The effect of preparation procedures on original canal shape and on apical foramen shape

Torsional and bending properties of stainless steel and nickel titanium Canal Master U and Flexogate instruments

The purpose of this study was to assess and to compare the torsional and bending properties of the Canal Master U (CMU) and Flexogate instruments made of stainless steel and nickel titanium. The bending moment, the torsional moment and angular deflection were measured according to ANSI/ADA specification number 28 and ISO reference number 3630. Ten instruments of each size, sizes 25 to 40 were used for each test. Nickel titanium instruments were significantly more flexible than stainless steel files. With regard to the torsional moment, values obtained were below the standards in all sizes except stainless steel CMU sizes 25, 35 and 40, and nickel titanium CMU size 25. Nickel titanium instrument also showed the highest angular deflection values. There were statistically significant differences between nickel titanium files and stainless steel Flexogates and between stainless steel Flexogates and stainless steel CMU. Based on these findings, the use of nickel titanium CMU and Flexogates is encouraged. Given the perceived advantages of both CMU and Flexogate instruments over conventional files for canal preparation, it would appear desirable to have the torque resistance of these instruments improved.

A comparison of bending and torsional properties of K-files manufactured with different metallic alloys

The purpose of this study was to compare bending (bending moment) and resistance to fracture by twisting (torsional moment and angular deflection) of triangular cross-section K-files made of either nickel titanium (Nitiflex, Naviflex), titanium (Microtitane) or stainless steel (Flexofile, Flex-R). A total of 200 files were tested, 10 instruments for each type from size 25 to 40, according to ANSI/ADA specification no. 28 and ISO reference no. 3630. Files made of nickel titanium, especially Nitiflex, were the most flexible. Stainless steel instruments presented a higher bending moment than files made of nickel titanium and titanium, particularly Flex-R sizes 35 and 40. With regard to resistance to fracture, measured by angular deflection at the failure point, Flexofile followed by Flex-R were the most resistant to fracture and Nitiflex were the least resistant. Differences in angular deflection among file groups were greater than those for torsional moment. Thus, it seems that angular deflection is a more specific measurement for assessing resistance to fracture by twisting.

Comparison of stainless steel and nickel-titanium instruments in molar root canal preparation

Forty mesial canals in extracted human molar teeth were embedded and sectioned at two root levels. Reassembled teeth were instrumented using a step-back technique with stainless steel (SS) or nickel-titanium (NT) K-type files. Superimposed pre- and postinstrumented cross-sectional root images were projected, traced, and scanned into a computer for analysis. The amount and direction of canal center movement, canal area change, and final canal shape were recorded. The results showed no significant difference in canal center movement or canal area change between the SS and NT groups. All canal centers deviated toward the furcation region at the height of curvature and in the opposite direction in apical sections. The degree of canal curvature had no correlation to canal center movement or canal area change. Fifty-three percent of SS and 68% of NT instrument preparations were classified as oval.

An in vitro comparison of the Excalibur handpiece and hand instrumentation in curved root canals

Root canal preparation may be the most technique-sensitive and labor-intensive procedure in endodontic therapy. Many automatic handpieces and machine-driven devices have been marketed to expedite this procedure. Excalibur is one such handpiece. The purpose of this study was to compare the Excalibur hand piece with traditional K-files for their effectiveness in shaping curved root canals. A total of 24 standardized canals in extracted human mandibular molars were randomly divided into two groups. They were instrumented either with Excalibur according to the manufacturer's instructions or manually using the step-down technique. The cross-sectional shapes of the root canal at the apical, midroot, and coronal levels were digitized before and after instrumentation. Image analyzer software was used to compare the images. The results showed that the methods removed similar amount of dentin at all three levels. Although the Excalibur handpiece had a slight tendency to straighten the canal more than hand instrumentation, the difference was not significant. Strip-perforation occurred in three specimens in the Excalibur group, but none in the manual group. There was no separation of instrument throughout the experiment.

Assessing apical deformation and transportation following the use of LightSpeed root-canal instruments

The LightSpeed root canal instrument is similar in design to the Canal Master instrument with the exception of being engine driven and fabricated from nickel-titanium alloy. The purpose of the design of these instruments is to reduce apical transportation of the canal during cleansing and shaping procedures. Twenty extracted human molar teeth with roots of varying degrees of curvature were used in this study. A double exposure radiographic technique was used to assess the presence or absence of apical transportation resulting between the initial instrument and the final instrument, a size 50 LightSpeed. Only one of the 20 teeth examined exhibited apical transportation. Results of this study suggest that little or no apical canal transportation could be expected when curved canals are instrumented using the LightSpeed root canal instruments.

An anti-zipping preparation system (method and instrument) for curved root canals: a preliminary report

A new instrument and method of preparation of curved canals, with which preparation effects such as "zips" and "elbowing" at the apical third can be easily eliminated, is described. The new system was designed to incorporate requirements previously established during clinical and laboratory experiments.

