endodontics

Editor: MILTON SISKIN, DDS

Suite 339 Union Plaza Building 1835 Union Avenue Memphis, Tennessee 38104

Photoelastic stress comparison of warm (Endotec) versus cold lateral condensation techniques Howard Martin, DMD, FACD,a and Eugene Fischer, DMD, MS,b Washington, D.C.

DENTAL DIVISION, VETERANS ADMINISTRATION MEDICAL CENTER, WASHINGTON, D.C., AND GEORGETOWN UNIVERSITY SCHOOL OF DENTISTRY

Stress generated during gutta-percha obturation of root canals can create microcracks and ultimately lead to failure. A new thermosoflening device, the Endotec, which develops a warm lateral condensation technique, was tested against the traditional lateral condensation procedure. The results indicated that the warm lateral condensation technique created less stress during obturation than did cold lateral condensation. (ORAL SURC ORAL MED ORAL PATHOL 1990;70:325-7)

L ateral condensation of gutta-percha is the root canal filling procedure used by more than 80% of dental practitioners. It has been shown, however, that condensation forces necessary to obturate the canal can lead to minute cracks, eventual fracture, and ul- timate failure of the endodontic treatment. Lateral condensation contributed to 80% of vertical root fractures,’ and dentinal cracks have been associated with vertical condensation procedures.* A new instru- ment, the Endotec device (L.D. Caulk Co., Milford, Del.), employing a self-contained method of heating to soften gutta-percha during condensation proce- dures, claims to reduce root stress and permit better adaptation within the root canal.

Stress forces can be visualized during obturation with the use of the photoelastic properties of specially annealed polycarbonate plastic when viewed through polarized light. The purpose of this study was to com-

BResearch Endodontist, Veterans Administration Medical Center; Clinical Associate Professor, Department of Endodontics, School of Dentistry, Georgetown University. bChief Dental Division, Veterans Administration Medical Center. 7/ IS/k444

pare, by means of a photoelastic model, the stress forces generated by traditional, cold lateral conden- sation of gutta-percha versus the warm lateral con- densation technique with the Endotec device.

MATERIAL AND METHODS

The photoelastic material was supplied as %-inch plastic sheets (PLl, Measurements Group Inc., Ra- leigh, N.C.). The sheets were cut into l-inch squares. Standardized “root canals” were prepared, and min- eral oil was used as a lubricant to reduce generated stress. The canal was prepared to a No. 40 K-file api- tally with a moderate flare and was photographed as a control. Previous studies using photoelastic stress determined the average forces applied to the root ca- nal condensing procedure and their resultant stress.3 Obturation forces for both lateral condensation and warm lateral condensation were accomplished by the same operator. The operator had used lateral con- densation routinely in practice before warm lateral condensation. It has already been demonstrated that the operator will repeat the pressure pattern of con- densation.3

A 35 mm single lens reflex camera with two circu-

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326 Martin and Fischer ORAL SURG ORAL MED ORAL PATHOL September 1990

Fig. 1. Traditional lateral condensation: Note high-stress concentration in middle and apical portion dur- ing lateral condensation. Fig. 2. Warm lateral condensation: Note more even distribution of stress after gutta-percha has been ther- a mosoftened by Endotec followed by cold spreader lateral condensation. Fig. 3. Endotec lateral condensation: Note even distribution of stress throughout when Endotec is used to thermosoften and condense in same procedure.

lar transmission polariscope filters was used for pho- penetration, three one-fourth turn rotations were ac- tography. No root canal sealer was used to limit vari- complished and photographs made during the proce- ables. As each condensation force was applied, pho- dure. Two more accessory points were added, with tographs were made. each following the same technique.

The actual condensation method was similar to the procedure used in a clinical setting. A master gutta- percha point (L.D. Caulk) was placed into the stan- dardized canal. This was then followed by a Dl 1 spreader placed into the canal within 2 to 3 mm of the prepared apical depth. Three one-fourth turn rota- tions were then applied with photographs made. This was followed by an accessory point and the spreader placed on the same side until resistance was met. At this point, the condensation procedure was repeated. A third gutta-percha point was then placed and the procedure duplicated.

A variant of the technique was tried with a cold Dl 1 spreader. After Endotec thermosoftening of the gutta- percha, a Dl 1 spreader was used to determine stress generated with this alternate combination technique of first thermosoftening followed by cold condensa- tion.

RESULTS

The warm lateral condensation technique method had a master gutta-percha point placed into the stan- dardized canal. The Endotec device tip was then placed along one wall until resistance was met. The instrument was activated and apical penetration was accomplished. The Endotec device was kept activated for 7 to 10 seconds. At the end of heat activation and

A three-series run for each technique was accom- plished on the prepared standardized prefabricated photoelastic blocks. Two-dimensional plane stress was visually evaluated, analyzed, and compared be- tween the cold lateral condensation and warm lateral condensation technique. The stress fringe lines were analyzed, and it was seen that cold lateral condensa- tion, on average, produced stress on the lateral walls of the preparation with a small amount of stress at the apical end of the preparation. Stress (Fig. 1) was greatest at the lateral walls and moved coronally as

Volume 70 Comparison of warm vs cold lateral condensation techniques 327 Number 3

obturation continued. As more gutta-percha was added, stress tended to increase but generally re- mained in the middle third of the preparation.

