Hand and nickel-titanium root canal instrumentation performed by dental students: a micro-computed tomographic study.

The aim of this study was to evaluate root canals instrumented by dental students using the modified double-flared technique, nickel-titanium (NiTi) rotary System GT files and NiTi rotary ProTaper files by micro-computed tomography (MCT). A total of 36 root canals from 18 mesial roots of mandibular molar teeth were prepared; 12 canals were prepared with the modified double-flared technique, using K-flexofiles and Gates-Glidden burs; 12 canals were prepared using System GT and 12 using ProTaper rotary files. Each root was scanned using MCT preoperatively and postoperatively. At the coronal and mid-root sections, System GT and ProTaper files produced significantly less enlarged canal cross-sectional area, volume and perimeter than the modified double-flared technique (P < 0.05). In the mid-root sections there was significantly less thinning of the root structure towards the furcation with System GT and ProTaper (P < 0.05). The rotary techniques were both three times faster than the modified double-flared technique (P < 0.05). Qualitative evaluation of the preparations showed that both ProTaper and System GT were able to prepare root canals with little or no procedural error compared with the modified double-flared technique. Under the conditions of this study, inexperienced dental students were able to prepare curved root canals with rotary files with greater preservation of tooth structure, low risk of procedural errors and much quicker than with hand instruments.

A reconstructed computerized tomographic comparison of Ni-Ti rotary GT files versus traditional instruments in canals shaped by novice operators.

AIM: The aim of this study was to compare the effects of preparation with conventional stainless steel Flexofiles and Gates Glidden burs versus nickel-titanium GT rotary files in the shaping of mesial root canals of extracted mandibular molars. METHODOLOGY: A total of 54 canals from 27 mesial roots of mandibular molar teeth were prepared using one of two methods by novice dental students. One canal in each root was prepared by a crown-down approach. utilizing stainless steel Flexofiles and Gates Glidden burs. The other canal was prepared using nickel-titanium GT rotary files in a crown-down fashion as recommended by the manufacturer. Preoperative CT scans of each root were recorded and 50 canal specimens were available for postoperative comparisons. Following canal shaping, postoperative scans were superimposed on the original images. Changes in canal area, canal transportation and thickness of remaining root structure at strategic levels of the root were analyzed. The time taken for each method was also noted. RESULTS: At the coronal and mid-root coronal one-third sections, the rotary GT files produced a significantly smaller postoperative canal area (P < 0.05). In the mid-root sections there was significantly less transportation of the root canal toward the furcation, and less thinning of the root structure with GT files compared to the stainless steel files (P < 0.05). Overall, there was greater conservation of structure coronally and more adequate shape in the mid-root level. The GT rotary technique was significantly faster than the stainless steel hand-held file technique (P < 0.0001). Two GT instruments fractured during the study. CONCLUSIONS: Under the conditions of this study, novice dental students were able to prepare curved root canals with Ni-Ti GT rotary files with less transportation and greater conservation of tooth structure, compared to canals prepared with hand instruments. The rotary technique was significantly faster.

The standardized-taper root canal preparation--Part 3. GT file technique in large root canals with small apical diameters.

AIM: To describe the preparation of Large Root canals with small apical diameters by the GT file technique. SUMMARY: Large Root canals with small apical diameters can usually be prepared with one to three GT files; one to nine clinical steps, and one to five minutes of clinical time. Following proper access, pulp tissue should be removed, and lubricant applied to prevent pulp compaction and blockage. Initial crown-down enlargement is accomplished with up to three standard GT rotary files 0.10, 0.08 and 0.06 taper, running at 300 r.p.m., and with light touch. Care should be taken not to overload instruments, and they should be withdrawn, cleaned and inspected whenever they bind. Sometimes, the shaping objective is achieved with a single instrument; often waves of instrumentation are required before the shaping objective file cuts to length. Prior to cone-fit, the apical resistance form is confirmed with conventional files, employed as feeler gauges of the tapering form created at the canal terminus. Regardless of the shaping time, canals should be soaked with sodium hypochlorite solution for at least 30 min for effective cleaning. KEY LEARNING POINTS: Large Root canals with small apical diameters should be prepared to shaping objectives 0.08 or 0.10 taper. Compacted pulp tissue causes many canal blockages. It should be removed early, and canals should be well lubricated. Large Root canals with small apical diameters should be prepared in crown-down sequence, with recapitulation of steps until the shaping objective is achieved. Apical resistance form should always be confirmed before cone-fit. Canals should be exposed to sodium hypochlorite for at least 30 min for effective cleaning.

The standardized-taper root canal preparation--Part 4. GT file technique in large root canals with large apical diameters.

AIM: To describe the GT file shaping steps required to create apical resistance in the presence of a wide root apex. SUMMARY: Canals are occasionally encountered with apices wider than 0.25 mm. These can be some of the most difficult to manage with conventional instruments, and overfills are common. Shaping such canals with GT files requires a paradigm shift of thinking, extending tapered files through the apex to create linear resistance in the apical few mm of the canal. GT standard and accessory files allow canals with apices up to around 0.7 mm to be prepared for tapered gutta percha cone-fit. Apices larger than this should be considered too large for further shaping, and repaired with MTA before filling. KEY LEARNING POINTS: Tapered apical preparations offer optimal resistance form for obturation. Tapered apical preparations can be prepared in most roots with wide apices by extending GT files and GT accessory files to or through the apex. Apices wider than 0.7 mm should be repaired with MTA prior to filling.

The standardized-taper root canal preparation--Part 2. GT file selection and safe handpiece-driven file use.

