All-ceramic and porcelain-fused-to-metal fixed partial dentures: a comparative study by 2D finite element analyses

All-ceramic fixed partial dentures (FPDs) have an esthetic approach for oral rehabilitation. However, metal-ceramic FPDs are best indicated in the posterior area where the follow-up studies found a lower failure rate. This 2D finite element study compared the stress distribution on 3-unit all-ceramic and metal-ceramic FPDs and identified the areas of major risk of failure. Three FPD models were designed: (1) metal-ceramic FPD; (2) All-ceramic FPD with the veneering porcelain on the occlusal and cervical surface of the abutment tooth; (3) All-ceramic FPD with the veneering porcelain only on the occlusal surface. A 100 N load was applied in an area of 0.5 mm² on the working cusps, following these simulations: (1) on the abutment teeth and the pontic; (2) only on the abutment teeth; and (3) only on the pontic. Relative to the maximum stress values found for the physiological load, all-ceramic FPD with only occlusal veneering porcelain produced the lowest stress value (220 MPa), followed by all-ceramic FPD with cervical veneering porcelain (322 MPa) and metal-ceramic FPD (387 MPa). The stress distribution of the load applied on the abutments was significantly better compared to the other two load simulations. The highest principal stress values were low and limited in a small area for the three types of models under this load. When the load was applied on the pontic, the highest stress values appeared on the connector areas between the abutments and pontic. In conclusion, the best stress values and distribution were found for the all-ceramic FPD with the veneering porcelain only on the occlusal surface. However, in under clinical conditions, fatigue conditions and restoration defects must be considered

Corrosion behavior of zirconia in acidulated phosphate fluoride

ABSTRACT Objective The corrosion behavior of zirconia in acidulated phosphate fluoride (APF) representing acidic environments and fluoride treatments was studied. Material and Methods Zirconia rods were immersed in 1.23% and 0.123% APF solutions and maintained at 37°C for determined periods of time. Surfaces of all specimens were imaged using digital microscopy and scanning electron microscopy (SEM). Sample mass and dimensions were measured for mass loss determination. Samples were characterized by powder X-ray diffraction (XRD) to detect changes in crystallinity. A biosensor based on electrochemical impedance spectroscopy (EIS) was used to detect ion dissolution of material into the immersion media. Results Digital microscopy revealed diminishing luster of the materials and SEM showed increased superficial corrosion of zirconia submerged in 1.23% APF. Although no structural change was found, the absorption of salts (sodium phosphate) onto the surface of the materials bathed in 0.123% APF was significant. EIS indicated a greater change of impedance for the immersion solutions with increasing bathing time. Conclusion Immersion of zirconia in APF solutions showed deterioration limited to the surface, not extending to the bulk of the material. Inferences on zirconia performance in acidic oral environment can be elucidated from the study

Colorimetric evaluation of the influence of five different restorative materials on the color of veneered densely sintered alumina

Purpose: Since the introduction of densely sintered alumina ceramic material in prosthetic dentistry for the fabrication of all-ceramic crowns, no scientific data have been presented on the color of these restorations in combination with different restorative materials. The purpose of this in vitro study was to evaluate the influence of five different restorative materials used for implant abutments or posts and cores on the color of veneered densely sintered alumina. Materials and Methods: Sixty discs, 0.6 mm in thickness and 10 mm in diameter, were made out of densely sintered alumina ceramic material (Procera®, Nobel Biocare, Gothenburg, Sweden) and veneered using feldspathic porcelain (AllCeram®, Ducera, Rosbach, Germany) for a total thickness of 2 mm. Ten of the discs were evaluated colorimetrically using the CIE, L*, a*, b* system (control group). In addition, 50 discs, 3 mm in thickness and identical diameter, were fabricated using the following restorative materials (five different materials used on 10 specimens each): (1) high-precious gold alloy, (2) aluminum-oxide ceramic material, (3) titanium metal alloy, (4) yttrium-stabilized zirconium dioxide ceramic material, and (5) glass-ceramic material. The 50 veneered densely sintered alumina specimens were bonded to the 50 restorative specimens using an autopolymerizing luting composite. L*, a*, b* color coordinates were measured 10 times for each veneered densely sintered alumina specimen. Color differences were calculated using the equation ΔE = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2. ΔE values correspond to differences between the control group and each of the five materials groups. Results: Mean color differences (ΔE) and SDs for each group were as follows: ΔE (1) = 1.42 ± 0.5, ΔE (2) = 1.53 ± 0.5, ΔE (3) = 1.55 ± 0.4, ΔE (4) = 1.95 ± 0.5, ΔE (5) = 1.23 ± 0.3. All restorative materials induced changes to the densely sintered alumina color relative to the original color. One-way analysis of variance (ANOVA) tests showed statistically significant differences in ΔE between the groups; however, the Student-Newman-Keuls test revealed that the only statistically significant difference was between groups 4 and 5. Color differences between the groups were not visually perceivable (ΔE < 2)

Evaluation of air-particle abrasion of Y-TZP with different particles using microstructural analysis

BACKGROUND: This study evaluated the effect of air-particle abrasion with different particle sizes on the surface roughness and phase transformation of yttria-stabilized tetragonal zirconia ceramics (Y-TZP). METHODS: Eighty-four Y-TZP discs of 15 mm diameter and 1.0 mm thickness were fabricated. The samples were divided into four groups (n = 21): (1) air-particle abrasion with 30 μm CoJet sand blast coating agent (CoJet, 3M ESPE); (2) 50 μm Al2O3 particles; (3) 110 μm Al2O3 particles; and (4) 250 μm Al2O3 particles. Each group was further divided into three subgroups each (n = 7) and treated for 5 seconds, 15 seconds and 30 seconds. Mean surface roughness was determined using a profilometer. The surfaces were analysed with a scanning electron microscope. XRD analysis was employed and the relative amount of the monoclinic phase was calculated. The results were statistically analysed by two-way analysis of variance (ANOVA, p < 0.05). RESULTS: Air-particle abrasion with 250 μm Al2O3 particles for 30 seconds had the highest surface roughness (p < 0.001) and a significantly higher amount of monoclinic phase compared to air-particle abrasion with 30 μm, 50 μm and 110 μm particles (p < 0.001). CONCLUSIONS: Duration and particle size of air-particle abrasion affects the roughness and phase transformation of Y-TZP. Longer treatment times with larger particles may result in degradation of material