Canal markings produced by endosonic instruments.

It has been recognised that ultrasonic files leave a diagonal pattern within the canal following endosonic instrumentation. There is confusion on the causative factor on the production of these marks. Furthermore there is little information about the marks produced by sonic files. An in vitro system consisting of highly polished dentin discs demonstrated that the ultrasonic K-file made a diagonal pattern that was an imprint of the cutting edges of the file. The sonic files produced different markings which were the result of their longitudinal and transverse motion. Root canals of extracted teeth were prepared with these instruments and similar grooves were observed. The ultrasonic K-file had diagonal grooves in the coronal and middle third of the root canal but longitudinal marks in the apical third. The rispisonic and shaper files produced debris even in the presence of NaOCl. This debris was formed into discrete parallel bands. Both longitudinal and transverse grooves were present and the canal had many other scratches similar to those seen with the dentin discs. There were differences between the marks produced by either ultrasonic or sonic endosonic instruments but it is unknown whether this influences the long term prognosis of the root canal therapy.     

Canal markings produced by endosonic instruments

Abstract It has been recognised that ultrasonic files leave a diagonal pattern within the canal following endosonic instrumentation. There is confusion on the causative factor on the production of these marks. Furthermore there is little information about the marks produced by sonic files. An in vitro system consisting of highly polished dentin discs demonstrated that the ultrasonic K-file made a diagonal pattern that was an imprint of the cutting edges of the file. The sonic files produced different markings which were the result of their longitudinal and transverse motion. Root canals of extracted teeth were prepared with these instruments and similar grooves were observed. The ultrasonic K-file had diagonal grooves in the coronal and middle third of the root canal but longitudinal marks in the apical third. The rispisonic and shaper files produced debris even in the presence of NaOCl. This debris was formed into discrete parallel bands. Both longitudinal and transverse grooves were present and the canal had many other scratches similar to those seen with the dentin discs. There were differences between the marks produced by either ultrasonic or sonic endosonic instruments but it is unknown whether this influences the long term prognosis of the root canal therapy.     

三种方法预备后牙细弯根管的比较

目的探讨逐步后退法、逐步深入法、被动逐步后退法（超声波与手用器械联合应用、三种不同方法预备后牙细弯根管对根管壁的清理能力及操作时间的差别。方法应用逐步后退法、逐步深入法、被动逐步后退法（超声波与手用器械联合应用）对45个新鲜拔除的人恒磨牙近中颊侧根管进行预备．并记录操作时间，将牙根纵向劈开，分为根冠1／3、根中1／3及根尖1／3，扫描电镜下评价其根管内壁牙本质碎屑和玷污层的形成情况。结果三种方法对根管清理能力差异无统计学意义（P〉0．05）而无论使用何种预备方法，其对根中1／3及根冠1／3处的清理能力优于根尖1／3部．两者差异有统计学意义（P〈0．05）。3种方法根管预备时间分别为：逐步后退法（12．8±1．26）min．逐步深入法（9．02±0．74）min，被动逐步后退法（超声与手用器械联合应用法）（12．21±1．90）min．三组差异无统计学意义（P〉0．05）。结论三种根管预备方法均不能达到完全的根管清理，尤其是对于根尖1／3部，清洁效果很不理想：总体上看，根中及根冠1／3清洁度显著优于根尖1／3。被动逐步后退法（超声与手用器械联合应用）及逐步后退法操作均较费时、费力，而逐步后退法根管预备时间略短于另两种方法且较省力。     

Effect of precurving endosonic files on the amount of debris and smear layer remaining in curved root canals.

Endosonic files are prone to constraint; this reduces their efficiency, particularly in the apical third and in curved root canals. Precurving the file may reduce constraint, thereby improving the file's ability to debride. This investigation was undertaken to compare both straight and precurved endosonic files as to debris and smear layer removal. Thirty-six curved root canals were randomly allocated into six groups. Each group was prepared using a step-down technique, then instrumented with either a straight or precurved endosonic file of size 15, 20, or 25. The tooth roots were split and examined under the scanning electron microscope. Blind examinations were made for debris and smear layer removal and evaluation scores were analyzed using a log linear approach. The root canals instrumented with the precurved files had a significantly lower debris score than those prepared with straight files. Precurving did not affect smear layer removal. In conclusion, precurving of files decreased the amount of debris but did not affect smear layer removal.     

