Effect of mechanical versus thermal removal of gutta-percha on the quality of the apical seal following post space preparation

Effect of mechanical versus thermal removal of gutta-percha on the quality of the apical seal following post space preparation

0099-2399/92/1809-0451/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists Printed in U.S.A. VOL. 18, No. 9...

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0099-2399/92/1809-0451/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists

Printed in U.S.A.

VOL. 18, No. 9, SEPTEMBER1992

Effect of Mechanical versus Thermal Removal of Gutta-percha on the Quality of the Apical Seal following Post Space Preparation Randall S. Hil ~er, DMD, James C. Kulild, DDS, MS, and R. Norman Weller, DMD, MS

The objective of this study was to compare the effects of a flame-heated endodontic plugger, an electrically-heated endodontic spreader, Peeso reamers, and GPX burs on the apical seal when guttapercha was removed from the root canal for post space preparation. Eighty-nine human canines were instrumented and obturated with gutta-percha and sealer to a standardized working length of 15 ram. An 11-mm segment of gutta-percha was removed from the roots in each of the four experimental groups of 20 teeth to simulate post space preparation. The teeth were immersed in India ink for 7 days and rendered transparent. The extent of linear dye leakage was measured with a stereomicroscope. There was no statistically significant difference in linear dye leakage among any of the experimental groups when 4 mm of gutta-percha remained.

resulted in no significant difference in apical leakage (3-8). Kwan and Harrington (9) and Madison and Zakariasen (8) found that post space preparation with Gates Glidden burs immediately after obturation actually decreased the amount of apical leakage. Other studies reported no significant difference in the amount of apical leakage after post space preparation between heated endodontic pluggers, Peeso reamers, and Gates Glidden burs (2, 8-11). Neagley (12) found that obturation of the root canal by the lateral condensation of GP resulted in less apical leakage after post space preparation than did warm GP and silver point obturation techniques. A more recent study by De Nys et al. (13) reported no significant difference in apical leakage after post space preparation when the canal had been obturated with either lateral or warm vertical condensation of GP, a combination of a silver cone and lateral condensation of GP, or the high- or low-temperature thermoplasticized injectable GP techniques. To date, studies investigating the effect of post space preparation on the apical seal have used pluggers heated by an uncontrolled flame or rotary instruments (Peeso reamers and Gates Glidden burs) to remove GP from the root canal space. The rotary instruments engage dentin on the lateral walls of the canal, alter the shape of the canal, and generate heat as a result of the friction according to Saunders and Saunders (14). New, electrically controlled heated instruments (Touch 'n Heat; Analytic Technology, Redmond, WA) have been introduced which can remove GP from the root canal. Additionally, a new rotary instrument (GPX; Brassler USA Inc., Savannah, GA) has been introduced which removes GP but does not remove dentin. The degree to which either of these instruments affects the quality of the apical seal has not been determined. The purpose of this study was to compare the effects on the apical seal when an electrically controlled heated spreader, a new rotary GP removal instrument, a flame-heated endodontic plugger, or Peeso reamers were used to prepare post space in a root canal previously obturated with GP and sealer.

A common method of restoring endodontically treated teeth is with a post, core, and cast metal restoration. The post is cemented in a prepared root canal space, the core replaces lost coronal tooth structure, and a crown is fabricated to cover and protect the core. The crown also reestablishes function and arch integrity, and provides esthetics. The length of the post depends on the root shape, length, and the height of the desired core (1). The root canal system must be prepared before a post can be placed. This preparation involves removal of the root canal filling material, removal of dentin along the wall of the root canal, or a combination of both. Although the length of the post within the root canal may vary, the apical 4 m m of the root canal filling material should not be disturbed. Previous studies (1, 2) have indicated that significant apical leakage may occur if less than 4 m m of apical gutta-percha (GP) remains within the root canal. The technique for GP removal does not appear to be as clinically significant as the amount of remaining GP. Schnell (3), using heated endodontic pluggers for GP removal, reported no significant difference in leakage of the apical seal after immediate or delayed post space preparation. Other investigators have confirmed that a delay of 48 h to 1 wk

M A T E R I A L S AND M E T H O D S Eighty-nine permanent human canine teeth previously extracted due to nonrestorable caries, periodontal disease, or orthodontic reasons were stored in a solution of 0.5 % NaOC1.



