Biaxial Flexural Strength Values Research Articles

Effect of femtosecond laser induced surface patterns on the flexural strength of monolithic zirconia.

To investigate how patterns generated by femtosecond (fs) laser and femtosecond laser power affect the surface roughness (Ra) and biaxial flexural strength (BFS) of monolithic zirconia. Eighty disk-shaped zirconia specimens were divided into eight subgroups (n = 10): Control (C), airborne-particle abrasion (APA), 400 mW fs laser (spiral [SP(400)], square [SQ(400)], circular [CI(400)]), and 700 mW fs laser ([SP(700)], [SQ(700)], [CI(700)]). Ra values were calculated by using a surface profilometer. One additional specimen per group was analyzed with scanning electron microscopy and x-ray diffractometry. BFS values were obtained by using the piston-on-3-ball test. One-way ANOVA and either Tukey's HSD (BFS) or Tamhane's T2 (Ra) tests were used to evaluate data (α = 0.05). Regardless of the pattern and power, fs laser groups had higher Ra than C and APA, while SP groups had lower Ra than CI and SQ groups (p ≤ 0.004). For each pattern, Ra increased with higher laser power (p < 0.001), while the laser power did not affect the BFS (p ≥ 0.793). CI and SQ groups had lower BFS than the other groups (p ≤ 0.040), whereas SP groups had similar BFS to C and APA (p ≥ 0.430). Fs laser microstructuring with spiral surface pattern increased the Ra without jeopardizing the BFS of zirconia. Thus, this treatment might be an option to roughen tested zirconia.

Effect of curing mode of resin composite cements on water sorption, color stability, and biaxial flexural strength

ObjectivesTo determine whether water sorption and solubility of a recently introduced self-adhesive cement is comparable to two clinically tested resin composite cements after thermal aging, and if this is affected by the curing mode. Whether water sorption is correlated with color difference and biaxial flexural strength was also investigated. MethodsWater sorption and solubility of three resin composite cements {RelyX Universal (RUV), (Panavia V5 (PV5), Panavia SA plus (PSA)} were measured after thermal aging. Disk-shaped specimens were either light-cured or autopolymerized (n = 15 per group). Color difference ΔE00 and biaxial flexural strength were also obtained. ResultsSorption was highest for RUV (auto: 54.9 ± 9.0 µg/mm3, light: 49.7 ± 4.9 µg/mm3), followed by PSA (auto: 37.7 ± 1.4 µg/mm3, light: 34.5 ± 1.1 µg/mm3) and PV5 (auto: 21.7 ± 0.7 µg/mm3, light: 22.1 ± 0.4 µg/mm3). Light-curing reduced solubility values, particularly for RUV (from 60.7 ± 20.8 µg/mm3 to 6.4 ± 0.8 µg/mm3). Color differences of ΔE00 > 1.8 (considered clinically not acceptable) were noted after aging for RUV and PSA. Sorption and ΔE00 values after aging were correlated linearly (R2 = 0.970). Biaxial flexural strength values were highest for PV5 (light: 153.4 ± 15.9 MPa; auto: 133.2 ± 18.0 MPa) and lowest for RUV (light: 99.3 ± 12.8 MPa; auto: 35.1 ± 8.3 MPa). SignificanceLight-curing has beneficial effects on sorption, color stability, and biaxial flexural strength of resin composite cements. Cements containing 2-hydroxymethacrylate such as RUV and PSA are more prone to water sorption and color changes.

Effect of thermocycling on the mechanical properties of permanent composite-based CAD-CAM restorative materials produced by additive and subtractive manufacturing techniques

