JOURNAL OF ENDODONTICS ] VOL 2, NO 4, APRIL 1971
S c a n n i n g electron m i c r o s c o p i c e x a m i n a t i o n of root canal f i l l i n g m a t e r i a l s
Ronald R. Wollazd, DDS" Steven O. Brouqh, DDS: Joseph Macjqio, DDS~ and Samuel Seltzer, DDS, Philadelphia
The root c a n a l s of 130 freshly extracted, anterior teeth were p r e p a r e d a n d filled with various root c a n a l fillings b y various techniques. The a d h e s i o n a n d a d a p t a t i o n of the filling materials to the walls of the root c a n a l s w e r e then e x a m i n e d with the s c a n n i n g electron microscope. In general, zinc oxide-eugenol cements a d h e r e d well, w h e r e a s greater variability occurred with zinc p o l y c a r b o x y l a t e cements. Silver a n d gutta-percha cones h a d no a d h e s i o n a n d required a sealer to fill the interface b e t w e e n c o n e s a n d dentin. None of the techniques for inserting gutta-percha into the root c a n a l w a s effective in obliterating the root c a n a l space.
Endodontic therapy includes thorough debridement of the root canal and complete obturation of the root canal space. 1-5 Although it is commonly acknowledged that the root canal space should be filled, the rationale for filling has been disputed for many years. Furthermore, methods and materials for filling root canals vary greatly. A number of reasons for filling root canals have been advanced. Rickert and Dixon 4 studied tissue reactions to steel and platinum hypodermic needles implanted in rabbit skin. Macroscopic examination showed ir-
98
ritation around the ends of the metal tubes, but, in the medial portions the tubes were apparently well tolerated. Transposing those findings to endodontic therapy, they concluded that the root canal space must be well filled to eliminate voids in which stagnation of fluids, and microorganisms could occur. They reasoned that toxic products elaborated from this stagnated fluid could cause persistence of periapical inflammation. However, Torneck 6 did not verify those findings. He implanted polyethylene tubes of varying lengths and diameters into the subcutaneous tissues of rats. Half
of the tubes were open at both ends, whereas the other half had one end closed. After 60 days, histologic examinations showed the development of a connective tissue bridge in the lumens of some open tubes; others showed no ingrowth of connective tissue. In tubes that were sealed at one end, connective tissue ingrowth was prevented. Torneck concluded that "the principle of tissue stagnation in the lumen of an implanted tube as a chemical irritant to induce inflammation at the end of that tube could not be verified." Goldman and Pearson r did similar studies with hollow Teflon
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tubes. Their results indicated that there was a flow of tissue fluids in and out of the tubes, but there was no evidence of an inflammatory response at the open ends of the Teflon implants. Seltzer s offered two reasons for filling the root canal. Complete obturation of the root canal space is necessary to prevent leakage of saliva or salivary products through the occlusal opening, possibly to the root apex. Furthermore, should gingival recession or periodontal disease develop, the possibility of exposure of lateral root canals and accessory foramina would then be enhanced. Thus, emphasis has been placed on the necessity for thoroughly filling the root canal space. Various studies have been undertaken to discover the most efficacious means of filling the root canal space. The permeability of the interface between the filling material and the dentin has been examined by means of dyes, radioactive tracers, and fluorometric assays. 9 Dye studies. Massler and Ostrovsky 9 tested the sealing ability of various filling materials against a glass interface with gentian violet and methylene blue dyes. They found that baseplate gutta-percha, temporary stopping, zinc phosphate cement, and cold-curing acrylic resin were not effective sealers against dye penetration. In a similar study, Curson and Kirk 1 observed the depth of penetration of methylene blue between glass tube walls and various root canal cements. They found that zinc oxide-eugenol, Rickert's cement, Diaket, Kerr Tubliseal, and AH-26 were all satisfactory sealers. However in both of these experiments, the interface between a filling material (or cement) and glass, not dentin, was investigated. Antoniazzi, MjSr, and NygaardOstby 10 studied methylene dye penetration along the interface between
root canal sealer and dentin. The root canals of extracted teeth were filled with gutta-percha and sealer, and some with sealer only. Kloroperka, AH-26, and Kerr sealer were tested both immediately after setting and after a 48-hour setting time. They found that none of the tested materials were impermeable to dye penetration. However, they admitted that "due to difficulties in standardizing the method of evaluation, it may be concluded that only limited information can be obtained from in vitro studies." Variables such as variance in pH, pulpal architecture, time of immersion of the material in the dye solution, and difficulty in rendering the external cementum impermeable, were difficult to control. Furthermore, the validity of the use of dyes in diffusion studies is questionable because of the molecular size of the dye particles. 9 Isotope studies. Dow and Ingle, ~ using radioisotopes, attempted to show that more than half of all endodontic failures were caused by poorly obturated canals. Their studies indicated that no leakage occurred in weliobturated canals. However, adequate controls were lacking. Marshall and Massler 11 used six different isotopes and 11 different filling techniques on extracted teeth. They concluded that the least permeable root canal filling was a single-fitted gutta-percha cone used in conjunction with a root canal sealer. Yee, Lugassy, and Peterson 12 also studied the in vitro permeability of 12 root canal fillings to radioactive isotopes. They claimed that the root canal could always be sealed against the ingress of radioactive ions. The validity of Marshall and Massler's results may be questioned because evaluations were made immediately after the root canals were filled. Dimensional changes
in cements after setting could have altered their findings. In the study by Lee, Lugassy, and Peterson, the teeth were stored for 24 hours at 100% relative humidity. In radioactive isotope studies, the penetration of the tracer may be partly a function of polarity or it may be related to particle size. 13 Kapsimalis and Evans a4 modified the autoradiographic technique, using polar 35S and nonpolar tritiated glucose because of their differing polarity and particle size. Their findings revealed leakage in all but two of eight sealers tested. The criticisms of radioactive isotope studies are multitudinous. Marshall and Massler's work revealed that ionic charge, chemical reactivity, and particle size are all variables that affect marginal penetration of isotopes. Going, Massler, and Dute an have shown that "the charge on the ion and its chemical affinity, greatly influenced its absorption on the surface of the filling material and on the tooth surface, as well as its penetrability through the margins of the restorations." Furthermore, Kapsimalis and Evans a4 were able to show that "change in functional group, accompanied by a change in pH, had some influence on the results . . . . " Finally, in vitro studies do not take into account the effects of moisture or warmth of vital tissues. 9 Fluorometric studies. Fluorometric assays of the apical seal of root canal fillings were conducted by Ainley. 15 Root canals obturated with various materials and techniques were investigated with the use of rhodamine B, a fluorescent dye. He found minute apical leakage of root canals sealed with gutta-percha or split silver cones. However, he concluded: "No determination could be made of a superior obturating technique because of the overlapping range of leakage values between the test groups and the broad consistent range of values within a 99
IOOI'~NAL OF ENDODONTICS [ VOL 2, NO 4, APRIL 1976
given test group." Thus, in vitro dye, radioisotope, and fluorometric studies have many inherent faults. Furthermore, no specific material or method of filling the root canal space has been proven to be substantially superior to others. In this study, we decided to examine directly the interface between filling material and root canal dentin with the scanning electron microscope and to examine the adhesive capacity of the cement to dentin. The root canal filling materials examined were standard solid core filling materials, such as silver and guttapercha cones, cemented into the root canals with various sealers. In addition, we decided to study the sealing properties of polycarboxylate cements because of the claims of their improved adhesion to calcified tissue. 16-19 The liquid component of this cement is an aqueous solution of polyacrylic acid. The powder is a modified zinc oxide. The end product of the reaction between these two components is zinc carboxylate. The adhesion of this cement to enamel and, to a lesser extent, to dentin, occurs because of chelation by adjacent carboxyl groups of polyacrylic acid with the calcium present in the apatite of tooth structure. a9 According to Mizrahi and Smith, 17 tensile bond strength develops rapidly, within the first 30 minutes, to approximately 70 k g / s q cm. The rate then drops dramatically as the strength increases slowly to a maximum of approximately 104 k g / s q cm. Furthermore, prolonged immersion in water at 37 C does not appear to have a marked adverse effect on the cement bond. They also found that thermal cycling did not significantly affect the bond strength within the range of 15 to 60 C. Polycarboxylate cements containing additions of calcium hydroxide and calcium and stannous fluoride also were examined. The reasons for 100
Fig l--Radiographs o/ experimental teeth. Top IeJt: Preoperative Jaciolingual view. Top right: Postoperative [aciolingual view. Bottom le[t: Preoperative mesiodistal view. Bottom right: Postoperative mesiodistal view. testing these additives were based on a number of other investigations. F o r example, Furseth 2~ has shown a high degree of mineralization in fluoridetreated surfaces of cementum and dentin. Feagin and associates 21 have shown that the rate of remineralization of partly demineralized enamel increased linearly with an increase in calcium concentration in the solution. Furthermore, Swartz, Phillips, and Norman 22 demonstrated that the solubility of intact enamel surfaces was reduced by contact with zinc oxide formulations to which sodium fluoride or stannous fluoride was added. Studies by Goldhaber 23 also have revealed that when fluoride was
added to bone in tissue culture, bone resorption was reduced without producing toxic effects.
