الفهرس 
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Abstract
Teeth whitening procedures continue to grow in popularity due to the increased desire for whiter teeth with increasing number of articles being published on the subject in the popular press and on television in regular intervals. This has resulted in renewed interest from the dental profession in the process of teeth whitening, as the procedure itself is relatively simple and non-invasive to carry out. Current bleaching systems are based primarily on hydrogen peroxide or carbamide peroxide.
The chemical bleaching systems usually exist in a form of a gel which is applied on the tooth surface and activated to form free radical ions. Long-chained molecules that ”stain” the tooth react with the free radicals, altering the optical structure of the molecule and creating different optical structure. Although tooth bleaching is effective in lightening tooth color, concerns have been expressed regarding to associate post-bleaching complications including alteration in the surface morphology of enamel, changes in its chemical composition, and notable changes in its mechanical properties.
The patient population, always enthralled by LASER, was very keen to try LASER bleaching, which was promoted as a procedure superior to earlier bleaching methods. LASERs are intended to enhance the efficiency of bleaching materials. This serves to increase and speed the release of the oxygen ions into the stained tooth surface.
The present study aimed to compare the effect of chemical tooth bleaching and diode LASER activated tooth bleaching on enamel surface and subsurface of extracted human maxillary central incisors through evaluating morphological and chemical profile changes of enamel surface and subsurface, using Scanning Electron Microscope attached with Energy Dispersive X-ray Analyzer.
Forty non-carious human maxillary anterior extracted teeth were collected and prepared for the study. The collected teeth were divided into:
A. Control Chemical bleaching group (CC group): This group contained the mesial labial halves of twenty teeth. It was covered by pink wax during bleaching treatment.
B. Experimental Chemical bleaching group (EC group): This group contained the distal labial halves of the same twenty teeth in CC group. It was applied to chemical bleaching treatment as a triple application of 38% HP gel (WHITE smile, Power Whitening, Germany) for 15 minutes, then application of desensitizing gel for 15 minutes .
C. Control LASER activated-bleaching group (CL group): This group contained the mesial labial halves of twenty teeth. It was covered by pink wax during bleaching treatment.
D. Experimental LASER activated-bleaching group (EL group): This group contained the distal labial halves of the same twenty teeth in CL group. It was applied to LASER activated bleaching treatment with Laserwhite*20, BIOLASE. It contains HP at a concentration of 38% supported in gel consistency. Diode LASER activated-bleaching regime procedures were done according to the manufacturer’s instruction.
The mesial and distal enamel labial surfaces of all groups were scanned and chemically analyzed to measure Ca, P, C weight % using SEM-EDXA. These teeth were then fractured as a cross cut in a linguo-labial direction at the middle one third of the crown. The fractured labial enamel subsurface was scanned and chemically analyzed at 50 µm depth and 100 µm depth using SEM-EDXA.
In The present study, after application of chemical bleaching régime on surface of EC group specimens, there was a non-significant increase in the C wt.% with a decrease in P wt.%. In SEM examination, the morphology of enamel surface in EC group showed apparently increased surface irregularities, pits, pores and crater like depressions with appearance of fish scales like erosion and ill-defined perikymata.
The EDXA examination of ECT groups at 50 µm and 100 µm depths represented significant demineralization of enamel (significant decrease in Ca:P ratio at 50 µm depth and significant loss of P wt.% with C wt.% increase at 100 µm depth) which represented in Ternary diagram as slight shifting to a demineralized area. Enamel subsurface SEM examination of ECT group showed multiple surface defects extended to various depths and some of it was ended by a channel through the inter-prismatic region in addition to the appearance of irregular concavities on each individual prism structure.
Comparing the chemical profile of ELS with CLS group, after application of LASER-activated bleaching régime, there was a non-significant decrease in all examined mineral weight % which was reflected as almost no shift in the Ternary diagram. The morphological results of ELS group revealed that the enamel surface appeared in general as a molten surface and perikymata grooves were hardly defined
In the current study, EDXA result of ELT group in comparison with CLT group was a significant decrease in the Ca:P ratio at 50 µm and 100 µm depths, which may represent a decrease in the enamel subsurface mineralization. However, in the Ternary diagram, a shifting to a more mineralized area appeared at 50 µm depth. The subsurface morphological results of EL group showed ill-defined enamel structure with loss of prismatic enamel integrity. It appeared at higher magnification with flat surface of individual prisms, in which observed the disappearance of the bulging pattern of individual prisms, and it was difficult to identify prisms and inter-prismatic structure.