Root canal preparation

Prior to each preparation, pre-flaring was performed with

Gates Glidden burs (Komet, Lemgo, Germany)

in the

crown-down technique in the upper-third of the canal.

Figure 1 Purpose-designed stand for standardised photograph.

 Preparation for testing Serial numbers from one to 20 were engraved into the

acrylic blocks with the simulated root canals.

A 0.1% aqueous methylene blue solution (Pharmacy of Philipps University) was injected into the canals to enhance the image contrast for the subsequent photographic documentation and to verify that the canals were suitable for

instrumentation.

If the solution failed to emerge through the apical foramen, the block was discarded and replaced   Determination of Root Canal Curvatures After each change of instrument the root canals were irrigated with water to remove debris. The working length of the industrially produced blocks was set at 18 mm, corresponding to a distance of 1 mm

from the apical foramen.

The working length of each instrument was set by the students themselves with rubber stoppers prior to the start of treatment and was

checked in the course of treatment.

Preparations were performed with a new set of instruments for each preparation

system.

The conicity was 2% (taper 0.02) with manual preparation, and 4% (taper 0.04) with rotary

preparation.

Manual preparation was performed with stainless steel

or Ni-Ti K-files with a working length of 25 mm.

For optimised canal preparation, the stainless steel instruments were pre-bent by the students and applied with slight apically directed pressure with a 1/8 turn clockwise and

counterclockwise direction (14).

Rotary preparation was done with 25 mm long Ni-Ti FlexMaster® files and Profile® instruments, which were lightly coated with Glyde® (Dentsply De Trey, Konstanz,

Germany) before being inserted into the canal.

Both systems were driven at 250 rpm by a torque-controlled lowspeed motor (Endo IT control; VDW, Munich, Germany) adapted to the individual instruments. Between each change of instruments the canals were irrigated with

water.

If necessary, the canals could be recapitulated with a previously used, smaller file. The instrument application sequence is shown in

Tables 2 and 3.

All prepared root canals were photographed once again with a digital camera in standardised position and the

image data were stored in the PC.

In contrast to the first photo, however, the canals were not dye-penetrated and

the blocks were photographed against a black background.