Comparison of the quality of obturation following endosonic versus hand instrumentation

This study was undertaken to compare the quality of root canal obturation following preparation by endosonic or hand instrumentation. Forty single-canal, extracted lower premolar teeth were selected. One group of 20 teeth was prepared using a standard step-back technique, the other 20 teeth were prepared with an ultrasonic machine. The groups were subdivided, with two operators preparing 10 teeth of each group. The teeth were obturated by a third operator using cold laterally condensed gutta percha. The root apices were then immersed in methylene blue dye for 48 h and the teeth sectioned longitudinally. Image analysis recorded the amount of sealer and void within the obturated canal. The linear distance of dye penetration was measured to provide an indication of apical seal. Examination of the root canal shape resulting from the different preparation techniques used was also undertaken. No significant difference was noted in the percentage of sealer and void present in the root canals obturated after endosonic or hand instrumentation. There was a slightly greater although not significant increase in the degree of linear penetration of dye in canals prepared endosonically. The endosonic technique used in this study appeared to produce a canal preparation of slightly less continuous taper than that obtained with hand preparation.     

Comparison of balanced forces, endosonic, and step-back filing instrumentation techniques: quantification of extruded apical debris

Randomly assigned groups of 15 single-canal, extracted human teeth were instrumented by one of three techniques: balanced forces, endosonic, or step-back filing. Debris extruded from the apical foramen during instrumentation was collected onto preweighed filters using a suction filtration apparatus. Following desiccation, weight determinations were made on an analytical electrobalance. A one-factor analysis of variance was performed on the debris weight data revealing that the endosonic technique apically extruded significantly more debris than the balanced forces technique (p less than 0.05). Further analysis of the data, excluding debris weights greater than 1 SD from the mean, using a one-factor analysis of variance revealed the balanced forces technique apically extruded significantly less debris than either endosonic or step-back filing techniques (p less than 0.05). No significant difference was demonstrated between endosonic and step-back filing techniques.     

The effect of maintaining apical patency on periapical extrusion.

Thirty-three human maxillary incisors were secured in the openings of a glass vial. Root canals were instrumented to the apical constriction with a step-back technique and a patency file was not used throughout the root canal preparation. The irrigant, 1% NaOCl, was delivered by means of a plastic syringe with a 23-gauge needle and the overflow was suctioned with an aspirator. The total volume of irrigant used was 10 ml. Apically extruded debris and NaOCl were measured. The apical constriction was then deliberately enlarged. With a step-back technique a new 'apical constriction' was created, coronally to the original one. A patency file was again not used, and irrigation was identical to the that used during the initial root canal preparation. Extruded debris and NaOCl in each bottle were again measured. Results indicated that there was significant difference in the amounts of extruded material before and after the enlargement of the apical constriction with greater extrusion when the constriction remained intact.     

Scanning electron microscope study on the efficacy of root canal wall debridement of hand versus Lightspeed instrumentation

