Significant Decrease In Flexural Strength Research Articles

Evaluation the Flexural Strength of Emax Cad and E_Max Press After Thermocycling Ageing

Aim: To investigate the impact of thermocycling ageing on the flexural strength of E-max cad and E-max press The objective of this research is to evaluate the impact of aging via various thermocycling protocols on the flexural strength of a feldspathic ceramic. Material and Methods: Thirty six bars of ceramic, ivoclar e max, with dimensions of 16×4×2 mm were utilized. Bars were distributed randomly into three groups (n=6) that were defined in accordance with the number of thermal cycles (TCy): G0-no TCy; G5000-5000 cycles of TCy, G10000-10 TCy. After aging, samples were subjected to a three-point bending test in a universal test machine with a speed of 1mm/min and a load of 1kgf until the catastrophic failure was reached. Results: Concerning the mechanical test, the following values of mean and standard deviation values (MPa), were obtained: G0cad (612.12± 83.16) ; G5000cad (445.44 ± 34.99); G10000cad (366.34± 41.30) and G0press (534.09±42.83) ;G5000press (428.68±17.40) and G10000press (382±38.49).Variance analysis of was conducted using the regression equation (p=0.387) and it showed that there was a significant correlation between the flexural strength and the thermal cycles number. Conclusion: One can conclude that aging in water per se through various temperature cycles numbers has an effect on the flexural strength of a feldspathic ceramic. The thermocycling of both type of lithium disilicate has negative effect on the flexural strength, Cad ceramic showed more significant decrease in flexural strength than press ceramic which was less negatively affected.

RETRACTED: The Effect of Treatment Temperature on Microstructure and Mechanical Behavior of a Fine-Grained YSZ–NiO(Ni) Anode Material

Reduction–oxidation (redox) cycling of a solid oxide fuel cell (SOFC) due to leakage of a fuel or standby and shutdown cycling is an issue that has attracted the attention of many research groups for a long time. The researchers mainly note the harmful effects of redox cycling on the microstructure of SOFC constituents and search for ways to mitigate or diminish them. The purpose of this study was to use reduction and oxidation stages in an appropriate mode as a positive preconditioning to improve redox cycling stability of Ni-containing SOFC anode materials. The redox treatment was applied to YSZ–NiO(Ni) anode substrate specimens at 600 °C and 800 °C. The mechanical tests (flexural strength, microhardness, and fracture toughness) were performed on these specimens and the results were compared to those for as-sintered and one-time reduced specimens. Microstructure and fracture surface morphology of material in corresponding modes were analyzed. The main findings were summarized as follows: (i) Redox treatment at 600 °C provides an increase in flexural strength and electrical conductivity of YSZ–NiO(Ni) anode cermets; (ii) the treatment at 800 °C causes formation of a gradient microstructure with lateral cracks that result in a significant decrease in flexural strength; (iii) the mode of redox treatment at 600 °C for 4 h in Ar–5% H2/air atmosphere provides an increase in flexural strength of YSZ–NiO(Ni) anode cermets (up to 127 ± 4 MPa), while electrical conductivity was provided at a comparatively high level (7 × 105 S/m).

Acid dissolution of ultrathin glass-ceramic and its correlation with flexural strength

