In vitro attachment of oral microorganisms to solid surfaces: evaluation of a controlled flow method

A flow cell method was modified to provide shear-controlled experimental conditions for monitoring initial attachment and detachment of oral microorganisms to solid surfaces. Whole unstimulated human saliva was collected and circulated at a flow rate of 1 ml/min, through a cell composed of two parallel test plates. Infrared-transparent plates of medium surface energy served as test substrata in these initial calibration experiments. The plates presented a similar distribution of polar forces and dispersion forces at the surface as that of human tooth enamel and some restorative dental materials. Internal reflection infrared spectroscopy verified the presence of deposited organic material. After saliva had been circulated through the flow cells for 15 min at 37 degrees C, sterilized distilled water was introduced at the same flow rate and time of exposure to remove unattached microorganisms. Morphologic characterizations and counts of adherent Gram-stainable microorganisms were performed using incident light microscopy. Three different surface zones corresponding to the inlet area, the middle area and the outlet area of the flow cell were analyzed, and compared with enumerations of microorganisms in the whole saliva samples. Numbers of attached microorganisms in the three zones followed predictions from the laminar flow conditions, with a positive correlation shown between total numbers of microorganisms in saliva and total numbers of microorganisms attached. Cocci and rods were the only morphotypes observed on the plates, and no significant difference could be detected between the percentage of cocci and rods attached in the three different zones.(ABSTRACT TRUNCATED AT 250 WORDS)