Cutting efficiency of endodontic instruments. Part III. Comparison of sonic and ultrasonic instrument systems

Three-dimensional assessment of obturation volume in lateral canals after three obturation techniques with bioceramic sealer: an in vitro comparative study

OBJECTIVE

This study aimed to evaluate the obturation ability of simulated lateral canal in mandibular premolars at three levels (3, 5, and 7 mm) from the apex using gutta-percha and BC Sealer HiFlow (BCHiF) with different obturation techniques, including continuous wave compaction (CWC), cold lateral condensation (CLC), and single cone (SC) techniques, by a 3D assessment method of the obturation volume with cone beam computed tomography (CBCT) and MIMICS software analysis.

METHODS

Thirty intact human mandibular premolars were decoronated, instrumented up to #30 taper 4%, and uniformly irrigated with 5.25% NaOCl and 17% EDTA. Six simulated lateral canals (3 pairs) were prepared at 3, 5, and 7 mm from the apex in each root, using #10 modified C-file. CBCT images were obtained, and lateral canal volumes were calculated using MIMICS software. The samples were divided into three groups: CWC (n = 10), CLC (n = 10), and SC (n = 10). All groups were obturated with BCHiF and gutta-percha. Another CBCT image was taken post-obturation, and 3D lateral canal obturation volume percentages were calculated using MIMICS software. Data were analyzed using SPSS software with One-way ANOVA and Sidak tests (α = 0.05).

RESULTS

Significant differences were observed in the 3D lateral canal obturation volume percentage at all three levels (P < 0.05). Both CWC and CLC techniques demonstrated higher 3D lateral canal obturation volume percentages (x ¯  = 89.64% andx ¯   =  73.28%; respectively) compared to the SC group)x ¯   =  43.10%).

CONCLUSION

BCHiF combined with the CWC technique has a higher ability to achieve preferable 3D obturation volume in the simulated lateral canal at 3, 5, and 7 mm.

CLINICAL RELEVANCE

In cases requiring endodontic treatment with lateral canals, the CWC obturation technique using BCHiF with gutta-percha may offer better outcomes compared to other obturation techniques.

A critical appraisal of research methods and experimental models for studies on root canal preparation

It is the aim of this review to present a critical overview and summary on the contemporary possibilities, limitations and challenges of research related to root canal preparation. Frequently used research tools and contemporary research designs will be presented and discussed critically focussing on shortcomings and benefits with special regard to clinical relevance and scientific evidence. A plethora of experimental set-ups for assessing the shaping of root canals have been described in the endodontic literature using a considerable number of techniques and instruments. Nevertheless, it can be stated that scientific evidence demonstrating the clinical impact of many investigated topics is questionable or even missing. Instead of technical, radiographic and geometrical parameters, further research should focus on biological aspects and clinical evidence of the impact of root canal preparation on the outcome of root canal treatment.

Evaluation of Cutting Efficiency of Ultrasonic Tips Used in Orthograde Endodontic Treatment

The purpose of the present study was to evaluate the cutting efficiency of the three different ultrasonic tips for orthograde endodontic treatment: stainless steel, zirconium nitride-coated, and diamond-coated tips. An ultrasonic handpiece was mounted on a custom-made automated balance, and each tip repeatedly penetrated dental stone blocks to a depth of 3 mm for 10 times. The amount of time taken to penetrate 3 mm of stone was measured. The diamond-coated tips showed significantly greater cutting efficiency than either stainless steel tips or zirconium-nitride coated tips. The stainless steel tips showed initial better cutting efficiency, but over time , there is no significant difference between the cutting efficiency of the stainless steel tips and the zirconium nitride coated tips. The diamond coated tips were the only group that showed breakage in this study.

Comparison of the Cutting Efficiency of Two Ultrasonic Units Utilizing Two Different Tips at Two Different Power Settings

The objective of this in vitro study was to set up a testing protocol and utilize it to evaluate and compare the cutting efficiency of ultrasonic units. Evaluation of two ultrasonic units utilizing two different tips was done by measuring the weght of a dentin specimen before and after ultrasonic treatment for set time periods. The difference in weight was the amount of dentin removed. The ultrasonic units tested were the P5 Booster (Staelec, France) and the Spartan (Obtura-Spartan, Fenton, MO) machines. The tips tested were the CPR-2D and ETD20 types. The units were tested at maximum and medium power. All the experimental variables, ultrasonic unit type, power setting and tip type were found to have an effect on the cutting efficiency (P<0.0001). The P5 ultrasonic unit was more effective at dentin removal than the Spantan ultrasonic unit at both power settings. The ETD-20 tip was more effective at dentin removal than the CPR-2D tip on both units at both power settings.

