Adhesive Sealing of the Pulp Chamber

JOURNAL OF ENDODONTICS Copyright © 2001 by The American Association of Endodontists Printed in U.S.A. VOL. 27, NO. 8, AUGUST 2001 Adhesive Sealing of the Pulp Chamber Sema Belli, DDS, PhD, Yi Zhang, DDS, Patricia N. R. Pereira, DDS, PhD, and David H. Pashley, DMD, PhD The purpose of this in vitro study was to evaluate quantitatively the ability of four different filling materials to seal the orifices of root canals as a secondary seal after root canal therapy. Forty extracted human molar teeth were used. The top of pulp chambers and distal halves of the roots were removed using an Isomet saw. The canal orifices were temporarily sealed with a gutta-percha master cone without sealer. The pulp chambers were then treated with a self-etching primer adhesive system (Clearfil SE Bond), a wet bonding system (One-Step), a 4-methacryloyloxyethyl trimellitate anhydride adhesive system (C&B Metabond), or a reinforced zinc oxide-eugenol (IRM). The specimens were randomly divided into four groups of 10 each. A fluid filtration method was used for quantitative evaluation of leakage. Measurements of fluid movement were made at 2-min intervals for 8 min. The quality of the seal of each specimen was measured by fluid filtration immediately and after 1 day, 1 wk, and 1 month. Even after 1 month the resins showed an excellent seal. Zinc oxide-eugenol had significantly more leakage when compared with the resin systems (p < 0.05). Adhesive resins should be considered as a secondary seal to prevent intraorifice microleakage. The purpose of this study was to evaluate quantitatively the sealing properties of a self-etching primer system (Clearfil SE Bond), a wet bonding system (One-Step), a 4-methacryloyloxyethyl trimellitate anhydride adhesive system (C&B Metabond), and a reinforced zinc oxide-eugenol (IRM) placed in pulp chambers in extracted human molars treated with NaOCl. A fluid filtration method, first described by Derkson et al. (10) and later adapted for endodontics (9), was used for quantitive evaluation of leakage in a nondestructive longitudinal study. MATERIALS AND METHODS Tooth Preparation Forty recently extracted human molar teeth were used in this study. Crown segments were prepared from the teeth by removing the top of pulp chamber using an Isomet saw (Buehler Ltd., Lake Bluff, IL). The roots were then removed ;2 mm below the bifurcation (Fig. 1A). The pulp tissue was removed by hand instruments and endodontic files. The canal orifices were widened with Gates-Gliden burs and obturated with a gutta-percha master cone without sealer. The pulp chamber area was treated with 5% NaOCl for 5 min and then rinsed with warm water for 2 min. Specimens were then randomly divided into four treatment groups of 10 each. In each group the entire floor of the pulp chamber was treated with one of the four materials and then the upper-cut surfaces of the crown segments (Fig. 1B) were cemented onto 2 3 2 3 0.7 cm pieces of Plexiglass with an adhesive material, C&B Metabond (Parkell, Farmingdale, NY). The pieces of Plexiglass had 18-gauge stainless-steel tubes placed through their centers, ending flush with the upper surfaces. The access openings of the tooth segments were then positioned over the tubes to permit a direct communication between the pulp chamber and the micropipette/microsyringe system as shown in Fig. 2. Then the unsealed gutta-percha cones were removed, and the pulp chamber was filled with water through the 18-gauge needle using a 26-gauge needle, taking care to remove all air bubbles that could be seen through the transparent Plexiglass. The empty root canals beneath the sealing materials were also filled with water to maintain hydration of the dentin. Coronal leakage is an important cause of failure of root canal treatments (1–7). Swartz et al 1983 (8) found that the failure rate was almost twice as high in cases without an adequate restoration compared with cases that were properly restored. Therefore several materials have been used within the pulp chamber in an attempt to provide a second line of defense against the leakage of bacteria, if the sealing quality of the material used to close the access