AIM: The aim of this in vitro study was to compare the efficacy of root canal wall debridement following hand versus LightSpeed instrumentation. METHODOLOGY: Twenty recently extracted single-rooted teeth were paired and randomly placed into two treatment groups of 10 teeth each. In group 1, a step-back instrumentation without initial coronal flaring with stainless steel Hedstroem files was used; group 2 was instrumented with Ni-Ti LightSpeed instruments. Both groups had the same irrigation regimen: 2.5% NaOCl and a 15% EDTA solution. The teeth were then decoronated and each root split longitudinally into two halves to be examined using the scanning electron microscope (SEM). The presence of superficial debris and smear layer was evaluated by a standardized grading system, and the resulting scores submitted to nonparametric statistics. RESULTS: Under the conditions of this study, the removal of superficial debris was generally excellent with both canal preparation techniques. Both techniques resulted in variable presence of residual smear layer, with a canal wall covered by smear layer as the predominant characteristic. Generally, the amount of smear layer was greater in the apical than in the middle third of the root, however, this difference was statistically significant (P < 0.005) only in hand-instrumented teeth. The use of LightSpeed instruments was associated with significantly more (P < 0.05) smear layer presence in the middle region of the root when compared with hand instrumentation. In addition, less smear layer was present in the apical region following LightSpeed instrumentation than stainless steel hand files, but this difference was not statistically significant. Differences in debridement between the two halves of the same root were more evident with LightSpeed than manual instrumentation, however, there was no statistical significance. CONCLUSIONS: It may be inferred that the choice between hand and LightSpeed instrumentation should be based on factors other than the amount of root canal debridement, which does not vary significantly according to the instruments used.     

Preparation of the apical part of the root canal by the Lightspeed and step-back techniques

This study measured in vitro the displacement of natural canal centres in 18 human teeth before and after shaping by the step-back or Lightspeed techniques. Experimental roots ( n = 9 per group), embedded in clear plastic, were cross-sectioned using a 0.1-mm-thick band saw at distances 1.25 mm, 3.25 mm and 5.25 mm from the apices. A stereo microscope was used to take 35 mm slides of the cut surfaces of the sectioned roots and canals. The slides of the uninstrumented canals were scanned into a computer and saved. Each sectioned root was then reassembled and the canals shaped by the step-back or Lightspeed technique. File size 40 and instrument size 50 were selected as the master apical file and master apical rotary for the step-back and Lightspeed groups, respectively. The 18 prepared canals were photographed, and the 35 mm slides scanned and computer stored as previously. This allowed the positions of the pre- and postinstrumented roots to be electronically superimposed for subsequent analyses. Displacements of the root canal centres before and after preparation were assessed in relation to the cross-sectional diameter of the files or instruments used. In addition, increases in cross-sectional area of the root canals after preparation were evaluated in relation to the cross-sectional area of the files or instruments used. Engine-driven nickel-titanium Lightspeed instruments caused significantly less ( P < 0.001) displacement of the canal centres, so roots in the Lightspeed group remained better centred than those in the step-back group. The mean cross-sectional area after preparation in the Lightspeed group was significantly less ( P < 0.001) than that recorded in the step-back group. Clinically, this implies less apical transportation and less dentine destruction with the Lightspeed technique than with the step-back technique.     

Reduction in intracanal bacteria during root canal preparation with and without apical enlargement

AIM: To compare in vitro intracanal bacterial reduction using nickel-titanium rotary instruments with and without apical enlargement. METHODOLOGY: Thirty-eight palatal roots of maxillary molar teeth, with mature apices were subdivided according to lengths and then randomly assigned to two experimental and one control groups. The roots were sterilized and then reinfected with Enterococcus faecalis, which served as a bacteriological marker. All roots in the experimental groups were prepared in a step-down sequence with engine-driven GT rotary files at 350 rpm. In experimental group A (n = 16) additional apical enlargement to ISO size 35 was performed. In group B (n = 16) a serial step-back technique was followed with no apical enlargement. This was combined in groups A and B with irrigation with NaOCl and EDTA. In the control group (group C, n = 6) irrigation only was carried out, with no mechanical preparation. Samples were then taken from the root canals to determine the numbers of remaining bacteria. RESULTS: In groups A and B, 15 (94%) and 13 (81%) specimens were rendered bacteria-free, respectively. In the control group C none of the specimens were bacteria-free. There was a significant difference (P < 0.001) in the antibacterial effects of experimental and control regimens. There was, however, no significant difference (P = 0.276) between the preparation methods used in the experimental groups. CONCLUSIONS: There was no significant difference in intracanal bacterial reduction when Ni-Ti GT rotary preparation with NaOCl and EDTA irrigation was used with or without apical enlargement preparation technique. It may therefore not be necessary to remove dentine in the apical part of the root canal when a suitable coronal taper is achieved to allow satisfactory irrigation of the root canal system with antimicrobial agents.     