Statement of problemWhen glass-ceramics are treated with hydrofluoric acid (HF), not only the area of application is affected but also other surfaces. Information regarding the correlation of the dissolution caused by HF and the flexural strength of the ceramic is lacking. PurposeThe purpose of this in vitro study was to investigate the effect of HF etching protocols on the flexural strength of 2 glass-ceramics, the correlation of their flexural strength with the internal and lateral dissolution, and the differences in Weibull characteristics concerning the etching protocols. Material and methodsSpecimens (4×12×0.3mm) of leucite-reinforced glass-ceramic—LEU (IPS Empress) and of lithium disilicate-reinforced glass-ceramic—LD (IPS e.max) were prepared. The specimens were divided into 5 groups (n=12) according to etching protocol: control—untreated; hydrofluoric acid (HF) 5% for 20 seconds (HF5%20s); HF5%60s; HF10%20s; and HF10%60s. Flexural strength was evaluated through 3-point bend testing. The fractured specimens were submitted to a morphological and metrical analysis of each pattern (LEU I–IV, LD I–III) on the lateral surface (LS) and of the dissolution areas (μm2) on the internal surface (IS) using a scanning electron microscopy (SEM) and a software program (FIJI). Flexural strength (MPa) values were analyzed by 1-way ANOVA, Bonferroni test, and Weibull and the correlation between flexural strength and dissolution by Pearson correlation coefficient (α=.05). ResultsANOVA revealed that the HF etching protocol was significant (P<.001) for LEU ceramic. When HF10%60s was applied, LEU showed Weibull characteristic strength (σθ) values lower than those of the other protocols. LD showed no difference in σθ and reliability (m) among the groups. The internal dissolution areas concerning LEU had a significant high negative correlation with the flexural strength (r=-0.6; P<.001). LEU-IV on the LS was the only pattern to show a significant decrease in flexural strength (r=-0.3, P<.05). ConclusionsSpecial care should be taken when applying hydrofluoric acid on glass-ceramic restorations. Protocols with higher hydrofluoric acid concentrations and longer application times were more related to greater internal areas of dissolution which reduced the flexural strength of leucite ceramics.

CAD-CAM Fabricated Denture Base Resins: In Vitro Investigation of the Minimum Acceptable Denture Base Thickness.

To investigate the influence of reducing material thickness on flexural properties of computer-aided design and computer-aided manufacturing (CAD-CAM) denture base resins. Four CAD-CAM denture base acrylic resin materials were selected; two were made via the subtractive method (AvaDent and IvoCad) and two were made with the additive method (FormLabs and NextDent). One heat-polymerized denture base material was used as a control. Specimens were fabricated with varying thicknesses (n = 10/group): 3.3 mm, 2.5 mm, 2 mm, or 1.5 mm. Flexural strength was evaluated via a three-point bending test. One- and two-way ANOVA were used for data analysis along with Tukey's post hoc comparison (α = 0.05). Reducing the thickness of materials made via the subtractive method did not influence flexural strength up to 2 mm (p > 0.05). However, the difference was significant at a 1.5 mm thickness (p ˂ 0.001). For materials made via the additive method, NextDent specimens had no significant decrease in flexural strength when the thickness was reduced to 2 mm (p = 0.58). FormLabs specimens showed a significant decrease (p ˂ 0.001), although the values of flexural strength were clinically acceptable. During testing, specimens manufactured via the additive method at a 1.5 mm thickness bent without fracturing and were therefore excluded. All materials showed a reduction in elastic modulus as the thickness decreased (p ˂ 0.001). Heat-polymerized, AvaDent, and IvoCad materials may be used for denture base fabrication at a minimum thickness of 1.5 mm. FormLabs and NextDent may be fabricated at a 2 mm minimum thickness, with clinically acceptable flexural properties.

Evaluation of the effects of different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC

Considering the studies on the effects of bleaching materials on properties of dental materials, The aims of this in vitro study were to evaluate the effects of two different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC. In this experimental in vitro study, 30 rectangular-shaped specimens (2 mm width × 2 mm height × 12 mm length) for flexural strength and 30 specimens (5 mm width × 5 mm length × 2 mm height) for microhardness tests were prepared from VITA ENAMIC blocks 12 × 14 × 18 mm. The specimens were polished using silicon-carbide sandpapers 400, 600, 800, 1200, 2000 under flow of water for 60 s each. The prepared samples for flexural strength and microhardness were divided into 3 subgroups (n = 10): control group (C), samples bleached using Opalescence PF 15% (B15), and samples bleached with Opalescence Xtra Boost 40% (B40). Flexural strength measurement was done using a universal testing machine, and microhardness test was done using Vickers. Data were analyzed using analysis of variance and post hoc tests and P < 0.05 was considered significant. The mean microhardness values of C, B15, and B40 groups were 255.46 ± 3.02, 249.86 ± 4.18, and 235.53 ± 4.61 kgf/mm2. Opalescence PF 15% and Opalescence Xtra Boost 40% affected microhardness of ENAMIC significantly (P < 0.05). The mean flexural strength values of C, B15, and B40 groups were 155.26 ± 16.13, 142.14 ± 11.52, and 133.39 ± 16.13 MPa. A significant decrease in flexural strength was found between the C and B40 groups (P = 0.007). However, the difference between flexural strength of the C and B15 groups was not significant (P > 0.05). Our study showed that both concentrations of bleaching agents can affect microhardness of ENAMIC. Moreover, hydrogen peroxide 40% has a negative effect on the flexural strength of ENAMIC.

