An In Vitro Evaluation of the Sealing Ability of a New Root-canal–obturation System

JOURNAL OF ENDODONTICS Copyright © 2003 by The American Association of Endodontists

Printed in U.S.A. VOL. 29, NO. 10, OCTOBER 2003

An In Vitro Evaluation of the Sealing Ability of a New Root-canal– obturation System Brian P. Kardon, DMD, Sergio Kuttler, DDS, Patrick Hardigan, PhD, and Samuel O. Dorn, DDS

suring leakage than linear dye-penetration–measurement techniques (7). Dye-penetration studies have limitations because trapped air has been shown to restrict the penetration of dye (9, 10). Furthermore, if the specimen is sectioned, leakage can be measured on the cut surface, and the tooth must be destroyed so longitudinal studies cannot be performed (11). It may be more relevant to measure the amount of fluid traversing through a canal than measuring the length of a gap in a filled canal (11). A new hydrophilic, urethane-dimethacrylate– based resin sealer, EndoRez (Ultradent, South Jordan, UT), has been developed for use with a single, gutta-percha cone for canal obturation. The goal of this study was to compare apical microleakage, using a fluidfiltration model, of teeth filled with this new product to those filled with single gutta-percha cones with AH Plus sealer (Dentsply, Konstanz, Germany) and warm vertically compacted gutta-percha with AH Plus sealer.

In this study the sealing ability of a new urethane methacrylate resin-based sealer, EndoRez, was evaluated using a fluid-filtration model. Sixty-four single-rooted lower bicuspids were decoronated, instrumented, and divided into 3 groups of 20 each with 4 teeth used as controls. In group A, the roots were obturated with EndoRez and a single cone of gutta-percha, group B with AH Plus and a single cone of gutta-percha, and group C was obturated using gutta-percha with warm vertical compaction and AH Plus sealer. All specimens were allowed to set for 7 days in 100% humidity at 37°C. The groups were compared for differences in the amount of leakage (mm/h) using a Chi-square test. The leakage of group A was significantly higher at p ⴝ 0.01 than the other two groups. There was no significant difference in leakage between groups B and C.

MATERIALS AND METHODS Sixty-four, single-rooted, lower premolars were obtained for study. Any excess calculus and soft tissue was removed with scalers. All roots were cross-sectioned at the CEJ with a carborundum disk (Brasseler USA, Savannah, GA). A #10 K-file (Kerr, Romulus, MI) was placed in the canal until visible at the apex and pulled back 1 mm to determine the working length. Instrumentation for all teeth was performed using Greater Taper Profiles, size #35 0.12 taper (Dentsply, Tulsa, OK), and Profiles, 0.04 taper, sizes 40 to 20 (Dentsply, Tulsa, OK) in a crown-down sequence until a #40 file fit at working length. Irrigation was performed using 1 ml of 5.25% NaOCl between each file. A #15 file was used to maintain a patent apex. On completion of instrumentation, the smear layer was removed from the canals by rinsing with 2 ml of 17% EDTA solution for 5 min, followed by flushing again with 2 ml of 5.25% NaOCl. The canals were dried with paper points. The prepared specimens were then randomly divided into 3 groups of 20 with the remaining four used as controls. Group A roots were obturated using the EndoRez filling system. This entailed fitting a #40 standardized gutta-percha point (Ultradent) to a snug tug-back, and then placing the resin sealer with 30-gauge application tips to within 3 mm of the working length. The sealer was expressed into the canals and the syringe was backed out as sealer was observed to fill up the canal space. The gutta-percha cone was seated and seared off 2 to 3 mm below the CEJ with a System B (Analytic Endodontics, Orange, CA).

It has been long established that the apical region of the root canal must be well sealed at the completion of root-canal therapy. There are many reasons why the canal space in a root canal must be obliterated during obturation. The main reason is that spaces between the root-canal filling and canal wall may harbor microorganisms, which could lead to irritation of periapical tissue (1). Obtaining an impervious seal is extremely difficult. The use of sealers, along with well-adapted gutta-percha gives the operator a better chance to reach this goal. The ideal obturation is one where a complete three-dimensional fill is achieved in the canal system (2). Examples of commonly used methods to reach this goal are warm vertical compaction, warm and cold lateral compaction, and Thermafil. There is, however, no one method that may satisfy all clinical cases (3). Single gutta-percha– cone methods have been shunned because leakage studies have generally found them to provide inferior seals compared with techniques that use additional compaction (4, 5). Some studies, however, have shown favorable results using single-cone methods with dentinal bonding resins (6) and/or epoxy resins (7) as sealers. Fluid filtration has been used to measure microleakage since 1986 (8). This method has been deemed more effective in mea658

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FIG 1. Diagram of the fluid filtration model used in this study.

