This systematic review aimed to investigate whether minimally invasive root canal preparation ensures higher fracture resistance compared to conventional root canal preparation in endodontically treated teeth (ETT). A comprehensive search strategy was conducted on the “PubMed, Web of Science, and Scopus” databases, alongside reference and hand searches, with language restrictions applied. Two independent reviews selected pertinent laboratory studies that explored the effect of minimally invasive root canal preparation on fracture resistance, in comparison to larger preparation counterparts. The quality of the studies was assessed, and the risk of bias was categorized as low, moderate, or high. The electronic search yielded a total of 1,767 articles. After applying eligibility criteria, 8 studies were included. Given the low methodological quality of these studies and the large variability of fracture resistance values, the impact of reduced apical size and/or taper on the fracture resistance of the ETT can be considered uncertain. This systematic review could not reveal sufficient evidence regarding the effect of minimally invasive preparation on increasing fracture resistance of ETT, primarily due to the inherent limitations of the studies and the moderate risk of bias.

Currently, various Nickel-Titanium rotary files are used in endodontic treatment, but there is no one perfect system that can be applied to any clinical situation. Therefore, the combined uses of various file systems which can emphasize the advantages of each system are introduced as hybrid instrumentation.

The ProTaper system is efficient in body shaping and apical pre-enlargement but is reported to have more possibility of transportation and produce more aberrations and deformation in more or less severe curved canals. Recently, new ProTaper system (ProTaper Universal) with different configuration and cross-sectional design to overcome the week points of ProTaper have been marketed.

The purpose of this study was to compare and evaluate the shaping abilities of ProTaper, ProTaper Universal system, and two hybrid methods using S-series of ProTaper Universal and Hero Shaper or ProFile.

The time lapses for instrumentation were measured and the used files were inspected for distortion. The pre- and post-instrumented root canals were scanned and superimposed to evaluate the aberrations and reduction of root canal curvature and change of radius of canal curvature. The increased canal width and apical centering ratio were calculated at 1, 2, 3, 4 and 5 mm levels from apical foramen.

Under the conditions of this study, the ProTaper Universal seems to have better shaping ability than ProTaper in terms of instrumented width and instrumentation time. It may be suggested that the ProTaper Universal system is efficient as much as hybrid instrumentation using ProTaper and other constant-tapered NiTi file systems in highly experienced operators.

This study was done to evaluate transportation of the apical foramen after 0.5 mm overinstrumentation by ProFile, ProTaper and K³ in simulated resin root canal.

Sixty simulated resin root canal with a curvature of J and S-shape were divided into two groups. Each group consisted of three subgroups with 10 blocks according to the instruments used: ProFile®, ProTaper™, and K^3TM. Simulated resin root canal was prepared by ProFile, ProTaper and K³ with 300 rpm by the crown-down preparation technique. Pre- and post-instrumentation apical foramen images were overlapped and recorded with Image-analyzing microscope 100X (Camcope, Sometech Inc, Korea). The amounts of difference in width and dimension on overlapped images were measured after reference points were determined by Image Analysis program (Image-Pro® Express, Media Cybernetic, USA). Data were analyzed using Kruskal-Wallis and Mann-Whitney U-test.

The results suggest that ProFile showed significantly less canal transportation and maintained original apical foramen shape better than K³ and ProTaper.

The purpose of this study was to compare the centering abilities of four root canal instrument systems and the amounts of dentin removed after root canal shaping using them.

The mesial canals of twenty extracted mandibular first molars having 10 - 20° curvature were scanned using X-ray micro-computed tomography (XMCT)-scanner before root canals were instrumented. They were divided into four groups (n = 10 per group). In Group 1, root canals were instrumented by the step-back technique with stainless steel K-Flexofile after coronal flaring. The remainders were instrumented by the crown-down technique with Profile (Group 2), ProTaper (Group 3) or K3 system (Group 4). All canals were prepared up to size 25 at the end-point of preparation and scanned again. Scanned images were processed to reconstruct three-dimensional images using three-dimensional image software and the changes of total canal volume were measured. Pre- and post-operative cross-sectional images of 1, 3, 5, and 7 mm from the apical foramen were compared. For each level, centering ratio were calculated using Adobe Photoshop 6.0 and image software program.

ProTaper and K3 systems have a tendency to remove more dentin than the other file systems. In all groups, the lowest value of centering ratio at 3 mm level was observed. And except at 3 mm level, ProTaper system made canals less centered than the other systems (p < 0.05).

