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 (Wsp), mass sorption (Ms%), and % expansion within the tested groups reached equilibrium within 180 days. A noticeable difference was observed in groups Z and E for (Wsp)/(Ms%) 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 (Wsl)/mass desorption (Md%) 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.

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

Statement of Problem: Polymethyl methacrylate (PMMA) denture resins commonly fracture as a result of the denture being dropped or when in use due to heavy occlusal forces. Purpose: To investigate the effects of E-glass fibre, ZrO2 and TiO2 nanoparticles at different concentrations on the fracture toughness and impact strength of PMMA denture base. Materials and Methods: To evaluate fracture toughness (dimensions: 40 × 8 × 4 mm3; n = 10/group) and impact strength (dimensions: 80 × 10 × 4 mm3; n = 12/group), 286 rectangular tested specimens were prepared and divided into four groups. Group C consisted of the PMMA specimens without any filler (control group), while the specimens in the remaining three groups varied according to the concentration of three filler materials by weight of PMMA resin: 1.5%, 3%, 5%, and 7%. Three-point bending and Charpy impact tests were conducted to measure the fracture toughness and impact strength respectively. Scanning Electron Microscope (SEM) was utilised to examine the fractured surfaces of the specimens after the fracture toughness test. One-way analysis of variance (ANOVA) followed by Tukey post-hoc tests were employed to analyse the results at a p ≤ 0.05 significance level. Results: Fracture toughness of groups with 1.5 and 3 wt.% ZrO2, 1.5 wt.% TiO2, and all E-glass fibre concentrations were significantly higher (p < 0.05) than the control group. The samples reinforced with 3 wt.% ZrO2 exhibited the highest fracture toughness. Those reinforced with a 3 wt.%, 5 wt.%, and 7 wt.% of E-glass fibres had a significantly (p < 0.05) higher impact strength than the specimens in the control group. The heat-cured PMMA modified with either ZrO2 or TiO2 nanoparticles did not exhibit a statistically significant difference in impact strength (p > 0.05) in comparison to the control group. Conclusions: 1.5 wt.%, 3 wt.% of ZrO2; 1.5 wt.% ratios of TiO2; and 1.5 wt.%, 3 wt.%, 5 wt.%, and 7 wt.% of E-glass fibre can effectively enhance the fracture toughness of PMMA. The inclusion of E-glass fibres does significantly improve impact strength, while ZrO2 or TiO2 nanoparticles did not.

Chemical Characterisation of Silanised Zirconia Nanoparticles and Their Effects on the Properties of PMMA-Zirconia Nanocomposites.

Objectives: The objective of this study was to investigate the mechanical properties of high-impact (HI) heat-cured acrylic resin (PMMA) reinforced with silane-treated zirconia nanoparticles. Methods: Forty-five PMMA specimens reinforced with zirconia were fabricated and divided into three groups: Pure HI PMMA (control group), PMMA reinforced with 3 wt.% of non-silanised zirconia nanoparticles and PMMA reinforced with 3 wt.% of silanised zirconia nanoparticles. Silanised and non-silanised zirconia nanoparticles were analysed with Fourier Transform Infrared (FTIR) Spectroscopy. For measuring the flexural modulus and strength, a Zwick universal tester was used, and for surface hardness, a Vickers hardness tester were used. Furthermore, raw materials and fractured surfaces were analysed using Scanning Electron Microscopy (SEM). A one-way ANOVA test followed by a post-hoc Bonferroni test was employed to analyse the data. Results: The results showed that the mean values for flexural strength (83.5 ± 6.2 MPa) and surface hardness (20.1 ± 2.3 kg/mm2) of the group containing 3 wt.% treated zirconia increased significantly (p < 0.05) in comparison to the specimens in the group containing non-treated zirconia (59.9 ± 7.1 MPa; 15.0 ± 0.2 kg/mm2) and the control group (72.4 ± 8.6 MPa; 17.1 ± 0.9 kg/mm2). However, the group with silanised zirconia showed an increase in flexural modulus (2313 ± 161 MPa) but was not significantly different (p > 0.05) from the non-silanised group (2207 ± 252 MPa) and the control group (1971 ± 235 MPa). Conclusion: Silane-treated zirconia nano-filler improves the surface hardness and flexural strength of HI PMMA-zirconia nanocomposites, giving a potentially longer service life of the denture base.

