Fracture Resistance of Nano Hybrid Ceramics Versus Lithium Di-Silicate Restorations with Two Finish Line Curvatures : (In Vitro study) /

Abstract

Beauty is chased and demanded by the population as the technology and the media expands. The visual perception of esthetics is relative, though people seek what they believe is beauty. A good smile has a great impact of a person’s impression received by others. Thus, the increased esthetic demands of patients requires seeking dental cosmetic treatments.1 The introduction of dental ceramic restorations passed through many developmental steps that started with porcelain fused to metal (PFM). At that time, the porcelain used for restorations didn’t show optimum mechanical properties to be used by itself. The porcelain itself is biocompatible with the oral tissues and showed promising physical propertied. Its main drawback is the surface flaws and voids, brittleness, low fracture toughness and low tensile strength, thus required a metal core. A thickness of 1.5 mm is required to produce a mechanically and physically acceptable metal-ceramic restoration. Designing a new ceramic material that can withstand occlusal forces without metal core made a significant impact in dental technology and market. The goal to fabricate a ceramic restoration was to eliminate the drawbacks of PFM as metal showing at the margins, color and shade mismatch and chipping of veneered porcelain. Since mid 1980’s dental ceramic technology has changed by producing pressable ceramics to fabricate ceramic restorations. To withstand forces, fillers were added to the glass matrix, such as leucite, aluminium and zirconia as a method of strengthening glass ceramics. Hybrid ceramics are combination of two or more ceramic materials or a combination of ceramic and resin polymer material. The concept of hybrid ceramics was invented to gain the

advantages of the two mixed materials together without compromising mechanical nor physical properties of the final resultant material.5–7 Since Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) technology have been introduced into the dental field, dental restoration fabrication became faster and easier. Dental ceramics manufacturers’ aims were directed to invent ceramic blocks that can be fabricated with less laboratory steps, less wasted materials and to diminishing the human errors. Conservatism is one of the main objectives and principles of modern dental approaches, treatments and methods. As dental cosmetic treatments begin from a conservative scaling and polishing procedure ending with implant-supported restorations, dental ceramics plays a leading role with many esthetically restorative options. Tooth preparation, especially finish line design has an influence on the marginal fit of ceramic restorations and their fracture resistance. Clinically and during preparation, curvatures may be present at the finish line configuration. The influence of the finish line curvature on the marginal gap of restoration has been investigated. Though, its impact on the fracture resistance of ceramic restoration lacks documentation.