opening fails. These include placement of an additional material such as IRM, Cavit, and/or sealing with restorative material (8, 9). Several studies have examined the sealing qualities of various restorative materials against the floor of the pulp chamber, but they have not been quantitative and they have not used the latest adhesive materials. Sealing Agents GROUP 1 Universal Dentin Activator A from a C&B Metabond kit (Parkell, Farmingdale, NY) was applied to the pulp chamber of 10 teeth 521 522 Belli et al. Journal of Endodontics FIG 2. Schematic of the apparatus used to measure fluid flow around the sealed floor of the pulp chamber as a hydraulic conductance. Fluid exited from the pressurized reservoir through tubing containing a micropipette to the tooth segment. The movement of a tiny air bubble, controlled by the microsyringe, was proportional to the microleakage. (Bisco, Inc., Schaumburg, IL), and rinsed thoroughly. Excess water was removed with a brief burst of air leaving the dentin slightly, but visibly, moist. Two coats of One-Step adhesive were applied to the pulp chamber without waiting between coats. The adhesive was then thoroughly air-dried for 10 s to remove residual solvent and water and then was light-cured for 10 s. A second layer of One-step adhesive was applied, followed by thorough air-drying and lightcuring for 10 s. One-Step adhesive that remained on the brush tip was applied followed by brief air-drying without light-curing. Approximately one-third of the volume of the lower half of the pulp chambers was then filled with a low modulus microhybrid low-viscosity flowable composite (Aelite Flo LV, Bisco, Inc., Schaumburg, IL) and light-cured 20 s. GROUP 3 FIG 1. (A) Schematic illustration of the tooth segment created by removal of the upper half of the tooth and removal of the distal half of the roots. The black material designates gutta-percha that was used to temporarily obturate the canals while the sealing materials (cross-hatched) were applied. (B) After application of the sealing material (cross-hatching), gutta-percha was removed to ensure that it did not contribute to the seal. The sealed specimen was inverted onto a piece of Plexiglass and bonded in place with C&B Metabond for fluid filtration measurements. for 15 s and rinsed thoroughly. C&B Metabond was then applied to the walls and floor of the pulp chamber using the brush tip application technique to a depth of 2 to 3 mm using the clear polymethyl methacrylate powder. GROUP 2 The pulp chambers were etched for 15 s with Uni-Etch, 32% phosphoric acid gel conditioner of the One-Step adhesive system The pulp chambers were treated with Clearfil SE Bond Primer (Kuraray Co., Ltd., Osaka, Japan) for 20 s and then gently air-dried for 3 to 5 s. Clearfil SE Bond adhesive was then applied with a brush and light-cured for 10 s. Then approximately one-third of the volume of the lower half of the pulp chambers was then filled with a light-cured composite, Palfique transparent (Tokuyama Corp., Tokyo, Japan). GROUP 4 IRM (L. D. Caulk Co., Milford, DE) was prepared by determining the weight of 3 drops of liquid and then adding twice that weight of powder. This produced a powder-to-liquid ratio of 2.0. The fresh IRM was then condensed to the pulp chambers with a cotton pellet saturated with the material. Measurement of Sealing Properties The sealing qualities of the four test materials (Table 1) were quantitated by following the progress of a tiny air bubble traveling within a 25 ml micropipette (Microcaps, Fisher Scientific, Philadelphia, PA). All tubing, pipette, and syringe (Fig. 2) were filled with distilled water under a pressure of 20.7 KPa or 211 cm H2O. Measurements of fluid movement were made at 2-min intervals for Vol. 27, No. 8, August 2001 Adhesive Sealing of the Pulp Chamber TABLE 1. Materials Product Name Manufacturer Composition C&B Metabond Parkell Co. Farmingdale, NY Conditioner: 10% citric acid, 37% ferric chloride Liquid: 5% 4-META/95% MMA; catalyst: TBBO Powder: polymethyl methacrylate Bisco, Inc. Schaumburg, IL Conditioner: 32% phosphoric acid gel; adhesive: mixture of Bis-GMA, BPDM, and HEMA in acetone TABLE 2. Microleakage of four materials used