Aim:  To determine if anaerobic bacteria routinely found in infected dentine and root canals require the presence of heme in the environment in order for them to invade dentinal tubules.

Methodology:  Noncarious, unrestored human teeth with single root canals were prepared for invasion experiments and soaked in either TSB-M supplemented with hemin (5 μg mL−1) (n = 12 roots), TSB-M media (n = 12 roots) or TSB-M media followed by hemin soak (n = 12 roots) for 2 days, then inoculated with either Prevotella intermedia ATCC 25611 or Peptostreptococcus micros ATCC 33270 and incubated anaerobically for 14 days. Roots were prepared for light microscopy, stained with Brown and Brenn or antisera raised to the bacteria, and invasion within tubules assessed using a tubule invasion index (TI). Data were analysed using Student's t-test and Mann–Whitney U-test.

Results: Prevotella intermedia (TI = 0.7 ± 0.04) and P. micros (TI = 0.96 ± 0.08) showed low invasion when grown in the presence of hemin with cells generally restricted to the superficial 20 μm of the tubules, whilst neither bacteria invaded tubules (TI = 0) when hemin was absent from the growth media (P < 0.01).

Conclusions:  Hemin was required in the growth medium for P. intermedia and P. micros to invade dentinal tubules.