0099-2399/92/1805-0232/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists
Printed in U.S.A.
VOL, 18, NO. 5, MAY 1992
Effect of Precurving on the Performance of Endosonic K Files P. J. Lumley, BDS, MDentSc, FDSRCPS, and A. D. Walmsley, BDS, MSc, PhD, FDSRCPS
When a straight file is placed in a curved canal it is constrained and assumes a "load." This load may prevent the endosonic file from oscillating and reduce the effectiveness of the system (9, 10). Walmsley and Williams (6) suggested that this type of constraint may be minimized by first shaping the coronal and middle parts of the root canal, thus allowing the file tip to oscillate more freely. This should result in greater debridement of the apical canal space. Such a "step-down" approach (11) is known to be of benefit with some classes of endosonic instrumentation (12). However, it cannot be used always because of danger of perforation in curved roots. Another approach to the problem of constraint within curved root canals could be to precurve the endosonic files, although the effect of this procedure on their oscillatory pattern is not known. In curved canals the production of elbows and zips (13) causes problems which can be increased with endosonic instrumentation (9). In curved root canals #15 endosonic files can be used safely (14, 15) but #20 and 25 produce straightening of curved root canals in natural teeth (16). It is unclear in the latter study whether the #20 and 25 files were precurved in a similar fashion to the #15 file. This investigation assessed the effect of precurving endosonic files on changes in their performance. The patterns of the files oscillating unconstrained in air and oscillating constrained in Endovue blocks plus in a natural tooth were evaluated.
This study compared the performance of precurved and straight endosonic files. Size 15, 20, and 25 endosonic K files were precurved to different degrees (20 to 90 degrees) and the resultant oscillatory pattern showed no significant difference compared with corresponding straight files. Endovue blocks were prepared with either a # 15, 20, or 25 endosonic file which was either straight or precurved. Those blocks prepared with precurved files had a continuous taper while blocks prepared with straight files had constrictions along their lengths. Finally, a curved root of a human natural tooth had windows prepared along its length so that the oscillatory pattern of the file could be observed. The precurved file oscillated more freely than a straight file as observed by the presence of antinodes along the file and the accumulation of dentin chips within the canal. The results of this study suggest that it is advantageous to precurve endosonic files before using them in curved canals.
Since the introduction of endosonic instruments in the late 1970's and early 1980's their use has become an established part of endodontic practice (1,2). Claimed advantages include a faster and more efficient canal preparation together with increased cleaning from the associated presence of microstreaming within the irrigant (3, 4). Such instruments were developed from the ultrasonic scaler which initially had a file attached to the end of the scaling tip (5). Current systems are, however, far more sophisticated devices with an endosonic driver supplied with a selection of files. When activated the driver vibrates in a longitudinal manner and this initiates a transverse mode of action in the file which is attached at about 70 degrees to the driver. Such an oscillation may often prove to be inefficient as both the tip and the mid-third of the file are prone to constraining influences when a load is applied to the system. Furthermore, the oscillation may change depending upon where the constraining influence is applied (6). Some studies have shown that endosonic files may not be effective in small curved canals where the file could be prevented from oscillating (7, 8).
MATERIALS AND METHODS
Oscillatory Pattern The outside plastic sleeve of an endosonic driver (CaviEndo ultrasonic unit; C. D. Caulk, Dentsply, York, PA) was clamped rigidly to a stand so that the inner metal stack of the driver could easily be seated within the plastic sleeve. A file was inserted in the head of the endosonic driver and the tip was observed with the aid of a microscope at a magnification of x 100. A strong directional light was shone onto the length of the file so that a small point of light could be seen reflecting off a cutting edge. When the file was activated, the small spot of light became elongated into a horizontal line which represented the amplitude of the file. The displacement amplitude was taken as half the peak to peak displacement of the file
(6). 232
Vol. 18, No. 5, May 1992
F~G 1. Diagram showing the method of measurement used forthe Endovue blocks.