Flexural Strength and Hardness of Filler-Reinforced PMMA Targeted for Denture Base Application.

The aim of this work was to evaluate the flexural strength and surface hardness of heat-cured Polymethyl methacrylate (PMMA) modified by the addition of ZrO2 nanoparticles, TiO2 nanoparticles, and E-glass fibre at different wt.% concentrations. Specimens were fabricated and separated into four groups (n = 10) to measure both flexural strength and surface hardness. Group C was the control group. The specimens in the remaining three groups differed according to the ratio of filler to weight of PMMA resin (1.5%, 3%, 5%, and 7%). A three-point bending test was performed to determine the flexural strength, while the surface hardness was measured using the Vickers hardness. Scanning Electron Microscope (SEM) was employed to observe the fractured surface of the specimens. The flexural strength was significantly improved in the groups filled with 3 wt.% ZrO2 and 5 and 7 wt.% E-glass fibre in comparison to Group C. All the groups displayed a significantly higher surface hardness than Group C, with the exception of the 1.5% TiO2 and 1.5% ZrO2 groups. The optimal filler concentrations to enhance the flexural strength of PMMA resin were between 3-5% ZrO2, 1.5% TiO2, and 3-7% E-glass fibre. Furthermore, for all composites, a filler concentration of 3 wt.% and above would significantly improve hardness.

Impact of Peracetic Acid on the Dynamic Cyclic Fatigue of Heat-Treated Nickel-Titanium Rotary Endodontic Instrument.

Peracetic acid (PAA) is widely used as a sterilizing/disinfecting agent, and, in endodontics, it has been introduced as a promising irrigant in root canal treatment. It has been used at different concentrations to achieve various functions. However, endodontic instruments in contact with PAA of a certain concentration may affect their fatigue resistance. Therefore, the aim of this study was to investigate the impact of PAA on the cyclic fatigue resistance of three commercial heat-treated nickel-titanium (NiTi) rotary files. Three types of heat-treated NiTi rotary files were selected: One Curve (OC), ProTaper Gold (PTG), and Wave One Gold (WOG). Each type was divided into three subgroups (n = 6 for each file type): (1) untreated instruments; (2) files immersed in 0.002% PAA; and (3) files immersed in 0.35% PAA. The performance of each file type was tested in a simulated canal. The number of cycles to fracture (NCF) was determined to assess cyclic fatigue resistance of the files. Independent sample t-test was applied to compare each treated file within a subgroup with its respective control group, and one-way ANOVA was used for comparison among the main groups. All types of tested files revealed a significant decline in the cyclic fatigue resistance after exposure to 0.002% PAA except the PTG (P=0.209). After exposure of the files to a higher concentration (0.35% PAA), a dramatic reduction was demonstrated by all the groups. Before and after exposure of the files to PAA, PTG displayed the highest cyclic fatigue resistance, followed by the WOG, while the OC showed the lowest resistance. Exposure of heated-treated NiTi files to PAA in a relatively high or low concentration adversely affects the cyclic fatigue resistance. The PTG files demonstrated the best performance among the tested types and can be disinfected with 0.002% PAA for clinical purpose.

Assessing Tensile Bond Strength Between Denture Teeth and Nano-Zirconia Impregnated PMMA Denture Base.

PURPOSE: This study evaluated tensile bond strength (TBS) between anterior acrylic teeth and denture bases made of high-impact heat-cured acrylic resin (HI PMMA) impregnated with zirconia nanoparticles. MATERIALS AND METHODS: A total of 30 specimens (each specimen containing a set of six upper anterior teeth) were fabricated from HI PMMA denture base acrylic resin reinforced with different weight concentrations of zirconia nanoparticles: 0% (control), 1.5%, 3%, 5%, 7% and 10%. TBS was tested according to a British standard (BS EN ISO 22112: 2017). A one-way analysis of variance (ANOVA) was employed with a Tukey post-hoc test. RESULTS: TBS values between the anterior teeth (central and lateral incisors and canine) and HI-PMMA denture base groups containing 7 wt.% (261.5 ± 66.0 N, 172.5 ± 57.4 N and 271.9 ± 86.3 N) and 10 wt.% (332.1 ± 122.9 N, 165.4 ± 48.7 N and 301.6 ± 73.2 N) zirconia were significantly lower compared to the control group (645.4 ± 84.8 N, 306.1 ± 81.6 N and 496.7 ± 179.1 N) and the other nanocomposite groups. However, TBS values for HI PMMA with 1.5 wt.% (534.4 ± 115.3 N, 304.7 ± 86.4 N, 514.0 ± 143.2 N), 3 wt.% (685.7 ± 159.6 N, 281.1 ± 78.3 N, 462.6 ± 122.1 N) and 5 wt.% (514.5 ± 134.3 N, 229.8 ± 67.3 N, 387.2 ± 99.4 N) zirconia showed slightly lower values than that of the control group but these were not significant. Failure modes between the teeth and denture base nanocomposites were predominantly cohesive fractures, which were clinically acceptable according to the Standard. CONCLUSION: The addition of zirconia nanoparticles to HI PMMA denture base at high concentration (7 wt.% and 10 wt. %) significantly (p<0.05) reduced the bonding strength for all types of anterior teeth compared to the control group.

