International Endodontic Joumal (\99\) 24,15-23

The influence of diflFerent root canal instruments on root canal preparation: an in vitro study B, M, BRISENO & E, SONNABEND Department of Conservative Dentistry, University of Munich, Germany Summary. Nine endodontic instruments from different manufacturers (Reamers, K-files, Hedstrom files, K-Flex files, Flexofiles, S-files, Bums Unifiles, Flexicut files and Flex-R files) were used to prepare 180 simulated root canals in resin blocks. The instrument's ability to reproduce a theoretical pre-established ideal canal shape was assessed by comparing the original canal path with the resulting enlarged canal shape by a double exposure photographic method. The individual ability of each instrument to transport debris was also observed during instrumentation under a stereomicroscope. Regardless of the instrument type, none was able to reproduce ideal results; however, clinically acceptable results could be obtained with all of them. The coronal and apical debris transportation characteristics proved to be similar with all instruments.

apical foramen transportation significantly compared with the stepback technique. Some of the instruments tested in this study have been tried in previous studies (Gutierrez & Garcia 1968, Jungmann et al. 1975, Klayman & BrUliant 1975, Weine et al. 1975, 1976) and significant differences were found between some of them, and between different instrumentation techniques (Powell et at. 1986, Sepic «fl/, 1989), The purpose of this study was to compare tn vitro the ability of nine different types of root

Introduction Cleaning and shaping the root canal is one of the main objectives of endodontic therapy (Schilder 1974), The maintenance of the original root canal shape between the apical foramen and the neck of the tooth during instrumentation is of great innportance in the success of endodontic therapy (Heuer 1963, Schilder 1974, Weine i982). In recent years practitioners have been confronted with the development of different types of instrument design to instrument root canals more efficiently, thus creating confusion about which would be the best instrument to use. The stepback technique has proved to be superior to other instrumentation techniques (Weine et al. 1975, Walton 1976), and has been recommended as the standard when comparing new instrumentation techniques {Hill & del Rio 1983), On the other hand, Sepic et al. (1989) have claimed that the balanced force concept for instrumentation reduces Correspondence: Dr B, M. Brisefio, Poliklinik fur Zahnerhaltung und Parodontologie, Goethestr, 70, 8000 Munchen 2, Germany.

Fig, I. Diagram showing how the degree of curvature of the canals in clear casting resin was determined. 15

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B. M. BriseHo S E. Sonnabend

Fig, 2, The mounting device for photographing the blocks. canal instrutnent to follow tbe original canal curvature with a slightly modified stepback technique (Briseiio et al. 1988), by quantifying in two dimensions the areas of simulated root canals which were shaped not at all, adequately or severely. Materials and methods Commercially available blocks' in clear casting resin which had simulated root canals with a curvature between 40° to 50° were utilized. Only blocks whose apical and coronal diameters were 0,15 and O.SOtnm (±0,02mm), respectively, were used. Their degree of curvature was established by slightly modifying Schneider's (1971) method (Fig, 1) Twenty canals were randomly distributed and shaped per instrument. The instruments tested were: (i) Reamers^; (ii) K-files''; (iii) Hedstrom files^; (iv) K-Flex files'; (v) Flexofiles^; (vi) S-Files'; (vii) Burns Unifiles'; (viii) Flexicutfiles^;and (ix) Flex-R files', ' Peccina and Assoc,, Waukeegan, Illinois, USA, ^ Antaeos, Miinchen, Germany, 'Kerr, Romulus, Michigan, USA, * Maillefer, Ballaigues, Switzerland, 'Svenska Dental Instruments, Upplands Vasby, Sweden, ' Caulk, Milford, Delaware, USA, ' Union Broach, New York, USA,

Photographic procedures

A mounting device was developed for accurately locating the resin blocks, A transparent millimetre foil was fixed between tbe mounting plate and light source in order to allow accurate measurement of tbe amount of material removed from tbe canals in the resulting slides (Fig, 2). A double exposure ofthe same frame of the fiim was obtained by first photographing the stained original canal path, blocking thefilmwinder and then re-exposing the same frame with the widened canal after repositioning in the mounting device. None of the resulting slides containing the superimposed canals showed any kind of visual distortion (Figs 3a, 3b and 3c), Instrumentation procedures

All root canals were stained (Ceristan R*) prior to instrumentation. The working length was established with a size 10 instrument. The master apicalfile(MAF) was established three file sizes after the pre-established initial apical file (IAF), At this enlargement phase an approximate 45° to 60° clockwise and counterclockwise rotary motion similar to the balanced force concept (Roane 1985) and filing 'Erythrosin B, Merk, Darmstadt, Germany,

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Fig. 3. Double exposed prints of canals prepared with (a) Flexicut, (b) Flex-R and (c) K-Fle.x files. were used, apart from reamers in which only a reaming motion was utilized. To analyse similar results, canals whose MAF was smaller or larger than a size 30 were discarded. .After establishing the MAF, the canals were shaped coronaOy until afinalcoronal file (FCF) size 80 was reached with an approximate taper of 1 instrument per mm. At this phase, the stepback technique was modified by recapitulating every file used after the MAF in a similar manner to the stepdown and Schilder's (1974) techniques (Fig. 4), avoiding ledge formation and transportation of resin chips into the 'apical foramen'. No irrigation was used during instrumentation. In an attempt to reduce fatigue of the operator's dexterity, which has an influence on the results, only three canals were shaped at a time. Also, in an effort to eliminate most of the debris and to maintain the files centred in the root canals during instrumentation, the resin blocks were placed under a stereomicroscope ( X 17) during instrumentation. ' Zeiss, Wetzlar, Germany.

