0 0 9 9 - 2 3 9 9 / 8 3 / 0 9 0 3 - 0 1 1 4 / $ 0 2 . 0 0 / 0 JOURNAL OF ENDODONTICS Copyright �9 1983 by American Association of Endodontists

Printed in the U.S.A. MOL. 9, NO. 3, MARCH 1983

CLINICAL ARTICLES

The Effect of Instrumentation on Root Canal Length as Measured with an Electronic Device

Jesse P. Farber, DDS, and Monroe Bernstein, DDS

The study was designed to measure what effect the instrumentation of a canal would have on its length as measured electronically. Ninety-seven canals were measured with the Sono-Explorer before and after instrumentation. Fifty canals showed some change; in all but two, the second measurement was shorter than the first. The mean shortening of all of the canals was found to be 0 .40 mm.

It is widely advocated that the instrumentation and filling of the root canal be carried out to the cemento- dentinal junction. It is reasoned that, if the constriction of the canal at this point is not enlarged, then traumatic instrumentation of the periapical tissues is avoided, and a stop is provided for the packing of the root canal filling. Thus, overfilling of the canal is minimized.

Since the cemento-dentinal junction is usually lo- cated 0.5 to 1 mm from the radiographical apex and cannot usually be seen on the radiograph, electronic measurement of the canal length seems to offer an advantage over radiographic measurement. Studies by O'Neill (1) and Plant and Newman (2) comparing the Sono-Explorer measurement with the measure- ment obtained visually after the extraction of the tooth have found the Sono-Explorer to be quite accurate. Kaufman et al. (3) concluded that the Sono-Explorer does, in fact, measure canal length to the cemento- dentinal junction.

We have noticed that, if a second measurement is taken after instrumentation of the canal has been completed, it is often shorter than the first. Caldwell (4), in a study conducted on extracted molar teeth, has shown that instrumentation does, in fact, shorten the length of the canal; the more curved the canal, the greater the shortening. This study was designed to measure the influence of instrumentation of the root canal on its length measurement as determined by an electronic measuring device, the Sono-Explorer.

114

MATERIALS AND METHODS

Ninety-seven canals, in single and multirooted teeth, were used in this study. The teeth were all in patients routinely being treated in an endodontic prac- tice. A periapical radiograph was taken before starting treatment. Access to the canals was obtained and the canal lengths were measured initially with the Sono- Explorer before any instrumentation had taken place. These initial measurements were obtained with a #10, #15, or a #1 file. The measurements were recorded and the instrument set aside. The canals were instru- mented to the recorded measurement up to a # 2 5 or to a #25 or a #3 file, then they were funneled short of the measurement to a #35 or a #4 file. EDTA was used to facilitate the enlargement of narrow canals, and zepharin chloride solution was used for irrigation. The use of sodium hypochlorite was avoided lest some residue of this material interfere with the accuracy of the measurements (1).

After instrumentation and irrigation, the canals were dried with paper points and measured again at the same visit, using the same file used for the initial measurement. The second measurement was re- corded, and the difference between it and the first measurement was calculated to the nearest 0.5 mm by subtracting the smaller figure from the larger.

RESULTS

Of the 97 canals, 47 showed no change of length, 48 showed some shortening in the second measure- ment, and 2 showed some lengthening. Of the canals showing shortening following instrumentation, 19 were shorter by 0.5 mm, 25 by 1.0 mm, 2 by 1.5 ram, and 2 by 2 mm. One canal showed a lengthening of 0.5 mm and one canal a lengthening of 2.0 mm. All 97 canals showed a mean shortening of 0.4 mm (Table 1 ).

Vol. 9, No, 3, March 1983

TABLE 1. Canal measurements

Measurement No. of Canals

Change (mm)

0 47 - 0 . 5 19

- 1 . 0 25 - 1 . 5 2

- -2 .0 2 + 0 . 5 1 + 2 . 0 1

Mean measurement - 0 . 4 97 (total no. of canals)

DISCUSSION

When Caldwell (4) measured the shortening of mo- lar canals due to instrumentation, he found less shortening than we did. The mean amounts of shorten- ing he found ranged from 0.03 mm in palatal maxillary canals to 0.35 mm in mesiobuccal maxillary canals.

We see two reasons for the difference between our results and Caldwelrs. First, Caldwell flattened the occlusal cusps to provide a firm seat for the measuring instrument. We quote from Caldwelh "As long as the occlusal reference point was rigidly maintained, changes approaching 1 mm were never encountered. If the occlusal reference point was allowed to shift, even slightly, changes approaching 1 mm and greater were common. In the less controlled clinical situation, changes greater than those encountered in this ex- periment might be expected."

Second, and equally important, Caldwell flattened the apices of the roots to allow for more accurate measurement. We feel that, in the clinical situation, when the canal is enlarged from a small dimension to a larger one, the tiny apical opening may be enlarged, permitting a more direct path of egress for the meas- uring instrument. That is, in the taking of the initial measurement with a fine instrument, the instrument will follow the curve of the canal at the narrow tip of the root. If the apex is opened and the curve lessened, the instrument will not have to bend as much before it contacts the periodontal membrane.

In this study the apical portions of the canals were enlarged to a #25 or a #3 file and the remainder of the canals were funneled to a #35 or a # 4 file. Techniques which call for greater enlargement of ca- nals may result in even more shortening of canals than we found, especially in curved canals.

Instrumentation and Canal Length 115

Clearly, the common practice of taking an initial measurement of the root canal length, instrumenting to that measurement, and filling to that measurement will result in the frequent enlargement of the apical constriction, overinstrumentation, and overfilling of canals. Considering the results of the present study, two methods are recommended for avoiding these difficulties. The first is periodic monitoring of the length of the canal during the enlargement proce- dures, either by radiograph or electronic measure- ment. The second, and perhaps the more practical method, is to carry out the instrumentation 1 mm short of the initial measurement. Then measure again, and if any additional instrumentation is needed to get to the apical constriction, it can be carried out at this point.

SUMMARY AND CONCLUSIONS

This study was designed to measure what effect the instrumentation of a canal would have on its length as measured electronically. Ninety-seven canals were measured with the Sono-Explorer before and after instrumentation. Fifty canals showed some change and, in all but two, the second measurement was shorter than the first. The mean shortening of all of the canals was found to be 0.40 mm. We feel that instrumentation carried out to the initial measurement will often result in overinstrumentation and overfilling of the canal. It is suggested that periodic monitoring of the canal length during instrumentation, or instru- mentation 1 mm short of the initial measurement and correction before filling the canal will solve this prob- lem.

The electronic device used {n this study was the Sono-Explorer, American Medical and Dental Corp. P.O. Box 3422 Cherry Hill, NJ 08034.

Requests for reprints should be sent to Dr. Jesse P. Farber, 595 Madison Ave., New York, NY 10022.

REFERENCES

1. O'Neill JJ. A clinical evaluation of electronic root canal measurement. Oral Surg 1974;383:469-473.

2. Plant J J, Newman RF. Clinical evaluation of the Sono-Explorer. J Endodon 1976;2:215-6.

3. Kaufman AY, Heling B, Sechaiek M. What apex does the Sono-Ex- plorer really read? Quintessence Int 1979; 12:63-71.

4. Caldwell JJ. Change in working length following instrumentation of molar canals. Oral Surg 1976;411:114-8.