Hiltner et al.

The teeth were sectioned with a separating disc at the cementoenamel junction perpendicular to the long axis of the root. A #10 K-Flex file (Kerr Manufacturing Co., Romulus, MI) was placed into the root canal until it was just visible at the apical foramen. The working length was established by subtracting 1 m m from this length. A high-speed diamond wheel (#863; Premier Dental Products Co., Norristown, PA) was used to plane the coronal portion of the root until the working length was standardized at 15 m m for all of the specimens. The canal was cleaned and shaped using a standard step-back technique until a #50 K-Flex master apical file could be placed to the working length. A #10 K-Flex file was used to ensure patency of the apical foramen between each change in the file size. Saline was used as the irrigation solution. The canal was then dried with coarse paper points (Premier Dental Products Co.) and obturated using standard lateral condensation of GP (Hygenic Corp., Akron, OH) and sealer (Roth 801; Roth Drug Co., Chicago, IL). A radiograph of each specimen was exposed to confirm satisfactory obturation of the root canal. Approximately 3 m m of coronal GP was removed with a flameheated endodontic plugger and the remainder vertically condensed with room temperature endodontic pluggers. A temporary restoration (IRM; L. D. Caulk Co., Milford, DE) was placed in the coronal access. The teeth were stored at 100% humidity at 37°C for 1 wk to allow the sealer to set. The roots were randomly divided into one of four experimental groups of 20 teeth each. Six teeth were used as positive controls and three as negative controls. The teeth were then dried and the temporary restorations were removed. A #3 Peeso reamer in a slow-speed handpiece was used to remove all but the apical 4 m m of GP in the roots in group 1. A #50 GPX bur was used to remove all but the last 4 m m of GP in group 2. In group 3, a butane burner (Wall Lenk Corp., Kingston, NC) was used to heat one end of a #9-11 endodontic plugger (Union Broach, New York City, NY) cherry red. GP was removed with this instrument until 4 m m of GP remained. In group 4, an electrically controlled, large anterior heated spreader (Touch 'n Heat; Analytic Technology) was used at a control setting of 5 in the touch/charge mode to remove GP until 4 m m of the GP remained. A rubber stopper was placed on the spreader to verify depth of the instrument within the canal and ensure that 4 mm of intact GP remained in the apical portion of the root canal. Figure 1 demonstrates the instruments used to remove the GP from the canals. The remaining apical guttapercha was gently vertically condensed with the #9 end of a room temperature #9-11 endodontic plugger (Union Broach). A radiograph of each specimen was exposed to confirm that 4 mm of GP remained. No GP was removed in three positive controls. In a second set of three positive controls, the root canal was obturated with a loose-fitting GP cone with no sealer in the canal. An amalgam restoration approximately 3 mm in depth was placed in the access opening of each of the controls. Following post space preparation, amalgam (Tytin; Kerr Manufacturing Co.) was condensed into all experimental post space preparations to simulate a post. The roots were then covered with sticky wax except for the apical 2 mm. The remaining root surface was covered with two coats of fingernail polish (Maybelline Co., N. Little Rock, AR), leaving only the apical foramen exposed. The entire root of three speci-

Journal of Endodontics

mens, serving as negative controls, was completely coated with nail polish. The roots in all of the experimental groups and the control teeth were placed in separate containers of India ink (Hunt Speedball, Statesville, NC) at 37°C for 7 days. The teeth were then washed in tap water to remove the ink and the sticky wax and nail polish were removed. The roots were decalcified by immersion in 5% nitric acid for 72 h with daily changes of the acid. The roots were dehydrated in absolute methyl alcohol for 3 days with daily changes of the alcohol. Methyl salicylate was used to complete the clearing process. The extent of linear ink penetration was measured by a single operator from the apical extent of the gutta-percha to the most coronal level of ink penetration. Measurements were recorded to the nearest 0.01 mm with a stereomicroscope (Wild MPS 51S; Wild, Heerbrugg, Switzerland) at x6 magnification with a calibrated ocular eyepiece. The experimental and control groups were assigned coded numbers so the operator could not identify which roots were being measured. Statistical analysis was performed by one-way analysis of variance and Tukey's honestly significant difference test with a 0.05 confidence level for significance. RESULTS The results are listed in Tables 1 and 2. Group 3 demonstrated the greatest number of canals exhibiting no apical leakage (12 specimens). Group 4 demonstrated the fewest roots exhibiting no linear apical microleakage (five specimens). Group 3 also had the greatest range in leakage of all groups from 0.00 to 1.42 ram. Group 2 had the lowest average