In group B, the roots were obturated with a single, gutta-percha cone and AH Plus sealer by fitting a #40 gutta-percha point to the working length, coating the point with sealer, placing it into the canal space, and repeating until a filled canal space was observed visually and radiographically (Trophy USA, Danbury, CT). The teeth in group C were filled with warm vertical condensation using the System B and Obtura II (Obtura/Spartan, Fenton, MO) by fitting a fine/medium nonstandardized cone (Dentsply, Tulsa, OK) to the working length. The fitted cone was then cut back 1 mm and coated with AH Plus sealer. It was placed in the canal, seared off, and condensed to 4 mm of the working length with a System B. An Obtura II was used to back-fill the canal with gutta-percha to 2 to 3 mm below the CEJ. Two positive controls were filled with a gutta-percha cone and no sealer. Two negative controls were instrumented and obturated using the same method as group C. In addition, the external surface of the apex was sealed with two coats of nail varnish. All teeth were radiographed using digital radiography from mesial-distal and buccal-lingual angulations to confirm adequate obturation. After obturation, the teeth were stored at 37°C at 100% humidity for 7 days to allow the sealing materials to fully set. The teeth were then tested for microleakage by using a fluid-filtration device (Fig. 1). This modified testing model was based on one that was used in previous leakage studies (12). Both ends of the root specimens were inserted into heavy-walled rubber tubing and secured by twisting brass-ligature wire around the tubing. The tubing was attached to two luer-lock adapters that were attached to polyethylene tubing (PE, Clay Adams, Parsippany, NJ). All of the polyethylene tubing was filled with water from a beaker placed in a modified pressure cooker. The modifications included an inlet port for compressed gas and an 18-gauge, stainless-steel tube, which passed from the beaker of water inside the pressurized container to the outside where it was connected to the PE 190 polyethylene tubing (Fig. 1). Water under 16 psi of pressure (1125.0 cm H2O) entered the apical end of the filled root canals. The coronal end of the root was connected by polyethylene tubing to a T-tube connector, which joined a microsyringe to the fluid-filled system. The microsyringe was used to introduce a minute air bubble into the glass capillary tube of uniform diameter (25 ␮l Microcap, Fisher Scientific, Atlanta, GA), which had a ruler adjacent to it to permit accurate measurements of air-bubble displacement in millimeters. The polyethylene tube distal to the glass capillary tube emptied into a plastic

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cup. Measurements were taken over 30 min or until the air bubble traversed 50 mm of the glass capillary tube. Two measurements were taken for each specimen and totaled. Leakage was determined by measuring in millimeters the displacement of the air bubble over time. Statistical analysis was performed by first using a nominal logistic regression to determine that root length did not have a significant effect on leakage. A Chi-square analysis was performed to determine if there were any statistically significant differences in leakage among the three test groups. Results were obtained by determining the number of teeth that had leakage values greater or less than 1.5 mm of bubble displacement per hour. On completing the measurements, two specimens taken from each of groups A and B were split and the sealer/dentin interface was observed under scanning electron microscope (SEM). This was achieved by grooving the roots longitudinally with a disk and splitting them with a chisel. The specimens were allowed to dry and then were sputter coated with palladium using a Technics Sputter Coater (Alexandria, VA). The specimens were finally placed in an ISI DS130 SEM (Avon, CT) for observation.

RESULTS The nominal logistic regression showed that root length had no predictive value on leakage. The results of the leakage measurements are shown in Table 1. One of the teeth in group A was excluded from the study because it was found to have two separate canals. Group A had more specimens that leaked more than 1.5 mm/h than groups B or C. Three of 19 specimens showed leakage of more than 50 mm within 30 min, and 8 of 19 displaced more than 1.5 mm after two 30-min measurements. Only 2 of 40 samples in the other two groups showed more than 1.5 mm/h of displacement (Table 1). The statistical analysis showed a Chi-square value of 12.6 at 2 degrees of freedom. This indicated that a significant difference existed between group A and the other test groups at p ⫽ 0.01. There was no significant difference in leakage between groups B and C. The negative controls did not leak. One positive control leaked too fast to be measured, whereas the other leaked 72 mm in 60 min. The SEM images showed the sealer in specimens from group A to have a honeycombed appearance (Fig. 2). The sealer in specimens from group B appeared to have a more solid consistency (Fig. 3).

