Effect of Vital Tooth Bleaching on Surface Roughness and Streptococcal Biofilm Formation on Direct Tooth-Colored Restorative Materials.

OBJECTIVE: To compare the effect of simulated bleaching with a 10% carbamide peroxide (CP) or a 40% hydrogen peroxide (HP) system on surface roughness of resin composite and resin-modified glass ionomer cement (RMGI) and streptococcal biofilm formation on these surfaces. METHODS AND MATERIALS: Specimens of nanofilled resin composite and RMGI (n=108 each) were randomly divided into three groups (n=36 each): no treatment control, 10% CP, and 40% HP. The surface roughness values (Ra) were measured before and after treatments. The specimens in each group were randomly divided into three subgroups (n=12) and incubated with Streptococcus mutans, Streptococcus sanguinis, and trypticase soy broth control for 24 hours. Biofilm formation was quantified by crystal violet staining, and the structure was visualized by scanning electron microscopy. The differences between the mean changes in Ra between the 10% CP and 40% HP groups of each material were evaluated with an independent t-test. The quantity of biofilm formation on each material was analyzed with one-way analysis of variance with the post hoc Tukey test ( α=0.05). RESULTS: Surface roughness significantly increased after bleaching in all groups. There was no significant difference between the 10% CP and 40% HP groups of each material. For S. mutans biofilm formation, bleaching with 10% CP and 40% HP increased biofilm on both materials compared to controls. However, S. sanguinis biofilm formation was significantly higher on bleached resin composite but not on RMGI specimens. CONCLUSIONS: Simulated bleaching with 10% CP or 40% HP increased both surface roughness and biofilm formation on resin composite and RMGI, except for S. sanguinis biofilm on RMGI.

Effect of alpha/gamma phase ratio on corrosion behavior of dual-phase stainless steels.

Dual-phase stainless steels have been developed in order to reduce the nickel content, which is potentially responsible to an allergic reaction when these steels are used as medical or dental applications. In this study, two different dual-phase stainless steels (2205 and Z100) were electrochemically tested to evaluate their corrosion resistance in three corrosive solutions (i.e., synthetic saliva, 0.9% NaCl solution, and Ringer solution). Particularly, an attempt was made to correlate the corrosion resistance to a metallographic parameter, which is, in this study, the alpha/gamma phase ratio. It was concluded that (1) type 2205 stainless steel exhibited excellent corrosion resistance in all three corrosion media; however 2205 stainless steel decreases its corrosion resistance by increasing chloride concentration in tested electrolytes from synthetic saliva through 0.9% NaCl solution to Ringer solution. (2) X-ray diffraction analysis indicated that the alpha/gamma phase ratio of 2205 (1.735) was higher than that of Z100 (0.905). As a result, it is suggested that by increasing the alpha/gamma phase ratio the material shows more corrosion-prone behavior when being subjected to a hostile environment containing higher chloride ion concentration.