Internatioml Bndodontic louma! (1992) 2 5 , 5 7 - 6 6
Comparison of sixfilesto prepare simulated root canals. Part 1 M. A. 0, AL-OMARI, P, M. H. DUMMER & R. G, NEWCOMBE* Department of Conservative Dentistry, and ^Department of Medical Computing and Statistics, University of Wales College of Medicine, Cardiff, UK
Summary A total c^ 300 simulated root canals cX various angles and positions tf curvature in clear resin blocks were [separed by hand using eith^- K-files, K-Flex files, Ftesofiles. Flex-R files, Hedstromfilesor Unifiles, Eachfiletype was used to prepare 50 canals em^oying a linear filing motion and an anticurvature stepback technique. Part 1 of this two-part report describes the efiScacy ofthe files in terms of preparation time, instrument feilure, loss of canal length and weight loss from the blocks. Two-way analysis of variance ccmfinned that there was significant variation for each parameter between instruments, between canal t)rpes, and with interaction between instnmients and canal types. Overall, pr^mration with Hedstrom files was significantly quicker dian with any otherfile,whilst preparation with K-files and K-Flex files took significantly loiter. Fracture and deformation of instruments occurred substantially less dten with Flex-R and Hedstrom files, but significantly more often with Unifiles, Loss of working distance occurred with all file types, but was significantly greater in canals prepared with K-files, Unifiles and Hedstrnnfileswere responsible for significantly more weight toss than the other files, whilst K-files {mtduced significantly less weight loss. Canals with rough undulating walls were created most (rfiten by Hedstrom files and Unifiles. Overall, under the conditions of this study, Flexofiles, Flex-R files and Hedstromfilesappeared to be substantially more effective than K-files, K-Flexfilesand Unifiles,
cutting tip and lack of flexibility, is not the ideal instrument for shaping root canals. Indeed, a number of reports have described how K-files produce zips, elbows and other canal aberrations with disappointing regularity (Hoskinson 1982, ElDeeb & Boraas 1985, Alodeh etfli.19 8 9). The venerable Hedstromfilehas been shown to produce fewer and less pronounced defects (ElDeeb & Boraas 1985, Alodeh & Dummer 1989) and, together with its known cutting efficiency (Machian et d. 1982), would seem to be a more than adequate alternative. However, its frailty, particularly in the smaller sizes, often precludes its use in narrow curved canals. Although a variety of new instruments have been designed, their potenticd to shape canals effectively has not been demonstrated fully, as most reports have been limited to inclusion of only one or at best two new instruments (ElDeeb & Boraas 1985, Powell et oJ. 1988, Sabala etfli.1988, Sepic et aJ. 1989). This has made it impcKsible to compEire objectively the ability of all the instruments currently aveiilable. The aim of this study was to ass^s and compare the efficiency of six different files during the shaping of simulated root canals in clear resin blocks, A range of canal types were used in order to determine whether the angle and position of canal curvature had any influence on file performance.
Materials and methods Construction of simulated canals
Keywords: endodontics,files,root canals, shaping.
Introduction It is becoming increasingly obvious that the traditional K-file, with its square cross-sectional design, sharp Correspondence: Dr P. M. K. Dummer, Department oS Conservative Dentistry, Dental School, University of Wales CoDege of Medicine, Hea& Park, Cardiff CF4 4XY, UK.
