Developing porcelain manufacturing technology provides lower fusing porcelains to avoid thermal stresses in metal substructure, particularly for titanium and gold alloys. So far, aesthetic properties of low fusing ceramics have not been well documented. The purpose of this study was, therefore, to estimate the long-term colour stability of low fusing ceramics by using an accelerated aging procedure. Four different ceramics (Vita Omega 900, Vita Titankeramik, Ceramco Finesse, Ceramco II) were used. Porcelain samples 11 +/- 0.5 mm in diameter and 1.4 +/- 0.2 mm in thickness were prepared in three commonly used shades to provide 10 samples of each group. The samples were fired in accordance with the recommendations of the manufacturers. CIE Lab readings were recorded with a spectrophotometer prior to experiments and after a 100 h accelerated aging. The results revealed that only Ceramco Finesse porcelain had a colour change (DeltaE > 1) that is noticeable by human eye. When the shades of porcelains were compared, C3 had greater colour change compared with A3 and B3 shades (P < 0.05).

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Objective:For most endodontically treated teeth, tooth-colored post-core systems are preferable for esthetic reasons. Therefore, improvements in material strength must also consider tooth colored post-core complexes. The objective of this study was to evaluate the difference in tooth colored post–core complex strengths.Materials and Methods:A total of 33 human maxillary central incisor teeth were used for this study, with three groups of 11 teeth. Three different methods were used to fabricate all-ceramic post-core restorations: zirconia blanks, Cerec 3D-milled to one-piece post-core restorations (Test Group 1); feldspathic cores (from feldspathic prefabricated CAD/CAM blocks) adhesively luted to CosmoPost zirconia posts (Test Group 2); and IPS Empress cores directly pressed to CosmoPost zirconia posts (Test Group 3). All-ceramic crowns from feldspathic ceramic were constructed using a CAD/CAM system (Cerec 3D) for all specimens. The post-core complexes were tested to failure with the load applied at 45° angled relative to the tooth long axis. The load at fracture was recorded.Results:The maximum fracture strength of the milled zirconia cores (Test Group 1) was 577 N; corresponding values for the milled feldspathic cores (Test Group 2) and the pressed cores (Test Group 3) were 586 and 585 N, respectively. Differences were not statistically significant at P < 0.05 (P = 0.669).Conclusions:All-ceramic cores adhesively luted on zirconia posts and one-piece all-ceramic zirconium post–core structures offer a viable alternative to conventional pressing.

The retention in root canals of Flexi-Posts, Para-Posts and Brasseler/Vlock-Posts was measured using tensile and compressive/shear forces. Forty-two extracted maxillary anterior teeth were embedded in self-curing acrylic resin and treated endodontically. Each root canal was prepared with the appropriate matching drills for the post-core system chosen. Each post-core was cemented in the canal with zinc phosphate cement. A tensile force was applied along the long axis of each tooth and the force needed to dislodge the post-core was recorded. There was no difference in retention between the small diameter posts, but the difference between the medium and the large diameter posts, however, was significant. In the medium diameter post group, the Flexi-Post was approximately twice as retentive as the other two post-core systems evaluated. In the second series of tests compressive/shear force was applied at an angle of 130 degrees to the long axis of the tooth. The retention difference between the small diameter posts was found to be statistically significant, Flexi-Posts being more retentive than Para-Posts and B/V-Posts.

This study evaluated the adhesion of zirconia core ceramics with their corresponding veneering ceramics, having different thermal expansion coefficients (TECs), when zirconia ceramics were coloured at green stage. Zirconia blocks (N=240; 6 mm×7 mm×7 mm) were manufactured from two materials namely, ICE Zirconia (Group 1) and Prettau Zirconia (Group 2). In their green stage, they were randomly divided into two groups. Half of the specimens were coloured with colouring liquid (shade A2). Three different veneering ceramics with different TEC (ICE Ceramic, GC Initial Zr and IPS e.max Ceram) were fired on both coloured and non-coloured zirconia cores. Specimens of high noble alloys (Esteticor Plus) veneered with ceramic (VM 13) (n=16) acted as the control group. Core–veneer interface of the specimens were subjected to shear force in the Universal Testing Machine (0.5 mm⋅min−1). Neither the zirconia core material (P=0.318) nor colouring (P=0.188) significantly affected the results (three-way analysis of variance, Tukey's test). But the results were significantly affected by the veneering ceramic (P=0.000). Control group exhibited significantly higher mean bond strength values (45.7±8) MPa than all other tested groups ((27.1±4.1)−(39.7±4.7) and (27.4±5.6)−(35.9±4.7) MPa with and without colouring, respectively) (P<0.001). While in zirconia–veneer test groups, predominantly mixed type of failures were observed with the veneering ceramic covering <1/3 of the substrate surface, in the metal–ceramic group, veneering ceramic was left adhered >1/3 of the metal surface. Colouring zirconia did not impair adhesion of veneering ceramic, but veneering ceramic had a significant influence on the core–veneer adhesion. Metal–ceramic adhesion was more reliable than all zirconia–veneer ceramics tested.

RFA is not a reliable method in the assessment of the initial contact loss at bone-implant interface.