Summary of Research Proposal
This is an ex-vivo study designed to evaluate and compare the biologic shapes prepared by two rotary files systems operated under different kinematics. iRace versus Twisted adaptive files will be compared and characterized for the biomechanical parameters of the root canal geometry before and after root canal preparations on freshly human extracted premolars with a predetermined criteria utilizing the state of the art of Micro-Computed Tomography technology.
Introduction
Shaping of the root canal system is an essential step in preparation for 3 D obturation(1, 2) . Recently several NiTi instrument systems have been introduced to the market aiming for better mechanical and biological preparation. One of the drawbacks of the current instruments is the sudden separation (3). This might partially be caused by the mode of manufacturing of most of NiTi files. With the exception of the twisted NiTi files, machine grinding makes all the NiTi instrument systems. Which in turn results in fatigue without pre-separation signs of deterioration on the flutes (4-6).
In order to overcome such inherited deficiencies, manufacturing companies have been trying to find novel ways to manufacturing. The emergence of M-wire and the newly introduced controlled memory and thermal technology (7-10) are recent examples that claim solving this problem. Another drawback for the use of the current instrumentations systems is changing root canal anatomy particularly in the apical third of root canal spaces (8, 11). This will result in biologic violation of the principles of root canal anatomy to preserve the natural path and reduce the incidence of artificial spaces that has the potential to harbor bacteria (12)
Two emerging NiTi file designs have been developed recently with claims to reduce these two drawbacks. One of them is used in continuous rotation (iRace) and the other one in a combination of continuous rotation and reciprocation (TF adaptive). It has been reported that reciprocating files result (13) in marked improvement in cyclic fatigue resistance . The TF Adaptive system utilizes a combination of continuous rotation and a reciprocation motion rendering a unique kinematics. The file uses continuous rotation when the amount of pressure based on the file is minimal. It uses reciprocal motion when it engages dentin and load is applied. Manufacturers claimed that this adaptive technology and twisted file design increase flexibility and allow file to adjust to intracanal torsional stress.
On the other hand, iRace files have been shown to show another promising horizon for better clinical performance (14). However, no reports have been published to compare these two systems directly to explore their effect on the biologic shapes they prepare inside root canals. The aim of the present study is to evaluate and compare –in an ex vivo model-the shaping ability of adaptive reciprocation kinematics and continuous rotation instrumentation movement using iRace files and TF adaptive files utilizing the state of the art micro computed tomography.
Literature Review
Since the cause effect relationship between microorganisms and apical periodontitis was proven (15) , the primary objective of root canal treatment became to prevent or heal apical periodontitis. This can be achieved by properly removing debris, pulp tissue, and microorganisms from the root canal system by chemo mechanical preparation (7). In day to day practice of endodontics, this is achieved by shaping and chemically cleaning the root canal system by mechanical instruments and irrigation solutions (16). With the introduction of nickel-titanium (NiTi) in to the practice of endodontics (17) , They were found to show high elasticity which resulted in preparation of predictable shapes particularly in curved root canal anatomy (2, 18, 19).
The optimum clinical results in endodontic is attained when proper root canal shaping is attained without procedural accidents. One of the drawbacks of instruments is their tendency to change the root canal anatomy by deviating from the natural path which in turn violates the basic principles of root canal preparation (2, 18, 20-22). Occurrence of such iatrogenic changes might have a significant effect of the treatment outcome.
The manufacturing companies in the files are striving to find out innovative ways to improve the metallurgy of the NiTi files by increasing its flexibility but yet maintain their efficiency in preparing root canals. Heat treatment of NiTi wires is witness on the advances that took place in this filed (23). The M-wire and the newly introduced controlled memory and thermal technology are recent examples (24, 25) On another hand, Race instruments are manufactured with a triangular cross-section and distinct positive cutting angles. iRaCe files have improved cyclic fatigue resistance and said to have better centering ability (26).
The R-phase on the other hand, is a phase with martensitic nature, it’s claimed to improve the mechanical properties of rotary instruments (27, 28). This is done by a special thermal treatment during twisting process. The main advantages of this process are gaining flexibility, strength and modification of the crystalline structure of the alloy. This gives the instrument resistance to internal stress caused by manufacturing process (29). Many systems in the market are manufactured by the R-Phase process. For example, Twisted files, K3XF and recently TF Adaptive rotary system.
