Assessing Fracture Toughness and Impact Strength of PMMA Reinforced with Nano-Particles and Fibre as Advanced Denture Base Materials

Development and characterization of 3D-printed denture base resin composites having self-healing potential

OBJECTIVE

This study aims to develop and characterize 3D-printed denture resin composites containing self-healing polyurea formaldehyde (PUF) microcapsules (TEGDMA as the core healing agent) for arresting microcracks formation and enhancing the mechanical durability of 3D-printed dentures.

METHODS

The PUF microcapsules containing TEGDMA as core material were synthesized in oil-in-water emulsion and characterized for size, surface morphology and thermal stability. 3D-printed denture base resin with 0, 5, 15, and 25 wt% content of the synthesized PUF were printed and evaluated by degree of conversion, surface morphology, topography, surface hardness, flexural strength, fracture toughness, self-healing efficiency, and fluorescent microscopic visualization of the microcracks' self-healing event through the in-situ release of rhodamine B labelled healing agent from ruptured PUF microcapsules inside the resin matrices.

RESULTS

As compared to the control, a slight decrease was observed in the degree of conversion, surface hardness and flexural strength of the 3D-printed denture base composite modified with the PUF microcapsules. Results demonstrated that an increase in the microcapsule content significantly (p ≤ 0.05) enhances the fracture toughness and self-healing efficiency. The HPLC results analysis of the experimental groups demonstrated a controlled release profile of healing agent over time with the maximum release on day 7. The microscopic visualization findings demonstrated the successful encapsulation and intentional triggered release of the rhodamine B. labelled healing agent in the crack plane.

SIGNIFICANCE

The 3D-printed denture base resin composites modified with the PUF microcapsules showed a significant potential for microcrack self-healing and enhanced fracture toughness based on the content (wt%) of microcapsules.

Effects of 5 Nanosilica Concentrations and Humid Environments at 6 Different pH Levels on Fracture Toughness and Moisture Absorption of Dental Polymethyl Methacrylate Resin‎ Reinforced With Silica Nanoparticles: An Explorative Experimental Scanning Electron Microscopy Study

INTRODUCTION

No study has assessed the effects of nanosilica within polymethyl methacrylate (PMMA) resin and environmental pH on resin's fracture resistance and moisture absorption.

METHODS

A total of 90 specimens were divided into 30 subgroups of three, as per the ASTM D5045 standard: five groups of nanosilica percentages (0%/2%/5%/7%/10%), each ‎divided into six subgroups of pH levels (pH = 5/6/7/8/9, + "dry" control). The specimens were prepared by mixing silica nanoparticles with PMMA powder in a vacuum mixer. Then, the specimens were mixed with a diluent liquid (TEGDMA) according to the manufacturer's instructions. For each of the five weight percentages, 36 samples were produced. The 18 specimens in each group were randomly divided into six subgroups of pH levels. The specimens were kept in containers of liquid at different pH levels at room temperature for 1 week. Their before- and after-storage weights were recorded to calculate moisture absorption. The fracture resistance test was performed (ASTM D5045 standard) using the three-point bending method. Scanning electron microscopy was performed. Data were analyzed.

RESULTS

Both nanosilica extents and pH levels significantly affected the fracture toughness with a significant interaction (p < ‎‎0.00001). All post hoc comparisons of different pH levels (except pH= 5 vs. 6) were significant (p < ‎‎0.0001). All post hoc comparisons of different nanosilica concentrations were significant (p < ‎‎0.0001). Both nanosilica extents and pH levels significantly influenced the fracture toughness with a significant interaction (p < ‎‎0.00001). All post hoc comparisons of different pH levels and also between different nanosilica concentrations were significant (p < ‎‎0.0001). The correlation between moisture absorption and fracture toughness was significant (R = -0.382, p = 0.0009).

CONCLUSIONS

Fracture toughness decreases when placed in humid and acidic environments. Also, the samples that were placed in a humid environment suffered a brittle fracture. Increasing silica nanoparticles improved fracture toughness (becoming optimal at 5 wt% nanosilica).

