Abstract not available

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this study was to investigate the effect of nano ceramic fiber fillers on the physical properties of VST-50HD silicone maxillofacial prosthesis. Nano alumina fibers at 2 percent, 4-percent, and 6-percent wt were mixed into the VST-50HD silicone elastomer (Factor II Inc., Lakeside, AZ), a commercially-available poly(dimethylsiloxanes). Ten dumb-bell-shaped specimens were used to determine the tensile strength according to ISO 37:2005 and elongation at fracture. Ten trouser-shaped test pieces were used to determine the tear resistance according to ISO 34-1:2004. Shore A test method was used to measure the hardness of the material. The data collected from all quantitative studies of the modified silicones were analyzed using one-way ANOVA with concentration of nano ceramic fiber as the main variable. Specimens from VST- 50HD were also made and tested as control. Results: The mean values for tensile strength (MPa) of control group, 2-percent, 4-percent, and 6-percent reinforced nano ceramic fiber fillers were from 3.43 ± 0.12 to 5.48 ± 0.71. Tear strength (MPa) were from 2.34 ± 0.37 to 5.01 ± 0.39. Elongations at fracture were from 699.66 ± 43.69 to 793.51 ± 57.27. Shore A hardness were from 25.76 ± 2.18 to 38.76 ± 1.83. Conclusion: There was a significant difference (p < 0.001) in the mean tensile, tear and Shore A hardness strengths between the control group and 2-percent, 4-percent, and 6-percent percent reinforced nano ceramic fiber fillers; however, there was not a significant difference (p > 0.05) between 2-percent, 4-percent, and 6-percent reinforced nano ceramic fiber fillers. There was a significant difference (p < 0.001) in the mean elongation at fracture between the 2-percent and control group, 4-percent, and 6-percent reinforced nano ceramic fiber fillers; however, there was not a significant difference (p > 0.05) between control group, 4-percent, and 6-percent reinforced nano ceramic fiber fillers. The properties of the experiment were all lower than the control. Further research is needed to determine the appropriate material and amount of dispersing agent, coupling agent, and determination of the hydprophilicity of the nano ceramic fiber fillers with great emphasis on the dispersing agent.

Indiana University-Purdue University Indianapolis (IUPUI) / The objectives: 1. To compare the flexural strength, flexural modulus, and fracture toughness of specimens fabricated from recently marketed translucent full-contour zirconia, traditional zirconia, and lithium disilicate glass ceramic. 2. To compare the load-to-failure of crowns fabricated from recently marketed translucent full-contour zirconia, traditional zirconia, and lithium disilicate glass ceramic at their recommended tooth-reduction thickness. Methodology: Four groups of translucent zirconia (BruxZir, KDZ Bruxer, CAP FZ, Suntech zirconia), one group of traditional zirconia (CAP QZ) and IPS e.maxCAD) were tested. Twelve bars of each material were made and tested for flexural strength, and fracture toughness. Fracture patterns were imaged under SEM. Forty-eight crowns (8 from each group) were fabricated with CAD/CAM technique following manufacturers’ recommendations for the amount of tooth reduction. All the crowns were cemented to prepared epoxy resin dies with RelyX Unicem and tested for static load to failure in a universal machine. Result: In bar-shape samples, CAP QZ (traditional zirconia) showed the highest flexural strength (788.12 MPa), fracture toughness (6.85 MPa.m1/2), and fracture resistance (2489.8 N). All translucent zirconia groups show lower mechanical properties than QZ. However, there were no differences between translucent and traditional zirconia in the fracture resistance of the crown-shape samples. There was no significant difference in fracture resistance between IPS e.max crowns at recommended thickness and other zirconia crowns at recommended thickness. Conclusion: With less reduction of tooth structure, a high inherent strength and chip resistance make full-zirconia crowns a good alternative to porcelain-fused-to-metal crowns and all other ceramic crowns.