A comparison of spreader penetration depth and load required during lateral condensation in teeth prepared using various root canal preparation techniques

AIM: To compare the influence of various root canal preparation techniques on spreader penetration depth and load required during lateral condensation with gutta-percha and sealer. METHODOLOGY: Eighty extracted human teeth with single and straight canals were used. Twenty teeth were instrumented using one of four root canal preparation techniques. The four preparation techniques were: step-back technique without Gates-Glidden drills, step-back technique with Gates-Glidden drills, crown-down pressureless technique and hybrid technique (step-down/step-back). After root canal preparation had been completed a simulated periodontal ligament was fabricated from a uniform layer of silicone impression material. The roots were then mounted in an acrylic resin to simulate the physical condition found in tooth socket. A standardized stainless steel hand spreader of the same size as the master apical file was mounted in an Instron testing machine and lateral compaction with gutta-percha and sealer was performed. The load value was recorded from the Instron testing machine. The spreader penetration depths were measured with an endodontic ruler. The data obtained were analysed statistically using anova and Student's t-tests. RESULTS: No significant difference in initial spreader load needed to condense the master cone was found amongst the four canal preparation techniques (P > 0.05). The step-back technique with Gates-Glidden drills and the hybrid technique demonstrated the least difference between the initial spreader penetration and the working length (mean 1.925 and 2.25 mm, respectively). The step-back technique without Gates-Glidden drills and the crown-down pressureless technique had the greatest difference between initial spreader penetration and the working length (mean 4.425 and 4.75 mm, respectively). CONCLUSION: The flare created by canal preparation affected spreader penetration depth, but had no effect on the spreader load.     

Effects of constraint on the oscillatory pattern of endosonic files

When operated in air, the transverse oscillation of the endosonic file exhibits a series of nodes and antinodes along its length with the greatest displacement amplitude occurring at the unconstrained tip. Endosonic files of varying design, length, and thickness exhibit differences in their oscillation. Preliminary work has revealed that the endosonic file is susceptible to constraint when working within the root canal and a model system was designed to investigate this problem. The constraining influence was found to be greatest when it was applied at those antinodes nearest the tip. This effect was further enhanced if the file was angled. Furthermore, constraint applied at the nodes also influenced the file oscillation. Such results may explain in situ observations on the occasional inefficiency of the system, especially when negotiating the apical third of a curved root canal. Clinical techniques utilizing an endosonic file may require reappraisal in order to minimize such constraint.     

A case of unusual anatomy: a mandibular second premolar with four canals

AIM: The aim of this case report is to describe conventional root canal treatment on a mandibular second premolar with four canals. SUMMARY: The pulp of a mandibular second premolar had become irreversibly inflamed, probably as a result of bacterial microleakage from a carious lesion. The general dental practitioner had initiated root canal treatment, but due to procedural difficulties referred the case. Conventional root canal treatment was then performed with magnification. Preparation was undertaken in a crown-down manner using balanced force hand instrumentation with flexible K-type files and files of Greater Taper. The root canals were obturated with vertically condensed gutta-percha technique. KEY LEARNING POINTS: Good illumination and magnification are vital during root canal treatment. Crown-down preparation using the balanced force technique with flexible files makes instrumentation easier and prevents many of the procedural errors that can occur with filing techniques. Greater Taper instruments made of nickel-titanium are sufficiently flexible to be used in complex curved canals and obviate the need for step-back flaring of the apical preparation. Vertical compaction of warm gutta-percha may simplify the obturation of complex root canal systems. When the technical difficulty of a procedure exceeds the expertise of the practitioner, specialist referral may be required.     