OBJECTIVE AND MATERIALS

The objective of this study was to investigate the fracture toughness of dental samples made of PMMA reinforced with various percentages of nanosilica at various pH levels. For this purpose, dental resins with various amounts of nanosilica were placed in moist media at different pH values ranging from 5 to 9 (mimicking the normal pH range of the human mouth).

Evaluation of the Bond Strength between the Acrylic Teeth and Reinforced or Non-reinforced Complete Denture Base

Objective

The aim of this study was to examine whether the method of surface treatment of the acrylic teeth and reinforcement of the denture base (carbon fibers) affect the reduction of stress concentration for gap initiation at the interface of acrylic teeth and denture base as a measure of bond strength.

Materials and methods

Samples of cross-sections of acrylic teeth and denture base were isolated from four pairs of complete acrylic dentures (with and without reinforcement of the denture base) and were subsequently subjected to compressive loading in a universal testing machine simulating two different occlusions. Selected groups of acrylic teeth (central incisors, first premolars, and first molars) from complete dentures were treated in various ways (untreated, mechanical, chemical, and mechanical-chemical). The gap size at the interface of acrylic tooth and denture base was measured using a light inverted microscope on selected acrylic teeth of individual quadrants. The one-way analysis of variance was used to investigate the influence of denture base reinforcement and different methods of surface treatment of the acrylic tooth on bond strength at the level of statistical significance of p ≤ 0.001.

Results

Microscopic analysis of gap size measured at five selected points at the interface between the acrylic teeth and the base of the complete denture ranged from 40 to 144 micrometers. The one-way analysis of variance showed a statistically significant difference between the arithmetic means of the measured gap sizes concerning different methods of surface treatment of the acrylic teeth.

Conclusion

The fracture strength, or load-bearing capacity, of complete dentures reinforced with carbon fibers was increased compared to complete dentures with non-reinforced bases. Reduction in gap size at the interface between the acrylic teeth and the base of complete dentures was influenced by the mechanical-chemical treatment of the lower surface of acrylic teeth, while reinforcement of the complete denture base with carbon fibers had no effect on the bond strength.

Mapping the research landscape of nanoparticles and their use in denture base resins: a bibliometric analysis

BACKGROUND

Nanoparticles are increasingly used in dentistry for various applications, including enhancing the mechanical properties of denture base resins. This study aimed to comprehensively review and analyze the research landscape of nanoparticles and their effect on the flexural strength of denture base resins to identify key research areas and trends and to highlight the importance of collaboration between authors and institutions.

METHODS

A Bibliometric Analysis was conducted using the Keywords "Nanoparticle*" AND "Denture*" OR "CAD/CAM." The literature search from the WOS database was restricted to the publication years 2011 to 2022.

RESULTS

Key findings encompass an increase in research publications but a decline in citations. Saudi Arabia, China, and Iraq led this research, with specific institutions excelling. Notable journals with high impact factors were identified. Authorship patterns show variations in citation impact. Additionally, keyword analysis revealed that current research trends offer insights into influential authors and their networks.

CONCLUSIONS

The analysis of nanoparticles and denture base resins reveals a dynamic and evolving landscape that emphasizes the importance of collaboration, staying current with research trends, and conducting high-quality research in this ever-evolving domain.

A biomechanical reinforcement of PMMA denture base material with sericin and fibroin: A preliminary screening study

BACKGROUND

Polymethyl methacrylate (PMMA) is a commonly used denture base material, but susceptibility to fracture under functional loading remains a challenge.

OBJECTIVE

This preliminary screening study aims to investigate the potential of sericin and fibroin as reinforcing agents in the PMMA denture base material.

METHODS

The flexural and impact strengths of PMMA incorporated with 0.01% sericin, and 0.01% each of sericin and fibroin, were evaluated. The control group consisted of PMMA without any additives. The maximum load and energy required to break the samples were measured. Statistical analysis was performed using one-way ANOVA test and Scheffe Post Hoc tests to compare mean values between subgroups.

