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 »  Home  »  Endodontic Articles 5  »  Effect of three root canal sealers on the retentive strength of endodontic posts luted with a resin cement
Effect of three root canal sealers on the retentive strength of endodontic posts luted with a resin cement
Introduction - Materials and methods.



M. S. Hagge, R. D. M. Wong & J. S. Lindemuth
Departments of Restorative Dentistry and Endodontics, University of the Pacific, San Francisco, USA.
Department of General Dentistry Resident Training, Travis Air Force Base, Fairfield, California, USA.


Introduction.
Composite cements have been reported to produce 150–200% the retention strength of zinc phosphate and glass ionomer cements (Albers 1993), and their use in dentistry, including for post cementation, has expanded greatly in recent years (Christensen 1997, 1998, Boone et al. 2001).
Eugenol, like all phenols, has considerable radical scavenging properties (Ganss & Jung 1998), and this is thought to inhibit composite polymerization. However, the literature is divided on whether this interaction is clinically significant. al-Wazzan et al. (1997) reported a significant reduction in the bond strength of two composite core materials to dentine pretreated with a eugenol-containing temporary cement. Tjan & Nemetz (1992) found that the presence of eugenol substantially decreased the retention of endodontic posts cemented with composite. Other authors have also reported adverse interactions between eugenol and composite (Hansen & Asmussen 1987, Paul & Scharer 1997). Farah & Powers (1998) and others recommend avoiding eugenol-containing products prior to bonding procedures. Interestingly, a number of other studies have reported contradictory findings. Ganss & Jung (1998) investigated the strength of composite bonded to dentine pretreated with eugenol-containing and noneugenolcontaining cements, and found no differences. Schwartz et al. (1992) have reported similar results.
Noneugenol replacement products have existed for some time for use in restorative dentistry. However, development of effective noneugenol root canal sealers has not been accomplished as easily. Calcium hydroxide and resin sealers have been developed, but investigations have had highly equivocal findings. Based upon their long history of clinical success, eugenol-containing sealers remain the primary choice of endodontists. However, if eugenolcontaining sealers do result in inferior post retention, alternative sealers might be indicated, at least when canals will receive subsequent bonding procedures.
Post retention studies comparing different cements have been carried out. However, many of these omitted the clinically relevant step of preparing post spaces in previously root-filled canals. Some reports that did use obturated canals to examine cement retention did not compare sealers or use unobturated controls (Standlee & Caputo 1992, Mendoza & Eakle 1994). Paschal et al. (1997) compared the post retention of two cements in obturated (gutta-percha with a eugenol-based sealer) and unobturated canals, and reported significantly lower post retention values in canals that had been obturated, regardless of cement type.
Schwartz et al. (1998) compared the retention strengths of endodontic posts cemented with zinc phosphate and composite cements into root canals previously obturated using eugenol- and resin-based sealers. They found that the eugenol-based sealer did not adversely affect post retention with either cement. Other studies have reported comparable findings (Russo et al. 1999, Burns et al. 2000, Boone et al. 2001, Adamian et al. 2001), whilst Bergeron et al. (2001) found a resin-based sealer resulted in higher post retention values than a eugenol-based sealer.
At present, no study has compared the three major classes of sealers and unobturated controls. Therefore, the purpose of this investigation was to evaluate the effect of three root canal sealers on the retention strength of a prefabricated endodontic post luted with composite cement.