Displacement amplitude measurements were made of straight endosonic # 15, 20, and 25 K files. The measurements were made at the tip and at intervals of 1 m m along the length of the file in order to look at any change in nodal and antinodal positions. Five measurements were made at each point. The files were then removed and precurved; the degree of curvature being measured by drawing a tangent of the file curvature and measuring the angle. The displacement amplitude measurements of each endosonic K file were repeated for different degrees of curvature which increased from 20 to 90 degrees.
Endovue Blocks Thirty Endovue blocks were chosen with canals of matched curvature and were split into 15 pairs. Each pair was prepared with hand K-Flex files so that either a #15, 20, or 25 file could freely pass to the end of each simulated canal. The blocks were then prepared with the same size endosonic file as the last file which had been used for hand preparation. One block of the pair was prepared with a straight endosonic file and the other with a file precurved to the shape of the canal. The endosonic preparation was carried out for 2 min in each canal in an up and down and circumferential manner. Water
Precurving Endosonic Files
233
FtG 2. Photograph of mesiobuccal root of upper first molar with windows cut in it to the level of the root canal.
irrigation was used continuously with a predetermined flow rate of 20 ml/min. In addition five blocks were prepared using the # 15, 20, and 25 files in series for 2 min each with continuous irrigation, giving a total time of preparation of 6 min. As before, one block was prepared with precurved files and the other with straight files; however, in these canals the init,.'al enlargement was only to a # 15 K-Flex file. An additional five blocks were prepared in series using straight endosonic files inserted in the driver but used without ultrasonic activation. The width of the canals was then measured using a light microscope (Wild 3M stereomicroscope; 3M Center, St. Paul, MN) at magnification x25. These widths were measured at the apex and at 1.5-mm intervals along the prepared canal. The width was measured perpendicular to the canal walls (Fig. 1). In Vitro Oscillation In the third part of the study an upper molar tooth was selected with a curved mesiobuccal root. Windows were cut in the sides of the root at 3-mm intervals to the level of the root canal (Fig. 2). This enabled a file placed within the canal to be observed under the light microscope. The root canal was enlarged to a #25 K-Flex file with hand instrumentation which allowed an endosonic file # 15 to be placed freely. The
234
Lumley and Walmsley
Journal of Endodontics
TABLE 1. Displacement amplitude of the file in air (in ~m) at three-quarters full power setting* Size 15 Straight 20 degrees 45 degrees 90 degrees Analysis of variance F value p
62 62 62 61
(__0.5) (+_0,5) (+_0.5) (+_2)
0.96 >0.01
Size 20 63.5 63.5 63 61.25 3,41 >0.05
(+_0.5) (+_0.5) (+_0.5) (+_0.5)
are two narrowings in the canal produced by the files. The first is at a distance of 3 mm from the apex for all files and the second is 7.5 m m from the apex for #15 and 20 but 9 m m for #25 file. Figure 4 shows the width of the canal against increasing distance from the apex where precurved files were used to instrument the canal. It can be seen that the width increases in a continuous manner with increasing canal length for the blocks prepared with the precurved files. The two narrowings are most noticeable in the canals that were prepared in series with straight endosonic files when ultrasonic preparation was of 6-min duration (Fig. 5). The canals prepared with the precurved files in series, however, show a continuous taper. The canals prepared by straight endosonic files used by hand all showed a continuous taper (Fig. 5).
Size 25 43 43 43 42
(+_2.5) (+_2.5) (+_2.5) (+_0.5)
0.13 >0.01
* The results of analysis of variance are shown for each column (five readings were t a k e n in e a c h cell error = 1 SD)
oscillatory pattern of a straight and a precurved endosonic file was observed under light microscopy. Straight and precurved files were interchanged to avoid bias brought about by further enlargement of the canal.