Quality of preparation of oval distal root canals in mandibular molars using nickel-titanium instruments

AIM

The aim of this study was to compare the preparation of oval distal root canals in mandibular molars using three different nickel-titanium (NiTi) instruments: Lightspeed (Lightspeed Inc., San Antonio, TX, USA). ProFile .04 (Maillefer Ballaigues. Switzerland) and Quantec SC (Tycom, Irvine, CA, USA).

METHODOLOGY

Three groups of 20 extracted mandibular molars with oval distal root canals were embedded in a muffle system as described by Bramante et al. (1987) and modified by Hülsmann et al. (1999). Preparation of the root canals was performed with particular emphasis on the buccal and lingual extensions of the oval shape. The following parameters were evaluated: comparison of pre- and postoperative photographs with regard to the buccal and lingual extensions of the preparation, safety issues (file fractures, perforations, apical blockages, loss of working length), cleaning ability (SEM investigated using a 5-score system for remaining debris and smear layer) and working time.

RESULTS

Superimposition of pre- and postoperative cross-sections in the majority of specimens revealed uninstrumented or incompletely instrumented buccal or lingual extensions (Lightspeed and Quantec SC, 56.7%; ProFile .04, 55%) For debris removal, Quantec SC achieved the best results (54.2% scores 1 and 2), followed by ProFile .04 (52.5%) and Lightspeed (46.7%). Preparation resulted in substantial smear layer covering the canal walls for every system (ProFile .04, 38.3%; Quantec SC, 36.6%; Lightspeed, 28.3%). Differences between the three systems were not significant for any of the parameters investigated. Preparation with Lightspeed resulted in two fractured instruments; with Quantec SC. two apical blockages occurred. With ProFile .04, no complications were noticed. Mean working time was shorter for ProFile .04 (261.2 s) than for Quantec SC (272.4 s) and Lightspeed (338.9 s); the differences were not significant.

CONCLUSIONS

The flexibility of the NiTi instruments investigated in this study did not allow controlled preparation of the buccal and lingual extensions of oval root canals. The instruments frequently produced a circular bulge in the canal whilst the buccal and lingual extensions remained unprepared, leaving smear layer and debris.

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, Besançon, 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.

Cutting ability of Heliosonic, Rispisonic, and Shaper files

The aim of this study was to investigate the cutting ability of the Heliosonic, Rispisonic, and Shaper files supplied with the MM 1500 sonic handpiece. A model system was used and the following variables evaluated; file type (Heliosonic, Rispisonic or Shaper), power (air inlet ring opening of half, three quarters or fully open), width (15, 25 or 35), and load (25, 50 or 100 grams). A 3(4) full factorial analysis with two replications was performed. A new file with water irrigation was used for each cut. The substrate used was 1 mm thick sections of bovine bone. The differences between the variables were significant (ANOVA, p < 0.001). The most significant variable to affect cutting was load, followed by file type, power, and width. It is suggested that operators should select the file type for use appropriately and press the file against the root canal wall for optimum cutting.

Measurement of the cutting efficiency of endodontic instruments: a new concept

The cutting efficiency of endodontic instruments was measured using an original experimental technique that incorporates new concepts to simulate clinical conditions. Five designs of #ISO 030 endodontic instruments, K-reamer (Maillefer), Flexofile (Maillefer), Helifile (Micro-mega), K-flex (Kerr), and Unifile (De Trey), were chosen and their cutting efficiency assessed at their full working length of 16 mm on two Plexiglas parallelepipeds tilted to follow the 2% conicity of the instruments. For each instrument, four series of 25 cuts were carried out and each cut made on a new flat, smooth Plexiglas surface with an even hardness of 33 VHN. Instruments were tested under a simulated clinical condition of a quarter clockwise turn ROTARY MOTION followed by a PULL ACTION at 16 mm/s rate, with a fixed load on the instrument of 325 g. Water irrigation at a rate of 85 ml/s was supplied before each procedure. Cutting efficiency was evaluated in terms of mass of Plexiglas cut (using a Mettler analytic balance with accuracy of 3 x 10(-5) g) per unit of energy used by the instrument, i.e. mg/J. Unifile was found to have the best cutting efficiency of 0.80 +/- 0.01 (Mean +/- SD) and lowest cutting efficiency loss followed by Flexofile 0.70 +/- 0.03 then Helifile 0.36 +/- 0.01 then K-flex 0.51 +/- 0.07. K-reamer was found to have the lowest cutting efficiency of 0.16 +/- 0.05.