BackgroundThe aim of the study was to determine and compare the biaxial flexural strength (BFS) and Vickers hardness (VHN) of additive and subtractive manufactured permanent composite-based restorative materials, before and after thermal aging.MethodsA total of 200 specimens were prepared; 100 disc-shaped specimens (diameter 13 × 1.2 mm) for the BFS test and 100 square specimens (14 × 14 × 2 mm) for the VHN test. The specimens were made from various materials: two subtractive composite-based blocks (Cerasmart 270 [CS], Vita Enamic [VE]), two additive composite-based resins used for two different vat polymerization methods (digital light processing [DLP]; Saremco Print Crowntec [SC] and stereolithography [SLA]; Formlabs Permanent Crown Resin [FP]), and one feldspathic glass-matrix ceramic block (Vita Mark II [VM]) as the control group. Specimens of each material were divided into two subgroups: thermal cycled or non-thermal cycled (n = 10). BFS and VHN tests were performed on all groups. Data were analyzed with two-way ANOVA and post hoc Tukey test (α = 0.05).ResultsThe type of restorative material used for the specimen had a statistically significant influence on both BFS and VHN values. However, thermal cycling did not affect the BFS and VHN values. After thermal cycling, the results of the BFS test were ranked from best to worst as follows: CS, FP, SC, VE, then VM. For the VHN values, the order from best to worst was as follows: VM, VE, CS, FP, then SC.Conclusions3D printed and milled composite groups showed higher BFS than feldspathic ceramics. When the VHN results were examined, it was seen that the 3D resin groups had the lowest VHN values. Furthermore, it was observed that the thermal cycle had no effect on BFS or VHN.

Effect of Addition of ZrO2 on Biaxial Flexural Strength of Calcium Phosphate Ceramics

The aim of this study is to investigate the effect of addition of ZrO2 on the biaxial flexural strength (BFS) of ceramics fabricated using a conventional powder technology. Various compositions of hydroxyapatite (HAp) Ca10(PO4)6(OH)2 and zirconia powder ZrO2, ranging from 10 to 90 wt% ZrO2, were prepared using a wet mixing process. Ten compacts (13.5mm3mm) were made for each group, pressed and sintered in air at sintering temperatures from 1100 to 1450oC for up to 12 hours. The bulk density, porosity, linear shrinkage and BFS. The porosity reduced and linear shrinkage increased with increasing sintering temperature and amounts of zirconia, whereas the sintering time had little effect. The highest mean value achieved for the BFS was 26920 MPa for a composition of 70% ZrO2 and 30% HAp fired at 1450oCfor 6 hours. From the experimental results can be conclude that sintering temperature and composition affect densification behaviour of calcium phosphate/ ZrO2 composites. The BFS increases with a reduction of porosity and increases with both sintering temperature and additions of ZrO2. It was noted that there is considerable scope for improvement in the BFS values by reducing the porosity of these composites.

Effects of Different Surface Treatments on Flexural Strength of Zirconium Oxide Cores

Objective: The aim of this study was to investigate the effect of different surface treatments on the biaxial flexural strength of zirconia and to determine phase transformation before and after sintering. Materials and Methods: 150 cylindrical specimens with the dimensions 15 mm diameter and 1,3 mm height were obtained from semi-sintered Y-TZP blocks. These specimens were randomly separated into subgroups; sandblasting, Er:YAG laser, Nd:YAG laser, Er:YAG laser+sandblasting, Nd:YAG laser+sandblasting, fine grain bur, coarse grain bur. Half of the semi-sintered Y-TZP samples were treated before sintering and the others were treated after the sintering procedures. No treatment was performed in control group. Biaxial flexural strength test was performed to all samples. X-ray diffraction analysis (XRD) were performed to identify transformed monoclinic phase. The data were analyzed by Kruskal-Wallis, Man Whitney U test and Wilcoxon test (p&amp;lt;0,05). Results: Specimens that were treated before sintering had lower biaxial flexural strength. The highest biaxial flexural strength values in all groups were seen in sandblasting groups and the lowest in grinding groups. According to the XRD analysis the highest phase transforme was determined in sandblasting groups. Sandblasting, Er-YAG laser+sandblasting and Nd-YAG laser+sandblasting were greatly increased the biaxial flexural strength of all the surface treatments after sintering. All the sandblasting treatments were found more monoclinic phase was found than other groups. Conclusions: Surface treatments were found to affect both the mechanical properties and phase changes of zirconia.

