Milos Milosevic

Effects of a low-shrinkage methacrylate monomer and monoacylphosphine oxide photoinitiator on curing efficiency and mechanical properties of experimental resin-based composites.

This study investigated the degree of conversion, depth of cure, Vickers hardness, flexural strength, flexural modulus and volumetric shrinkage of experimental composite containing a low shrinkage monomer FIT-852 (FIT; Esstech Inc.) and photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO; Sigma Aldrich) compared to conventional composite containing Bisphenol A-glycidyl methacrylate (BisGMA) and camphorquinone-amine photoinitiator system. The degree of conversion was generally higher in FIT-based composites (45-64% range) than in BisGMA-based composites (34-58% range). Vickers hardness, flexural strength and modulus were higher in BisGMA-based composites. A polywave light-curing unit was generally more efficient in terms of conversion and hardness of experimental composites than a monowave unit. FIT-based composite containing TPO showed the depth of cure below 2mm irrespective of the curing light. The depth of cure of FIT-based composite containing CQ and BisGMA-based composites with either photoinitiator was in the range of 2.8-3.0mm. Volumetric shrinkage of FIT-based composite (0.9-5.7% range) was lower than that of BisGMA-based composite (2.2-12% range). FIT may be used as a shrinkage reducing monomer compatible with the conventional CQ-amine system as well as the alternative TPO photoinitiator. However, the depth of cure of FIT_TPO composite requires boosting to achieve clinically recommended thickness of 2mm.

Compressive strains and displacement in a partially dentate lower jaw rehabilitated with two different treatment modalities

BACKGROUND Understanding of the biomechanical consequences of the stresses generated to the supporting bone during occlusal loading is significant for improving the design and clinical planning process in partial edentulism therapy. OBJECTIVE   The aim of this study was to analyse the distribution of strain and displacement on the partially dentate lower jaw rehabilitated with an partial denture (RPD) and to compare it to the strain and displacement distribution on a partially dentate lower jaw rehabilitated with a cantilever fixed partial denture (FPD). MATERIAL AND METHODS The experimental models were a partially dentate mandible with full-arch PFM crowns and RPD and a partially dentate mandible rehabilitated with a full-arch cantilever FPD. Strains and displacement were measured using the Digital Image Correlation Method. RESULTS Displacement values of the first experimental model ranged from 0.31 to 0.54 mm with strains from 1.35 to 2.34%. Analysis of the second experimental model results showed displacement values from 0 to 0.34 mm, while strains were in the range of 0-1.40%. CONCLUSION Higher displacements and strains of bone tissue were observed below the RPD, especially in the region of the distal abutment and distal portion of the free-end saddle. Strains within bone and the bone-denture contact area were mostly influenced by the teeth and denture vertical displacement.

Local deformation fields and marginal integrity of sculptable bulk-fill, low-shrinkage and conventional composites.

OBJECTIVE To compare strain and displacement of sculptable bulk-fill, low-shrinkage and conventional composites as well as dye penetration along the dentin-restoration interface. METHODS Modified Class II cavities (N=5/group) were filled with sculptable bulk-fill (Filtek Bulk Fill Posterior, 3M ESPE; Tetric EvoCeram Bulk Fill, Ivoclar Vivadent; fiber-reinforced EverX Posterior, GC; giomer Beautifil Bulk, Schofu), low-shrinkage (Kalore, GC), nanohybrid (Tetric EvoCeram, Ivoclar Vivadent) or microhybrid (Filtek Z250, 3M ESPE) composites. Strain and displacement were determined using the 3D digital image correlation method based on two cameras with 1μm displacement sensitivity and 1600×1200 pixel resolution (Aramis, GOM). Microleakage along dentin axial and gingival cavity walls was measured under a stereomicroscope using a different set of teeth (N=8/group). Data were analyzed using analyses of variance with Tukeys post-test, Pearson correlation and paired t-test (α=0.05). RESULTS Strain of TEC Bulk, Filtek Bulk, Beautifil Bulk and Kalore was in the range of 1-1.5%. EverX and control composites showed 1.5-2% strain. Axial displacements were between 5μm and 30μm. The least strain was identified at 2mm below the occlusal surface in 4-mm but not in 2-mm layered composites. Greater microleakage occurred along the gingival than axial wall (p<0.05). No correlation was found between strain/displacements and microleakage axially (r2=0.082, p=0.821; r2=-0.2, p=0.605, respectively) or gingivally (r2=-0.126, p=0.729, r2=-0.278, p=0.469, respectively). SIGNIFICANCE Strain i.e. volumetric shrinkage of sculptable bulk-fill and low-shrinkage composites was comparable to control composites but strain distribution across restoration depth differed. Marginal integrity was more compromised along the gingival than axial dentin wall.

