Root canal instruments for manual use: a review

Root canal instruments can be subdivided into instruments made of different alloys (stainless steel, nickel-titanium and nickel-aluminium) and instruments with different geometric forms (e.g., instruments with short cutting segments). Several types of stainless steel and titanium-based instruments are presented and assessed by a review of the current literature. In summary, flexible stainless steel instruments with noncutting tips seem to be a decisive improvement in the development of an ideal root canal instrument. They are superior to titanium-based instruments in both cutting efficiency and instrumentation of curved root canals.     

A comparison of canal preparation using the K-file and Lightspeed in resin blocks

Twenty-four resin blocks with simulated curved canals of approximately 38 degrees were divided into two groups of 12 each. One group was instrumented with stainless steel K-files and the other group with nickel-titanium Lightspeed Rotary instruments. The efficiency of canal preparation was evaluated at 1, 3, 5, and 7 mm from the apex using magnified images (x4) of the radiographed blocks. The results showed that K-files caused more widening at the apical end, with a higher incidence of transportation, zipping, and elbow formation. The Lightspeed instrument stayed centered in the canals maintaining the central axis, with minimal incidence of transportation, elbow formation, and zipping. Thus, the Lightspeed instrument may be considered more suitable for efficient preparation of curved canals than the K-type file.     

In utero partial liver resection in the rabbit model: a study on fetal tissue regeneration

This study compared step-back preparations in curved canals of resin blocks using nickel-titanium K-files and stainless steel K-files. Forty canals in resin blocks were cross-sectioned at 3 levels: 1 to 2 mm from the apical foramen, middle of the curve, and coronal. Direct digital computer images were recorded before and after instrumentation. Superimposition of the images combined with digital subtraction computer software allowed direct measurement of area instrumented, distance of transportation, and shape analysis. Time for instrumentation was recorded. Results showed Ni-Ti files to cause significantly less transportation and remain more centered at the apical level (p < 0.05). Area removed by instrumentation was significantly greater for stainless steel files at the middle level (p < 0.05). Cross-sectional shape of the instrumented canal was not significantly different (p < 0.05). It took significantly longer to prepare a canal with Ni-Ti K-files in resin blocks compared to stainless steel (p < 0.05). Resin simulated canals showed similar results compared to canals in extracted roots using an identical methodology.     

Leydig cell tumor--comparison of results of radical and testis-sparing surgery in a single center

Twenty-two mesial roots of extracted human mandibular molars were divided into two groups based on root curvature and length. The mesiolingual canals were instrumented using either Flexofiles in a step-back anticurvature filing method, or they were instrumented with engine-driven 0.02 taper nickel-titanium files. Ground sections were prepared at 1-, 2.5-, and 5-mm levels from the working length. The mesiobuccal canal was used as an uninstrumented control for predentin character. Digitizing software was used to calculate the instrumented portion as a percentage of the total canal perimeter. The results indicated no significant difference in overall canal wall planning between the two groups and no significant difference at each of the three levels.     

The challenge of preparing the curved root canal

Heavily restored teeth which become pulpally involved are now often root canal treated rather than extracted. While this is laudable it has a significant impact on the practice of endodontics today. The curved calcified canal can prove very difficult to prepare to its natural shape by conventional techniques and there is always the likelihood of iatrogenic damage. To compensate for this many clinicians tend to under-prepare these canals, perhaps leaving them inadequately cleaned and certainly remarkably difficult to fill to length. The purpose of this article is to outline the stages of and the rationale behind a hand instrumentation preparation method which uses the balanced force method of movement of files from canal entrance to apical constriction. In the authors' experience this technique has gone a long way towards solving the problem of cleaning and shaping the fine curved canal. With some practice, but no extra expense, the technique described will not only speed up canal preparation but will also make it more predictable.     

Bacterial reduction with nickel-titanium rotary instrumentation

The purpose of this study was to compare intracanal bacterial reduction on teeth instrumented with 0.04 tapered nickel-titanium (NiTi) rotary instrumentation to bacterial reduction when using a stainless-steel K-file step-back technique using sterile saline irrigation. Forty-eight patients with apical periodontitis were randomly assigned treatment type. The canals were sampled before, during, and after instrumentation. The samples were incubated anaerobically for 7 days at 37 degrees C, colony-forming unit numbers calculated, and a log transformation performed to normalize the counts. Teeth exhibiting apical periodontitis were uniformly infected, whereas vital control teeth were not. A similar and uniform reduction occurred with progressive filing, regardless of technique (p < 0.0001). There was no detectable difference in colony-forming unit count after NiTi rotary or stainless-steel hand instrumentation (p = 0.42). Neither technique could predictably render canals free of bacteria. The results of this study indicate NiTi rotary and stainless-steel hand K-file step-back instrumentation techniques were not significantly different in their ability to reduce intracanal bacteria.     