Dental zirconia microwave-sintering followed by rapid cooling protocol

ObjectivesThis study aimed to evaluate the effect of microwave sintering temperature and cooling rate (MS) on 3Y-TZP ceramics and its influence on the ceramic microstructure and mechanical properties. Specifically, to optimize the sintering process, reducing the total sintering time compared to conventional sintering. Materials and methodsEighty-four pre-sintered Y-TZP discs (Vipi block Zirconn, VIPI) (ISO 6872) were divided into seven groups (n = 12) according to the sintering conditions: conventional sintering (CS) at 1530 °C for 120 min and microwave sintering at 1400 °C (MS1400) and 1450 °C (MS1450) for 15 min followed by different cooling conditions: rapid cooling (RC), cooling at 400 °C (C400) and 25 °C (C25). The specimens were submitted to apparent density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy, and biaxial flexural strength test. Data was statistically analyzed through two-way ANOVA, Tukey, Sidak, Dunnett and Weibull (α = 0.05). ResultsAll MS1400 groups presented lower density values than the CS and MS1450 groups. Two-way ANOVA revealed that the MS temperature and cooling rate affected the biaxial flexural strength of the Y-TZP (p < 0.01). Group MS1400RC presented lower biaxial flexural strength values (681.9 MPa) than MS1450RC (824.7 MPa). The cooling rate did not statistically decrease the biaxial strength among the groups submitted to microwave sintering at 1450 °C. XRD analysis showed that the sintering and cooling temperature did not induce tetragonal to monoclinic phase transformation. ConclusionsMicrowave sintering at 1450 °C for 15 min followed by rapid cooling can be a viable fast alternative protocol for Y-TZP sintering, compared with the conventional sintering, reducing the total sintering time by 75% and reducing the energy used for the sintering process without affecting the Y-TZP biaxial flexural strength and relative density compared to the conventional sintering. Moreover, the microwave technique promoted smaller grains and did not induce monoclinic phase formation.

The influence of core-build up materials on biaxial flexural strength of monolithic strength-gradient zirconia; an in-vitro study

BackgroundSince their introduction, there has been limited research regarding the mechanical properties of novel strength-gradient monolithic zirconia. In addition to that, studies evaluating the effect of different core-build materials on the strength of indirect restorations are scarce. Therefore, the aim of this study was to investigate the effect of using different core build-up materials on biaxial flexural strength of a new monolithic multilayered zirconia material.MethodsForty zirconia discs were fabricated from IPS e.max ZirCAD Prime (Ivoclar Vivadent AG, Schaan, Liechtenstein) and divided into 2 groups (n = 20). Forty composite discs were prepared from Tetric N-Ceram (Ivoclar Vivadent AG, Schaan, Liechtenstein) and MultiCore Flow (Ivoclar Vivadent AG, Schaan, Liechtenstein). The zirconia discs were adhesively cemented to the 2 types of composite forming 2 groups (Zirconia-Tetric N-Ceram and Zirconia-MultiCore Flow). Biaxial flexural strength was determined using a piston-on-3-ball test. The data were statistically analyzed with an independent t-test for significant differences (p = 0.05).ResultsTetric N-Ceram had significantly higher strength than MultiCore Flow (p < 0.001) but no statistically significant differences were found in strength values between Zirconia-Tetric N-Ceram and Zirconia-MultiCore Flow bilayered samples (p = 0.27).ConclusionsIt was concluded that although the tested composite core materials significantly differ in their biaxial flexural strength values, they had no influence on the biaxial flexural strength of the overlying zirconia.

Porphyromonas gingivalis can degrade dental zirconia

ObjectivesThe aim of present study was to examine the effect of Porphyromonas gingivalis (P.g.) adhesion on dental zirconia by characterizing the physical and chemical properties. MethodsEighty polished-sintered zirconia discs were prepared and randomly distributed to 5 groups (n = 16): Zirconia cultured with - Group 1: broth containing P.g. for – 3 days; Group 2: 7 days; Group 3: broth (alone) for – 3 days; Group 4: 7 days; and Group 5: dry discs (negative control). After experimental period, broths were analyzed for pH and Zr release with inductively coupled plasma-optical emission spectroscopy (ICP-OES). The zirconia surface was evaluated by scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), water contact angle (WCA), and biaxial flexural strength (BFS). ResultsThe mean pH with zirconia adhesion to P.g. group was significantly higher than the broth control (p < 0.05). As per ICP-OES, Zr ion/particulate release with P.g. adhesion to zirconia were significantly higher than the controls (p < 0.05). Post-experimental incubation, no defects were found on zirconia surfaces; tetragonal phase remained constant with no transformation to monoclinic phase but lower peak intensities were identified in experimental groups. WCA of zirconia surfaces with P.g. bacteria for 3 days (12.04° ± 2.05°) and 7 days (15.09° ± 2.95°) were significantly higher than zirconia surfaces immersed with broth (only) for 3 days (7.17° ± 1.09°) and 7 days (7.55° ± 0.65°), respectively (p < 0.05). BFS values of zirconia with P.g. for 3 days (632.57 ± 119.96 MPa) and 7 days (656.17 ± 100.29 MPa) were significantly lower than zirconia incubated in broth alone (765.01 ± 20.12 MPa) conditions (p < 0.05). SignificanceUnder the conditions of present study, it can be concluded that P.g. adhesion on zirconia leads to structural alterations of dental zirconia further contributing to zirconia degradation.

