The Effect of Acrylic Surface Preparation on Bonding Denture Teeth to Cellulose Fiber-Reinforced Denture Base Acrylic.

Patients who require dental prosthetic restoration using frame dentures in the front part of the mouth very frequently report that teeth fall out of their dentures. However, the available scientific papers are insufficient to compare the various methods of improving the connection between the denture base and the artificial tooth and choosing the best solution. This paper focuses on providing all parameters, enabling the reproduction of tests, and accounting for all variables. The paper uses an original method of creating grooves, sandpaper, sandblasting, and cutting the acrylate layer with a burr in one and two directions. Developed surfaces were additionally subjected to detailed examination. This study used 180 specimens divided into three groups and subjected to various environments (dry, artificial saliva, and thermocycles). Shearing and tensile strength tests were performed. The best results were obtained with a carbide burr. The increase in connection durability was as follows in the case of the shear test: 116.47% in dry samples, 155.38% in samples soaked in artificial saliva, and 46.59% in samples after thermocycles. The increase in tensile resistance was: 198.96% in a dry environment, 88.10% before being soaked in artificial saliva, and 94.04% after thermocycles.

Bonding and Strengthening the PLA Biopolymer in Multi-Material Additive Manufacturing.

3D printing is a revolutionary additive manufacturing method that enables rapid prototyping and design flexibility. A variety of thermoplastic polymers can be used in printing. As it is necessary to reduce the consumption of petrochemical resources, alternative solutions are being researched, and the interest in using bioplastics and biocomposites is constantly growing. Often, however, the properties of biopolymers are insufficient and need to be improved to compete with petroleum-based plastics. The paper aims to analyze the available information on elements produced from more than one material, with additive manufacturing resulting from 3D printing using biopolymer Polylactic Acid (PLA). The study notes the possibility of modifying and improving the properties of PLA using layered printing or by modifying PLA filaments. Several modifications improving and changing the properties of PLA were also noted, including printing parameters when combined with other materials: process temperatures, filling, and surface development for various sample geometries.

Assessment of the deformation model of the proximal tibia in the course of degenerative disease: analysis of the 3-dimensional mathematical model.

Background: The high tibial osteotomy (HTO) is an effective knee-saving procedure, which relieves arthritis symptoms and prolongs the life of the knee joint. This procedure requires detailed preoperative planning. Usually, the contralateral side is used as a template for this purpose. Some intra-operative complications made us thinking how exactly the degenerative disease alter the epiphysis if the tibia. Our study aimed to assess morphological differences between healthy knees and degenerative knees using a three-dimensional mathematical model. Methods: Twenty-three computed tomography (CT) examinations were collected out of 237 individuals screened for inclusion/exclusion. The inclusion criteria were: age between 40 and 69 years, degenerative knees with visible varus deformation, and signs of radiological osteoarthritis (OA) in the knee joint (such as joint space narrowing, subchondral sclerosis, subchondral cyst formation, and osteophytes. The average age of the included patients was 56.2 years. Nine men's and 14 women's knee joints were used for the calculation and comparisons. Results: Female varus knees showed much more significant variability in tibial plateau dimensions according to sides of the body than male ones. These differences were statistically significant (P=0.03). In comparison between the basal bone and bones with OA, variability in 3D dimensions was statistically significant only for lateral condyles in males' right knees (P=0.025). Compared to the degenerative knees to the most average, healthy knees, there were significant differences in the measured surface area of males' right knees for both condyles: for the medial P=0.0046, for lateral P=0.005. Male varus knees had a statistically more considerable (P=0.028) surface area for all measured condyles. Angles of inclination differ significantly between knees with OA and healthy knees in the male population for the medial condyle plateau in the left knees. The female population for the lateral condyle in left knees and the medial condyle in right knees. Conclusions: The proximal tibial plateau deformation showed high variability in the two-dimensional and three-dimensional analysis in the designed mathematical models. This finding must be considered during preoperative planning.

The Influence of the Depth of Grinding on the Condition of the Surface Layer of 20MnCr5 Steel Ground with the Minimum Quantity Lubrication (MQL) Method.