Comparison of the effect of different glide path files on amount of apically extruded debris in curved root canals

It is essential to create a glide path before root canal preparation with nickel–titanium rotary files to avoid file breakage and preserve the original canal structure. The aim of this study was to compare the amount of apically extruded debris after using different glide path files. A total of 96 first mandibular molars with curved mesial roots were randomly divided into six groups (n = 16) which are K-files, Proglider, R-Pilot, TruNatomy Glider, WaveOne Gold Glider and group without a glide path. Apically extruded debris was measured after glide path and canal preparation. The highest amount of debris was found in the control group without a glide path and using a glide path file caused less debris and significant differences were observed between R-Pilot, TruNatomy Glider, ProGlider, WaveOne Gold Glider and K-file groups. It may be recommended to create a glide path before root canal shaping to reduce the amount of extrusion debris from the apical. Especially in curved and narrow root canals, it is recommended to use an R-Pilot file before root canal shaping in order to reduce the amount of apically extruded debris.     

The efficacy of sonic and ultrasonic appliances on root canal debridement

The purpose of this study was to compare the debridement efficacy of hand, sonic (MM-3000), and ultrasonic (Cavi-Endo) appliances, utilizing the same K-type files and a constant flow irrigation system, in the mesial root canals of extracted human mandibular 1st and 2nd molars. Only those roots with a canal curvature of between 10 and 30 degrees, by Schneider's method, were used in this study. The instrumentation time per mesial root canal for each treatment group was also evaluated. Following canal preparation and histological processing, the middle and apical cross-sections were examined to determine the percentage of canal and isthmus cleanliness, and the percentage of planed canal walls in the main canal area. Statistical analysis indicated no significant difference in canal and isthmus cleanliness at the middle and apical levels. All techniques achieved a high level of canal cleanliness. However, step-back hand instrumentation had the greatest percentage of planed canal walls in the main canal area at every portion of the root. Sonic instrumentation, in this study, was significantly faster than hand instrumentation in preparing the root canal system.     

The removal of the smear layer using the Quantec system. A study using the scanning electron microscope

AIM: The aim of this study was to determine the ability of the Quantec Series 2000 rotary nickel-titanium endodontic system to remove dentinal debris and smear layer produced during canal preparation. METHODOLOGY: A first group (control) of 12 curved root canals was prepared using conventional manual instruments and the step-back technique. A second group of 12 curved root canals was instrumented using the complete Quantec sequence according to the manufacturer's instructions. In both groups, irrigation was performed using a 3% NaOCl solution. The canal walls were observed under a scanning electron microscope and the coronal, middle and apical thirds of each canal photographed at a magnification of 500. The views were divided into 10 subareas by overlaying a grid, and the absence or presence of a smear layer was rated and scored on three appearances using the scale described by Ciucchi et al. (1989). RESULTS: The scores were higher (i.e. less debris was present) in the middle third (P < 0.0001) and in the apical third (P < 0.0001) of canals prepared with the Quantec system when compared with those prepared with K-files. Nevertheless, in canals prepared with Quantec instruments, the scores were significantly higher in the coronal third compared with the apical third (P < 0.005). CONCLUSIONS: The Quantec rotary system produced cleaner canal walls than conventional manual instrumentation, particularly in the middle and apical thirds. This finding may imply that stresses applied to the cutting regions of Quantec instruments by accumulation and compression of the smear layer are minimized.     

声波器械去除根管玷污层能力的比较研究

目的:比较声波、超声波和手用器械去除根管玷污层能力。方法:收集离体单根管的前磨牙40个,随机分为4组,分别由声波器械、超声波器械、手用器械以及声波和手用器械联合行根管预备,应用扫描电镜进行观察,采用Wilcoxon秩和检验进行统计学分析,根据根管表面的玷污层的量和牙本质碎屑比较声波器械去除根管玷污层的能力。结果:根尖1/3部分,在去除玷污层方面,声波器械组、超声波器械组以及声波器械和手用器械联合组,与手用器械组之间有显著性差异(P<0.05);在去除牙本质碎屑方面,超声波器械组与手用器械组之间亦有显著性差异(P<0.05),声波器械组以及声波器械和手用器械联合组与手用器械组之间有非常显著性差异(P<0.01)。声波器械组以及声波器械和手用器械联合组,与超声波器械组在去除玷污层和牙本质碎屑方面无显著性差异(P>0.05)。根中1/3和根上1/3部分,各组间比较均无显著性差异(P>0.05)。结论:根尖1/3根管预备,声波器械去除玷污层和牙本质碎屑的能力优于手用器械,尤其是去除牙本质碎屑的能力更强;与超声波器械近似。     