METHODS A N D M A T E R I A L S One hundred and thirty freshly extracted, single-rooted teeth were used. The teeth were fixed immediately after extraction in 10% Formalin solution. The teeth were then radiographed in two planes, mesiodistal and faciolingual, before and after root canal instrumentation and obturation (Fig 1). Radiographs were taken at a one-second exposure time with a 15ma, 60-kv machine with a cone 6 inches from the film. The root canals of the teeth were
JOURNAL OF ENDODONTICS [ VOL 2, NO 4, APRIL 1976
Table 9 Root canal filling materials and techniques examined.
Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Material Silver cone and Grossman's cement Silver cone and AH-26 Silver cone and Kerr Tubliseal Polycarboxylate cement Polycarboxylate cement with 5% stannous fluoride Polycarboxylate cement with 5% calcium fluoride Polycarboxylate cement with 5% calcium hydroxide Polycarboxylate cement with 10% stannous fluoride Polycarboxylate cement with 10% calcium fluoride Polycarboxylate cement with 10% calcium hydroxide Silver cone and polycarboxylate cement and 5% stannous fluoride Silver cone and polycarboxylate cement and 5% calcium fluoride Silver cone and polycarboxylate cement and 5% calcium hydroxide Silver cone and polycarboxylate cement and 10% stannous fluoride Silver cone and polycarboxylate cement and 10% calcium fluoride Silver cone and polycarboxylate and 10% calcium hydroxide Silver cone and polycarboxylate cement Gutta-percha and Grossman's cement lateral condensation technique Gutta-percha and Grossman's cement--vertical condensation technique Gutta-percha with chloropercha
prepared according to the standard procedures. Operators recorded the specific techniques used. All of the root canals were then irrigated with a 0.5% sodium hypochlorite solution followed by rinsing with normal saline solution. The canals were dried with paper points and then filled with various materials and by various techniques (Table). A m i n i m u m of five specimens in each group was examined. In the canals filled with polycarboxylate cements, the cement was refrigerated until needed. Before insertion of the cement, a small amount of polycarboxylate liquid was placed into the canal. Excess liquid was then removed with a paper point. The polycarboxylate was mixed (1:1 ratio) on a chilled glass slab. After obturation of the root canal, the pulp chamber was fiiled with a layer of polycarboxylate cement followed by amalgam. The teeth were then returned to a 10% Formalin solution. The specimens were dehydrated by
the critical point technique of Anderson24 and then embedded in Epon 812.* After embedding the teeth were ground longitudinally. Gross reduction was done by a mechanical grinder. Further reduction was done by hand with metallurgical reducing grits. Final polishing of the specimens was accomplished on a mechanical polishing wheel, using 5/zm alumina particles followed by 0.5/zm alumina particles. The particles were then removed by immersing in 10% hydrofluoric acid for 30 seconds. The sample was rinsed in water, air dried, and coated with gold (200 A) before placing in the vacuum chamber of the scanning electron microscope (model JMS-2). The samples were then examined and photomicrographs were taken of the apical, middle, and occlusal areas at magnifications ranging from • 37 to • 6,000. The photomicrographs were taken of areas representing the worst and best adhesion and adaptation of the materials to the root canal walls. In addition, photomicrographs of various interest-
ing and unusual anatomic structures and other features were taken. Electron microprobe analyses also were made of the various root canal cements and hard core materials that were used. Three individuals judged the photomicrographs. A rating for adhesion (actual joining of parts to each other, that is, cement particles to dentin wall) and adaptation (the degree of proximity and interlocking of filling material to a cavity wall) of the materials to the root canal wall was made by each judge in a range of one to three. One meant best and three meant worst. RESULTS
Photomicrographs were examined and it soon became obvious that ratings were subjective and were restricted to the appearances recorded on the photomicrographs. Therefore, the rating scale was discarded. Besides, the observation and recording of adhesion and adaptation was necessarily limited to examination of only one predetermined level and not to a three-dimensional view of the entire circumference of the root canal. Thus, the results reported here are in general. terms and represent subjective evaluations rather than scientifically precise recordings. In the mixing and insertion of all of the root canal cements, air bubbles were trapped. The voids created were generally infiltrated with Epon which appeared as black areas in the photomicrographs (Fig 2). When doubt existed, electron microprobe analyses were made. Line and point scans of the Epon always revealed the presence of chlorine. Solid
Core
Materials
9 Silver c o n e s a n d sealer. Vari~.tions were noted in the adaptation and adhesion of all of the materials tested. No sealer was superior to the others
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Fig 2--Polycarboxylate cement embedded in Epon. Left: Epon (E) has infiltrated polycarboxylate cement (P) (orig mag • 60):. Right: Higher magnification of left photomicrograph (orig mag • 180).
for filling the interface between the solid core materials and the wall of the root canal. When cones were used that were similar in bore to that of the prepared root canal, little interface remained. The cements used to fill such closely adapted cones did not appear to fill completely the interfaces (Fig 3). There was poor adaptation of the sealer and many voids were observed, possibly as a result of air entrapment. Conversely, better cement adaptation occurred when the cones were loosely fitted into the canals (Fig 4). Such findings are probably contrary to the generally accepted concept that the solid core materials should closely approximate the walls of the root canal. When silver cones were inserted with zinc oxide-eugenol cements, generally good adaptation resulted, despite the presence of air bubbles (Fig 5, top left and right). A line scan of K e r r Tubliseal indicated the presence of silver particles (Fig 5, bottom left). In one unusual case, Tubliseal extruded from the dentinal tubules (Fig 5, bottom right).
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When silver cones were inserted in conjunction with the polycarboxylate cements, the cements did not adhere well to the cones. Some degree of adhesion to the dentin was observed. However, no adhesion was seen in some areas (Fig 6). Organic debris left on the canal walls may have been responsible for the lack of adhesion in those instances. Where polycarboxylate cements with additives were used, greater Epon infiltration of the cement occurred as compared to that of the zinc oxideeugenol cements (Fig 7). AH-26 exhibited the poorest adaptation; infiltration of Epon was the greatest compared with all of the cements tested (Fig 8).
