Strain gauge analysis of the effect of porcelain firing simulation on the prosthetic misfit of implant-supported frameworks.

OBJECTIVES: This study investigated the effect of porcelain firing on the misfit of implant-supported frameworks and analyzed the influence of preheat treatment on the dimensional alterations. MATERIALS AND METHODS: Four external-hex cylindrical implants were placed in polyurethane block. Ten frameworks of screw-retained implant-supported prostheses were cast in Pd-Ag using 2 procedures: (1) control group (CG, n = 5): cast in segments and laser welded; and test group (TG, n = 5): cast in segments, preheated, and laser welded. All samples were subjected to firing to simulate porcelain veneering firing. Strain gauges were bonded around the implants, and microstrain values (µÎµ = 10⁻6ε) were recorded after welding (M1), oxidation cycle (M2), and glaze firing (M3). Data were statistically analyzed (2-way analysis of variance, Bonferroni, α = 0.05). RESULTS: The microstrain value in the CG at M3 (475.2 µÎµ) was significantly different from the values observed at M1 (355.6 µÎµ) and M2 (413.9 µÎµ). The values at M2 and M3 in the CG were not statistically different. Microstrain values recorded at different moments (M1: 361.6 µÎµ/M2: 335.3 µÎµ/M3: 307.2 µÎµ) did not show significant difference. CONCLUSIONS: The framework misfit deteriorates during firing cycles of porcelain veneering. Metal distortion after porcelain veneering could be controlled by preheat treatment.

The effect of glazing on the biaxial flexural strength of different zirconia core materials.

The aim of this study was to evaluate the effect of glazing on biaxial flexural strength of different zirconia core materials. Disc-shaped zirconia (ZirkonZahn, Cercon, Ceramill) specimens (15 mm x 1.15+/-0.02 mm) were prepared according to manufacturers' instructions. The specimens from each system were divided into 2 groups (N= 10): unglazed and glazed. Glaze liquid was applied on the entire surface of the specimens of the glazed group and fired according to manufacturers' instructions. Flexural strength test was performed in a universal testing machine (crosshead speed: 1 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (p= 0.05). The mean flexural strength values for unglazed ZirkonZahn specimens (1388+132 MPa) were significantly higher than those of unglazed Cercon (1104+124 MPa) and unglazed Ceramill (1172+127 MPa) specimens. The mean flexural strength of glazed specimens did not show any statistically significant difference. Glazing decreased the flexural strength results significantly for all systems (p< 0.05). Glazing decreased the flexural strength values for ZirkonZahn, Cercon and Ceramill specimens. Unglazed ZirkonZahn specimens revealed significantly higher mean flexural strength values than that ofunglazed and glazed zirconia materials tested in this study.

The effect of glazing on the biaxial flexural strength of different zirconia core materials

El objetivo de este estudio fue evaluar el efecto del glaseado sobre la resistencia flexural biaxial de diferentes tipos de materiales para núcleo a base de circonia. Se confeccionaron especímenes de circonia en forma de disco (15 mm x 1.15±0.02 mm) de acuerdo con las instrucciones delfabricante. Los especímenes de cada sistema fueron divididos en dos grupos (n=10): glaseados y sin glasear. El líquido glaseador fue aplicado sobre toda la superficie de los especímenes del grupo glaseado y fue cocido de acuerdo con las instrucciones del fabricante. Se llevó a cabo el ensayo de resistencia flexural en una máquina universal (velocidad de desplazamiento del cabezal: 1mm/min). Los datos fueron analizados estadísticamente pormedio de ANOVA de dos vías y prueba de Tukey (p=0.05). El valor medio de resistencia flexural para los especímenes sin glasear ZirkonZahn (1388±132 MPa) fue significativamentemás elevado que los especimenes sin glasear Cercon (1104±124 MPa) y Ceramill (1172±127 MPa). El valor medio de resistencia flexural para los especimenes glaseados no mostródiferencias significativas. El glaseado disminuyó significativamente la resistencia flexural de todos los sistemas (p<0.05). El glaseado disminuye los valores de resistencia flexural de los especímenes de ZirkonZahn, Cercon y Ceramill. Los especimenes sin glasear ZirkonZahn revelaron valores significativamente máselevados que aquellos materiales glaseados y sin glasear a basede circonia empleados en este estudio.