Effect of immediate dowel space preparation on the apical seal of endodontically filled teeth Frederick J. Schnell, Lieutenant Colonel, DC, USA The purpose of thisstudy was to investigate in vitro the effect of using hot endodonticpluggers for immediate dowel space preparation on the apical seal of endodonticahy treated teeth tilled by a chloropetcha technique. The results demonstratedthat, when the coronal half of the root canal filling material was removed immediately after placement with pluggers, there was a loss of the apical seal and leakage in thirteen of twenty teeth. There was also leakage in thirteen of twenty teeth in which dowel spaceswere not prepared. This study did not demonstratea significant difference statistically in loss of apical seal and leakage between teeth prepared with and those without immediate dowel spacepreparationswith pluggers using a chioroperchafilling technique. Immediatepreparationof the dowel spaceshad no effect on the apical seat. The chloroperchatechniqueby itself showedevidence of very high leakage when used to fill the root canal.
D entists are frequently confronted with the need to treat badly broken-down vital or
nonvital maxillary anterior teeth endodontically. After completion of endodontic therapy, these teeth must then be restored to provide function, good appearance,and protection from fracture. The following components are necessary to restore an endodontically treated anterior tooth’s 2: (1) A dowel (post, pin, or substructure)that is the length of the crown or one half the length of the root to provide internal support. (2) A core (superstructure) to replace lost tooth structure and provide retention for the separatecrown. The dowel and core are cast as one unit. (3) A porcelain-fused-to-metalcrown with a collar of gold and margins on tooth structure to add more reinforcementand a good fit to the tooth. Creating a dowel space for the dowel or post is a very critical phase for the fixed prosthetic treatment becauseit necessitatesremoval of a portion of the root canal filling material. During preparation of a dowel space with rotary instruments on either guttapercha or silver points, the possibility exists of twisting the entire filling or creating vibrations and breaking the seal. Additional hazardsof using rotary instruments are root perforation and overpreparation of the tooth. The loss of the apical seal is the major causeof endodontic failures, with the second most common causebeing root perforation.3-6 There are several advantagesif the endodontist preparesthe dowel spaceat the time the root canal is filled. One advantageis that the treatmenttime for the construction of the fixed prosthesis by the prosthodontist would be reduced. The most important advantage, 470
Effect of immediate dowel space preparation
however, is that the endodontist is well acquaintedwith the length of the tooth, the angle of inclination, and the morphologic features of the endodontic system. All proceduresin the preparation of the dowel spaceshould be performed with the rubber dam in place. The use of hand instruments will greatly minimize the possibility of root perforation and overpreparation of the internal tooth structure. Filling materials and methods used in endodontics could also affect the apical seal. Neagley,’ using fissured burs and peeso reamers, prepared dowel spacesin teeth treated with silver cones and gutta-percha. His results demonstratedcomplete dye penetration in eight of nine specimensfilled with silver cones when the rotary instruments touched the silver cones. There was no leakagein seventeeth filled with silver coneswhen the silver cones were not encroachedupon. He also obtained leakage in one of fourteen teeth filled with gutta-percha and sealer when the dowel spaceswere prepared. Leakage occurred in seven or eight teeth when only retrograde amalgams were placed. A dye visible under ultraviolet light was used to examine for leakage. In an unpublished study, Zeiglera prepareddowel spaceswith peesoreamersin fortyfour teeth filled with gutta-perchaand sealer. He obtained marginal and complete leakage in twelve of the teeth. Radioisotopeswere used to test for leakage. Both Neagley and Zeigler’s studies were on the effect of delayed dowel spacepreparation, that is, a period of time elapsed between the completion of endodontic therapy and the preparation of the dowel spacein order to allow the complete setting of the root canal sealing agent. Schroedefl sealedmethylene blue dye above the root canal fillings and centrifuged the teeth. Gutta-percha points sealed with chloropercha leaked, with and without centrifuging. According to Phillips,1o, r1 gutta-perchais not a satisfactory temporary filling material becauseextreme gross leakage occurs. Gutta-percha exhibits low flow and high rigidity and does not adapt well to tooth structure. Few dental materials show greater marginal leakage. Cements such as zinc oxide and eugenol have to be used in addition to this rubber-like material in order to make it serviceable as a root canal filling material. The purposeof this study was to investigate in vitro the effect of using hot endodontic pluggers for immediate dowel space preparation on the apical seal of endodontically treated teeth filled by a chloropercha technique. MATERIALS AND METHODS
