In between appointment, endodontic flare up is caused by:

In a case of asymptomatic apical periodontitis, there is a balance between infectious microflora and defensive mechanisms of human immune system in the periodontal tissues. This phenomenon is called "local adaptation syndrome”. In the case of symptomatic apical periodontitis, when the tooth is sensitive to percussion, predominant strains of microorganisms are Parvimonas micro, Eubacterium, Porphyromonas (P. endodontalis, P. gingivalis) and Prevotella. Especially, the BPB (black - pigmented bacteria) have gained much attention.