Analysis of Composite Shrinkage Stresses on 3D Premolar Models with Different Cavity Design Using Finite Element Method

Local polymerization stress occurs due to polymerization shrinkage of resin based composites adhesively bonded to tooth tissues. Shrinkage causes local displacements of cavity walls, with possible occurrence of micro-cracks in the enamel, dentin and/or material itself. In order to design a cavity for experimental testing of polymerization shrinkage of dental composites using 3D optical analysis, in this paper finite element method (FEM) was used to analyze numerical models with different cavity radiuses. 3D optical strain and displacement analysis of composite materials and cavity walls is limited by equipment sensitivity i.e. 0.01% for strain and 1 micron for displacement. This paper presents the development of 3D computer premolar models with varying cavity radiuses, and local stress, strain and displacement analysis using FEM. Model verification was performed by comparing obtained results with data from the scientific literature. Using the FEM analysis of local strains, displacements and stresses exerted on cavity walls, it was concluded that the model with 1 mm radius was optimal for experimental optical 3D displacement analysis.

Local Strain and Stress Analysis of Globe Valve Housing Subjected to External Axial Loading

Globe valves have widespread application in various industrial sectors. Due to this variety, valve is subjected to different working loads (static, dynamic, thermal etc.) that can cause valve failures. In this paper, the analysis is performed on globe valve subjected to external axial loading caused by pipeline dilatations. Experimental analysis was focused on determining local mechanical properties of critical areas, i.e. on local areas of globe valve housing with high geometrical discontinuities. Experimental analysis and numerical model verification were performed using system Aramis based on Digital Image Correlation method. Using full-field experimental results, numerical model behavior was improved and enabled acquiring more accurate results in transition areas that cannot be found in currently available literature. Determining local mechanical properties of critical areas enables better understanding of complex structures such as valve housing and provides an opportunity for further development and improvement for practical industrial application.

Digital image correlation analysis of biomaterials

Digital image correlation method (DIC) is becoming a common method in determining mechanical properties of biomaterials. DIC using 3D optical measuring system has very broad application in dentistry research field. Application of DIC technique in experimental biomechanical analysis using software Aramis for 3D displacement/strain measurement is presented in this paper.

Experimental Dimensional Accuracy Analysis of Reformer Prototype Model Produced by FDM and SLA 3D Printing Technology

The subject of this paper is the evaluation of the dimensional accuracy of FDM and SLA 3D printing technologies in comparison with developed reformer polymer electrolyte membrane (PEM) fuel cell CAD model. 3D printing technologies allow a bottom-up approach to manufacturing, by depositing material in layers to final shape. Dimensional inaccuracy is still a problem in 3D printing technologies due to material shrinking and residual stress. Materials used in this research are PLA (Polylactic Acid) for FDM technology and the standard white resin material for SLA technology. Both materials are commonly used for 3D printing. PLA material is printed in three different height resolutions: 0.3 mm, 0.2 mm and 0.1 mm. White resin is printed in 0.1 mm height resolution. The aim of this paper is to show how layer height affects the dimensional accuracy of FDM models and to compare the dimensional accuracy of FDM and SLA printed reformer models with the same height resolution.

Thermal and Mechanical Characteristics of Dual Cure Self-etching, Self-adhesive Resin Based Cement

One of the main objectives in research and development of resin based cements (RBCs) is to enhance their clinical longevity and ease of use. In spite of the undeniable technological advances introduced in the last few decades, the polymerization shrinkage i.e. strain that accompanies the chain-growth polymerization of dimethacrylate monomers remains one of the major concerns for the clinical performance of composite restorations. Also, RBCs can produce a considerable amount of heat, due to the light energy from the curing lights and exothermic reaction of polymerization.

Measuring of Strain and Displacements in Welded Joints Subjected to Tensile Load Using Stereometric Methods

During the experimental testing of a welded joint, made of steel P460NL1, complete strain and displacement fields, which provide full insight into the behaviour of a welded joint under tensile load, were obtained using an optical stereometric measuring method. Optical stereometric method involved the application of digital image correlation. Presented in this paper are the strain and displacement for various load levels are shown, along with the behaviour of the welded joint as a whole. As a result of this approach, concrete and accurate values of the observed strain field as a whole can be compared directly, rather than as chosen representative parts that would be tested using a strain gauge in a single position, and provide a more detailed insight into the behaviour of the tested joint. With the aid of images obtained using cameras, the development of strain over time can be monitored, while pointing out the critical parts of a welded joint, allowing the determining of potential locations with increased stress intensity factor.

Influence of geometry on pressure and velocity distribution in packed-bed methanol steam reforming reactor

The main tasks of this research is to propose several changes in the packed bed micro methanol steam reformer geometry in order to ensure its performance. The reformer is an integral part of the existing indirect internal reforming high temperature PEMFC and most of its geometry is already defined. The space for remodeling is very limited.