Microstructure and mechanical properties of an experimental lithium disilicate dental glass-ceramic

After testing over 50 experimental lithium disilicate (LS2)-based glass-ceramic (GC) compositions and evaluating their glass-forming ability and the effect of various heat treatments on their crystallized fraction, crystal size, and morphology, a particularly promising formulation was selected for the optimization of the mechanical properties of materials. The specimens were divided into groups submitted to a nucleation heat treatment at different times and temperatures, i.e., T1 (500 °C/90′), T2 (500 °C/180′), T3 (500 °C/360′) and T4 (480 °C/360′), followed by a crystal growth treatment to induce the lithium metasilicate (700 °C) and LS2 (840 °C) phases. However, a third (minor) phase, lithium phosphate, also precipitated. IPS e.max CAD was used as the control group (C, 500 °C/360′). The elastic modulus (E) was measured by the impulse excitation technique (ASTM E 1876-15), while the Vickers hardness (HV) and biaxial flexural strength (BFS) were determined by indentation and the piston-on-three balls test (ISO 6872), respectively. The E and HV results were analyzed by ANOVA one-way with Games–Howell post-hoc test, whereas the BFS data were investigated by Kruskal-Wallis with Dunn's post-hoc test (α = 0.05). The E of all GCs were within the expected range for commercial LS2 glass-ceramics. The T2 and T4 GCs exhibited the best properties when compared to the C group, and despite their relatively small crystallized fraction (∼57 %), they showed a hardness of 5.8 ± 0.2 GPa, a value that is adequate and statistically equal to that of the control group. The same groups reached BFS values of 359 ± 89 MPa and 493 ± 147 MPa, respectively, which are also statistically equal to that of the C group (338 ± 61 MPa). The mechanical properties of the material studied was successfully optimized through variations in the nucleation temperature and time, reaching values comparable to (but not better than) commercial dental glass-ceramics.

Surface hardness and flexural strength of dual-cured bulk-fill restorative materials after solvent storage

BackgroundThis study aimed to evaluate the surface hardness (VHN) and biaxial flexural strength (BFS) of dual-cured bulk-fill restorative materials after solvent storage.MethodsTwo dual-cured bulk-fill composites (Surefil One® and Activa™ Bioactive), a light-cured bulk-fill composite (Filtek One Bulk-Fill) and a resin-modified glass ionomer (Fuji II LC) were investigated. Surefil One and Activa were used in the dual-cure mode, all materials were handled according to manufacturer’s instructions. For VHN determination, 12 specimens were prepared from each material and measured after 1 h (baseline), 1 d, 7 d and 30 d of storage in either water or 75% ethanol–water. For BFS test, 120 specimens were prepared (n = 30/material) and stored in water for either 1, 7 or 30 d before testing. Repeated measures MANOVA, two-way and one-way ANOVA followed by the Tukey post hoc test (p ≤ 0.05) were used to analyze the data.ResultsFiltek One had the highest VHN, while Activa had the lowest. All materials exhibited a significant increase in VHN after 1d of storage in water, except for Surefil One. After 30 d of storage, VHN increased significantly in water except for Activa, while ethanol storage caused a significant time-dependent reduction in all tested materials (p ≤ 0.05). Filtek One showed the highest BFS values (p ≤ 0.05). All the materials, except for Fuji II LC, exhibited no significant differences between 1 and 30 d BFS measurements (p > 0.05).ConclusionsDual-cured materials had significantly lower VHN and BFS compared to the light-cured bulk-fill material. The low results of Activa VHN and Surefil One BFS, indicate that these materials should not be recommended in posterior stress-bearing areas.

