Effect of post preparation on the apical seal of teeth obturated with plastic thermafil obturators

Effect of post preparation on the apical seal of teeth obturated with plastic thermafil obturators

Yd. 76 iV0. 6 Editor: December 1993 Smnuel Seitzer Effect of post preparation on the apical seal of teeth obturated with plastic thermafil obtura...

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Yd. 76 iV0. 6


December 1993



Effect of post preparation on the apical seal of teeth obturated with plastic thermafil obturators Dilek M. Dalat, DDS, PhD,a and Larz S.W. Spangberg, DDS, PhD,b Farmington, Conn. UNIVERSITY






The effect of post canal preparation on the apical seal of endodontically obturated teeth with plastic Thermafil obturators was studied in vitro. Fifty-four extracted human maxillary anterior teeth were divided into four experimental and two control groups, Two groups were obturated with lateral condensation or plastic Thermafil obturator techniques; this was followed by post space preparation. Two groups were obturated as described above except that post space was not prepared. Apical leakage was determined with the use of 2% methylene blue dye solution at an absolute pressure of 75 mm Hg. There were no statistrcally significant differences between any of the groups. The clinical implication of these findings is discussed. (ORAL SURC ORAL MED ORAL PATHOL 1993;76:760-5)

The restoration of endodontically treated teeth often requires intracanal post retention. The post fits into a space created by the removal of a portion of the root canal filling material. Recent studies have investigated the leakage of endodontic obturation techniques and materials related to post preparation. During the preparation of post space, the root canal filling material may become dislodged creating voids in the obturation. Several studieslw4 have reported that no statistical difference in apical leakage could be observed before or after post preparation with various techniques. This lack of significance, however, might be the result of a suboptimal way of demonstrating obturation voids.s Recently a new obturation method was introduced that involves the use of a stainless steel, titanium, or plastic obturator coated with alpha gutta-percha.6 The gutta-percha is plasticized by heat before obturation. When stainless steel or titanium obturators are used for obturation of teeth intended for post retention, the core is usually prenotched for separation and “Professor and Chairperson, Department of Endodontics, Ankara University, Turkey, and Visiting Professor, University of Connecticut Health Center. bProfessor and Head, Department of Restorative Dentistry and Endodontology, University of Connecticut Health Center. Copyright c 1993 by Mosby-Year Book, Inc. 0030.4220/93/$1.00 + .lO 7/16/50728

the coronal portion removed. Lately, flexible guttapercha-coated plastic obturators were introduced to eliminate the need for segmented obturation. The microleakage potential of the plastic core obturators was studied by Chohayeb’ who found no statistical difference between metal and plastic obturators. The advantage of a plastic core obturator is that it can be reduced by drilling when the post space is prepared. During such removal, however, the plastic is more difficult to prepare than the gutta-percha, and it may become dislodged within the canal. This effect was observed by Jeffrey and Saunders8 when removing conventional gutta-percha fillings. The use of heat to soften gutta-percha for post space preparation has been shown not to create more leakage than mechanical removals.‘, 3 Recently, a new mechanical device, Prepi (Fig. l)(Thermafil, Tulsa, Okla.), which generates friction heat, was introduced for the heat removal of these plastic core obturators. This device, which consists of a spherical smooth head mounted on a bur shaft, is operated in a high-speed handpiecc. The head comes in six sizes, with head sizes varying between 0.5 mm and 1.2 mm. Clinically, this device is very efficient, but little is known about the effect on the integrity of the remaining root filling. Therefore the purpose of this study was to determine if the removal of root-filling material with heat using Prepi followed by conventional reamers after


