Early Polylysine Release from Dental Composites and Its Effects on Planktonic Streptococcus mutans Growth

The study aim was to assess the effect of incorporating polylysine (PLS) filler at different mass fractions (0.5, 1 and 2 wt%) on PLS release and Streptococcus mutans planktonic growth. Composite containing PLS mass and volume change and PLS release upon water immersion were assessed gravimetrically and via high-performance liquid chromatography (HPLC), respectively. Disc effects on bacterial counts in broth initially containing 8 × 10⁵ versus 8 × 10⁶ CFU/mL Streptococcus mutans UA159 were determined after 24 h. Survival of sedimented bacteria after 72 h was determined following LIVE/DEAD staining of composite surfaces using confocal microscopy. Water sorption-induced mass change at two months increased from 0.7 to 1.7% with increasing PLS concentration. Average volume increases were 2.3% at two months whilst polylysine release levelled at 4% at 3 weeks irrespective of composite PLS level. Early percentage PLS release, however, was faster with higher composite content. With 0.5, 1 and 2% polylysine initially in the composite filler phase, 24-h PLS release into 1 mL of water yielded 8, 25 and 93 ppm respectively. With initial bacterial counts of 8 × 10⁵ CFU/mL, this PLS release reduced 24-h bacterial counts from 10⁹ down to 10⁸, 10⁷ and 10² CFU/mL respectively. With a high initial inoculum, 24-h bacterial counts were 10⁹ with 0, 0.5 or 1% PLS and 10⁷ with 2% PLS. As the PLS composite content was raised, the ratio of dead to live sedimented bacteria increased. The antibacterial action of the experimental composites could reduce residual bacteria remaining following minimally invasive tooth restorations.