Effect of Aging Treatments on Properties of Zirconia with Different Levels of Translucency

Purpose: The aim of this study was to evaluate the effect of low-temperature degradation(L-TD), and weathering process on translucency, surface roughness, biaxial-flexural strength, and crystalline phase identification of zirconia with different levels of translucency. Materials and methods: A total of ninety-six (N= 96) zirconia discs were fabricated in this study. Samples were divided into three groups (n=32 each) according to type of zirconia: IPS EmaxZirCAD of low, medium translucency and Incoris translucent Zirconia of high translucency. Translucency measurements, surface roughness, biaxial flexural strength determination and phase identification were carried out before and after aging. Each group was then sub-divided into 2 subgroups (n=16); (subgroup A): Low-temperature degradation(L-TD) at 134ºC, (subgroup B): Accelerated aging by means of a weathering process (WP). Results: Statistical analysis using two-way ANOVA test revealed that there was a significant effect on translucency parameter (TP), and L-TD showed statistically significantly higher mean TP than WP. L-TD showed significantly lower mean roughness than WP. There was no significant difference between biaxial flexural strength values before aging and after L-TD and WP. There was no phase transformation identified before and after aging indicating resistance to different types of artificial aging. Conclusions: Low-temperature degradation and weathering process affect translucency parameter and surface roughness of zirconiabased materials. Artificial aging doesn’t affect the biaxial flexural strength, and phase identification of different zirconia translucencies.

Effect of Aging Treatments on Properties of Zirconia with Different Levels of Translucency

Purpose: The aim of this study was to evaluate the effect of low-temperature degradation(L-TD), and weathering process on translucency, surface roughness, biaxial-flexural strength, and crystalline phase identification of zirconia with different levels of translucency. Materials and methods: A total of ninety-six (N= 96) zirconia discs were fabricated in this study. Samples were divided into three groups (n=32 each) according to type of zirconia: IPS EmaxZirCAD of low, medium translucency and Incoris translucent Zirconia of high translucency. Translucency measurements, surface roughness, biaxial flexural strength determination and phase identification were carried out before and after aging. Each group was then sub-divided into 2 subgroups (n=16); (subgroup A): Low-temperature degradation(L-TD) at 134ºC, (subgroup B): Accelerated aging by means of a weathering process (WP). Results: Statistical analysis using two-way ANOVA test revealed that there was a significant effect on translucency parameter (TP), and L-TD showed statistically significantly higher mean TP than WP. L-TD showed significantly lower mean roughness than WP. There was no significant difference between biaxial flexural strength values before aging and after L-TD and WP. There was no phase transformation identified before and after aging indicating resistance to different types of artificial aging. Conclusions: Low-temperature degradation and weathering process affect translucency parameter and surface roughness of zirconiabased materials. Artificial aging doesn’t affect the biaxial flexural strength, and phase identification of different zirconia translucencies.

The effects of heating rate and sintering time on the biaxial flexural strength of monolithic zirconia ceramics.

The strength of zirconia ceramic materials used in restorations is dependent upon sintering. Varying sintering protocols may affect the biaxial flexural strength of zirconia materials. This invitro study was conducted to investigate the effects of sintering parameters on the biaxial flexural strength of monolithic zirconia. Two different monoblock zirconia ceramics were used. Following coloration, samples of both types of ceramics were divided into groups according to whether or not biaxial flexural strength testing was performed directly after sintering or following thermocycling. Biaxial flexural strength data was analysed with a Shapiro Wilk normality test, followed by 1-way ANOVA, Tukey post hoc tests for inter-group comparisons, and paired samples t-tests for intra-group comparisons. Asignificant difference was found between the biaxial flexural strengths of Zircon X and Upcera ceramics before thermocycling (p<0.05). In both Zircon X and Upcera ceramic groups, the thermocycling process created a significant difference in the biaxial flexural strength values of the ceramic samples in Group 6 (p<0.05) which had the slowest heating rate and longest holding time. The zirconia ceramics have higher BFS at higher heating rates either before or after thermocycling. The holding time has significant effects on thermocycling and flexural strength. The zirconia achieved its optimum strength when it sintered at longer time regardless of heating rates.

Influence of Surface Treatment and Accelerated Ageing on Biaxial Flexural Strength and Hardness of Zirconia.