Effect of Cleansers on the Colour Stability of Zirconia Impregnated PMMA Bio-Nanocomposite.

Exposure of denture base acrylic resins to the oral environment and storage media for extended periods of time results in colour change due to changes in the properties of the material. The purpose of this in vitro study was to assess the colour stability of high-impact heat-polymerized denture base acrylic resin (HI PMMA) impregnated with zirconia nanoparticles after storage in distilled water (DW) and denture cleaners such as Steradent (STD) and Milton (MIL) for 180 days. Ninety specimens of PMMA + Zirconia nanocomposite with varying nanoparticle concentrations (1.5 wt.%, 3.0 wt.%, 5.0 wt.%, 7.0 wt.% and 10 wt.%) were prepared with a diameter and thickness of 25 ± 1.0 mm × 2 ± 0.1 mm and divided into six groups, while each group was further divided into three subgroups: storage in DW (control), STD and MIL. Colour changes were measured with a Minolta Chroma Meter (Minolta, Osaka, Japan), and assessed using the CIE L*a*b* colorimetric system. Data were statistically analysed for colour change with Friedman's Two-way and Kruskal-Wallis tests at a pre-set alpha value level of 0.05. The colour change (ΔΕ) exhibiting significant differences were found among all groups immersed in denture cleaners, and all values increased with time. According to the National Bureau of Standards, the control group displayed the lowest colour change value (ΔΕ = 1.22), and the highest value was for 10 wt.% ZrO2 while stored in MIL (ΔΕ = 6.07). The values of colour change for storage in water ranged from 0.49 (control) to 1.82 (10 wt.% ZrO2). The colour change value for the composite group containing 3 wt.% zirconia was clinically acceptable. However, high concentrations of denture cleaners should be avoided, and the shortest cleaning time is recommended to improve the clinical life of the nanocomposite denture base.

Long-Term Sorption and Solubility of Zirconia-Impregnated PMMA Nanocomposite in Water and Artificial Saliva.

Exposure of denture base acrylic resins to the oral environment and storage media for extended periods of time results in sorption of saliva or water, leading to a reduction in physical properties and thus clinical service life. The purpose of this in vitro study was to assess the sorption and solubility of high-impact heat-polymerised denture base acrylic resin (HI PMMA) impregnated with zirconia nanoparticles after being stored for 180 days in distilled water (DW) and artificial saliva (AS). The specimens were divided into six groups for each storage medium, according to the concentration of zirconia nanoparticles (0, 1.5, 3.0, 5.0, 7.0, and 10.0 wt.%). Data were statistically analysed for sorption and solubility using one-way and two-way ANOVA statistical tests. Sorption in DW and AS for all groups containing zirconia showed sorption values lower than the control group at 90 days, though not significantly different (p > 0.05) compared to the control group. For both the DW and AS groups, the lowest solubility value was measured in the group containing 3 wt.% zirconia, however, there was no significant difference compared to the control group except when observing 10 wt.% zirconia in AS, which showed a significantly higher solubility (p < 0.05). High-impact PMMA, impregnated with low concentrations of ZrO2, showed the lowest sorption and solubility in both media, but was not significantly different compared to pure HI PMMA.

Evaluation of Equivalent Flexural Strength for Complete Removable Dentures Made of Zirconia-Impregnated PMMA Nanocomposites.