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: New glass ceramics and Computer-Aided Design/Computer Assisted Manufacture (CAD/CAM) have become common aspects of modern dentistry. The use of posterior ceramic crowns with a high level of esthetics, fabricated using the CAD/CAM technology is a current treatment modality. Several materials have been used to fabricate these crowns, including lithium disilicate glass-ceramics, which have not been fully investigated in the literature. Objective: to investigate the load to fracture of lithium disilicate glass ceramic posterior crowns fabricated by CAD/CAM technology with different material thicknesses adhesively cemented on epoxy resin. Methods: Four groups of different ceramic thicknesses (0.5 mm, 1 mm, 1.5 mm, and 2 mm) were fabricated by milling CAD/CAM lithium disilicate IPS emax CAD blocks. A total of 68 posterior crowns were surface treated and luted with a resin adhesive cement on an epoxy resin model. Samples were fatigued then loaded to fracture using a universal testing machine to test the fracture strength. Statistical comparisons between various crown thicknesses were performed using one-way ANOVA followed by Fisher's Protected Least Significant Differences. Results: There was a significant difference in the load-to-fracture (N) value for all comparisons of the four thickness groups (p < 0.0001), except 2 mm vs. 1.5 mm (p = 0.325). The mean load-to-fracture (N) was significantly higher for 2 mm than for 1 mm or 0.5 mm. Additionally, the mean load-to-fracture was significantly higher for 1.5 mm than for 1 mm or 0.5 mm. Furthermore, the mean load-to-fracture was significantly higher for 1 mm than for 0.5 mm. Conclusion: Within the limitation of this study, it is advisable for clinical applications to consider a crown thickness of 1.5 mm or greater of milled lithium disilicate for posterior single teeth.

Indiana University-Purdue University Indianapolis (IUPUI) / The use of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), normally employed as a framework for all-ceramic restorations, has now started to be used without any veneering ceramics in patients with parafunctional activities. The aims of this study were to evaluate the influence of Y-TZP surface roughness on the wear behavior (volume/height loss) against glass-based ceramics (i.e., IPS Empress CAD and IPS e.max CAD, Ivoclar-Vivadent). Thirty-two Y-TZP full-contour zirconia (Ardent®) sliders (ϕ=2 mm, 1.5 mm in height) were milled in a CAD/CAM unit and sintered according to the manufacturer instructions. Sliders were embedded in brass holders using acrylic resin and then randomly allocated into 2 groups according to the surface treatment (n=16): G1-as-machined and G2-glazed (Diazir®). Empress and e.max antagonists were cut into tabs (13×13×2 mm) wet-finished and also embedded in brass holders. Two-body pin-on-disc wear testing was performed at 1.2 Hz for 25,000 cycles under a 3-kg load. Non-contact profilometry was used to measure antagonist height (μm) and volume loss (mm3). Qualitative data of the testing surfaces and wear tracks were obtained using SEM. Statistics were performed using one- and two-way ANOVAs (α=0.05). The results indicated that G1 yielded significantly higher mean roughness values (Ra=0.83 μm, Rq=1.09 μm) than G2 (Ra=0.53 μm, Rq=0.78 μm). Regarding antagonist loss, G1 caused significantly less antagonist mean height and volume loss (68.4 μm, 7.6 mm3) for Empress than G2 (84.9 μm, 9.9 mm3) while no significant differences were found for e.max. Moreover, Empress significantly showed lower mean height and volume loss than e.max (p<0.0001). SEM data revealed morphological differences on wear characteristics between the two ceramics against Y-TZP. Within the limitations of this study, e.max wear was not affected by Y-TZP surface roughness. However, Empress wear was greater when opposing glazed Y-TZP. Overall, based on our findings, surface glazing on full-contour Y-TZP did not minimize glass-ceramic antagonist wear when compared with as-machined group.