A total of 3 00 simulated root canals in clear plastic blocks were constructed (Dummer et al, 1991). Annealed silver points (size 20) were used as templates to form the canals and these were embedded in a self-polymerizing resin (Stycast Resin 1266; Hitek Electronic Materials Ltd, Scunthorpe, UK) and then removed when the resin had fully polymerized to leave narrow channels of the same shape and length as the points. Clear spectrophotometer cuvette were i^ed as moulds to retain the resin. Using a canal fonner, the silver points were precurved prior to 57
58
M. A. O. Al-Omari, P, M, H. Dummer &R.G. Newcombe
Length- 16 mm No c m s
Lwigth - 1 7 rtHti Oegra« of cuve - 40° Position of c w v a 12 mmftomorifice
Lwigth- 17nnm De^«e of curve - 40° Position of curve8 nun frofn ofifico
Length -16.5 mm Degree of ciBve-20° Position of curve12 mm from orifice
Length - 1 6 . 5 mm i}e^«e of airve - 20° Position af curve 8 mfn from orifice
Fig. 1. Diagrammatic representation of the various canal types used in the study.
use. The designated position of the curve from the orifice and the angle of ctirvature were imparted to the annealed points by sliding them into narrow channels cut in a block of clear perspex. The channels were accurately prepared to the specific shap« outlined in Fig, 1, A total of 60 silver points of each shape were prepared in this way to give a range of canals, from those with mild curves to those with severe curves. The position of the beginning ofthe curves was either 8 or 12 mm from the eventual orifice ofthe canals. The method of assessment of canal ctirvature was essentially the same as that described by Schneider (1971). The radius ofthe arc that comprised the curved portion of the canals was 16 mm, Figtire 2 shows the various canal types within the clear resin blocks, Pre^ration of simulated canak All canals were prepared by hand using either K-files (Kerr, Romulus, Michigan, USA), K-Flex files (Kerr, Romulus, Michigan, USA), Flexofiles (Maillefer, Ballaigues, Switzerland), Flex-R files (Union Broach Corp, Long
Island City, NY, USA), Hedstrom files (Micro-Mega Ltd, Geneva, Switzerland), or Unifiles (Dentsply, Milford, Itelaware, USA), Ten canals of each shape were prepared with each file t}rpe, making a total of 300 canals in all. This degree of replication proved more than adequate to reveal highly significant differences between instruments and between canal shapes, A standardized stepback enlargement technique tising anticurvature filing was adopted for eachfileand was performed by one operator. AD canals were prepared well short of their actual end points: straight canals were prepared to a length of 16 mm, the 20° canals to a length of 16.5 mm and the 40° canals to a length of 17 mm. File sizes 15 to 2 5 were used to prepare only one canal, whilst larger sizes were used to prepare three canals if possible before being discarded. Files that became distorted or fractured before scheduled withdrawal were immediately replaced and the fact recorded. During the preparation procedure each resin block was placed in a holder to aid the handling of the block and to ensure that the process was carried out with purely tactile sensation. The direction of the curve and the shape of each canal was always known. Straight canals. The objective of the preparation for straight canals was to enlarge the end point to size 40 at a distance of 16 mm from the oriflce, and to stepback and fleure the remainder ofthe canal. Initially a size 15filewas introduced to the full working distance and then used in a simple in/out linear filing or rasping motion in a circumferential manner around the walls. No rotation of the files was performed. Use of the size 15 instrument continued imtii a size 20 file could be placed at the working distance without force. Apical preparation continued in a similar manner withfllesizes 20 to 3 5, tintii a size 40 file was able to reach the full working distance. Copious irrigation with water was used throughout the proc^ure, and was introduced with a sjringe and needle. Irrigant was used initially to moisten the canals and then between each instmment; a total volume of 50 ml was used per canal. The remaining part of each canal was fiared using a stepback technique and circumferential filing. At first a size 45filewas introduced 1 mm short ofthe full working distance and used in a linear filing action. This was followed byfilesizes 50, 5 5 and 60, which were used 2,3 and 4 mm short of the working distance, respectively. Recapitulation was c a r r i ^ out between steps with a size 40 file and copious irrigation was used throughout. Curved canals. The objective of the preparation for curved canals was to enlarge the end point to size 3 5 for
Preparation of simulated root canals. Part 1
59
Fig, 2, Examples of clear resin blocks containing the various cana! types. From the left these are: 20", 12 mm: straight: 40', 8 mm: 40', 12 mm: 20'", 8 mm.
the 20° curves and size 30 for the 40° curves, and to stepback and flare the remainder of the canal. The apical preparation technique was similar to that outlined above for straight canals, except that all files were precurved to the appropriate shape prior to use. Flaring of the remaining canal was again carried out with a stepback technique, but on this occasion using anticurvature filing (Abou-Rass et al 1980). Copious irrigation and recapitulation were performed as described previously.
