Effect of the combination of a crosslinking agent and a thiourethane additive on the properties of acrylic denture bases processed with microwave energy

Studies on the Removal of Malachite Green from Its Aqueous Solution Using Water-Insoluble β-Cyclodextrin Polymers

The rising global pollution of natural waters by dyes has brought to light the need for adaptable and efficient removal techniques. To create water-insoluble β-cyclodextrin (β-CD) polymers like CA/-CD, TA/-CD, and MA/-CD, several organic acids including citric acid (CA), tartaric acid (TA), and malic acid (MA) were cross-linked with β-cyclodextrin in this study. The obtained polymers were characterized by different advanced analytical techniques such as FTIR, SEM, and UV-vis spectrophotometry. Malachite green dye was removed from aqueous solutions using the synthesized polymers by adsorption. The adsorption investigation was conducted under several conditions, including pH, adsorbent mass, dye concentration, temperature, contact time, adsorption isotherm, and kinetics. The adsorbent CA/β-CD shows the highest adsorption of MG dye in all of the conditions because it contains a high number of carboxyl groups. The negatively charged carboxyl ions of CA/β-CD attract the positively charged MG dye electrostatically and remove MG from aqueous media with an efficiency of 91%. As a result, the findings indicated that water-insoluble polymers based on β-cyclodextrin are well-suited as inexpensive adsorbents to remove colors from aqueous media.

The Effects of Cross-Linking Agents on the Mechanical Properties of Poly (Methyl Methacrylate) Resin

Cross-linking agents are incorporated into denture base materials to improve their mechanical properties. This study investigated the effects of various cross-linking agents, with different cross-linking chain lengths and flexibilities, on the flexural strength, impact strength, and surface hardness of polymethyl methacrylate (PMMA). The cross-linking agents used were ethylene glycol dimethacrylate (EGDMA), tetraethylene glycol dimethacrylate (TEGDMA), tetraethylene glycol diacrylate (TEGDA), and polyethylene glycol dimethacrylate (PEGDMA). These agents were added to the methyl methacrylate (MMA) monomer component in concentrations of 5%, 10%, 15%, and 20% by volume and 10% by molecular weight. A total of 630 specimens, comprising 21 groups, were fabricated. Flexural strength and elastic modulus were assessed using a 3-point bending test, impact strength was measured via the Charpy type test, and surface Vickers hardness was determined. Statistical analyses were performed using the Kolmogorov-Smirnov Test, Kruskal-Wallis Test, Mann-Whitney U Test, and ANOVA with post hoc Tamhane test (p ≤ 0.05). No significant increase in flexural strength, elastic modulus, or impact strength was observed in the cross-linking groups compared to conventional PMMA. However, surface hardness values notably decreased with the addition of 5% to 20% PEGDMA. The incorporation of cross-linking agents in concentrations ranging from 5% to 15% led to an improvement in the mechanical properties of PMMA.

Influence of Air-Barrier and Curing Light Distance on Conversion and Micro-Hardness of Dental Polymeric Materials

This study aims to assess the conversion degree and hardness behavior of two new commercial dental restorative composites that have been submitted to light curing in different environments (air and glycerin, respectively) at various distances from the light source (1 to 5 mm) and to better understand the influence of the preparation conditions of the restorative materials. Through FT-IR spectrometry, the crosslinking degree of the commercial restorative materials have been investigated and different conversion values were obtained (from ~17% to ~90%) but more importantly, it was shown that the polymerization environment exhibits a significant influence on the crosslinking degree of the resin-based composites especially for obtaining degrees of higher polymerization. Additionally, the mechanical properties of the restorative materials were studied using the nanoindentation technique showing that the nano-hardness behavior is strongly influenced not only by the polymerization lamp position, but also by the chemical structure of the materials and polymerization conditions. Thus, the nanoindentation results showed that the highest nano-hardness values (~0.86 GPa) were obtained in the case of the flowable C3 composite that contains BisEMA and UDMA as a polymerizable organic matrix when crosslinked at 1 mm distance from the curing lamp using glycerin as an oxygen-inhibitor layer.