RESULTS

The results indicated significant improvement in the flexural and impact strengths of PMMA with the addition of sericin and fibroin. The subgroups with 0.01% sericin, and 0.01% each of sericin and fibroin, demonstrated higher mean values in load and energy measurements compared to the control group. The statistical analysis confirmed the significance of these findings.

CONCLUSION

The addition of 0.01% sericin and 0.01% each of sericin and fibroin to PMMA denture-based resin material significantly increases its flexural and impact strengths. These preliminary findings suggest the potential of sericin and fibroin as effective reinforcing agents in PMMA denture base materials, thereby enhancing their biomechanical properties.

Evaluating the Translucency, Surface Roughness, and Cytotoxicity of a PMMA Acrylic Denture Base Reinforced with Bioactive Glasses

The colonisation of the surface of removable acrylic dentures by various types of microorganisms can lead to the development of various diseases. Therefore, the creation of a bioactive material is highly desirable. This study aimed to develop a denture base material designed to release bioactive ions into the oral environment during use. Four types of bioactive glasses (BAG)-S53P4, Biomin F, 45S5, and Biomin C-were incorporated into the PMMA acrylic resin, with each type constituting 20 wt.% (10 wt.% non-silanised and 10% silanised) of the mixture, while PMMA acrylic resin served as the control group. The specimens were subsequently immersed in distilled water, and pH measurements of the aqueous solutions were taken every seven days for a total of 38 days. Additionally, surface roughness and translucency measurements were recorded both after preparation and following seven days of immersion in distilled water. The cytotoxicity of these materials on human fibroblast cells was evaluated after 24 and 48 h using Direct Contact and MTT assays. Ultimately, the elemental composition of the specimens was determined through energy-dispersive X-ray (EDX) spectroscopy. In general, the pH levels of water solutions containing BAG-containing acrylics gradually increased over the storage period, reaching peak values after 10 days. Notably, S53P4 glass exhibited the most significant increase, with pH levels rising from 5.5 to 7.54. Surface roughness exhibited minimal changes upon immersion in distilled water, while a slight decrease in material translucency was observed, except for Biomin C. However, significant differences in surface roughness and translucency were observed among some of the BAG-embedded specimens under both dry and wet conditions. The composition of elements declared by the glass manufacturer was confirmed by EDX analysis. Importantly, cytotoxicity analysis revealed that specimens containing BAGs, when released into the environment, did not adversely affect the growth of human gingival fibroblast cells after 48 h of exposure. This suggests that PMMA acrylics fabricated with BAGs have the potential to release ions into the environment and can be considered biocompatible materials. Further clinical trials are warranted to explore the practical applications of these materials as denture base materials.

Controllable One-Step Assembly of Uniform Liquid Crystalline Block Copolymer Cylindrical Micelles by a Tailored Nucleation-Growth Process and Their Application as Tougheners

The fabrication of uniform cylindrical nanoobjects from soft materials has attracted tremendous research attention from both fundamental research and practical application points of view but has also posed outstanding challenges in terms of their preparation. Herein, we report a one-step method to assemble cylindrical micelles (CMs) with highly controllable lengths from a single liquid crystalline block copolymer by an in situ nucleation-growth strategy. By adjusting the assembly conditions, the lengths of the CMs are controlled from hundreds of nanometers to micrometers. Several influencing factors are systematically investigated to comprehensively understand the process. Particularly, the solvent quality is found determinative in either enhancing or suppressing the nucleation process to produce shorter and longer CMs, respectively. Taking advantage of this strategy, the lengths of CMs can be nicely controlled over a wide concentration range of four orders of magnitude. Lastly, CMs are produced on decent scales and applied as additives to dramatically toughen glassy plastic matrix, revealing an unprecedented length-dependent toughening effect.

The efficacy of reinforcement of glass fibers and ZrO2 nanoparticles on the mechanical properties of autopolymerizing provisional restorations (PMMA)

Objective

to investigate and compare the reinforcing effects of glass fibers (GFs) and ZrO2 nanoparticles at different ratios on the Flexural Strength (FS), Microhardness (MH), and Surface Roughness (SR) of autopolymerizing provisional PMMA.