Assessment of canal preparation Preparation time. The time taken to enlarge each canal was recorded in minutes and seconds. It included only active instrumentation, and not irrigation time or the changing of files. Instrument failure. Throughout the study a record was kept of the numbers and sizes of instruments that fractured or became permanently deformed during use. Loss of working distance. Following preparation, the final length of each canal was determined and recorded to the nearest 0.5 mm. The final length of the canal was then subtracted from the original length to give the loss of working distance. In the case of straight canals, positive values indicate a gain of working distance.
Loss of weight. Before and after the preparation procedure each resin block was weighed to 10"* g precision. Loss of weight was calculated bj' subtracting the post-preparation weight from tbe pre-preparation weight. Smoothness of canal walls. A subjective assessment of the smoothness of canal walls was made following preparation. A simple scoring sj'steoi was employed consisting of a score of zero for a smooth ivali and a score of one for a rough wall displaying a rippled effect. Recording, storage and analysis of data. Data were
recorded directly on coding sheets and then keyed into and stored in a VAX VMS mainframe computer. Following error and range checks the data were analysed using MiNiTAB. an interactive statistics package. Results Preparation time The time taken to complete the preparation of the simulated canals with the various hand instruments is shown Ln Table 1. Each combination of instrument and preset shape is represented by the mean of 10 replicate specimens. Two-way analysis of variance indicated highly significant variation (P< 0.001) in preparation time betiveen instruments and between canal types. The interaction betm'een instrument and canal type was
60
M. A 0. Al-Omari, P. M. H. Dummer & R. G. Newcombe
Table 1. The mean preparatioa time (min) for each category
Comparison of sixfilesto prepare simulated root canals. Part 1 M. A. 0, AL-OMARI, P, M. H. DUMMER & R. G, NEWCOMBE* Department of Conservative Dentistry, and ^Department of Medical Computing and Statistics, University of Wales College of Medicine, Cardiff, UK
Summary A total c^ 300 simulated root canals cX various angles and positions tf curvature in clear resin blocks were [separed by hand using eith^- K-files, K-Flex files, Ftesofiles. Flex-R files, Hedstromfilesor Unifiles, Eachfiletype was used to prepare 50 canals em^oying a linear filing motion and an anticurvature stepback technique. Part 1 of this two-part report describes the efiScacy ofthe files in terms of preparation time, instrument feilure, loss of canal length and weight loss from the blocks. Two-way analysis of variance ccmfinned that there was significant variation for each parameter between instruments, between canal t)rpes, and with interaction between instnmients and canal types. Overall, pr^mration with Hedstrom files was significantly quicker dian with any otherfile,whilst preparation with K-files and K-Flex files took significantly loiter. Fracture and deformation of instruments occurred substantially less dten with Flex-R and Hedstrom files, but significantly more often with Unifiles, Loss of working distance occurred with all file types, but was significantly greater in canals prepared with K-files, Unifiles and Hedstrnnfileswere responsible for significantly more weight toss than the other files, whilst K-files {mtduced significantly less weight loss. Canals with rough undulating walls were created most (rfiten by Hedstrom files and Unifiles. Overall, under the conditions of this study, Flexofiles, Flex-R files and Hedstromfilesappeared to be substantially more effective than K-files, K-Flexfilesand Unifiles,
cutting tip and lack of flexibility, is not the ideal instrument for shaping root canals. Indeed, a number of reports have described how K-files produce zips, elbows and other canal aberrations with disappointing regularity (Hoskinson 1982, ElDeeb & Boraas 1985, Alodeh etfli.19 8 9). The venerable Hedstromfilehas been shown to produce fewer and less pronounced defects (ElDeeb & Boraas 1985, Alodeh & Dummer 1989) and, together with its known cutting efficiency (Machian et d. 1982), would seem to be a more than adequate alternative. However, its frailty, particularly in the smaller sizes, often precludes its use in narrow curved canals. Although a variety of new instruments have been designed, their potenticd to shape canals effectively has not been demonstrated fully, as most reports have been limited to inclusion of only one or at best two new instruments (ElDeeb & Boraas 1985, Powell et oJ. 1988, Sabala etfli.1988, Sepic et aJ. 1989). This has made it impcKsible to compEire objectively the ability of all the instruments currently aveiilable. The aim of this study was to ass^s and compare the efficiency of six different files during the shaping of simulated root canals in clear resin blocks, A range of canal types were used in order to determine whether the angle and position of canal curvature had any influence on file performance.