Human saliva penetration of coronally unsealed obturated root canals

Studies have shown significant coronal dye and bacterial leakage following exposure of sealed root canals to artificial and natural saliva. The purpose of this study was to determine the time needed for bacteria in natural saliva to contaminate the entire length of root canals obturated by lateral and vertical condensation techniques. Forty root canals were cleaned and shaped using a step-back technique. Thirty root canals were obturated with gutta-percha and root canal sealer using either lateral or vertical condensation techniques. Forty root canals were obturated without a root canal sealer and served as positive controls. After obturation, the coronal 3 mm of five root canals were sealed with sticky wax and served as negative controls. The coronal portions of the filling materials were placed in contact with human saliva and the number of days required for bacteria in saliva to penetrate the entire root canals were determined. No bacterial leakage occurred in the negative control group. Complete bacterial leakage occurred within 2 days in the positive control group. All root canals were recontaminated in less than 30 days. No statistical significant difference was found between the two methods of obturation.     

Lichen myxoedematosus associated with human immunodeficiency virus infection--report of two cases and review of the literature

The transportation produced in the apical and middle areas of 30 mesiobuccal root canals of human mandibular molars was evaluated after circumferential instrumentation using stainless steel K-files (group A), nickel-titanium K-files (group B), and clockwise/counterclockwise file rotation using Flexogates (group C). The canals were instrumented with files #15 to #35 in size. Apical transportation was assessed radiographically while that occurring in the middle area was studied microscopically in cross-sections. Although apical transportation was greatest in the canals of group A, this difference was not statistically significant (P > 0.05). With respect to the middle area of the root canal, considerable transportation was observed in 7 of the 30 instrumented roots. Of these, five belonged to group A and two to group B, a difference which was not statistically significant (P > 0.05). The best results for transportation in the middle area of the canal were obtained in group C, in which no transportation occurred. This difference was significant when compared with the transportation observed in group A (P = 0.02) but not with that in group B (P > 0.05).     

Scanning electron microscopic evaluation of two compaction techniques using a composite resin as a root canal filling material

The canals of 20 human dental roots were instrumented using a a step- back technique. The smear layer was removed, and the canals were obturated with composite resin. Two different techniques of compaction were used: either vertical or lateral motions were used to condense composite resin inside the root canal that was then photopolymerized layer by layer using the argon laser (488 nm). The beam was delivered into the root canal by means of an optical fiber 320 micrometers in diameter. Longitudinal and cross-sections of the samples and resin replicas of the root canals were examined using a light and scanning electron microscope. Scanning electron microscopic examination revealed that laterally compacted resin fillings showed fewer voids than those obtained by vertical compaction. In both experimental groups, adhesion of the resin to the dentin walls, pulled-out resin tags, microfailure, and resin fracture, leaving a layer of resin associated with the wall surface were observed.     

An in vitro comparison of thermoplasticised gutta-percha obturation techniques with cold lateral condensation

This study compared the apical sealing ability, obturation time and extrusion of gutta-percha and sealer when root canals were obturated using either cold lateral condensation or one of the three methods using thermoplasticised gutta-percha (Alpha Seal, Thermafil or JS Quick Fill) in vitro. One hundred and thirty-one root canals from 78 extracted human teeth were used; 116 canals were divided into five groups so that they were balanced with respect to prepared canal anatomy, and the remaining 15 canals were used as positive and negative controls. The canals in the first four groups were prepared with hand files using the step-down technique to a standard apical size and flare. The last group was prepared using engine-driven rotary nickel-titanium files (McSpadden) to a similar apical size and flare. One of the four obturating techniques was used to fill the canals in each of the first four groups. The fifth group was obturated using the Alpha Seal technique. The roots were immersed in india ink, demineralised and rendered transparent to assess the extent of maximum lincar dye penetration. The Alpha Seal groups had the highest number of specimens without any leakage. There was a significant difference in the proportions of specimens that did not leak when the Alpha Seal (P < 0.01) and cold lateral condensation groups (P < 0.05) were compared with JS Quick Fill. Cold lateral condensation had a higher proportion of specimens with leakage in canals with curvature greater than 20 degrees than in canals with curvatures less than 20 degrees (P < 0.05). The curvature of canals had no effect on the sealing ability of the other techniques. The method of canal preparation had no effect on the sealing ability of Alpha Seal. Alpha Seal, Thermafil and JS Quick Fill were significantly quicker to perform than cold lateral condensation.     