Relationship between file size and stiffness of nickel titanium instruments

The purpose of this study was to evaluate the relationship existing between file size and stiffness for 3 endodontic files made of nickel titanium. Three groups of instruments with different cross-sections were tested: a triangular cross-section, a square cross-section and a modified triangular cross-section. The instruments were tested from size 15 to size 40 or 60 according to ANSI/ADA specification no. 28 for binding moment evaluation. There was a statistically significant difference between the 3 groups: the square cross-section K files presented a larger bending moment than the triangular cross-section K files, which presented a larger bending moment than the modified cross-section K files. Like the stainless steel instruments, there was an exponential relationship between file size and bending moment for triangular and square cross-section K files, but a linear relationship between file size and bending moment for the files with a modified triangular cross-section.

Effectiveness of nickel-titanium files for preparing curved root canals

In this study, the effect of 2 different endodontic files on the final shape of curved root canals of extracted single rooted teeth were examined in the scanning electron microscope. The instruments tested were a newly designed nickel-titanium endodontic file and a conventional K-type file. The files were used with in and out linear movements with a circumferential motion starting with a size 15 file. Final preparation of the apical thirds of the canals was performed with a size 35 file. Shaping effectiveness of the tested instruments was evaluated in terms of respect for conservation of the apical constriction and the presence or absence of ledging. Our observations revealed that more centered and tapered preparations were obtained with the use of the nickel-titanium files than with the conventional K-type files.

A comparison of maintenance of canal curvature using balanced-force instrumentation with three different file types

Forty-five extracted human molar teeth with curved facial or mesial canals were instrumented to a #45 file with three different file types using balanced-force (BF) instrumentation. Pre- and postoperative X-rays were taken, projected, and file location traced to determine the canal curvature according to the method of Schneider. Results showed statistically less reduction in canal curvature with nickel-titanium (NT) files compared with either Flex-R (FR) (p < 0.05) or K-Flex (KF) files (p < 0.0021). There was no significant difference comparing FR with KF files (p > 0.05). Under the conditions of this study, NT files used with the BF technique were significantly less likely to change canal curvature than either FR or KF files when instrumenting curved root canals.

Comparison of three files to prepare curved root canals

Flex-R, Ultra-Flex (Ni-Ti construction), and K-type files were compared using a circumferential filing technique on 96 extracted human maxillary molars. Buccal canals with minimal initial curvature of 24 degrees were used. The maximal initial curvature was 52 degrees. Canal curvature was measured before and after filling, and changes were analyzed statistically. The angle of curvature was better maintained with the Flex-R and Ultra-Flex files.

Efficacy of three techniques in cleaning the apical portion of curved root canals

Various techniques for root canal instrumentation may have different effects in cleaning curved root canals, especially their apical portions. One hundred thirty-five mesiobuccal canals with an average curvature of 25 degrees from human mandibular molars were treated with step-back, crown-down pressureless, or balanced-force techniques with 2% sodium hypochlorite used as an irrigant. The cleaning efficacy of these techniques was evaluated by counting the remaining surface debris under a stereomicroscope with a calibrated eyepiece micrometer. The results indicated that the apical portion of the canal was less clean than the middle and coronal portions regardless of the technique performed and that the balanced-force technique produced a cleaner apical portion of the canal than did the other techniques studied.

A comparison of canal preparation with nickel-titanium and stainless steel instruments

Maintaining the original canal path during instrumentation is a challenge in narrow curved canals. This study compared the maintenance of the original canal path of curved root canals during instrumentation with nickel-titanium (Mac) hand files, nickel-titanium engine-driven files, and stainless steel (K-Flex) files. Canal path maintenance was determined by superimposing instrumentation radiographs over an initial file radiograph and examining for discrepancies. Nickel-titanium hand and engine-driven instruments maintained the original canal path in all cases. The incidence of deviation from the original canal path during instrumentation with stainless steel files increased with file size. The difference between nickel-titanium groups and stainless steel became statistically significant with instruments larger than size 30. In this study, nickel-titanium files were more effective in maintaining the original canal path of curved root canals when the apical preparation was enlarged beyond size 30.

Transportation of curved canals prepared with canal master U, canal master U niti, and stainless steel K-type files

The purpose of this study was to evaluate and to compare root canal configuration after preparation with three different hand instruments and techniques: the canal master U preparation technique (Brasseler, Savannah, GA.), using stainless steel or nickel-titanium canal master U instruments, and the step-back technique using precurved conventional stainless steel K-type files. Sixty-three simulated curved canals were divided in three groups of 21 each. Each group was prepared using one of the three instruments. Comparison of root canal configuration was evaluated with pre- and postoperative photographs that measured the difference in canal diameter and the mesial and distal transportation of the canal walls at the canal length and at levels 1, 2, 3, 4, 5, 6, 7, and 8 mm coronal to the canal length. Data obtained were analyzed statistically using an analysis of variance. Instrument breakage was also recorded. Results showed that the final diameter of the prepared canals as well as canal transportation were significantly different between both canal master U instruments and the stainless steel K file. Three stainless steel canal master U instruments separated during instrumentation whereas none in the nickel-titanium canal master U and stainless steel K-type file groups separated. The results of this study show that the canal master U instruments and technique provide a better canal configuration than K files using the step-back technique and that the nickel-titanium canal master U and stainless steel K-type file offers a greater safety factor against breakage than the stainless steel canal master U.