Evaluation h 1:20 scale was established by projecting the resulting slides over a fixed distance on to a hard projection screen. Three measurements were made at the concave side and another three at the convex side of the canal ( + 0.05 mm) at three different levels: 1, 6 and 11.5 mm from the 'apical foramen' (Fig. 5). The original canal axis served as a reference point for all measurements. The theoretically ideal \-alues of the root canal after instrumentation were: for level 1, 0.30 mm; level 2, 0.55 mm; and level 3,0.80 mm. These values were derived theoretically after having established a MAF of size 30 and a taper of 1 mm per instrument. Such values were given as a comparison unit simulating ideal results. The results obtained with the different instruments were not compared with each other but with the corresponding ideal values. The Duncan test was used for statistical analysis.

Results Level! The convex side was enlarged in almost every case up to twice the idea! shape (Fig. 6a).

B. M. Briseno (S E. Sonmbend

Fig, 4, The sequence of procedures for canal enlargement.

Flexicut and Hedstrom files removed no material in any canal (Table I), Level 2 At this point the shaping tendency was the opposite of that at level 1, Although tbe material removed at the convex side was smaller than ideal with every instrument (Fig, 7a), few statistically significant differences were found (Table I), According to the mean results, Hedstroms, Burns Unifiles and S-Files came nearer to ideal (Fig, 7a), At the concave side a tendency to remove more material than ideal was observed in most cases (Fig, 7b), However, no significant differences were found between most instruments and tbe ideal root canal shape (Table I), CONVEX SIDE

Fig. 5. Diagrammatic representation of the points used for quantitative evaluation. Hedstromfilesin one block showed removal of 0,30 mm. From the mean values, the K-Flex and Flexicut files showed the nearest to ideal results (Fig, 6a), Only Flexicut, Flex-R and K-Flex files showed no statistical differences when compared with the ideal values (Table I). On the contrary, the concave side of the canal showed in almost every case no enlargement at all (Fig, 6b), Burns Unifiles, K-files,

Level 3 At this level the material removed from the convex side was higher than the opposite side (Figs 8a and 8b), Results at the concave side of the root canal were near ideal (Fig, 8b), No significant differences between the ideal shape and any instruments were found on this side (Table I), At the convex side all instruments removed more material than ideal (Fig, 8a), most being statistically significantly higher (Table I), Almost no statistically significant differences were found between the different instruments themselves at all measuring levels. However, when taking the ideal values as

Influence of root canal instruments

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reference points, statistical differences were found in several cases (Table I). Discussion The double exposure method provided enlarged images of root canals which could be clearly elucidated and accurateiy quantified. The method provided a clear view of the areas that were enlarged or remained unchanged

after instrumentation. The use of clear casting resin blocks appears to be valid when compared witb root canals in natural teeth (Lim & Webber 1985), and is of great help for improving our understanding of the behaviour of endodontic instruments in root canals. Most authors (Schilder 1974, Weine et al. 1975, Roane et al. 1985) agree that when enlarging a root cana! the critical point lies at

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B. M. Briseno (S E. Sonnahend

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Fig, 7a, b. the apical foramen, Tiie instrumentation of this part ofthe canat, when a curvature is present, demands great skill. Much attention has been focused on the transportation ofthe apical foramen. On the other hand, little concern has been given to the concave side, which is often not or only barely enlarged at this level (Figs 3a, 3b, 3e and fib); therefore it is inevitable that pulp or necrotic tissue would remain in this area, and this might be one cause of treatment failure. In contrast, at the convex side the elimination of pulp or necrotic tissue would be ensured; however, it is at this point

where apical transportation often occurs. With the technique employed in this research, most ofthe apicai transportation was observed microscopically to be done with the cutting edges and not with the tip of the instrument, Weine (1982) recommends enlarging the apical portion of the root canal using two to three instruments after having established the IAF, Our observations showed that it is often not the tip of an instrument which provides resistance during instrumentation, but the cutting edges at diflferent levels. This means

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Fig, 8a, b. that the apical foramen is not being enlarged at this point and therefore the criteria for selecting tbe IAF and MAF vary according to individual anatomical and morphological considerations, AU the instruments tested proved to have a straightening, elbowing or transporting effect at the three measuring levels, A canal straightening tendency could be clearly observed at level 2 {Figs 3a, 3b, 3c, 7a and 7b), Only the Flexicnt and Flex-Rfilesdemonstrated a relatively balanced removal of material between

the concave and convex side at this level (Figs 3a, 3b, 7a and 7b). The lack of significant differences between the instruments themselves is in contrast witb studies by other workers (Roane et al. 1985, Powellffa/, 1986,Soutbardrta/. 1987,PoweU et al. 1988). A statistical difference was found between the ideal root canal shape and tbe concave or convex side at every measuring level (Table I), Thesefindingsindicate that tbe ideal was unattainable. Our research partly supports that conducted by ElDeeb & Boraas (1985),

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B. M. Brisem !S E. Smnabend Table I. Statistical results for resin removal at the three measuring points Level 1 Instrument type Reamer K-file He

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

Nine endodontic instruments from different manufacturers (Reamers, K-files, Hedstrom files, K-Flex files, Flexofiles, S-files, Burns Unifiles, Flexicu...
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