Forty maxillary anterior teeth with completed root formation were collected after extraction from patients at Craven Dental Clinic, Fort Knox, Kentucky. These patients required complete maxillary immediate denturesbecauseof generalizedperiodontitis. The teeth were placed in a 10 percent formalin solution. Next, the forty teeth were transferred to a 5.25 percent sodium hypochlorite solution for 2 days and then held in an isotonic saline solution prior to testing. The crowns were removed at the cementoenameljunction, and the pulps were extirpated with barbed broaches. The root canals were instrumented and filled by a chloropercha technique. The root canals were instrumented with standardized files (Nos. 10-50) in a sequential order. Files no larger than No. 20 were allowed to passthrough the apical foramen. The larger files after No. 20 were dropped back 0.5 mm. from the apical foramen and then instrumented to a depth short of the apical foramen to establish an apical stop. The canalswere cleanedand sized by the peripheral circumferen-
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Table 1. Leakage induced by immediate dowel spacepreparation Control-No
No. of teeth
Subgroup of teeth
Subgroup of teeth
Gutta-percha Chloropercha Sealer
*$ = No significant difference.
tial vertical filing motion on all the walls of the canals, The canals were kept wet and were irrigated frequently with saline solution during instrumentation. When they were dry, the canalswere filled. A standardgutta-perchapoint was selectedwhich fit to within 1 mm. of the apical stop and provided resistanceon withdrawal. The sealer* was mixed to a thick consistency,placed on a No. 20 file, and rotated counterclockwise inside the root canal to coat the walls. The apical 1 to 2 mm. portion of the mastergutta-perchapoint was dipped in chloropercha, then firmly seatedinto the canal with a back-and-forth pumping action. Spreaderswere used to laterally condenseand provide spacefor accessorygutta-percha points. The apical portion of the accessorypoints were coated with sealer prior to their insertion into the canal, Successiveaccessorypoints were addeduntil the root canalswere entirely filled. The teeth were divided into two subgroups. In one subgroup, twenty teeth were filled to the cementoenameljunction and servedas controls. In the other subgroupof twenty teeth, dowel spaceswere prepared in the coronal half of the roots. The dowel spaceswere preparedimmediately with hot endodontic pluggers, with the use of vertical pressureto remove the coronal portion of the filling material. After the dowel spaceswere created, vertical pressurewith cold pluggers wasapplied to the remaining apical portion of the filling material. The forty teeth were x-rayed in two dimensions (buccolingual and mesiodistal) in order to evaluate the adequacyof the fills. The sealerin the forty teeth was allowed to set for 10 days. The teeth were then ready for testing for dye penetration by capillary action, with the use of methylene blue dye. Surgident periphery wax,? which is soft and tacky, was molded over the roots, except for the apical foramen, which was left exposed. The roots were maintained in a vertical direction with the apical portions submerged in the dye for 2 days. The teeth were then sectioned in a longitudinal direction with a safe-sideddiamond disc and examined for dye penetration. The sectioned teeth were examined under a strong light, but without magnification, to determine whether leakage had occurred. Any penetration, from marginal to complete, was counted as leakage. RESULTS
On the basis of radiographic evidence, the forty endodontic fillings were judged to be satisfactory. The results of the use of hot endodontic pluggers for immediate dowel space preparation on the apical seal of teeth filled endodontically by a chloropercha technique showed loss of apical seal and leakage in thirteen of twenty teeth. In the control *Procosol, manufactured by Star Dental Manufacturing Co., Inc., Conshohocken, Pa. 19428. tLactona Corporation Distributor, Academy and Red Lion Roads, Philadelphia, Pa. 19114.