Root canal instruments for manual use: cutting efficiency and instrumentation of curved canals

The cutting efficiency of different endodontic hand instruments and the effects of instrumentation on curved canal shape were investigated under standardized experimental conditions using an automatic testing device. Cutting efficiency in rotary motion was assessed by determination of the maximum penetration depth of the instruments into a cylindrical canal in a special resin block (size 25 and size 35 instruments). Changes in canal shape were determined by instrumentation of standardized canals (42 degrees curvature) incrementally from size 15 to size 35. Except in the case of one instrument, size 35, in both sizes tested flexible instruments reached significantly (P < 0.05) greater maximum penetration depths than conventional reamers or K-files. Changes in the canal shape differed significantly between the different instruments in 13 of the 14 measuring points. Drastic undesirable changes in the canal shape (e.g. straightening or zip and elbow) occurred after instrumentation with reamers and K-files, but these changes were less noticeable after instrumentation with flexible instruments with conventional tips. After instrumentation with flexible instruments with modified tips there were few undesirable changes in shape. The conclusion could be drawn that flexible instruments, especially those with modified tips, were clearly superior to conventional reamers and K-files with regard to cutting efficiency and instrumentation of curved canals.

Assessing the shape of root canals: an in vitro method using microradiography

The aim of this paper is to describe an in vitro method which provides clear and accurate details of root canal shape. The method utilizes the technique of contact microradiography to produce high resolution, two-dimensional, real-size images of canals in a longitudinal plane. Specimens can be accurately rotated through 90 degrees allowing images to be produced in a bucco-lingual and mesio-distal direction. The method is simple, relatively rapid and can process large numbers of teeth without the need for complicated and expensive mounting blocks or film holders. The technique can be used to produce pre- and post-operative images of canal shape which can be superimposed to delineate the dentine removed during canal preparation. The method is thus suitable for the evaluation of the shaping ability of endodontic instruments and preparation techniques.

A comparison of root canal preparations using Ni-Ti hand, Ni-Ti engine-driven, and K-Flex endodontic instruments

This study used a modified Bramante technique and new digital subtraction software to compare root canals prepared by nickel-titanium (Ni-Ti) hand, Ni-Ti engine-driven, and stainless steel hand endodontic instruments. Sixty mesial canals of extracted human mandibular molars were randomly divided into five groups. The roots were embedded in clear resin and cross-sectioned in the apical and mid-root areas. In group A, canals were instrumented using a quarter turn/pull technique with K-Flex files. In group B, canals were prepared with Ni-Ti hand files (Mity files) using the same technique as in group A. Group C was prepared with NT Sensor engine-driven files. Group D canals were prepared with Ni-Ti Canal Master "U" hand instruments. Group E was prepared with engine-driven Ni-Ti Lightspeed instruments. Digitized images of the uninstrumented canals were compared with images of the instrumented canals. Engine-driven Ni-Ti instruments (Lightspeed and NT Sensor file) and hand instrumentation with the Canal Master "U" caused significantly less canal transportation (p < 0.05), remained more centered in the canal (p < 0.05), removed less dentin (p < 0.05), and produced rounder canal preparations than K-Flex and Mity files. Engine instrumentation with Lightspeed and NT Sensor file was significantly faster than hand instrumentation (p < 0.05).

A comparison of four instrumentation techniques on apical canal transportation

The ability of four instrumentation techniques to enlarge and maintain the central axis of 51 curved canals was evaluated radiographically. Curved canals in extracted human teeth were instrumented using a step-back preparation with K-files, crowndown preparation with K-files, sonic instrumentation with Shaper-Sonic files, and the NiTiMatic preparation system. Following coronal preflaring, each canal was instrumented to a #35 file 1 mm from the anatomic foramen. Radiographs were taken with mercury filling the canal system using a specially designed model that allowed for the pre- and postinstrumentation canal to be viewed on the same radiograph. Canal enlargement and apical transportation resulting from the various instrumentation techniques were evaluated using computer analysis. No statistically significant differences were found for canal transportation. Sonic instrumentation significantly increased coronal flaring. The crown-down and sonic techniques produced more ledges. Elbow formation was associated with all instrumentation techniques. The model system developed for this study provided an accurate method of assessing the preparation techniques and the instrument effects on the canal walls.

