Fluorides may affect the oxide layer on titanium surface. Caries preventive mouthwashes or gels contain fluorides and are applied at low pH. The aim of the present work was to study whether various concentrations of fluoride at acidic pH cause changes in the surface structure on the polished region of Ti implants, and alter the adherence and colonization of bacteria. Commercially pure Ti grade 4 discs with a polished surface were treated with a mouthwash containing 0.025% fluoride, a gel containing 1.25% fluoride or a 1% aqueous solution of NaF (pH 4.5). The change of surface roughness of the samples and the colonization of Porphyromonas gingivalis strains were studied by scanning electron microscopy after 5 days of anaerobic incubation. The quantity of the bacterial protein was determined by protein assay analysis. Agents with high fluoride concentration at acidic pH increased the roughness of the Ti surface. A slight increase in the amount of bacteria was found on the surfaces treated with 1% NaF and gel in comparison with the control surface. This study suggested that a high fluoride concentration at acidic pH may hinder the development of a healthy transgingival epithelial junction on Ti implants, due to bacterial colonization.