FiG 1. Instruments used to remove GP from the root canal specimens. A, #9 end of a #9-11 endodontic plugger; B, #50 GPX bur; C, #3 Peeso reamer; D, large anterior Touch 'n Heat spreader. TABLE 1. Linear apical microleakage (mm) Group


Range (mm)

Mean (mm)


No Leakage

1 2 3 4

20 20 20 20

0.00-1.01 0.00-0.64 0.00-1.42 0.00-1.13

0.29 0.17 0.20 0.28

0.31 0.20 0.34 0.25

9 9 12 5

Vol. 18, NO. 9, September 1992

Post Space Preparation

TABLE 2. Statistical analysis (analysis of variance)* Source

Sum of Squares


Mean square

Between groups Within groups

0.2074838 6.052115

3 76

0.0691613 0.0796331




F ratio 0.868

* Significancelevel: p = 0.4613(not significant).

leakage, the lowest standard deviation, and the narrowest leakage range. The three negative controls demonstrated no apical leakage. The three positive controls which were obturated but not prepared for post space showed no leakage. The three positive controls with a loose fitting GP cone showed dye leakage the entire length of the canals. There was no statistical significant difference between any of the experimental group at a confidence level of p < 0.05 using one-way ANOVA. DISCUSSION The methodology of GP removal for post space preparation used in the present investigation was designed to simulate a clinical situation as much as possible. Mattison et al. (2) reported that the mechanical removal of GP with a Gates Glidden drill was the most desirable method of post space preparation compared with chemical solvent or heated instrument. In this present investigation, the use of G P X burs yielded the lowest mean leakage but the difference was not statistically significant. Madison and Zakariasen (8) found no statistically significant difference in linear apical dye leakage when GP was removed by flame-heated endodontic pluggers or Peeso reamers when 5 m m of apical GP remained. The present study confirms no statistically significant difference in apical dye leakage between flame-heated endodontic pluggers and Peeso reamers when 4 m m of apical GP seal remained. Lateral condensation of GP with sealer was used to obturate all of the specimens since this has been the most popular root canal filling technique. Suchina and Ludington (10), Camp and Todd (11), Neagley (12), and De Nys et al. (13) showed that alternate obturation techniques yielded no statistical difference in apical leakage provided 4 to 5 m m of GP remained at the apex. Four millimeters of remaining apical GP was chosen in this study. Portell et al. (4) reported that 3 m m showed statistically increased leakage (p < 0.01) over 7 m m if post space preparation was delayed for 2 wk. Dickey et al. (7) reported significant apical leakage if the sealer was not allowed to set when 3 m m of GP remained at the apex. However, their results may have been due to an insufficient amount of remaining GP rather than the time of post space preparation. Advantages and disadvantages exist for each of the GP removal techniques used in the present study. Peeso reamers are inexpensive and remove the GP very rapidly. The rotary action creates parallel walls which provide optimal retention form for the post. Disadvantages of Peeso reamers include the possibility of creating root perforation, canal transportation, overenlargement of the canal resulting in weakened remaining root structure, and instrument separation. Peeso


