Quantification of Attached Streptococci on Dental Biomaterial Surfaces

The formation of microbial plaque on dental biomaterial surfaces often leads to clinical problems such as secondary caries, gingivitis or mucositis that may eventually require replacement of the material. It is assumed that the physico-chemical properties of a biomaterial surface influence composition and quantity of early colonising bacteria. Objective: To establish a method for the quantification of attached bacteria on various dental biomaterial surfaces. Methods: Samples of different dental materials such as zinc phosphate cement, glass ionomer cement, composite, fissure sealant, methacrylate, paraffine wax, and silicone were embedded as duplicates in epoxy resin and ground to roughnesses of 120, 240, 600, and 4,000 grit. Each experiment was performed three times. The detection of attached bacteria was performed directly on the biomaterial surfaces by a chemifluorescence-based modification of the bacterial overlay assay. Specimens with and without prior adsorption of pooled human whole saliva, were overlaid by biotinylated Streptococcus gordonii DL1 for one hour and washed thereafter. Attached bacteria were detected by avidin-D-alkaline phosphatase and chemifluorescent signals were recorded by a fluorescence scanner. Densitometric analysis of signals was performed using the Optimas software. Quantification of attached bacteria was achieved by extrapolation from a standard serial dilution of a defined bacterial suspension immobilized on a dot blot.

Results: Number of attached bacteria/mm² (median)

b.d. = below detection limit of 0.39e3 bacteria/mm²

These data show that bacterial attachment is dependent on the type of dental biomaterial and is influenced by surface roughness and prior precoating with saliva. Conclusion: This novel method for quantification of bacteria attached on surfaces was validated in the present study and, thus, might become useful for pre-clinical testing of biomaterials.