F. Kont Cobankara, N. Adanir, S. Belli & D. H. Pashley
Department of Endodontics, Facultyof Dentistry, Selcuk University, Konya, Turkey.
Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA, USA.

Introduction.
It is well known that microleakage between the rootcanal filling and root-canal walls may adversely affect the results of root-canal treatment (Mannocci et al. 1999). Therefore, complete obturation of the root canal with an inert filling material and creation of an apical seal have been proposed as goals for successful endodontic treatment (Nguyen1984).
Different endodontic filling materials and techniques have been introduced to the dental community in an attempt to improve apical seal. It is, therefore, important to assess the obturation quality of sealing materials (Haikel et al.1999) and leakage studies have been most commonly used. However, a universally accepted method for the evaluation of leakage does not exist (Wu &Wesselink 1993). Examples include: coloured dye penetration (Starkey et al.1993), bacterial penetration (Chailertvanitkul et al.1996), radiolabefilled tracer penetration (Matloff et al.1982), dissolution of hard tissue (Larder et al.1976), clearing of teeth (Robertson et al. 1980), spectrometry of radioisotopes (Czonstkowsky et al. 1985), electrochemical methods (Delivanis & Chapman 1982) and gas chromatography (Kersten et al. 1988). However, many studies either showed no significant difference between the techniques or were contradictory (Miletic et al. 1999).The variety of evaluative methodologies and their assessment parameters are major reasons for such disagreement.
This lack of standardization and consequent noncomparability of studies led Wu & Wesselink (1993) to question the relevance of leakage studies and to recommend the use of a fluid filtration system to enhance reliability. This system, first described by Derkson et al. (1986), was designed to evaluate the sealing properties of temporary filling materials by Pashley et al. (1988) and was modified by Wu et al. (1993) for endodontic leakage studies.
The aim of this in vitro study was to quantitatively evaluate the sealing properties of four commonly used root-canal sealers using a flfluid filtration method.

Materials and methods.
Forty maxillary anterior teeth with straight root canals, extracted for periodontal reasons, were selected. Roots with resorptive defects, caries, cracks, or open apices were excluded. Teeth were carefully cleaned with curettes to remove any calculus or soft tissue debris and were stored in deionized water until ready for use.
The crowns were removed with carborundum disks to leave uniform 15-mm apical sections of root and prepared as follows. The canal length was visually established by placing a size 15 K-type le (Kerr, Romulus, MI, USA) into each root canal until the tip was visible at the apical foramen. The working length was established 1mmshort of the apex. The coronal 6 mm was enlarged by slowly rotating Gates-Glidden drills (Dentsply, Maillefer, Ballaigues, Switzerland) sizes 2 and 3 before instrumentation. The apical portion of all the roots were enlarged to a size 60 K-type le at the working length, and the rest of the canals were flared to a size 70 and 80 K-type le with a circumferential filing action using the step-back technique. After every change of a le size and at the completion instrumentation, the canals were irrigated with 2 mL of 5.25% NaOCl solution. The canals were dried with paper points, and standardized guttapercha master cones (Hygenic, Akron, OH, USA) fitted with tugback at working length. The specimens were randomly divided into four equal groups of10 and filled with the sealers showed in Table 1as follows:

• Group 1: The canals were obturated with Sultan, in conjunction with laterally condensed gutta-percha. Sealer was introduced into the canal using a lentulo spiral instrument (Dentsply, Maillefer). The master gutta-percha cone was then coated with the sealer and placed into the root canal to the working length. A size 30 finger spreader (Dentsply, Maillefer) was then inserted into the canal to a level _1mm short of working length. Lateral condensation with fine accessory gutta-percha cones was performed until the entire canal was obturated. The excess guttapercha was removed with a heated ball burnisher and compacted vertically 1mm using Machtou’s heat-carrier pluggers (Dentsply, Maillefer).
• Group 2: Root canals were obturated with Ketac-Endo in the same manner as in Group 1. In this group, two root sections could be filled from one capsule.
• Group3: Canals were filled as forGroup1withAHPlus sealer.
• Group 4: Canals were obturated as for Group 1 with RoekoSeal sealer.