Materials and methods Construction of simulated canals
Keywords: endodontics,files,root canals, shaping.
Introduction It is becoming increasingly obvious that the traditional K-file, with its square cross-sectional design, sharp Correspondence: Dr P. M. K. Dummer, Department oS Conservative Dentistry, Dental School, University of Wales CoDege of Medicine, Hea& Park, Cardiff CF4 4XY, UK.
A total of 3 00 simulated root canals in clear plastic blocks were constructed (Dummer et al, 1991). Annealed silver points (size 20) were used as templates to form the canals and these were embedded in a self-polymerizing resin (Stycast Resin 1266; Hitek Electronic Materials Ltd, Scunthorpe, UK) and then removed when the resin had fully polymerized to leave narrow channels of the same shape and length as the points. Clear spectrophotometer cuvette were i^ed as moulds to retain the resin. Using a canal fonner, the silver points were precurved prior to 57
58
M. A. O. Al-Omari, P, M, H. Dummer &R.G. Newcombe
Length- 16 mm No c m s
Lwigth - 1 7 rtHti Oegra« of cuve - 40° Position of c w v a 12 mmftomorifice
Lwigth- 17nnm De^«e of curve - 40° Position of curve8 nun frofn ofifico
Length -16.5 mm Degree of ciBve-20° Position of curve12 mm from orifice
Length - 1 6 . 5 mm i}e^«e of airve - 20° Position af curve 8 mfn from orifice
Fig. 1. Diagrammatic representation of the various canal types used in the study.
use. The designated position of the curve from the orifice and the angle of ctirvature were imparted to the annealed points by sliding them into narrow channels cut in a block of clear perspex. The channels were accurately prepared to the specific shap« outlined in Fig, 1, A total of 60 silver points of each shape were prepared in this way to give a range of canals, from those with mild curves to those with severe curves. The position of the beginning ofthe curves was either 8 or 12 mm from the eventual orifice ofthe canals. The method of assessment of canal ctirvature was essentially the same as that described by Schneider (1971). The radius ofthe arc that comprised the curved portion of the canals was 16 mm, Figtire 2 shows the various canal types within the clear resin blocks, Pre^ration of simulated canak All canals were prepared by hand using either K-files (Kerr, Romulus, Michigan, USA), K-Flex files (Kerr, Romulus, Michigan, USA), Flexofiles (Maillefer, Ballaigues, Switzerland), Flex-R files (Union Broach Corp, Long
Island City, NY, USA), Hedstrom files (Micro-Mega Ltd, Geneva, Switzerland), or Unifiles (Dentsply, Milford, Itelaware, USA), Ten canals of each shape were prepared with each file t}rpe, making a total of 300 canals in all. This degree of replication proved more than adequate to reveal highly significant differences between instruments and between canal shapes, A standardized stepback enlargement technique tising anticurvature filing was adopted for eachfileand was performed by one operator. AD canals were prepared well short of their actual end points: straight canals were prepared to a length of 16 mm, the 20° canals to a length of 16.5 mm and the 40° canals to a length of 17 mm. File sizes 15 to 2 5 were used to prepare only one canal, whilst larger sizes were used to prepare three canals if possible before being discarded. Files that became distorted or fractured before scheduled withdrawal were immediately replaced and the fact recorded. During the preparation procedure each resin block was placed in a holder to aid the handling of the block and to ensure that the process was carried out with purely tactile sensation. The direction of the curve and the shape of each canal was always known. Straight canals. The objective of the preparation for straight canals was to enlarge the end point to size 40 at a distance of 16 mm from the oriflce, and to stepback and fleure the remainder ofthe canal. Initially a size 15filewas introduced to the full