented the highest DTS mean values. CONCLUSION: All cements presented maximal strength at 24 hours. The dual-curing resin cements, even when nonphotopolymerized, demonstrated higher DTS than the zinc phosphate cement and similar or lower values than the autopolymerizing resin cement.

Lot sizing and furnace scheduling in small foundries

A lot sizing and scheduling problem prevalent in small market-driven foundries is studied. There are two related decision levels: (1) the furnace scheduling of metal alloy production, and (2) moulding machine planning which specifies the type and size of production lots. A mixed integer programming (MIP) formulation of the problem is proposed, but is impractical to solve in reasonable computing time for non-small instances. As a result, a faster relax-and-fix (RF) approach is developed that can also be used on a rolling horizon basis where only immediate-term schedules are implemented. As well as a MIP method to solve the basic RF approach, three variants of a local search method are also developed and tested using instances based on the literature. Finally, foundry-based tests with a real-order book resulted in a very substantial reduction of delivery delays and finished inventory, better use of capacity, and much faster schedule definition compared to the foundry's own practice. © 2006 Elsevier Ltd. All rights reserved.

Heuristics and meta-heuristics for lot sizing and scheduling in the soft drinks industry: A comparison study

This chapter studies a two-level production planning problem where, on each level, a lot sizing and scheduling problem with parallel machines, capacity constraints and sequence-dependent setup costs and times must be solved. The problem can be found in soft drink companies where the production process involves two interdependent levels with decisions concerning raw material storage and soft drink bottling. Models and solution approaches proposed so far are surveyed and conceptually compared. Two different approaches have been selected to perform a series of computational comparisons: an evolutionary technique comprising a genetic algorithm and its memetic version, and a decomposition and relaxation approach. © 2008 Springer-Verlag Berlin Heidelberg.

Dual path: A concept to improve the esthetic replacement of missing anterior teeth with a removable partial denture

The dual path of insertion concept for removable partial denture (RPD) design may be used in esthetically demanding situations. When compared to conventional RPDs, the main advantage of this design is the minimal use of clasps. This clinical report describes the treatment of a patient with an anterior maxillary edentulous area using a dual path RPD. The diagnostic cast was surveyed to ensure the adequacy of the undercuts on the mesial surfaces of the anterior abutments, where rigid minor connectors were placed. Inverted V-shaped canine cingulum rest seats were prepared to provide resistance to tooth movement during function. The dual path RPD concept allows excellent esthetic results, minimizes tooth preparation, and reduces the tendency toward plaque accumulation in a Kennedy class IV partially edentulous arch. © 2008 by The American College of Prosthodontists.

Evaluating genetic algorithms with different population structures on a lot sizing and scheduling problem

This paper studies the use of different population structures in a Genetic Algorithm (GA) applied to lot sizing and scheduling problems. The population approaches are divided into two types: single-population and multi-population. The first type has a non-structured single population. The multi-population type presents non-structured and structured populations organized in binary and ternary trees. Each population approach is tested on lot sizing and scheduling problems found in soft drink companies. These problems have two interdependent levels with decisions concerning raw material storage and soft drink bottling. The challenge is to simultaneously determine the lot sizing and scheduling of raw materials in tanks and products in lines. Computational results are reported allowing determining the better population structure for the set of problem instances evaluated. Copyright 2008 ACM.

