Influence of different formulations of bleaching agents on enamel and dentin physical and chemical properties / Influencia de diferentes formulações de agentes clareadores nas propriedades fisicas e quimicas do esmalte e dentina

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Section A: Effects of bleaching agents on dental enamel Since the introduction of the nightguard vital bleaching technique using 10% carbamide peroxide (10% CP), reports have evaluated the effects of bleaching agents on human enamel. Evidences show that CP is able to alter the composition and morphology of enamel substrate. In order to reduce the adverse effects produced by these agents on enamel surface, manufactures have added fluoride and other ions in the bleaching agent formulation. However, little is known about the effects of these agents on sound and early caries affected enamel. Therefore, the aim of this study is to evaluate sound and early caries affected enamel 10% CP bleaching with the addition or not of fluoride and calcium ions. Enamel fragments obtained from bucal and lingual third molars surfaces were used and prepared to initial microhardness measurement. After selection of the specimens, half of them were submitted to enamel demineralization in order to produce early caries on this substrate. A new microhardness measurement was performed after enamel demineralization and the phosphate concentration of sound and demineralized enamel was determined by means of Fourier Transformed Raman Spectroscopy (FTRS). Sound and early caries affected enamel were randomly divided into six experimental groups (n=10): (PLA) Placebo; (W) Whiteness (10% PC); (O) Opalescence F (10% PC); (PN) Pola Night F(10% PC) and experimental bleaching agents (F) 10% PC + 0.5% F e (Ca) 10% PC + 0.2% Ca. Bleaching was carried out during 6 hours a day and after each application, specimens were kept in remineralizing solution until the next bleaching application. Bleaching treatment was performed during 12 days. On the 1st, 6th and 12th days of bleaching, microhardness measurements were performed and the rinsing water was used to determine the concentration of fluoride, calcium and inorganic phosphate by means of ion-selective electrode, atomic absorption spectroscopy and colorimetric analysis, respectively. After 12 days of bleaching, new FTRS analysis was performed and specimens were prepared to cross-sectional microhardness measurement and polarized light microscopy. The results showed that there was a decrease on sound and demineralized enamel microhardnessa after bleaching, specially when enamel was submitted to 10% CP application with no ionsaddition in its composition (Whiteness 10%). Chemical analysis indicated that there was a decrease in the ion concentration of sound and demineralized enamel after bleaching due to an increase in the content of calcium, fluoride and inorganic phosphorus in the rinsing water solution. Cross-sectional microhardness and polarized light microscopy confirmed the demineralization of enamel submitted to 10% CP with no fluoride or calcium additin (Whiteness 10%). High-concentrated calcium bleaching agent controlled demineralization on sound enamel, whereas, high-concentrated fluoride agent was important for the physical properties of early caries affected enamel Section B: Effects of intracoronal bleaching agents on dentin surface The aim of this study was to verify the influence of four intra-coronal bleaching agents on sound and etched dentin. Bovine incisors were prepared to intracoronal bleachingtreatment. Half of them were submitted to previous demineralization with 37% phosphoric acid for 15 seconds. The sound and etched incisors were randomly divided into 5 experimental groups: (C) Control ? no bleaching treatment; (PH 35%) hydrogen peroxide 35%; (PH 25%) hydrogen peroxide 25%; (PC 35%) carbamide peroxide 35% e (PS) sodium perborate mixed with distilled water. Bleaching agents were applied to the pulp chamber 4 times with a 72-hour interval among applications. Specimens were kept in individual recipients in humidity during bleaching. Control group was not bleached and remained in relative humidity during bleaching treatment. In order to determine the ultimate strength and structure of bleached intern dentin, immediately after bleaching, dentin fragments were obtained from internal bucal dentin. From each fragment, slices (0,8 mm thick) were obtained. Trimming was performed in the central area of each slice to produce a cross-sectional central area of 0,7mm2. After 24 hours, the ultimate strength of specimens was tested by means of microtensile test. Results were statistically analyzed. Additional fragments were treated and prepared to evaluation of sound and etched bleached dentin, through Transmission Electron Microscopy (TEM). The results of the first part of the study indicated that sound and etched ultimate strength decreased after intracoronal bleaching. Morphological alterations were observed through ultra-structural analysis (TEM). The second part of the research determined the bond strength of resin-dentin after bleaching. Bond strength was determined immediately, 7 and 14 days after intracoronal bleaching. After treatment of the specimens, according to previous descriptions, fragments obtained from bucal dentin were randomly divided into 3 groups: (0) Bond strength immediately after treatment; (7) Bond strength 7 days after bleaching treatment; (14) Bond strength 14 days after bleaching treatment. Specimens were kept in remineralizing solution and 24 hours before testing, they were removed from the solution and prepared to microtensile test. The fragments were restored with one-step total acid conditioning adhesive system and a composite block was build up on dentin surface to microtensile test.Results obtained were statistically analyzed. Additional specimens from each group were prepared to nanoleakage evaluation of sound and etched bleached dentin, by means of TEM. Bond strength of sound and etched bleached dentin decreased immediately after intracoronal bleaching. After 14 days of bleaching treatment, bond strength of sound bleached dentin increased for all groups, whereas for etched bleached dentin, sodium perborate was the only group with bond strength similar to control group. Sound and etched dentin of all treated and not-treated groups, presented nanoleakage immediately after bleaching. After 14 days, nanoleakage decreased for all groups tested

ASSUNTO(S)

dentistica fluor calcio fluorine dentes - clareamento calcium dentistry tooth bleaching

ACESSO AO ARTIGO

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