Supervisor : Ihab Mosleh Mostafa, Hanaa Hassan Zaghloul.Morsi, Mohamed Tarek Anwar,2022-01-172022-03-272022-01-172022-03-272020.EG-CaMIUThs338https://iorep.miuegypt.edu.eg/handle/20.500.13071/71DISSERTATION NOTE-Degree type M.Sc.DISSERTATION NOTE-Name of granting institution Misr International University, Faculty of Oral and Dental MedicineIncludes Arabic Summary.Includes bibliographic references (pages 121-138)The increased demand for high esthetics initiated the development of tooth colored restorative materials having superior esthetic and mechanical properties to withstand the occlusal forces. Dental ceramic restorations provide high esthetics that mimic the dental appearance of natural dentition producing satisfactory results to the patients and clinicians. Dental ceramics have variable compositions with different crystalline content such as feldspathic glass porcelain, zirconia, lithium disilicate, fluroapatite or leucite-reinforced ceramics. Glass ceramics consist of glassy matrix with imbedded crystalline structures. As the glassy matrix increases, the ceramics become more translucent. The crystalline content provides strength on the expense of its esthetic appearance. IPS e.max Press (first introduced into the market in 2005) consists of lithium disilicate crystalline structures (70% by volume) embedded into a glassy matrix7,8. The crystals have plate-like shape that are randomly distributed in the glassy matrix. The random distribution and the needle-like structure of the crystals would deflect cracks and prevent their propagation. GC InitialTM LiSi Press is a newly introduced lithium disilicate pressable ceramic, which is empowered by HDM technology (high density micronization) to provide improved physical properties (unsurpassed flexural strength of more than 450 MPa) while obtaining superior esthetics. With the advent of adhesive dentistry, ceramic veneers can be produced with high optical and mechanical properties in a minimum thickness up to 0.3 mm13–16. Aside from the layering fabrication technique, ceramic veneers can be constructed from ingots or blocks by heat pressing technique and computer assisted design/ computer assisted manufacturing (CAD/CAM) technique. The ceramic’s thickness has a noticeable effect on the optical properties of the ceramic restoration. Increased thickness affects color and translucency, making the ceramic darker more reddish/yellowish and increases the ceramic’s opacity. The bonding between the restoration and the dental structure is enhanced by the surface treatment of the ceramic surface. However, the modification of the internal surface of the ceramic by creating microporosities that would increase the surface area for bonding. The different surface treatments of ceramics affect the surface roughness which influences the optical properties of the ceramics. The roughness on the ceramic’s surface makes the light that goes through the ceramic pass with the different incidence and direction. Using Hydrofluoric acid etchant as a surface treatment is considered a standard classic method. Hydrofluoric acid removes the glassy matrix of ceramic material. Once the glassy matrix has been removed, the crystalline content is exposed creating micro-roughness on the surface of the ceramic. However, Hydrofluoric acid etchant as a surface treatment is considered hazardous to the dentist and the patient31. Er,Cr:YSGG Laser irradiation is a new technology that has been introduced lately to different fields of dentistry. Er,Cr:YSGG laser can make surface roughness on the glass ceramics as a surface treatment prior to bonding similar to that made by hydrofluoric acid etching. Reviewing the dental literature, there is a considerable debate regarding the effect of Er,Cr:YSGG Laser as a surface treatment protocol for producing surface roughness on the ceramic’s surface and its effect on the optical properties of the ceramic. In view of the unreported health hazards of laser irradiation in dentistry, it is worth to assess its effect as a surface treatment protocol on the surface roughness, color and translucency parameters of two pressable lithium disilicate ceramic materials with different thicknesses before and after aging.138 pages : illustrations, photo ; 28 cmtextapplication/pdfengFixed Prosthodonticstext