Changes on degree of conversion of dual-cure luting light-cured with blue LED

The indirect adhesive procedures constitute recently a substantial portion of contemporary esthetic restorative treatments. The resin cements have been used to bond tooth substrate and restorative materials. Due to recently introduction of the self-bonding resin luting cement based on a new monomer, filler and initiation technology has become important to study the degree of conversion of these new materials. In the present work the polymerization reaction and the filler content of dual-cured dental resin cements were studied by means of infra-red spectroscopy (FT-IR) and thermogravimetry (TG). Twenty specimens were made in a metallic mold (8 mm diameter × 1 mm thick) from each of 2 cements, Panavia® F2.0 (Kuraray) and RelyX™ Unicem Applicap (3M/ESPE). Each specimen was cured with blue LED with power density of 500 mW/cm 2 for 30 s. Immediately after curing, 24 and 48 h, and 7 days DC was determined. For each time interval 5 specimens were pulverized, pressed with KBr and analyzed with FT-IR. The TG measurements were performed in Netzsch TG 209 under oxygen atmosphere and heating rate of 10°C/min from 25 to 700°C. A two-way ANOVA showed DC (%) mean values statistically significance differences between two cements (p < 0.05). The Tukey's test showed no significant difference only for the 24 and 48 h after light irradiation for both resin cements (p > 0.05). The Relx-Y™ Unicem mean values were significantly higher than Panavia® F 2.0. The degree of conversion means values increasing with the storage time and the filler content showed similar for both resin cements. © 2009 Pleiades Publishing, Ltd.

The dual divergence: growth successes and collapses in the developing world since 1980

Includes bibliography

A nonlinear model for the long-term hydro-thermal generation scheduling problem over multiple areas with transmission constraints

This paper presents a nonlinear model with individual representation of plants for the centralized long-term hydrothermal scheduling problem over multiple areas. In addition to common aspects of long-term scheduling, this model takes transmission constraints into account. The ability to optimize hydropower exchange among multiple areas is important because it enables further minimization of complementary thermal generation costs. Also, by considering transmission constraints for long-term scheduling, a more precise coupling with shorter horizon schedules can be expected. This is an important characteristic from both operational and economic viewpoints. The proposed model is solved by a sequential quadratic programming approach in the form of a prototype system for different case studies. An analysis of the benefits provided by the model is also presented. ©2009 IEEE.

Dealing with 'the global governance' and 'the dual constituency' syndromes in emerging countries

Includes bibliography

Effect of light energy density on conversion degree and hardness of dual-cured resin cement

This study evaluated the effect of different light energy densities on conversion degree (CD) and Knoop hardness number (KHN) of RelyX ARC (RLX) resin cement. After manipulation according to the manufacturer's instructions, RLX was inserted into a rubber mold (0.8 mm X 5 mm) and covered with a Mylar strip. The tip of the lightcuring unit (LCU) was positioned in contact with the Mylar surface. Quartz-tungsten-halogen (QTH) and light-emitting diode (LED) LCUs with light densities of 10, 20 and 30 J/cm2 were used to light-cure the specimens. After light curing, the specimens were stored dry in lightproof containers at 37°C. After 24 hours, the CD was analyzed by FT-Raman and, after an additional 24-hours, samples were submitted to Knoop hardness testing. The data of the CD (%) and KHN were submitted to two-way ANOVA and the Tukey's test (α=0.05). QTH and LED were effective light curing units. For QTH, there were no differences among the light energy densities for CD or KHN. For LED, there was a significant reduction in CD with the light energy density set at 10 J/cm2. KHN was not influenced by the lightcuring unit and by its light energy density. © Operative Dentistry.

Effect of thickness of indirect restoration and distance from the light-curing unit tip on the hardness of a dual-cured resin cement

This study evaluated the Knoop hardness and polymerization depth of a dual-cured resin cement, light-activated at different distances through different thicknesses of composite resin. One bovine incisor was embedded in resin and its buccal surface was flattened. Dentin was covered with PVC film where a mold (0.8-mm-thick and 5 mm diameter) was filled with cement and covered with another PVC film. Light curing (40 s) was carried out through resin discs (2, 3, 4 or 5 mm) with a halogen light positioned 0, 1, 2 or 3 mm from the resin surface. After storage, specimens were sectioned for hardness measurements (top, center, and bottom). Data were subjected to split-plot ANOVA and Tukey's test (α=0.05). The increase in resin disc thickness decreased cement hardness. The increase in the distance of the light curing tip decreased hardness at the top region. Specimens showed the lowest hardness values at the bottom, and the highest at the center. Resin cement hardness was influenced by the thickness of the indirect restoration and by the distance between the light-curing unit tip and the resin cement surface.

