Changes in enamel surface roughness and adhesion of Streptococcus mutans to enamel after vital bleaching

Objectives. The purpose of this in vitro study was to observe the influence of vital bleaching on changes to the enamel surface and adhesion of Streptococcus mutans to tooth enamel.

Methods. The coronal part of each of 70 extracted third molars was cut in half, with either the buccal or lingual half used for experiments or controls. Experimental halves were assigned to the following conditions: (A) enamel was bleached 1, 3 or 5 times using a bleaching material with or without etching; or (B) etched condition without bleaching. All control samples were kept intact in physiological saline solution. Surface roughness (Ra; roughness center-line average: μm) of enamel was measured for 35 pairs of specimens. TS broth culture medium containing 3% glucose was inoculated with S. mutans and cultured for 72 h before adding the other 35 pairs of specimens. Under scanning electron microscopy, the number of S. mutans colonies was counted and statistically analysed.

Results. Compared to controls, bleached enamel displayed increased colonies of S. mutans. Repeated bleaching further increased bacterial adhesion and maximal colonies counts were found under conditions of five bleaching treatments plus etching (p≤0.01). Compared to controls, roughness increased after etching. However, no linear correlation was found between number of S. mutans colonies and roughness.

Conclusion. We conclude that both surface roughness and adhesion of S. mutans to the enamel surface increase after bleaching.