An in vivo experimental study was performed according to the resolution 8430 from the Colombian Ministry of Health regarding ethical issues in research involving human tissues, and was approved by the bioethics committee of the University Colegios de Colombia (RN27/02/22/2017). Written informed consent was obtained from each patient participating in the study (18-30 years old, healthy, not medicated, and non-smoking human donors). This study was made following the guidelines of use of CBCT in research on human beings based on the evidence on when to use it in Endodontics . in patients who need double CBCT. one for diagnosis and the other for the control of orthodontic treatment of dento-maxillofacial anomalies such as maxillary and mandibular asymmetries .
Thirty lower premolars from healthy humans were used, in which extraction was indicated for orthodontic reasons. All the teeth used were caries- and restoration-free with complete root development determined both visually and radiographically, without signs of periodontal disease or traumatic occlusion and without orthodontic forces. Teeth had only one straight canal (canal curvatures over 25º were not included). Each premolar was assigned randomly for one of the experimental groups, consisting of 10 premolars each: a) Reciproc Blue (VDW, Munich, Germany); b) WaveOne Gold (Dentsply/Maillefer, Ballaigues, Switzerland); and c) XP EndoShaper (FKG/Dentaire, La-Chaux-de-Fonds, Switzerland). The sample size was estimated based on the behaviour of variables and confirmed with the TAMAMU 1.1® program (Tokyo, Japan)
An initial CBCT was taken for each premolar with the Carestream Dental CS 8100 3D (CARECAPITAL ADVISORS LIMITED / Rochester, New York, United States), with a 100 kVp voltage and 3-8 mGy / cm2 current. The scan time was approximately 10 seconds for each premolar. Images were analyzed with the Nobel-clinician software (Nobel Biocare Inc, USA). At the axial plane, slices were made at 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm and 7mm, and measures of the root canal and the root were taken from vestibular to palatal and from mesial to distal for three-dimensional reconstruction. Snapshot images of the different sections were imported with the Rhinoceros 3D 5.0 software (Robert McNeel & Associates, Washington, USA) to draw the canal and the root using the poly-line command (Fig. 1 and 2). A digital file in 3dm format was obtained with the reconstruction of the sample previous to root canal preparation [10, 12] (Fig. 3).
Preparation of experimental samples:
All patients underwent prophylaxis with hydrogen peroxide and prophylactic brush, then they were anaesthetized with an inferior alveolar nerve block technique using 1.8 mL of 4% prilocaine without vasoconstrictor. Rubber dam isolation was placed and the cavity access was performed with a Zekrya bur. Canal patency was confirmed with a #10 K file (Dentsply/Maillefer, Ballaigues, Switzerland), working length was established (at -0.5 mm from apical foramen) with the Root ZX apex locator (J Morita, Japan) and verified with a periapical radiography. The root canal samples were prepared with the correspondent technique for each group following the manufacturer’s instructions, using a VDW Silver Reciproc endodontic motor (VDW, Munich, Germany) as follows:
Reciproc Blue group:
The root canal was prepared using one new Reciproc Blue file (VDW, Munich, Germany) (size 25, 0.08 taper) activated in a VDW Silver Reciproc motor (VDW, Munich, Germany), set at the RECIPROC ALL program, following the manufacturer’s recommendations. The file was used with short up and down motion with slight apical pressure in three cycles, one to prepare each third of the canal (cervical, middle and apical). After each cycle, the file was cleaned with wet gauze to remove dentine debris, and the canal was irrigated with 3 mL of 5.25% sodium hypochlorite (NaOCl) using a Monoject syringe with a 30-gauge needle placed 2 mm short of working length to complete a total of 9 mL of NaOCl for each canal. Effective working time of the file inside the canal did not exceed 1 min.
WaveOne Gold group:
The root canal was prepared using one new WaveOne Gold primary file (Dentsply/Maillefer, Ballaigues, Switzerland) (size 25, 0.07 taper) activated in a VDW Silver Reciproc motor (VDW, Munich, Germany), set at the WAVEONE ALL program, following the manufacturer’s recommendations. Irrigation volume and effective working time of the file inside the canal were the same as described for the Reciproc Blue group.
XP EndoShaper group:
The root canal was prepared using one new XP EndoShaper (FKG/Dentaire, La-Chaux-de-Fonds, Switzerland). (size 30, 0.01 taper) activated in a VDW silver motor (VDW, Munich, Germany) strictly following the manufacturer’s recommendations. Irrigation volume and effective working time of the file inside the canal were the same as described for the Reciproc Blue and WaveOne Gold groups.
Post-preparation tomographic analysis:
A second tomographic analysis was performed with CBCT. Taking advantage of orthodontic control for dento-maxillofacial anomalies presented in the selected patients that needs to be followed up. Following the same steps as the initial CBCT, a digital file in 3dm format was obtained with the reconstruction of the sample after root canal preparation to carry out the superposition of preparation images before and after in order to evaluate the variables proposed in the study.
Pre- and post-operative dental reconstruction process:
Sixty CBCT scans of the teeth were obtained from before and after root canal preparations with slices at 0.5, 1, 2, 3, 4, 5, 6 and 7 mm with Rhinoceros 3D. The tomography was framed with the poly-line command, to be used later as a reference point. These slices with the frame were exported to the Rhinoceros software (Robert McNeel & Associates, Washington, USA) one by one, both of the root and the canal. Also, a reference line was drawn connecting the point of intersection of the aforementioned lines in the root and the canal, to make sure that the position of the canal inside the root was not altered in the previous steps (Fig. 4).
Superimposition of pre- and post-preparation reconstruction:
With the guide lines and the table of measurements, each root and canal was given its corresponding measure in μm with the scale 1D command, enlarging or reducing the drawing according to the table of measurements. All the reference lines used were removed to clean the drawing and when all the slices were scaled, it was proceeded to join each pre-operative slice to its corresponding original millimeter, this was done with the move command using as reference points, both the frame of the tomography that was preserved at the beginning and the root itself (Fig. 5).
The above procedure reduces the number of slices to 6 and in each root the canal was located both before and after the endodontic preparation. The next step was to place the three dimensionally slices on top of each other at the corresponding heights with the move command, giving a diagram of millimeter by millimeter heights of the root and the canal. When having the slices in this position, a complex surface was created between all slices for each element with the loft command and the result was a surface for the root, one for the original canal and one for the prepared canal (Fig 6).
Three surfaces remain that are then covered with the plane and split commands to generate a solid form, finally the edge of the canals is created following an hourglass shape with the loft command, this was covered with the commands mentioned above and finally, details such as the colors and the transparency of the root were added with the material editor command (Fig. 7 and 8).
Measurement of canal volume:
The total volume of the root canal was measured before and after root canal preparation by using the volume command in the Rhinoceros 5.0 software. This function gives the volume result of a solid in mm3. Student t test analysis for paired data were used to determine statistically significant differences between the before and after canal volumes. Percentage of volume increase was also calculated to compare the volume increase for each group. Anova test was used to determine statistically significant differences in the percentage of canal volume increase between the experimental groups.