SCIENTIFIC ARTICLES
T h r e e - d i m e n s i o n a l o b t u r a t i o n of t h e root c a n a l using injection-molded, thermoplasticized dental gutta-percha
Fulton S. Yee, DDS; Jay Marlin, DMD; Alvin Arlen Krakow, DDS; and Poul Gron, DMD, Boston
The t e c h n i q u e of injection-moldinq w a s a p p l i e d to thermoplasticized dental qutta p e r c h a in vitro. Teeth w e r e b i o c h e m i c a l l y instrumented before obturation of the root c a n a l space. Thermoplasticized quttap e r c h a w a s injected, with a n d without the u s e of a sealer, usinq a p r e s s u r e syrinqe. The quality of the seal w a s a s s e s s e d b y d y e p e n e t r a t i o n studies. The findinqs s h o w e d that the injection-moldinq technique l e a d s to a seal c o m p a r a b l e to that of c o n v e n t i o n a l a p p r o a c h e s . The technique h o l d s p r o m i s e for in v i v o use.
With the exception of the paste techniques, obturation of the root canal space involves the use of solid cores, such as silver or gutta-percha cones, in combination with a sealer. Heated gutta-percha possesses the property of flow, whereas silver does not. Advantage of this property was taken as early as 1865 by Clark (cited by Noyes 1), who used warm guttapercha for root canal obturationl; several papers describing the use of semiplastic gutta-percha segments have been published. 2-r However, the process of thermoplastic injectionmolding of gutta-percha has not been used in endodontics. Basically, thermoplastic injection-molding involves heating a polymer to the molten state and forcing it under mechanically
168
generated pressure into a relatively cool mold. On dissipation of the applied heat, the injected material solidifies and retains the shape determined by the internal outline of the mold cavity. The current investigation was undertaken to study the feasibility of root canal obturation by using thermoplasticized, injectable gutta-percha. An experimental method was devised for introducing thermoplasticized gutta-percha into prepared root canals with the endodontic pressure syringe. The suitability of injectable, warm gutta-percha as an endodontic filling material then was evaluated in vitro by two methods: direct visual examination of recovered root canal fillings achieved with the adopted technique,
and assessment of the adaptation between the filling material and the root canal walls by means of a dye.
MATERIALS AND METHODS P r e l i m i n a r y Experiments Initial work was directed toward selection of a needle temperature required for plasticizing dental guttapercha, and pressure necessary for generating flow of the heated material. The three variables were closely interrelated. Preliminary tests were performed with an 18-gauge needle because it was the maximum size that fit into the root canals of human maxillary anterior teeth prepared to the largest practical dimensions. Gutta-percha cones manually loaded into the pressure syringe were
JOURNAL OF ENDODONTICS I VOL 3, NO 5, MAY 1977
heated by immersing the barrel, with needle attached, in a glycerin bath contained in a modified Thiele-Dennis melting tube (Fig 1). The temperature of the glycerin was gradually increased until extrusion of a small amount of gutta-percha was observed at 110 C. However, needle hubs ruptured frequently. After experimentation, it was determined that an unrestrained flow of gutta-percha could be repeatedly achieved through an 18gauge needle with the pressure syringe heated to 160 C (Fig 2). The lateral spread of injected thermoplasticized gutta-percha was observed in initial experiments where the needle opening was placed midway in the root canal system, far short of the apex. The radiograph in Figure 3 shows .a high degree of lateral flow and suggests excellent adaptation to the dentinal walls. The following experimental procedure was adopted on the basis of these initial experiments. Experimental
:i.;
., :
~..' .,'.
,.
~;~.::,;.,,
,
Fig 2--Unrestrained [low o/thermoplasticized gutta-percha [rom endodontic pressure syringe heated to 160 C.
Fig 1--Glycerin bath in Thiele-Dennis melting tube. Notice that protective glove is used to handle pressure syringe.