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Numerous studies have reported the use of hydrofluoric (HF) acid as one of the most effective methods for the achievement of a durable bond between glass-based ceramics and resin cements. Nevertheless, there is little information available regarding the potential deleterious effect on the ceramic mechanical strength. Objectives: (1) to investigate the effect of HF acid etching regimens on the biaxial flexural strength of a low-fusing nanofluorapatite glass-ceramic (IPS e.max ZirPress, Ivoclar Vivadent), (2) to study the ability of an unfilled resin (UR) to restore the initial (i.e., before etching) mechanical strength, and (3) to evaluate the effect of HF acid etching on the ceramic surface morphology before and after UR treatment via scanning electron microscopy (SEM). Methods: One hundred and forty-four disc-shaped (15 ± 1 mm in diameter and 0.8 ± 0.1 mm in thickness) IPS e.max ZirPress specimens were allocated into 12 groups, as follows: G1-control (no etching), G2-30 s, G3-60 s, G4-90 s, G5-120 s, G6- 60 + 60 s. Meanwhile, groups (G7- G12) were treated in the same fashion as G1-G6, but followed by silane and UR applications. Surface morphology evaluation of non-etched and etched IPS e.max ZirPress (G1-G12) was carried out by scanning electron microscopy (SEM). The flexural strength was determined by biaxial testing as described in ISO 6872. Statistics were performed using two-way ANOVA and the Sidak multiple comparisons (α = 0.05). In addition, the Weibull statistics were estimated. Results: A significant effect of etching time (p=0.0290) on biaxial flexural strength was observed. Indeed, G4 led to a significantly (p=0.0392) higher flexural strength than G1. Correspondingly, G10 revealed a considerably higher flexural strength than G7 (p=0.0392). Furthermore, biaxial flexural strength was significantly higher for G7 – G12 than for G1 – G6 (p<0.0001). For G1 – G6, G4 showed the highest Weibull characteristic strength while the lowest Weibull characteristic strength was seen in G6. In G7 – G12, the highest Weibull characteristic strength was presented in G10 whereas G7 had the lowest. Finally, the SEM data revealed that the HF acid etching affected the surface of IPS e.max ZirPress by generating pores and irregularities and more importantly that the UR was able to penetrate into the ceramic microstructure. Conclusion: Within the limitations of this study, HF acid etching time did not show a damaging effect on the biaxial flexural strength of the IPS e.max ZirPress ceramic. Moreover, the ceramic biaxial flexural strength could be enhanced after UR treatment.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Elucidating the lithium disilicate system like the popular IPS e.max® CAD (LS2), made specifically for Computer-Aided Design and Computer-Aided Manufacturing (CAD-CAM), as a function of temperature unravels new ways to enhance material properties and performance. Objective: To study the effect of various thermal processing on the crystallization kinetics, crystallite microstructure, and strength of LS2. Methods: The control group of the LS2 samples was heated using the standard manufacturer heating-schedule. Two experimental groups were tested: (1) an extended temperature range (750-840 °C vs. 820-840 °C) at the segment of 30 °C/min heating rate, and (2) a protracted holding time (14 min vs. 7 min) at the isothermal temperature of 840 °C. Five other groups of different heating schedules with lower-targeted temperatures were evaluated to investigate the microstructural changes. For each group, the crystalline phases and morphologies were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Differential scanning calorimeter (DSC) was used to determine the activation energy of LS2 under non-isothermal conditions. A MTS universal testing machine was used to measure 3-point flexural strength and fracture toughness, and elastic modulus and hardness were measured by the MTS Nanoindenter® XP. A one-way ANOVA/Tukey was performed per property (alpha = 0.05). Results: DSC, XRD, and SEM revealed three distinct microstructures during LS2 crystallization. Significant differences were found between the control group, the two aforementioned experimental groups, and the five lower-targeted-temperature groups per property (p<0.05). The activation energy for lithium disilicate growth was 667.45 (± 28.97) KJ/mole. Conclusions: Groups with the extended temperature range (750-840 °C) and protracted holding time (820-840 °C H14) produced significantly higher elastic-modulus and hardness properties than the control group but showed similar significant flexural-strength and fracture-toughness properties with the control group. In general, explosive growth of lithium disilicates occurred only when maximum formation of lithium metasilicates had ended.