,g099.2399/84/1008-0349/$02 00/0 I~I(~uRN,I,L OF ENDODON)'ICS ;CopyrJgl~t @ 1984 by the AmerE, an AssooatK:)n of EncloOonbsts

CIENTIFIC ARTICLES Printed In USA

VOL 10. NO 8, AUGUST 1984

ICIockwise or Counterclockwise

Rotacion en Sentido de las Agujas del Reloj o Sentido Contrario

~James B. Roane, BS, DDS, MS, and Clyde Sabala, BS, DOS

Four-hundred ninety three K-type files collected as clinical discards exhibiting distortion and or sepa- ration of their working portion were examined to establish the direction of rotation associated with their existing structural damage. Characteristic types of damage were observed for both clockwise and counterclockwise rotation, with five types of ~amage recognized. Analysis of the data indicates ~hat rotating a K-type file counterclockwise is least ~ikely to structurally damage it. Counterclockwise ~tation accounted for 33.3% of the total of structural ~separations. The results lead us to conclude: if one /is intent upon rotating a K-type file, they are less

i iikely to encounter physical damage to that instru- ment when it is rotated counterclockwise. ~ ueron examinadas 493 limas tipo K reunidas por ~lescarte clinico exhibiendo distorsion y/o separa- ~ibn de su porcion de trabajo, para establecer la ~ireccibn de rotacion asociada a su deterioro es- ~ructural existente. Fueron observados tipos carac- ]eristicos de deterioro en ambas rotaciones en el Sentido de las agujas del reloj y en sentido contrario con cinco tipos de daho reconocidos. El analisis de los datos indican que la rotacion en sentido contrario al de las agujas del reloj de la lima tipo K es menos probable que dahe su estructura. Le rotacion en sentido contrario al de las agujas del reloj responde a un 33.3% del total de separaciones estructurales. Los resultados permiten a los autores Ilegar a esta conclusion: cuando se intentan rotar una lima tipo K hay menos probabilidad de provocar dafm fisico a dicho instrumento si se Io rota en sentido inverso a las agujas del reloj.

Should one rotate an endodontic instrument clockwise or counterclockwise? This seems a simple question to

answer. In fact, one may cite two recent articles, Cher- nick et al. (1) and Lautenschlager et al. (2), which conclude that clockwise is the only safe direction of rotation with a K-type instrument, either a file or a reamer. Closer examination of this conclusion is needed as it is in conflict with clinical impressions that counter- clockwise rotation is not more likely to break instru- ments. It may be that the clinical observations are in error or that there is an interpretive error made by drawing clinical conclusions from the reported data. The fact that both studies obtained data under con- trolled laboratory conditions and did not take into ac- count variables that exist clinically may result in totally different conclusions when the clinical situation is eval- uated. Clinical variables could alter the conclusions to be drawn from measured physical characteristics and, therefore, clinical trials are necessary before conclu- sions relating to clinical circumstances can be made.

An instrumentation technique that involves clockwise placement of the instrument and counterclockwise ro- tational cutting has created a further need to evaluate damaged instruments (3). The purpose of this evalua- tion is: (a) to determine if instrument damage from clockwise or counterclockwise rotation in the clinical situation is similiar, related to, or is different than that reported in the laboratory; (b) to evaluated the types of damage that occur; and (c) to report their frequency of occurrence.

349

MATERIALS AND METHODS

Damaged root canal files were collected from a sin- gle-doctor endodontic practice which utilizes the instru- mentation technique of alternate clockwise and coun- terclockwise rotation to produce root canal enlarge- ment (3; J. B. Roane and M. G. Duncanson, submitted for publication). This method specifies clockwise instru- ment rotation as a placement motion and counterclock- wise instrument rotation as a cutting motion with the

350 Roane and Sabala

frequency of one direction to the other being approxi- mately equal. All root canal files discarded over a 2- month period were collected and examined for evidence of rotational damage. Those instruments discarded for nontorsional reasons were eliminated from the study. This elimination included excessively bent instruments and instruments with broken or loose handles. The instruments collected were all from the same manufac- turer and were files sizes 08 through 60.

After collection the instruments were viewed under an Olympus dissecting microscope to ensure adequate visualization of the damaged region. Each instrument was closely examined to determine the nature and the extent of the damage.

