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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 7  »  Shaping ability of GT Rotary Files in simulated resin root canals
Shaping ability of GT Rotary Files in simulated resin root canals
Materials and methods.



Construction of simulated canals.
A total of 40 simulated root canals were made in clear resin blocks (Dummer et al.1991). Annealed silver points size 20 were used as root canal templates. Four different canal types (Fig.1) were made by precurving silverpoints using canal formers. The bent silver points were then checked under magnification (8x) for their alignment to the canal former, and inappropriate points were discarded. Clear spectrophotometer cuvettes were used as moulds to retain the self-polymerizing resin (Stycast 1266, Emerson & Cuming, Westerlo, Belgium) that was poured around the preformed silver points. The finished clear resin blocks were 3.5 cm long.
In all, 40 simulated canals were produced, with either 408 and 608 curves and with a straight section prior to the curve of either 8 or12 mm. The four different canal types are pictured in Fig.1. The angle and radius of the curvature were determined according to Pruett et al. (1997); the radius was 6 mm.

Figure 1. The four different canal types.

The four different canal types

Instruments.
The instruments in the GT Rotary File system (Dentsply Maillefer) feature flat outer edges with a U-file design which prevent self-threading. The files have variable tapers, common tip sizes, radial-landed flutes, maximum flute diameters and non-cutting tips. According to the manufacturer, they also posses the properties of nickel-titanium alloy which allows creation of a tapered funnel around curvatures, whilst keeping the preparation in the canals original position. The system comprises three types of instruments. The first four instruments are the GT Rotary Files with a taper of 6, 8,10 and 12%. The instruments all have the same tip diameter of 0.20 mm. The second four instruments are the GT Rotary Files 0.04 having a 4% taper with a tip diameter ranging from size 20 to size 35. These files are used for the preparation of the apical third and are identical to the ProFile series. The final files are the GT Accessory Files with a 12% taper and a tip diameter of size 35, size 50 and size 70.

Preparation of simulated canals.
All canals were prepared with  GT Rotary instruments using a 128 :1 reduction hand piece (Anthogyr, Endodontic Ni-Ti Contra Angles, Sallanches, France) powered by an electric motor (40 000 rpm). Ten canals of each shape were prepared by the operator to a working length of 16 mm using a constant speed of 312 rpm. The preparation followed the instructions of the manufacturer. The basic method was a‘crown-down/stepback’ method. A new set of instruments was used per canal. The files were wiped off on a gauze to remove resin particles. Irrigation with tap water using disposable syringes was performed after each file. A size15 Flexofile (Dentsply  Maillefer) was used as a patency file. The method for preparation was as follows:
  1. a file with taper 0.12 and tip diameter 20 was used to prepare the first 4 mm of the straight section with a slight in and out movement;
  2. a file with taper 0.10 and tip diameter 20was used to a depth of 8 mm;
  3. a file with taper 0.08 and tip diameter 20was used to a depth of12 mm;
  4. a file with taper 0.06 and tip diameter 20was used to a depth of14 mm;
  5. a file with taper 0.04 and tip diameter 20 was used to the full working length of16 mm;
  6. a file with taper 0.04 and tip diameter 25 was then used to full working length;
  7. a file with taper 0.04 and tip diameter 30 was used to full working length minus 0.5 mm;
  8. a file with taper 0.04 and tip diameter 35 was then used to full working length minus1mm.
During preparation, each resin block was placed in a copper holder, masking the entire canal, to aid handling (Fig. 2). Masking the resin blocks ensured that the process was carried out with purely tactile sensation.

Figure 2. Each resin block was placed in a copper holder, masking the entire root canal, to aid handling during root canal preparation.

Each resin block was placed in a copper holder, masking the entire root canal, to aid handling during root canal preparation

Assessment of canal preparation.
The results of the canal preparations were assessed using a video camera (CCTV Camera, Panasonic WVBL604, Matsushita Industrial Co, Osaka, Japan) connected to a light microscope (Reichert-Jung Polyvar, Reichert optische werke AG, Wien, Austria) and attached to a Pentium III computer with image analysis software (Interactive Bild-analyse System (IBAS), Kontron Electronic Gmbh, Germany). Measurements were made on superimposed pre- and post-operative digitized images. In order to achieve a standardized position of the resin blocks under the microscope, a holder was made in which the resin blocks could be placed and repositioned in exactly the same position. Reference points were recorded by means of the microscope’s nonius scale. At the experimental magnification, it was impossible to visualize the entire canal. One image on screen corresponded to 2.3 mm of the real canal length. Depending on the canal type,8-10 images were needed to assemble the entire canal. Both X and Y coordinates on the microscope’s nonius scale were recorded for each image, allowing repositioning and reproduction of the pictures at any given moment (i.e. pre- and postoperative).
For each resin block, the captured images, representing parts of the canal, were precisely aligned to form a picture of the entire canal. The centre of the original canal path was calculated by the software.
After preparation with the GT Rotary Files the simulated canals were viewed again in the microscope. For each resin block, setting the previously recorded X and Y coordinates of the original canal, corresponding images of the post-operative canal were captured and aligned to forma picture of the entire canal after instrumentation. Both pre- and postoperative images were then superimposed.
At this stage, five points were determined on each central canal path, for measuring the canal width, using a modification of the method described by Alodeh & Dummer (1989) (Fig. 3):
  • position1: the canal orifice (O);
  • position 2: a point half-way from the beginning of the curve to the orifice (HO);
  • position 3: the beginning of the curve (BC);
  • position 4: the apex of the curve of the original canal (AC), determined by the intersection of two lines (one along the coronal aspect of the central line, and the second along the apical portion of the central line);
  • position 5: end point of preparation (EP).
All measurements were carried out perpendicular to the axis of the original central canal path to the nearest 0.001mm, using the image analysis software.
The canal aberrations to be scored were zips and elbows, ledges, perforations, and danger zones (Alodeh & Dummer1989) as well as the‘outer widening’ (Bryant et al. 1999). In this respect, a representative composite print of superimposed pre- and postoperative canals with apical zip and elbow is shown in Fig. 4.

Figure 3. Composite print of a type II canal outlining the 5 positions of measurement. The white region defines the image of the canal before preparation, the grey region defines the canal after preparation.

Composite print of a type II canal outlining the 5 positions of measurement

Figure 4. Composite image of the simulated resin canals (type IV) with apical zip and elbow in the GT Rotary File technique. The white region defines the image of the canal after the preparation, and the black region defines the canal before preparation.

The white region defines the image of the canal after the preparation, and the black region defines the canal before preparation

Recording, storage, and analysis of data.
All data were stored on PC from the image processing software directly to a database file. Following error and range checks, the data were analyzed using SPSS, a statistical analysis program. Differences at the five measuring points between the mean total widths, the mean inner widths and the mean outer widths were statistically analyzed using anova. Statistical analysis of the number of canals transported towards the inner and outer aspect of the curve was done by the Kruskal-Wallis Test.