Methods

A total of one hundred and twenty specimens of autopolymerizing PMMA were prepared for FS, MH, and SR tests and grouped as follows: no additives (control group), for the tested groups, different ratios of GFs and ZrO2 at 5% of autopolymerizing PMMA were incorporated. The ratios of GFs/ZrO2 nanoparticles were 0%-5%, 1%-4%, 2%-3%, 2.5%-2.5%, 3%-2%, 4%-1% and 5%-0% (n = 5). The FS was evaluated using the three-point bending test, MH was evaluated using the Vickers microhardness tester and SR was evaluated using a contact-type profilometer. Data were analyzed using ANOVA, Tukey's test, and Person correlation at 0.05 level of significance.

Results

The unreinforced group had the lowest FS, MH, and SR mean values followed by (0%GFs + 5% ZrO2), (1% GFs + 4% ZrO2), (2% GFs + 3% ZrO2), (2.5% GFs + 2.5% ZrO2), (3% GFs + 2% ZrO2), (4% GFs + 1% ZrO2) and (5% GFs + 0% ZrO2) which had the highest values.

Conclusion

Hybrid reinforcement with GFs, ZrO2 nanoparticles, or a combination of them effectively improved flexural strength and microhardness of autopolymerizing provisional PMMA that would create provisional restorations with extended clinical service. GFs demonstrated superior reinforcing effects compared to ZrO2 nanoparticles. However, reinforcement with 2.5-5% GFs increased the surface roughness for provisional restoration.

Effect of Adding Silver-Doped Carbon Nanotube Fillers to Heat-Cured Acrylic Denture Base on Impact Strength, Microhardness, and Antimicrobial Activity: A Preliminary Study

Poly (methyl methacrylate) (PMMA), is an acrylic polymer substance that is mostly used for denture base applications. The purpose of this laboratory study was to investigate the effect of adding 0.05 wt.% Ag-doped carbon nanotubes (CNT) to PMMA-based (PMMA and MMA) denture base material on the impact strength, microhardness, and antimicrobial activity. A total of 60 heat-cured acrylic resin specimens were prepared. The specimens were randomly divided into two main groups (n = 30/group), according to the powder used: (a) control group, using heat-cured PMMA; (b) treatment group, using a powder prepared by blending 0.05 wt.% silver-doped CNT nanoparticles with heat-cured PMMA. The impact strength, microhardness and anticandidal activity for each group were assessed via the Charpy, Vickers and agar diffusion tests, respectively (n = 10/test for each subgroup). Data were analyzed using independent-sample t-tests (p ≤ 0.05). The results of the impact strength test revealed that the treated heat-cured PMMA-MMA with Ag-doped CNT (2.2 kJ/mm²) was significantly higher than that of the control heat-cured PMMA (1.6 kJ/mm²). Similarly, the Vickers microhardness of the treatment group (52.7 VHN) was significantly higher than that of the control group (19.4 VHN). Regarding the agar diffusion test, after 24 h of incubation, the treated heat-cured PMMA with the Ag-doped CNT exhibited significantly higher anticandidal activity than that of the control group. Therefore, Ag-doped carbon nanotubes could be considered as promising fillers for the dental heat-cured acrylic resin to improve the resistance of the resultant denture against sudden fractures, scratching, and candida invasion.

Mechanical and Biocompatibility Properties of 3D-Printed Dental Resin Reinforced with Glass Silica and Zirconia Nanoparticles: In Vitro Study

This study aimed to assess the mechanical and biocompatibility properties of dental resin reinforced with different nanoparticle additives. Temporary crown specimens were 3D-printed and grouped based on nanoparticle type and amount, including zirconia and glass silica. Flexural strength testing evaluated the material's ability to withstand mechanical stress using a three-point bending test. Biocompatibility was tested using MTT and dead/live cell assays to assess effects on cell viability and tissue integration. Fractured specimens were analysed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) for fracture surface examination and elemental composition determination. Results show that adding 5% glass fillers and 10-20% zirconia nanoparticles significantly improves the flexural strength and biocompatibility of the resin material. Specifically, the addition of 10%, 20% zirconia, and 5% glass silica by weight significantly increases the flexural strength of the 3D-printed resins. Biocompatibility testing reveals cell viabilities greater than 80% in all tested groups. Reinforced 3D-printed resin holds clinical potential for restorative dentistry, as zirconia and glass fillers have been shown to enhance mechanical and biocompatibility properties of dental resin, making it a promising option for dental restorations. The findings of this study may contribute to the development of more effective and durable dental materials.