reamers should be used only in straight canals or short of any apical curvature. They should also be used in increasingly larger sizes until dentinal dust appears. Enlarging the canal space beyond this point generates frictional heat and increases the danger of canal overenlargement, transportation, or perforation. Dentinal dust was often found in the apical portion of the post space in this study. Air from the three-way syringe was not sufficient to remove this debris. GPX burs are tapered rotary instruments that, according to the manufacturer, match standardized endodontic file sizes #25 to #50. Engaging the GP causes slight frictional heat which softens the GP before removal. Although developed for complete GP removal in retreatment cases, the GPX was also fast and effective in post space preparation. The bur does not engage the dentin so canal shape remains unaltered and the frictional heat generated is minimal. The burs are relatively inexpensive. Length control was more difficult than with the Peeso reamer because excessive build-up of the removed GP on the bur shank displaced the rubber stopper. Cleaning the GP mass from the bur before it reached the stopper lessened this problem. A disadvantage of the GPX could be instrument separation. This could occur if the instrument bound in a canal irregularity or was used past a canal curvature. No GPX burs separated in this experiment while removing GP. Flame-heated endodontic pluggers are a fast and inexpensive means of GP removal and there is no canal shape alteration. A disadvantage of this technique is the burn potential for the dentist, dental assistant, or the patient. Gloves and the rubber dam offer scant protection. Damage to the periodontal ligament by flame-heated pluggers does not appear to be a problem. Hand et al. (15) found that flame-heated endodontic pluggers did not cause any permanent damage to the periodontium when used for vertical condensation. Another disadvantage of flame-heated pluggers is the rapid heat dissipation in smaller pluggers which slows GP removal. Additionally, length control can be a problem because the rubber stopper for canal depth measurement may catch fire or degrade so rapidly that it slides freely on the plugger. The Touch 'n Heat electrically heated spreader was not designed for GP removal for post space preparation, but the device was effective in this ancillary role. It was able to rapidly remove GP from the obturated canals due to its ability to sustain a high temperature. Additionally, the thin spreader allows precurving, if required, and the canal shape remains unaltered during GP removal. Disadvantages of the Touch 'n Heat are its high cost and burn potential for patients and staff. The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the United States Army or Department of Defense. Dr. Hiltner is assistant chief, endedontics, US Army Dental Activity, Fort Stewart, GA. Dr. Kulild is director and Dr. Weller is former director, endodontic residency program, US Army Postgraduate Program, US Army Dental Activity, Fort Gordon, GA. Address request for reprints to COL James C. Kulild, US Army Dental Activity, Fort Gordon, GA 30905-5660.

References 1. Baraban DJ. The restoration of endodontically treated teeth: an update. J Prosthet Dent 1988;59:553-8. 2. Mattison GD, Delivanis PD, Thacker RW, Hassell KJ. Effect of post preparation on the apical seal. J Prosthet Dent 1984;51:785-9. 3. Schnell FJ. Effect of immediate dowel space preparation on the apical seal of endodontically filled teeth. Oral Surg 1978;45:470-4.


Hiltner et al.

4. Portell FR, Bernier WE, Lorton L, Peters DD. The effect of immediate vs delayed dowel space preparation on the integrity of the apical seal, J Endodon 1982;8:154-60. 5. Zmener O. Effect of dowel preparation on the apical seal of endodontically treated teeth. J Endodon 1980;6:687-90. 6. Bourgeois RS, Lemon RR. Dowel space preparation and apical leakage. J Endodon 1981 ;7:66-9. 7. Dickey DJ, Harris GZ, Lemon RR, Luebke RG. Effect of post space preparation on apical seal using solvent techniques and peeso reamers. J Endodon 1982;8:351-4. 8. Madison S, Zakariasen KL. Linear and volumetric analysis of apical leakage in teeth prepared for posts. J Endodon 1984;10:422-7. 9. Kwan EH, Harrington GW. The effect of immediate post preparation on apical seal. J Endodon 1981 ;7:325-9,

Journal of Endodontics 10. Suchina JA, Ludington JR. Dowel space preparation and the apical seal. J Endodon 1985;11:11-7. 11. Camp LR, Todd M J. The effect of dowel preparation on the apical seal of three common obturation techniques. J Prosthet Dent 1983;50:121-6. 12. Neagley RL. The effect of dowel preparation on the apical seal of endodontically treated teeth. Oral Surg 1969;28:739-45. 13. De Nys M, Martens L, De Coster W, Thys M Evaluation of dowel space preparation on the apical seal using an image processing system. Int Endod J 1989;22:240-7. 14. Saunders EM, Saunders WP. The heat generated on the external root surface during post space preparation, int Endod J 1989;22:169-73. 15. Hand RE, Huget EF, Tsaknis PJ. Effects of a warm gutta-percha technique on the lateral periodontium. Oral Surg 1976;42:395-401,

The Way It Was The proliferation of the scientific literature bids fair to be out of control. How are we to isolate from these masses of data the few words such as these from a 1929 paper by Alexander Fleming which have changed the world? " . . . it was noticed that around a large colony of a contaminating mould the staphylococcus colonies became transparent and were obviously undergoing lysis." Wallace Sturr