Introduction - Materials and methods.
F. Kont Cobankara, N. Adanir, S. Belli & D. H. PashleyDepartment 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 Machtouâ€™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).