9 Gutta-percha cones and sealer. The technique of insertion of gutta-percha cones, whether by lateral or vertical condensation, made little difference in the adaptation. One wall of the root canal generally exhibited better guttapercha adaptation than the other (Fig 9). However, when the canals were filled by the vertical condensation method, more cracks in the den-
VOL 2, NO 4, APRIL 1976
tin were discernible than were seen in the teeth filled by lateral condensation. These cracks were filled partially with gutta-percha (Fig 10) or sealer (Fig 11). Although Epon infiltration generally was less than in those cases filled with silver cones and sealers, numerous voids were noted between the main cone and the accessory cones (Fig 12, top left and right). Guttapercha had no adhesive properties; cements or sealers filled many of the voids between the gutta-percha and canal walls and between the main and accessory cones (Fig 12, bottom left and right). In one case, a large lateral canal was discovered which was unfilled by gutta-percha or sealer (Fig 13, left). In the cases filled with chloropercha, shrinkage was noted, resulting in poor adaptation to the root canal walls (Fig 14). Good adaptation was found on some walls (Fig 13, center and right); extremely poor adaptation was seen in other areas of the same canal. Although faciolingual radiographs showed apparently good gutta-percha condensation, the mesiodistal view revealed voids; those voids were seen in the scanning electron microscopic examination (Fig 14). Secrlers
9 Zinc oxide-eugenol cements. Zinc oxide-eugenol cements appeared to adapt well to the root canal walls; few voids were noted at the interfaces (Fig 15, top left and right). However, some air entrapment was noted in the bulk of the set cements. In all cases, a fair degree of adhesion seemed to be present. 9 Polycarboxylate cements. The manipulation and insertion of the polycarboxylate cements presented some problems. The cements tended to stick to metal instruments, such as root canal pluggers, and condensation into the root canals was difficult.
JOURNAL OF ENDODONTICS [ %'OL 2, NO 4, APRIL 1976
Fig 3---Left: Tightly fitted cone, inserted with polycarboxylate cement (orig mag x60). Center: Higher magnification of left photomicrograph (orig mag x600). Right: Higher magnification of center photomicrograph (orig mag X1,800).
at a magnification of • no voids between dentin and cement could be observed (Fig 16). Even irregularities were filled in some instances (Fig 17, left). However, in some cases unremoved tissue and air entrapment prevented adhesion to the root canal wails (Fig 17, center and riKht). DISCUSSION
Fig 4 Left: Loosely fitted silver cone, inserted with Grossman's cement (orig mag • Right: Higher magnification of cone (S) dentin (D) interface filled with cement (C) (orig mag • 180).
Thus, voids were frequently observed in the central masses of the material (Fig 15, bottom left). The additives to the polycarboxylate cements made the cements denser. The additive particles appeared to fill the micellar structure of the polycarboxylate
framework (Fig 15, bottom right). In many cases, when the polycarboxylate cements without or with additives were used as the sole filling material of the root canal, the adaptation and adhesion to the walls of the root canal were superb. Even
The technique used, that is, embedding the teeth with filled root canals in Epon, permitted the sectioning of the teeth without loss or dislodgment of the filling materials. As a result of the vacuum embedding, the Epon infiltrated the voids present from filling techniques or inadequate adhesion or adaptation of the root canal filling materials to the root canal wails. During processing of the samples, cracks developed in the dentin as a result of dehydration. Other cracks may have been present before the experimental procedures. However, it
103
Fig 5 ~ T o p left: Silver cone insert with Kerr Tubliseal (orig mag • Top right: Higher magnification of photomicrograph of top left (orig mag >(600). Bottom left: Line scan (white line) shows presence of silver particles (Ag) (orig mag • 1,800). Bottom right: Sealer extruding from dentinal tubules (orig mag X 1,800). Fig 6~Silver cone cemented with polycarboxylate cement. Top left: Interface between cone (Ag) and dentin (D) is well filled with cement (P) (orig mag • Top right: Higher magnification of photomicrograph at top left (orig mag • 1,000). Bottom left: Interface at middle portion of canal (• 300). Bottom right: Higher magnification of bottom left photomicrograph (orig mag • 1,000).
JOURNAL OF ENDODONTICS [ VOL 2, NO 4, APRIL 1976
Fig 7--Top: Silver cone inserted with zinc polycarboxylate cement plus 10% calcium fluoride (orig mag • Middle: Higher magnification of top photomicrograph showing Epon (E) infiltration (orig mag • 180). Bottom: Higher magnification of middle photomicrograph (orig mag • 600).
was our impression that some fractures of the dentin occurred because of the pressures of the insertion of the root canal filling materials. The presence of gutta-percha or sealer or both in these cracks reinforced this impression. Obturation of root canals by cements or sealers alone appeared to be more complete than when the central solid core materials were used. These findings tend to corroborate those of Goerig and Seymour. 25 However, whether or not the insertion of pastes or cements alone would permit greater extrusion into the periapical tissues could not be determined in this experiment. These findings are only suggestive of the physical properties of various root canal filling materials and have no relationship to their biologic characteristics. Our findings tend to corroborate those of other researchers a~ that most root canal fillings do not completely obturate root canals. The reasons appear to be lack of or poor adhesion or chemical bonding of sealers to dentin and solid core materials 27 and difficulties in the manipulation and insertion of some cements, especcially the polycarboxylates.26,2s Such bonding is interfered with by inadeequate debridement, presence of culde-sacs, and inaccessible areas within the root canal. 29 Solid core materials such as silver and gutta-percha cones have no adhesive qualities. Therefore, cements or sealers must be used in conjunction with them. Gutta-percha, regardless of the technique used, is either poorly condensed or shrinks from the walls of the root canal; this confirms the finding of Brayton, Davis, and Goldman. g~ SUMMARY
The root canals of 133 freshly extracted, anterior teeth were prepared and filled with various root canal fill-
Fig 8--Top: Coronal area of canal filled with silver cone and AH-26. Epon (E) has infiltrated voids in cement (orig mag • Middle: Middle portion of root canal (orig mag • 37). Bottom: Apical portion of root canal (orig mag •
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Fig 9--Gutta-percha inserted by lateral condensation method. Top left: Good adaptation on one side. GP, gutta-percha; C, cement; D, dentin (orig mag • 180). Top right: Higher magnification of top le/t photomicrograph (orig mag • Bottom left: Poorer adaptation of gutta-percha (GP) on other canal wall cement (C). D, dentin (orig mag • Bottom right: Higher magnification of bottom left photomicrograph (orig mag • 600).
Fig 10 Dentinal fracture in tooth after insertion of gutta-percha by vertical condensation (orig mag • 60). Middle: Higher magnification of top photomicrograph showing gutta-percha (GP) in crack (orig mag • Bottom: Higher magnification of middle photomicrograph. GP, guttapercha (orig mag •
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Fig ll---Dentinal fractures after insertion of gutta-percha by vertical condensation. Top: orig mag • Middle: Higher magnification of top photomicrograph showing sealer (S) in crack (orig mag • 600). Bottom: Higher magnification of middle photomicrograph. S, sealer (orig mag • 1,800).