Dalat and Sphgberg


obturation with plastic Thermafil obturator or lateral condensation increased the occurrence of microlumina in the apical part of the root canal. MATERIAL AND ME.THODS Fifty-four extracted human maxillary anterior teeth were collected and stored in a 10% formalin solution-. Before t.he experiment, the teeth were placed into 5.25% sodium hypochlorite (NaOCI) for 8 hours to remove any organic debris. After cleansing, the teeth were rinsed with tap water for 1 hour and stored in saline solution. With the use of a high-speed fissure bur with water spray, the crown of each tooth was removed at the cemento-enamel junction. After the gross pulp tissue was removed a K-file IS0 No. #OlO (Kerr, Romulus, Mich.) was introduced into the root canal until it could be seen at the apical foramen. One millimeter was subtracted from this length to determine the working 1engthL.Each root canal was prepared to an apical size ISO No. 045 and flared with the use of a step-back technique. The coronal two-thirds of the root canal was enlarged with No. 3 and No. 4 GatesGlidden burs (Union Broach, Long Island, N.Y.). Irrigation with 2 ml of 1% NaOCl was used after each file. The canals were dried with paper points, and a K-file size IS0 No. 010 was placed into the root canal to maintain patency of the apical foramen. The roots were randomly divided into four experimental groups, two positive controls, and two negative controls. AH26 (DeTrey, :Ziirich, Switzerland) was used as the sealer in all groups. Before placing the sealer, all root canals were flushed with 95% ethyl alcohol and dried with paper points. Group 1A was treated with lateral condensation technique. This group consisted of 15 roots. A standard size (IS01 No, 045) gutta-percha cone (Premier Dental Products Co., Morristown, Pa.) was fitted to the working length with tug back. AH26 sealer was mixed according to the manufacturer’s directions and placed into the canal wall with a rotary paste filler to the working length. After placing the sealer, the master cone was coated with sealer and gently seated to the working length. A Dl 1 root canal spreader (Premier Dental Products Co., Morristown, Pa.) was introduced to within 2 mm of the working length, and lateral condensation with fine-fine accessory guttapercha cones coated with sealer was carried out until they could not be introduced more than 3 mm into the root canal. Group 1B was treated with a lateral condensation technique followed by post preparation. This group consisted of 10 roots. All root canals were obturated as in Group 1A.

Fig. 1. Prepi pre-post preparation instrument.

Group 2A was treated with a thermafil technique. This group consisted of 15 roots. The correct size of the plastic core Thermafil obturator (Tulsa Dental Products, Tulsa, Okla.) was selected with the use of the Thermafil size verification kit. The Thermafil obturators were heated in a ThermaPrep oven for a maximum of 15 minutes according to the manufacturer’s instructions. AH26 sealer was lightly applied into the root canal with paper point, and the Thermafil device was inserted to the predetermined length. The shank of each carrier was cut with an inverted cone bur while holding the handle of the obturator at the root canal orifice. The circumferential gutta-percha was condensed vertically. Group 2B was treated with a thermafil technique followed by post preparation. This group consisted of 10 roots. All root canals were obturated as in Group 2A. After the obturation of each group radiographs were taken from the buccal and mesial aspects of each root to visually evaluate the obturation. Gutta-percha was removed from the coronal 3 mm of all obturated root canals with a warm instrument,




and Sp&gberg



I. Linear methylene blue dye penetration, in mm, for each sample in the various groups: individual sample values, mean and standard deviation (SD) for each group


Sample number 1 2 3 4 5 6 I 8 9 10 11 12 13 14 15 Mean SD

Lateral condensation 3.00 1.00 4.25 4.75 2.50 0.75 3.25 3.75 2.25 1.oo 1.50 0.75 3.75 0.50 0.75 2.25 1.46

Lateral condensation -Ipost preparation


1.25 1.oo 0.15 1.oo 0.75 1.25 6.00t 6.00' 2.00 1.25

0.25 0.50 0.50 2.00 0.75 3.50 1.50 3.25 0.50 1.oo 3.15

Therma$l + post preparation 0.25

1.75 0.75 0.50 1.75 1.oo 0.15 1.50 6.00' 5.50'

1 .oo

1.00 1.oo 0.75 1.41 1.16

2.13 2.07

1.97 2.06

t = total penetration

and the coronal part of all canals were sealed with Cavit (ESPE, GmbH, Seefeld, Germany). The sampleswere stored for 48 hours at 37” C and 100% humidity to ensure setting of the sealer, after which the roots in groups 1B and 2B were prepared to accept a post. The coronal gutta-percha was removed with a Prepi (Tulsa Dental Products, Tulsa, Okla.) sizes varying from 0.5 to 1.2 mm leaving 5 to 6 mm of the root filling. The root canals were then enlarged with a 1.25 mm Para Post drill (Whaledent International, New York, N.Y.). The post spacewas left empty, and the coronal accesscavity was sealed with Cavit. The roots were covered with two layers of nail polish and sticky wax to within 2 mm of the apex. The two positive control teeth were filled with a loosely fitted gutta-percha cone, and the accesspreparation sealed with Cavit. The roots, except the apical foramen, were covered with nail polish and sticky w&x. The two negative control teeth w-erenot obturated and completely sealedwith nail polish and sticky wax, after the accesscavity was sealed with Cavit. All specimens were immersed in a vacuum Aask containing 2% aqueous methylene blue dye solution. The air was evacuated with a vacuum pump (Doerr Electric Corporation, Cedarburg, Wis.) to an absolute pressure of 75 mm Hg. The specimenswere removed from the chamber after 30 minutes and were allowed to remain in the dye solution at 37” C for an