Dental Material Selection for the Additive Manufacturing of Removable Complete Dentures (RCD)

This research addresses the development of a formalized approach to dental material selection (DMS) in manufacturing removable complete dentures (RDC). Three types of commercially available polymethyl methacrylate (PMMA) grades, processed by an identical Digital Light Processing (DLP) 3D printer, were compared. In this way, a combination of mechanical, tribological, technological, microbiological, and economic factors was assessed. The material indices were calculated to compare dental materials for a set of functional parameters related to feedstock cost. However, this did not solve the problem of simultaneous consideration of all the material indices, including their significance. The developed DMS procedure employs the extended VIKOR method, based on the analysis of interval quantitative estimations, which allowed the carrying out of a fully fledged analysis of alternatives. The proposed approach has the potential to enhance the efficiency of prosthetic treatment by optimizing the DMS procedure, taking into consideration the prosthesis design and its production route.

Assessing the Antifungal Activity of a Soft Denture Liner Loaded with Titanium Oxide Nanoparticles (TiO2 NPs)

Aim: Soft denture lining materials are susceptible to be colonized by different microorganisms, especially by Candida albicans (C. albicans), causing denture-induced stomatitis. This study was designed to evaluate the effectiveness of incorporating titanium dioxide nanoparticles (TiO2 NPs) into a soft denture liner towards reducing microbial activity. Method: A total of 40 PEMA-TiO2 nanocomposites samples were fabricated by adding 0.0 wt.% (control), 1.0 wt.%, 1.5 wt.%, and 2 wt.% TiO2 NPs to a heat cured soft denture lining material (polyethyl methacrylate, PEMA). The prepared samples were divided into four groups (n = 10) according to the content of TiO2 NPs. The uniformity of TiO2 NPS distribution within the denture liner matrix was assessed using a Scanning Electron Microscope (SEM). The viable count of C. albicans was evaluated to test the antifungal resistance of the developed composite. Results: The SEM images showed fairly homogeneous dispersion, with patches of TiO2 NPs agglomeration within the PEMA matrix and an increasing concentration of NPs with higher NP content. The particle map and EDX analysis confirmed the evidence of the TiO2 NPs. The mean viable count results for the control (0.0 wt.%) and 1.0 wt.%, 1.5 wt.%, and 2 wt.% TiO2 groups were 139.80, 12.00, 6.20, and 1.00, respectively, with a significant difference from the control group (p < 0.05). The antifungal activity also increased with the increase in the concentration of TiO2 NPs. Conclusions: The addition of TiO2 NPs into a heat-cured soft denture liner provided antifungal activity as evidenced by the reduced colonization of C. albicans. The antimicrobial activity of the liner material increased with the increased concentration of TiO2 NPS.

Study of the radical polymerization mechanism and its application in the preparation of high-performance PMMA by reactive extrusion