AIM: To present guidelines on GT file selection, and safe operation. SUMMARY: It is not necessary to remove excessive dentine for effective root canal preparation. GT files allow safe, standardized preparation, and should be selected to fit the case in hand. Small Root canals should be prepared with 0.06 and 0.08 taper GT files, whilst Large Root canals should be prepared with 0.10 GT or 0.12 Accessory GT files. The greatest challenge is un-learning habits acquired from traditional instrumentation methods. GT files should be used with light touch, and without up-down pumping motions. Spin speeds should be controlled below 300 r.p.m. for routine preparation. GT files are subject to fatigue and should be tracked to avoid overuse. It is recommended that GT files are discarded after the equivalent of five root canal preparations. For severe curvatures, GT files should be single-case tools. KEY LEARNING POINTS: The standard GT file set comprises three instruments of 0.06, 0.08 and 0.10 taper. All are size 20 at the tip, and have a maximum diameter of 1 mm. Accessory GT files have a standard taper 0.12, and maximum diameter of 1.5 mm. They are available in tip sizes 35, 50 and 70. Large Roots are lower canines, upper anteriors, upper and lower single-rooted premolars, palatal roots of upper molars and distal roots of lower molars. They should be prepared with 0.10 GT or 0.12 Accessory GT files. Small Roots are lower incisors, multirooted premolars, buccal roots of upper molars and mesial roots of lower molars. They should be prepared with 0.06 or 0.08 GT files. All GT files should be used with light force and at the correct spin speed. GT files should be discarded after the equivalent of five root canal uses.

The standardized-taper root canal preparation--part 5. GT file technique in small root canals.

AIM: To describe the shaping of Small Root canals with GT files. SUMMARY: Small Roots are lower incisors, two and three canal bicuspids, buccal roots of upper molars, and mesial roots of lower molars. The Shaping Objective instrument for such cases is usually a 0.08 or 0.06 taper GT file. After proper access, pulp tissue should be removed to prevent its compaction and canal blockage. Orifice shaping and smoothing is then achieved with a 35-0.12 accessory GT File, running at full slow-speed r.p.m. (5-20K).Crown-down preparation commences with the 0.10 GT file, followed by the 0.08 and 0.06 tapers as needed. Occasionally, a 20-0.04 Profile is required to reach length. Files are rotated at 300 r.p.m. with steady, light pressure, and withdrawn frequently for cleaning and inspection. Once one of these files has cut to length, the canal terminus is enlarged to Shaping Objective. If difficulty is encountered, be willing to accept a 0.06 instead of the original 0.08 taper Shaping Objective. If the terminal diameter is 0.2 mm you will have plenty of apical resistance form in a tortuous canal with the 0.06 taper preparation. It is definitely better to end up with a smaller shape than originally planned, than to experience the heartache of separation. KEY LEARNING POINTS: Small Root canals should be prepared to a Shaping Objective 0.08 or 0.06 taper. Pulp tissue should be removed before preparation to prevent compaction and blockage. Preparation follows in a crown-down sequence, and may occasionally require the use of small Profiles. Final apical shaping is easily achieved when root length is reached.

The standardized-taper root canal preparation--part 6. GT file technique in abruptly curved canals.

AIM: To describe the application of GT files in roots with abrupt curvatures. SUMMARY: Most dentists interpret obstructions to instrument progress as calcification, rather than abrupt curvature. Basically, there are not any apically calcified canals, only clinicians who are not clever enough or patient enough to sneak to patency. Dentists should be on their guard and sensitive to the 'rubber band' sensation of residual pulp tissue, and the 'loose resistance' sensation of the curved or ledged canal. Residual pulp tissue should be removed and the canal lubricated. The ledged or curved canal will only be helped by file bending. The size 10 file test is the key to identify canals requiring pre-bent instruments. The canal should first be flared short of the obstruction, before shaping the canal after it with regular, pre-bent K-files. Pre-bent GT hand-files can then be used with care to blend the apical and more coronal regions for final shape. Cone-fit may then require chilling and pre-bending GP cones (pre-bend more than one), before packing the canal. KEY LEARNING POINTS: Root canals do not calcify apically. File progress is prevented by pulp tissue, abrupt curvatures or ledging. Loose resistance to the passage of a size 10 file shows the canals that require instrument pre-bending. This test should be repeated at intervals during the preparation. Even NiTi GT files can be pre-bent for use in abrupt curves. Gutta percha cones can be pre-bent after chilling.

The standardized-taper root canal preparation--Part 1. Concepts for variably tapered shaping instruments.

AIM: To introduce the concept of variable taper instruments for predictable and ergonomic root canal preparation, and demonstrate the design features of Greater Taper files. SUMMARY: Optimal root canal shaping is difficult to practice and teach with traditional instruments. Instrument sequences are complex, with up to 18 instruments and 63 procedural stages, providing almost limitless scope for poor results and iatrogenic error. In the first of six articles, Dr Buchanan describes the Variable Taper concept, which grew from such frustrations, and represents a new concept in file design. Milled from NiTi alloys in tapers of 0.06, 0.08, 0.10 and 0.12 mm mm-1, with accessory files for wide canals, their design embodies the key shaping features of adequate coronal enlargement, full deep shape, and predictable apical resistance form case after case. The ease and simplicity of their use is described, and enhanced cleaning and obturation outcomes discussed in relation to their unique design features. KEY LEARNING POINTS: Canal preparation is difficult to practice and teach with traditional K-files and Gates Glidden drills. Variable Taper files are designed to offer the optimal preparation features of adequate (not excessive) coronal enlargement, full deep shape, and apical resistance form in a simple instrument sequence. Variable Taper technique is simple to master, and offers predictable cleaning and obturation outcomes, even in inexperienced hands.