An in-vitro comparison of bacterial microleakage of gutta-percha and the Guttacore cross-linked gutta-percha core obturator

Abstract

Root canal therapy requires three important steps accomplished in concert to achieve long-term success: canal shaping, disinfection, and obturation. Traditionally gutta-percha has been used with sealer in a cold lateral condensation technique. Schilder introduced the concept of warm vertical compaction of gutta-percha in 1967 to attempt to obturate more canal irregularities. Johnson presented the use of stainless steel files with thermally plasticized gutta-percha in 1978, and later the metal carrier was changed to plastic and named Thermafil. Thermafil has shortcomings in that it does not always fulfill Grossman’s obturation material properties, such as apical extent of the material (extrusion) and ease of retreatment. A new obturation material by Dentsply Tulsa, the GuttaCore cross-linked gutta-percha core obturator, has been introduced that replaces the plastic core with a cross-linked gutta-percha core. The manufacturer states removal of the obturation material and 89 core is fast and easy. To date, no microleakage studies have been done to test this newer obturation material. Methods used to study microleakage have included the use of dyes, radioisotopes, electrochemicals, fluid filtration, and microorganisms. A microbial leakage model has been constructed using a modified two-chamber apparatus as described by Torabinejad et al. and has been used successfully. Green fluorescent protein (GFP) from the jellyfish Aequorea victoria is useful as a bacterial label because the fluorescent marker can be exhibited in the bacterial host without having to use stains. A plasmid that encodes for a copy of the green fluorescent variant gene was transferred into the E. faecalis. The marker glows green under a standard fluorescence microscope and has been used successfully to evaluate microleakage. The purpose of this investigation was to evaluate the sealing ability of a new obturation material, GuttaCore, to determine if there will be a significant decrease in microleakage of AH Plus with GuttaCore obturator versus AH Plus with gutta-percha. Sixty-two human, single-rooted premolars extracted for periodontal considerations were accessed and instrumented for non-surgical root canal therapy. Hand and rotary instrumentation was accomplished to MAF size 40.04, and irrigation was accomplished with 6.0-percent NaOCl and 17-percent EDTA with use of EndoActivator. Teeth were randomly assigned to two experimental groups of 27 teeth each. Group I (conventional method) teeth were obturated with gutta-percha and AH Plus sealer using warm vertical condensation, and Group II (test method) teeth were obturated with GuttaCore and AH Plus sealer. Two control groups containing four teeth each 90 served as positive and negative controls. The positive and negative control groups ensured that the microleakage model was working correctly. The teeth were evaluated for microbial microleakage of E. faecalis green fluorescent protein (GFP) construct using a dual chamber leakage model. If turbidity is observed in the lower chamber, it will indicate microleakage and an inadequate seal of the obturation method. The teeth were sectioned and viewed with a standard fluorescence microscope to determine the depth of microleakage utilizing the inherent fluorescence of the E. faecalis GFP construct. No microleakage was observed in the negative control groups. Microleakage was observed in both gutta-percha positive control groups and in one of the two GuttaCore positive control groups. One of 27 GuttaCore samples displayed turbidity, which occurred at day 14. None of the 26 gutta-percha samples displayed turbidity at any point. The 95-percent confidence intervals (CI) for the percentage of samples with turbidity were 0.1 percent to 19 percent for GuttaCore and 0.0 percent to 13.2 percent for gutta-percha using a Fisher’s Exact Test. The two groups did not have a significantly different percentage of samples with turbidity (p =1.00). No E. faecalis GFP was visualized under fluorescent microscopy in either the turbid GuttaCore sample or the gutta-percha positive control in the apical, middle or coronal thirds. Both samples that demonstrated microleakage had confirmation that the lower chamber broth contained E. faecalis GFP when cultured on blood agar plates. Within the limitations of this study, there was no significant decrease in microleakage between the GuttaCore obturator and warm vertical condensation with gutta-percha. Turbidity of the broth in samples that leaked was not associated with 91 noticeable bacteria when using fluorescent microscopy, which indicated that leakage may be the result of very few bacteria.