Basic Informations

C.V

Master Title

Effect Of Loading Angles On The Fracture Resistance Of Two Non-Metallic Posts and Core Systems

Master Abstract

This study was designed to evaluate the effect of different loading angles on the fracture resistance of two types of non-metallic, fiber reinforced and ceramic posts. Twenty intact upper central incisors were selected, decoronated horizontally and aligned in acrylic blocks then subjected to uniform reduction using lathe cut machine. Zirconium dioxide ceramic post (Cosmopost), glass fiber-reinforced post (Easypost) and composite core were fabricated for each tooth using a specially designed core former to have standardized preparation. Direct wax patterns were fabricated for each tooth then cast in NiCr alloy. The fracture resistance of teeth restored by 2 types of posts was measured under oblique (135 degree) and vertical loading using universal testing machine. For each tested post, the mean fracture load of samples tested at axial loading was significantly higher than that tested at oblique (135-degree) loading. Also for each tested loading angle, the Zirconium dioxide Ceramic post group showed significant higher mean fracture load value compared to Glass fiber-reinforced post group.

PHD Title

Evaluation of wear and fracture resistance of zirconia monolithic restorations: an in vitro study

PHD Abstract

This in vitro study was designed to evaluate the wear effect and the fracture resistance of monolithic translucent zirconia (TZI) based restorations. In the first part of this study, the effect of different surface finish of tested ceramic bar-shaped specimens on the wear of human enamel was evaluated. A total of twenty eight ceramic bar-shaped specimens was cut out from CAD/CAM blocks, fourteen of monolithic TZI (Group Z) and fourteen of feldspathic porcelain (Group P) using electrical high-precision microsaw. Each group was subdivided into two subgroups of seven specimens each according to the surface finish, polished one (Subgroup p) and glazed one (Subgroup g), then were exposed to wear testing in a custom made chewing simulator specially fabricated for this study. The bar-shaped specimens were subjected to wear testing for 50.000 cycles at frequency of 1.2 Hz (72 cycles/min) under a weight of 50 N. scanning electron microscope (SEM) was used to examine one surface from each subgroup exposed to wear testing.The weight loss of human enamel caused by different ceramic bar-shaped specimens was calculated. The mean (SD) weight loss values of human enamel after wear test were 0.167±0.004 gm for the polished Zirconia (Zp), 0.169±0.005 gm for glazed Zirconia (Zg), 0.166±0.003 gm for polished Porcelain (Pp) and 0.172±0.006 gm for glazed Porcelain (Pg). Summary and Conclusions 143 Two-way ANOVA test was used to study the effect of material, surface treatment and their interactions on weight loss of human enamel. The results showed that material, surface treatment and the interaction between the two variables had no statistically significant effect on mean weight loss. Regardless of surface treatment, there was no statistically significant difference between weight losses in the two materials. Regardless of material, there was no statistically significant difference between weight losses after polishing or glazing. In the second part of this study, the fracture resistance of zirconia based FDPs after artificial aging procedures was evaluated. Monolithic TZI 3-unit FDPs were fabricated using a CAD/CAM machine on two full crown master models prepared from stainless steel with 1 mm deep circumferential chamfer preparation and were fixed into a stainless steel holder to simulate a prepared second lower premolar and a second lower molar. A total of fourteen 3-unit FDPs were divided into two groups of seven specimens each, the first aged TZI group (Group A) was subjected to accelerated artificial ageing procedures in an autoclave at hydrothermal conditions 134 ?C /2 bars for 5 hours. The second non-aged TZI group (Group B) was not subjected to any ageing procedures and was designed as control group. Specimens of both groups were loaded compressively in a universal testing machine at cross head speed 0.5 mm/min until fracture occurred. Scanning electron microscope (SEM) was used to examine the fractured surfaces. Also A representative part taken from specimen of each tested groups at fractured site was examined X-ray diffraction (XRD) device to detect the percentage of monoclinic (m) phase. Summary and Conclusions 144 Student’s t-test was used to compare between fracture resistances of both groups. the fracture resistance mean (SD) values of non-aged TZI (Group B) was 2406.9±306.8 N which showed statistically significantly higher than that of aged group (Group A) which was 1964.5±234.5 N. The percentage of monoclinic (m) phase detected by XRD device software in non-aged TZI (Group B) was nearly 0 weight % and in aged TZI (Group A) was about 42 weight %. Conclusions Within the limitations of this in vitro study, the following conclusions were drawn: 1. Monolithic TZI and feldspathic porcelain based restorations manufactured from CAD/CAM blocks and subjected to different surface finish (polishing and glazing) have similar wear effect on human enamel. 2. Accelerated artificial aging decreases the fracture resistance of monolithic TZI FDPs.