Abstract
This study aimed to investigate matrix metalloproteinase (MMP) activity in human dentin using in-situ and gelatin zymography, after at-home and in-office bleaching, related to their clinical exposure times. Dentin specimens (n = 5) were treated with 35% hydrogen peroxide (50 min per session/4 sessions), 10% carbamide peroxide (180 min/21 sessions), or no treatment. All were subjected to in-situ zymography. Dentin slices were, subsequently, obtained, covered with fluorescein-conjugated gelatin, and examined with confocal laser-scanning microscopy. The fluorescence intensity was quantified and statistically analyzed using one-way ANOVA and Bonferroni tests (α = 0.05). Furthermore, gelatin zymography was performed on protein extracts obtained from dentin powder (N = 8 teeth), treated with hydrogen peroxide or carbamide peroxide, with different exposure times (10/50 min for hydrogen peroxide; 252/1260 min for carbamide peroxide). The results of the in-situ zymography showed no statistical differences between the bleached specimens and the control group, with a medium level of gelatinolytic activity expressed in the dentin tubules. The results of gelatin zymography showed an increased expression of pro-MMP-9 in carbamide peroxide groups. The expression of pro-MMP-2 decreased in all the experimental groups. The bleaching treatments performed on the enamel of sound teeth do not influence dentinal enzymatic activity. However, when unprotected dentin tissue is bleached, matrix metalloproteinases are more expressed, particularly when carbamide peroxide is used, proportional to the exposure time.
Highlights
Esthetics has gained growing recognition in dentistry, reflecting an increasing demand of patients who consider the smile a factor of great relevance [1,2]
Bleaching occurs as a result of the breakdown of pigmented molecules located in the enamel and dentin, caused by reactive oxygen species (ROS) released from bleaching agents, such as hydroxyl radicals (OH−) and singlet oxygen
A medium level of gelatinolytic activity was noted within the dentinal tubules, while a low level of activity was observed in the intertubular dentin in all the groups
Summary
Esthetics has gained growing recognition in dentistry, reflecting an increasing demand of patients who consider the smile a factor of great relevance [1,2]. One of the most important aspects regarding tooth appearance is its color, and dental bleaching is a conservative technique that can remove discolorations from the tooth tissues In this context, professionals are acutely aware of the importance of tooth bleaching in the clinical practice [3–6]. Bleaching occurs as a result of the breakdown of pigmented molecules located in the enamel and dentin, caused by reactive oxygen species (ROS) released from bleaching agents, such as hydroxyl radicals (OH−) and singlet oxygen (1O2) [7]. These chemicals rapidly diffuse through the enamel and dentin and, according to some authors, could cause changes in the elastic modulus, microhardness, and morphology of hard dental tissues [4,5]. Some studies suggest induced chemical degradation within the collagen fibrils, which can cause oxidative agents to denature proteins in dentin [5,8]
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