Fig 12--Voids in gutta-percha filling after insertion by vertical condensation method. Top left: orig mag • 60. Top right: Higher magnification of top le[t photomicrograph (orig mag • Bottom left: Cement (C) [ills interface between gutta-percha (GP) and dentin (D) and also between main and accessory cones (orig mag • 60). Bottom right: Higher magnification of bottom left photomicrograph (orig mag • 180). 107
JOUBNAL OF ENDODONTICS ] VOL 2, NO 4, APRIL 1976
Fig 13--Left: lateral canal (lc), unfilled by lateral condensation method (orig mag X60). Center: Good adaptation to canal wall by chloropercha (CP) (orig mag X180). Right: Higher magnification of center photomicrograph (orig mag X 600).
Fig 14--Chloropercha filling. Top left: orig mag X 60. Top right: Higher magnification of top left photomicrograph (orig mag X180). Bottom left: Higher magnification of top right photomicrograph (orig mag X600). Bottom right: Left radiograph is ]aciolingual riew; right radiograph is mesiodistal view. 108
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Fig 15---Canal filled with zinc oxide-eugenol showing good adaptation. Top le/t: orig mag X 180. Top right: orig mag • 600. Bottom left: Canal filled with zinc polycarboxylate cement (orig mag • Bottom right: Canal filled with polycarboxylate plus 5% calcium hydroxide (orig mag • 180).
Fig 16--Canal filled with zinc polycarboxylate cement. Le/t: orig mag X300. Middle: orig mag • 1,000. Right: orig mag X 3,000. 109
Fig 17---Left: Canal filled with zinc polycarboxylate cement plus 10% calcium fluoride (orig mag • 35). Middle: Tissue (T) prevents adhesion of polycarboxylate cement (PC) to dentin (D) (orig mag • Right: Higher magnification o/ middle photomicrograph (orig mag • 600). ings and by various techniques. The adhesion and adaptation of the filling materials to the walls of the root canals were examined with a scanning electron microscope. In general, zinc oxide-eugenol cements adhered well, whereas greater variability was found with zinc polycarboxylate cements. Silver and gutta-percha cones had no adhesion and required a sealer to fill the interface between cones and dentin. None of the techniques for inserting gutta-percha into the root canal was effective in obliterating the root canal space. * Tissues were embedded in Beem capsules filled with accelerated EponAraldite mixture. Capsules were placed in a 60 C oven for 72 hours. EponAraldite: Araldite 6005, 16 ml; Epon 812, 20 ml; DDSA, 48 ml; DBP, 3.2 ml; and DMP-30, 1.6% of total volume added before placing tissue under vacuum. Drs. Wollard, Brough, and Maggio formerly were advanced education students in endodontics, Temple University, Philadelphia. They are currently in private practice. Dr. Wollard practices in Kansas City, Mo; Dr. Brough in San Francisco; and Dr. Maggio in Oak Brook, Ill. Dr. Seltzer is professor and chairman, department of endodontology, Temple University. Reprint requests should be directed to Dr. Samuel Seltzer, School of Dentistry, Temple University, 3223 N Broad St, Philadelphia 19140. References
I. Curson, I., and Kirk, E. An assessment of root canal-sealing cements. Oral Surg 26:229 Aug 1968. 2. Dow, P.R., and Ingle, J.I. Isotope determination of root canal failure. Oral Surg 8:1100 Oct 1955. 3. Ingle, J.L. Endodontics. Philadelphia, Lea and Febiger, 1965. 4. Rickert, V.G., and Dixon, C.M. The controlling of root surgery. Trans Int Dent Cong (8th) Sec l l l a , 1931, p 15. 5. Sommer, R.F.; Ostrander, F.D.; 110
and Crowley, M.C. Clinical endodontics; a manual of scientific endodontics. Philadelphia, Saunders, 1966. 6. Torneck, C.D. Reaction of rat connective tissue to polyethylene tube implants. I. Oral Surg 21:379 March 1966. 7. Goldman, M., and Pearson, A.H. A preliminary investigation of the "hollow tube" theory in endodontics: studies with neo-tetrazolium. J Oral Ther 1:618 May 1965. 8. Seltzer, S. Endodontology. Biologic considerations in endodontic procedures. New York, McGraw-Hill, 1971. 9. Massler, M., and Ostrovsky, A. Sealing qualities of various filling materials. J Dent Child 21:228 Fourth Quart 1954. 10. Antoniazzi, J.H.; Mjtir, I.A.; and Nygaard-Ostby, B. Assessment of the sealing properties of root filling materials. Odon,tol Tidskr 76:261 June 1968. 11. Marshall, F. J., and Massler, M. Sealing of pulpless teeth evaluated with radioisotopes. J Dent Med 16:172 Oct 1961. 12. Yee, F.S.; Lugassy, A.A.; and Peterson, J.N. Filling of root canals with adhesive materials. J Endod 1:145 April 1975. 13. Going, R.E.; Massler, M.; and Dute, H.L. Marginal penetration of dental restorations by different radioactive isotopes. J Dent Res 39:273 March-April 1960. 14. Kapsimalis, P., and Evans, R. Sealing properties of endodontic filling materials using radioactive polar and nonpolar isotopes. Oral Surg 22:386 Sept 1966. 15. Ainley, J.E. Fluorometric assay of the apical seal of root canal fillings. Oral Surg 29:753 May 1970. 16. Friend, L.A. Handling properties of a zinc polycarboxylate cement. An investigation. Br ,Dent J 127:359 Oct 1969. 17. Mizrahi, E., and Smith, D.C. The bond strength of a zinc polycarboxylate cement. Investigations into the behaviour under varying conditions. Br Dent J 127:410 Nov 1969. 18. Mortimer, K.V., and Tranter, R.C. A preliminary laboratory evaluation of polycarboxylate cements. Br Dent J 127: 365 Oct 1969. 19. Smith, D.C. A new dental cement.
Br Dent J 124:381 Nov 1968. 20. Furseth, R. A study of experimentally exposed and fluoride treated dental cementum in pigs. Acta Odontol Scand 28:833 Dec 1970. 21. Feagin, F.; Patel, P.R.; Koulorides, T.; and Pigman, W. Study of the effect of calcium phosphate, fluoride and hydrogen ion concentrations on the remineralization of partially demineralized human and bovine enamel surfaces. Arch Oral Biol 16:535 May 1971. 22. Swartz, M.L.; Phillips, R.W.; and Norman, R.D. Effect of fluoride-containing zinc oxide-eugenol cements on solubility of enamel. J Dent Res 49:576 May-June 1970. 23. Goldhaber, P. The inhibition of bone resorption in tissue culture by nontoxic concentrations of sodium fluoride. Israel I Med Sci 3:617 Sept-Oct 1967. 24. Anderson, T.F. A method for eliminating gross artifacts in drying specimens, in Congres de microscopie electronique. Paris, Editions de la Revue d'Optique, 1952, pp 567-576. 25. Goerig, A.C., and Seymour, F.W. Comparison of common root canal filling techniques and sealers with the simplified pressure injection method and zinc oxide-eugenol as the sealing agent. JADA 88:826 April 1974. 26. Barry, G.N., and Fried, I. L. Sealing quality of two polycarboxytate cements used as root canal sealers. J Endod 1:107 March 1975. 27. Sanders, S.H., and Dooley, R.J. A comparative evaluation of polycarboxylate cement as a root-canal sealer utilizing roughened and nonroughened silver points. Oral Surg 37:629 April 1974. 28. Barry, G.N., Heyman, R.A., and Fried, I.L. Sealing quality of instruments cemented in root canals with polycarboxylate cements. J Endod 1:112 March 1975. 29. Baker, N.A.; Eleazer, P.D.; Averbach, R.E.; and Seltzer, S. Scanning electron microscopic study of the efficacy of various irrigating solutions. J Endod 1:127 April 1975. 30. Brayton, S.M.; Davis, S.R.; and Goldman, M. Gutta-percha root canal fillings. An in vitro analysis. I. Oral Surg 35:226 Feb 1973.
