Influence of apical preparation size and irrigation technique on root canal debridement: a histological analysis of round and oval root canals.

Root canals prepared to a larger size (40) were cleaner than those prepared to a smaller size (20), when irrigation was performed with a syringe and needle. When the irrigant was ultrasonically activated, smaller preparations resulted in canals that were as clean as larger preparations. This finding was common to both round and oval canals of freshly extracted premolars with vital pulp tissue.