Mechanical, Surface, and Optical Properties of PMMA Denture Base Material Modified with Azadirachta indica as an Antifungal Agent

The present study assessed the influence of Azadirachta indica (AI) powder on the mechanical, surface, and optical properties of heat-polymerized polymethyl methacrylate (PMMA) denture base material. A total of 300 heat-polymerized PMMA acrylic resin specimens were fabricated with dimensions of 65 × 10 × 3.3 ± 0.01 mm for flexural strength, 50 × 6 × 4 ± 0.01 mm for impact strength testing, and 15 × 2 ± 0.01 mm for surface roughness, hardness, and translucency testing. The specimens were distributed into six groups (n = 10) based on AI powder concentration: An unmodified control group and AI powder-modified groups with 0.5, 1, 1.5, 2, and 2.5 wt% of acrylic resin powder. Universal testing machine was used to measure flexural strength and Charpy's impact tester for impact strength. Surface roughness, hardness, and translucency were assessed using a profilometer, Vicker hardness tester, and spectrophotometer, respectively. One-way analysis of variance (ANOVA) and posthoc Scheffe's test were utilized; p ≤ 0.05 was considered a statistically significant difference. ANOVA showed no significant differences in terms of impact strength (p = 0.175) and surface roughness (p = 0.371), while significant differences were detected in terms of flexural strength, hardness, and translucency (p = 0.001). According to post hoc Scheffe's test, there was a significant decrease in flexural strength for AI groups (p < 0.001) except 0.5% AI group (p = 0.66), while impact strength had no significant difference between AI groups (p = 0.175). Hardness had an insignificant difference between control and modified groups (p>0.05), with exception of 2.5% AI group (p = 0.001). For translucency, a significant difference was found between control and all modified groups (p<0.05). Incorporating AI powder into heat-polymerized denture base material did not significantly alter impact strength, surface roughness, or hardness, except at 2.5% AI concentration, where hardness decreased. On the contrary, flexural strength and translucency were significantly affected. This study contributes to establishing a new approach for denture stomatitis disease treatment and prevention with the lowest adverse effect on denture properties.

Insight into the high temperature performances of alumina foams

Understanding the causal relations between the load situation and the lifetime at high temperature is extremely important in the application of alumina foams in high temperature industry. In this work, alumina foams were obtained at the sintering temperature of 1700 °C. The observation of microstructure of alumina foams showed that the structure of grains in the pore wall were of point contact structure. Key properties, such as flexural strength, elastic modulus, compressive creep, coefficient of thermal expansion and thermal conductivity of alumina foams were measured from room temperature to 1400 °C. The variation of the above properties of alumina foams as a function of temperature was investigated. The results showed that significant decrease in flexural strength and elastic modulus were observed when the temperature was over 1000 °C. Under this unique structure, minor liquid phase at the grain boundary could lead to the grain slip and further the remarkable decreases of the high temperature performance.

Is Micro X-ray Computer Tomography a Suitable Non-Destructive Method for the Characterisation of Dental Materials?

