Effect of Novel Gallium-Silver-Phosphate Based Glasses on Porphyromonas gingivalis

Methods: Novel gallium-silver-PBG rods (5 × 2mm) were produced using a conventional melt quenching method and degradation studies for up to 6 days were carried out using a weight loss method. Fastidious anaerobic agar (FAA) plates were inoculated with standardised cultures of P. gingivalis on which the glass discs were placed. The diameters of any zones of inhibition (i.e. zones of no visible bacterial growth) that had formed around the glass samples were measured. Broth assay was conducted in modified tryptic soy broth (TSB) medium with controlled iron content. The numbers of P. gingivalis colony-forming units (CFUs) in the broth at different time intervals were determined by spreading serial dilutions on FAA plates and incubating them for 48h anaerobically at 37°C. The experiments were conducted in triplicate and silver or gallium free PBGs were used as controls.

Results: The results showed that ion release rates are correlated to the weight losses of the glasses. The zones of inhibition were found to be larger in size for the gallium-silver-PBGs (50.2 ± 0.2mm) with the lowest calcium concentration. In the modified TSB broth assay, the glasses with calcium concentrations of 10, 11 and 12 mol % caused significant (p <0.001) reduction in log₁₀ CFU of P. gingivalis at 6, 24, 48, 72, 96, 168 and 240h compared with controls at the same time intervals. There was approximately a 5 log₁₀ reduction in the numbers of CFU maintained after 24h by the 10 mol% calcium containing glasses compared with the controls.

Conclusions: Both silver and gallium were found to inhibit P. gingivalis growth. The novel gallium-silver-PBG displayed synergistic antibacterial action of gallium and silver indicating their potential use as a therapeutic agent in the treatment of periodontal disease.