Relationship between file size and stiffness of stainless steel instruments

The purpose of this study was to evaluate the relationship existing between file size and stiffness for three endodontic files of different cross-sections. Three groups of instruments were tested: Flexofiles from the Maillefer company, K Files and K-Flex from the Kerr company. Flexofiles have a triangular cross-section, K Files a square cross-section, and K-Flex instruments a rhombus cross-section from size 15 to size 40. For each group, 10 files from size 15 to size 40 were compared according to ANSI/ADA specification N degrees 28 for bending moment evaluation. There was a statistical difference between the three groups: the square cross-section K files presented a larger bending moment than the rhombus cross-section K Flex, which presented a higher bending moment than the triangular cross-section Flexofiles. There was an exponential relationship between file size and bending moment.

Effectiveness of two different methods for preparing curved root canals

In this study, the effect of using two different methods for preparing curved root canals of extracted, single-rooted teeth were analyzed with the scanning electron microscope. The instrumentation systems tested were the Canal Master and a standard circumferential filing technique in which conventional K-files were used. Shaping effectiveness was qualitatively evaluated in terms of respect for conservation of the apical constriction and the presence or absence of ledging, specially in the apical third of the root canals. As a result of our observations, it appeared that the Canal Master instrumentation technique provided well-centered and tapered preparations. Conversely, the use of conventional K-files with a standard circumferential filing technique resulted in frequent alterations of the initial pattern of the root canals, showing transportation of the apical foramen and ledge formation.

Comparison of three instruments in the preparation of the curved root canal using the modified double-flared technique

Fifty-one extracted intact human first molar teeth with mature root apices were radiographed in a standardized way; their root curvature was determined and they were divided into three groups. One root canal in the mesial root of the mandibular molars, or the major mesiobuccal root in maxillary molars, was prepared with the modified double-flared technique, in one of three ways. The modified double-flared technique involves coronal flaring followed by working length determination and apical preparation. In group 1, unmodified tipped instruments (Flexofile) were manipulated with a balanced force technique. In groups 2 and 3, Flexogates files and Canal Master U files were operated in the manner recommended by the manufacturers. After preparation, the teeth were radiographed. The processed images of the root canals were traced using an image analysis computer software package. Comparisons were made between the preoperative and postoperative shapes of each root canal. A low viscosity polyvinyl siloxane was injected into the prepared root canals and the specimens were demineralized, dehydrated, and cleared. The preparation was evaluated subjectively according to desirable or undesirable criteria. The overall quality of preparation was rated. Statistical analysis showed that there was no significant difference in the overall change of area between the three groups (p = 0.994). There was a significant proportional increase in mesiodistal width in the coronal part of the canals in the Canal Master U group and more of the instruments in this group fractured.(ABSTRACT TRUNCATED AT 250 WORDS)

Critical analysis of the balanced force technique in endodontics

The "balanced force" technique was introduced in 1985 and it was reported that the resistance of the dentin, as it circumferentially contacted the flutes of a file in a curved root canal, would be sufficient to override and mask any tendency of the file to straighten during rotational instrumentation. An alternative mechanism based on compressive force and file flexure is presented in this article. In a laboratory study, the apical force necessary to cause files of sizes #10 to #70 to bend and conform to an average canal curvature was determined. These measurements were then related to the apical forces applied to teeth when utilizing the Balanced Force technique in a simulated clinical setting. It was then proposed that the apically directed force necessary to prevent coronal movement of the file and to effect dentinal shearing during counterclockwise rotation placed the file in compression, flexing it to conform to the curvature of the canal. This explanation was consistent with the experimental data for the files used in this study up to size #60 for an average canal curvature and for average instrumentation forces.

Effectiveness of apical clearing: histological and radiographical evaluation

Preparation of the apical one-third in curved canals is difficult both in debridement and maintaining canal shape. A technique of final apical preparation, "apical clearing," attempted to debride and increase the apical size without transportation. Apical clearing is defined as: following cleaning and shaping, sequentially rotating files two to four sizes larger than the initial (master) apical file at working length, then rotating the largest apical file again after a final irrigation and drying. This study evaluated histologically and radiographically the quality of apical preparation with or without apical clearing. Examined were (a) extent of transportation and (b) debris accumulation in the apical third. Fifty-four extracted teeth with vital pulps and curved canals were divided into two groups. After step-back preparation, 29 had apical clearing and 25 did not. Pre- and postpreparation double-exposed radiographs evaluated canal deviation. The apical one-third of the canals was examined histologically and ranked, based on remaining tissue, predentin, dentin shavings, other debris, and canal walls planed. Radiographically, the apically cleared group showed slight deviation of the canal during preparation. Histologically, canals in the apically cleared group had significantly less remaining tissue, predentin and debris, as well as more canal walls planed. This experiment showed that apically the apical clearing technique resulted in better debridement, with minimal increase in apical transportation.

Passive step-back technique

Several techniques have been advocated to clean and shape pathologically involved root canal systems. Studies have shown that most of these techniques transport the original shape of the apical portion of the root canals. This article describes a step-by-step method, Passive Step Back Technique, which uses a combination of hand and rotary instruments to clean and shape root canals.

