Biological properties of IRM with the addition of hydroxyapatite as a retrograde root filling material.

The effect of adding 10% & 20% hydroxyapatite (HAP) on the antibacterial activity and cytotoxicity of IRM (Intermediate Restorative Material) when used as a retrograde root filling was compared with amalgam, a commonly used material. The antibacterial activity was assessed using the agar diffusion inhibitory test. Forty standardized pellets of each material were produced. Fresh materials, and materials aged for 1 week in sterile distilled water, were placed on blood agar plates inoculated with Streptococcus anginosus (milleri) or Enterococcus faecalis. The presence and diameter of zones of inhibition were recorded at intervals of 3, 7 and 10 days. There was no statistically significant overall difference in the response of the two bacteria tested. However, there were statistically significant overall differences in diameters of the zones of inhibition related to different materials, period of exposure and ageing of materials (P < 0.001). The diameter of the zones of inhibition increased with time for all materials, fresh and aged. IRM and both the HAP-modified forms produced large zones of inhibition. Amalgam produced no measureable zones of inhibition whether aged or fresh, regardless of period of exposure and was different from the other materials (P < 0.001). The cytotoxicity was assessed using the Millipore filter method. Ten standardized pellets of each material were produced and aged by storage in sterile distilled water for 72 h. Ten filters were included as controls. Amalgam produced a consistent cytotoxic score of 1, and the difference between amalgam and the other materials was statistically significant (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)