الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 133 |  |  |
| | | from | 133 | | |
Abstract
Ceramic materials have several appealing properties making it highly on demand. As esthetics have become of major importance, ceramic’s fluorescence, natural look, chemical stability and biocompatibility made its usage favorable. The success of a ceramic restoration is mainly dependent on the bond strength between the ceramic, cement and underlying tooth structure. This bond is influenced by the strength of the adhesive cement responsible for maintaining the integrity of this connection.
The optimal curing of the adhesive cement is essential to reach high bond strength. The degree of conversion of resin cements is based upon the cross-linking of monomers to form polymers. This defines the unique mechanical and physical properties of the composite luting material. However, this mechanism is affect by several intrinsic and extrinsic factors such as, the type of monomer and the inorganic component of the cement, its shade, thickness of overlying ceramic restoration, light intensity of curing unit, distance of curing, and temperature.
The amount of light energy reaching the luting layer is strongly attenuated by the thickness of the indirect restoration, the shade of ceramic used and by its absorbing characteristics reducing the total amount of light reaching the adhesive cement. This attenuation is dependent on the crystal structure, thickness and shape of the indirect ceramic restoration. Even though dual-cured resin cements have been developed to overcome the inability of light to completely reach the bonding resin underneath indirect restorations, the reduction of transmitted irradiance when light curing is performed through the ceramic restorations can influence bond strength and degree of polymerization of dual-cure adhesives systems.
Dual cured cements lack color stability unlike light cured resin cements and therefore are not the prime choice for luting esthetic anterior restorations. But recently, dual cured cements of high color stability have been introduced to the market. where the manufacturer and researchers
Summary
66
claim they have esthetic properties comparable to those of the light cured cements.
Anterior restorations made from ultra-translucent zirconia which has the advantage of conservative tooth preparation are greatly demanded nowadays, as they provide a highly esthetic solution for anterior defects, through a very conservative preparation. This approach, serves to conserve most of the precious tooth enamel, maintaining the tooth integrity. The evolution in adhesive dentistry aided the advancement of these highly conservative esthetic restorations. Again, the high degree of polymerization of luting resin cements is crucial for the success of anterior restorations, in terms of mechanical success and also the final shade of the restoration.
In this study we used Spectrophotometer device to evaluate the effect of mode of curing on ceramic translucency, chroma and shade. Translucency and color change was calculated for each ceramic sample before and after cementation by both types of resin cements. These values give us an idea about which type of the resin cement has more color stability and is better used under ultra- translucent zirconia restoration.
Another value to estimate is the degree of polymerization of light and dual cured resin cement. Several methods have been addressed in the literature. Direct and indirect methods have been used. In this study Fourier Transform Infrared spectroscopy was the method of choice. The amount of remaining unreacted C=C after the complete polymerization of the resin cement is detected and the degree of conversion calculated. This value gives us an idea about the effect of different clinical factors on the polymerization reaction and hence the physical and mechanical properties of the cement used. These properties have huge effect on the final outcome of the dental restoration. These factors should be carefully considered on choosing the ceramic materials, luting resin cement and mode of polymerization.
Again, Aim of the study was to evaluate the degree of polymerization of light and dual cured resin cements under different thicknesses of same ceramic material and translucency and color change of ceramic after cementation.
Summary
67
Materials and methods: 28 ceramic samples were prepared from BruxZir Anterior ceramic material, Samples were divided into two groups according to the type of resin cement used Dual cure (D) (n=14) and Light cure (L) (n=14). The samples were further divided according to the Thickness into two subgroups 0.7 mm (T) (n=28) and 0.3mm (S) (n=28). A Teflon mould was fabricated with specific dimensions, where the ceramic disc was placed followed by light cured RelyX Veneer and dual cured RelyX Ultimate resin cement then a glass slab with finger pressure applied (same operator for standardization). Curing with Bluephase Ivoclar Vivadent light cure unit for 20 seconds took place, where the tip was in direct contact with the ceramic sample. Each sample was subjected to spectrophotometer to calculate (TP) and (ΔE) after cementation. Cement film was then separated from the ceramic sample and subjected to analysis by Fourier Transform Infrared Spectroscope. Uncured cement samples were also subjected to analysis. Both values were used in the equation below to obtain the degree of conversion.
For composites having internal standard, the percentage of unreacted aliphatic C=C bonds remaining after the polymerization reaction is obtained by the equation:
where Abs can be the height or the area of absorption band.
DC is determined by subtracting the residual percentage of aliphatic C=C from 100% (DC%=100-(%C=C)
Results showed a significant change in translucency and color before and after cementation as the ceramic samples became less translucent after cementation by both types of resin cements. Samples cemented by dual cured RelyX Ultimate showed a significant higher color change than of light cured RelyX Veneer ceramic samples.
Results also showed that degree of polymerization of RelyX Ultimate resin cement was non-significantly higher than of RelyX veneer under small thicknesses of Bruxzir Anterior ceramic restoration.