Oscillation in the Root Canal
Observation of the straight endosonic K file in the curved root canal showed little or no evidence of oscillation at the tip which lay against the outer wall of the canal; however, oscillation could be seen more coronally. The file precurved to the shape of the root canal lay more centrally and oscillation could be seen at the tip and along its length. The nodal and antinodal points were found to correspond with those noted in air and the displacement amplitude was the same. However, when the files were moved in an up and down manner, as they were when used in preparing the blocks, the oscillation was found to change. The tip of the straight file remained along the wall of the canal but had a greater tendency to oscillate as it moved more coronally. This oscillation was not, however, in a regular nodal and antinodal pattern, rather it was haphazard. The precurved file at all times oscillated more freely. However, the displacement amplitude did vary, ranging from a tendency to become constrained to an increase in displacement amplitude limited by the width of the canal. This change in displacement amplitude was also associated with inconsistency in the nodal and antinodal position along the file.
RESULTS Oscillation in Air
Table 1 shows the difference in the oscillatory pattern of the different sizes of files and the effect of degree of curvature. The displacement amplitudes were not significantly different as shown by analysis of variance regardless of degree of curvature of the file (p > 0.05). Neither the characteristic oscillatory pattern of the file nor the position of nodal and antinodal points changed regardless of precurving. Whether the curve was positioned at a node or antinode did not affect the characteristic oscillatory pattern or displacement amplitude. Excessive oscillation of the file was not a feature even with the 90-degree curvature. Endovne Blocks
Figure 3 shows the width of the canals prepared with straight files against increasing distance from the apex. There
Straight
. . . . . . .
#25 --#20
#15
,,t ..... t ..... ..... I Width
,"
I
L
.-..
T
1_r
r
(ram) .4
T
D i s t a n c e from Apex
(ram)
FIG 3. Graphical representation of the width of the canals prepared with straight files plotted against distance from the apex (n = 5, error bars = _+1 SD).
Vol. 18, No. 5, May 1992
Precurving Endosonic Files
235
Precurved
#25
. . . . . . .
--#20 -
-
#
1
5
-e
Width -
(ram) .4
Distance
from Apex
(sam)
FIG 4. Graphical representation of the width of the canals prepared with precurved files plotted against distance from the apex (n = 5, error bars
= ___1so). Series
I Hand s s
/
p
Straight Precurved
.6
Width (ram) ,4
Distance from Apex
(ram)
FiG 5. Graphical representation of the width of the canals prepared with straight or precurved files in series plotted against distance from the apex (n = 5, error bars = +1 SD).
DISCUSSION The results of this study have shown that there is no significant difference (p > 0.05) in the oscillatory pattern of precurved endosonic files compared with straight endosonic files. Therefore, precurving of files does not affect the oscillatory properties of the file and this suggests that there may be many advantages associated with the use of precurved files in curved canals. The endovue block study confirmed these advantages. A continuous taper is apparent in the blocks which were prepared with precurved files. The blocks prepared with the straight files show narrowings part of the way down the canal and a continuous taper is not present. This feature is consistent for the blocks prepared with the 15, 20, and 25 files,
respectively. It becomes more noticeable when one looks at the blocks prepared in series with #15, 20, and 25. These blocks were ultrasonically prepared for 6 min in total as opposed to 2 min for the blocks prepared with one size of file. However, the blocks prepared with straight endosonic files used by hand showed a continuous taper. The combination of a straight file and ultrasonic energy apparently caused narrowings in the canal which were not as pronounced when the files were precurved. The sizes or the apical 1.5 mm of the preparation of the blocks prepared with straight endosonic files in series whether activated or not were the same, thus indicating that the files may have been constrained. This was confirmed in the extracted tooth study. Any metallic object that is strained has a degree of memory. A straight file that sits within a curved
236
Lumleyand Walmsley