additional 7 days at 1 atm. At that time the specimens were rinsed with water, all of the nail polish and sticky wax was removed with a razor blade, and the teeth were split longitudinally in labiolingual direction. The fracture line was determined by first scoring the root surfaces with a diamond disk. The linear measurement of dye penetration was made with a stereomicroscope (Nikon SMZ-2T, Tokyo, Japan) at a magnification of Xl to 6.3 with a millimeter ruler (Union Broach, Long Island, N.Y.) and an ocular micrometer with a precision of 0.25 mm. To determine the most coronal point of linear dye leakage, two measurements were made. First, after splitting the roots, dye penetration was measured from the apex to the most coronal extent of dye visible on the gutta-percha filling material or root canal walls. Second, after the gutta-percha filling material had been removed with an endodontic explorer, dye penetration was measured on the canal walls. The measurementsof dye penetration were compared, and the larger value was used as the most coronal point of linear dye leakage. The obtained results were submitted for statistical analysis with the use of an unpaired t test. RESULTS

The radiographs of the obturated roots showed no voids in any of the root canals. The negative control roots showed no dye penetration. Both of the positive control roots showed complete dye penetration.


Dalat and Spkngberg

Fig. 2. Lateral condensation. Root canal prepared for post retention leaving 6 mm of remaining gutta-percha. A, ELxampleof low level of dye leakage (arrow) (1.25 mm). B, Dye has leaked into the post space(arrow) (6 mm).

Fig. 3. Thermafil obturation. Root canal prepared for post retention leaving 6 mm of remaining obturation. A, Example of high level of dye leakage (arrow) (6 mm). Dye has leaked into the post space.B, Example of low level of dye leakage (arrow) (1.25 mm).


Dalat and Sphgberg

The mean and standard deviations of linear dye penetration measurements are listed in Table I. The mean leakage for roots obturated with lateral condensation technique followed by post preparation (Group 1B) was 2.13 +- 2.07 mm, in the group obturated with Thermafil technique followed by post preparation (Group 2B) 1.97 I 2.06 mm, in the group obturated with lateral condensation, (Group 1A) 2.25 f 1.46mm, and in the group obturated with Thermafil technique (Group 2A) 1.41 + 1.16 mm. Figs. 2 and 3 illustrate some typical findings. There were no statistically significant differences in the length of dye leakage between any of the groups 4p 3 0.05). DlSCUSSlON Various techniques for the removal of gutta-percha materials for post preparation have been described. The results of these studies have shown that the integrity of the remaining obturation after removal of root canal filling materials depends on a number of factors.3 Some of these factors are time of sealer setting, techniques usedfor removal, and the instruments used. The length of the remaining materials is also important. l-4>6,7,9-15Prepi (Tulsa Dental Products, Tulsa, Okla.), which creates frictional heat when operated, removes the plastic obturator of Thermafil quickly and efficiently. It also eliminates the potential for root perforations as it has a smooth and noncutting head. Frictional heat, which is generated by this rotary instrument using a water cooling system, softens and removesthe gutta-percha and the plastic obturator from the pulp space.Some authors16have investigated the possibility that deleterious frictional heat may be generated during the mechanical removal of the gutta-percha. It has been shown, however, that during normal post spacepreparation only a minimal temperature increase was generated. With the effective use of a high-speed multijet water coolant systemand intermittent preparation in the present study no temperature increase was noted in the root dentin. Studies have shown that it is essential that sufficient time is allowed for the root canal sealer to set 2,rz, l3 although some studies suggest that immediate removal would be superior.t4, t5 In the present study we allowed 48 hours, which is sufficient time for the AH26 sealer to set firmly. Another factor that affects the apical leakage during the preparation of post space is the remaining length of the root canal filling material. It has been shown that shorter lengths of root canal fillings are associatedwith more leakage.‘O,l4 It is generally rec-