The TF Adaptive rotary system is a unique system that utilizes a combination of continuous rotation and a reciprocation motion rendering a unique kinematics (30).The developers claims that the TF adaptive system when used with the Elements Motor with Adaptive Motion Technology, it gives the operator total control of the file rather than the file control the operator in a screw down effect. Also it gives him better durability and less separation of the instrument inside the canal thanks for the surface treatment. The system consist of 3 files to finish and clean the canal probably. It uses a friendly system, easy to use and memories since the color coded is similar to a traffic light signal. It’s safer for the patients because it’s less probability to separate because it’s twisted rather than grinded(31). The system consist of 6 files 3 used for small canals SM1 20/0.4, SM2 25/0.6 and SM3 35/0.4 to full working length. Other 3 files used for medium and large canals ML1 25/0.8, ML2 35/0.6 and ML3 50/0.4 to full working length
On the other side, iRace manufacturer stuck on the continuous rotation motion but changed in the design of the file and developed in the manufacturing process. They used electrochemical polishing to enhance resistance against fatigue and corrosion. Triangular cross-section with sharp edges to increase cutting efficiency. They developed alternating cutting edges to reduce screwing-in effect they also used a rounded safety tip to center the instrument in the canal (32, 33). The system consist of 3 files R1 15/0.6, R2 25/0.4 and R3 30/0.4 and recommended to be used up to the full working length. The system also have 2 extra files iRace Plus R1a 20/0.2 and R1b 25/0.2, used in cases of severe curvature when the first file R1 couldn’t reach up to the full working length.
With the introduction of micro-ct technology, 3D visualization of the teeth architecture allowed us to easily study and visualize root canal anatomy in noninvasive mode (34, 35). It also helped us to correlate the reading with histology(32). We can measure exact enamel thickness, study root canal anatomy and morphology, evaluate root canal after preparation, study the effect of rotary system on apical third of the canal, construct micro finite element model and discover micro-cracks(36).
Objectives
The aim of the present study was to evaluate and compare utilizing the micro-CT technology, the shaping characteristics of continuous rotation and adaptive kinematics in the preparation of root canal systems in an ex-vivo model
Material and Methods:
Experimental Teeth Protocol:
80 freshly extracted maxillary and mandibular single rooted premolars extracted for orthodontic reasons stored in 0.1% thymol solution at 4 C. Pre-scaning using a high-resolution micro-CT (resolution of 72 Microm at 70 kV and 114 Micro A). Determination of root canal curvature using Schnedier method (37) by using data collected from micro-CT.
Inclusion criteria:
Maxillary and mandibular premolars with single canal with single apical foramina. Free of caries with completely formed roots. Root curvature range from 0-10.Canal width near apex approximately equal to size 15 K-file. Randomization of the samples using stratified random sampling software.
Teeth Prepration Protocol:
Access Cavity preparation using diamond-coated bur, dentin blocked canal orifice is removed by using ultra sonic tip. Working length is determined by negotiation of size 8-K file until become visible beyond the apex, and then confirming the WL by taking an X-ray with size 15 K-file after subtracting 1 mm from the visible working length.
Irrigation Protocol:
Irrigation with 30 guage side-vented needle with 5 ml syringe. The needle is inserted up to 1 mm shorter than the working length. The total amount of irrigant is 10 ml 5.25% NaOCL and 5 ml EDTA 17% as a final flush after preparation of the canal. Teeth are irrigated by 2 ml 5.25% NaOCL before instrumentation, between each instrument and after instrumentation. A final flush with 5 ml EDTA 17%.
Group 1 iRace Protocol:
40 premolars teeth are prepared using iRace rotary system. After establishing glide path to full working length using hand file size 20 K-file. Teeth are prepared with R1 15/0.6 , R2 25/0.4 and R3 30/0.4 to full working length using Elements Motor by Sybronendo with 600 RPM and 1.5 Ncm torque in continuous rotation motion. Irrigation between each file with 5.25% NaOCL and a final flush with 17% EDTA. Single use of the rotary system per tooth.
Group 2 TF Adaptive Protocol:
40 premolars teeth are prepared using TF Adaptive rotary system. After establishing glide path to full working length using hand file size 20 K-file. Teeth are prepared SM1 20/0.4, SM2 25/0.6 and SM3 35/0.4 to full working length using Elements Motor by Sybronendo using the installed recommended setting for TF Adaptive in adaptive motion. Irrigation between each file with 5.25% NaOCL and a final flush with 17% EDTA. Single use of the rotary system per tooth.
Micro Ct Scaning procedures and evaluation Protocol:
Prepared samples are pre and post scanned with a high-resolution MCT system (resolution of 72 Microm at 70 kV and 114 Micro A). Virtual root canal models will be constructed on basis of micro CT scan and superimpose with the pre-preparation image. To study Volume, Structure model index, Thickness, Straightening, canal transportation and uninstrumented surface area.
Qualitative assessment
By superimposition of constructed three dimensional images. By creating a green image for uninstrumented canal and pink image for the instrumented canal.
Quantitative assessment:
Volume and surface area of root canals
Evaluation is done from triangulated data by marching cubes algorithm. By substracting the scores for the pre and post instrumentation scores.
Structure Model index and thickness:
Evaluation is done from triangulated data by determing the thickness of the canal by using distance transformation techniques.
Staightening:
The centers of gtavity of the canal is calculated by conncting the z-axis by fitted line.
Canal transportation:
Evaluation of canal transportation by comparing the center of gravity before and after instrumentation in apical, middle and coronal third.
Uninstrumented surface area:
By evaluation of superimposed images by matching images of surface area of the canal before and after preparation by assuming that surface voxels remained in the same place before and after preparation.
Statistical Analysis
Calculation of differences between groups or within groups by using t test or analysis of variance with SPSS 11.0 (SPSS Inc, Chicago,IL).
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