This study was conducted to evaluate the insertion depth of Buchanan plugger after shaping by various Ni-Ti rotary files. It was conducted to determine which size of plugger are appropriate, when root canals are shaped with Ni-Ti rotary files and obturated by Continuous wave of condensation technique.

Two type of eighty simulated resin blocks were used : J-shaped and straight shaped canal. The simulated canals were instrumented by ProTaper and ProFile. Buchanan pluggers were inserted into the canal, and then the image was recorded to scanner. The distance from the apex of the canal to the plugger tip was measured by image analysis program. Data were analyzed by one-way ANOVA followed by Scheffe's test.

The results were as follows

1. In straight canal finished up to ProTaper F2 and F3 file, F and FM pluggers were inserted more than 5 mm short of working length.

2. In J-shaped canal finished up to ProTaper F2 file, F pluggers were inserted more than 5 mm short of working length. Finished up to ProTaper F3 file, F and FM pluggers were inserted more than 5 mm short of working length.

3. In straight and J-shaped canal finished up to ProFile .06/#20 and .06/#25, any of Buchanan plugger could not be inserted more than 5 mm short of working length.

These results suggest that canals shaped by ProTaper could be obturated by Continuous wave of condensation technique with F and FM size Buchanan plugger.

The purpose of this study was to investigate influence of each file step of ProTaper® system on canal transportation.

Twenty simulated canals were prepared with either engine-driven ProTaper® or manual ProTaper®. Group R-resin blocks were instrumented with rotary ProTaper® and group M-resin blocks were instrumented with manual ProTaper®. Pre-operative resin blocks and post-operative resin blocks after each file step preparation were scanned. Original canal image and the image after using each file step were superimposed for calculation of centering ratio. The image after using each file step and image after using previous file step were superimposed for calculation of the amount of deviation. Measurements were taken horizontally at five different levels (1, 2, 3, 4 and 5 mm) from the level of apical foramen.

In rotary ProTaper® instrumentation group, centering ratio and the amount of deviation of each step at all levels were not significantly different (p > 0.05). In manual ProTaper® instrumentation group, centering ratio and the amount of deviation of each step at all levels except of 1 mm were not significantly different (p > 0.05). At the level of 1 mm, F2 file step had significantly large centering ratio and the amount of deviation (p < 0.05).

Under the condition of this study, F2 file step of manual ProTaper® tended to transport the apical part of the canals than that of rotary ProTaper®.

The purpose of this study was to compare and evaluate the shaping abilities of various hybrid instrumentation method using constant tapered file systems with ProTaper® S1 and the difference between experts and inexperienced clinicians in use of NiTi file.

Three hybrid methods used in this study were composed of ProTaper® S1 and K-Flexofile® (group S), ProTaper® S1 and HeroShaper® (group H), and ProTaper® S1 and ProFile® (group P), respectively. The ProTaper®-alone method (group C) was introduced as a control group.

After canal preparation, the lapse of time was recorded. The images of pre- and post-operative canal were scanned and superimposed. Amounts of instrumented canal widths and centering ratio were measured at apical 1, 2 and 3 mm levels and statistical analysis was performed.

In this study, both of the group C and S took more time to prepare canals than other groups. Inexperienced operators required more time for the entire preparation with the groups C and H than the experienced (p < 0.05). And the centering ratio of group P were preferable to ProTaper®-alone method or the hybrid technique using stainless steel files. As such, within experienced operators, group H also showed better results in addition to the group P.

Under these condition, the hybrid methods of each the ProFile® system and HeroShaper® with ProTaper® are recommendable comparative to ProTaper®-alone method. According to the results, the hybrid instrumentation method is a more appropriate method of canal preparation than single file system for narrow or curved canals.

The purpose of this study was to compare the canal configuration after shaping by ProTaper rotary files and ProTaper hand files in resin simulated canals.

Forty resin simulated canals with a curvature of J-shape and S-shape were divided into four groups by 10 blocks each. Simulated root canals in resin block were prepared by ProTaper rotary files and ProTaper hand files using a crown-down pressureless technique. All simulated canals were prepared up to size #25 file at end-point of preparation. Pre- and post-instrumentation images were recorded with color scanner. Assessment of canal shape was completed with an image analysis program. Measurements were made at 0, 1, 2, 3, 4, 5, 6 and 7 mm from the apex. At each level, outer canal width, inner canal width, total canal width, and amount of transportation from original axis were recorded. Instrumentation time was recorded. The data were analyzed statistically using independent t-test.

The result was that ProTaper hand files cause significantly less canal transportation from original axis of canal body and maintain original canal configuration better than ProTaper rotary files, however ProTaper hand files take more shaping time.