A new ultrasonic canal preparation system with electronic monitoring of file tip position

A new ultrasonic root canal preparation system has been developed that electronically monitors the location of the file tip during all instrumentation procedures. The Root ZX has been adapted for this purpose, and its filter circuit effectively cuts out the large spike noise of the ultrasonic unit. During enlargement of the canal, the ultrasonic vibration of the file can be stopped at any desired position on the meter. Extracted human tooth models with electronically measurable canals were used to test the device. Pre- and postoperative shapes of the root canals were evaluated using contact microradiography. The autostop mechanism worked correctly. Using a weak power and fine files, straightening, ledge formation, and file breakage were minimal. It seems that this system minimized the danger of overinstrumentation and could be safely applied in clinical practice.     

Comparative study of two filling techniques using glass-ionomer (Ketac-endo) root canal cement on fracture resistance of endodontically treated roots (in vitro)

Forty freshly single rooted teeth were selected for this study. The coronal part of teeth were decapitated and the root canals were prepared by modified step-back technique with K-flex files to size 35# at the apex, five ml of 5.25% NaOCl was used as irrigating solution. According to the dentin thickness at the mesio-distal direction of the prepared roots, roots were divided into two groups: Group (I), dentin and cementum thickness from 1.5-2 mm, and Group (II), dentin and cementum thickness 1 mm. According to the filling technique used the teeth were subdivided into four subgroups each of five teeth; Subgroup (A) single gutta-percha cone and Ketac-endo root canal sealer, Subgroup (B) lateral condensation technique with gutta-percha and Ketac-endo sealer, Subgroup (C) laterally condensed gutta-percha with Roth 801 cement and Subgroup (D) teeth left unfilled as negative controls. The prepared roots were placed into acrylic resin so that 10 mm of the root was exposed. A slowly increasing force was applied vertically using a blunt punch with 1 mm tip thickness attached to Instron testing machine. The results showed that group (I) with 1.5-2mm dentin thickness required greater force to fracture in all experimental groups, than that of group (II) with 1 mm dentin thickness. So the amount of remaining dentin thickness significantly affected the resistance to fracture of the prepared roots.     

Intrusive thoughts and avoidance behaviors are associated with sleep disturbances in bereavement-related depression

Three methods for temporarily filling root canals with calcium hydroxide pastes were compared. Each of 20 root canals of extracted, human, single-rooted teeth was shaped with hand instruments under standardized conditions up to ISO size 50 and filled using a syringe system, a lentulo spiral or an endodontic reamer. Quality of fillings was assessed radiographically and by inspecting ground preparations. Ridit (relative to an identified distribution) analysis was employed to confirm differences in frequencies of certain quality criteria obtained with various application methods. With regard to degree of obturation and occurrence of porosities, application of temporary fillings with a lentulo spiral or syringe system revealed significantly better results than application with hand instruments (reamer). No differences with regard to degree of obturation were detected when comparing results obtained with syringe or lentulo. Fewer porosities in the apical part of the root canal were seen, both on radiographs and ground sections, with the syringe system compared with the lentulo spiral. In the presence of some contradictory reports found in the literature, the present study suggests that, after straight or slightly curved root canals have been shaped up to at least ISO size 50, high quality temporary root canal fillings may be obtained by application of an aqueous suspension of calcium hydroxide with a syringe system.     

Antibacterial activity of calcium hydroxide-containing endodontic sealers on Enterococcus faecalis in vitro

Nickel-titanium instruments purportedly resist deformation and loss of sharpness better than do stainless steel instruments but may be more susceptible to breakage. The processes of wear and breakage of nickel-titanium and stainless steel instruments were examined. Sixty files of five types (12 each) and three manufacturers were used. All were used repeatedly in curved canals until failure or for a maximum of 22 minutes. Each instrument was examined with scanning electron microscopy both new (control) and at spaced intervals for evidence of wear and fatigue. All new instruments were of good quality. Stainless steel instrument tended to wear the most rapidly, and next were nickel-titanium rotary instruments; the most resistant to wear were nickel-titanium hand instruments. There were few instrument separations. In general, nickel-titanium (particularly hand) instruments resisted deterioration better than did stainless steel. Nickel-titanium rotary instruments (2 of 12) had the most breakage.     

Root canals in two-rooted maxillary second molars

The aim of this study was to register the root canal number, root canal position, and root canal cross-section in human two-rooted, permanent maxillary second molars. One hundred and fifty-nine such teeth extracted in Denmark were cross-sectioned at the mid-root level and apically in accordance with precise guidelines. The observations were made in a stereomicroscope, corresponding to the above-mentioned section levels. At mid-root there were two canals present in 11% of the teeth examined; the canals were located mesially and distofacially, mesiofacially and distally, or facially and lingually. Three canals positioned mesiofacially, distofacially, and lingually were observed in 89% of the teeth. At the same level 62% of the canal cross-sections were noncircular, some being, for instance, C-shaped, whereas 38% of the cross-sections were circular. Apically, two canals were found, representing 19% of the teeth, with the canal position as at mid-root; 81% of the teeth were three-canaled with the same canal position as at mid-root. At the apical level 60% of the canal cross-sections were noncircular, whereas 40% of the cross-sections were circular.     