Effect of immediate dowel space preparation
group, leakageoccurred in thirteen of twenty teeth when dowel spaceswere not prepared (Table I). This study did not demonstratea significant difference statistically in leakagebetween teeth prepared with and those without immediate dowel spacepreparation with pluggers using a chloropercha filling technique. Immediate preparation of the dowel spaceshad no effect on the apical seal. The chloroperchatechnique by itself showedevidence of a great amount of leakage when used to fill root canals. DISCUSSION
The high incidence of leakage in the teeth filled by means of the chloropercha technique was probably due to the dimensional change which occurs subsequentto the evaporation of the chloroform. This evaporation causes considerable shrinkage of the filling material so that it draws away from the walls and shrinks toward a center within the mass, thus leaving a spaceat the periphery. It has been shown that, at best, even when additional gutta-perchacones are addedto chloropercha, there is still about a 7.5 percent loss in volume due to shrinkage.12 Gutta-perchaand zinc-oxide are listed in dental materials books as being suitable only for temporary fillings. They are used in endodontics as permanent root canal filling materials. In many studies, gutta-perchahas shown leakageand is not a sealing agent but an obturator or core. The sealing effect in endodontic therapy is derived from the sealer. Of all currently useddental cements,zinc oxide-eugenol hasbeenproven to give the most clinically acceptableseal. Endodontic successdepends on creating an environment in which repair can take place. Even if the apical foramen is not 100 percent sealed in 100 percent of the teeth treated, repair and healing can occur. Most likely, there is a critical leakagefactor beyond which biologic repair cannot progress. SUMMARY AND CONCLUSIONS
The purposeof this study was to investigate in vitro the effect of using hot endodontic pluggers for immediate dowel space preparation on the apical seal of endodontically treated teeth filled by a chloropercha technique. The results demonstratedthat, when the coronal half of the root canal filling material was removed immediately after placement with pluggers, there was a loss of the apical seal and leakage in thirteen of twenty teeth. There was also leakage in thirteen of twenty teeth in which dowel spaceswere not prepared. This study did not demonstratea significant difference statistically in loss of apical seal and leakage between teeth preparedwith and those without immediate dowel spacepreparations with pluggers using a chloropercha filling technique. I conclude that immediate preparation of the dowel spaceshad no effect on the apical seal. REFERENCES
I. Radke, R. A.: The Restoration of Endodontically Treated Anterior Teeth, United States Army Regional Dental Activities Bulletin No. 63, May, 1975. 2. Barahan, D. J.: The Restorationof Pulpless Teeth. Dent. Clin. North Am., Nov. 1967, pp. 633-653. 3. Ingle, J. I.: Root Canal Obtoration, J. Am. Dent. Assoc. 53: 47-57, 1956. 4. Ingle, J. I.: Endodontics,ed. 1, Philadelphia, 1965, Lea & Febiger, pp. 63-65, 614. 5. Schilder, H.: Filling Root Canals in Three Dimensions, Dent. Clin. North Am., Nov. 1967, pp. 723-744. 6. Seidler, B.: Irrationalized Endodontics:Nz and Us Too, J. Am. Dent. Assoc. 89: 1318-1331, 1974. 7. Neagley, R. L.: Effect of Dowel Preparation on the Apical Seal of Endodontically Treated Teeth, ORAL SURG.28: 739-745, 1969.
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8. Zeigler, P. E.: The Effects of Instrumentation for a Post Preparation on the Apical Seal of Endodontically Filled Teeth, Research Project, U. S. Naval Hospital, San Diego, Calif., July. 1965. 9. Schroeder, A.: The Problem of a Bacteria-Proof Root Canal Treatment, ZWR 19: 531. 1957. 10. Phillips, R. W.: Skinner’s Science of Dental Materials. ed. 7. Philadelphia, 1973, W. B. Saunders Co. I I. Phillips, R. W.: Materials for the Practicing Dentist, St. Louis, 1969, The C. V. Mosby Co., p. 56. 12. McElroy, D. L.: Physical Properties of Root Canal Filling Materials, J. Am. Dent. Assoc. 50: 433-m. 1955. Reprint
Lieutenant Colonel Frederick J. Schnell 92nd Medical Detachment (Dental Service) APO New York
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