S c a n n i n g electron m i c r o s c o p i c e x a m i n a t i o n of root canal f i l l i n g m a t e r i a l s
Ronald R. Wollazd, DDS" Steven O. Brouqh, DDS: Joseph Macjqio, DDS~ and Samuel Seltzer, DDS, Philadelphia
The root c a n a l s of 130 freshly extracted, anterior teeth were p r e p a r e d a n d filled with various root c a n a l fillings b y various techniques. The a d h e s i o n a n d a d a p t a t i o n of the filling materials to the walls of the root c a n a l s w e r e then e x a m i n e d with the s c a n n i n g electron microscope. In general, zinc oxide-eugenol cements a d h e r e d well, w h e r e a s greater variability occurred with zinc p o l y c a r b o x y l a t e cements. Silver a n d gutta-percha cones h a d no a d h e s i o n a n d required a sealer to fill the interface b e t w e e n c o n e s a n d dentin. None of the techniques for inserting gutta-percha into the root c a n a l w a s effective in obliterating the root c a n a l space.
Endodontic therapy includes thorough debridement of the root canal and complete obturation of the root canal space. 1-5 Although it is commonly acknowledged that the root canal space should be filled, the rationale for filling has been disputed for many years. Furthermore, methods and materials for filling root canals vary greatly. A number of reasons for filling root canals have been advanced. Rickert and Dixon 4 studied tissue reactions to steel and platinum hypodermic needles implanted in rabbit skin. Macroscopic examination showed ir-
98
ritation around the ends of the metal tubes, but, in the medial portions the tubes were apparently well tolerated. Transposing those findings to endodontic therapy, they concluded that the root canal space must be well filled to eliminate voids in which stagnation of fluids, and microorganisms could occur. They reasoned that toxic products elaborated from this stagnated fluid could cause persistence of periapical inflammation. However, Torneck 6 did not verify those findings. He implanted polyethylene tubes of varying lengths and diameters into the subcutaneous tissues of rats. Half
of the tubes were open at both ends, whereas the other half had one end closed. After 60 days, histologic examinations showed the development of a connective tissue bridge in the lumens of some open tubes; others showed no ingrowth of connective tissue. In tubes that were sealed at one end, connective tissue ingrowth was prevented. Torneck concluded that "the principle of tissue stagnation in the lumen of an implanted tube as a chemical irritant to induce inflammation at the end of that tube could not be verified." Goldman and Pearson r did similar studies with hollow Teflon
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tubes. Their results indicated that there was a flow of tissue fluids in and out of the tubes, but there was no evidence of an inflammatory response at the open ends of the Teflon implants. Seltzer s offered two reasons for filling the root canal. Complete obturation of the root canal space is necessary to prevent leakage of saliva or salivary products through the occlusal opening, possibly to the root apex. Furthermore, should gingival recession or periodontal disease develop, the possibility of exposure of lateral root canals and accessory foramina would then be enhanced. Thus, emphasis has been placed on the necessity for thoroughly filling the root canal space. Various studies have been undertaken to discover the most efficacious means of filling the root canal space. The permeability of the interface between the filling material and the dentin has been examined by means of dyes, radioactive tracers, and fluorometric assays. 9 Dye studies. Massler and Ostrovsky 9 tested the sealing ability of various filling materials against a glass interface with gentian violet and methylene blue dyes. They found that baseplate gutta-percha, temporary stopping, zinc phosphate cement, and cold-curing acrylic resin were not effective sealers against dye penetration. In a similar study, Curson and Kirk 1 observed the depth of penetration of methylene blue between glass tube walls and various root canal cements. They found that zinc oxide-eugenol, Rickert's cement, Diaket, Kerr Tubliseal, and AH-26 were all satisfactory sealers. However in both of these experiments, the interface between a filling material (or cement) and glass, not dentin, was investigated. Antoniazzi, MjSr, and NygaardOstby 10 studied methylene dye penetration along the interface between
root canal sealer and dentin. The root canals of extracted teeth were filled with gutta-percha and sealer, and some with sealer only. Kloroperka, AH-26, and Kerr sealer were tested both immediately after setting and after a 48-hour setting time. They found that none of the tested materials were impermeable to dye penetration. However, they admitted that "due to difficulties in standardizing the method of evaluation, it may be concluded that only limited information can be obtained from in vitro studies." Variables such as variance in pH, pulpal architecture, time of immersion of the material in the dye solution, and difficulty in rendering the external cementum impermeable, were difficult to control. Furthermore, the validity of the use of dyes in diffusion studies is questionable because of the molecular size of the dye particles. 9 Isotope studies. Dow and Ingle, ~ using radioisotopes, attempted to show that more than half of all endodontic failures were caused by poorly obturated canals. Their studies indicated that no leakage occurred in weliobturated canals. However, adequate controls were lacking. Marshall and Massler 11 used six different isotopes and 11 different filling techniques on extracted teeth. They concluded that the least permeable root canal filling was a single-fitted gutta-percha cone used in conjunction with a root canal sealer. Yee, Lugassy, and Peterson 12 also studied the in vitro permeability of 12 root canal fillings to radioactive isotopes. They claimed that the root canal could always be sealed against the ingress of radioactive ions. The validity of Marshall and Massler's results may be questioned because evaluations were made immediately after the root canals were filled. Dimensional changes
in cements after setting could have altered their findings. In the study by Lee, Lugassy, and Peterson, the teeth were stored for 24 hours at 100% relative humidity. In radioactive isotope studies, the penetration of the tracer may be partly a function of polarity or it may be related to particle size. 13 Kapsimalis and Evans a4 modified the autoradiographic technique, using polar 35S and nonpolar tritiated glucose because of their differing polarity and particle size. Their findings revealed leakage in all but two of eight sealers tested. The criticisms of radioactive isotope studies are multitudinous. Marshall and Massler's work revealed that ionic charge, chemical reactivity, and particle size are all variables that affect marginal penetration of isotopes. Going, Massler, and Dute an have shown that "the charge on the ion and its chemical affinity, greatly influenced its absorption on the surface of the filling material and on the tooth surface, as well as its penetrability through the margins of the restorations." Furthermore, Kapsimalis and Evans a4 were able to show that "change in functional group, accompanied by a change in pH, had some influence on the results . . . . " Finally, in vitro studies do not take into account the effects of moisture or warmth of vital tissues. 9 Fluorometric studies. Fluorometric assays of the apical seal of root canal fillings were conducted by Ainley. 15 Root canals obturated with various materials and techniques were investigated with the use of rhodamine B, a fluorescent dye. He found minute apical leakage of root canals sealed with gutta-percha or split silver cones. However, he concluded: "No determination could be made of a superior obturating technique because of the overlapping range of leakage values between the test groups and the broad consistent range of values within a 99
IOOI'~NAL OF ENDODONTICS [ VOL 2, NO 4, APRIL 1976
given test group." Thus, in vitro dye, radioisotope, and fluorometric studies have many inherent faults. Furthermore, no specific material or method of filling the root canal space has been proven to be substantially superior to others. In this study, we decided to examine directly the interface between filling material and root canal dentin with the scanning electron microscope and to examine the adhesive capacity of the cement to dentin. The root canal filling materials examined were standard solid core filling materials, such as silver and guttapercha cones, cemented into the root canals with various sealers. In addition, we decided to study the sealing properties of polycarboxylate cements because of the claims of their improved adhesion to calcified tissue. 16-19 The liquid component of this cement is an aqueous solution of polyacrylic acid. The powder is a modified zinc oxide. The end product of the reaction between these two components is zinc carboxylate. The adhesion of this cement to enamel and, to a lesser extent, to dentin, occurs because of chelation by adjacent carboxyl groups of polyacrylic acid with the calcium present in the apatite of tooth structure. a9 According to Mizrahi and Smith, 17 tensile bond strength develops rapidly, within the first 30 minutes, to approximately 70 k g / s q cm. The rate then drops dramatically as the strength increases slowly to a maximum of approximately 104 k g / s q cm. Furthermore, prolonged immersion in water at 37 C does not appear to have a marked adverse effect on the cement bond. They also found that thermal cycling did not significantly affect the bond strength within the range of 15 to 60 C. Polycarboxylate cements containing additions of calcium hydroxide and calcium and stannous fluoride also were examined. The reasons for 100
Fig l--Radiographs o/ experimental teeth. Top IeJt: Preoperative Jaciolingual view. Top right: Postoperative [aciolingual view. Bottom le[t: Preoperative mesiodistal view. Bottom right: Postoperative mesiodistal view. testing these additives were based on a number of other investigations. F o r example, Furseth 2~ has shown a high degree of mineralization in fluoridetreated surfaces of cementum and dentin. Feagin and associates 21 have shown that the rate of remineralization of partly demineralized enamel increased linearly with an increase in calcium concentration in the solution. Furthermore, Swartz, Phillips, and Norman 22 demonstrated that the solubility of intact enamel surfaces was reduced by contact with zinc oxide formulations to which sodium fluoride or stannous fluoride was added. Studies by Goldhaber 23 also have revealed that when fluoride was
added to bone in tissue culture, bone resorption was reduced without producing toxic effects.