Analysis of the surface cut by sonic files

The purpose of this investigation was to compare 3D profilometry and SEM analysis of a polished surface of bovine bone instrumented by sonic files. Two situations where investigated, i) no operator assisted movement, ii) operator assisted movement. Heliosonic, Rispisonic and Shaper files were investigated at full power setting and an interfacial load of 100 grams. The specimens were subjected to analysis using a 3D Form Talysurf prior to being sputter coated with gold and viewed under an SEM. The 3D surface analysis was found to be complimentary to SEM evaluation in that each provided additional information to the other. 3D analysis proved to be excellent for showing the topographical nature of the cut surface and gave a better indication of depth than the SEM. Debris was however more apparent on SEM evaluation. Each file showed distinctive characteristics in the shape that was cut. The cutting appeared to be as a result of abrasion with no operator assisted movement and was as a result of the longitudinal file action. However when movement was superimposed on this action continuous chip formation was apparent especially for the Rispisonic and Shaper files.

Intra-canal cutting ability of MM1500 files

The aims of this study were to develop a model system capable of monitoring lateral forces during root canal preparation and to measure the cutting ability of files activated by the MM1500 sonic handpiece. Forces were monitored by a calibrated model system which utilized a combination of spring steel beams fitted with strain gauges, these were interfaced through two strain gauge amplifiers to an x-y recorder. Single rooted canine teeth (n = 36; 32 experimental, four control) were mounted in a two-part acrylic mould (which was an integral part of the model system) prior to sectioning horizontally 11 mm from the tooth apex. A 2(4) full factorial experiment with two replications was performed. Four variables were selected for evaluation, load (50 and 100 g), power (air inlet ring half or fully open), file type (Heliosonic or Shaper) and stroke rate (1 or 2 cycles per second). A new file (size 25) was used for 1 min in each canal with water irrigation. The control group was not instrumented. The cross-sectional root canal area was measured before and after instrumentation using image analysis and increase in area was used as an indication of cutting ability. The results showed that the increase in load, power and the Shaper file all produced a significant increase in cutting ability (ANOVA, P < 0.001). However, stroke rate was not found to have a significant effect (P > 0.05). None of the interactions between the variables were significant and there was no significant difference in the control group (P > 0.05). In conclusion, this work has developed a model system to monitor lateral forces and has shown that instrument design and operator usage affect dentine removal from a root canal wall.

Factors affecting the wear of sonic files

The aim of this study was to investigate factors affecting the wear and cutting ability of sonic files. A model system was used and the following variables evaluated, file type; Heliosonic, Rispisonic or Shaper, load; 25, 50 or 100 grams and length of time in use; new, 30 or 60 seconds. A 3(3) full factorial analysis with two replications into the effect of the above variables on the cutting ability of the Heliosonic, Rispisonic and Shaper files powered by the MM1500 sonic instrument was performed. A new file size 25 (Heliosonic and Shaper) or No 3 (Rispisonic) was used for each cut together with water irrigation and the substrate used was 1 mm thick sections of bovine bone. All variables had a significant effect on cutting (ANOVA. p < 0.001). However examination of the F values showed that the most significant variable was load, followed by file type, and time. The most significant interaction was between file type and load followed by time and file type. The interaction between time and load was not significant (p > 0.05). The Rispisonic file was most susceptible to wear during use especially at higher loads and the Heliosonic file cut least. It is suggested that the Shaper file is the better design of the three with respect to cutting ability and wear with use.

Factors affecting the cutting ability of sonic files

The aim of this study was to investigate the cutting ability of sonic files. A model system was developed and the following variables evaluated: file type. Heliosonic or Shaper; file length, 21 or 29 mm; power, air inlet ring opening of half or fully open; stroke length, 2 or 4 mm; stroke rate, one or two cycles per second; and load 50 or 100 g. A 2(6) full-factorial analysis with two replications into the effect of the above variables on the cutting ability of the MM1500 sonic instrument was performed. A new size 25 file was used for each cut, together with water irrigation, and the substrate used was 1-mm thick sections of bovine bone. The differences between the variables were significant (ANOVA, P < 0.001). However, examination of the F-values showed that the most significant variable to affect cutting was load, followed by power, file type, stroke length and stroke rate, with the least significant variable being file length. The most significant interaction was between rate and length of stroke. An increase in stroke rate from one to two cycles per second at a stroke length of 2 mm produced an increase in cutting for both the Heliosonic and Shaper files. However, at the longer stroke length of 4 mm, the same increase in rate resulted in a decrease in cutting for the Shaper files. Therefore, it is suggested that operators should press the file against the canal wall and move it slowly to maximise cutting.