The Endotec device used to thermosoften the gutta- percha, followed by a Dl 1 spreader, developed stress fringe orders that were less severe than lateral con- densation. However, the stress fringe orders were slightly more pronounced than when the Endotec de- vice was used alone (Fig. 2).

Endotec stress, used as a condenser itself, produced the most uniform stress pattern, with the fringe orders being the least pronounced compared with lateral condensation (Fig. 3).

DISCUSSION

Visual analysis of photoelastic stress fringe lines indicates that there is greater root stress developed with cold lateral condensation than with the warm lateral condensation technique.

If stress is to be kept minimal, the obturation forces would have to be moderate rather than vigorous. To achieve a proper condensation, some form of ther- mosoftening of the gutta-percha is required. Solvents have been used but may cause shrinkage and have the potential to irritate the periapical tissue. Heat appli- cation has been shown to cause less than 0.45% shrinkagem4 The operator-controlled method of heat- ing would seem to be an appropriate method of ther- mosoftening the gutta-percha.

The term lateral condensation is not an accurate description of the procedure. All lateral condensation techniques will have a vertical component, and all vertical condensation methods will have a lateral component. Multiple vector forces are involved de- pending on the clinical usage of the condensing instrument and the physical characteristics of the gutta-percha being condensed.

Gimlin and coworkers,5 in using engineering com- puter models, illustrated that vertical condensation developed higher average lateral stress and lateral condensation higher localized stress. It is the stress point on the root canal surface that could lead to a crack or fracture. Also, because lateral condensation is an asymmetric placement of a spreader, the stress areas would likely be increased.

Hatton and coworkers6 confirmed that there is no effect on the quality of the apical seal resulting from increased condensation forces. Holcomb and associates7 point out that the amalgam condensation procedure may be too severe for gutta-percha obtura- tion. This has particular clinical relevance for thin roots. They also determined that 26% of the roots treated had incomplete fractures.

Excessive force is not necessary for good obturation and sealing of the canal. Rather, apical penetration of the spreader as near the apex as possible, with

reasonable pressure, is the most important factor.8 Thrust resistance of gutta-percha has been shown to be reduced if heat softening takes place.’ Therefore it would be most desirable to thermosoften the gutta- percha so as to reduce stress and allow for ease and depth of penetration of the spreader to the apical area of the canal preparation. Because the stress pattern is more consistent and reduced with warm lateral con- densation, it would indicate a more uniform and ho- mogeneous obturation. Harvey and colleagues10 thought that another benefit of more diffuse distribu- tion of stress may be a better condensation of the root filling. Preliminary obturation leakage studies with the warm lateral condensation technique by the En- dotec device confirm this hypothesis.”

CONCLUSION

It has been determined that the operator-controlled thermosoftening of gutta-percha allows for ease of lateral condensation with reduced stress points and fringe lines. The significance of this determination is that during the root canal obturation stage, the warm lateral condensation technique with the Endotec de- vice will reduce the potential for creating craze or fracture lines within the root canal.

REFERENCES

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1. Meister F, Tennvson L, Gerstein H. Diagnosis and possible causes of vertical-root fractures. ORAL &JR; ORAL MOD ORAL PATHOL 1980;49:243-53. Wollard R, Brough S, Maggio J, Seltzer S. Scanning electron microscope examination of root canal filling materials. J En- dod 1976;2:98-110. Pitts D, Matheny H, Nicholls J. An in vitro study of spreader loads required to cause vertical root fracture during lateral condensation. J Endod 1983;9:554-50. Wong M, Peters D, Lorton J. Comparison of gutta-percha filling techniques: compaction (mechanical), vertical (warm) and lateral condensation techniques, part 1. J Endod 1981;7: 55 l-84. Gimlin D, Parr C, Aquirre-Ramirez G. A comparison of stresses produced by lateral and vertical condensation using engineering models. J Endod 1986;12:235-41. Hatton J, Ferrillo P, Wagner P, Stewart G. The effect of con- densation pressure on the apical seal. J Endod 1988;14:305-8. Holcomb J, Pitts D, Nicholls J. Further investigation of spreader loads required to cause vertical root fracture during lateral condensation. J Endod 1986;13:277-84. Allison D, Michelich R, Walton R. The influence of master cone adaptation on the quality of the apical seal. J Endod 1981;7:61-5. Gurney B, Best E, Gervasio G. Physical measurements of gut- ta-~~~~~~.ORALSURGORALMEDO~ALPATHOL 1971;32:260- 70. Harvey T, White J, Leeb J. Lateral condensation stress and root canals. J Endod 1981;7:151-5. LaBounty G. Director, Endodontic Program, Walter Reed Army Medical Center, Washington, DC. Personal communi- cation.

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7.

8.

9.

10.

11.

Reprint requests to: Dr. Howard Martin 909 Pershing Dr. Silver Spring, MD 20910