The purpose of this study was to evaluate which type of Ni-Ti files are able to maintain canal configuration better in the simulated canal with abrupt curvature near it's apex.

Ninety six simulated root canals were made in epoxy resin and #15 finger spreader was used as root canal templates. The simulated root canals were made with radius of curvature of 1.5 mm, 3.0 mm, 4.0 mm, 6.0 mm respectively and the angle of curvature of all simulated canals were adjusted to 90 degree. The simulated canals were instrumented by ProFile, ProTaper, Hero 642, and K³ at a 300 rpm using crown-down pressureless technique. Pre-instrumented and post-instrumented images were taken by digital camera and were superimposed with Adobe Photoshop 6.0 program. Images were compared by image analysis program.

The changes of canal width at the inner and outer side of the canal curvature, canal transportation were measured at 9 measuring point with 1 mm interval. Statistical analysis among the types of Ni-Ti files was performed using Kruskal-Wallis test and Mann-Whitney U-test.

The result was that ProFile maintain original canal configuration better than other engine driven Ni-Ti files in the canals above 3.0 mm radius of curvature, and in the 1.5 mm radius of curvature, most of Ni-Ti flies were deformed or separated during instrumentation.

The purpose of this study was to evaluate the canal configuration after shaping by ProFile, ProTaper and K-Flexofile in simulated resin canals with different angles of curvature.

Three types of instruments were used : ProFile, ProTaper, K-Flexofile. Simulated root canals, which were made of epoxy resin, were prepared by ProFile, ProTaper with rotary instrument using a crown-down pressureless technique, and hand instrumentation was performed by K-Flexofile using a step-back technique. All simulated canals were prepared up to size 25 file at end-point of preparation. Pre and post instrumentation images were recorded with Scanner. Assessment of canal shape was completed with Image Analysis program. Measurements were made at 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 mm from the apex. At each level, outer canal width, inner canal width, total canal width, and amount of transportation from original axis were recorded. Instrument deformation and fracture were recorded. Data were analyzed by means of one-way ANOVA analysis of variance and the Sheffe's test.

The result was that ProFile and ProTaper maintain original canal shape regardless of the increase of angle of curvature than K-Flexofile. ProFile show significantly less canal transportation and maintained original canal shape better than ProTaper.

The aim of this study was to evaluate the microleakage of teeth according to root canal preparation with & without apical enlargement in various size of apical foramen. 60 extracted one canal roots were cross-cutted at 5 mm from root apex and divided into two groups according to their apical foramen size of large (L) and small (S). Each group was subdivided into two groups accordance with their cross-sectional configuration at 5 mm from apex, round (R) and ovoid (O); SR Group, SO Group, LR Group, LO Group. Each group was shaped in .02 taper by Quantec series Nickel-Titanium (NiTi) rotary file, obturated by lateral condensation method. Leakage was measured using a fluid transport model under 40 cmH₂O pressure. After the leakage test, blocks which had showed the leakage retreated with .04 taper and .06 taper and evaluated the degree of fluid filtration in each group. The data was analysed statistically using chi-square test and fisher's exact test.

The results obtained were as follows:

1. Significant difference in leakage was found in groups which had different apical foramen size in .02 taper instrumentation (p < 0.05), but not in .04 taper instrumentation (p > 0.05).

2. The difference in microleakage according to the shape of canal was not evident at 5 mm from apex (p > 0.05).

3. There was correlation between .02 taper instrumentation and .04 taper instrumentation in LR group , LO group (p < 0.05).

The purpose of this study was to compare the shaping ability of the three ProTaper® instrumentation techniques in simulated canals.

Thirty resin blocks were divided into 3 groups with 10 canals each. Each group was instrumented with manual ProTaper® (Group M), rotary ProTaper® (Group R), and hybrid technique (Group H). Canal preparation time was recorded. The images of pre- and post-instrumented root canals were scanned and superimposed. The amounts of canal deviation, total canal width, inner canal width, outer canal width and centering ratio were measured at apical 1, 2, 3, 4, 5 and 6 mm levels.

1. Canal preparation time was the shortest in R group (p < 0.05).

2. The amounts of total canal width in R group was generally larger than the other groups, but no significant differences were observed except at the 1, 3 mm levels (p > 0.05).

3. The amounts of inner canal width in R group was larger than M group at the 1 mm level and H group was larger than R group at the 6 mm level (p < 0.05). The amounts of outer canal width in R group was larger than H group only at the 1 mm level (p < 0.05).