Field Evaluation of Level Spreaders in the Piedmont of North Carolina

Level spreaders are commonly used in combination with riparian buffers as a stormwater best management practice in many parts of the United States. These systems have not been extensively studied in urbanized environments to determine if they can provide a long-term water quality benefit. In winter 2005, 24 level spreaders were evaluated in the Piedmont of North Carolina. Detailed observations were made at 20 of these locations. The results of the study indicate that level spreaders may not be the versatile structure they are perceived to be. No level spreader-riparian buffer system was able to provide diffuse flow through the riparian buffer from the level spreader to the stream. Common causes for failure to maintain diffuse flow included: lack of maintenance (12 cases), poor design (11), riparian topography/content (11), level spreader lip not level (seven), built with easily eroded materials (six), poor construction methods (three), and human interference (two). This field evaluation indicates that level spreader systems may need design revisions, construction guidance, and maintenance requirements before they continue to be used en masse.     

Obturation of root canals in vivo with a new vacuum technique

It was demonstrated in vitro that it is possible to achieve obturation of the root canal system with a system utilizing a reduced pressure of 15 hPa (15 mbar). The purpose of this study was to develop a procedure to reach a vacuum of at least 15 hPa within root canals in vivo. It was also determined if root canals could be obturated in daily practice with this vacuum technique. After hand instrumentation of the root canals a tooth was prepared for obturation of the canals with the new technique by obtaining a tightly fitting attachment to a vacuum pump. The result showed that it was possible in vivo to reach reduced absolute pressures of 10 hPa in roots and to fill the root canal system with the new system.     

A comparative study on the effect of three methods of instrumentation on the shape of root canal (an in-vitro study)

This study compared the ability of three types of engine driven instrumentation techniques to negotiate and prepare small, slightly curved root canals. Forty five mesial roots of extracted maxillary and mandibular first permanent molars were classified into three groups. Group (I) was prepared by Canal Leader system, group (II) was prepared by Nickel Titanium files and group (III) was prepared by Canal Master technique. Radiographs of the root canal space before and after preparation was carried out by the aid of an experimental model. Enlarged photographic prints obtained from radiographs were scored for shaping effectiveness of the three techniques in respect to canal course, position & width of apical constriction and lack of ledge formation. The results indicated that the Canal Leader system was an efficient technique in maintaining canal curvature, absence of zipping, transportation or ledge formation in almost all of the specimen tested, followed by the Nickel Titanium files and then the Canal Master technique which produced more straightening and destruction of apical constriction.     

Comparison of two endodontic handpieces during the preparation of simulated root canals

The objective of this in vitro study was to compare and assess two endodontic handpieces during the preparation of simulated root canals. One hundred and sixty simulated root canals in clear resin blocks, of two angles and positions of curvature, were prepared using either Shaper files activated by the MM1500 Sonic Air handpiece (Micro-Mega, Besan?on, France) or Excalibur files activated by the W & H Excalibur 969 handpiece (W & H, Bürmoos, Austria). Files of 21-mm or 25-mm length were used. When preparing the canals, the files were used either in line with or perpendicular to the canal curvature. Preparation of the canals was carried out using a technique described in the manufacturers' literature. A variety of parameters were used to compare the handpieces, including an assessment of the canal preparation time, the deformation or fracture of instruments, loss of canal length, weight loss from the resin blocks and the overall postpreparation canal shape. Both handpieces provided an efficient and easy method of preparing and shaping the root canal with little operator fatigue. The MM1500 Sonic Air handpiece took significantly more time (P < 0.001) to prepare the canals and was associated with both more loss of working length (P < 0.05) and more loss of weight (P < 0.001). Both handpieces created a high percentage of aberrations in the shapes of prepared canals. The MM1500 Sonic Air handpiece created significantly more aberrations than the Excalibur handpiece (P < 0.05 for zip and elbow, P < 0.05 for danger zone and coronal narrow). The effects of the variables, canal curvature, file length and the plane of use of the file, on the performance of the handpieces, were also assessed.     

Holmium: YAG laser resection of prostate (HoLRP) for patients in urinary retention

The differing morphological manifestations of the root canal system have been the subject of research, and the incidence of various shapes of root canal systems has been classified. The present case describes the root canal treatment of a rare morphological pattern, namely a mandibular permanent canine with three root canals. No report of a similar case has been published previously.