The aim was to investigate how the surface treatment and the process of accelerated ageing of zirconia for dental implants affect the biaxial flexural strength and hardness. Zirconia discs with a diameter of 12.6 mm were subjected to either one of the following treatments: polishing (Zp); polishing and heat treatment at 1250 °C for 1 h (Zpt); machining (Zm); machining and heat treatment (Zmt); or sandblasting, acid-etching, and heat treatment (Z14) (n = 45 per group). Biaxial flexural strength and Martens hardness (HM) were measured without further treatment and after accelerated ageing for 5 h or 5 × 5 h according to ISO 13356 (n = 15 per group). Two-way ANOVA was applied to test the effect of surface treatment and ageing (α = 0.05). The reliability of the specimens was described with Weibull two-parameter distribution of biaxial flexural strength data. Overall, the surface treatment (p < 0.001) and ageing (p = 0.012) revealed a significant effect on biaxial flexural strength values, while HM was only affected by the surface treatment (p < 0.001) but not ageing (p = 0.160). Surface treatment significantly affected HM (p < 0.001) but not ageing (p = 0.160). The applied surface treatments affected the biaxial flexural strength and HM of zirconia. For accelerated ageing, a duration of both 5 h and 5 × 5 h is recommended to evaluate the effect of surface treatments. Zm was the most reliable surface as it was least affected by ageing and provided low standard deviations of biaxial flexural strength values.

Optical properties, biaxial flexural strength, and reliability of new-generation lithium disilicate glass-ceramics after thermal cycling.

To investigate the color stability, translucency, biaxial flexural strength (BFS), and reliability of nano-lithium disilicate and fully crystallized lithium disilicate after thermal cycling and to compare with those of a commonly used lithium disilicate. Three lithium disilicate glass-ceramics were used to prepare disk-shaped specimens (ø:12 mm, thickness: 1.2 mm) from A2 shaded HT blocks (Amber Mill, AM; Initial LiSi Block, IN; IPS e.max CAD, EX). AM and EX specimens were crystallized, and all specimens were polished with a polishing paste (Diamond Polish Mint). A spectrophotometer (CM-26d) was used to measure color coordinates before and after thermal cycling. BFS test was performed after thermal cycling. Color differences (ΔE00 ) and relative translucency parameter (RTP) values were calculated. One-way analysis of variance (ANOVA) (ΔE00 and BFS), two-way ANOVA followed by Tukey's HSD tests (RTP), and chi-square tests (Weibull modulus and characteristic strength) were used for the statistical analyses (α=0.05). No significant differences were observed among the ΔE00 values of tested materials (df=2, F=2.933, p=0.070). RTP values were only affected by material type (p<0.001) as AM had the highest RTP (p<0.001), whereas IN and EX had similar values (p≥0.165). BFS values varied among tested materials (df=2, F=21.341, p<0.001). AM and EX had similar BFS values (p=0.067) that were higher than that of IN (p≤0.001). Weibull moduli of the materials were similar (p=0.305), whereas EX had the highest and IN had the lowest characteristic strength values (p<0.001) CONCLUSIONS: Although nano-lithium disilicate had the highest translucency, all materials had imperceptible color and translucency changes after thermal cycling when reported threshold values were considered. Newly introduced lithium disilicate glass-ceramics had adequate flexural strength as compared to the precursor material.

Translucency, color stability, and biaxial flexural strength of advanced lithium disilicate ceramic after coffee thermocycling.