Comparison of Conventional Pressure-packed and Injection Molding Processing Methods for an Acrylic Resin Denture based on Microhardness, Surface Roughness, and Water Sorption

Polymethyl methacrylate (PMMA) is a widely used material in prosthetics and is used to fabricate denture bases. The main disadvantage of this material is its polymerization shrinkage which causes clinical problems during use. The present study aimed to investigate and compare the microhardness, surface roughness, and water sorption of a commercial acrylic resin denture, which were processed by two different methods including conventional and pressure-packed injection molding techniques. A total of 60 polymethyl methacrylate samples were prepared in two groups: conventional acrylic resin (vertex) for the compression molding method and injection acrylic resin (vertex) for the injection molding method (10 samples of each material per test). The microhardness test was performed using a Vickers microhardness test device, the surface roughness test was performed by using a profilometer, and the water sorption test was performed using a digital scale. Data were analyzed using an independent sample t-test with Statistical Package for the Social Sciences (SPSS), version 17. The significant level was considered to be 0.05. According to the results, there was a significant difference between microhardness, surface roughness, and water sorption of the samples in the two groups. The results of the independent t-test showed that the microhardness of injection vertex acrylic resin samples was significantly higher than that of conventional pressure-packed vertex acrylic resin samples (P value<0.05). Also, the surface roughness and water sorption of injection vertex acrylic resin samples were significantly lower than those of conventional pressure-packed vertex acrylic resin samples (P value <0.05). According to the obtained results, denture fabrication by the injection molding method can improve the quality and durability of dentures due to the increased microhardness, the decreased surface roughness, and the decreased water absorption of the denture base compared with the conventional method.

Mechanical Properties of the Modified Denture Base Materials and Polymerization Methods: A Systematic Review

Amidst growing technological advancements, newer denture base materials and polymerization methods have been introduced. During fabrication, certain mechanical properties are vital for the clinical longevity of the denture base. This systematic review aimed to explore the effect of newer denture base materials and/or polymerization methods on the mechanical properties of the denture base. An electronic database search of English peer-reviewed published papers was conducted using related keywords from 1 January 2011, up until 31 December 2021. This systematic review was based on guidelines proposed by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The search identified 579 papers. However, the inclusion criteria recognized 22 papers for eligibility. The risk of bias was moderate in all studies except in two where it was observed as low. Heat cure polymethyl methacrylate (PMMA) and compression moulding using a water bath is still a widely used base material and polymerization technique, respectively. However, chemically modified PMMA using monomers, oligomers, copolymers and cross-linking agents may have a promising result. Although chemically modified PMMA resin might enhance the mechanical properties of denture base material, no clear inferences can be drawn about the superiority of any polymerization method other than the conventional compression moulding technique.

Adhesive strength of fiberglass posts treated with thio-urethane-based experimental silanes

Purpose:

The aim of this study was to evaluate the adhesive bond strength of fiberglass posts treated with experimental silanes based on thio-urethane and submitted to thermo and mechanical cycles.

Materials and methods:

Bovine roots were divided into six groups: RX-RU2 (RelyX CP + RelyX U200); PETMP-HDDI-RU2 (PETMP-HDDI + RelyX U200); PETMP-BDI-RU2 (PETMP-BDI + RelyX U200); RX-RU (RelyX CP + RelyX Ultimate); PETMP-HDDI-RU (PETMP-HDDI + RelyX Ultimate); PETMP-BDI-RU (PETMP-BDI + RelyX Ultimate). One slice from each root third (n=10) was submitted to the push-out test and the values evaluated with R Program statistical analysis, while the failure pattern assessed in percentage.