DISCUSSION Previous studies involving leakage tests on teeth obturated using a single-cone method have shown differing results. The singlecone method has been advocated for canals with parallel walls and when the primary cone fits tightly in the apical one-third (13). This implies that if a round shape is made in the canal preparation a well-fit single cone with sealer can be used for adequate obturation. In this study, all canals were prepared with a 0.04 taper to the working length. The standardized 0.02 tapered cone fit snugly but only in the most apical extent. This lack of an intimate fit had little effect on the sealing ability of AH Plus in group B. It is possible that this had an effect on group A. Single-cone methods of obturation have been shown to be inferior in providing an apical seal in numerous in vitro studies (4, 5). This may not have a significant impact clinically, because it has

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Journal of Endodontics TABLE 1. Leakage measurements

Group

⬍1.5 mm Leakage

ⱖ 1.5 mm Leakage

Total

Chi-square

p Value

DF ⫽ 2

A B C Positive control Negative control Total

11 19 19 0 2 51

8 1 1 2 0 12

19 20 20 2 2 63

12.6

0.01

Significant

DF ⫽ Degrees of Freedom. .

FIG 2. SEM a split specimen from Group A (EndoRez) at 1.11 K times magnification showing dentin on the right, sealer in the middle and gutta-percha on the left.

FIG 3. SEM a split specimen from Group B (AH Plus) at 914 times magnification showing dentin on the right, sealer in the middle and gutta-percha on the left.

been found that there is no correlation between sealing ability and biological success (14). There have been multiple studies in which a single-cone method of obturation was successfully used. A recent study has shown a high clinical success rate in cases treated with a single-cone technique with an epoxy resin-based sealer (15). In a success/failure study using Ketac-Endo, a glass-ionomer– based sealer, Friedman et al. (16) found no difference in success between cases that were obturated with single cones verses lateral compaction. A bacterial leakage test was performed comparing Super EBA and Ketac-Endo using single-cone method of obturation and found no leakage after 60 days (17). AH Plus has been evaluated for its sealing abilities using apical dye-leakage methods. In one study (18), AH Plus was compared to another epoxy resin-based sealer, AH 26. It was found that AH Plus leaked more than AH 26. The authors speculated that AH Plus did not adapt well to dentin walls because of the hydrophobic properties of epoxy resins (18). In this study, AH Plus provided a superior seal to the newly marketed hydrophilic-urethane-methacrylate– based sealer. Ahlberg and Tay (19) studied a methacrylatebased sealer and found favorable results using a dye-leakage test. The sealer also was found to bind to both root dentin and guttapercha when viewed under SEM. It is difficult to draw conclusions from that study because no other sealer was included for comparison. In this study, one of the positive control groups leaked too fast to be measured, whereas the other leaked at a slower, measurable rate. It has been determined that leakage in roots filled with only

gutta-percha decreases with time (20). It is presumed that guttapercha expands in the presence of humidity and closes microgaps (20). Expansion of gutta-percha may have occurred in this experiment because of the moisture present during the setting and testing periods. This may have enhanced the sealing ability of all groups tested. Endodontic-filling materials should be impervious, biocompatible, and dimensionally stable (19). The quality of the apical seals was not consistent in group-A specimens. After the 7-day incubation period, EndoRez sealer had not consistently set up, and in some instances was bubbling out of the specimens. In contrast, both of the AH Plus groups were completely set after the incubation period. This finding is a possible reason for the relatively poor sealing ability in this experiment. The manufacturer’s directions describe an initial set at 15 min and a final set at 2 h. The initial set was observed during obturation because the applicator syringe became jammed by an increase in viscosity. The final set was not consistently observed, even several weeks after application. A possible explanation for this observation is that oxygen in the air may have inhibited the propagation of free radicals leading to poor conversion of monomers to polymers. None of the specimens had a coronal seal and were thus exposed to oxygen and moisture after obturation and during testing. The SEM images of the sealer/dentin interface revealed a possible reason for the greater amount of leakage in group A. The sponge-like appearance of the set EndoRez sealer (Fig. 2) may be indicative of the sealer’s porosity, which allowed water to leak

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through the root canal. In contrast, the SEM imaging of specimens from group B (Fig. 3) showed AH plus sealer to appear consistent and dense when set. This may be why it was so effective at sealing the root segments in this experiment.

CONCLUSION The results of this experiment indicated that EndoRez, when used as a sealer with a single, gutta-percha cone, is not as effective at sealing the apex as AH Plus when used with a single cone or warm vertical compaction. Warm vertical compaction and the single-cone method with AH Plus showed no statistical difference in ability to seal the canal. EndoRez did not seem to consistently set up in our experimental model. More research is needed to determine if this new product is an effective sealer. The authors thank Dr. David Pashley and Dr. Alex McLean for their technical advice and help with setting up the fluid-filtration–testing model. Dr. Kardon is a former postgraduate resident, Department of Endodontics, Dr. Kuttler is a professor and chairperson of endodontics, Dr. Dorn is professor and director of postgraduate endodontics, Nova Southeastern University School of Dental Medicine, and Dr. Hardigan is associate dean and professor, Nova Southeastern University College of Allied Health, Ft. Lauderdale, FL. Address requests for reprints to Brian Kardon, DMD, 201 E. 87th Street #21N, New York, NY 10128.

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