In this study, the mechanism of radical polymerization was further explored by pre-dissolving different polymers and studying the kinetics of the bulk polymerization of methyl methacrylate (MMA) under shear-free conditions. Based on the analysis of the conversion and absolute molecular weight, it was found that, contrary to the shearing effect, the inert polymer with viscosity was the key factor to preventing the mutual termination of radical active species and reducing the termination rate constant k _t. Therefore, pre-dissolving the polymer could increase the polymerization rate and molecular weight of the system simultaneously, making the polymerization system enter the automatic acceleration zone faster and greatly reducing the generation of small molecular weight polymers, leading to a narrower molecular weight distribution. When the system entered the auto-acceleration zone, k _t decreased rapidly and greatly and entered the second steady-state polymerization stage. Then, with the increase in the polymerization conversion, the molecular weight gradually increased, while the polymerization rate gradually decreased. In shear-free bulk polymerization systems, k _t can be minimized and radical lifetimes maximized, but the polymerization system is at best a long-lived polymerization rather than a living polymerization. On this basis, by using MMA to pre-dissolve ultrahigh molecular weight PMMA and core-shell particles (CSR), the mechanical properties and heat resistance of the PMMA with pre-dissolved polymer obtained by reactive extrusion polymerization were better than for pure PMMA obtained under the same conditions. Compared with pure PMMA, the flexural strength and impact strength of PMMA with pre-dissolved CSR were up to 166.2% and 230.5%. With the same quality of CSR, the same two mechanical properties of the samples obtained by the blending method were just improved by 29.0% and 20.4%. This was closely related to the distribution of CSR in the pre-dissolved PMMA-CSR matrix with a distribution of spherical single particles 200-300 nm in diameter, which enabled PMMA-CSR to exhibit a high degree of transparency. This one-step process for realizing PMMA polymerization and high performance shows extremely high industrial application prospects.

Zirconia Nanoparticles as Reinforcing Agents for Contemporary Dental Luting Cements: Physicochemical Properties and Shear Bond Strength to Monolithic Zirconia

Nanofillers in resin materials can improve their mechanical and physicochemical properties. The present work investigated the effects of zirconia nanoparticles (NPs) as fillers in commercial dental luting cements. Two dual-cured self-adhesive composites and one resin modified glass ionomer (RMGI) luting cement were employed. Film thickness (FT), flexural strength (FS), water sorption (W_sp), and shear bond strength (SBS) to monolithic zirconia were evaluated according to ISO 16506:2017 and ISO 9917-2:2017, whereas polymerization progress was evaluated with FTIR. Photopolymerization resulted in double the values of DC%. The addition of 1% wt NPs does not significantly influence polymerization, however, greater amounts do not promote crosslinking. The sorption behavior and the mechanical performance of the composites were not affected, while the film thickness increased in all luting agents, within the acceptable limits. Thermocycling (TC) resulted in a deteriorating effect on all composites. The addition of NPs significantly improved the mechanical properties of the RMGI cement only, without negatively affecting the other cements. Adhesive primer increased the initial SBS significantly, however after TC, its application was only beneficial for RMGI. The MDP containing luting cement showed higher SBS compared to the RMGI and 4-META luting agents. Future commercial adhesives containing zirconia nanoparticles could provide cements with improved mechanical properties.

Medical and Dental Applications of Titania Nanoparticles: An Overview

Currently, titanium oxide (TiO₂) nanoparticles are successfully employed in human food, drugs, cosmetics, advanced medicine, and dentistry because of their non-cytotoxic, non-allergic, and bio-compatible nature when used in direct close contact with the human body. These NPs are the most versatile oxides as a result of their acceptable chemical stability, lower cost, strong oxidation properties, high refractive index, and enhanced aesthetics. These NPs are fabricated by conventional (physical and chemical) methods and the latest biological methods (biological, green, and biological derivatives), with their advantages and disadvantages in this epoch. The significance of TiO₂ NPs as a medical material includes drug delivery release, cancer therapy, orthopedic implants, biosensors, instruments, and devices, whereas their significance as a dental biomaterial involves dentifrices, oral antibacterial disinfectants, whitening agents, and adhesives. In addition, TiO₂ NPs play an important role in orthodontics (wires and brackets), endodontics (sealers and obturating materials), maxillofacial surgeries (implants and bone plates), prosthodontics (veneers, crowns, bridges, and acrylic resin dentures), and restorative dentistry (GIC and composites).