The aim of the study was to investigate the effect of X-rays used in micro X-ray computer tomography (µXCT) on the mechanical performance and microstructure of a variety of dental materials. Standardised bending beams (2 × 2 × 25 mm3) were forwarded to irradiation with an industrial tomograph. Using three-dimensional datasets, the porosity of the materials was quantified and flexural strength was investigated prior to and after irradiation. The thermal properties of irradiated and unirradiated materials were analysed and compared by means of differential scanning calorimetry (DSC). Single µXCT measurements led to a significant decrease in flexural strength of polycarbonate with acrylnitril-butadien-styrol (PC-ABS). No significant influence in flexural strength was identified for resin-based composites (RBCs), poly(methyl methacrylate) (PMMA), and zinc phosphate cement (HAR) after a single irradiation by measurement. However, DSC results suggest that changes in the microstructure of PMMA are possible with increasing radiation doses (multiple measurements, longer measurements, higher output power from the X-ray tube). In summary, it must be assumed that X-ray radiation during µXCT measurement at high doses can lead to changes in the structure and properties of certain polymers.

Antimicrobial properties, anti-virulence activities, and physico-mechanical characteristics of orthodontic adhesive containing C-phycocyanin: a promising application of natural products.

Antimicrobial orthodontic adhesives aim to reduce enamel demineralization, white spot lesions, and incipient tooth decay around bonded orthodontic brackets, but they should not imperil its mechanical properties. To evaluate the antimicrobial and physico-mechanical properties of acrylic containing different concentrations of C-phycocyanin on Streptococcus mutans, Lactobacillus acidophilus, and Candida albicans. The mechanical properties of acrylic resins were measured by flexural strength test after preparation of acrylic resin samples with concentrations of 1%, 2%, 5%, 7.5%, and 10% of C-phycocyanin. Then we evaluated the antimicrobial effects of acrylic resin containing the maximum concentration of C-phycocyanin with clinically acceptable flexural strength and the changes in expression of virulence factors. The highest and lowest means of flexural strength were obtained in acrylic resins containing 0% and 10% concentrations of C-phycocyanin at 50.2±4.5 and 30.1±3.3 MPa, respectively. Adding 1%, 2%, and 5% of C-phycocyanin showed no significant decrease in flexural strength (p>0.05). The maximum mean diameter of the growth inhibition zone was observed around discs containing 5% of C-phycocyanin. Until day 30 of the study, no microbial biofilms were formed on any acrylic disc. Only microbial biofilms of C. albicans were able to form on discs containing 5% of C-phycocyanin at 90 days. 5% C-phycocyanin could significantly decrease the expression levels of gtfB, hsp16, and ALS9 6.1-, 7.3-, and 3.9-fold, respectively. It can be concluded that the most acceptable concentration of C-phycocyanin in acrylic resin is 5% based on the results of flexural strength tests and antimicrobial activities of acrylic resin containing various concentrations of C-phycocyanin.

Assessment of Flexural Strength and Cytotoxicity of Heat Cure Denture Base Resin Modified with Titanium Dioxide Nanoparticles: An In Vitro Study

To assess the effect of titanium dioxide nanoparticles (NPs) on flexural strength and cytotoxicity of heat-cured polymethyl methacrylate (PMMA) resins. Sixty-four rectangular and 12 circular specimens were fabricated from metal dies to test flexural strength and cytotoxicity, respectively. The rectangular specimens were grouped into four (16 specimens each)-control group (Group 1), Group 2 with 3% TiO2, Group 3 with 5% TiO2, and Group 4 with 7% TiO2. They were tested for flexural strength using universal testing machine. The circular specimens were grouped into two (six specimens each)-control group and the test group which included the group which showed a highest flexural strength. They were tested for cytotoxicity using MTT assay. The analysis of variance (ANOVA) test was used to analyze the mean flexural strength of each group and Tukey's post hoc test, for pairwise group comparison (p <0.05). An independent sample t-test was used to analyze the cytotoxicity between the groups (p <0.05). The study showed that there was a significant decrease in the flexural strength from the control group (mean: 298.95), which reduced as the concentration of TiO2 increased. However, the toxicity reduced considerably from 24 hours to 7 days in both groups while the test group showed better cell viability (%) than the control group. The flexural strength of heat cure acrylic resin (modified and unmodified) was much higher than the recommended flexural strength for these resins. On adding TiO2 NPs, flexural strength decreased when compared to the control group. However, with 3% TiO2 NPs, there was no significant decrease in flexural strength as compared to conventional resins. TiO2 NP-modified heat cure acrylic resin showed less toxicity on day 1 and even lesser toxicity after 7 days indicating that it is biocompatible. TiO2 NPs incorporated at 3% concentration in denture base resin had less cytotoxicity and adequate flexural strength, to be used as a promising alternative to conventional denture base resin.