To compare the color stability, translucency, and biaxial flexural strength (BFS) of differently glazed advanced lithium disilicate (ALDS) with those of lithium disilicate (LDS) and zirconia-reinforced lithium silicate (ZLS) after coffee thermocycling. Forty disk-shaped specimens were prepared from three lithium silicate based materials (CEREC Tessera, ALDS; IPS e.max CAD, LDS; Vita Suprinity, ZLS). ALDS specimens were divided into two subgroups according to glazing procedures (reduced glaze duration, ALDS-S and normal glaze duration, ALDS-N), while LDS and ZLS specimens were crystallized and glazed. Color coordinate measurements were performed before and after coffee thermocycling. Color differences (ΔE00 ) and relative translucency parameters (RTP) were calculated. Specimens were then subjected to BFS test. Statistical analysis was performed by using 1- (ΔE00 and BFS) and 2-way (RTP) ANOVA tests (α=0.05). ΔE00 values of tested materials were similar (df=3, F=0.150, p=0.929). Two-way ANOVA showed the significant effect of material type, coffee thermocycling, and the interaction between these parameters on RTP values (p < 0.001). Both before and after thermocycling, LDS had the highest (p ≤ 0.001) and ZLS had the lowest (p < 0.001) RTP values, while ALDS-N had higher RTP than ALDS-S (p ≤0.001). Among tested materials, only LDS had similar RTP values before and after thermocycling (p=0.865) as the other materials had lower RTP values after thermocycling (p < 0.001). ALDS-N had higher BFS values than ALDS-S (p=0.005), while LDS had similar values to ALDS specimens (p ≥ 0.201). ZLS had the highest BFS (p ≤ 0.007). ALDS had comparable values to those of other materials. However, reduced glazing duration resulted in decreased translucency and BFS of ALDS. ALDS may be an appropriate restorative material for those patients with increased coffee consumption considering its color stability and ability to maintain translucency, particularly when glazed by using a conventional porcelain furnace.

Chemical and mechanical properties of dual-polymerizing core build-up materials

ObjectivesTo investigate the chemical (degree of conversion (DC)) and mechanical properties (Martens hardness (HM), elastic indentation modulus (EIT), and biaxial flexural strength (BFS)) of four dual-polymerizing resin composite core build-up materials after light- and self-polymerization.Materials and methodsRound specimens with a diameter of 12 mm and a thickness of 1.5 mm were manufactured from CLEARFIL DC CORE PLUS (CLE; Kuraray), core·X flow (COR; Dentsply Sirona), MultiCore Flow (MUL; Ivoclar Vivadent), and Rebilda DC (REB; VOCO) (N = 96, n = 24/material). Half of the specimens were light-polymerized (Elipar DeepCure-S, 3 M), while the other half cured by self-polymerization (n = 12/group). Immediately after fabrication, the DC, HM, EIT, and BFS were determined. Data was analyzed using Kolmogorov–Smirnov, Mann–Whitney U, and Kruskal–Wallis tests, Spearman’s correlation, and Weibull statistics (p < 0.05).ResultsLight-polymerization either led to similar EIT (MUL; p = 0.119) and BFS (MUL and REB; p = 0.094–0.326) values or higher DC, HM, EIT, and BFS results (all other groups; p < 0.001–0.009). When compared with the other materials, COR showed a high DC (p < 0.001) and HM (p < 0.001) after self-polymerization and the highest BFS (p = 0.020) and Weibull modulus after light-polymerization. Positive correlations between all four tested parameters (R = 0.527–0.963, p < 0.001) were found.ConclusionsFor the tested resin composite core build-up materials, light-polymerization led to similar or superior values for the degree of conversion, Martens hardness, elastic indentation modulus, and biaxial flexural strength than observed after self-polymerization. Among the tested materials, COR should represent the resin composite core build-up material of choice due to its high chemical (degree of conversion) and mechanical (Martens hardness, elastic indentation modulus, and biaxial flexural strength) properties and its high reliability after light-polymerization. The examined chemical and mechanical properties showed a positive correlation.Clinical relevanceThe chemical and mechanical performance of dual-polymerizing resin composite core build-up materials is significantly affected by the chosen polymerization mode.

Comparative Properties of Porous Phyllosilicate-Based Ceramics Shaped by Freeze-Tape Casting

Porous phyllosilicate-based ceramics were manufactured by freeze-tape casting from clays of different particle size and morphology in order to characterize their microstructure and stress to rupture changes before and after firing. Three raw clays were selected: HCR (77% Halloysite–10Å), KORS (29% kaolinite), and KCR kaolin (98% kaolinite). These clays exhibited a monomodal distribution and were used to prepare four slurries, three with each clay material and one consisting of a mixture of KCR and HCR labeled KHCR. After shaping by freeze-tape casting, the porosity and stress to rupture obtained by a biaxial flexural test were collected for disk-like samples after drying and sintering at 1200 °C. Results showed that KCR ceramic materials had the highest biaxial bending strength (70 ± 1.1 MPa) and those from KORS had the highest porosity value (80 ± 1%). SEM observation revealed a difference in microstructure and texture for the manufactured porous ceramic materials. In the KCR ceramic disks, the flattened pores appeared more textured, and the primary mullite crystallites formed a rigid skeleton within the amorphous phase. KORS ceramic materials showed a small quantity of secondary mullite needles which were randomly dispersed in a vitreous phase. The relatively important vitreous phase in the porous materials of HCR led to the bulk formation of small mullite particles. The biaxial flexural strength values were related to the presence of the mullite, as well as to the microstructure (volume, morphology, and size distribution of pores) after sintering.