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.

Pressure waves in root canals induced by Nd: YAG laser

Recently, root canal preparation using Nd:YAG laser has been introduced. Laser interaction with matter may generate cavitation and subsequent pressure waves. This study characterized the pressure waves induced in root canals by either Nd: YAG laser, sonically vibrated files, or ultrasonically vibrated files. The root canals of 14 single-rooted teeth were prepared conventionally and filled with water. In 12 teeth, a pulsed Nd:YAG laser was activated in the canal using optical fibers of various diameters and various power settings. In the remaining two teeth, either a sonic or ultrasonic file was activated. The pressure waves induced in the canals were detected by a piezoelectric transducer. The results were analyzed using correlation coefficient and coefficient of variation. Laser irradiation resulted in pressure waves with amplitudes varying from 35.78 to 79.26 mV, being positively correlated with the laser power density (R2 = 0.870). Sonic and ultrasonic vibrations resulted in pressure waves with mean amplitudes of 60.51 mV and 7.02 mV, respectively. It was concluded that Nd:YAG laser irradiation induced pressure waves, with different characteristics from waves induced by freely vibrating sonic and ultrasonic endodontic instruments when applied to water-filled root canals.

An in vitro investigation into the cutting ability of ultrasonic K files

Endosonic files vary in their oscillation when operated in air with the greatest displacement at the unconstrained tip. It was the aim of this study to investigate how files of different lengths and sizes varied in their ability to cut dentine. Single rooted teeth were sectioned to produce 1 mm dentine discs. These were positioned on a plastic block connected to a load transducer. Endosonic K-files (#15 to 25) were used to cut the disc for 10 s using operator assisted movement. The files contacted the disc at the following points along their length; apical (3 mm from tip), middle (8 mm from tip) and coronal (13 mm from tip) under applied loads of 30 and 50 g. The depth of cut produced by each file was measured using light microscopy. The #15 and #25 were similar in their pattern of dentine removal. The #20 file produced a large variation in its cutting ability and was also susceptible to fracture. The tip of the files was prone to constraint at higher loading with the thicker part of the file producing more cutting. It was concluded that the pattern of dentine removal of endosonic files was affected by the amount of load applied. The displacement amplitudes of endosonic files in air would not appear to be a good indicator of file cutting ability.

Effect of air inlet ring opening on sonic handpiece performance

This study investigated the effect of air inlet ring opening on the oscillatory pattern of the MM 1500 sonic handpiece and files. The oscillatory pattern of the driver head and files in air and under load was determined microscopically. The results showed that a critical opening of the air inlet ring was necessary to elicit oscillation of the driver head and sonic file. The driver oscillated in an elliptical manner, the displacement of which varied with air inlet ring opening. When operated in air the file exhibited an elliptical movement which was influenced by different design, length and thickness. This action was constrained under load and replaced by a longitudinal action of the same dimension for all files which appeared to have an efficient cutting action. This work shows that air inlet ring opening increases oscillation of the driver head once a critical opening has been reached and that clinical loading does not constrain the cutting action of the file.

Cutting efficiency loss of root canal instruments due to bulk plastic deformation, surface damage, and wear

Cutting efficiency loss of #15 H-type and K-type files was studied as a function of bulk plastic deformation and cutting edge wear. Instrumentation was done by purely extractive filing, without any significant torsional and/or bending strain. Cutting efficiency variations were assessed by means of cutting force measurement, while absolute cutting efficiency was obtained through three-dimensional scanning stylus profilometry. Bulk plastic deformation-induced flute modifications may lower the cutting efficiency of H-type files by approximately 50%. For this instrument special care is required in tip and flute machining to avoid in vivo breakage. On the contrary, within the normal life-span of an instrument of approximately 100 strokes cutting edge wear is seen to be negligible. The existence of such wear is "inferred" indirectly from a 10% drop in extraction efficiency.

Variations in stroke rate and loading using hand sonic or ultrasonic instrumentation

An in vitro model system was developed to investigate the stroke rate and loading during hand, sonic, or ultrasonic instrumentation. The model system consisted of a mandibular molar tooth attached to a strain gauge and interface to a computer. Ten clinicians instrumented the distal canal of lower molar teeth. Stroke rates used and loads applied were measured using different sized files with the three different preparation techniques. There was no significant difference in stroke rates between different file sizes (p > 0.05) within the same generator, however, stroke rate for hand was significantly slower than for sonic or ultrasonic (p < 0.01). Loading of the canal wall rose with increase in file size which was significant for hand (p < 0.01) and sonic (p < 0.05) but not ultrasonic (p > 0.05). There was a tendency for loading to be higher with hand instrumentation, this however was not significant (p > 0.05).