METHODS A N D M A T E R I A L S One hundred and thirty freshly extracted, single-rooted teeth were used. The teeth were fixed immediately after extraction in 10% Formalin solution. The teeth were then radiographed in two planes, mesiodistal and faciolingual, before and after root canal instrumentation and obturation (Fig 1). Radiographs were taken at a one-second exposure time with a 15ma, 60-kv machine with a cone 6 inches from the film. The root canals of the teeth were
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Table 9 Root canal filling materials and techniques examined.
Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Material Silver cone and Grossman's cement Silver cone and AH-26 Silver cone and Kerr Tubliseal Polycarboxylate cement Polycarboxylate cement with 5% stannous fluoride Polycarboxylate cement with 5% calcium fluoride Polycarboxylate cement with 5% calcium hydroxide Polycarboxylate cement with 10% stannous fluoride Polycarboxylate cement with 10% calcium fluoride Polycarboxylate cement with 10% calcium hydroxide Silver cone and polycarboxylate cement and 5% stannous fluoride Silver cone and polycarboxylate cement and 5% calcium fluoride Silver cone and polycarboxylate cement and 5% calcium hydroxide Silver cone and polycarboxylate cement and 10% stannous fluoride Silver cone and polycarboxylate cement and 10% calcium fluoride Silver cone and polycarboxylate and 10% calcium hydroxide Silver cone and polycarboxylate cement Gutta-percha and Grossman's cement lateral condensation technique Gutta-percha and Grossman's cement--vertical condensation technique Gutta-percha with chloropercha
prepared according to the standard procedures. Operators recorded the specific techniques used. All of the root canals were then irrigated with a 0.5% sodium hypochlorite solution followed by rinsing with normal saline solution. The canals were dried with paper points and then filled with various materials and by various techniques (Table). A m i n i m u m of five specimens in each group was examined. In the canals filled with polycarboxylate cements, the cement was refrigerated until needed. Before insertion of the cement, a small amount of polycarboxylate liquid was placed into the canal. Excess liquid was then removed with a paper point. The polycarboxylate was mixed (1:1 ratio) on a chilled glass slab. After obturation of the root canal, the pulp chamber was fiiled with a layer of polycarboxylate cement followed by amalgam. The teeth were then returned to a 10% Formalin solution. The specimens were dehydrated by
the critical point technique of Anderson24 and then embedded in Epon 812.* After embedding the teeth were ground longitudinally. Gross reduction was done by a mechanical grinder. Further reduction was done by hand with metallurgical reducing grits. Final polishing of the specimens was accomplished on a mechanical polishing wheel, using 5/zm alumina particles followed by 0.5/zm alumina particles. The particles were then removed by immersing in 10% hydrofluoric acid for 30 seconds. The sample was rinsed in water, air dried, and coated with gold (200 A) before placing in the vacuum chamber of the scanning electron microscope (model JMS-2). The samples were then examined and photomicrographs were taken of the apical, middle, and occlusal areas at magnifications ranging from • 37 to • 6,000. The photomicrographs were taken of areas representing the worst and best adhesion and adaptation of the materials to the root canal walls. In addition, photomicrographs of various interest-
ing and unusual anatomic structures and other features were taken. Electron microprobe analyses also were made of the various root canal cements and hard core materials that were used. Three individuals judged the photomicrographs. A rating for adhesion (actual joining of parts to each other, that is, cement particles to dentin wall) and adaptation (the degree of proximity and interlocking of filling material to a cavity wall) of the materials to the root canal wall was made by each judge in a range of one to three. One meant best and three meant worst. RESULTS
Photomicrographs were examined and it soon became obvious that ratings were subjective and were restricted to the appearances recorded on the photomicrographs. Therefore, the rating scale was discarded. Besides, the observation and recording of adhesion and adaptation was necessarily limited to examination of only one predetermined level and not to a three-dimensional view of the entire circumference of the root canal. Thus, the results reported here are in general. terms and represent subjective evaluations rather than scientifically precise recordings. In the mixing and insertion of all of the root canal cements, air bubbles were trapped. The voids created were generally infiltrated with Epon which appeared as black areas in the photomicrographs (Fig 2). When doubt existed, electron microprobe analyses were made. Line and point scans of the Epon always revealed the presence of chlorine. Solid
Core
Materials
9 Silver c o n e s a n d sealer. Vari~.tions were noted in the adaptation and adhesion of all of the materials tested. No sealer was superior to the others
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Fig 2--Polycarboxylate cement embedded in Epon. Left: Epon (E) has infiltrated polycarboxylate cement (P) (orig mag • 60):. Right: Higher magnification of left photomicrograph (orig mag • 180).
for filling the interface between the solid core materials and the wall of the root canal. When cones were used that were similar in bore to that of the prepared root canal, little interface remained. The cements used to fill such closely adapted cones did not appear to fill completely the interfaces (Fig 3). There was poor adaptation of the sealer and many voids were observed, possibly as a result of air entrapment. Conversely, better cement adaptation occurred when the cones were loosely fitted into the canals (Fig 4). Such findings are probably contrary to the generally accepted concept that the solid core materials should closely approximate the walls of the root canal. When silver cones were inserted with zinc oxide-eugenol cements, generally good adaptation resulted, despite the presence of air bubbles (Fig 5, top left and right). A line scan of K e r r Tubliseal indicated the presence of silver particles (Fig 5, bottom left). In one unusual case, Tubliseal extruded from the dentinal tubules (Fig 5, bottom right).
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When silver cones were inserted in conjunction with the polycarboxylate cements, the cements did not adhere well to the cones. Some degree of adhesion to the dentin was observed. However, no adhesion was seen in some areas (Fig 6). Organic debris left on the canal walls may have been responsible for the lack of adhesion in those instances. Where polycarboxylate cements with additives were used, greater Epon infiltration of the cement occurred as compared to that of the zinc oxideeugenol cements (Fig 7). AH-26 exhibited the poorest adaptation; infiltration of Epon was the greatest compared with all of the cements tested (Fig 8).