Impact of Polymerization Technique and ZrO2 Nanoparticle Addition on the Fracture Load of Interim Implant-Supported Fixed Cantilevered Prostheses in Comparison to CAD/CAM Material

ZrO₂ nanoparticles (ZNPs) have excellent physical properties. This study investigated the fracture load of implant-supported, fixed cantilevered prosthesis materials, reinforced with ZNPs and various polymerization techniques, compared with conventional and CAD/CAM materials. Sixty specimens were made from two CAD/CAM; milled (MIL) (Ceramill TEMP); and 3D-printed (NextDent Denture 3D+). Conventional heat-polymerized acrylic resin was used to fabricate the other specimens, which were grouped according to their polymerization technique: conventionally (HP) and autoclave-polymerized (AP); conventionally cured and reinforced with 5 wt% ZNPs (HPZNP); and autoclave reinforced with 5 wt% ZNPs (APZNP). The specimens were thermocycled (5000 cycles/30 s dwell time). Each specimen was subjected to static vertical loading (1 mm/min) using a universal Instron testing machine until fracture. Scanning electron microscopy was used for fracture surface analyses. The ANOVA showed significant fracture load differences between all the tested groups (p = 0.001). The Tukey post hoc tests indicated a significant difference in fracture load between all tested groups (p ˂ 0.001) except HP vs. HPZNP and AP vs. MIL. APZNP had the lowest mean fracture load value (380.7 ± 52.8 N), while MIL had the highest (926.6 ± 82.8 N). The CAD/CAM materials exhibited the highest fracture load values, indicating that they could be used in long-term interim prostheses. Autoclave polymerization improved fracture load performance, whereas ZrO₂ nanoparticles decreased the fracture load performance of cantilevered prostheses.

Effect of Different Solutions on the Colour Stability of Nanoparticles or Fibre Reinforced PMMA

This study aimed to evaluate the colour stability of polymethyl methacrylate (PMMA) denture base reinforced with ZrO2 nanoparticles, E-glass fibres, and TiO2 nanoparticles at various concentrations over 180-day storage in Steradent™ (STD) denture cleaner or coffee (CF). A total of 130 disc-shaped specimens were fabricated at various filler concentrations and divided into four main groups to measure the colour changes. Groups Z, T, and E consisted of PMMA reinforced with ZrO2 nanoparticles, TiO2 nanoparticles, or E-glass fibre, respectively, while Group C consisted of PMMA specimens without filler served as the control group (n = 10). The three reinforced groups were further subdivided according to the filler content (n = 10) added to the PMMA (1.5%, 3.0%, 5.0%, and 7.0% wt.%). Half of the specimens were stored in STD, while the other half was stored in CF for 180 days. A Minolta Chroma Meter was used to measure the colour changes (ΔE) at 7, 30, 90 and then 180 days. The results were assessed using two-way repeated-measures analysis of variance (RM-ANOVA) along with Bonferroni post hoc tests at a p ≤ 0.05 significance level. Significant different colour changes (ΔΕ) were observed between all tested groups and across different time points. TiO2-reinforced PMMA in coffee showed the lowest colour stability, while the E-glass fibre-reinforced PMMA in STD/CF showed the highest colour stability. Furthermore, coffee appeared to have the greatest impact on the CF change in comparison to the STD/CF. The results indicated that the filler type and concentration, type of solution, and length of storage all affected the colour stability of the tested specimens.

Dental Poly(methyl methacrylate)-Based Resin Containing a Nanoporous Silica Filler

Poly(methyl methacrylate) (PMMA)-based resins have been conventionally used in dental prostheses owing to their good biocompatibility. However, PMMA-based resins have relatively poor mechanical properties. In the present study, a novel nanoporous silica filler was developed and introduced into PMMA-based resins to improve their mechanical properties. The filler was prepared by sintering a green body composed of silica and an organic binder, followed by grinding to a fine powder and subsequent silanization. The filler was added to photocurable PMMA-based resin, which was prepared from MMA, PMMA, ethylene glycol dimethacrylate, and a photo-initiator. The filler was characterized by scanning electron microscopy (SEM), X-ray diffraction analysis, nitrogen sorption porosimetry, and Fourier transform infrared (FT-IR) spectroscopy. The PMMA-based resins were characterized by SEM and FT-IR, and the mechanical properties (Vickers hardness, flexural modulus, and flexural strength) and physicochemical properties (water sorption and solubility) were evaluated. The results suggested that the filler consisted of microparticles with nanopores. The filler at 23 wt % was well dispersed in the PMMA-based resin matrix. The mechanical and physicochemical properties of the PMMA-based resin improved significantly with the addition of the developed filler. Therefore, such filler-loaded PMMA-based resins are potential candidates for improving the strength and durability of polymer-based crown and denture base.