canal is made to curve but contains forces that tend to straighten it. This did not result in uneven shaping of the canal with the hand-operated file. However, the activated straight endosonic files did produce irregularities in canal shape. The narrowings were at 3 m m and between 7.5 and 9 mm from the apex of the canal. These are similar to the positions to where nodal points occur in air. However, the file was moved up and down during the preparation and one would not expect the narrowings to be in the same place as nodes in air. This is difficult to explain; the authors feel that the differing degrees of constraint that were noted in the extracted teeth along with the fact that the straight file lay against one side of the canal may have resulted in this uneven removal. The canals prepared with the precurved files showed more even preparation. The size of the apical preparation was smaller than with straight endosonic files with no ultrasonic activation. A freely oscillating file should produce larger apical preparation. This is also difficult to explain; the authors feel that the larger size of the apical preparation with the straight files is due to the file straightening causing enlargement on the outside of the curve. The precurved files being more centrally placed produced more even preparation. The canals prepared with the files used in series produced greater enlargement of the canals than when individual files were used. This was to be expected as the blocks were prepared for a longer period of time. In this study precurving of the files produced even shaping even in the larger sizes of 20 and 25, however it must be noted that it is easier to precurve a file to a canal that can be seen in a resin block than to a tooth. An argument against the benefits of precurving files is that root canals rarely have just one plane of curvature and any file precurved to a radiograph is only curved to a twodimensional picture. Therefore, it is possible that a precurved
Journal of Endodontics
file may in fact be constrained. Although this may be true in some teeth, our results show that precurving of the endosonic file will result in a looser fit and constraint will at least be reduced. Dr. Lumley and Dr. Walmsley are members of the Department of Restorative Dentistry, The Dental School, St. Chad's Queensway, Birmingham B4 6NN, United Kingdom.
References 1. Martin H, Cunningham WT. Endosonics--the ultrasonic synergistic system of endodontics. Ended Dent Traumato11985;1:201-6. 2. Nehammer CF, Stock CJR. Preparation and filling of the root canal. Br Dent J 1985;158:285-91. 3. Cunningham WT, Martin H, Pelleu GB, Stoops DE. A comparison of antimicrobial effectiveness of endosonic and hand root canal therapy. Oral Surg 1982;54:238-41. 4. Ahmad M, Pitt Ford TR, Crum LA. Ultrasonic debridement of root canals: An insight into the mechanisms involved. J Endodon 1987;13:93-101. 5. Martin H. Ultrasonic disinfection of the root canal. Oral Surg 1976;42: 92-9. 6. Walmsley AD, Williams AR. Effects of constraint on the oscillatory pattern of endosonic files. J Endodon 1989;15:189-94. 7. Langeland K, Liao K, Pascon EA. Work saving devices in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985;11:499-510. 8. Reynolds M, Walton R, Madison S, Krell K, Rittman B. An in vitro histological comparison of the step-beck, sonic, and ultrasonic instrumentation techniques in small curved canals. J Endedon 1987;13:307-14. 9. Walmsley AD. Ultrasound and root canal treatment: the need for scientific evaluation. Int Ended J 1987;20:105-11. 10. Lumley PJ, Walmsley AD, Laird WRE. Ultrasonic instruments in dentistry: 2. Endosonics. Dent Update 1988; 15:362-9. 11. Goerig AC, Michelich RJ, Schultz HH. Instrumentation of root canals in molars using the step-down technique. J Endodon 1982;8:550-4. 12. Murgel C, Walmsley AD, Walton RE. The efficacy of step down procedures during endosonic instrumentation. J Endodon 1991 ;17:111-5. 13. Weine FS. Endodontic therapy. 3rd ed. St. Louis: CV Mosby, 1982. 14. Chenail BL, Teplitsky PE. Endosonics in curved root canals. J Endodon 1988;11:369-74. 15. Tang MPF, Stock CJR. The effects of hand, sonic and ultrasonic instrumentation on the shape of curved root canals. Int Ended J 1989;22:5563. 16. Chenail BL, Teplitsky PE. Endosonics in curved root canals. Part I1. J Endodon 1988;22:55-63.
You Might Like to Know The use of sodium hypochlorite has a venerable history in endodontics. There is a very different and unusual application of this preparation by tattoo artists. These practitioners tattoo over unwanted designs with hypochlorite in an attempt to remove the offending dermal graffiti. By inducing a partial thickness burn, the hypochlorite produces a fair result. The fact remains that there is no known method of removing tattoos which does not result in permanent scarring (BMJ 303:380).