Technique
The clinical equipment ( F i g 4) included an endodonfic pressure syringe*; an assortment of disposable, threaded, 18- to 22-gauge needles; gutta-percha conest; a size no. 12 root canal plugger~t; and scissors. Also used were a Thiele-Dennis melting tube containing glycerin heated to 160 C over a Bunsen burner, a thermometer to monitor the temperature, and protective gloves. Required preparatory procedures were completed, and root canal obturation was performed in the following manner: Two preoperative radiographs were taken, one in the mesiodistal plane and the other in the faciolingual plane. Conventional access was obtained with a round bur. The root canal system was thoroughly cleaned and shaped to receive guttapercha. The largest syringe needle was selected so that it could negotiate the canal to within 4 m m of the root apex, and the depth of insertion was
confirmed radiographically ( F i g 5). The needle shaft was scored at a level corresponding to the coronal reference point of the tooth. The needle was removed from the canal and securely threaded onto the barrel of the pressure syringe. The large, flattened ends of eight gutta-percha cones were trimmed with scissors and were inserted into the open end of the pressure syringe (four of the cones were introduced into the barrel with the broad end first, while the remaining cones were inserted tip first, as shown in Fig 6). A size no. 12 root canal plugger was used to force the guttapercha to its furthest extent within the barrel ( F i g 7). The threaded plunger was engaged with the barrel to complete the assembly of the pressure syringe. Finally, the gutta-percha was heated for two minutes by placing the needle and barrel in the glycerin bath maintained at 160 C.
Fig 3--Radiograph shows mesiodistal view. Syringe needle was intentionally placed short to show that iniected thermoplasticized gutta-percha [lows laterally as it progresses apically. The number of turns of the plunger knob required to extrude a length of thermoplasticized gutta-percha, corresponding to the previously measured distance from the apex of the prepared canal to the tip of the fitted needle, was established. The extruded 169
JOURNAL OF ENDODONTICS
VOL 3, NO 5, MAY 1977
J
l
~t
4~
I IIII
I II ,#l
material was removed from the needle tip before its insertion to the predetermined depth. The plunger knob then was rotated to the extent established in the previous step. The syringe, thereafter, was gradually withdrawn while continuously extruding additional thermoplasticized guttapercha into the root canal. When slight resistance from the injected material was felt against the needle, the syringe was withdrawn coronally for a few millimeters, followed by additional turns of the plunger knob. The sequence was continued until obturation of the canal to the desired level had been accomplished. Visual inspection showed that the gutta-percha terminated at or within 0.5 m m short of the root apex, and in no instance did it extrude beyond that point. Postoperative radiographs were taken along mesiodistal and faciolingual planes (Fig 8). The time that had elapsed from placing the needle to its predetermined depth within the canal to the moment at which needle withdrawal reached the coronal pulp chamber was measured with a stopwatch. Evaluation
The in vitro evaluation of thermoplasticized injectable gutta-percha as an endodontic filling material was 170
Fig 4--Clinical equipment (left to righO: root canal plugger, assortment of needles, disassembled pressure syringe, scissors, and gutta-percha cones.
~
,,f
Fig 6--Placement of gutta-percha cones into syringe barrel. Notice interposition of narrow tips with broad ends.
J4 f
u~
t'
6
Fig 7--Compaction of gutta-percha into syringe barrel with root canal plugger.
Fig 5--Radiographic confirmation of needle positioned within apical third of prepared root canal.
conducted by radiographic and visual inspection of recovered root canal fillings .and determined by its ability to prevent dye penetration. Freshly extracted human anterior teeth and premolars were used in each experiment. Immediately after extraction, the teeth were fixed in a 10% Formalin solution for 48 hours and stored in 50% ethyl alcohol. The root
canals of :all teeth were cleaned and shaped to receive gutta-percha and returned to storage in 50% ethyl alcohol. 9 Radiographic and visual inspection of root canal fillings. Twenty singlerooted and four double-rooted teeth were rinsed with a water spray and dried with air. The root canals were dried with paper points and then filled with thermoplasticized, injectable gutta-percha. No root canal sealer was used so that actual adaptation of the gutta-percha to the canal walls could be assessed. Postoperative radiographs were obtained on completion of root canal obturation. The teeth were
JOURNAL OF ENDODONTICS [ VOL 3, NO 5, MAY 1977
Fig 8--Top: postoperative radiograph shows ]aciolingual view. Notice homogeneity and uniform density of gutta-percha filling. Bottom: postoperative radiograph shows mesiodistal view. Notice close adaptation of gutta-percha to internal outline of prepared root canal in all dimensions.