Results:

Among root thirds, RX-RU2 promoted greater strength at the cervical and apical thirds; PETMP-HDDI-RU2 showed highest values at the three thirds; and PETMP-BDI-RU2 was strongest at the apical third. RX-RU presented higher strength at the apical third, and PETMP-HDDI-RU and PETMP-BDI-RU had similar values at the three thirds. In each root third, PETMP-HDDI-RU2 showed similar strength at all thirds, and similar strength at the apical third was observed for other associations. Mixed and adhesive failures predominated.

Conclusion:

Experimental silanes promoted different bond strength values in the adhesion of fiberglass posts to the root thirds, with better results for PETMP-HDDI silane. The root region did not influence the failure pattern and most slices showed mixed (MCDP) or adhesive (ADP) failure.

Comparison of Fracture Resistance in Thermal and Self-Curing Acrylic Resins-An In Vitro Study

Thermal and self-curing acrylic resins are frequently and versatilely used in dental medicine since they are biocompatible, have no flavor or odor, have satisfactory thermal qualities and polishing capacity, and are easy and fast. Thus, given their widespread use, their fracture resistance behavior is especially important. In this research work, we comparatively analyzed the fracture resistance capacity of thermo and self-curing acrylic resins in vitro. Materials and Methods: Five prosthesis bases were created for each of the following acrylic resins: Lucitone®, ProBase®, and Megacryl®, which were submitted to different forces through the use of the CS^® Dental Testing Machine, usually mobilized in the context of fatigue tests. To this end, a point was defined in the center of the anterior edge of the aforementioned acrylic resin bases, for which the peak tended until a fracture occurred. Thermosetting resins were, on average, more resistant to fracture than self-curable resins, although the difference was not statistically significant. The thermosetting resins of the Lucitone® and Probase® brands demonstrated behavior that was more resistant to fracture than the self-curing homologues, although the difference was not statistically significant. Thermosetting resins tended to be, on average, more resistant to fracture and exhibited the maximum values for impact strength, compressive strength, tensile strength, hardness, and dimensional accuracy than self-curing resins, regardless of brand.

In vitro performance of 2-step, total etch adhesives modified by thiourethane additives

OBJECTIVES

Thio-urethane oligomeric additives have been shown to improve the mechanical properties of dental composites and resin cements. To try to harness those same properties in dental adhesives, in this study, these oligomers (TU) were added to the matrix and/or as filler functionalization of experimental adhesives, and the effects on conversion and mechanical properties were analyzed.

METHODS

BisGMA and HEMA (60/40 wt%) were used as the monomer matrix, made polymerizable by the addition of 0.2 wt% 2,2-dimethoxy-2- phenylacetophenone. 2,6-di-tert-butyl-4-methylphenol was added at 0.5 wt% as the inhibitor. This material was used as the unfilled control (BH). TU oligomers were added at 20 wt % to the matrix (BH+20%TU, unfilled) and/or used as filler functionalization (TF, 10 wt%). Fillers functionalized with methacrylate (MF, 10 wt%) served as the control. The experimental adhesives groups containing fillers were: BH+10%MF; BH+10%TF; BH+20%TU+10%MF; BH+20%TU+10%TF. Flexural properties were tested in three-point bending (wet and dry). Polymerization kinetics was followed in real-time in near-IR. Water Sorption/Solubility (WS/SL, ISO 4049) and Viscosity (rotational rheometry) were also evaluated. For Microtensile bond strength 40 vol% ethanol was added to adhesives, which was applied onto sound dentin from third human molars. The data were analyzed with one-way ANOVA and Tukey post-hoc test, and test t for the comparison between storage time of the microtensile bond strength test (alpha = 0.05).