Cosby Newel/
Printed in U.S.A.
VOL, 18, NO. 5, MAY 1992
Effect of Precurving on the Performance of Endosonic K Files P. J. Lumley, BDS, MDentSc, FDSRCPS, and A. D. Walmsley, BDS, MSc, PhD, FDSRCPS
When a straight file is placed in a curved canal it is constrained and assumes a "load." This load may prevent the endosonic file from oscillating and reduce the effectiveness of the system (9, 10). Walmsley and Williams (6) suggested that this type of constraint may be minimized by first shaping the coronal and middle parts of the root canal, thus allowing the file tip to oscillate more freely. This should result in greater debridement of the apical canal space. Such a "step-down" approach (11) is known to be of benefit with some classes of endosonic instrumentation (12). However, it cannot be used always because of danger of perforation in curved roots. Another approach to the problem of constraint within curved root canals could be to precurve the endosonic files, although the effect of this procedure on their oscillatory pattern is not known. In curved canals the production of elbows and zips (13) causes problems which can be increased with endosonic instrumentation (9). In curved root canals #15 endosonic files can be used safely (14, 15) but #20 and 25 produce straightening of curved root canals in natural teeth (16). It is unclear in the latter study whether the #20 and 25 files were precurved in a similar fashion to the #15 file. This investigation assessed the effect of precurving endosonic files on changes in their performance. The patterns of the files oscillating unconstrained in air and oscillating constrained in Endovue blocks plus in a natural tooth were evaluated.
This study compared the performance of precurved and straight endosonic files. Size 15, 20, and 25 endosonic K files were precurved to different degrees (20 to 90 degrees) and the resultant oscillatory pattern showed no significant difference compared with corresponding straight files. Endovue blocks were prepared with either a # 15, 20, or 25 endosonic file which was either straight or precurved. Those blocks prepared with precurved files had a continuous taper while blocks prepared with straight files had constrictions along their lengths. Finally, a curved root of a human natural tooth had windows prepared along its length so that the oscillatory pattern of the file could be observed. The precurved file oscillated more freely than a straight file as observed by the presence of antinodes along the file and the accumulation of dentin chips within the canal. The results of this study suggest that it is advantageous to precurve endosonic files before using them in curved canals.
Since the introduction of endosonic instruments in the late 1970's and early 1980's their use has become an established part of endodontic practice (1,2). Claimed advantages include a faster and more efficient canal preparation together with increased cleaning from the associated presence of microstreaming within the irrigant (3, 4). Such instruments were developed from the ultrasonic scaler which initially had a file attached to the end of the scaling tip (5). Current systems are, however, far more sophisticated devices with an endosonic driver supplied with a selection of files. When activated the driver vibrates in a longitudinal manner and this initiates a transverse mode of action in the file which is attached at about 70 degrees to the driver. Such an oscillation may often prove to be inefficient as both the tip and the mid-third of the file are prone to constraining influences when a load is applied to the system. Furthermore, the oscillation may change depending upon where the constraining influence is applied (6). Some studies have shown that endosonic files may not be effective in small curved canals where the file could be prevented from oscillating (7, 8).
MATERIALS AND METHODS
Oscillatory Pattern The outside plastic sleeve of an endosonic driver (CaviEndo ultrasonic unit; C. D. Caulk, Dentsply, York, PA) was clamped rigidly to a stand so that the inner metal stack of the driver could easily be seated within the plastic sleeve. A file was inserted in the head of the endosonic driver and the tip was observed with the aid of a microscope at a magnification of x 100. A strong directional light was shone onto the length of the file so that a small point of light could be seen reflecting off a cutting edge. When the file was activated, the small spot of light became elongated into a horizontal line which represented the amplitude of the file. The displacement amplitude was taken as half the peak to peak displacement of the file
(6). 232
Vol. 18, No. 5, May 1992
F~G 1. Diagram showing the method of measurement used forthe Endovue blocks.