4. The direction of canal deviation in H, R group at the 1, 2, 3 mm levels was outward and that in M group at the 1, 2 mm levels was inward. The amounts of canal deviation in H group was larger than R group at the 6 mm level (p < 0.05).

5. The amounts of centering ratio in H group was larger than R group at the 6 mm level (p < 0.05).

The aim of this study was to evaluate the shaping abilities of four different rotary nickel-titanium instruments with anticurvature motion to prepare root canal at danger zone by measuring the change of dentin thickness in order to have techniques of safe preparation of canals with nickel-titanium files.

Mesiobuccal and mesiolingual canals of forty mesial roots of extracted human lower molars were instrumented using the crown-down technique with ProFile, GT™ Rotary file, Quantec file and ProTaper™. In each root, one canal was prepared with a straight up-and-down motion and the other canal was with an anticurvature motion. Canals were instrumented until apical foramens were up to size of 30 by one operator. The muffle system was used to evaluate the root canal preparation. After superimposing the pre- and post-instrumentation canal, change in root dentin thickness was measured at the inner and outer sides of the canal at 1, 3, and 5 mm levels from the furcation. Data were analyzed using two-way ANOVA.

Root dentin thickness at danger zone was significantly thinner than that at safe zone at all levels (p < 0.05).

There was no significant difference in the change of root dentin thickness between the straight up-and-down and the anticurvature motions at both danger and safe zones in all groups (p > 0.05).

ProTaper removed significantly more dentin than other files especially at furcal 3 mm level of danger and safe zones (p < 0.05)

Therefore, it was concluded that anticurvature motion with nickel-titanium rotary instruments does not seem to be effective in danger zone of lower molars.

The purpose of this study was to investigate the quantity of debris which was extruded apically after canal instrumentation using different types of enlarging instrument in endodontic resin models.

Five groups of 9 endodontic resin models were instrumented using each different technique: hand instrumentation without early coronal flaring, hand instrumentation after early coronal flaring, and three nickel-titanium engine-driven instrumentations (Hero 642, Protaper, K³). Debris extruded from apical foramen during instrumentation was collected on preweighed CBC bottle, desiccated and weighted using electronic balance. The results were analyzed using Kruskal-wallis test and Mann-Whitney U rank sum test at a significance level of 0.05.

The results were as follows:

All of instrumentation techniques produced apically extruded debris.

The early coronal flaring is very important to reduce the amount of debris extruded apically.

The purpose of this study was to quantify the amount of remaining gutta-percha/sealer on the walls of root canals when three types of nickel-titanium rotary instruments(Profile, ProTaper and K³) and a hand instrument(Hedstrom file) used to remove these materials.

The results of this study were as follows:

In the total time for gutta-percha removal, Profile group was the fastest and followed by K³, Protaper, Hedstrom file group.

These results showed that instrumentation using nickel-titanium rotary instrument groups was faster than that using hand instrument group. The effect of gutta-percha removal using Profile group was better than that using Protaper and K³ group in the nickel-titanium rotary instrument groups.

There are increasing usage of Nickel-Titanium rotary files in modern clinical endodontic treatment because it is effective and faster than hand filing due to reduced step.

This study was conducted to evaluate the effect of canal preparations using 3 different rotary Nickel-Titanium files that has different cross sectional shape and taper on the maintenance of canal curvature. Simulated resin block were instrumented with Profile(Dentsply, USA), GT rotary files(Dentsply, USA), Hero 642(Micro-Mega, France), and Pro-Taper(Dentsply, USA).

The image of Pre-instrumentation and Post-instrumentation were acquired using digital camera and overspreaded in the computer. Then the total differences of canal diameter, deviation at the outer portion of curvature, deviation at the inner portion of curvature, movement of center of the canal and the centering ratio at the pre-determined level from the apex were measured.

Results were statistically analyzed by means of ANOVA, followed by Scheffe test at a significance level of 0.05.

The results were as follows;

1. Deviation at the outer portion of curvature, deviation at the inner portion of curvature were showed largest in Pro-Taper, so also did in the total differences of canal diameter(p<0.05).

2. All the groups showed movements of center. Profile combined with GT rotary files and Hero 642 has no difference but Pro-Taper showed the most deviation(p<0.05).

3. At the 1, 2, 3mm level from the apex movements of center directed toward the outer portion of curvature, but in 4, 5 mm level directed toward the inner portion of curvature(p<0.05).

As a results of this study, it could be concluded that combined use of other Nickel-Titanium rotary files is strongly recommended when use Pro-Taper file because it could be remove too much canal structure and also made more deviation of canal curvature than others.