This paper describes the research on abrasive machining conditions and their influence on microhardness and residual stresses distribution in the technological surface layer of 20MnCr5 steel. The roughness of ground samples was also measured. Samples underwent a vacuum carburizing process (LPC) followed by high-pressure gas quenching (HPGQ) in a 4D quenching chamber. Processes were realized with a single-piece flow method. Then, the flat surfaces of samples were ground with a Vortex type IPA60EH20VTX alumina grinding wheel using a flat-surface grinder. The samples were ground to three depths of grinding (ae = 0.01; 0.02; 0.03 mm) with grinding fluid supply using either flood method (WET) or minimum quantity lubrication (MQL) method. The condition of the technological surface layer was described using microhardness and residual stresses, as well as some selected parameters of surface roughness. The results obtained revealed that changes in microhardness as compared to microhardness of the material before grinding were lower in samples ground with grinding fluid supplied with MQL method. At the same time, the values of residual stresses were also better for samples ground using MQL method. Furthermore, the use of grinding fluid fed with MQL method produced lower values of surface roughness compared to the parameters obtained with WET method. It was concluded that for the tested scope of machining conditions, the MQL method can be a favourable alternative to the flood method of supplying grinding fluid into the grinding zone.

Influence of Resin Cement Thickness and Elastic Modulus on the Stress Distribution of Zirconium Dioxide Inlay-Bridge: 3D Finite Element Analysis.

The mechanical properties and the thickness of the resin cement agents used for bonding inlay bridges can modify the clinical performance of the restoration such as debonding or prosthetic materials fracture. Thus, the aim of this study was to evaluate the stress distribution and the maximum strain generated by resin cements with different elastic moduli and thicknesses used to cement resin-bonded fixed partial denture (RBFPD). A three-dimensional (3D) finite element analysis (FEA) was used, and a 3D model was created based on a Cone-Beam Computed Tomography system (CBCT). The model was analyzed by the Ansys software. The model fixation occurred at the root of the abutment teeth and an axial load of 300 N was applied on the occlusal surface of the pontic. The highest stress value was observed for the Variolink 0.4 group (1.76 × 106 Pa), while the lowest was noted for the Panavia 0.2 group (1.07 × 106 Pa). Furthermore, the highest total deformation value was found for the Variolink 0.2 group (3.36 × 10-4 m), while the lowest was observed for the Panavia 0.4 group (2.33 × 10-4 m). By means of this FEA, 0.2 mm layer Panavia F2.0 seemed to exhibit a more favorable stress distribution when used for cementation of posterior zirconium-dioxide-based RBFPD. However, both studied materials possessed clinically acceptable properties.

The Influence of 3D Printing Parameters on Adhesion between Polylactic Acid (PLA) and Thermoplastic Polyurethane (TPU).

A 3D printer in FDM technology allows printing with two nozzles, which creates an opportunity to produce multi-material elements. Printing from two materials requires special consideration of the interface zone generated between their geometrical boundaries. This article aims to present the possibility of printing with PLA and TPU using commercially available filaments and software to obtain the best possible bond strength between two different polymers with respect to printing parameters, surface pattern (due to the material contact surface's roughness), and the order of layer application. The interaction at the interface of two surfaces of two different filaments (PLA-TPU and TPU-PLA) and six combinations of patterns were tested by printing seven replicas for each. A total of 12 combinations were obtained. By analyzing pairs of samples (the same patterns, different order of materials), the results for the TPU/PLA samples were better or very close to the results for PLA/TPU. The best variants of pattern combinations were distinguished. Well-chosen printing parameters can prevent a drop in parts efficiency compared to component materials (depending on the materials combination).

Assessment of morphological differences of the proximal tibia in healthy knees: analysis of the 3-dimensional mathematical model.

BACKGROUND: High tibial osteotomy and many orthopedic surgical procedures around the knee joint requires precise preoperative planning. In-depth knowledge of the tibial plateau morphology is necessary to limit intraoperative complications like lateral hinge fracture. No studies were exploring the differences in proximal tibia surface geometry, in regards to gender and laterality, using a mathematical model. The aim of our study was to assess morphological differences in healthy knees using a three-dimensional mathematical model. METHODS: Eighty-seven computed tomography examinations collected from 52 patients were selected for the study. The inclusion criteria were: age between 20 and 40 years, knee joint without visible deformities, no history of significant trauma to index knee, no history of systemic and chronic disorders. The average age of the included patients was 32.5±8.9 years old. For the calculation and comparisons, 45 right knee joints (18 females and 27 males) and 42 left knee joints (17 females and 25 males) were used. RESULTS: The male tibial plateau was much larger than the female one, for the right (P=0.001) and left knees (P=0.001). Male knees showed much bigger variability in two-dimensional tibial plateau dimensions especially for the left knees (P=0.001), and there was also a marked difference in variability between sides in males. Three-dimensional variability was significant for medial condyles for both genders. Male knees had a statistically bigger (P=0.04) tibial plateau surface area for all measured condyles. CONCLUSIONS: The proximal tibial plateau showed in the designed mathematical models high variability in the two-dimensional and three-dimensional analysis. The males' knees presented great variability between sides and condyles. This finding must be considered during preoperative planning.

