Supervisor : Adel Ezzat Khairy, Inas Mohsen ElZayat, Ahmed Mohamed Hoseny Fayed.AL-Ghonaimy, Hadeel Essam Ahmed Aboufotouh,2022-01-172022-03-272022-01-172022-03-272021.EG-CaMIUThs376https://iorep.miuegypt.edu.eg/handle/20.500.13071/73DISSERTATION NOTE-Degree type M.Sc.DISSERTATION NOTE-Name of granting institution Misr International University, Faculty of Oral and Dental MedicineIncludes Arabic Summary.Bibliography: pges 75-83.In the last two decades, the demand for esthetic treatment has increased tremendously. Factors such as the increase of patient awareness about minimally invasive and noninvasive aesthetic procedures and the paradigm shift in technological energybased devices caused the growth of the global medical aest hetics market. Bleaching is a chemical process characterized by oxidative decomposition of bleaching agents to remove external stains from the tooth surface to reach lighter tooth color. The teeth bleaching market has been divided into two main groups: inoffice bleaching and athome bleaching. Inoffice bleaching offers the patient less exposure time to the bleaching agent, more acceptable results, and professional control over the treatment process to ensure its effectiveness. High concentration hydrogen peroxide (25% to 40%) or carbamide peroxide (35% to 38%) are usually the agents used in the inoffice bleaching. They are activated either by chemical means or by using external energy sources such as blue colored halogen curing lamps, advanced LED light, or by light amplification by stimulated emission of radiation "LASER". The need for external activation of the bleaching gel is one reason for the high treatment cost. Chemical activated bleaching is one of the most common methods used to increase the efficiency of the bleaching process. Bleaching agents are unstable molecules that undergo dissociation once applied on the tooth surface. The idea behind chemical bl eaching is incorporating a catalyst such as some enzymes and salts of transition metals to bleaching agents before use in order to increase the rate of its dissociation and the formation of free radicals. It was proposed that the use of high-intensity light in bleaching acts as an accelerator for bleaching agents by increasing its temperature, thus improving the effectiveness of the treatment. This theory was first reported in 1918 by Abbot. There are various types of external light sources used in the bleaching process. Still, unfortunately, there are no sufficient studies that can show the difference in results between them, indicating the source with the most acceptable outcome. A LASER is defined as an intense beam of coherent monochromatic light generated by stimulated photons' emission from excited atoms or electromagnetic radiation. LASERs were introduced recently in bleaching to accelerate bleaching efficiency by enhancing hydrogen peroxide's oxidization effect, thus reducing patient chair time and increasing acceptance. LASER types used in teeth whitening are argon LASERs, diode LASERs of a wavelength of (810 nm – 980 nm), or Nd: YAG LASERs with a wavelength of 1064 nm. One of the greatest concerns after bleaching is bleached color regression. Authors addressed some potential adverse effects on enamel when they evaluated the effect of various bleaching systems on extracted bovine and human extracted teeth such as porosities, change in microhardness, and surface roughness of enamel. The presence of microscopic enamel porosities was found to be one reason that can cause color change. The change in surface topography of an alteration in calcium phosphate ratio of tooth structure will cause surface roughness and irregularities that will affect the color stability of bleached teeth. The rough surface will be more susceptible to retain stains, and color rebound will occur. Another concern is the post bleaching most prevalent drawback of inhypersensitivity which is the office bleaching technique. Although being the most prevalent drawback, the etiology of post ble hypersensitivity is not yet fully understood. There is a great controversy when it comes to state aching which mode of activation has the best clinical results in terms of color stability after aging. Therefore, this research was designed to assess the effect of three different in office bleaching on color stability and post bleaching hypersensitivity.83 pages : illustrations, photo ; 29 cmtextapplication/pdfengDentistry, Operativetext