High-impact (HI) polymethyl methacrylate (PMMA), obtained from modification of conventional PMMA, is commonly used in prosthodontics as a denture base material for improved impact resistance. However, it suffers from poor flexural strength properties. The aim of this study was to investigate the flexural strength of complete removable dentures made of HI heat-polymerised PMMA resin reinforced with zirconia nanoparticles at two different concentrations. The effect of fatigue loading on the flexural strength behaviour of the dentures was also investigated. A total of 30 denture specimens were fabricated from PMMA with different concentrations of zirconia nanoparticles: 0 (control), 3, and 5 wt.%. Ten specimens in each group were divided into two subgroups, with five specimens in each, to conduct both flexural strength and fatigue loading test of each of the subgroups. Fatigue loading was applied on the dentures using a mastication simulator and equivalent flexural strength was calculated with data from bending tests with and without fatigue cyclic loading. One-way analysis of variance (ANOVA) of the test data was conducted with the Bonferroni significant difference post-hoc test at a preset alpha value of 0.05. Paired t-test was employed to identify any difference between the specimens with and without the application of fatigue loading. The fractured surface of the denture specimens was examined with a scanning electron microscope (SEM). The bending tests demonstrated that the mean equivalent flexural strength of reinforced HI PMMA denture specimens with 5 wt.% zirconia nanoparticles increased significantly (134.9 ± 13.9 MPa) compared to the control group (0 wt.%) (106.3 ± 21.3 MPa) without any fatigue loading. The mean strength of the dentures with PMMA +3 wt.% zirconia also increased, but not significantly. Although the mean strength of all specimen groups subjected to fatigue loading slightly decreased compared to that of the specimen groups without any fatigue cyclic loading, this was not statistically significant. Denture specimens made of HI heat-polymerised PMMA reinforced with 5 wt.% zirconia nanoparticles had significantly improved equivalent flexural strength compared to that made of pure PMMA when the specimens were not subjected to any prior fatigue cyclic loading. In addition, the application of fatigue cyclic loading did not significantly improve the equivalent flexural strengths of all denture specimen groups. Within the limitations of this study, it can be concluded that the use of zirconia-impregnated PMMA in the manufacture of dentures does not result in any significant improvement for clinical application.

Investigating the Mechanical Properties of ZrO2-Impregnated PMMA Nanocomposite for Denture-Based Applications.

Acrylic resin PMMA (poly-methyl methacrylate) is used in the manufacture of denture bases but its mechanical properties can be deficient in this role. This study investigated the mechanical properties (flexural strength, fracture toughness, impact strength, and hardness) and fracture behavior of a commercial, high impact (HI), heat-cured denture base acrylic resin impregnated with different concentrations of yttria-stabilized zirconia (ZrO2) nanoparticles. Six groups were prepared having different wt% concentrations of ZrO2 nanoparticles: 0% (control), 1.5%, 3%, 5%, 7%, and 10%, respectively. Flexural strength and flexural modulus were measured using a three-point bending test and surface hardness was evaluated using the Vickers hardness test. Fracture toughness and impact strength were evaluated using a single edge bending test and Charpy impact instrument. The fractured surfaces of impact test specimens were also observed using a scanning electron microscope (SEM). Statistical analyses were conducted on the data obtained from the experiments. The mean flexural strength of ZrO2/PMMA nanocomposites (84 ± 6 MPa) at 3 wt% zirconia was significantly greater than that of the control group (72 ± 9 MPa) (p < 0.05). The mean flexural modulus was also significantly improved with different concentrations of zirconia when compared to the control group, with 5 wt% zirconia demonstrating the largest (23%) improvement. The mean fracture toughness increased in the group containing 5 wt% zirconia compared to the control group, but it was not significant. However, the median impact strength for all groups containing zirconia generally decreased when compared to the control group. Vickers hardness (HV) values significantly increased with an increase in ZrO2 content, with the highest values obtained at 10 wt%, at 0 day (22.9 HV0.05) in dry conditions when compared to the values obtained after immersing the specimens for seven days (18.4 HV0.05) and 45 days (16.3 HV0.05) in distilled water. Incorporation of ZrO2 nanoparticles into high impact PMMA resin significantly improved flexural strength, flexural modulus, fracture toughness and surface hardness, with an optimum concentration of 3-5 wt% zirconia. However, the impact strength of the nanocomposites decreased, apart from the 5 wt% zirconia group.