الفهرس 
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Abstract
Aim of the study:The purpose of the present in vitro study was twofold: First, to evaluate and compare cutting efficiency of CM NiTi instrument (Typhoon CM) and conventional NiTi instrument (ProTaper F2) in terms of centering ability and transportation in moderately curved canals when using reciprocation or rotation motion using Cone Beam Computed Tomography (CBCT). Second, to examine the fatigue behavior of the two instruments when using reciprocation or rotation motion during canal preparation using Scanning Electron Microscope.
Materials and Methods:
A total of ninety six mesiobuccal root canals of freshly extracted human mandibular and maxillary first permanent molars were selected provided they have mature apex, Curvature of the mesiobuccal root canal ranges between 35 and 45 degrees according to Schneider’s method and canals should have unidirectional curvature in mesiodistal planes.
The teeth were thoroughly washed, immersed in 2.5% NaOCl for 1 hour to disinfect and dissolve the organic debris then the calculus was removed with ultrasonic scalers. Teeth were then stored in fresh physiologic saline solution. Crown decapitation was done using a high speed fissure bur under air water spray in order to standardize the total working length to be 12 mm.
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A custom-made plastic mold with 18 holes arranged in 6 columns and 3 rows was specially constructed into which cold-cured acrylic resin was packed. Each sample was embedded with its long axis parallel to the long axis of the mold to ensure standardization of the samples for the tomography images before and after root canal instrumentation. In order to prevent the resin from entering and polymerizing into the apical foramen, the apices of the roots were sealed with wax then acrylic resin was allowed to set. Samples of each group were coded with numbers for ease of identification. The preoperative angle of curvature was measured according to Schneider technique with Cone Beam Computed Tomography and any specimen that was out of the curvature range (35°-45°) was replaced.
Ninety six root canals were randomly assigned to two groups, each of 48 root canals. group A were prepared by Typhoon infinite flex rotary file while group B were prepared by ProTaper F2 rotary file. 24 root canals of each group A and B were subdivided into 2 subgroups; subgroup 1, root canals were prepared using reciprocation motion. Subgroup 2, root canals were prepared using rotation motion. Each 3 root canals were prepared with one file then the file was used in a fourth canal till separation (a total of 6 files were used for each subgroup).
X smart plus Endomotor was used to prepare the root canals of both reciprocation and rotation subgroups. Sodium hypochlorite (NaOCl) 2.5% was used as an irrigant in all subgroups after every time of file
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insertion with a total volume of 15 mL per each sample and Glyde was used as a lubricating agent in all subgroups.
For evaluation of shaping ability, Pre and post instrumentation CBCT images at 3, 5 and 8 mm from the apical constriction were retrieved for comparison. The dentin wall thickness of each root was measured from canal wall to the root surface in mesiodistal direction, before and after instrumentation to calculate transportation and centering ratio.
To assess the cyclic fatigue Scanning Electron Microscope was used where pre and post instrumentation scans were taken for 3 root canals in each sub-group. After using each file in preparation of three root canals, it was used in a fourth canal till separation.
Results:
1. For both groups; group A (Typhoon) and group B (ProTaper): in a reciprocation motion, statistical analysis showed no significant difference in both degree and direction of root canal transportation at 3 mm and 8 mm levels. While at 5 mm level, ProTaper revealed statistically significant higher mean of root canal transportation than Typhoon. With rotation motion, there was no statistically significant difference in both degree and direction of root canal transportation between the two systems at 3 mm and 5 mm levels. While at 8 mm level, ProTaper revealed statistically significant higher mean of degree and direction of root canal transportation than Typhoon. In centering ratio,
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statistical analysis showed no significant difference along different root canal levels in either reciprocation or rotation motion.
2. Using different motions, there was no statistically significant difference in degree of canal transportation along different root canal levels (3 mm, 5 mm and 8 mm levels) between reciprocation and rotation motions in both groups; group A (Typhoon) and group B (ProTaper). Regarding transportation direction; the only significant difference recorded between the two motions was in root canals prepared by ProTaper system at 5 mm level. In centering ratio, no statistically significant difference was found at different root canal levels prepared with either Typhoon or ProTaper systems whether used in reciprocation or rotation motion.
3. Along the three measured levels of root canal, statistical analysis revealed no significant difference in degree of canal transportation with either Typhoon or ProTaper systems used in either reciprocation or rotation motion. Regarding transportation direction, statistical analysis showed that, with Typhoon system, there was no statistically significant difference between the three levels using either reciprocation or rotation motion. With ProTaper system, there was no statistically significant difference between the three levels using reciprocation motion while using rotation motion, there was a statistically significant difference
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between the three levels. Centering ratio records showed no statistically significant difference along different root canal levels in either reciprocation or rotation motion.
4. Regarding the cyclic fatigue, root canals prepared with ProTaper system used in reciprocation motion showed statistically significant higher mean of cyclic fatigue resistance than rotation motion. While those prepared with Typhoon system showed no statistically significant difference between the two motions.
5. With the same motion, there was no statistically significant difference in cyclic fatigue resistance of ProTaper and Typhoon when used in reciprocation motion. Whereas when used in rotation motion, Typhoon showed statistically significant higher mean of cyclic fatigue resistance than ProTaper