Purpose: The aim of this study was to evaluate the effect of siwak extract and toothbrush using two brands of toothpaste one containing siwak extract and one without on the cariogenic bacteria and surface characteristic of enamel and two types of composite resin. Materials and Methods: A total of 90 specimens were used in the present study. The specimens were divided into three groups according to the type of material used (n=30); Enamel specimens, Feltk Z350 specimens, and Tetric-N-Ceram Specimens. Each group was further subdivided into 3 subgroups according to the method
of treatment (n=10); specimens treated with Siwak sticks, specimens treated with toothbrush and toothpaste containing Siwak, and specimens treated with toothbrush and toothpaste not containing Siwak. All specimens were stained by coffee and tea stains, then surface treatment was done using electrical toothbrushing machine. Color measurements,
surface roughness for all specimens and wear resistance for composite resin specimens were done after staining and then after surface treatment. Antimicrobial activity was done using minimum inhibitory concentration (MIC) method. Results:
Antimicrobial activity of toothpaste containing siwak showed the lowest significant (MIC) on all the tested microorganisms. There was a statistically significant differences in the ΔE values and ΔW values of the treated subgroups. Moreover, significant differences in Ra values were observed between the control and stained specimens, as well as between subgroups treated with Siwak sticks, toothpaste containing Siwak, and toothpaste not containing Siwak. Conclusions: Siwak and toothpaste containing siwak are effective in removing the stains from enamel and resin composite surface without increase surface roughness or causing wear of the resin composite, however, the impact of the toothpaste containing siwak was more effective than siwak extract on the tested microorganisms.