An In-Vitro Comparison of the Radiographic and Actual Gutta-Percha Terminus

The purpose of this study is to investigate the difference between the radiographic gutta-percha terminus and the actual gutta-percha terminus of human molars by comparing radiographic obturation results with actual obturation results. Forty maxillary palatal roots and 50 mandibular distal roots were randomly selected from a population of 540. They were then mounted in stone and radiographed. Conventional endodontic therapy was completed using stainless steel K-files and lateral condensation. Each radiographic gutta-percha terminus was evaluated under 4.5 x magnification by three examiners following the completion of root canal therapy. These results were recorded. Each tooth was then removed from its mounting, and the actual gutta-percha terminus was evaluated under 4.5 x magnification. These results were recorded and compared to the radiographic gutta-percha terminus results. In all 90 teeth examined, the actual gutta-percha terminus was equal to or longer than the radiographic gutta-percha terminus. In the 50 mandibular distal roots, the actual gutta-percha terminus averaged 0.645 mm longer than the radiographic gutta-percha terminus. In the 40 maxillary palatal roots, this difference measured 0.6375 mm.

In endodontic therapy, the apical constriction has long been recognized as the anatomical location to provide the barrier between the root filling material and the apical tissues. Historical studies including Kuttler in 1955,¹ Green in 1956² and 1960,³ and Chapman in 1969⁴ have examined the intricacies of the apical portion of the root. Thus, the ideal root canal filling would completely fill the obliterated pulp space and provide a seal at the dentinocemental junction. However, the anatomical location of the apical foramen is not exclusively located at the anatomical root apex.

In Seltzer’s 1969 study on periapical tissue reactions to root-filled teeth, optimum tissue results were obtained when root canals were instrumented and filled short of the apices of the teeth. Seltzer claimed that repair was delayed in the group of teeth in which the canals were overfilled.⁵

Palmer and colleagues stated in a 1971 study that the proper location of the apical foramen could not be discerned from a radiograph.<sup>6

I</sup>n a study of 100 mandibular molars in 1958, Green determined that the average distance between the major canal foramina and the apex of the distal root was 0.43 mm. In some instances, this discrepancy measured to be as great as 3 mm.⁷

In a follow-up study by Green in 1960,³ 700 maxillary and mandibular posterior teeth were evaluated. Approximately 50 percent of major foramina did not open at the anatomical apex. Those that did not open at the apex ranged from eccentric position to 2 mm from the apex.

In 1972, Burch and Hulen found that the frequency of deviation of the major foramen from the anatomical apex was found to range from 78.0 percent in maxillary incisors to a high of 98.9 percent for mandibular distal roots. The largest deviation was found to occur on distal mandibular molar roots. This average was 0.78 mm.⁸

In 1986, Abou-Rass stated that in posterior teeth the distance between the apical foramen and the root end averages 0.5 to 1.0 mm. Abou-Rass added that in 70 percent of molars, this foramen is not at the root end.⁹

These discrepancies between the anatomical and radiographic apex in the above and other studies is the motivation for this study. The purpose was to demonstrate that the radiographic representation of the root fill can be quite different from the anatomical location of that root fill.

Materials and Methods

Five hundred and forty extracted mature human first and second maxillary and mandibular molars were endodontically treated in the preclinical laboratory by second-year University of Southern California dental students. These teeth were mounted in a mixture of yellow stone and orthodontic acrylic with a 2 mm ball of red rope wax to allow for apical overfill The teeth were radiographed and accessed with a chamfer diamond bur. Working lengths were determined radiographically with #15 K-files in the canals. The canals were preflared with Gates-Glidden burs and cleaned and shaped using a standard crown-down technique. Irrigation was maintained with 5 percent sodium hypochlorite, and endo dilator was used if indicated. Canals were dried and coated with AH26 cement. The students were instructed to fill the canals 0.5 millimeters short of the radiographic apex. Radiographs were taken at various intervals during the treatment.

From these 540 teeth, 40 maxillary palatal roots and 50 mandibular distal roots were selected for the study by three second-year endodontic residents and the director of the advanced endodontic program. Teeth were eliminated for the following reasons: gross overfill or underfill, separated instruments, perforations, transportations, excessively poor technique, or damaged teeth from cast removal.