Passive step-back technique. A sequential use of ultrasonic and hand instruments

Step back, step down, crown down, balanced forces techniques and their variations have been proposed to clean and shape the root canal systems. Ultrasonic instruments have also been used to clean and shape pathologically involved root canals. Because neither of these techniques alone can completely clean complex root canal systems, a step-by-step sequential use of ultrasonic and hand instruments that uses the advantages of both techniques and eliminates most of their disadvantages is described in this article. Proper use of this technique produces cleaner canals and less transportation of root canals, reduces procedural accidents, and is convenient for the operator as well as the patient.

Effects of the Flexogates and Canal Master U on root canal configuration in simulated curved canals

The purpose of this study was to compare the Canal Master U (CMU) instrumentation technique with that of a similar instrument, the Flexogates (FG). Forty simulated curved canals were divided in two groups of 20 each. One group was prepared using the CMU instrumentation technique and the other using the FG technique. Comparison was made by measuring the diameter of the prepared canals and transportation that occurred at the canal length and at levels 1, 3 and 5 mm coronal to the canal length. Data obtained were analysed statistically. Results showed that the final diameter of the prepared canals was not significantly different between the CMU or the FG. However, the FG transported the outer wall of the curvature more than the CMU at the canal length and at 1 mm from the CL. Although the difference in the canal transportation was statistically significant it may not be of clinical importance.

Comparison by means of a computer-supported device of the enlarging characteristics of two different instruments

Numerous studies report different results when testing endodontic instruments with similar and/or different research protocols. However, objective studies that could eliminate the factors inherent to the operator have not yet been developed. Simulated root canals in clear casting resin were used as models. The Canal Master U and Flexogate were tested by using a double exposure photographic technique. A computer-aided device capable of reproducing three-dimensional enlarging movements and irrigation of the simulated canals was developed. The enlarging movements were programmed according to the step-back and step-down techniques. The enlarging of simulated root canals with this device proved to be constant and reproducible. Standard deviations were kept low and were dependent on the degree of canal curvature. The enlarged simulated root canals showed that both instruments could be kept centered in the path of the root canal. Results showed only a few significant differences between the effective material removed and a theoretical ideal amount of removed material.

The influence of different engine-driven, sound ultrasound systems and the Canal Master on root canal preparation: an in vitro study

Different methods and automated devices have been developed to accomplish the enlarging and debriding of root canals. The occurrence of undesired effects on the root canal walls was compared in vitro between a theoretically ideally shaped canal and the Canal Leader, Canal Finder, 3000 Endo Sonic Air, Cavi Endo 25, Enac System, Piezon Master 400 and the Canal Master. Clear casting resin models were used for this purpose. A photographic double exposure was used to superimpose the images of the original canals on the enlarged canals, thus enabling measurement of the material removed. Measurements were made at six different points. Significance was defined at the 5% level (P = 0.05). All instruments and/or devices, with the exception of the Cavi Endo 25, enlarged the convex side of the canals significantly greater at level 1 in comparison to the ideal. On the concave side, significantly smaller differences were found between the ideal and the results of all the enlarging devices, with the exception of the Canal Master. On the convex side at level 2, the Canal Leader, Canal Finder, Cavi Endo, Enac System and Endo Sonic Air showed no statistical differences between ideal and effective material removal. The Piezon Master showed significantly lower material removal in comparison to the ideal. The Canal Master demonstrated statistically higher differences when compared with the ideal.(ABSTRACT TRUNCATED AT 250 WORDS)

Apical third instrumentation of curved canals with K-type and canal master instruments

Forty acrylic blocks with curved canals were divided into two groups of 20 each. One group had canals with 30-degree curvature and the other with 45-degree curvature. Each group was divided into two subgroups of 10 blocks each. One subgroup was instrumented with precurved Kerr files and the other was instrumented with Canal Master hand instruments. The efficiency of the two instruments for preparing the apical third of curved canals was compared. In plastic blocks, Canal Master caused less transportation and was more suitable for instrumenting the canals.

Computerized analysis of the instrumentation of the root canal system

A method is proposed for a three-dimensional visualization of the root canal system before and after the cleaning and shaping procedure to analyze the relationships of the root canal walls. The first part of the study provided cross-sections of the root perpendicular to the root canal. A system for remounting the sections of the root before and after instrumentation was set up. Micrographs of the sections were transferred to a graphics computer which rebuilt and elaborated the sections, providing a three-dimensional model of the root with the image of the root canal system before and after instrumentation. This experimental computerized model enables sections of all kinds to be produced, with great possibilities for measurement and analysis.

Instrumentation of curved root canals: a comparison study

Flex-R, Flex-O, and K-Flex files were compared using a circumferential filing technique on 30 extracted human molars. The buccal canals of maxillary molars and mesial canals of mandibular molars were utilized. The minimal initial curvature was 18 degrees. Canal curvature was measured before and after filing, and changes were analyzed statistically. Analysis showed that, no matter which of the instruments was used, the angle of curvature was maintained with a high degree of accuracy.