Displacement amplitude measurements were made of straight endosonic # 15, 20, and 25 K files. The measurements were made at the tip and at intervals of 1 m m along the length of the file in order to look at any change in nodal and antinodal positions. Five measurements were made at each point. The files were then removed and precurved; the degree of curvature being measured by drawing a tangent of the file curvature and measuring the angle. The displacement amplitude measurements of each endosonic K file were repeated for different degrees of curvature which increased from 20 to 90 degrees.
Endovue Blocks Thirty Endovue blocks were chosen with canals of matched curvature and were split into 15 pairs. Each pair was prepared with hand K-Flex files so that either a #15, 20, or 25 file could freely pass to the end of each simulated canal. The blocks were then prepared with the same size endosonic file as the last file which had been used for hand preparation. One block of the pair was prepared with a straight endosonic file and the other with a file precurved to the shape of the canal. The endosonic preparation was carried out for 2 min in each canal in an up and down and circumferential manner. Water
Precurving Endosonic Files
233
FtG 2. Photograph of mesiobuccal root of upper first molar with windows cut in it to the level of the root canal.
irrigation was used continuously with a predetermined flow rate of 20 ml/min. In addition five blocks were prepared using the # 15, 20, and 25 files in series for 2 min each with continuous irrigation, giving a total time of preparation of 6 min. As before, one block was prepared with precurved files and the other with straight files; however, in these canals the init,.'al enlargement was only to a # 15 K-Flex file. An additional five blocks were prepared in series using straight endosonic files inserted in the driver but used without ultrasonic activation. The width of the canals was then measured using a light microscope (Wild 3M stereomicroscope; 3M Center, St. Paul, MN) at magnification x25. These widths were measured at the apex and at 1.5-mm intervals along the prepared canal. The width was measured perpendicular to the canal walls (Fig. 1). In Vitro Oscillation In the third part of the study an upper molar tooth was selected with a curved mesiobuccal root. Windows were cut in the sides of the root at 3-mm intervals to the level of the root canal (Fig. 2). This enabled a file placed within the canal to be observed under the light microscope. The root canal was enlarged to a #25 K-Flex file with hand instrumentation which allowed an endosonic file # 15 to be placed freely. The
234
Lumley and Walmsley
Journal of Endodontics
TABLE 1. Displacement amplitude of the file in air (in ~m) at three-quarters full power setting* Size 15 Straight 20 degrees 45 degrees 90 degrees Analysis of variance F value p
62 62 62 61
(__0.5) (+_0,5) (+_0.5) (+_2)
0.96 >0.01
Size 20 63.5 63.5 63 61.25 3,41 >0.05
(+_0.5) (+_0.5) (+_0.5) (+_0.5)
are two narrowings in the canal produced by the files. The first is at a distance of 3 mm from the apex for all files and the second is 7.5 m m from the apex for #15 and 20 but 9 m m for #25 file. Figure 4 shows the width of the canal against increasing distance from the apex where precurved files were used to instrument the canal. It can be seen that the width increases in a continuous manner with increasing canal length for the blocks prepared with the precurved files. The two narrowings are most noticeable in the canals that were prepared in series with straight endosonic files when ultrasonic preparation was of 6-min duration (Fig. 5). The canals prepared with the precurved files in series, however, show a continuous taper. The canals prepared by straight endosonic files used by hand all showed a continuous taper (Fig. 5).
Size 25 43 43 43 42
(+_2.5) (+_2.5) (+_2.5) (+_0.5)
0.13 >0.01
* The results of analysis of variance are shown for each column (five readings were t a k e n in e a c h cell error = 1 SD)
oscillatory pattern of a straight and a precurved endosonic file was observed under light microscopy. Straight and precurved files were interchanged to avoid bias brought about by further enlargement of the canal.
