Abstract
Teeth bleaching cases had increased with people’s desire for oral aesthetic; however, bleached teeth would still undertake chewing actions and remineralizing process in saliva. Nanotribological and nanomechanical properties are proper displays for dental performance of bleached teeth. The purpose of the research was to reveal the effect of bleaching and remineralization on the nanotribological and nanomechanical properties of teeth in wet environment. The specimens were divided into four groups according to the bleaching products used: 12 % hydrogen peroxide (HP) (12HP group); 15 % carbamide peroxide (CP) (15CP group); 35 % CP (35CP group); and artificial saliva (control group). The nanotribological and nanomechanical property changes of tooth enamel after bleaching and remineralization were evaluated respectively by nanoscratch and nanoindentation tests in wet environment, imitating the wet oral environment. The morphology changes were evaluated by statistical parametric mapping (SPM) and scanning electron microscopy (SEM). After bleaching, 12HP group and 15CP group showed increased scratch depth with more pile ups on the scratch edges, decreased nanohardness, and corroded surface appearance. While the 35CP group showed an increase in nanoscratch depth, no change in nanohardness and surface appearance was observed. The control group showed no change in these measurements. After remineralization, the three bleaching groups showed decreased nanoscratch depth and no change of nanohardness compared with the bleached teeth. And the control group showed no changes in nanotribological and nanomechanical properties. The nanotribological and nanomechanical properties of the 12HP group and 15CP group were affected by bleaching, but the nanotribological properties recovered partly and the nanomechanical properties got no change after 1 week of remineralization. As for the 35CP group, the nanotribological properties were influenced and the nanomechanical properties were not affected. These results remind us of taking actions to protect our teeth during bleaching.
Highlights
Dental bleaching could effectively improve teeth color and is receiving increasing popularity [1]
Comparing the results of the 12HP and 35CP groups, we found that the nanohardness of the former decreased about 5.6 % after bleaching, while that of the latter remained almost unchanged
Nanotribological behavior was related, but not determinant to nanomechanical behavior for tooth enamel [26, 27]. These results revealed that the bleaching products containing 12% hydrogen peroxide (HP) and 15% carbamide peroxide (CP) used in the study affected the nanotribological and nanomechanical properties of teeth, but the effects on nanotribological properties can be alleviated after remineralization
Summary
Dental bleaching could effectively improve teeth color and is receiving increasing popularity [1]. The oxidizability of HP or CP is nonspecific [6], so the target dark substances of teeth and other normal organic or inorganic substances might be oxidized during bleaching [7]. These chemical components of teeth, closely related to nanotribological and nanomechanical properties, might be changed during bleaching as well, resulting in the different performance of nanotribological and nanomechanical properties [8]. The measurement of nanotribological and nanomechanical properties of normal natural teeth, bleached teeth, and remineralized teeth in oral-like environment could help assess the bleaching effect of tooth function
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