Sealing ability of Thermafil with and without sealer.

The purpose of this study was to evaluate the apical sealing ability of root canals filled using three obturating techniques. Sixteen maxillary first molars were obturated with Thermafil, 16 with Thermafil and a ZOE sealer, and 16 with laterally condensed gutta-percha. Two canal instrumentation methods were used, conventional step-back preparation with K-Flex files and traditional instrumentation combining reaming with reamers and filing with K-Flex files. Following obturation, the teeth were prepared for evaluation of the seal using India ink and a Profile Projector. The depth of penetration of the dye was statistically evaluated for each of the three roots with an analysis of variance. For sealing ability, there was no significant difference at the p < 0.05 level between the conventional step-back preparation and the traditional instrumentation technique. However, a significant difference was present at the p < 0.05 level for the obturation techniques. The mean linear dye penetration for the Thermafil technique was greater than that for lateral condensation.     

Scanning electron microscope study comparing four root canal preparation techniques in small curved canals

Various instrumentation techniques have been proposed and examined with conflicting results. They include hand and ultrasonic techniques and combinations of the two. In the present study we assesed the effectiveness of four preparation methods for cleaning small, curved root canals, using backscattered-imaging scanning electron microscopy (SEM). The methods were: (i) step-back without initial coronal flaring; (ii) step-back with coronal flaring; (iii) step-back with initial coronal flaring and finished by ultrasonic irrigation; and (iv) ultrasonics only.
Eighty freshly extracted maxillary and mandibular molars were randomly placed into four treatment groups of 20 teeth each. After preparation, roots were sectioned longitudinally and examined wet by SEM. Each canal was qualitatively evaluated and the groups compared for removal of debris and smear layer, both overall and at each level (apical, middle and coronal).
There were no statistically significant differences between the techniques, either overall or within any of the regions. When comparing regions (regardless of technique) the middle level was cleaner than the apical or coronal levels.
In conclusion, efficacy differed little among the techniques; none of them completely removed smear layer and all left debris.     

Determination of root canal curvatures before and after canal preparation (part II): A method based on numeric calculus

The aim of this paper is to present a new method based on numeric calculus to provide data on any type of root canal curvature at any point of the long axis of the canal. Twenty severely curved, simulated root canals were prepared with rotary FlexMaster and Profile instruments in the crown-down technique and manually in the step-back technique. The inner and outer curvatures were registered in a system of coordinates before and after preparation in increments of 0.5 mm. Using an equalising function, the curvatures were first represented in graphic and algebraic form. The maximum and the mean curvature as well as the length of the arc from the apical foramen to the point of maximum curvature were determined mathematically. An increase in maximum curvature was registered for all four shaping systems investigated. The radius of the inner curvature decreased by 0.5-1.2 mm in the manual systems as a result of the preparation. The Profile system displayed the smallest changes in radius (-0.9 mm) even with the outer curvature, and manual preparation with stainless steel files the most pronounced change (-1.8 mm). The point of maximum curvature at the inner curvature was displaced by 1.6 mm to the apical foramen through manual preparation with Ni-Ti files. At the outer curvature, the maximum displacement (1.8 mm) recorded was also the result of preparation with Ni-Ti hand files, while a displacement of only 0.3 mm to the apical foramen was recorded with the other systems. The method offers a means of determining curvatures precisely without random specification of reference points. The method is also capable of registering only minor changes in curvature in the two-dimensional long axis of the canal.