Oscillation in the Root Canal
Observation of the straight endosonic K file in the curved root canal showed little or no evidence of oscillation at the tip which lay against the outer wall of the canal; however, oscillation could be seen more coronally. The file precurved to the shape of the root canal lay more centrally and oscillation could be seen at the tip and along its length. The nodal and antinodal points were found to correspond with those noted in air and the displacement amplitude was the same. However, when the files were moved in an up and down manner, as they were when used in preparing the blocks, the oscillation was found to change. The tip of the straight file remained along the wall of the canal but had a greater tendency to oscillate as it moved more coronally. This oscillation was not, however, in a regular nodal and antinodal pattern, rather it was haphazard. The precurved file at all times oscillated more freely. However, the displacement amplitude did vary, ranging from a tendency to become constrained to an increase in displacement amplitude limited by the width of the canal. This change in displacement amplitude was also associated with inconsistency in the nodal and antinodal position along the file.
RESULTS Oscillation in Air
Table 1 shows the difference in the oscillatory pattern of the different sizes of files and the effect of degree of curvature. The displacement amplitudes were not significantly different as shown by analysis of variance regardless of degree of curvature of the file (p > 0.05). Neither the characteristic oscillatory pattern of the file nor the position of nodal and antinodal points changed regardless of precurving. Whether the curve was positioned at a node or antinode did not affect the characteristic oscillatory pattern or displacement amplitude. Excessive oscillation of the file was not a feature even with the 90-degree curvature. Endovne Blocks
Figure 3 shows the width of the canals prepared with straight files against increasing distance from the apex. There
Straight
. . . . . . .
#25 --#20
#15
,,t ..... t ..... ..... I Width
,"
I
L
.-..
T
1_r
r
(ram) .4
T
D i s t a n c e from Apex
(ram)
FIG 3. Graphical representation of the width of the canals prepared with straight files plotted against distance from the apex (n = 5, error bars = _+1 SD).
Vol. 18, No. 5, May 1992
Precurving Endosonic Files
235
Precurved
#25
. . . . . . .
--#20 -
-
#
1
5
-e
Width -
(ram) .4
Distance
from Apex
(sam)
FIG 4. Graphical representation of the width of the canals prepared with precurved files plotted against distance from the apex (n = 5, error bars
= ___1so). Series
I Hand s s
/
p
Straight Precurved
.6
Width (ram) ,4
Distance from Apex
(ram)
FiG 5. Graphical representation of the width of the canals prepared with straight or precurved files in series plotted against distance from the apex (n = 5, error bars = +1 SD).
DISCUSSION The results of this study have shown that there is no significant difference (p > 0.05) in the oscillatory pattern of precurved endosonic files compared with straight endosonic files. Therefore, precurving of files does not affect the oscillatory properties of the file and this suggests that there may be many advantages associated with the use of precurved files in curved canals. The endovue block study confirmed these advantages. A continuous taper is apparent in the blocks which were prepared with precurved files. The blocks prepared with the straight files show narrowings part of the way down the canal and a continuous taper is not present. This feature is consistent for the blocks prepared with the 15, 20, and 25 files,
respectively. It becomes more noticeable when one looks at the blocks prepared in series with #15, 20, and 25. These blocks were ultrasonically prepared for 6 min in total as opposed to 2 min for the blocks prepared with one size of file. However, the blocks prepared with straight endosonic files used by hand showed a continuous taper. The combination of a straight file and ultrasonic energy apparently caused narrowings in the canal which were not as pronounced when the files were precurved. The sizes or the apical 1.5 mm of the preparation of the blocks prepared with straight endosonic files in series whether activated or not were the same, thus indicating that the files may have been constrained. This was confirmed in the extracted tooth study. Any metallic object that is strained has a degree of memory. A straight file that sits within a curved
236
Lumleyand Walmsley
