Effects of Two In-Office Bleaching Agents with Different pH on the Structure of Human Enamel: An In Situ and In Vitro Study

Abstract

This study evaluated the effects of two in-office bleaching agents (Beyond and Opalescence Boost) with different pH on the structure and mechanical properties of human enamel in vitro and in situ. One hundred and eight enamel slabs were obtained from freshly extracted premolars. The specimens were randomly distributed into nine groups (n=12), and the human saliva (HS) in the volunteers' oral cavities was used to simulate the in situ condition: Beyond + HS, Opalescence Boost (O-Boost) + HS, Control + HS, Beyond + artificial saliva (AS), O-Boost + AS, Control + AS, Beyond + distilled water (DW), O-Boost + DW, and Control + DW. The bleaching treatments were performed on the first and eighth day, and the total bleaching time was 90 minutes. Baseline and final surface roughness (RMS), surface morphology, microhardness, and fracture toughness (FT) were measured before the treatment and on the fifteenth day, respectively. Compared with control groups, surface alterations on enamel were found in the Beyond + AS and Beyond + DW groups under atomic force microscopy evaluation. Two-way analysis of variance and Tukey test revealed that the RMS showed significant intergroup differences for both storage condition and bleaching agent, whereas microhardness and FT revealed no significant alteration. The results indicated that in-office bleaching agents with low pH values could induce enamel morphology alterations under in vitro conditions. The presence of natural HS could eliminate the demineralization effect caused by low pH.

Impact of hydrogen peroxide activated by lighting-emitting diode/laser system on enamel color and microhardness: An in situ design

“…[7] Some studies assigned these structural modifications mostly to the gel pH. [73031] Neutral gels are recommended for tooth bleaching with the purpose of reducing deleterious effects on tooth enamel. In this study, the pH of the gels ranged from 6.5 to 8.5 and this may explain the results since the neutral pH caused no changes on enamel and did not alter microhardness.…”

“…[7] Dental bleaching was realized on the 2 nd and 9 th days in the laboratory under standardized conditions of illumination by a previously trained researcher.…”

“…After this, the volunteers used the palatal device for more 7 days,[7] and on the 15 th day, the slabs were removed and submitted to color assessment and microhardness test.…”

“…Since the by-products that result are colorless, the tooth receives a lightening effect. [45] Some in vitro studies using 35% HP found that the bleaching process can modify surface roughness,[67] decrease microhardness,[89101112] and change the calcium/phosphorus rates. [1314] However, in the presence of saliva, fluorides, and other remineralizing solutions, such changes may not occur.…”

How to designin situstudies: an evaluation of experimental protocols

“…Conventional holly-typed metal appliances tended to be replaced into acrylic palatal appliances 9. With an increasing number of in situ bleaching studies, soft bleaching trays were also modified with palatal extensions 10. The sterilization method of the tooth specimens is another issue, since the biological tissues obtained from other donors were attached to the intraoral appliances.…”