stored in 100% relative humidity for 24 hours to allow the filling materials to harden. The teeth then were demineralized in 5% nitric acid for a period of 120 hours, rinsed in distilled water, and then immersed in 5.25% sodium hypochlorite until the remaining collagen matrix was dissolved totally. The intact gutta-percha fillings were rinsed with distilled water and examined under a binocular dissecting microscope. Photographs were taken of the recovered specimens. The radiographs were evaluated for gross adaptation, while visual inspection of the specimens emphasized the apparent reproduction of the irregularities of the root canal surfaces. 9 Dye penetration. The efficacy of the dye penetration technique used was tested on control teeth. Forty single-rooted teeth were rinsed with a water spray and dried with air. The prepared root canals were dried with paper points. The teeth were numbered for identification and randomly allotted to four groups of ten teeth each. The cleaned and shaped root canals of all specimens were filled by using four different methods, as follows: group A, lateral condensation of gutta-percha cones and A H 2 6 sealerw with finger pluggers, a method described by Luks8; group B, vertical condensation of warm gutta-percha and Kerr Sealer,~: using the technique originally described by Schilderg,l~ group C, injection of thermoplasticized gutta-percha without sealer, using the experimental technique described in the current study; and group D, injection of thermoplasticized gutta-percha in conjunction with AH26 sealer introduced on a lightly coated paper point, before injection of the filling material. The access cavities of all teeth were sealed with Cavit.][ The teeth then were stored in 100% relative humidity for 24 hours to allow the filling materials to harden. Except for a 1-mm section of tooth structure on all sides
of the apical foramen, the entire crown and root surface of each specimen was rendered impermeable with a layer of nail varnish. After allowing the first layer of varnish to dry for 24 hours at room temperature, two additional layers were applied in a similar manner to prevent dye penetration through other surfaces than the intentionally exposed apical region. The teeth were placed in a 5% aqueous solution of methylene blue for 120 hours at room temperature. The specimens were rinsed under cool tap water to remove excess dye after the immersion period. The varnish was removed with acetone. A single, longitudinal cut was made on the mesiodistal plane with a diamond blade under a water spray. This approach permits visualization of the tooth-filling interface in its entire length. The recovered sections were examined in random order under a dissecting microscope, and the maximal extent of dye penetration from the apical terminus of the endodontic filling was measured. The specimens then were regrouped according to their assigned numbers, and the results of each test group were compared. Representative sections of each group were photographed. RESULTS Radiographic results typieally showed the injected thermoplasticized guttapercha fillings to be of uniform density, with the occasional exception of small voids possibly caused by air entrapment. In an effort to reduce the incorporation of these minor discrepancies in the final root canal filling, sealer was tested in conjunction with the adopted technique. No voids along the root canal walls could be detected radiographically when sealer was used. These fillings appeared to show close conformation to the radicular dentin. Under the exact conditions of the experimental method, extrusion of gutta-percha could be 171
JOURNAL OF ENDODONTICS ] VOL 3, NO 5, MAY 1977
achieved through needles as small as 22 gauge. The technique also permitted obturation of accessory and lateral canals (Fig 9). The usual length of time required to introduce the gutta-percha into a prepared root canal with the thermoplastic injection method was less than 20 seconds. On completion of the injection process, the gutta-percha retained sufficient plasticity to allow manual condensation for up to two minutes. However, the time required for obliteration of any voids left by the needle rarely approached a minute. Impressionlike reproductions of the complexities of the prepared root canals were typically achieved with thermoplasticized, injection-molded gutta-percha without the use of sealer or manual condensation. The fillings generally appeared homogenous. Accessory and lateral canals frequently were filled with solid gutta-percha. Multiple foramina and other apical ramifioations also were obturated with the injected material. Finlike extensions and culs-de-sac, many of which remained untouched during conventional biomechanical instrumentation procedures, were obturated by the injection technique (Fig 10). Weblike interconnections along the floor of the pulp chamber were revealed in several cases where multiple canals existed (Fig 11). Instrument marks along the canal walls also were reproduced on the guttapercha casts. The extent to which dye had visibly penetrated the tooth-filling interface was essentially similar among the specimens of the four treatment groups. In general, no single obturation method consistently showed a leakage pattern distinguishable from the others. Methylene blue was typically limited to the region surrounding the apical terminus of the endodontic filling. In no instance could dye penetration be shown along the root canal 172
Fig 9---Top left: postoperative radiograph shows faciolingual view of conventionally prepared root canal obturated with thermoplasticized gutta-percha, using experimental technique. Notice accessory canal, lateral canal (arrow), and gradual coronal-apical taper. Top right: postoperative radiograph shows mesiodistal view. Bottom left: recovered root canal filling of infected thermoplasticized gutta-percha. Notice accessory canal and irregular outline o] canal proper.