Today's sonics: using the combined hand/sonic endodontic technique

Combing sonic technology with hand instrumentation facilitates root canal preparation. The authors present an efficient and safe technique.

Ultrasound in dentistry. Part 2--Periodontology and endodontics

Ultrasound in the kHz frequency range is used widely in clinical dentistry. The most common uses are in the fields of periodontology and endodontics. The ultrasonic scaler works by the vibratory chipping action of the oscillating tip and is assisted by the presence of cavitational activity in the associated cooling water. When assessing clinical studies it is often difficult to interpret results from different workers due to the lack of standardization of the ultrasonic scaler. Operators should be aware of the oscillatory pattern of different instruments. Endosonics utilizes an ultrasonically oscillating endodontic file to clean and shape the root canal prior to obturation. The cleaning ability of such files is assisted by the occurrence of acoustic microstreaming forces. The endosonic file is prone to constraint when it contacts the canal wall which alters its oscillatory pattern. Clinical techniques should be modified to reduce this problem.

Anatomical and histological features of C-shaped canals in mandibular second molars

The mandibular second molar has many root canal variations. This investigation used two evaluation methods to examine the canal morphology of mandibular second molars having C-shaped canals. Fifteen extracted mandibular second molars with a conical root and C-shaped canal orifice were separated into two groups. A polyester cast resin technique allowed three-dimensional visualization of the root canal system in eight teeth; the remaining seven molars were prepared for histological examination in cross-section in the coronal, middle, and apical thirds for study under the light microscope. The results illustrated that C-shaped canals in mandibular second molars can vary in number and shape along the length of the root with the result that debridement, obturation, and restoration in this group may be unusually difficult.

High precision, simulated cutting efficiency measurement of endodontic root canal instruments: influence of file configuration and lubrication

A high precision method is presented for measurement of root canal instrument cutting efficiency in pure, linear movements. Operator-independent instrumentation is achieved by means of an automatic, mechanical test rig mounted as an accessory in an Instron tensile testing machine. It is now possible to do reliable cutting simulation that closely represents clinical motions. Cutting efficiency is assessed via "wear" volume measurement by means of three-dimensional surface mapping on bovine bone serving as a dentin substitute. A volume precision of 3 x 10(-3) mm3 is achieved which is equivalent to a weight resolution better than 10 micrograms. In particular, cutting efficiency data for K-type and H-type files is presented showing an enhanced performance (by roughly a factor of 3) in the latter case. Lubrication is also shown to increase the cutting efficiency (+200% for the K file and +30% for the H file). Water and 2.5% sodium hypochlorite solutions have equivalent effects.

Statistical models for evaluating the penetrating ability of endodontic instruments

An in vitro study was conducted to evaluate the penetrating ability of hand instruments (No. 10 K-file and "Pathfinder") and an automated device with a No. 08 (Canal Finder System) file in 270 extracted curved and narrow molar roots. The roots were randomly allocated to six groups, each one corresponding to a different permutation of the three instruments. The experiment was performed in three sequential stages, and Stages II and III were undertaken only in roots where no apical penetration was achieved in the previous stage(s). Statistical models were designed to fit the resulting clinical data. The No. 08 Canal Finder System and No. 10 K-file proved to be similar in their penetrating ability in Stage I (with estimated probabilities of 71.1% and 68.8%, respectively). The No. 08 Canal Finder was found to be the most efficient in Stage II and especially in Stage III, with a probability of penetration of 20.7%, compared with 9.8% for the "Pathfinder" and 7.4% for the No. 10 K-file.

Oscillatory pattern of sonically powered endodontic files

When operated in air, the sonic endodontic instrument produced a movement at the driver head which resulted in a large elliptical oscillation of the file. This motion had similar properties to ultrasonically operated files in that there was a distinct variability in the magnitude of the vibratory motion between files of different design, length and thickness. When the sonic file was loaded, the elliptical motion was eliminated leaving a pure longitudinal file oscillation. This mode of vibration was particularly efficient as it was largely unaffected by loading, with the displacement amplitude being similar for different types of file used. The oscillatory pattern of the sonic file may offer a useful mode of mechanically assisted root canal preparation.