Degradation of hybrid aramid/glass/epoxy composites hydrothermally aged in distilled water

The main objective of this paper is to investigate the effects of distilled water on the flexural and impact properties of glass/aramid fibers reinforced epoxy resin hybrid laminated composites. Four different groups of composite samples ([G6]S, [A6]S, [G3A3]S, [A3G3]S) were produced by the vacuum infusion method (VARIM), and treated with the distilled water at a temperature of 25 and 70°C for 1000 h. Mechanical tests were carried out under three different conditions, dry, wet, and re-dried. The mass gain ratio of the samples was examined for different periods. The fracture surfaces of the samples were examined using SEM. Results indicated that water intake of all composite samples followed as Fickian-like behavior. The stacking sequence of hybrid composite showed a major effect on water absorption features. The distilled water treatment caused a significant decrease in flexural strength, impact strength of all groups. Reduction of flexural strength and impact strength were increased as the temperature was increased for both impact tests.

Effect of amylase activity on mechanical properties of dental composite resin

The purpose of this study was to investigate the effect of amylase activity on the mechanical properties of three dental composite resin (Filtek Z350; Filtek Z250 and Polofil Supra). The specimens were immersed in amylase solution at four different activities (25, 50, 100 and 200 KIU/L) with an artificial saliva solution (AS) as a control. The flexural strength (FS) and elastic modulus (EM) were determined in a three-point bending test after immersion for periods up to 12 months. In addition, surface roughness and surface morphology also determined. The FS of Filtek Z350 reaching the lowest level of 67.86 MPa after AS immersion for one year. There was a general trend for FS to decrease following immersion in AS for all the tested materials. However, the amylase groups did not undergo a significant decrease in FS and EM, and there was a slight increase in FS and EM for Polofil Supra.

An experimental study on hydrothermal degradation of cubic-containing translucent zirconia.

PURPOSEThe aims of this study were to investigate mechanical properties and hydrothermal degradation behaviour of the cubic-containing translucent yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP).MATERIALS AND METHODSFour groups of Y-TZP (T, ST, XT, and P), containing different amount of cubic crystal, were examined. Specimens were aged by autoclaving at 122℃ under 2 bar pressure for 8 h. Phase transformation was analyzed using X-ray diffraction (XRD) to measure phase transformation (t→m). Kruskal-Wallis test was used to determine the difference. Surface hardness, biaxial flexural strength, and fracture toughness in values among the experimental groups and verified with Wilcoxon matched pairs test for hardness values and Mann Whitney U for flexural strength and fracture toughness.RESULTSXRD analysis showed no monoclinic phase in XT and P after aging. Only Group T showed statistically significant decreases in hardness after aging. Hydrothermal aging showed a significant decrease in flexural strength and fracture toughness in group T and ST, while group XT and P showed no effect of aging on fractural strength and fracture toughness with P<.05.CONCLUSIONHydrothermal aging caused reduction in mechanical properties such as surface hardness, biaxial flexural strength, and fracture toughness of Y-TZP zirconia. However, cubic-containing zirconia (more than 30% by volume of cubic crystal) was assumed to have high resistance to hydrothermal degradation. Clinical significance: Cubic-containing zirconia could withstand the intraoral aging condition. It could be suggested to use as a material for fabrication of esthetic dental restoration.