Effectiveness of different endodontic files for preparing curved root canals: a scanning electron microscopic study

In this study, the effect of using four endodontic files from different manufacturers on the final shape of 80 prepared curved root canals of extracted single-rooted teeth were comparatively analyzed with scanning electron microscopy. The instruments tested were Tri-files, Flex-R files, Flexofiles and conventional K-type files. All files were used with in and out linear movements with a circumferential motion starting with a size 15 file. Final preparation of the apical thirds was performed with a size 30 file. Shaping effectiveness of the tested files was qualitatively evaluated in terms of respect for conservation of the apical constriction and the presence or absence of ledging, specially in the apical third of the root canals. A well-centered and tapered preparation without apical transportation or ledging was detected when Tri-file or Flex-R files were used. Conversely, the use of Flexofile or conventional K-type files resulted in frequent alteration of the initial pattern of the root canals, showing an hour-glass preparation with alteration of the apical constriction and ledge formations.

A comparison of apical seal: chloroform versus halothane-dipped gutta-percha cones

A dye penetration study was done to compare apical leakage among three groups of extracted teeth obturated with a lateral condensation technique. In one group the master gutta-percha cones were customized in the apical portion of the canals after being dipped in chloroform. A second group used halothane as the customizing agent. No dip was used in the third group, and all three were then laterally condensed. The teeth were cleared and dye penetration was measured. Statistical analysis using a Kruskal-Wallis one-way analysis of variance of the data showed no significant difference among the groups at the p < 0.05 level.

Comparison of six files to prepare simulated root canals. 2

A total of 300 simulated root canals of various angles and positions of curvature in clear resin blocks were prepared by hand using either K-files, K-Flex files, Flexofiles, Flex-R files, Hedstrom files or Unifiles. Each file type was used to prepare 50 canals employing a linear filing motion and an anticurvature stepback technique. Part 2 of this two-part report describes the efficacy of the files in terms of the prevalence of canal aberrations, the amount and direction of canal transportation and the overall postoperative canal shape. Hourglass shaped canals were found in 4.5% of curved canals, the majority of these being created by K-files and K-Flex files. Perforations were seen in 6.3% of curved canals, the majority being produced by Flex-R files and K-files. Excessive removal of material from along the inner aspect of the canal curve occurred in 10.4% of canals, by far the majority being created by Hedstrom files. Transportation of canals was a consistent finding with all instruments. Two-way analysis of variance revealed how significant differences in the absolute magnitude of transportation occurred between instruments, between canal types and by an interaction between instrument and canal type. In general, transportation was towards the outer aspect of the canal curve at the end-point of preparation and the zip and elbow, but towards the inner aspect at the beginning of the curve. Further towards the orifice, transportation reverted to the outer aspect of the canal curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of six files to prepare simulated root canals. 1

A total of 300 simulated root canals of various angles and positions of curvature in clear resin blocks were prepared by hand using either K-files, K-Flex files, Flexofiles, Flex-R files, Hedstrom files or Unifiles. Each file type was used to prepare 50 canals employing a linear filing motion and an anticurvature stepback technique. Part 1 of this two-part report describes the efficacy of the files in terms of preparation time, instrument failure, loss of canal length and weight loss from the blocks. Two-way analysis of variance confirmed that there was significant variation for each parameter between instruments, between canal types, and with interaction between instruments and canal types. Overall, preparation with Hedstrom files was significantly quicker than with any other file, whilst preparation with K-files and K-Flex files took significantly longer. Fracture and deformation of instruments occurred substantially less often with Flex-R and Hedstrom files, but significantly more often with Unifiles. Loss of working distance occurred with all file types, but was significantly greater in canals prepared with K-files. Unifiles and Hedstrom files were responsible for significantly more weight loss than the other files, whilst K-files produced significantly less weight loss. Canals with rough undulating walls were created most often by Hedstrom files and Unifiles. Overall, under the conditions of this study, Flexofiles, Flex-R files and Hedstrom files appeared to be substantially more effective than K-files, K-Flex files and Unifiles.

Comparison of conventional root canal obturation techniques with Thermafil obturators

This study compared microleakage of Thermafil Obturators to the single cone technique in Lexan blocks simulating root canals (n = 20) stained with Prussian blue dye. The microleakage of Thermafil and laterally condensed extracted human teeth was also investigated after the teeth were stained with India ink or Prussian blue dye over 1- or 2-wk dye immersion periods. In Lexan blocks there was no statistical difference in mean leakage between the single cone technique and Thermafil. Teeth with Thermafil Obturators exhibited greater leakage than those with the lateral condensation. Greater leakage was also seen where India ink was used. Dye immersion time did not have a significant influence on leakage scores. The combination of India ink with Thermafil demonstrated the greatest average leakage. This study demonstrated that Lexan canal simulating blocks do not mimic extracted human teeth for evaluating microleakage.