ommended that approximately 6 mm gutta-percha should remain in the root canal.9 As can be seenin Table I, no statistically significant differences were observed between the obturations when post preparation was performed compared w-ith unprepared obturations. The results, which were obtained with the use of a highly effective vacuum method, show findings similar to other reports.17 Although there were no statistically significant differencesin the extent of dye penetration before or after removal of gutta-percha in this study, we observed that in root canal prepared samples, two total penetrations from periapex to the post spacewere found in each group. None of the unprepared obturations with lateral condensation or Thermafil had a microlumen reaching as far as 6 mm from the radiographic apex (Table I). From a clinical point of view, this total penetration is a catastrophic failure of the integrity of the root canal filling. This illustrates that statistical comparison of data may not always reveal important observation without examining the raw data. Regardless of mechanisms, however, there were no more problems associatedwith Thermafil obturations than with lateral condensation. Results from this and other studies in our laboratory indicates that most gutta-percha root fillings have apical microlumina that should be considered when preparing root canals for post retention. Thus even without disturbing the integrity of the root filling material during post space preparation, microlumina with periapical communication may be exposed. The reaming of root canals after root fillings must therefore be done under the same aseptic conditions as when the original root filling was placed. Using rubber dam and asepsis, the removal of root filling materials and fabrication of posts will reduce the risk for long-term failures associatedwith post placement after endodontic treatment. REFERENCES 1. Madison S, Zakariasen KL. Linear and volumetric analysis of apical leakage in teeth prepared for posts. J Endodon 1984; 10:422-7. 2. Ewart A, Saunders WP. An investigation into the apical leakage of root-filled teeth prepared for a post crown. Int Endodon J 1990;23:239-44. 3. Hiltner RS, Kulild JC, Weller RN. Effect of mechanical versus thermal removal of gutta-percha on the quality of the apical seal following post space preparation. J Endodon 1992; 18:451-4. 4. Saunders WP, Saunders EM, Gutmann JL, Gutmann ML. An assessment of the plastic Thermatil obturation technique. Part 3: the effect of post space preparation on the apical seal Int Endodon J 1993;26:184-9. 5. Spdngberg LSW, Acierno TG, Cha BY. Influence of entrapped air on the accuracy of leakage studies using dye penetration methods. J Endodon 1989;15:548-51.

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ORAL SURGERY GMEDICINE ORAL PATHOLOGY Volume 76, Number ti 6. Johnson WB. A new gutta-percha technique. J Endodon 1978; 4:184-8. I. Chohayeb APL. Microleakage comparison of apical seal of plastic versus metal ‘Thermafil root canal obturators. J Endodon 1992;18:613-5. 8. Jeffrey IWM, Saunders WP. An investigation into the bond strength between a root canal sealer and root-filling points. Int Endodon J 1987;20:217-22. 9. DeCleen MJH. The relationship between the root canal filling and post space preparation. Int Endodon J 1993;26:53-8. 10. Mattison GD, Delivanis PD, Thacker RW, Hassell KJ. Effect of post preparation on the apical seal. J Prosthet Dent 1984;51:785-9. 11. Camp LR, Todd MJ. The effect of dowel preparation on the apical seal of lthree common obturation techniques. J Prosthet Dent 1983;50:664-6. 12 Zmener 0. Elfect of dowel preparation on the apical seal of endodontically treated teeth. J Endodon 1980;6:687-90. 13 Bourgeois RS, Lemon RR. Dowel space preparation and apical leakage. J Endosdon 1981;7:67-9.

14. Porte11 FR, Bernier WE, Lorton L, Peters DD. The effect of immediate versus delayed dowel space preparation on the integrity of the apical seal. J Endodon 1982;8:154-60. 15. Kwan EH, Harrington GW. The effect of immediate post preparation on apical seal. J Endodon 1981;7:325-9. 16. Saunders EM, Saunders WP. The heat generated on the external root surface during post space preparation. Int Endodon J 1989;22:169-73. 17. Mattison GD, Hwang CL, Cunningham C, Pink FE. The effect of post preparation in the apical seal in teeth filled with Thermafil. IADR, July 1992, Abstract 676. J Dent Res 1992;72:600. Reprint requests: Larz S. W. Spangberg, DDS, PhD Department of Restorative Dentistry and Endodontology University of Connecticut Health Center Farmington, CT 06030-17 15

CALL FOR REVIEW ARTICLES The January 1993 issue of ORAL SURGERY,~RAL MEDICINE,~RAL PATHOLOGY contained an Editorial by the Journal’s new Editor in Chief, Larry J. Peterson, that called for a Review Article to appear in each issue. Thlese Review Articles should be designed to review the current status of matters that are important to the: practitioner. These articles should contain current developments, changing trends, as well as reaffirmation of current techniques and policies. Please consider submitting your article to appear as a Review Article. Information in each issue of ORAL SURGERY, ORAL MEDICINE,~RAL PATHOLOGY. We look forward to hearing from you.


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