Evaluation of Flexural Strength of Heat Cure PMMA Denture Base Material Reinforced with Various Concentrations of Zirconium Oxide Nanoparticle: An In-vitro Study

Objective: The aim of this study was to investigate the effect of zirconium oxide (ZrO2) nanoparticle dispersion on the flexural property of heat-cure polymethylmethacrylate denture base material. &#x0D; Methods: Eighty specimens were divided into 10 groups of eight specimens; Group 1 unreinforced acrylic, group 2: treated with ethanol alcohol, Groups 3,4,5 and 6 reinforced acrylic specimens with 1, 3, 5, and 7 wt% of untreated zirconium oxide nanoparticle (u- ZrO2) and Groups 7,8,9 and 10 reinforced acrylic specimens with treated and sonicated zirconium oxide nanoparticle in ethanol alcohol (t-ZrO2). X-ray diffraction test (XRD) was used to study the dispersion quality of the tested specimens, and universal testing machine was used to evaluate flexural strength and flexural modulus. SPSS software program used to compare groups results statistically.&#x0D; Results: The results revealed significant decrease in flexural strength with u-ZrO2 nanoparticle addition in different concentration groups (p&lt;0.05), while with t-ZrO2 nanoparticle addition, above 3 wt% statistically significant decrease was noted as compared to the conventional group. However, the flexural modulus increased with increasing the both of u-ZrO2 and t-ZrO2 nanoparticles addition. XRD results showed better dispersion quality of the t-ZrO2 than u-ZrO2 throughout the acrylic resin denture base material.&#x0D; Conclusions: Flexural strength decreased inversely with increasing u-ZrO2 concentration, while it decreases significantly above 3 wt% of t-ZrO2 nanoparticle concentration. The flexural modulus increased with increasing both of u-ZrO2 and t-ZrO2 nanoparticles. Reduced nanoparticle’s cluster size of t-ZrO2 allows more nanofiller to be incorporated to denture base materials with less adverse effect on the mechanical properties.

MECHANICAL EVALUATION OF POLYETHERETHERKETONE COMPARED WITH ZIRCONIA AS A DENTAL IMPLANT MATERIAL

INTRODUCTION: Dental implants are currently one of the main pillars of restorative dentistry. Titanium and its alloys were and still are the gold standard for dental implant materials. However, Titanium is not a perfect material and has many drawbacks thus the search for a more ideal material is ongoing. Zirconia and Polyetheretherketone are two viable alternatives to titanium as dental implant materials. They show different mechanical behavior invitro and invivo, so they are investigated and compared to each other. OBJECTIVES: Evaluate and compare the different material properties of Polyetheretherketone and yttrium-stabilized tetragonal polycrystalline zirconia when used as dental implant material. MATERIALS AND METHODS: Microbars of zirconia and Polyetheretherketone were prepared using precision cutter and low speed micro motor under water cooling and used to assess the following properties for the two materials: 1) Vickers Microhardness 2) Flexural strength before and after cyclic loading RESULTS: There was a highly significant difference between hardness of zirconia and Polyetheretherketone. There was also a highly significant difference between flexural strength of zirconia and Polyetheretherketone (both before and after cyclic loading). There was significant decrease in flexural strength of zirconia after cyclic loading. No significant difference was found for Polyetheretherketone after cyclic loading. CONCLUSIONS: Polyetheretherketone is a promising alternative to titanium and zirconium as a dental implant material.

Modification of filler surface treatment of composite resins using alternative silanes and functional nanogels

ObjectivesThis study probes how modifiedapproaches for filler surface treatment in dental composites based on alternative silanes and functional nanogel additives affects physicochemical properties of these materials with a focus on polymerization stress development. MethodsNanogels were synthesized from isobornyl methacrylate, ethoxylated bisphenol-A dimethacrylate and isocyanatoethyl methacrylate followed by partial further reaction with 2-hydroxyethyl methacrylate to provide both isocyanate and methacrylate functionalization. A barium glass filler (˜1 μm particle size) was treated with either γ-methacryloxypropyltrimethoxysilane (MPS), N-methylaminopropyltrimethoxy (MAP) or N-allylaminopropyltrimethoxy (AAP) silanes. The reactive nanogels were then covalently attached to the aminosilane-treated fillers. Surface treatment was characterized by thermogravimetric analysis (TGA) and diffuse reflectance infrared spectroscopy (DR-IR). Composites were formulated with 60 wt% of the various functionalized fillers and the materials were evaluated for polymerization kinetics, polymerization stress (PS), volumetric shrinkage, mechanical properties and photorheology. Data were evaluated by one-way ANOVA and Tukey’s test at 5% significance level. ResultsFiller surface treatments were confirmed by TGA and DR-IR analyses. Nanogel-functionalized fillers significantly reduced PS up to 20%, while the degree of conversion and elastic modulus were not compromised. Similar storage modulus development during polymerization was observed among materials by photorheology although the rate of polymerization was significantly increased for nanogel-based treatments. A significant decrease in flexural strength was observed for amino functional silane groups; however, there was no statistical difference in strength for the MPS control group compared with the nanogel-modified composites. SignificanceFiller surface treatment modified with a reactive nanogel enables significant PS reduction, without compromise to degree of conversion or mechanical properties of dental composites.