RESULTS

There was no significant difference between groups when yield strength (YS) and flexural modulus (FM) were evaluated in dry conditions. After water storage, all the groups containing TU in the matrix showed statistically lower YS/FM values. This was true in spite of the statistically higher conversion for those same groups. The maximum rate of polymerization (Rpmax) was higher for BH+10%TF and no significant difference was found for the groups BH and BH+10% MF. The lowest Rpmax values were found for BH+20%TU+10%TF and BH+20%TU. BH+20%TU+10%TF showed the highest viscosity values followed by BH+20%TU+10%MF and BH+20%TU, with statistically significant difference between them. For the microtensile bond strength test at 24h (p = 0.13) and 6 months (p = 0.11) and WS/SL (p > 0.05), no significant difference was found among groups. The storage time (24 h and 6 months) did not affect the microtensile bond strength results.

CONCLUSION

In spite of improving the conversion, the addition of TU in the matrix reduced the mechanical properties of the adhesives tested after water storage. This did not affect the bond strength at 24 h or 6 months.

Strategies for Potential Toughening of Acrylic Denture Bases Polymerized With Microwave Energy

Thiourethane additives have been shown to improve properties in several dental polymer applications. The aim of this study was to verify the effect of the addition of thiourethane oligomers and acrylamide or isobornyl-based plasticizers on the physical properties of the denture base acrylic resin polymerized with microwaves. Thiourethane oligomer (TU) was synthetized and added to microwaved acrylic resin in proportions varying between 3 and 14 wt%. Separate experimental groups included the addition of dimethyl acrylamide (DMAM) and isobornyl methacrylate as plasticizers, at concentrations varying from 5 to 20 wt%. Samples were polymerized using microwave energy at 500 Watts for 3 min, deflasked at room temperature, stored in water at 37 °C for 24 h, and evaluated for: linear dimensional change, gloss, Knoop hardness, surface roughness, impact strength, yield strength, elastic modulus, toughness, yield strength, viscosity, glass transition temperature and network heterogeneity, and water sorption/solubility. Data were analyzed with ANOVA/Tukey's post-hoc test (a=5%). The addition of TU led to properties that were similar or worse than the materials to which it was not added, except for dimensional stability. The impact on properties was statistically significant for all materials above 20% addition of TU. The addition of DMAM at 5 wt% or isobornyl methacrylate at 10 wt% improved yield strength and modulus, but increased water sorption and solubility. Except for dimensional stability, the addition of thiourethane oligomers to acrylic denture base materials compromised most tested properties. The use of DMAM and isobornyl methacrylate improved properties for selected compositions.

Influence of High-Pressure Polymerization on Mechanical Properties of Denture Base Resins

PURPOSE

The purpose of this study was to study the influence of high-pressure (HP) polymerization on the mechanical properties of denture base PMMA resins compared with conventional thermopolymerization and PMMA discs for digital dentures.

MATERIALS AND METHODS

Three groups of blocks were prepared: Probase Hot (Ivoclar Vivadent, Lichtenstein) conventionally heat polymerized at 100°C, Probase Hot heat polymerized at 100°C under HP (200 MPa) and Ivobase CAD (Ivoclar Vivadent, Lichtenstein). Samples for mechanical/physical (n = 30) and samples for viscoelastic (n = 10) characterizations were cut from the blocks. Flexural strength (σ_f ), elastic modulus (E_f ), hardness, density (ρ), flexural deformation at maximal flexural stress, flexural load energy (U_r ) and viscoelastic properties (E', E'', Tanδ, T_g ) were analyzed using one-way ANOVA (α = 0.05), Scheffé multiple means comparisons (α = 0.05) and Weibull statistics (for σ_f ). SEM images of the fractured surfaces were obtained.

RESULTS

E_f , E', E'' and density of HP polymerized Probase hot were significantly higher than conventional heat polymerized Probase Hot, whereas T_g was significantly lower and σ_f , Tanδ, hardness, flexural deformation at maximal flexural stress, U_r were not significantly different. The highest values for σ_f , flexural deformation at maximal flexural stress, U_r and Weibull modulus were obtained with Ivobase CAD.

CONCLUSION

HP polymerization does not significantly increase the mechanical properties of denture base resins.