Objective: To assess the influence of changing the thickness ratio between the framework material which was either 3-YTZP or PEEK, and the veneering milled lithium disilicate on color difference and translucency parameter of bilayered restorations.
Materials and Methods:Sixty disc-shaped specimens composed of partially stabilized tetragonal nano-crystalline zirconia or PEEK veneered with milled lithium disilicate (IPS e.max CAD) were randomly divided into two groups (n=30) according to the framework material implemented. Each group was split into 3 subgroups based on the thickness ratio between the framework and the overlying lithium disilicate. The thickness ratios of the framework to the lithium disilicate (T FM : T VLD ) were 0.5mm:1mm, 0.7mm:0.8mm, and 1mm:0.5mm. Color difference (∆E) and translucency parameter (TP) of all specimens were measured using a laboratory spectrophotometer.Results: Two-way ANOVA results showed that the type of framework, the thickness ratio, and the interaction between both variables, had a significant effect (p<0.001) on (∆E). T FM : T VLD =0.5mm:1mm subgroup showed the lowest (∆E) values in both groups. For (TP), two-way ANOVA results showed that only the framework material and thickness ratio had a significant effect (p<0.001) on (TP). (ZIR) group specimens showed statistically significantly (p<0.001) higher (TP) values than (PK) group specimens when all thickness ratios were considered. T FM : T VLD =0.5mm:1mm subgroup in both groups displayed the highest (TP) values.
Conclusions:Changing the ratio between the framework thickness and that of IPS e.max CAD had a significant impact on color difference and translucency parameter with both materials in all thickness ratios.
Objective
The purpose of this study was evaluating the biaxial strength of bi-layered PEEK restorations before and after aging using different veneering materials in different thickness ratios.
Material and Methods
Ninety specimens of thickness 1.5 mm were divided into three groups according to their veneering material. Group (CAD LD): BioHPP discs veneered with CAD milled lithium disilicate (n=30), group (CAD C): BioHPP discs veneered with CAD milled composite (n=30), and group (LC): BioHPP discs veneered with conventionally layered composite (n=30). Each group was subdivided into 3 subgroups (n=10) according to the different thickness ratios between the core and the veneering material (TC:TV). Subgroup 1: TC:TV=1:0.5, subgroup 2: TC:TV=0.7:0.8, and subgroup 3: TC:TV=0.5:1. Half of the specimens of each subgroup were subjected to thermocycling, and the bi-axial flexural strength of all specimens was tested before and after aging. Three-way ANOVA followed by Bonferroni’s post hoc test were used for data analysis. The significance level was set at P ≤ 0.05.
Results
Material, thickness ratio, and aging all had a significant effect on biaxial flexural strength. (LC) group had the highest biaxial flexural strength. TC:TV=0.5:1 showed the lowest biaxial flexural strength. All groups showed significant decrease in biaxial flexural strength after aging.
Conclusions
Veneering material for PEEK together with the thickness ratio between the core and veneering material greatly affect the flexural strength of bi-layered restorations. Thermocycling negatively impacts the flexural strength of PEEK bi-layered restorations.
Clinical significance
According to the results of that study, PEEK cores are best veneered with conventionally layered composite with core to veneering thickness ratio being 1:0.5.
Objective: To evaluate the flexural strength of different combinations of modified PEEK and 3-YTZP veneered restorations as well as the effect of aging on those combinations.
Materials and Methods:Two core materials; partially sintered tetragonal monolithic zirconia and modified PEEK, and three veneering materials; lithium disilicate glass-ceramic, packable composite, and veneering porcelain were used. A total of sixty specimens were randomly divided into 3 groups (n=20). The specimens were constructed in the form of bilayered core/veneer disks of diameter12 mm and total thickness 1.5 mm. Half of the specimens of each group were tested for biaxial flexural strength using the piston-on-three-balls test. The other half of the specimens were subjected to artificial aging and then tested for biaxial flexural strength.Results: Two-way ANOVA showed there was a significant effect for the material of the bilayered restoration, aging, and the interaction between them on biaxial flexural strength. Unaged veneered Zirconia and Crea.lign veneered PEEK had significantly higher values (398.85±29.58) and (391.31±15.59) respectively than IPS e.maxCAD veneered PEEK (222.13±18.77). For the aged subgroups, veneered Zirconia (303.51±35.64) and Crea.lign veneered PEEK (277.10±13.37) also showed significantly higher values than IPS e.maxCAD veneered PEEK (198.10±6.57). For IPS e.max CAD veneered PEEK, there was no significant difference between unaged and aged sub-groups (p=0.100). However, for other materials, aging caused significant decrease in biaxial flexural strength values (p<0.001).Conclusions: Both Crea.lign veneered PEEK and porcelain veneered 3-YTZP could be used with the same efficiency, regarding flexural strength, as bi-layered restorations. Aging has a negative effect on both materials' combinations
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