Effect on the mechanical properties of human and bovine dentine of intracanal medicaments and irrigants.

Evidence is lacking concerning the suitability of using bovine dentine in endodontic research. This study compared the mechanical properties of human and bovine root dentine using endodontic medicaments and irrigants. Standardized human and bovine dentine bars were allocated to six experimental groups (n = 15): calcium hydroxide paste (Calasept® Plus); Odontopaste® ; 0.5% and 1% NaOCl gels; 1% and 4% NaOCl solutions. The bars were exposed to the materials for 7 days and then immediately subjected to a three-point bend test and Vickers microhardness test. Data were analysed using analysis of variance with Fisher's pairwise comparisons, with P < 0.05. Human dentine displayed a significantly higher modulus of elasticity (P = 0.001), higher microhardness (P < 0.001), and lower flexural strength (P = 0.004) compared with bovine dentine. Calcium hydroxide and Odontopaste® did not result in a significant change to the mechanical properties of human dentine. In human dentine, 0.5% NaOCl gel caused a significant decrease in flexural strength (P < 0.001) and microhardness (P = 0.02). Bovine dentine was a suitable substrate relative to human dentine. The use of a 0.5% or 1% NaOCl gel as an intracanal medicament is not supported by this study.

Effect of heat polymerization conditions and microwave on the flexural strength of polymethyl methacrylate.

Objective:The objective of this study is the effect of different heat polymerization conditions on the strength of polymethyl methacrylate (PMMA) resin base is unknown. Distinguishing one method that provides improved mechanical properties may be beneficial to the clinical success of complete and partial dentures and overdentures. The purpose of this study was to evaluate the effect of different polymerization methods on the flexural strength of a dental PMMA resin.Materials and Methods:Forty PMMA specimens (64 mm × 10 mm × 4 mm) were prepared with 4 different polymerization methods (n = 10); heat polymerization at 74°C for 9 h, at 100°C for 40 min, and with 620 kPa pressure at 100°C for 20 min. The remaining group of specimens was microwave polymerized at 180 W for 6 min. All specimens were thermocycled at 5°C and 55°C for 5000 times. Three-point flexure test was used to measure the flexural strength of specimens. One-way ANOVA and Tukey Honestly Significant Difference were applied to analyze the differences in flexural strengths (α = 0.05).Results:The flexural strength of heat-polymerized groups was similar. The flexural strength of microwave polymerized group was significantly different and lower than the other groups (P < 0.05).Conclusion:Polymerizing conventional heat-polymerizing PMMA resin with microwave energy resulted in a significant decrease in flexural strength. The results of this study suggest that clinicians may benefit from using heat polymerization when processing PMMA denture bases instead of microvawe polymerization when tested brand is used.