Effect of noncutting tipped instruments on the quality of root canal preparation using a modified double-flared technique

Fifty-one extracted human first molar teeth with intact crowns and mature root apices were divided into three groups. Root curvature was determined. One of the root canals in the mesial root of lower molars, or the mesiobuccal root in maxillary molars, was prepared in one of three ways. In group 1 the root canals were instrumented using a modified double-flared technique with noncutting tipped files (Flex R); in group 2 the same files were used with a step-back technique. Group 3 was prepared with conventionally tipped files (K-Flex) using the step-back technique. A low viscosity polyvinyl siloxane impression material was injected into the prepared root canals and the specimens were decalcified, dehydrated, and cleared. The preparation was evaluated subjectively according to various desirable or undesirable criteria. A rating for overall quality of preparation was given. Statistical analysis showed that the teeth in group 1 had better overall preparation than those in group 3 (p < 0.05). There were no other statistically significant differences between the groups. The mean time required for each preparation technique was not statistically significantly different (p > 0.1). The use of a modified double-flared technique with non-cutting tipped files was shown to be an effective method for the preparation of curved root canals.

Effect of preflaring on canal transportation. Evaluation of ultrasonic, sonic, and conventional techniques

This study evaluated the effect on canal transportation when acrylic canals were preflared with Peeso reamers before the use of ultrasonic, sonic, and hand instrumentation techniques. Twenty resin blocks with simulated curved root canals were shaped with each technique to a size 40 file 0.5 mm from the apical foramen. Ten of the canals were preflared in the cervical region with No. 1 and No. 2 Peeso reamers before instrumentation; 10 canals that were not preflared served as controls. Transportation was measured on the inside canal curvature 3 mm from the canal orifice and 8 mm cervical to the working length, and on the outside canal curvature 1 mm cervical to the working length. Statistical analysis with Student's t test did not show a significant reduction in canal transportation for the preflared groups. In some areas the amount of transportation was less for the preflared groups; in other areas it was greater.

Tooth length determination: a review

Tooth length determination is a crucial step in endodontic treatment. Until the late 1970s, tooth length determination was based mainly on radiographic interpretation. The advent of apex locators, which identify the difference in the electrical resistance between the root canal and the periodontal membrane, ushered in a new era for measuring tooth length. However, the accuracy of these devices has been questioned. Pertinent literature is discussed with the aim of providing information on the development of the concept, techniques, and devices for tooth length determination.

Comparison of undergraduate endodontic teaching programmes in the United Kingdom and in some dental schools in Europe and the United States

The pattern of teaching root canal therapy within dental schools of the UK was determined and compared with that carried out within several dental schools in Europe and the USA. Although it appeared that 'teachers of endodontics' in the UK were advocating techniques adopted elsewhere, it was clear that, within the dental undergraduate curriculum as a whole, the teaching of root canal therapy was given a lower priority than that in some schools in Europe and the USA. Recommendations to remedy this unsatisfactory position are provided.

A method for the construction of simulated root canals in clear resin blocks

A method for the construction of simulated root canals in clear resin blocks is described. The canals are inexpensive, simple to produce and are of high enough quality for use in both undergraduate and continuing education. With minor modifications, the canals can also be used for research, particularly during the assessment of instruments and preparation techniques.

The effects of Canal Master, Flex-R, and K-Flex instrumentation on root canal configuration

The purpose of this study was to compare the Canal Master instrument and instrumentation technique (CM/CMI) to Flex-R files used with a "balanced force" technique (FR/BF) and K-Flex files used with a step-back filing technique (KF/SB). Thirty-six root canals in extracted human mandibular molars were equally divided into three groups. The roots were sectioned, then photographed and evaluated before and after instrumentation. Evaluation included canal shape, direction and extent of transportation, amount of dentin removed, and centering ability. Canal Master instrumentation and Flex-R/balanced force techniques both produced more round preparations than the K-Flex/step-back. All three techniques resulted in canal transportation, although to varying degrees. Flex-R/balanced forces and Canal Master instrumentation transported very little up to a #30, and Canal Master instrumentation transported significantly less after the #45 instrument at mid-root. K-Flex/step-back removed the most dentin while Flex-R/balanced force removed the least in the apical sections and Canal Master instrumentation removed the least at mid-root. The ability of Canal Master instrumentation to keep instruments centered in the canals was significantly better than for K-Flex/step-back.

The influence of different root canal instruments on root canal preparation: an in vitro study

Nine endodontic instruments from different manufacturers (Reamers, K-files, Hedstrom files, K-Flex files, Flexofiles, S-files, Burns Unifiles, Flexicut files and Flex-R files) were used to prepare 180 simulated root canals in resin blocks. The instrument's ability to reproduce a theoretical pre-established ideal canal shape was assessed by comparing the original canal path with the resulting enlarged canal shape by a double exposure photographic method. The individual ability of each instrument to transport debris was also observed during instrumentation under a stereomicroscope. Regardless of the instrument type, none was able to reproduce ideal results; however, clinically acceptable results could be obtained with all of them. The coronal and apical debris transportation characteristics proved to be similar with all instruments.