to seal the floor of the pulp chamber Material Metabond One-Step One-Step Clearfil SE Bond Kuraray Co., Ltd. Osaka, Japan Primer: MDP, HEMA silica Microfiller; adhesive: MDP, HEMA, and BisGMA IRM Powder: 80% ZnO, 20% PMMA Liquid: 85% eugenol, 15% olive oil L. D. Caulk Co. Milford, DE 4-META, 4-acryloyloxyethyl trimellitate anhydride; MMA, methylmethacrylate; TBBO, oxidized tri-n-butyl borane; Bis-GMA, 1:2 addition product of bisphenol-A diglycidyl ether and methacrylic acid; BPDM, 1:2 addition product of 3,4,39,49-biphenyltetracarboxylic acid anhydride and 2-HEMA; HEMA, 2-hydroxyethyl methacrylate; MDP, 10-methacryloyloxydecamethylene phosphoric acid; PMMA, polymethyl methacrylate. 8 min, which were then averaged. The quality of the seal of each specimen was measured immediately (i.e. within 30 min), and at 1 day, 1 wk, and 1 month. The fluid flow rate through the 18-gauge needle in the Plexiglass in unsealed specimens was measured by weighing the amount of water that could flow through the needle in 1 min (18.50 g/min at 211 H2O or 87.7 ml min21 cm H2O21); this value served both as a positive control and as 100% leakage, to which the sealed values could be expressed (as a percent). Scanning Electron Microscopy (SEM) Parallel specimens, prepared exactly like the test specimens, were prepared for SEM evaluation by cutting the sealed tooth longitudinally into two equal halves. Each half was polished through finer and finer abrasive paper, and then with 3, 1, and 0.5 mm diamond paste. After ultrasonication the specimens were critical point dried and then coated with gold in preparation for SEM. They were examined in a JEOL scanning electron microscope. Statistics A two-way analysis of variance (ANOVA) was used (bonding material and time as the two factors) to analyze data for significant differences. Multiple comparisons were performed using the Student-Newman-Keuls test on ranks, setting a 5 0.05. RESULTS The results of the evaluation of the sealing qualities of the four materials are shown in Table 2. All of the resins gave very good seals regardless of when they were evaluated. The IRM sealed 523 SE Bond IRM Period Lp (ml min21 cm22 cm H2O21) Immediate 1 day 1 week 1 month Immediate 1 day 1 week 1 month Immediate 1 day 1 week 1 month Immediate 1 day 1 week 1 month 0.159 3 1024 6 0.205 3 1024 a 0.638 3 1024 6 0.738 3 1024 b 1.937 3 1024 6 2.948 3 1024 b 1.873 3 1024 6 3.646 3 1024 b 1.292 3 1024 6 1.329 3 1024 b 1.838 3 1024 6 1.172 3 1024 b 1.166 3 1024 6 0.014 3 1024 b 1.118 3 1024 6 2.242 3 1024 b 0.884 3 1024 6 0.965 3 1024 b 1.59 3 1024 6 1.998 3 1024 b 1.16 3 1024 6 0.958 3 1024 b 1.838 3 1024 6 4.957 3 1024 b 4.869 3 1024 6 5.33 3 1024 c 1.848 3 1024 6 1.92 3 1024 b 161.2 3 1024 6 319.1 3 1024 d 1517.83 3 1024 6 2934 3 1024 e Values are means 6 SD. n 5 10. Different superscript letters indicate groups that are significantly different. Groups identified with the same superscript letters are not significantly different (p . 0.05). specimens leaked more (p , 0.05) immediately than they did 1 day later, but by 1 wk they showed significantly (p , 0.05) more leakage. After 1 month the IRM leaked significantly more (p , 0.05) than the 1-wk values. There were no statistically significant differences in microleakage between any of the resin groups at any time period, except Metabond which when measured immediately had the lowest microleakage (p , 0.05). However all of the resins had significantly lower microleakage (p , 0.05) than IRM. When the results were expressed as a percentage of the unsealed control, the results of the statistical analyses were the same (data not shown). Scanning electron microscopy revealed significant differences between the resin materials. Pulp chambers sealed with C&B Metabond exhibited wide, funneled resin tags (Fig. 3A) due to the loss of peritubular dentin matrix by the acidic conditioner. The resin tags appeared to fill the tubules perfectly, with no evidence of voids or debonding. The SEM appearance of C&B Metabond in the resin tags was the same as the appearance of the overlying adhesive. It appeared uniform and without the presence of any filler particles. When the polished interface was briefly