Table 1. Composition of the tested sealers as given by the manufacturers.

The access cavities were then filled with Cavit-G (ESPE, Seefeld, Germany) and the teeth left in physiological saline solution for 1 week at 378C. Each tooth was then placed in to a device designed to measure microleakage by fluid transport, first described by Derkson et al. (1986) and later adapted for endodontic leakage studies by Wu et al. (1993).

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 with in a 25-mL micropipette (Microcaps, Fisher Scientic, Philedelphia, PA,USA). All pipettes, syringes and the plastic tubes at apical sides of the specimens were filled with distifilled water. The micropipette was connected to the plastic tube at the outlet side of the specimen (Fig.1).Water was sucked back with the microsyringe for _2 mm in the other end of the micropipette. In this way, an air bubble was created in the micropipette and adjusted to a suitable position with the syringe. Finally, O2 from a pressure tank of 3 psi (0.2 atm) was applied at the apical side and water was forced through the voids along the root-canal filling, displacing the air bubble in the capillary tube by transport of the water. The volume of the fluid transport was measured by observing the movement of this air bubble. Measurements of fluid movement were made at 2-min intervals for 8 min, which were then averaged. The quality of the seal of each specimen was measured at 7, 14, and 21 days. The fluid flow rate throughthe18-gaugeneedle in the unsealed root canal was measured by weighting the amount of water that could flow through the needle in 1min (1.850 g min_1 at 239 cm H2O or 113 mL min_1 per cm H2O); this value served both as a positive control and as 100% leakage, to which the sealed values could be expressed (as a percent). Between the readings, the samples were stored in isotonic saline solution with 0.2% sodium azide (to inhibit bacterial growth) at room temperature.

Figure 1. Schematic of the apparatus used to measure fluid flow along the obturated root canals as a hydraulic conductance.

Statistical analysis.
A two-way analysis of variance (anova) was used (rootcanal sealer and time as the two factors) to analyze the data for significant differences. Kruskal-Wallis one way anova and Mann-Whitney U-tests were used to analyze the differences amongst the Lp values of four root-canal sealers, for each time period. For each sealer, the difference amongst the Lp values of four root sealers according to three time periods was analyzed using Friedman one-way anova and Wilcoxon signed rank tests. The confidence level used was 95% (P < 0.05).

Results.
The results of the quantitative evaluation of the sealing properties of the four root-canal sealers are shown in Table 2.
All of the sealers gave better seal after 21 days than 7 days (P < 0.05). Sultan showed significantly more leakage when compared to the other sealers at all time periods (P < 0.05). Although RoekoSeal showed better sealing values after 21 days when compared to Ketac-Endo and AH Plus, there was no statistically significant difference (P > 0.05).

Table 2. Microleakage of four sealers used to obturate the root canals.