The 90 roots were numbered and evaluated independently by each of the three residents on the basis of root end fill discrepancy from the radiographic apex under 4.5 x magnification. An average was taken from the three measurements for each tooth. The range of these data was from 1.5 mm underfill to 0.5 mm overfill.

Once these data was recorded, each tooth was carefully removed from its cast and placed in a coin envelope with the number of the tooth hidden inside. Each tooth was then independently and blindly evaluated by the same three residents anatomically using a 4.5 x magnification. The results were averaged and compared to the radiographic results using a paired t-test. The paired t-test is the optimal statistical test when comparing two matched groups of quantitative data that is parametrically distributed as is the case in this study.

Results

Maxillary

In the 40 maxillary palatal roots examined (Table 1), the average discrepancy from radiographic gutta-percha terminus to the actual terminus was 0.6375 mm. The radiographic terminus was determined to average 0.2875 mm short of the radiographic apex. When these same teeth were examined clinically, the average actual gutta-percha terminus was 0.35 mm long of the apical foramen. The breakdown of each tooth’s measurement discrepancy is shown in Figure 1. Using the paired t-test, these results were found to be quite significant.

Table 1. The Difference Between the Radiographic and Anatomical Apices in the Maxillary Teeth
	N	Mean	Std. Dev.
Radiographic	40	-0.2875	0.4065
Actual	40	0.35	0.2931
Difference		-0.6375	0.412
P< 0.001

Mandibular

In the 50 mandibular distal roots examined (Table 2), the average discrepancy from the actual gutta-percha terminus to the radiographic terminus was 0.645 mm. The radiographic terminus was determined to average 0.235 mm short of the radiographic apex. When these same teeth were examined clinically, the actual terminus was 0.41 mm long of the apical foramen. The breakdown of each tooth’s measurement discrepancy can be found in Figure 2. Using the paired t-test, these results were found to be quite significant

Conclusion

The intention of this study was to show that the practice of standardly finishing an obturation at the radiographic apex would result in many anatomical overfills. The literature supported these intentions. As the results in this study clearly demonstrate, the radiographic apex is frequently more apical than the actual foramen.

Root canal obturation should not be blindly placed at the radiographic apex. Rather, tactile sensation, operator experience, and aids such as apex locators should serve as a modifier for the radiograph during the course of root canal treatment.

Authors

M. Sadegh Namazikhah, DMD, MSEd, is a professor of clinical dentistry, acting chairman of the Endodontic Department, and director of the Advanced Endodontic Program at the University of Southern California School of Dentistry.

Mojgan Ghiai, DDS, is a second-year resident in the Graduate Endodontic Department at USC.

Matthew J. Parkin, DDS, is a second-year resident in the Graduate Endodontic Department at USC.

Lawrence Puccinelli, Jr., DDS, is a second-year resident in the Graduate Endodontic Department at USC.

References

1. Kuttler Y, Microscopic investigation of root apexes. J Am Dent Assoc 50:544-552, 1955.

2. Green D, A stereo-microscopic study of the root apices of 400 maxillary and mandibular anterior teeth. Oral Surg Oral Med Oral Pathol 9:1224, 1956.

3. Green D, Stereomicroscopic study of 700 apices of maxillary and mandibular posterior teeth. Oral Surg 13:728, 1960.

4. Chapman C, A microscopic of the apical region of human anterior teeth. J Br Endod Soc 3:52-8, 1969.

5. Seltzer S, Soltanoff W, Sinai I, Biologic aspects of endodontics. IV Periapical tissue reactions to root-filled teeth whose canals had been instrumented short of their apices. Oral Surg Oral Med Oral Pathol 28:724, 1969.

6. Palmer M, Weine F, Healey HJ, Position of the apical foramen in relation to endodontic therapy. J Can Dent Assoc 37:305-8, 1971.

7. Green D, A stereo-binocular microscopic study of the root apices and surrounding areas of 100 mandibular molars. Oral Med Oral Surg Oral Pathol 10:1298, 1958.

8. Burch J, Hulen S, The relationship of the apical foramen to the anatomic apex of the tooth root. Oral Surg Oral Med Oral Pathol 3:114, 1977.

9. Abou-Rass M, Endodontic Preparation and Filing Procedures. The California Institute for Continuing Education, 1986, p 8.

To request a printed copy of this article, please contact/ M. Sadegh Namazikhah, DMD, MSEd, USC School of Dentistry, 925 W. 34th St., Room 124C, Los Angeles, CA 90089-0641.