acid-etched with 6 N HCl for 10 s, rinsed with water, and then treated with 5% NaOCl for 2 min, the dentin matrix surrounding the resin tags was removed, revealing their diameter length and density (Fig. 3B). SEM of pulpal floors sealed with One-Step/Aelite-Flo LV flowable composite revealed some unusual differences in the adaptation of this adhesive system to dentin compared with C&B Metabond. Although four layers of One-Step were applied to dentin, SEM examination clearly shows that the adhesives soaked into the dentin leaving no residual adhesive layer on the dentin surface. When the flowable composite was added, it adapted directly to the dentin rather than on to an adhesive layer. Some of the filler particles actually entered the top of the resin tags (Fig. 4A). The thickness of the resin-infiltrated dentin (i.e. hybrid layer) was 3 to 5 mm. When the polished cross-sections were treated sequentially with HCl/NaOCl to expose the underlying resin tags (Fig. 4B), they could be seen to be ;2 to 3 mm in diameter, over 15 mm long, and packed so closely together that there was little intertubuler dentin matrix between them. Clearfil SE Bond resin sealed dentin well (Fig. 5). The hybrid layer was so thin that it could barely be 524 Belli et al. Journal of Endodontics FIG 3. (A) Polished cross-sections of the wall of the pulp chamber sealed with C&B Metabond (MB). Note the wide, funneled tubules that were well sealed with resin tags. The 2-mm-thick bulk of C&B Metabond was continuous with the material in the resin tags and contained no filler particles. (32500, scanning electron micrograph.) (B) Polished cross-sections of the wall of the pulp chamber sealed with C&B Metabond after sequential treatment with 6 N HCl followed by 5% NaOCl. The dentin surrounding the resin tags was removed, revealing their diameter, length, and density. (32500, scanning electron micrograph.) distinguished. The hybrid layer was covered by an adhesive layer of variable (0.5 to 10 mm) thickness that in turn was covered by filled resin composite. The interface between IRM and dentin showed a great deal of porosity (Fig. 6), but the tubules were well-filled with zinc oxide-eugenol. DISCUSSION All of the adhesive resins produced seals that were superior to those produced by IRM. The IRM results obtained in this study confirmed the good sealing qualities of low power-to-liquid ratios of zinc oxide-eugenol and IRM previously reported by us (11). Stiff mixes of these temporary filling materials (high power-toliquid ratios) are less effective at sealing dentin than are more fluid mixes. The powder-liquid ratio used in this study is the one recommended by the manufacturer and the one widely used clinically. The apparent clinical success of IRM even though it leaked some is probably due to the antibacterial properties of zinc and the anti-inflammatory properties of eugenol (12–15). FIG 4. (A) Polished cross-sections of the wall of the pulp chamber sealed with One-Step (OS). The hybrid layer (dark layer between composite and mineralized dentin) was ;5 mm thick. Note the filler particles in the overlying resin composite. There was no adhesive layer between the top of the hybrid layer and the bottom of the composite because the adhesive rapidly penetrated deep into the tubules to form dark resin tags. (32500, scanning electron micrograph.) (B) When the polished cross-sections of One-Step sealed tooth were treated sequentially with HCl/NaOCl to expose the underlying resin tags, they could be seen to be packed so closely together that there was little intertubuler dentin matrix between them. (32500, scanning electron micrograph.) The three resin adhesive systems used in this study were equally effective. Two of them (Clearfil SE Bond and One-Step) required the use of a filled resin composite on top of the adhesive layer, because they were only ;10 mm thick. Filled composites are more difficult to remove if retreatment of the root canal is required because they are harder and stiffer than unfilled resins. We used Palfique transparent composite resin (Tokuyama Corp., Tokyo, Japan) with Clearfil SE Bond in an attempt to permit visualization of the orange color of the gutta-percha