Introduction
Obturation (obturatio, Latin: closing) is the last step of root canal treatment: the cleaned, shaped and disinfected canal is filled with a solid core material and a sealer. A filling that leaks lets bacteria recolonise the canal – a main cause of persistent apical periodontitis. Filling techniques are topic 47, their evaluation topic 48.
Aims and timing
The aim of obturation is a three-dimensional, fluid-tight seal of the whole root canal system, from the orifice to the apical constriction. The filling ends at the working length, usually 0.5–1 mm short of the radiographic apex. It should:
- prevent reinfection from the mouth (coronal leakage);
- entomb bacteria surviving in tubules, isthmuses and lateral canals, leaving them no space or nutrients;
- seal apically, so tissue fluid cannot seep in and feed surviving bacteria.
As commonly taught, the canal is filled only when it is:
- shaped and clean – planned apical size and taper reached, final irrigation done, smear layer removed (EDTA);
- dry – paper points come out without exudate or blood, no foul odour;
- in an asymptomatic tooth – no pain, no tenderness to percussion, no swelling, sinus tract closed; temporary filling intact.
A weeping canal or an acute exacerbation is not filled: it is dressed again with calcium hydroxide. After a vital pulpectomy the canal can be filled in the same visit.