9 Gutta-percha cones and sealer. The technique of insertion of gutta-percha cones, whether by lateral or vertical condensation, made little difference in the adaptation. One wall of the root canal generally exhibited better guttapercha adaptation than the other (Fig 9). However, when the canals were filled by the vertical condensation method, more cracks in the den-
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tin were discernible than were seen in the teeth filled by lateral condensation. These cracks were filled partially with gutta-percha (Fig 10) or sealer (Fig 11). Although Epon infiltration generally was less than in those cases filled with silver cones and sealers, numerous voids were noted between the main cone and the accessory cones (Fig 12, top left and right). Guttapercha had no adhesive properties; cements or sealers filled many of the voids between the gutta-percha and canal walls and between the main and accessory cones (Fig 12, bottom left and right). In one case, a large lateral canal was discovered which was unfilled by gutta-percha or sealer (Fig 13, left). In the cases filled with chloropercha, shrinkage was noted, resulting in poor adaptation to the root canal walls (Fig 14). Good adaptation was found on some walls (Fig 13, center and right); extremely poor adaptation was seen in other areas of the same canal. Although faciolingual radiographs showed apparently good gutta-percha condensation, the mesiodistal view revealed voids; those voids were seen in the scanning electron microscopic examination (Fig 14). Secrlers
9 Zinc oxide-eugenol cements. Zinc oxide-eugenol cements appeared to adapt well to the root canal walls; few voids were noted at the interfaces (Fig 15, top left and right). However, some air entrapment was noted in the bulk of the set cements. In all cases, a fair degree of adhesion seemed to be present. 9 Polycarboxylate cements. The manipulation and insertion of the polycarboxylate cements presented some problems. The cements tended to stick to metal instruments, such as root canal pluggers, and condensation into the root canals was difficult.
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Fig 3---Left: Tightly fitted cone, inserted with polycarboxylate cement (orig mag x60). Center: Higher magnification of left photomicrograph (orig mag x600). Right: Higher magnification of center photomicrograph (orig mag X1,800).
at a magnification of • no voids between dentin and cement could be observed (Fig 16). Even irregularities were filled in some instances (Fig 17, left). However, in some cases unremoved tissue and air entrapment prevented adhesion to the root canal wails (Fig 17, center and riKht). DISCUSSION
Fig 4 Left: Loosely fitted silver cone, inserted with Grossman's cement (orig mag • Right: Higher magnification of cone (S) dentin (D) interface filled with cement (C) (orig mag • 180).
Thus, voids were frequently observed in the central masses of the material (Fig 15, bottom left). The additives to the polycarboxylate cements made the cements denser. The additive particles appeared to fill the micellar structure of the polycarboxylate
framework (Fig 15, bottom right). In many cases, when the polycarboxylate cements without or with additives were used as the sole filling material of the root canal, the adaptation and adhesion to the walls of the root canal were superb. Even
The technique used, that is, embedding the teeth with filled root canals in Epon, permitted the sectioning of the teeth without loss or dislodgment of the filling materials. As a result of the vacuum embedding, the Epon infiltrated the voids present from filling techniques or inadequate adhesion or adaptation of the root canal filling materials to the root canal wails. During processing of the samples, cracks developed in the dentin as a result of dehydration. Other cracks may have been present before the experimental procedures. However, it
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Fig 5 ~ T o p left: Silver cone insert with Kerr Tubliseal (orig mag • Top right: Higher magnification of photomicrograph of top left (orig mag >(600). Bottom left: Line scan (white line) shows presence of silver particles (Ag) (orig mag • 1,800). Bottom right: Sealer extruding from dentinal tubules (orig mag X 1,800). Fig 6~Silver cone cemented with polycarboxylate cement. Top left: Interface between cone (Ag) and dentin (D) is well filled with cement (P) (orig mag • Top right: Higher magnification of photomicrograph at top left (orig mag • 1,000). Bottom left: Interface at middle portion of canal (• 300). Bottom right: Higher magnification of bottom left photomicrograph (orig mag • 1,000).
JOURNAL OF ENDODONTICS [ VOL 2, NO 4, APRIL 1976
Fig 7--Top: Silver cone inserted with zinc polycarboxylate cement plus 10% calcium fluoride (orig mag • Middle: Higher magnification of top photomicrograph showing Epon (E) infiltration (orig mag • 180). Bottom: Higher magnification of middle photomicrograph (orig mag • 600).
was our impression that some fractures of the dentin occurred because of the pressures of the insertion of the root canal filling materials. The presence of gutta-percha or sealer or both in these cracks reinforced this impression. Obturation of root canals by cements or sealers alone appeared to be more complete than when the central solid core materials were used. These findings tend to corroborate those of Goerig and Seymour. 25 However, whether or not the insertion of pastes or cements alone would permit greater extrusion into the periapical tissues could not be determined in this experiment. These findings are only suggestive of the physical properties of various root canal filling materials and have no relationship to their biologic characteristics. Our findings tend to corroborate those of other researchers a~ that most root canal fillings do not completely obturate root canals. The reasons appear to be lack of or poor adhesion or chemical bonding of sealers to dentin and solid core materials 27 and difficulties in the manipulation and insertion of some cements, especcially the polycarboxylates.26,2s Such bonding is interfered with by inadeequate debridement, presence of culde-sacs, and inaccessible areas within the root canal. 29 Solid core materials such as silver and gutta-percha cones have no adhesive qualities. Therefore, cements or sealers must be used in conjunction with them. Gutta-percha, regardless of the technique used, is either poorly condensed or shrinks from the walls of the root canal; this confirms the finding of Brayton, Davis, and Goldman. g~ SUMMARY
The root canals of 133 freshly extracted, anterior teeth were prepared and filled with various root canal fill-
Fig 8--Top: Coronal area of canal filled with silver cone and AH-26. Epon (E) has infiltrated voids in cement (orig mag • Middle: Middle portion of root canal (orig mag • 37). Bottom: Apical portion of root canal (orig mag •
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Fig 9--Gutta-percha inserted by lateral condensation method. Top left: Good adaptation on one side. GP, gutta-percha; C, cement; D, dentin (orig mag • 180). Top right: Higher magnification of top le/t photomicrograph (orig mag • Bottom left: Poorer adaptation of gutta-percha (GP) on other canal wall cement (C). D, dentin (orig mag • Bottom right: Higher magnification of bottom left photomicrograph (orig mag • 600).
Fig 10 Dentinal fracture in tooth after insertion of gutta-percha by vertical condensation (orig mag • 60). Middle: Higher magnification of top photomicrograph showing gutta-percha (GP) in crack (orig mag • Bottom: Higher magnification of middle photomicrograph. GP, guttapercha (orig mag •
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Fig ll---Dentinal fractures after insertion of gutta-percha by vertical condensation. Top: orig mag • Middle: Higher magnification of top photomicrograph showing sealer (S) in crack (orig mag • 600). Bottom: Higher magnification of middle photomicrograph. S, sealer (orig mag • 1,800).
Fig 12--Voids in gutta-percha filling after insertion by vertical condensation method. Top left: orig mag • 60. Top right: Higher magnification of top le[t photomicrograph (orig mag • Bottom left: Cement (C) [ills interface between gutta-percha (GP) and dentin (D) and also between main and accessory cones (orig mag • 60). Bottom right: Higher magnification of bottom left photomicrograph (orig mag • 180). 107
JOUBNAL OF ENDODONTICS ] VOL 2, NO 4, APRIL 1976
Fig 13--Left: lateral canal (lc), unfilled by lateral condensation method (orig mag X60). Center: Good adaptation to canal wall by chloropercha (CP) (orig mag X180). Right: Higher magnification of center photomicrograph (orig mag X 600).
