Fitting Accuracy And Microstructural Changes Of Two Monolithic Zirconia Systems As Influenced

Abstract

Appearance of monolithic translucent Zirconia restorations as an alternative for conventional veneered Zirconia. Zirconia has the advantage of high strength and biocompatibility, the main disadvantage is the decreased translucency of such type of restorations. This study aims to assess the effect of hydrothermal aging (steam autoclaving) and cyclic loading (custom made cyclic loading machine) on the properties of two monolithic Zirconia systems (wet and dry milling), including marginal fit, internal fit, microstructural changes assessed by XRD and SEM analysis , surfacetopography and fracture resistance as a result of such microstructural changes. A total of twenty identical CAD /CAM monolithic Zirconia crowns fabricated from two different monolithic Zirconia systems. Crowns were divided into two major groups according to the system used for their fabrication (either wet or dry), and were used to asses marginal and internal fit before and after aging , by measuring the gap between the crowns and their corresponding epoxy dies using stereomicroscope. Twenty discs with similar dimension (10 mm diameter and 1.5 mm thickness) were also divided into two major groups according to system used for their fabrication. Furthermore each group of discs was further divided into two subgroups according to being subjected to aging or not. Discs were used to assess microstructural changes using XRD, SEM and stereo microscope to assess surface roughness following aging, as well as fracture resistance using universal testing machine. Results revealed acceptable marginal and internal fit before and after aging, yet dry milling system showed more superior results than wet milling samples. Such results were also confirmed on the microstructural level, as dry milling system samples showed less microstructural changes regarding XRD, SEM and Ra than that of the wet milling system ones. Flexural strength testing revealed no significant effect of aging on both systems, meanwhile the flexural strength of wet milling system was lower than that of the dry milling system.