Effect of microbial contamination and pH changes in storage solutions during in vitro assays of bonding agents

A study of pH changes in, and microbial colonization of, storage solutions being utilized during an in vitro evaluation of luting agent solubility has been made. Microbial growth in storage solutions was observed to occur at as high as 10(5) colony-forming units (cfu)/mL after seven days' incubation. A strong time-dependent inverse correlation between pH and cfu was found, with the pH dropping to as low as 5.3 (p less than 0.01). Decreases in pH were not found in presterilized control samples (p less than 0.05). Further, it was demonstrated that presterilization with ethylene oxide or the addition of respiratory inhibitors prevented both microbial colonization and the pH drop when compared with controls (p less than 0.001). These data suggest that studies of dental materials which include incubations in various fluids should be controlled for the potential effects of micro-organisms and their effect on pH.