Robocasting of dense zirconia parts using commercial yttria-stabilized zirconia granules and ultrafine particles. Paste preparation, printing, mechanical properties

In this work, a commercial 3 mol% yttrium oxide partially stabilized zirconia spray-dried granules were used as such, and after intensive milling, for the production of dense samples by robocasting technique. The aim was to evaluate the suitability of using spray-dried granules instead of submicron particles in robocasting of ceramic parts. To this aim, robocasting pastes were produced from the as-received granules as well as from nanometric particles obtained from an effective ball milling of the granules. The formulation of the pastes was optimized in order to achieve optimal printability. The drying conditions were optimized as well, and the control of temperature and humidity either in the printing and drying chambers allowed to eliminate any warping issue. After sintering at 1450 °C, the monolithic dense parts were characterized by ultra-fine and highly sintered microstructures, with the highest density achieved by the sample produced from granules. This material not only did not show the typical defects of granules-derived ceramics but was also characterized by fewer and smaller defects than the sample produced by the fine particles. It seemed that the presence of large granules, and thus large intergranular space, favored the debinding process and limited the formation of the typical processing flaws. The ball-on-three balls test was used for the evaluation of the mechanical properties of the dense samples. Biaxial flexural strength values in the range from ∼100 to 500 MPa (with an average value of 255 ± 93 MPa) were determined for the samples made from granules while these values ranged from ∼100 to 300 MPa (with an average strength of 198 ± 52 MPa) for the samples prepared from the milled particles. In spite of low, these values are in line with literature data, obtained on 3 mol% Y 2 O 3 –ZrO 2 samples fabricated by the robocasting technique, and suitable to demonstrate the feasibility to use as-received granules as feeding material for robocasting parts.

Time-dependent degree of conversion, Martens parameters, and flexural strength of different dual-polymerizing resin composite luting materials

ObjectiveTo investigate the degree of conversion (DC), Martens hardness (HM), elastic indentation modulus (EIT), and biaxial flexural strength (BFS) of six dual-polymerizing resin composite luting materials initially and after 2 and 7 days of aging.Materials and methodsSpecimens fabricated from Bifix QM (BIF; VOCO), Calibra Ceram (CAL; Dentsply Sirona), DuoCem (DUO; Coltène/Whaledent), G-CEM LinkForce (GCE; GC Europe), PANAVIA V5 (PAN; Kuraray Europe), and Variolink Esthetic DC (VAR; Ivoclar Vivadent) (n = 12 per material) were light-polymerized through 1 mm thick discs (Celtra Duo, Dentsply Sirona). DC, HM, and EIT were recorded directly after fabrication, and after 2 and 7 days of aging. As a final test, BFS was measured. Univariate ANOVAs, Kruskal–Wallis, Mann–Whitney U, Friedman, and Wilcoxon tests, and Weibull modulus were computed (p < 0.05).ResultsWhile CAL presented low DC, HM, EIT, and BFS values, DUO and BIF showed high results. Highest Weibull moduli were observed for VAR and DUO. DC and Martens parameters increased between the initial measurement and 2 days of aging, while aging for 7 days provided no further improvement.ConclusionsThe choice of dual-polymerizing resin composite luting material plays an important role regarding chemical and mechanical properties, especially with patients sensitive to toxicological issues. DUO may be recommended for bonding fixed dental prostheses, as it demonstrated significantly highest and reliable results regarding DC, HM, and BFS. As DC and HM showed an increase in the first 48 h, it may be assumed that the polymerization reaction is not completed directly after initial polymerization, which is of practical importance to dentists and patients.Clinical relevanceThe chemical and mechanical properties of dual-polymerizing resin composite luting materials influence the overall stability and long-term performance of the restoration.