Numerical Analysis of the Bond Strength between Two Methacrylic Polymers by Surface Modification.

The creation of acrylic dentures involves many stages. One of them is to prepare the surfaces of artificial teeth for connection with the denture plates. The teeth could be rubbed with a chemical reagent, the surface could be developed, or retention hooks could be created. Preparation of the surface is used to improve the bond between the teeth and the plate. Choosing the right combination affects the length of denture use. This work focuses on a numerical analysis of grooving. The purpose of this article is to select the shape and size of the grooves that would most affect the quality of the bond strength. Two types of grooves in different dimensional configurations were analyzed. The variables were groove depth and width, and the distance between the grooves. Finally, 24 configurations were obtained. Models were analyzed in terms of their angular position to the loading force. Finite element method (FEM) analysis was performed on the 3D geometry created, which consisted of two polymer bodies under the shear process. The smallest values of the stresses and strains were characterized by a sample with parallel grooves with the grooving dimensions width 0.20 mm, thickness 0.10 mm, and distance between the grooves 5.00 mm, placed at an angle of 90°. The best dimensions from the parallel (III) and cross (#) grooves were compared experimentally. Specimens with grooving III were not damaged in the shear test. The research shows that the shape of the groove affects the distribution of stresses and strains. Combining the selected method with an adequately selected chemical reagent can significantly increase the strength of the connection.

Chemical Modification of Cellulose Microfibres to Reinforce Poly(methyl methacrylate) Used for Dental Application.

The mechanical properties of dental acrylic resins have to be improved in the case of a thin denture plate. This can be achieved by cellulose addition, playing the role of active filler. But to provide the excellent dispersion of cellulose microfibres within the hydrophobic polymer matrix, its surface has to be modified. Cellulose microfibres with average length from 8 to 30 µm were modified with octyltriethoxysilane and (3-methacryloxypropyl)methyldimethoxysilane. The latter also participated in the polymerisation reaction of methyl methacrylate. Dental composites were prepared following the general procedure provided by the supplier. The successful modification of the microfibres led to the improved compatibility of the cellulose and poly(methyl methacrylate). The fibres after modification were uniformly distributed within the matrix, resulting in the improved mechanical performance of obtained materials. Cellulose microfibres are good candidates for the dental materials to be used as the active filler. The simple and straightforward approach for the cellulose modifications with silanes provides good potential for its future practical application.

A Study of Second-Phase Precipitates and Dispersoid Particles in 2024 Aluminum Alloy after Different Aging Treatments.

Aluminum alloys such as AA2024 are popular in the automotive and aircraft industries. The application of artificial aging significantly improves their mechanical properties by precipitation hardening. However, commercial alloys very often contain different amounts of elements such as Si and Fe that make the evolution of the microstructure harder to control. Large intermetallic particles can influence the overall results of heat treatment and cause deterioration of material properties. The authors decided to examine changes in the microstructure of three commercial 2024 alloys with varying chemical compositions by applying three different types of aging treatments. The results show considerable differences in the amount, size and morphologies of the precipitates. Second-phase Al2Cu and Al2CuMg precipitates were identified in one of the alloys. Other interesting types of multiphase particles were discovered in alloys with higher Si contents. The results show that even small variations in the composition can lead to a completely different microstructure.

Glutathione S-transferase pi as a target for tricyclic antidepressants in human brain.

GST pi, the main glutathione S-transferase isoform present in the human brain, was isolated from various regions of the brain and the in vitro effect of tricyclic antidepressants on its activity was studied. The results indicated that amitripyline and doxepin--derivatives of dibenzcycloheptadiene, as well as imipramine and clomipramine--derivatives of dibenzazepine, inhibit the activity of GST pi from frontal and parietal cortex, hippocampus and brain stem. All these tricyclics are noncompetitive inhibitors of the enzyme with respect to reduced glutathione and noncompetitive (amitripyline, doxepin) or uncompetitive (imipramine, clomipramine) with respect to the electrophilic substrate. Their inhibitory effect is reversible and it depends on the chemical structure of the tricyclic antidepressants rather than on the brain localization of the enzyme. We conclude that the interaction between GST pi and the drugs may reduce their availability in the brain and thus affect their therapeutic activity. On the other hand, tricyclic antidepressants may decrease the efficiency of the enzymatic barrier formed by GST and increase the exposure of brain to toxic electrophiles. Reactive electrophiles not inactivated by GST may contribute in adverse effects caused by these drugs.