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Abstract
Summary
Several studies have established the whitening effectiveness as well as the safety of bleaching agent on the dental structures, but, they were contradictory and not covering all types of whitening systems especially the high concentration in office systems. The aim of the present study was to investigate the effect of two in-office bleaching systems (power and chemical bleach) on the whitening efficiency. Moreover, surface roughness and hardness, histochemical changes of surface and sub surface layer and bond strength to bleached enamel and dentin using total etch and two self etch adhesives were also tested. Three hundred and sixty polished flat dental slabs were prepared and divided equally into two main groups; enamel and dentin. Each group was sub divided into three subgroups according to the treatment; control, power bleaching and chemical bleaching. Each subgroup was divided into four sub groups according to the testing procedures. Regarding, whitening efficiency was evaluated before bleaching, 24 hours, one month, three months and six months after bleaching. Meanwhile, for bond strength testing, half of the specimens were subjected to themocycling. The results revealed that both chemical and power bleaching enhance whitening of enamel and dentin, especially the power bleaching. Color relapse was detected after three months of bleaching except in chemically bleached dentin specimens which began after one month only. The relapse was grater with power bleaching in enamel specimens, while, for dentin specimens chemical bleach had more deterioration. Surface roughness was elevated especially by power bleaching, while, Surface microhardness was reduced significantly with the two bleaching systems. Furtherly, some surface alteration was noticed with more pronounced change was found on the power bleached enamel specimens, moreover, chemical bleaching showed more sub surface depth of penetration than power bleaching and both of them caused chemical changes of enamel and dentin. Bond strength was found to be dependant on the type of bleaching, type of adhesive, thermocycling and the tissue to be bonded.
Finally, it was concluded that both type of bleaching resulted in significant whitening and adversely affected the surface roughness, hardness and mineral contents, moreover, bond strength to enamel was not affected by bleaching with the use of potent bonding agents and thermocycling had a deleterious effect on bond strength.