• archaea;
  • bacteria;
  • root canal infections;
  • RT-PCR


Aim  To investigate, by reverse transcription polymerase chain reaction (RT-PCR), the presence and association of bacteria and archaea in primary and secondary root canal infections.

Methodology  A total of 77 root canal samples from 77 Chinese patients, 42 with necrotic pulp tissues (primary infection) and 35 with failed prior conventional root canal treatment (secondary infection), aseptically exposed at the first patient visit, were studied. Total RNA was isolated directly from each sample, and 16S rRNA gene-based RT-PCR assays were used to determine the presence of bacteria and archaea, respectively.

Results  Bacteria were detected in 39/42 (93%) of root canal samples from teeth with primary infections, and archaea in 16/42 (38%). In the cases diagnosed as secondary root-infected canals, bacteria were detected in 30/35 (86%), whilst archaea were detected in 6/35 (17%) of cases. Amongst the canals, which were positive for bacteria, archaea were always found in combination with bacteria. The incidence of symptomatic cases positive for both bacteria and archaea (16/22, 73%) were significantly higher than those positive for bacteria alone (21/47, 45%) (P < 0.05).

Conclusions  This study confirms the presence of archaea in root canal infections and further implicates them in an association with clinical symptoms. The nature of this association requires further study.