wails in teeth from group A. One instance of gross dye penetration was noticed among teeth from group B. However, elose inspection of the specimen did reveal the presence of a vertical hairline fracture along the entire length of the root. It was not possible to determine whether this
minute defect was present before obturation. Some dye penetration was observed within the middle third of the root in two specimens obturated with injected thermoplasticized guttapercha without sealer (group C). No instance of dye penetration was noticed when sealer was used together with injeeted gutta-percha (group D). DISCUSSION
The current investigation is of a preliminary nature. Nevertheless, the results show that effective root canal obturation can be achieved with injection-molded, thermoplastieized gutta-percha in vitro.
JOURNAL OF ENDODONTICS ] VOL 3, NO 5, MAY 1977
Fig l O--Top: postoperative radiograph shows mesiodistal view. Bottom: recovered root canal filling of injected thermoplasticized gutta-percha. Notice obturation of [inlike extensions, untouched during biomechanical instrumentation.
Radiographic results obtained with the method showed uniform density and close adaptation to irregularities of the root canal walls. Visual examination of recovered fillings showed that injected thermoplasticized guttapercha produced a delicately detailed replica of the root canal system. The same types of morphologic variations noticed on these gutta-percha casts have been reported by Davis, Brayton, and Goldman, 11 who injected silicone impression material to produce casts of instrumented root canals. Methylene blue dye has been used by numerous investigators to assess the marginal adaptation of filling materials to tooth structure. 12-1T In this study, we found that injected thermoplasticized gutta-percha could produce an effective apical seal, especially when used in conjunction with sealer. The extent of dye penetration via the apex observed was similar, regardless of whether the lateral condensation method, vertical condensation technique, or injection-molding process was used. Only minor voids were seen occasionally with the injection technique. They were probably created by air entrapment upon loading of guttapercha cones into the syringe. The incorporation of air in the syringe might be minimized by precompacting the gutta-percha into dense, solid masses before insertion into the barrel. The loaded syringe and needle were heated to 160 C to render the guttapercha sufficiently plasticized for practical use. However, the actual temperature attained by the guttapercha probably was lower. It was determined that, on extrusion, the plasticized gutta-percha was tolerated well by human oral mucosa. Thus, it seems that the injected gutta-percha would probably be compatible with human periapical tissues. Additionally, no adverse thermal effects were noticed in clinical tests. Clinical results will be reported subsequent to
Fig 11--Top: postoperative radiograph shows mesiodistal view. Bottom: recovered root canal filling of injected thermoplasticized guttapercha. Notice weblike interconnection along pulp chamber floor. Apical segment was lost during preparation of specimen.
