Factors affecting the clinical efficiency of ultrasonic endodontics: a scanning electron microscopy study

The purpose of this pilot study was to investigate some of the clinical variables in ultrasonic endodontics. forty extracted human teeth with a single, straight root 21-25 mm in length were prepared using combinations of the following variables: hand or ultrasonic instrumentation; apical seat prepared to file sizes 35, 40, 45 or 50; 1 ml of water, 4% sodium hypochlorite or EDTAC as irrigant between each instrument size; three brands of ultrasound generator and inserts; a 'low', 'medium' or 'high' effective power output; a tuned or untuned circuit; post-instrumentation ultrasonic irrigation with either 4% sodium hypochlorite, EDTAC, or the two used in sequence. The specimens were viewed in a scanning electron microscope and scored for the presence or absence of a smear layer at levels < 1 mm, 5 mm and 10 mm from the apical seat. The most effective combination, as tested, was hand instrumentation to file size 40 with 1 ml EDTAC irrigation between each instrument size, supplemented by intermittent flush irrigation with EDTAC with ultrasound then 4% sodium hypochlorite with ultrasound. This technique left a minimum smear layer restricted to the apical seat. Other combinations of instrumentation and irrigation were not consistent in their effectiveness.