Discussion.
Leakage studies still have a place in evaluating factors involved in root-canal sealing. In this study, an endodontic fluid transport model proposed by Wu et al. (1993) was used to evaluate the sealing ability of root fillings incorporating four different root-canal sealers (AH Plus, RoekoSeal, Ketac-Endo and Sultan). This method has been shown to be more sensitive than dye penetration for the detection of full length voids along root canals and to be highly reproducible (Wu et al. 1993, 1994a). This type of system overcomes some of the disadvantages of previous studies. A major advantage of the method is the ability to measure microleakage without destroying the root specimens. Repeated observation of the same specimens over time to reveal changes in sealing ability is, therefore, possible (Wu et al. 1995, Belli et al. 2001). The model uses positive pressure to help rule out problems caused by entrapped air or fluid which may skew outcomes in dye penetration studies (Goldman et al. 1989). The sensitivity of the system can be adjusted by altering the pressure used and altering the diameter of the micropipette (Fogel 1995).
In order to avoid anatomical variations and to obtain standardization for the leakage measurements in this study, the length of the specimens was kept same. Wu et al. (1993) also advised controlling the length of the samples, canal diameter, and canal anatomy used to reduce the variability of these studies. The use of hand instrumentation and laterally condensed gutta-percha technique was a realistic clinical approach.
A wide variety of root-canal sealers are available commercially, and they are divided into groups according to their chemical composition. There is no consensus on which materials seal most effectively. Sealers based on organic resin (AH Plus), zinc oxide-eugenol (Sultan), glass ionomer (Ketac-Endo) and polyvinylsiloxane (RoekoSeal) were included in our study.
Endodontic sealers based on ZnOE have been used clinically for several decades because they have satisfactory physicochemical properties (Benatti et al. 1978). But in the present study the ZnOE-based sealer (Sultan) showed significantly more leakage when compared to the polydimethylsiloxane (RoekoSeal), glass ionomer (Ketac-Endo), and epoxy resin (AH Plus)-based sealers after 21 days (P < 0.05).
The glass ionomer sealers were introduced into rootcanal treatment because of their adhesion to dental hard tissues (Powis et al. 1982, Aboush & Jenkins 1986). Ketac-Endois specially formulated as a root-canal sealer. In an in vitro study, Kochet al. (1994) demonstrated better sealing with Ketac-Endo than with ZnOE sealer (Grossman’s sealer).Wu et al. (1994b) also found better sealing with Ketac-Endo. On the other hand, Smith & Steiman (1994) and Rohde et al. (1996) observed more leakage with Ketac-Endo than with sealers based on ZnOE. Timpawat & Sripanaratanakul (1998) showed that there is no clear difference between using a ZnOE sealer and Ketac-Endo.
Excellent apical sealing has been found with epoxy resin-based sealers (Grossman1976, Limkangwalmongkol et al.1991). Recently, AHPlus, a sealer based on epoxy resin, was introduced to the market. According to the manufacturer, it has excellent sealing properties without the release of formaldehyde. In an in vitro study, De Almeida et al. (2000) observed that leakage with AHPlus was significantly less than that with the ZnOE sealer (Fill Canal) as well as the glass ionomer sealer (Ketac-Endo). Greater measured leakage for sealers based on ZnOE compared with epoxy resin-based sealers was also found by other authors (Limkangwalmongkol et al.1991, Oguntebi & Shen1992). DeGee et al. (1994) also showed the apical seal of resin-based cements to be superior to that of glass ionomer-based cements.
In this study, statistical analysis showed that all the tested materials showed less leakage after 21 days than 7 days (P < 0.05).
De Gee et al. (1994) and Wuet al. (1994b) indicated that AH26 showed diminished leakage by the time. De Gee et al. (1994) explained this as a result of the slow setting properties of the material. They reported that this property may allow sufficient time for the development of adhesion to dentine but the shrinkage stress may fracture the still weak unset sealer cohesively. On the other hand, the improving seal of Ketac-Endo was explained by the ability of glass ionomer cement to ‘self-repair’ (Davidson & Abdalla 1993). This material expansion (Wiener & Schilder1971) or self-repair may compensate for the volumetric change caused by the setting shrinkage or dissolution of the material (Wu et al.1994b).
RoekoSeal is a recently marketed polydimethylsiloxane- based material. Limited data are available with regard to its sealing or other properties. Bartuskova & Perinka (2001) found that there were no significant differences between the apical leakage of RoekoSeal and AH26. In our study, whenthe1-week results were evaluated, it was noted that root fillings with RoekoSealwere leaking more than others, but after 21 days, the situation was reversed. The slow setting properties of this material could be an explanation for diminished leakage. The clinical significance of these findings is not clear and further studies are needed to clarify the sealing ability of this new material and evaluate its clinical performance.

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