Test fractures were produced in the laboratory to provide clockwise and counterclockwise damaged files for evaluation control. These were produced by clamp- ing the file in a hemostat, then rotating the instrument clockwise or counterclockwise until it separated. The type of separation was characteristic for each rotational direction and was noted to be the same as those described by Chernick et al. (1).

By using the test instruments as controls, the instru- ments damaged in clinical use were divided into groups either by the nature or by the extent of damage they exhibited. The groups were identifiable as follows: (a) separated by counterclockwise rotation; (b) separated by clockwise rotation; (c) partially separated by clock- wise rotation; (d) damage by counterclockwise rotation; and (e) damage by clockwise rotation.

Journal of Endodontict

aration characteristic of those ductile fractures Pro. duced by clockwise rotation (Fig. 2). Partial separation was not detectable before brittle fractures occurred so no instruments displayed partial separation related to counterclockwise rotation. Twenty-one (4.3%) exhib. ited partial separation related to clockwise rotation (Fig~ 3). Thirteen instruments (2.6%) displayed distortions of their flutes/blades that were related to counterclock. wise rotation (Fig. 4), while 393 (79.7%) were discarded because of distortions of the flutes/blades related to clockwise rotation (Fig. 5).

The total 493 instruments consisted of 451 (91.5%) instruments discarded from damage related to clock- wise rotational motion. (This included complete sepa- ration, incomplete separation, and distorted flutes/ blades.) Forty-two (8.5%) instruments were discarded because of counterclockwise damage. (This included complete separation and distorted flutes/blades.)

RESULTS

Four-hundred ninety-three instruments were accu- FIG 2. This instrument illustrates the typical tearing and splitting apart mulated which exhibited tortional related alterations of of the instrument shaft observed when the separation has occurred their cutting blades. Twenty-nine (5.9%) displayed a during clockwise rotation. Thirty-seven instruments were noted to complete instrument separation characteristic of those have failed in this manner. brittle fractures produced by counterclockwise rotation (Fig. 1). Thirty-seven (7.5%) displayed a complete sep-

FIG 1. This instrument illustrates the typical clean separation produced when instrument failure occurs during counterclockwise rotation. Twenty-nine instruments were noted to have failed in this manner.

.FIG 3. This instrument illustrates a partial separation which was identified in the larger instrument sizes and only associated with clockwise rotation. Twenty-one instruments were discarded because of this type of defect. The presence of such a defect apparently results in a separated instrument if no canal access preparation exists: the inadvertantly lodged instrument perhaps?

~/oL 10, No. 8, August 1984 Clockwise or Counterclockwise 351

will embed the instrument deeper and deeper into the dentin as it moves apically. Continued clockwise rota- tion eventually results in a torsional load which exceeds the structural strength of the instrument. At that point,

:=G 4. This instrument is representative of those that suffered per- nanent distortions during counterclockwise rotation. This is difficult o identify clinically, as it does not produce shiny facets. Only careful }xamination will reveal the overwinding that is present (A to B). rhirteen were identified.

These findings are presented by instrument sizes in Table 1.

DISCUSSION

A couple of observations are readily apparent. First, complete or incomplete fracture of the files used clini- cally in this study was more likely to occur when the stress was applied by clockwise rotation. The ratio was 2:1, clockwise fractures to counterclockwise fractures. Second, the vast majority of damaged instruments discarded under the circumstances of this study were damaged by clockwise rotation. This ratio was approx- imately 10:1, clockwise damage to counterclockwise damage.

These findings appear to be in conflict with the pre- viously reported findings of Chemick et al. (1) and Lautenschlager et al. (2); however, a closer examination of the laboratory study and the clinical situation may offer an explanation. The testing procedure in the re- ported laboratory studies related the fracture of the instruments when the tip was rigidly fixed and the instrument rotated. In the clinical situation, the operator has the potential to release the load on the tip of the instrument, especially in a counterclockwise rotation. ;This results in less occurrences of the rigidly held tip and therefore less damage from a counterclockwise rotation.