Clinical factors associated with ledged canals in maxillary and mandibular molars

No clinical studies have been done to explore the relationship of ledging to the clinical practice of endodontics. The purpose of this study was to examine 171 cases completed by third-year dental students and to identify variables that were associated with ledging. A total of 336 canals were examined and tooth number, canal location, working length, the master apical file size, and root canal curvature were recorded. Of 336 canals, 46% were found to have been ledged. Analysis of variance revealed that No. 15 had a significantly higher incidence of ledging. Working lengths and master apical file sizes were not found to be significant variables. The main factor consistently related to the presence of ledges was canal curvature. The number of ledged canals increased significantly after 20 degrees and surpassed the number not ledged after 30 degrees. Multiple regression with the use of the five categories as the dependent variables and ledging as the independent variable resulted in an r = 0.397 and F = 12.216, p less than 0.0001. Curvature was found to have the highest significant t value (7.412) followed by "teeth" (2.471), whereas no other categories were identified as being significant. All the determinants for ledging were not identified with this study, and further research is indicated.

Comparison of mechanical and standard hand instrumentation techniques in curved root canals

The original and postinstrumentation shapes of the mesial root canal system of 12 mandibular molars were compared after being instrumented with a mechanical handpiece and a hand instrumentation technique. Area of dentin removed and amount and direction of transportation were evaluated in relation to degree of root canal curvature. Pre- and postinstrumentation measurements were taken of the root canal system in the cervical, middle, and apical thirds. The mechanical handpiece removed dentin and transported the root canal more than the hand instrumentation in the cervical and apical thirds. Both techniques transported to the distal in the cervical third and to the mesial in the apical third. In the middle third, the mechanical handpiece transported more to the mesial and the hand instrumentation more to the distal. Degree of root canal curvature had no influence on the amount of dentin removed or transportation of the root canal.

Remaining dentin/cementum thickness after hand or ultrasonic instrumentation

A quantitative study was undertaken to measure remaining dentin/cementum thickness after using step-down, step-back hand instrumentation or ultrasonically energized instrumentation techniques. A model system was used which enabled the same canal system of extracted human mandibular molars to be accurately evaluated and measured before and after instrumentation. Although no statistical difference was demonstrated in the encroachment upon the furcal aspect of mesial roots of mandibular molars, both techniques came dangerously close to creating stripping and perforations in a high percentage of cases.

Dentine-removing characteristics of an ultrasonically energized K-file

This in vitro study evaluated the pattern of dentine removal when an ultrasonically energized file (Cavi-Endo-size 25 file) was applied to flat surfaces of dentine under standardized conditions. The influences of power setting, interfacial force between file and dentine, direction of file oscillation and operator-assisted movement were examined. Impressions of the instrumented surfaces revealed characteristic patterns consisting of a series of oblique crests, each one parallel to the next and separated by a constant distance along the line of contact with the file. Determination of height, width and separation of these crests with a Reflex microscope aided objective assessment. The simplest pattern was formed when the energized file was held against the dentine (power setting = 1; interfacial force = 30 g). Increasing the power setting to 8 caused deeper troughs over the apical 5 mm. The width of the crests corresponded to the taper of the file except at the apical tip where the crests were relatively wider. However, increasing the interfacial force to 60 g reduced the efficiency of the apical part of the file. The superimposition of operator-induced movement greatly increased the extent of dentine removal, resulting in a tapering groove with a persistent crestal pattern. Oscillation of the file perpendicular to the dentine surface had a significantly greater influence on dentine removal, producing a deeper groove than was obtained with oscillation parallel to the surface. These findings may be of relevance in aiding controlled root canal preparation when using the Cavi-Endo instrument.

The validity of using simulated root canals as models for ultrasonic instrumentation

The validity of using simulated root canals in resin blocks for evaluating the effects of ultrasonic root canal instrumentation was examined. Curved canals in resin blocks and in natural teeth were ultrasonically instrumented using the Cavi-Endo unit at power setting 1. Canal shapes were compared qualitatively and quantitatively from photographs and subtraction macroradiographs of simulated canals and teeth, respectively. The following measurements were taken: apical and coronal areas, changes in width at the elbow and at 0.5 mm apical to the elbow, and apical transport width. Qualitatively, there did not appear to be any differences in the manner of removal of material along the length of the canal in both test models. Quantitatively, there was a similarity in the following: areas of canal walls removed, the incidence of elbows, the change in width at the region of the elbow, and the apical transport width. The lack of differences showed that the ultrasonic file cut in a similar fashion in both test models and indicated that simulated canals are valid models for evaluating the effects of ultrasonic instrumentation.