in the underlying canal. This was successful. Similarly when C&B Metabond liquid was mixed with its powder, we chose the clear powder to impart a transparency to the adhesive layer, so that we could identify the location of the canal orifice through the material. This, too, worked very well. Both Clearfil SE Bond and One-Step are light-cured. Both C&B Metabond and One-Step require separate acid-etching steps, unlike Clearfil SE Bond, which is a self-etching/self-priming system. The manufacturers have increased the concentration of acidic adhesive Vol. 27, No. 8, August 2001 FIG 5. Polished cross-section of the wall of pulp chamber sealed with Clearfil SE Bond/Palfique transparent composite, following sequential treatment with HCl/NaOCl to expose the resin tags. Well-filled resin tags are apparent. The adhesive layer, which varied in thickness between 0.5 to 10 mm, is clearly different from the more granular overlying composite. (32500, scanning electron micrograph.) FIG 6. Polished cross-section of the wall of the pulp chamber sealed with IRM, following sequential treatment of HCl/NaOCl to expose the “resin” tags. The porosity in the IRM is probably the result of the high vacuum used for SEM and may represent regions where eugenol volatilized. (32500, scanning electron micrograph.) monomers to decrease the pH to 1.5. These monomers are dissolved in hydroxyethylmethacrylate, which is a common primer monomer. It is applied for 20 s to permit the acidic monomer to etch through the smear layer into the underlying dentin (16). It is then simply air-dried to evaporate the solvents. No rinsing step is required. Then an adhesive layer is applied over it and light-cured. Of the three adhesive systems test, Clearfil SE Bond was the simplest to use, but it does require subsequent application of resin composite because it is very thin, and it does require light-curing. The second easiest system to use was C&B Metabond. It has the advantage of being self-curing and does not require the use of a resin composite. C&B Metabond is a primerless, self-curing adhesive system (17) that can be used as an adhesive or as a resin cement. When used to seal the pulp chamber, it was used without a composite. Multiple applications of it were made until it reached a thickness Adhesive Sealing of the Pulp Chamber 525 of ;2 mm. Unlike conventional bonding systems, such as OneStep, which use a relatively thin (;10 mm) adhesive layer covered with a thick (2 mm) layer of filled resin composite, C&B Metabond is an unfilled adhesive. The liquid component is 5% 4-methacryloyloxyethyl trimellitate anhydride in 95% methyl methacrylate (Table 1), whereas the powder component is clear prepolymerized polymethyl methacrylate. The polymerization of the system is catalyzed by partially oxidized tri-n-butyl borane that is mixed with the liquid component before application to dentin. If adhesive resin seals are to be placed over gutta percha-filled canals in single root teeth that have no pulpal floor, then as much as half of the bonded surface area will be composed of guttapercha. The resin must be able to polymerize on top of the guttapercha and it should adapt well to its surface. Preliminary studies indicate that Clearfil SE Bond and C&B Metabond polymerized well on gutta-percha but that One-Step does not. This may be because the acetone solvent of One-Step may leach some component from gutta-percha that inhibits polymerization. All of the resin systems worked well at sealing the floor and walls of mandibular molars. How well they work on single-rooted teeth without dentin floors remains to be determined. By using a 2 to 3 mm thick layer C&B Metabond over the floor of the pulp chamber, it not only provides an excellent secondary seal, but it also provides sufficient bulk to prevent penetration of the pulpal floor during removal of hard restorative materials, such as amalgam buildups during retreatment. Zinc oxide-eugenol sets by forming a chelate between two molecules of eugenol and one molecule of zinc oxide (18). The tags of material in the specimens sealed with IRM probably were composed of zinc-eugenolate. This chelate is known to slowly hydrolyze in the presence of water