Fig 14--Chloropercha filling. Top left: orig mag X 60. Top right: Higher magnification of top left photomicrograph (orig mag X180). Bottom left: Higher magnification of top right photomicrograph (orig mag X600). Bottom right: Left radiograph is ]aciolingual riew; right radiograph is mesiodistal view. 108
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Fig 15---Canal filled with zinc oxide-eugenol showing good adaptation. Top le/t: orig mag X 180. Top right: orig mag • 600. Bottom left: Canal filled with zinc polycarboxylate cement (orig mag • Bottom right: Canal filled with polycarboxylate plus 5% calcium hydroxide (orig mag • 180).
Fig 16--Canal filled with zinc polycarboxylate cement. Le/t: orig mag X300. Middle: orig mag • 1,000. Right: orig mag X 3,000. 109
Fig 17---Left: Canal filled with zinc polycarboxylate cement plus 10% calcium fluoride (orig mag • 35). Middle: Tissue (T) prevents adhesion of polycarboxylate cement (PC) to dentin (D) (orig mag • Right: Higher magnification o/ middle photomicrograph (orig mag • 600). ings and by various techniques. The adhesion and adaptation of the filling materials to the walls of the root canals were examined with a scanning electron microscope. In general, zinc oxide-eugenol cements adhered well, whereas greater variability was found with zinc polycarboxylate cements. Silver and gutta-percha cones had no adhesion and required a sealer to fill the interface between cones and dentin. None of the techniques for inserting gutta-percha into the root canal was effective in obliterating the root canal space. * Tissues were embedded in Beem capsules filled with accelerated EponAraldite mixture. Capsules were placed in a 60 C oven for 72 hours. EponAraldite: Araldite 6005, 16 ml; Epon 812, 20 ml; DDSA, 48 ml; DBP, 3.2 ml; and DMP-30, 1.6% of total volume added before placing tissue under vacuum. Drs. Wollard, Brough, and Maggio formerly were advanced education students in endodontics, Temple University, Philadelphia. They are currently in private practice. Dr. Wollard practices in Kansas City, Mo; Dr. Brough in San Francisco; and Dr. Maggio in Oak Brook, Ill. Dr. Seltzer is professor and chairman, department of endodontology, Temple University. Reprint requests should be directed to Dr. Samuel Seltzer, School of Dentistry, Temple University, 3223 N Broad St, Philadelphia 19140. References
I. Curson, I., and Kirk, E. An assessment of root canal-sealing cements. Oral Surg 26:229 Aug 1968. 2. Dow, P.R., and Ingle, J.I. Isotope determination of root canal failure. Oral Surg 8:1100 Oct 1955. 3. Ingle, J.L. Endodontics. Philadelphia, Lea and Febiger, 1965. 4. Rickert, V.G., and Dixon, C.M. The controlling of root surgery. Trans Int Dent Cong (8th) Sec l l l a , 1931, p 15. 5. Sommer, R.F.; Ostrander, F.D.; 110
and Crowley, M.C. Clinical endodontics; a manual of scientific endodontics. Philadelphia, Saunders, 1966. 6. Torneck, C.D. Reaction of rat connective tissue to polyethylene tube implants. I. Oral Surg 21:379 March 1966. 7. Goldman, M., and Pearson, A.H. A preliminary investigation of the "hollow tube" theory in endodontics: studies with neo-tetrazolium. J Oral Ther 1:618 May 1965. 8. Seltzer, S. Endodontology. Biologic considerations in endodontic procedures. New York, McGraw-Hill, 1971. 9. Massler, M., and Ostrovsky, A. Sealing qualities of various filling materials. J Dent Child 21:228 Fourth Quart 1954. 10. Antoniazzi, J.H.; Mjtir, I.A.; and Nygaard-Ostby, B. Assessment of the sealing properties of root filling materials. Odon,tol Tidskr 76:261 June 1968. 11. Marshall, F. J., and Massler, M. Sealing of pulpless teeth evaluated with radioisotopes. J Dent Med 16:172 Oct 1961. 12. Yee, F.S.; Lugassy, A.A.; and Peterson, J.N. Filling of root canals with adhesive materials. J Endod 1:145 April 1975. 13. Going, R.E.; Massler, M.; and Dute, H.L. Marginal penetration of dental restorations by different radioactive isotopes. J Dent Res 39:273 March-April 1960. 14. Kapsimalis, P., and Evans, R. Sealing properties of endodontic filling materials using radioactive polar and nonpolar isotopes. Oral Surg 22:386 Sept 1966. 15. Ainley, J.E. Fluorometric assay of the apical seal of root canal fillings. Oral Surg 29:753 May 1970. 16. Friend, L.A. Handling properties of a zinc polycarboxylate cement. An investigation. Br ,Dent J 127:359 Oct 1969. 17. Mizrahi, E., and Smith, D.C. The bond strength of a zinc polycarboxylate cement. Investigations into the behaviour under varying conditions. Br Dent J 127:410 Nov 1969. 18. Mortimer, K.V., and Tranter, R.C. A preliminary laboratory evaluation of polycarboxylate cements. Br Dent J 127: 365 Oct 1969. 19. Smith, D.C. A new dental cement.
Br Dent J 124:381 Nov 1968. 20. Furseth, R. A study of experimentally exposed and fluoride treated dental cementum in pigs. Acta Odontol Scand 28:833 Dec 1970. 21. Feagin, F.; Patel, P.R.; Koulorides, T.; and Pigman, W. Study of the effect of calcium phosphate, fluoride and hydrogen ion concentrations on the remineralization of partially demineralized human and bovine enamel surfaces. Arch Oral Biol 16:535 May 1971. 22. Swartz, M.L.; Phillips, R.W.; and Norman, R.D. Effect of fluoride-containing zinc oxide-eugenol cements on solubility of enamel. J Dent Res 49:576 May-June 1970. 23. Goldhaber, P. The inhibition of bone resorption in tissue culture by nontoxic concentrations of sodium fluoride. Israel I Med Sci 3:617 Sept-Oct 1967. 24. Anderson, T.F. A method for eliminating gross artifacts in drying specimens, in Congres de microscopie electronique. Paris, Editions de la Revue d'Optique, 1952, pp 567-576. 25. Goerig, A.C., and Seymour, F.W. Comparison of common root canal filling techniques and sealers with the simplified pressure injection method and zinc oxide-eugenol as the sealing agent. JADA 88:826 April 1974. 26. Barry, G.N., and Fried, I. L. Sealing quality of two polycarboxytate cements used as root canal sealers. J Endod 1:107 March 1975. 27. Sanders, S.H., and Dooley, R.J. A comparative evaluation of polycarboxylate cement as a root-canal sealer utilizing roughened and nonroughened silver points. Oral Surg 37:629 April 1974. 28. Barry, G.N., Heyman, R.A., and Fried, I.L. Sealing quality of instruments cemented in root canals with polycarboxylate cements. J Endod 1:112 March 1975. 29. Baker, N.A.; Eleazer, P.D.; Averbach, R.E.; and Seltzer, S. Scanning electron microscopic study of the efficacy of various irrigating solutions. J Endod 1:127 April 1975. 30. Brayton, S.M.; Davis, S.R.; and Goldman, M. Gutta-percha root canal fillings. An in vitro analysis. I. Oral Surg 35:226 Feb 1973.