Materials and methods.
An a priori power calculation was performed and it was determined that for highly substantial power (90%) to detect a 35% difference on post failure strength scores at the = 0.05 level, 16 samples were needed in each group.
Sixty-four extracted, single-rooted human teeth were selected from a larger collection that had been stored in tap water. The teeth were decoronated at the cemento– enamel junction using a high-speed carbide bur with water spray, the coronal pulpal tissue was removed, and the root canal spaces were debrided manually using broaches. Teeth deemed to have significantly smaller or larger root canal spaces were discarded to standardize the extent of dentine preparation for the posts as much as possible. All teeth were prepared, obturated, and had posts placed by a single operator (RW). Using 4 surgical telescopes, the canals were negotiated with sizes 10 and 15 K-files (Dentsply/Maillefer, Ballaigues, Switzerland) until the tip of the size 15 file was observed at the apical foramen. Working length was then established 0.5 mm short of this length. The coronal portion of each canal was shaped with sizes 2–5 Gates–Glidden drills (Dentsply/ Maillefer). The canals were then subsequently cleaned and shaped using an electric motor system (Aseptico, Dentsply/Tulsa Dental, Tulsa, OK, USA). A constant ISO size 44 was obtained by placing a 0.12 taper GT file (Dentsply/Tulsa Dental) 2 mm past the working length to maximize consistency of the apical foramen and canal flaring. Three millilitres of 5.25% sodium hypochlorite was introduced into canals after every instrument using a 10-mL syringe with a 27-gauge tip. Additionally, canals were recapitulated with a size 10 K-file to ensure patency of the canal terminus.
The teeth were then randomly divided into four groups of 16 teeth each. One of these groups served as a control and was not obturated. The remaining 48 teeth were obturated using three different root canal sealers: a formulation containing eugenol (Kerr’s Pulp Canal Sealer, Kerr Dental, Orange, CA, USA), calcium hydroxide (Sealapex, Kerr Dental), or epoxy resin (AH-26, Dentsply/ Maillefer). Autofit gutta-percha (Dentsply/Tulsa Dental) was placed into the canals and fitted to the working length with tugback established. Canals were then dried with coarse and fine paper points (Coltene Whaledent, Mahwah, NJ, USA). Sealers were prepared and used according to manufacturers’ instructions. A guttapercha cone, covered with the appropriate sealer, was placed to length twice to ensure that the sealer coated the root canal walls. A System B with a medium–large Buchanan plugger (Sybron/Analytic Technology, Orange, CA, USA) was used as the heat source. Schilder vertical pluggers (Hu-Friedy, Chicago, IL, USA) sizes 12, 10, and 9 were inserted to manipulate the warm guttapercha within 3 mm of the working length. The samples were then stored in 100% humidity for 1 week at room temperature.
Following removal from storage, the coronal 10 mm of each root canal was instrumented with a size 6 Gates– Glidden drill (Dentsply/Maillefer) to remove guttapercha, sealer, and enough of each canal wall to establish a fresh dentine surface and provide an adequate dimension for cement around the passive-design post (size 5 Parapost, Coltene/Whaledent). Size 6 Gates–Glidden drills were deemed necessary for canal enlargement because the preliminary study for this investigation had shown that very low post retention strengths resulted when smaller (size 5 Parapost and size 5 Gates–Glidden) post space drills were used.
The canals were rinsed with water using a Stropko irrigator (Sybron/Analytic Technology) with a 22-gauge Endo EZ Clip needle irrigating tip (Ultradent Products, South Jordan, UT, USA), and air-dried. A fine Ball Point Applicator (Pinnacle Products Inc., Lakeville, MN, USA) was used to carry 70% isopropyl alcohol into the canal for a final cleansing and to aid in desiccation. Canals were again gently dried with air. Thirty-four per cent phosphoric acid gel (Dentsply/Caulk) was then placed into the canals for 15 s using a 1.2-mL syringe with an attached 20-gauge needle (Ultradent Products). The canals were again rinsed and air-dried as described above.

Figure 1. Sample being mounted using surveyor to ensure parallelism of post to path of removal.

Sample being mounted using surveyor to ensure parallelism of post to path of removal

A dentine bonding primer (ED Primer, J Morita Co., Irvine, CA, USA) was dispensed and applied to the canal walls according to the manufacturer’s instructions. A gentle stream of air was directed over the canal orifice for 2 s to aid in evaporation of the solvent. An autopolymerizing resin cement (Panavia 21 OP, J Morita Co., Irvine, CA, USA) was then dispensed from an automixing syringe. Resin cement was placed on the posts by hand, and into the canal spaces using 20-gauge Accudose Needle Tubes (Centrix Dental Incorporated, Shelton, CT, USA). Because of this cement’s extremely rapid set when deprived of oxygen, posts were placed immediately following the application of the cement. The posts were manually inserted as close to the centre of the post space as possible to maintain an even film thickness of cement circumferentially. Cement flash was removed with a hand scaler, and a polyethylene glycol gel (Oxyguard II, J Morita Co.) was placed over the exposed cement to facilitate setting. After setting was complete, the samples were returned to storage as described previously for 48 h.
After removal from storage, roots were gently notched with a size 169 L high-speed carbide bur, and the samples were mounted into 19 mm inside diameter PVC pipe using tray acrylic resin (Fastray, HJ Bosworth, Skokie, IL, USA). Dental surveyors (Degussa-Ney, Yucaipa, CA, USA) were used when mounting the samples (Fig. 1), to enable subsequent post removal in a direction parallel to the long axes of the posts. Immediately after the tray acrylic reached its doughy stage, samples were detached from the surveyors and placed into a cool water bath so that polymerization reaction heat from the setting acrylic diffused away from the samples. When the mounting acrylic had cooled to bath temperature, the samples were dried with compressed air and bench dried for 2 h. The samples were then secured and the posts were extracted using vice clamps mounted in a universal testing machine (Model no. 5566, Instron Co., Canton, MA, USA) operated in tensile mode at 1 mm min –1 (Fig. 2). Data were recorded in kilograms and subsequently examined using analysis of variance ( anova ) and Bonferroni tests. Modes of failure were also recorded.

Figure 2. Post gripped in vise clamps prior to removal.

Post gripped in vise clamps prior to removal