to release eugenol (19, 20) and may be responsible for the slow loss of its sealing ability. The results clearly indicate that adhesive resins provide excellent seals for as long as 1 month, although these adhesive seals were not subjected to any stresses. However, the intention of using adhesive resins is to obtain an excellent seal of the root canal from the pulp chamber. The resin seals should be protected, in turn, by materials with good compressive strength, such as amalgam, glass ionomer cements, or resin composites. This work was supported in part by Grant DE 06427 from the National Institute of Dental and Craniofacial Research. The authors are grateful to Shirley Johnston for secretarial support. Dr. Belli is affiliated with the Department of Operative Dentistry, Selcuk University, Dental School, Konya, Turkey. Drs. Zhang and Pashley are affiliated with the Department of Oral Biology and Maxillofacial Pathology, Medical College of Georgia, Augusta, GA. Dr. Pereira is affiliated with the Department of Operative Dentistry, University of North Carolina, Chapel Hill, NC. Address requests for reprints to Dr. David H. Pashley, Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129. References 1. Swanson K, Madison S. An evaluation of coronal microleakage in endodontically treated teeth. Part I. Time periods. J Endodon 1987;13:56 –9. 2. Madison S, Swanson K, Chiles SA. An evaluation of coronal microleakage in endodontically treated teeth. Part II. Sealer types. J Endodon 1987;13: 109. 3. Madison S, Wilcox LR. An evaluation of coronal microleakage in endodontically treated teeth. Part III. In vivo study. J Endodon 1988;14:455– 8. 4. Magura ME, Kafrawy AH, Brown CE, Newton CW. Human saliva coronal microleakage in obturated root canals. An in vitro study. J Endodon 1991;17: 324 –31. 5. Torabinejad M, Borosmy U, Keltering JD. In vitro bacterial penetration 526 Belli et al. of coronally unsealed endodontically treated teeth. J Endodon 1990;16:556 –9. 6. Lin LM, Skribner JR, Gaengler P. Factors associated with endodontic treatment failures. J Endodon 1992;18:543–9. 7. Saunders W, Saunders E. Coronal leakage as a cause of failure in root canal therapy: a review. Endod Dent Trauma 1994;10:105– 8. 8. Swartz DB, Skidmore AE, Griffin JA. Twenty years of endodontic success and failure. J Endodon 1983;9:198 –202. 9. Anderson RW, Powell BJ, Pashley DH. Microleakage of three temporary endodontics restorations. J Endodon 1988;14:497–501. 10. Derkson GD, Pashley DH, Derkson ME. Microleakage measurements of selected restorative materials: a new in vitro method. J Prosthet Dent 1986;56:435– 40. 11. Pashley DH, Tao L, Pashley EL. The sealing properties of temporary filling material and bases. J Prosthet Dent 1988;60:292–9. 12. Azuma Y, Ozasa N, Ueda Y, Takagi N. Pharmacological studies on the anti-inflammatory action of phenolic compounds. J Dent Res 1986;65:53– 6. 13. Hashimoto S, Uchiyama K, Maeda M, Ishitsuka K, Furumoto K, Nakamura Y. In vivo and in vitro effects of zinc oxide-eugenol (ZOE) on biosyn- Journal of Endodontics thesis of cyclo-oxygenase products in rat dental pulp. J Dent Res 1988;67: 1092– 6. 14. Meeker HG, Linke HAB. The antibacterial action of eugenol, thyme oil, and related essential oils used in dentistry. Compendium 1988;9:32– 41. 15. Hashimoto S, Maeda M, Yamakita J, Nakamura Y. Effects of zinc oxide-eugenol on leukocyte number and lipoxygenase products in artificially inflamed rat dental pulp. Arch Oral Biol 1990;35:87–93. 16. Nakatsuka K. Characteristics of “Clearfil Mega Bond.” In: Mamoi Y, Akimoto N, eds. Modern trends in adhesive dentistry. Proceedings of the Adhesive Dentistry Forum 99, Tsurumi, Yokohama, Japan 2000 (in press). 17. Nakabayashi N, Pashley DH. Hybridization of dental hard tissues. Quintessence Publishing Co., Tokyo, 1998:37–56. 18. Craig RG. Restorative dental materials. 10th ed. St. Louis: Mosby, 1997:315. 19. Hume WR. In vitro studies on the local pharmacodynamics, pharmacology and toxicology of eugenol and zinc-oxide eugenol. Int Endod J 1988; 31:130 – 4. 20. Hashieh IA, Camps J, Dejou J, Franquin JC. Eugenol diffusion through dentin related to dentin hydraulic conductance. Dent Mater 1998;14:229 –236.