173
IOURNAL OF ENDODONTICS I VOL 3, NO 5, MAY 1977
an adequate follow-up. Studies are in progress to investigate the interface between thermoplasticized, injectionmolded gutta-percha and the dentinal walls, using scanning eleotron micro,copy. O u r results demonstrate that effective root canal obturation can be accomplished with thermoplasticized, injection-molded gutta-percha. The syringe technique is ,also offers potential advantages, such as the following: a simpler method for introducing sufficient gutta-percha to fill the canal, the deposition starting at the apex; reduction in chairside time because the syringe can be prepared by an assistant; and reduction in the amount of manipulative procedures necessary for condensation of the gutta-percha. Obviously, some practical aspects of the injection of thermoplasticized gutta-percha need technical improvement and development before the method can be clinically ,applied on a large scale. The temperature imparted to the injection apparatus is high for manual handling in clinical situations. W e used protective gloves, but insulation of the delivery system may obviate their need. Alternate modes of heating the barrel and needle m a y permit reduced temperatures. T h e possibility also exists that a dental gutta-percha may be compounded that plasticizes at a lower temperature. I n consideration of the bioacceptability of heated guttapereha, it bears emphasis that the heat capacity of the material is low. I n this context, we would like to point to the fact that gutta-percha heated in an open flame, as in the sectional, warm gutta-percha technique, appears to be clinically most successful. A specific listing of indications for clinical use of injection-molded, thermoplasticized gutta-percha would seem premature at this time. However, this method holds promise of combin174
ing the advantages of ease of manipulation offered by paste techniques is with the superior quality of filling obtained in solid-core techniques. In addition to its use in the usual eases, the injection method potentially could be used in obturating root canals in replanted or transplanted teeth where minimum time and manipulation are important for a favorable prognosis. Furthermore, the injection method may be advantageous in surgical endodontics for the obturation of the root canal system from a retrograde approach before the insertion of apical seals. *Pulpdent Corp. of America, Brookline, Mass. tMynol, Inc., BroomaU, Pa. :~Kerr Manufacturing Co., Romulus, Mich. w Trey Freres S.A., Zurich, Switzerland. ][Premier Dental Products Co., Philadelphia. Dr. Yee, a postdoctoral student in the endodontics program at Harvard School of Dental Medicine and Forsyth Dental Center in Boston while this research was conducted, is now in practice limited to endodontics in Stockton, Calif. Dr. Marlin is a lecturer on endodontics at the Harvard School of Dental Medicine and an assistant clinical professor of endodontics at the Forsyth Dental Center. Dr. Krakow is associate clinical professor of endodontics at Harvard School of Dental Medicine, staff associate at the Forsyth Dental Center, and chairman of the department of endodontics at both institutions. Dr. Gron is senior staff member, Forsyth Dental Center. Requests for reprints should be directed to Dr. Alvin A. Krakow, Department of Endodontics, Forsyth Dental Center, 140 The Fenway, Boston, 02115. References
1. Clark, cited by Noyes, E. Fifty years of root canal fillings. JADA 9: 784 Sept 1922. 2. Coolidge, E.D. The teaching of the technic of cleaning, cnretting and filling root canals. J Nail Dent Assoc 5:335 April 1918. 3. Gethro, F.W. The treatment and
filling of root canals. J Nail Dent Assor 6:812 Sept 1919. 4. Blayney, J.R. The biologic aspect of root-canal therapy. Dent Items of Interest 49:681, 1927. 5. Conrad, W.K. Materials used in root-canal technique in dental practice. Dent Cosmos 76:311 March 1934. 6. Berg, B. The endodontic management of multirooted teeth. Oral Surg 3:399 March 1953. 7. Coolidge, E.D., and Kesel, R.O. A textbook of endodontology, ed 2. Philadelphia, Lea & Febiger, 1956, p 250. 8. Luks, S. Gutta-percha versus silver points in practice of endodontics. NY State Dent I 31:341, 1965. 9. Schilder, H. Filling root canals in th.ree dimensions. Dent CIin North Am, Nov 1967, p 723. 10. Marlin, J., and Schilder, H. Physical properties of gutta-percha when subjected to heat and vertical condensation. Oral Surg 36:872 Dec 1973. 11. Davis, S.R.; Brayton, S:M.; and Goldman, M. The morphology of the prepared root canal: a study utilizing injectable silicone. Oral Surg 34:642 Oct 1972. 12. Grossman, L.L Present status of plastic root canal filling materials. In Grossman, L.I., ed. Transactions of the Third International Conference on Endodontics. Philadelphia, University of Pennsylvania, 1963, p 125. 13. Massler, M., and Ostrovsky, A. Sealing qualities of various filling materials. J Dent Child 21:228 Fourth Quarter 1954. 14. Antoniazzi, /.H.; Mj6r, L.A; and Nygaard-Ostby, B. Assessment of the sealing properties of root filling materials. Odontol Tidskr 76:261 June 28, 1968. 15. Curson, I., and Kirk, E.E. An assessment of root canal-sealing cements. Oral Surg 26:229 Aug 1968. 16. Barry, G.N., and Fried, I . L Sealing quality of two potycarboxytate cements used as root canal sealers. J Endod 1:107 March 1975. 17. Wayman, W.H., and Mullaney, T.P. A comparative study of apical leakage with endodontic implant stabilizers. I Endod 1:270 Aug 1975. 18. Krakow, A.A., and Berk, H. Efficient endodontic procedures with the use of the pressure syringe. Dent Clin North Am, July 1965, p 387.