Effect of different aging methods on the mechanical behavior of multi-layered ceramic structures

ObjectiveTo evaluate the effect of two aging methods (mechanical cycling and autoclave) on the mechanical behavior of veneer and framework ceramic specimens with different configurations (monolithic, two and three-layers). MethodsThree ceramics used as framework for fixed dental prostheses (YZ—Vita In-Ceram YZ; IZ—Vita In-Ceram Zirconia; AL—Vita In-Ceram AL) and two veneering porcelains (VM7 and VM9) were studied. Bar-shaped specimens were produced in three different designs: monolithic, two layers (porcelain–framework) and three layers (porcelain–framework–porcelain). Specimens were tested for three-point flexural strength at 1MPa/s in 37°C artificial saliva. Three different experimental conditions were evaluated (n=10): control; mechanical cycling (2Hz, 37°C artificial saliva); and autoclave aging (134°C, 2 bars, 5h). Bi-layered specimens were tested in both conditions: with porcelain or framework ceramic under tension. Fracture surfaces were analyzed using stereomicroscope and scanning electron microscopy. Results were statistically analyzed using Kruskal–Wallis and Student-Newman–Keuls tests. ResultsOnly for AL group, mechanical cycling and autoclave aging significantly decreased the flexural strength values in comparison to the control (p<0.01). YZ, AL, VM7 and VM9 monolithic groups showed no strength degradation. For multi-layered specimens, when the porcelain layer was tested in tension (bi and tri-layers), the aging methods evaluated also had no effect on strength (p≥0.05). Total and partial failure modes were identified. SignificanceMechanical cycling and autoclave aging protocols had no effect on the flexural strength values and failure behavior of YZ and IZ ceramic structures. Yet, AL monolithic structures showed a significant decrease in flexural strength with any of the aging methods.

Influence of aging on flexural strength of translucent zirconia for monolithic restorations

Statement of problemConcern has been raised with regard to the low-temperature degradation (LTD) of translucent yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) for monolithic zirconia restorations. PurposeThe purpose of this in vitro study was to assess the LTD behavior of 4 commercially available translucent Y-TZP materials by accelerated aging specimens in steam at 134°C, 0.2 MPa. Material and MethodsThin bars (22×3×0.2 mm) of Y-TZP, including Katana ML (Kuraray Noritake Dental Inc), Katana HT13 (Kuraray Noritake Dental Inc), Prettau (Zirkonzahn), and BruxZir (Glidewell Laboratories) (n=30 for each group), were machined from sintered blocks. Control specimens were assessed in the nonaged condition. Artificially ageing (n=5 per group at 5, 50, 100, 150, and 200 hours) was conducted in steam at 134°C at 0.2 MPa. The specimens were characterized, tested in 4-point flexure, and the fracture surfaces were analyzed. The monoclinic-to-tetragonal (m/t) peak intensity ratio measured by x-ray diffraction was used to calculate the monoclinic phase fraction and monitor LTD. Linear regression with heteroscedasticity-consistent robust standard errors was used to test for the effect of LTD (aging time) on (σf) and m/t. The Spearman rank correlation coefficient was used to assess the relationship between σf and monoclinic phase fraction (α=.05). ResultsArtificial aging resulted in LTD as shown by an increase in the monoclinic phase fraction for all specimens. After aging for 200 hours, the mean ±SD monoclinic phase fraction increased from 2.90 ±0.34% to 76.1 ±0.64% for Prettau, 2.69 ±0.18% to 76.0 ±0.26% for BruxZir, 4.6 ±0.19% to 35.8 ±0.80% for Katana HT13, and 3.57 ±0.35% to 33.2 ±1.1% for Katana ML (all P<.001). Flexural strength changed from a mean ±SD of 1612 ±197 MPa to all fractured during aging for Prettau (P<.001); 1248 ±73.5 MPa to all fractured during aging for BruxZir (P<.001); 1052 ±84.2 to 1099 ±70 MPa ±130 for Katana HT13 (P=.45); and from 875 ±130 to 909 ±70 MPa (P=.82) for Katana ML. The mean flexural strength values of Prettau and BruxZir decreased with an increase in the monoclinic phase with Spearman rank correlation coefficients of −0.80 (P=.001) for Prettau and −0.63 (P=.022) for BruxZir. No significant changes in flexural strength were measured for Katana ML or Katana HT13 (P>.05). ConclusionsThe LTD of Y-TZP resulted in a significant decrease in flexural strength of Prettau and BruxZir, whereas Katana ML and Katana HT13 exhibited less LTD and no significant decrease in flexural strength.