It is apparent that a vice-like grip of the instrument t~p can be produced clinically with ease and significant frequency by simply rotating the instrument clockwise. Such rotation will vector forces generated by dentinal resistance off the inclines of the instrument's cutting edges. The forces thus derived cause the instrument to move apically and typically, it does so without the Operator being aware of such movement. As a result of the taper of the instrument, the clockwise rotation

FIG 5. The instruments in A and B display frequently observed types of clockwise damage. The instrument in A shows elongation of the flutes, returning the cutting edges to an axial position, while the instrument in B reveals the initiation of a reverse wind and an internal split of the metal. Both instruments present with shiny facets clinically. Three-hundred and ninety-three (79.7%) of the used instruments presented with damage of this type.

~-~--:;:;i;;~'.'.~ ~ .:~:.i ~ " :" ,~.~:! ~.~;~

FOG 6. This instrument is representative of the small diameter instru- ments used, in that it exhibits normal fluting at its tip (A), an area of flute elongation (B), and an area of reverse winding produced by a lodged tip during clockwise rotation (C).

352 Roane and Sabala Joumal of Endodorltt~

TABLE 1. Results obtained by instrument size

Direc- % of Sam-

Nature of Damage tion of Rotation pie

Complete CCW" 5.9 Separation CW 7.5 Incomplete CCW 000.0 Separation CW 4.3 Distorted CCW 2.6 Instruments CW 79.7

Totals 100.0 Distortion (%)

No. O~ Distdbut~n by File Size

se~ed 08 10 15 20 25 30 35 40 45 50 55

29 4 0 3 3 6 1 5 4 37 10 4 2 2 4 4 3 5 0 0 0 0 0 0 0 0 0

21 0 0 0 0 0 3 2 4 13 0 1 2 2 1 2 1 1

393 86 102 113 39 9 7 21 2

493 100 107 120 46 20 17 32 16 86 96 95.8 89.1 50 52.9 68.8 18.8

6O

3 0 0 0 3 0 0 0 0 0 0 0

10 1 0 1 2 1 0 0

12 2 0 0

30 4 0 1 46.7 75 NA NA

9 CCW, counterclockwise: CW, clockwise; NA, not applc, abSe.

the instrument distorts and may subsequently separate in a ductile fracture.

In simpler terms it can be stated that the instrument will thread itself into the root canal until it becomes wedged or locked, as if in a vice, following such an event it will either distort or break unless the operator immediately stops rotation of the instrument. Con- versely, when an instrument is turned counterclock- wise, the opposite forces are brought to bear and the instrument unthreads itself, reduces the depth the cut- ting edges are embedded into the dentin, removes any vise-like grip on the instrument tip, and finally is able to strip the dentin away. If clockwise placement of the instrument is extreme and the backing off with a coun- terclockwise motion is not possible, then an instrument fails to back out when rotated and a counterclockwise fracture will occur. This does not happen clinically as frequently as the clockwise damage even though the elastic limits before counterclockwise fracture are less than those before clockwise fracture (1, 2). Thus, it appears that the laboratory circumstances reported are infrequently encountered clinically during counterclock- wise instrument rotation.

The counterclockwise distorted instruments are very difficult to duplicate in the laboratory. Since the manu- facture of the file is accomplished by counterclockwise twisting of a blank wire, this distortion is actually an overwinding. Further overwinding is likely to lead to a brittle fracture and therefore the 13 instruments were discarded. This is a subtle change in the instrument and is difficult to visualize or recognize in the clinical setting. It is probably related to a wide distribution of forces restricting a portion of the instrument rather than just the tip. It is conceivable that this is also a manufac- turing defect; the overwinding being created in the original fabrication of the instrument. This distortion was observed 2.6% of the time in this study.

Partial separation of an instrument occurred only in the larger instruments. No partially separated instru- ments were recognized smaller than a size 30 file. The most frequent partially separated instrument was size

45. This observation may relate to two factors. The first consideration may be that this distortion is simply a function of the instrument size and the second consid. eration may be that it is related to the instrumentation technique. The root canal preparation procedure used includes a root canal access preparation with Gates- Glidden drills. That access is routinely created after enlarging the canal with a size 30 or 35 instrument. The removal of dentin associated with that access extends two-thirds of the length of the canal and may change the stress/loads applied to the root canal instruments in such a manner as to allow the shaft to split or to fracture one or two flutes and still be retrieved from the canal. It is postulated that this occurs because dentinal support is removed from the instrument along its cor- onal two-thirds and the typical instrument expansion observed in such circumstances does not cause the instrument to bind; therefore, the damaged instrument may be removed from the canal by the remaining intact metal. Instruments apparently suffer complete separa- tion below size 30. This we believe is related to the increased loading on the instrument and intimate con- tact of the dentinal walls not providing room for the split to expand. Thus, any partially separated (ex- panded) instrument size 30 and smaller became lodged and was completely separated while attempting to re- move it from the canal.