canal is made to curve but contains forces that tend to straighten it. This did not result in uneven shaping of the canal with the hand-operated file. However, the activated straight endosonic files did produce irregularities in canal shape. The narrowings were at 3 m m and between 7.5 and 9 mm from the apex of the canal. These are similar to the positions to where nodal points occur in air. However, the file was moved up and down during the preparation and one would not expect the narrowings to be in the same place as nodes in air. This is difficult to explain; the authors feel that the differing degrees of constraint that were noted in the extracted teeth along with the fact that the straight file lay against one side of the canal may have resulted in this uneven removal. The canals prepared with the precurved files showed more even preparation. The size of the apical preparation was smaller than with straight endosonic files with no ultrasonic activation. A freely oscillating file should produce larger apical preparation. This is also difficult to explain; the authors feel that the larger size of the apical preparation with the straight files is due to the file straightening causing enlargement on the outside of the curve. The precurved files being more centrally placed produced more even preparation. The canals prepared with the files used in series produced greater enlargement of the canals than when individual files were used. This was to be expected as the blocks were prepared for a longer period of time. In this study precurving of the files produced even shaping even in the larger sizes of 20 and 25, however it must be noted that it is easier to precurve a file to a canal that can be seen in a resin block than to a tooth. An argument against the benefits of precurving files is that root canals rarely have just one plane of curvature and any file precurved to a radiograph is only curved to a twodimensional picture. Therefore, it is possible that a precurved
Journal of Endodontics
file may in fact be constrained. Although this may be true in some teeth, our results show that precurving of the endosonic file will result in a looser fit and constraint will at least be reduced. Dr. Lumley and Dr. Walmsley are members of the Department of Restorative Dentistry, The Dental School, St. Chad's Queensway, Birmingham B4 6NN, United Kingdom.
References 1. Martin H, Cunningham WT. Endosonics--the ultrasonic synergistic system of endodontics. Ended Dent Traumato11985;1:201-6. 2. Nehammer CF, Stock CJR. Preparation and filling of the root canal. Br Dent J 1985;158:285-91. 3. Cunningham WT, Martin H, Pelleu GB, Stoops DE. A comparison of antimicrobial effectiveness of endosonic and hand root canal therapy. Oral Surg 1982;54:238-41. 4. Ahmad M, Pitt Ford TR, Crum LA. Ultrasonic debridement of root canals: An insight into the mechanisms involved. J Endodon 1987;13:93-101. 5. Martin H. Ultrasonic disinfection of the root canal. Oral Surg 1976;42: 92-9. 6. Walmsley AD, Williams AR. Effects of constraint on the oscillatory pattern of endosonic files. J Endodon 1989;15:189-94. 7. Langeland K, Liao K, Pascon EA. Work saving devices in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985;11:499-510. 8. Reynolds M, Walton R, Madison S, Krell K, Rittman B. An in vitro histological comparison of the step-beck, sonic, and ultrasonic instrumentation techniques in small curved canals. J Endedon 1987;13:307-14. 9. Walmsley AD. Ultrasound and root canal treatment: the need for scientific evaluation. Int Ended J 1987;20:105-11. 10. Lumley PJ, Walmsley AD, Laird WRE. Ultrasonic instruments in dentistry: 2. Endosonics. Dent Update 1988; 15:362-9. 11. Goerig AC, Michelich RJ, Schultz HH. Instrumentation of root canals in molars using the step-down technique. J Endodon 1982;8:550-4. 12. Murgel C, Walmsley AD, Walton RE. The efficacy of step down procedures during endosonic instrumentation. J Endodon 1991 ;17:111-5. 13. Weine FS. Endodontic therapy. 3rd ed. St. Louis: CV Mosby, 1982. 14. Chenail BL, Teplitsky PE. Endosonics in curved root canals. J Endodon 1988;11:369-74. 15. Tang MPF, Stock CJR. The effects of hand, sonic and ultrasonic instrumentation on the shape of curved root canals. Int Ended J 1989;22:5563. 16. Chenail BL, Teplitsky PE. Endosonics in curved root canals. Part I1. J Endodon 1988;22:55-63.
You Might Like to Know The use of sodium hypochlorite has a venerable history in endodontics. There is a very different and unusual application of this preparation by tattoo artists. These practitioners tattoo over unwanted designs with hypochlorite in an attempt to remove the offending dermal graffiti. By inducing a partial thickness burn, the hypochlorite produces a fair result. The fact remains that there is no known method of removing tattoos which does not result in permanent scarring (BMJ 303:380).
Cosby Newel/