The Effect of Zirconium Dioxide (ZrO2) Nanoparticles Addition on the Mechanical Parameters of Polymethyl Methacrylate (PMMA): A Systematic Review and Meta-Analysis of Experimental Studies

The number of studies on the subject of effects of zirconium dioxide (ZrO2) nanoparticles addition on the mechanical parameters of polymethyl methacrylate (PMMA) is still very limited. Therefore, in this research, the authors wanted to assess PMMA modified with the nano-ZrO2 additive in terms of changes in flexural, impact and tensile strength values in relation to PMMA without such component. A systematic review and meta-analysis were performed to evaluate the effect of incorporating nano-ZrO2 into PMMA on individual types of material strength. The obtained numerical data were tabulated and analyzed in the search for percentage changes in those parameters. It was then calculated for each set and the procured model was examined using residual sum of squares (RSS) to assess the discrepancy between the data and the estimation model whilst mean absolute deviation (MAD) was employed to determine robustness. The results of the systematic review were composed of data obtained from individual studies presented in eight independent articles. Overall, the addition of nano-ZrO2 increases the flexural strength of the composite with the PMMA matrix depending on the size of the ZrO2 grains administered. Unfortunately, these conclusions are based on a very limited amount of research and require further verification, especially regarding tensile strength.

Behaviour of PMMA Resin Composites Incorporated with Nanoparticles or Fibre following Prolonged Water Storage

When PMMA denture base acrylics are exposed to oral environments for prolonged periods, the denture base absorbs water, which has a negative influence on the denture material and the degree to which the denture base will be clinically effective. This study assessed the water sorption, desorption, and hygroscopic expansion processes within PMMA denture-base resins reinforced with nanoparticles or fibre in comparison to the non-reinforced PMMA. The surfaces of the fillers were modified using a silane coupling agent (y-MPS) before mixing with PMMA. Group C consisted of specimens of pure PMMA whereas groups Z, T, and E consisted of PMMA specimens reinforced with ZrO₂, TiO₂ nanoparticles, or E-glass fibre, respectively. The reinforced groups were subdivided into four subgroups according to the percentage filler added to the PMMA resin by weight (1.5%, 3.0%, 5.0%, or 7.0%). Five specimens in disc shape (25 ± 1 mm × 2.0 ± 0.2 mm) were tested for each group. To assess water sorption and hygroscopic expansion, specimens from each group were individually immersed in water at 37 ± 1 °C for 180 days. The samples were then desorbed for 28 days at 37 ± 1 °C, to measure solubility. Water sorption and solubility were calculated using an electronic balance in accordance with ISO Standard 20795-1, and hygroscopic expansion was measured using a laser micrometre. Statistical analysis was undertaken at a p ≤ 0.05 significance level using a one-way ANOVA followed by Tukey post-hoc tests. The results demonstrated that the values of sorption (W_sp), mass sorption (M_s%), and % expansion within the tested groups reached equilibrium within 180 days. A noticeable difference was observed in groups Z and E for (W_sp)/(M_s%) compared to the Group C, but this was not significant. However, the difference between Group C and Group T for these measurements was significant. Non-significant differences also existed between each respective reinforced group and the control group in terms of hygroscopic expansion % values. During the 28-day desorption period, there were no differences in the values of solubility (W_sl)/mass desorption (M_d%) between Group C and each of the reinforced tested groups. The findings indicate that the inclusion of ZrO₂ nanoparticles or E-glass fibres does not increase the water solubility/sorption of the PMMA. However, modifying the PMMA with TiO₂ did significantly increase the water sorption level.