working distance and then used in a simple in/out linear filing or rasping motion in a circumferential manner around the walls. No rotation of the files was performed. Use of the size 15 instrument continued imtii a size 20 file could be placed at the working distance without force. Apical preparation continued in a similar manner withfllesizes 20 to 3 5, tintii a size 40 file was able to reach the full working distance. Copious irrigation with water was used throughout the proc^ure, and was introduced with a sjringe and needle. Irrigant was used initially to moisten the canals and then between each instmment; a total volume of 50 ml was used per canal. The remaining part of each canal was fiared using a stepback technique and circumferential filing. At first a size 45filewas introduced 1 mm short ofthe full working distance and used in a linear filing action. This was followed byfilesizes 50, 5 5 and 60, which were used 2,3 and 4 mm short of the working distance, respectively. Recapitulation was c a r r i ^ out between steps with a size 40 file and copious irrigation was used throughout. Curved canals. The objective of the preparation for curved canals was to enlarge the end point to size 3 5 for
Preparation of simulated root canals. Part 1
59
Fig, 2, Examples of clear resin blocks containing the various cana! types. From the left these are: 20", 12 mm: straight: 40', 8 mm: 40', 12 mm: 20'", 8 mm.
the 20° curves and size 30 for the 40° curves, and to stepback and flare the remainder of the canal. The apical preparation technique was similar to that outlined above for straight canals, except that all files were precurved to the appropriate shape prior to use. Flaring of the remaining canal was again carried out with a stepback technique, but on this occasion using anticurvature filing (Abou-Rass et al 1980). Copious irrigation and recapitulation were performed as described previously.
Assessment of canal preparation Preparation time. The time taken to enlarge each canal was recorded in minutes and seconds. It included only active instrumentation, and not irrigation time or the changing of files. Instrument failure. Throughout the study a record was kept of the numbers and sizes of instruments that fractured or became permanently deformed during use. Loss of working distance. Following preparation, the final length of each canal was determined and recorded to the nearest 0.5 mm. The final length of the canal was then subtracted from the original length to give the loss of working distance. In the case of straight canals, positive values indicate a gain of working distance.
Loss of weight. Before and after the preparation procedure each resin block was weighed to 10"* g precision. Loss of weight was calculated bj' subtracting the post-preparation weight from tbe pre-preparation weight. Smoothness of canal walls. A subjective assessment of the smoothness of canal walls was made following preparation. A simple scoring sj'steoi was employed consisting of a score of zero for a smooth ivali and a score of one for a rough wall displaying a rippled effect. Recording, storage and analysis of data. Data were
recorded directly on coding sheets and then keyed into and stored in a VAX VMS mainframe computer. Following error and range checks the data were analysed using MiNiTAB. an interactive statistics package. Results Preparation time The time taken to complete the preparation of the simulated canals with the various hand instruments is shown Ln Table 1. Each combination of instrument and preset shape is represented by the mean of 10 replicate specimens. Two-way analysis of variance indicated highly significant variation (P< 0.001) in preparation time betiveen instruments and between canal types. The interaction betm'een instrument and canal type was
60
M. A 0. Al-Omari, P. M. H. Dummer & R. G. Newcombe
Table 1. The mean preparatioa time (min) for each category
