الفهرس 
English CoverOnly 14 pages are availabe for public view
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Abstract
Tooth discoloration is one of the most frequent reasons why a patient seeks dental care. It results from any change in enamel, dentin or pulp structures which is likely to cause an alteration in the outward appearance of the tooth caused by its light transmitting and reflecting properties. Tooth discoloration may be intrinsic, extrinsic or a combination of both. Bleaching is an oxidation process involves changing the color of teeth without changing their physical structure, eliminating the light absorbing molecules from enamel and dentin. There are two types of professional bleaching systems currently available, in office bleaching prescribed by dentists, and products that are issued to patients for in-home use under the dentists’ supervision. The rate of chemical reaction can be increased by increasing the temperature, where a 10 C rise can double the rate of reaction. The high-intensity light is used for raising the temperature of hydrogen peroxide and accelerating the rate of chemical bleaching of teeth. The halogen curing lights, plasma arc lamps, lasers and light-emitting diodes are accelerating the peroxide bleaching with simultaneous illumination of the teeth with various sources having a range of wavelengths and spectral power. On the other hand, some products that are used in light activated bleaching procedures contain ingredients that claim to aid the energy transfer from the light to the peroxide gel. There are two methods of laser bleaching. One is the photochemical in which the interaction induces chemical effects and reaction within the macromolecules or tissue. Photochemical bleaching uses the visible light energy to directly energize oxygen molecule. Another type of laser bleaching is photothermal bleaching which also known as the ”power-bleaching”. Photothermal bleaching is activation of a gel using high intensity light source (e.g. laser) that gives controlled heating of the gel and break down the peroxide compounds with it. This study was conducted in order to evaluate the effect of low intensity laser light on tooth bleaching compared to that of the other conventional and commercially used bleaching methods. Sixty freshly extracted human upper central Incisors were randomly divided into three main groups. Each group included twenty teeth, group I (Chemical bleaching group), group II (Light bleaching group), and group III (Laser bleaching group). To study the effect of stain type and staining time on the change in tooth color, the teeth of each group were randomly subdivided to 4 subgroups, (A) for 12 hours in tea stain, (B) for12 hours in coffee stain, (C) for one week in tea stain, and (D) for one week in coffee stain. All teeth were subjected to color assessment Visually by shade guide comparison, as well as digitally by digital spectrophotometry. Teeth of subgroups GI A, GII A, and GIII A were immersed in tea solution for 12 hours, while teeth of subgroups GI C, GII C, and GIII C were left for one week. Teeth of subgroups GI B, GII B, and GIII B were immersed in coffee preparation for 12 hours. While teeth of subgroups GI D, GII D, and GIII D were left for one week. Each tooth sample was then cleaned, dried, embedded from its root in a clay, and was subjected to color assessment. Post-staining records were compared with pre-staining records to detect the effect of staining time and stain type on tooth color. All teeth were subjected to bleaching gel application over their labial surfaces. Bleaching gel was left over the labial surfaces of the teeth of groups GI A, B, C, and D for 30 minutes for chemical bleaching, the teeth of groups GII A, B, C, and D were subjected to light bleaching by a LED source with a wavelength 340-600 nm and a power of 25 watts for 15 minutes for 3 sets, while the teeth of groups GIII A, B, C, and D were subjected to 1.5 watts of 980 nm diode laser in a continuous mode for 30 seconds. All teeth were subjected to color assessment Visually by shade guide comparison, as well as digitally by digital pectrophotometry .The results revealed no statistically significant difference (P≤ 0.05) between tea and coffee stains on staining results, as well as no statistically significant difference between the two staining periods on staining results. The application of t-test on the average change in values between the three bleaching modalities on the level of the color factors (Lightness, Hue and chroma) at P≤ 0.05 showed no statistically significant difference. By applying t-test at P ≤ 0.05 on each color factor separately within the three bleaching modalities before and after bleaching to detect the significance of changes in each factor, the results revealed that in laser bleaching group, the changes in both Lightness and Hue before and after laser bleaching were statistically significant, while there was no significant difference in chroma. In Light bleaching group, there was a statistically significant difference in Lightness, Hue and chroma before and after light bleaching. In chemical bleaching group, Hue was the only color factor that provided significant difference before and after bleaching, while Lightness and chroma didn’t show any difference from the previously mentioned, one could conclude that although the three bleaching modalities that were investigated in this study didn’t show significant differences that could outweigh one method over the other, but laser assisted bleaching could outperform by providing a shorter time of application that reduces the exposure of teeth and gum to the bleaching gel and thus diminishing the adverse effects such as teeth hypersensitivity and chemical mucosal burns in case the gel accidentally reached any site of oral mucosa. However, upon considering laser-assisted bleaching, one should take into consideration the investigation of the different laser wavelengths in relation to the corresponding photosensitizers that are added to the bleaching gel and could absorb laser at its specific wavelength. Furthermore, one should consider the variations in stain colors as they are an important factor for absorbing laser wavelength with subsequent changes in the absorbing stains. Further investigation and more research are needed in that direction to better understand difference and impact, thus improving the laser bleaching techniques.