Further examination of the data suggests that small diameter instruments distort without separation much more readily then the larger instruments. The smaller instruments, #08, #10, #15, and #20, were distorted 86, 96, 95.8, and 89.1% of the time. The percentages begin to drop dramatically with the size 25 file (50%). The size 40 file showed only 18.8% distortion; the rest exhibited either partial or complete separation.

The degree of distortion that an instrument can tol- erate before fracture must be related to the bulk and flexibility of the instrument. Smaller instruments tolerate more distortions as they are more flexible and contain less metal. The size 25 file appears to be the turning point where clinically less distortion and more separa-

iVo~. 10, No. 8, August 1984

~on occurs. Although the sample size is small it appears ~at the #40 file is the most brittle or the least ductile ~of the sizes examined.

SUMMARY

The data presented were obtained from an analysis of 493 clinically damaged root canal instruments. Each

i strument had received perceivable damage during inical usage in a root canal preparation technique that ~ilizes clockwise rotation for instrument placement and ~ounterclockwise rotation for instrument cutting. The {requency of clockwise to counterclockwise rotation used was approximately equal, since instrument place- ment typically preceded each cutting stroke. An analy- is was performed that related the direction of instru- ent rotation to the incidence and nature of instrument

~amage. The findings of that analysis may be summa- ~zed in the following statements:

1. Root canal files are more likely to receive damage leading to discard during clockwise rotation; i.e. 91.5% of the sample studied.

2. Root canal files are more likely to separate under the clinical circumstances reported during clock- wise rotation. This represented a total of 66.6% of all instruments separated and included com- plete as well as partial separations.

3. Root canal access preparation and perhaps wire diameter may be related to the appearance of incompletely separated instruments. All such in- struments were observed to be a result of clock- wise rotation.

4. Files were more brittle when rotated counterclock- wise and more ductile when rotated clockwise as was previously reported (1,2).

5. In clinical usage separation or distortion is less likely to occur during counterclockwise rotation

Clockwise or Counterclockwise 353

.

than during clockwise rotation. This observation is explained by the fact that counterclockwise rotation unthreads the instrument, decreasing its load and releasing its cutting edge. Clockwise rotation threads the instrument into the canal and increases its load until its cutting edges cease to rotate. At that point, the instrument shaft must either distort or separate unless the operator ter- minates the rotation. Small diameter instruments would appear to be more ductile than their larger counterparts; i.e. #08 to #20 more ductile than #25 to #45.

CONCLUSIONS

It may be concluded from the data presented that counterclockwise rotation stresses an instrument in its most vulnerable direction; however, instrument failure is infrequent. When counterclockwise failure is ob- served it is observed as a cleanly separated instrument. Clockwise rotation more commonly damages instru- ments and is more likely to be associated with sepa- rated instruments than is counterclockwise rotation in clinical usage.

Dr. Roane is an associate professor and c.~airman, Department of Endo- dontfcs, College of Dentistry. University of Oklahoma Health Sciences Center, Oklahoma Ctty, OK, and is engaged in a half-time private practF,,e in Norman, OK. Dr. SabaJa is a full-time assooate professor, Department of Endodontics, College of Dentistry, University of Oklahoma Health Sciences Center, Oklahoma City, OK. Address requests for reprints to Dr. Roane.

REFERENCES

1. Chernick LB, Jacobs J J, Lautenschlager EP, Heuer MA. Tortienal failure of endodontic Files. J Endodon 1976;2:94-7.

2. Lautenschlager EP, Jacobs J J. Marshall GW Jr, Heuer MA. Brittle and ductile tortional failures of endodontic instruments. J Endodon t 977;3:175-7.

3. Roane JB. Endodontics in a single visit lecture manual. Department of Endodontics, University of Oklahoma, 1982:33-4.