ABSTRACT
Objectives: This study was undertaken to correlate the shear bond strength of a Ni-Cr alloy bonded to conventional porcelain to their corrosion behavior in three different electrolytes
Methods: Twenty porcelain-metal discs were prepared, five were randomly selected to serve as controls. Electrochemical tests were performed, using a potentiostat, in three different media; artificial saliva, 4% acetic acid, and an alkaline borax solution. Corrosion testing was performed to determine the effect of changing the pH on the polarization parameters, the corrosion current density and the corrosion rates of the PFM. Changes in microstructure [SEM] and chemical composition [EDX] were determined. A universal testing machine was used to measure the shear bond strength of the control specimens and specimens after corrosion at a crosshead speed of 0.5 mm/min
Results: A significant change was notices in the corrosion parameters of the PFM in the acidic medium compared to the other two media. Elemental release from both the conventional feldspathic porcelain and the Ni-Cr alloy was significantly higher in the acidic medium. The highest mean shear bond strength was detected with the control group, while the lowest values were measured with those exposed to the acidic medium
Conclusions: Brief exposure [30 min] to 4% acetic acid increased the subsequent elemental release of Ni, Mo, and Cr from the alloy and promoted the leaching out of inorganic ions; Na, K, and Al from the porcelain side. Shear bond strength evaluation of the porcelain-metal specimens, revealed a strong relation between chemical degradability, corrosion susceptibility and bond strength
ABSTRACT
Statement of problem. The influence of taper angle of anterior abutment on the fracture strength of In-Ceram Zirconia FPDs in unclear
Purpose. The purpose of this study was to determine the effect of different taper angles of the anterior abutment on the fracture strength of In-Ceram Zirconia fixed partial dentures using a custom-made load-applicator
Materials and Methods: Three stainless steel, three-unit master models with a maxillary premolar and second molar as abutments were made. Design I had a 6-degrees taper premolar preparation, Design II and III had an 8-degrees and a 10-degrees axial taper. Fifteen In-Ceram Zirconia core frameworks were milled using copy-milling technique using the Celay system [5 frameworks for each design]. Epoxy resin models were made, and frameworks were cemented using Panavia F adhesive resin cement following the manufacturer specifications. Frameworks were stored in artificial saliva for 90 days during which they were intermittently thermocycled for 5,000 cycles. To simulate oral condition, frameworks were loaded cyclically for 100,000 cycles with a load of 500N using a universal testing machine. Fracture loads were recorded and statistically analyzed
Results: The highest failure loads were associated with Design I core frameworks, whereas, the lowest was that of Design III with no statistically significant difference between Design II and III
Conclusions: The smaller the angle of taper of the anterior abutment, the greater is the framework resistance to fracture. With the use of the new test approach, the use of In-Ceram Zirconia can be promising as a posterior FPD
ABSTRACT
This study was conducted to evaluate the stability of three different ceramic systems after their immersion in solutions with different pH values regarding the surface texture and ionic release. A total of 45 ceramic disc specimens were prepared. They were divided into 3 groups, 15 each according to the type of the tested ceramic material. These groups were further subdivided into 3 subgroups, 5 each depending on the proposed test media. Evaluation of the surface texture was carried out quantitatively by analyzing the surface roughness of the ceramic specimens before and after immersion in different test solutions using the Image analysis software. For qualitative analysis, scanning electron microscope was done to study the effect of immersion in different conditioning media with different pH values on the surface morphology of the three tested ceramic materials. The determination of elements leached from the ceramic materials [aluminum, silicon, lithium, sodium and potassium] was done with inductively coupled plasma optical emission spectroscopy
Results: The surface roughness; the control group of IPS Empress 2 exhibited the least surface roughness value which was significant among the other control groups. A significant increase in the mean Ra values was found over the experimental period for all tested ceramics immersed in different solutions. Concerning each ceramic, Duceram showed no significant change in its surface roughness in the three storage media. Meanwhile Duceram LFC's surface roughness was significantly different in the three immersion media, where citric acid caused the highest surface damage and lactic acid caused the least one. regarding IPS empress 2, conditioning in either acetic or citric acid caused comparable surface damage which was significantly higher than that caused by lactic acid. Interceramic comparisons revealed that acetic acid storage caused comparable surface damage to both Duceram LFC and IPS Empress 2. Their values were significantly higher than half of Duceram. On the other hand, citric acid immersion caused a significant increase in surface roughness of Duceram LFC followed by IPS Emress 2 and then Duceram. Finally lactic acid conditioning medium was destructive in a similar way to the surfaces of both Duceram and IPS Empress 2. Their Ra values were significantly higher than that of Duceram LFC
The ion release; all materials used released different ions which varied in amounts according to the storage media in which they were immersed. Generally, citric acid solution was the most corrosive one for the three ceramic materials regarding the aluminum, silicon and lithium ion release while lactic acid solution was the least corrosive medium. On the other hand lactic acid solution was the most corrosive medium for the three materials regarding sodium ion release and citric acid solution released the least amount of sodium. Concerning potassium ion release, interceramic comparisons revealed that in acetic acid solution, Duceram LFC recorded the highest value followed by IPS Empress 2 and finally Duceram. Meanwhile, in citric acid solution, IPS empress 2 occupied the first position, Duceram the second and Duceram LFC the last. In lactic acid solution, the comparable values of potassium ion release from Duceram LFC and IPS Empress 2 were significantly lower than that of Duceram
Conclusion: Surface roughness and chemical durability of the tested ceramic materials are dramatically affected by the pH values of the storage media and the composition of each ceramic system as well as their processing technique. The type and the amount of ion release from each ceramic varied according to the solution medium. Surface roughness and microstructure are influenced by the type and the amount of ion release from each ceramic system
Clinical relevance: Good oral hygiene is mandatory to avoid any possible damages to the surface as well as the microstructure of cceramic materials as they might be affected by variations in pH values
ABSTRACT
This study was conducted to evaluate the effect of the cement type on shear bond strength, seating and porcelain fracture resistance of the newly introduced galvanoceramic restoration. For measuring shear bond strength using universal testing machine, thirty disc shaped samples were constructed and were classified into three groups [10 per each] according to the cement type used to bond them in pairs. Groupl zinc phosphate cement, group 2 resin modified glass ionomer cement group 3 adhesive resin cement. For measuring the marginal accuracy using stereomicroscope, and porcelain fracture resistance using universal testing machine in compressive mode, 15 crown shaped samples were constructed according to the manufacturer instructions and classified into three groups [5 per each] according to the cement type used for cementation over epoxy die. Groupl zinc phos phate cement, group 2 resin modified glass ionomer cement group 3 adhesive resin cement. Results showed that porcelain firing cycle resulted in significant marginal discrepancy. After cementation resin modified glass ionomer showed least marginal discrepancy, higher shear bond strength and higher porcelain fracture resistance compared to adhesive resin and zinc phosphate cements. In cases of compromised tooth preparation, adhesive resin and resin modified glass ionomer cements can be successfully used in cementation of galvanoceramic restoration