Effect of Dental Plaque Extracts on Mammalian Cells in Culture: An In Vitro Investigation Into Chemical Factors From Dental Plaque Which May Be Responsible for Chronic Gingivitis in Man

Chronic gingivitis is generally believed to result from irritation to cells at the gingival junction. This is brought about by the accumulation of micro-organisms on teeth. These micro-organisms and their products are known as dental or bacterial plaque and constitute a bacterial ecosystem whose appearance and consistency differentiate it from other kinds of deposits on teeth. The dental plaque contains a variety of substances which are potentially pathogenic. Presumably some of these are extractable, and may be toxic in vitro. The aims of the present investigation were to examine the effects of extractable material from dental plaque on the growth of mammalian cells in culture, and to characterise any material having a cytotoxic effect. In addition, it was necessary to characterise the composition of the extractable plaque material, and to compare it with saliva and with serum. Dental plaque was collected from the exposed surfaces of teeth, extracted into a modified Earle's saline solution, and homogenised. The mixture was centrifuged and the supernatant fraction (the plaque extract) was sterilised by millipore filtration. Unstimulated saliva was collected by spitting into an ice cooled beaker and then centrifuged. The supernatant fraction was retained, and the sedimented fraction was extracted as described for plaque. The supernatant fraction was sterilised by millipore filtration but the sediment extract was too viscous to be sterilised in this way. All three preparations were fractionated by membrane or Sephadex ultrafiltration and iso-electric focusing in polyacrylamide gels, as well as being examined by immunoelectrophoretic techniques. The total solid extractable from 1 g wet plaque was determined after lyophilising samples of plaque extract. The ultraviolet spectra, and the amounts of protein, hexose, and sialic acid in these preparations were also determined. Mammalian cell cultures were grown in Eagle's medium with Earle's saline, calf serum to 10%, and penicillin and streptomycin each to 100 units/ml. Cells were incubated in 5% CO2 in air at 3