Simulation of computational grids scheduling politics

Computational grids allow users to share resources of distributed machines, even if those machines belong to different corporations. The scheduling of applications must be performed aiming at performance goals, and focusing on choose which processes can have access to specif resources, and which resources. In this article we discuss aspects of scheduling of application in grid computing environment. We also present a tool for scheduling simulation along with test scenarios and results.

Tabu search to solve the Synchronized and Integrated Two-Level Lot Sizing and Scheduling Problem

This paper proposes a tabu search approach to solve the Synchronized and Integrated Two-Level Lot Sizing and Scheduling Problem (SITLSP). It is a real-world problem, often found in soft drink companies, where the production process has two integrated levels with decisions concerning raw material storage and soft drink bottling. Lot sizing and scheduling of raw materials in tanks and products in bottling lines must be simultaneously determined. Real data provided by a soft drink company is used to make comparisons with a previous genetic algorithm. Computational results have demonstrated that tabu search outperformed genetic algorithm in all instances. Copyright 2011 ACM.

The effects of exposure time on the surface microhardness of three dual-cured dental resin cements

This study evaluated the exposure time of light-curing of the polymers used for cementation on microhardness test in different storage times. The polymers (specifically called resin cements) were RelyX ARC, RelyX U100, and SET. Five specimens of each group were prepared and photo-polymerized with exposure times of 20 s and 180 s, using a LED polymerization unit with wavelength of 440 ~ 480 nm and light output was consistently 1,500 mW/cm2. The Vickers hardness test was performed in a MMT-3 Microhardness Tester. Data were submitted to ANOVA and Tukey's test (α = 0.05). The values of RelyX ARC showed statistically significant difference to groups with light exposure when considering only chemical cure (p < 0.05). The groups with light exposure (20 s and 180 s) showed no significant difference between them (p > 0.05). The RelyX U100 cured only chemically showed statistically significant difference between 48 h and 7 days (p < 0.05). The SET resin cement showed no significant difference to groups without light exposure for all storage times (p > 0.05). The values of hardening of the dual-cured resin cements improved after setting by light and chemical activation demonstrating the importance of light curing. © 2011 by the authors.

Microhardness of dual-polymerized resin cement around a translucent fiber post in the intraradicular environment

Aim: In this study, we evaluated the effect of photopolymerization on Vickers microhardness of dual-polymerized resin cement at three locations when a translucent quartz fiber post was used. Materials and Methods: Single-rooted bovine teeth received quartz fiber post systems (length: 12 mm) using a dual-polymerized resin cement. In Group 1, the posts were cemented but not photopolymerized, and in Group 2, the posts were both cemented and photopolymerized. After cementation, approximately 1.5-mm thick sections were obtained (two cervical, two middle, and two apical) for regional microhardness evaluations. Statistical Analysis: Statistical analyses were performed using the SPSS software (ver. 11.0 for Windows; SPSS, Inc., Chicago, IL, USA). Microhardness (kg/mm 2 ) data were submitted to two-way analysis of variance (two-way ANOVA) and repeated measures with microhardness values as the dependent variable and polymerization status (two levels: with and without) and root region (three levels: cervical, middle, and apical) as independent variables. Multiple comparisons were made using Dunnett's T3 post-hoc test. P values of <0.05 were considered to indicate statistical significance in all tests. Results: Photopolymerization did not significantly change the microhardness values when compared with no photopolymerization. Microhardness values also showed no significant difference between the three regions in the root canals in both groups. Conclusions: The mode of polymerization of the cement tested in combination with the translucent quartz fiber post system did not affect the microhardness of the cement at the cervical, middle, or apical regions of the root.