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Influence of different endodontic filling materials on root fracture susceptibility Fernando C. Ribeiroa, Aline Evangelista Souza-Gabriela, Melissa A. Marchesana, Edson Alfredoa, Yara T. Correa Silva-Sousaa and Manoel D. Sousa-Netob, , aSchool of Dentistry, University of Ribeiro Preto, Ribeiro Preto, SP, Brazil bRibeiro Preto School of Dentistry, University of So Paulo, Ribeiro Preto, SP, Brazil Received 16 August 2007; revised 16 October 2007; accepted 17 October 2007. Available online 28 November 2007. Abstract Objective To evaluate the influence of different endodontic materials on root fracture susceptibility. Methods Seventy-two mandibular incisors were sectioned 1 mm below the cementoenamel junction to obtain roots of 12 mm length. Roots were submitted to chemomechanical preparation with the rotary instruments of Profile system. The obturation of root canals were performed with the following filling materials (n = 12): GI, unfilled teeth (control); GII, Endofill + gutta-percha; GIII, Sealer 26 + gutta-percha; GIV, AH Plus + gutta-percha; GV, Epiphany + gutta-percha; GVI, Epiphany + Resilon. After the sealers setting time, each root was embedded in acrylic resin. The specimens were then submitted to fracture resistance test using an Instron testing machine at 1 mm/min. ntsResults The ANOVA test showed no significant statistical difference (p .05) among GI (162.16 41.4N), GII (168.46 37.5N), GIII (164.83 35.7N), GIV (168.29 38.7N), GV (172.36 20.6N) and GVI (193.11 42.8N). Conclusion The core materials (gutta-percha or Resilon) combined with the tested endodontic sealers are not able to increase the root fracture resistance in canals submitted to chemomechanical preparation. Keywords: Endodontic treatment; Root fracture; Sealers Article Outline 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusion References 1. Introduction Teeth with root canal treatment seems be more susceptible to vertical fracture than those with intact pulps.1, 2, 3 and 4 This type of fracture ntshas an unfavorable prognosis and often leads to tooth extraction.5 and 6 Root fractures can be derived from dental tissue removal during canal instrumentation7 and 8, preparation of intraradicular post space2, intracanal medication for more than 30 days9 and excessive pressure during root obturation.3 and 6 However, conclusive epidemiological evidence of weakening in the root-filled teeth is still lacking.10 Considering that the endodontic treatment is necessary and that these procedures are important for therapy success, it would be advantageous if the radicular canal obturation, in addition to providing an adequate seal, could decrease the root fracture susceptibility through an adhesive filling material.4 and 11 Since the development of endodontic sealers with bond capacity (glass ionomer- and resin-based sealers), attempts have been made to reinforce weakened tooth structure with adhesive materials and the results were divergent. While Trope and Ray1 observed higher fracture resistance in tooth filled with glass ionomer-based sealers, Apicella et al.4 did not find a difference between this sealer and the nonfilled teeth. Cobankara et al.12 showed similar results between glass ionomer- and epoxy resin-based sealers, however, Lertchirakarn et al.13 concluded that glass ionomer sealers were more effective in root reinforcement than the epoxy resin-based sealers. Improvements in adhesive technology direct the attention to the filling material characteristics, aiming to decrease marginal, apical and coronary infiltration14 and reduce susceptibility to fracture after root canal treatment.15 Recently, a new dual-curing resin-based sealer commercially named as Epiphany (Pentron Clinical Technologies, Wallingford, USA) or Real Seal nts(SybronEndo, Orange, USA) has been introduced to replace gutta-percha and conventional sealers. The sealer matrix consists of bisphenol-A-glycidyldimethacrylate (BisGMA), ethoxylated BisGMA, urethane dilethacrylate and hydrophilic methacrilate with calcium hydroxide, barium sulfate, barium glass, bismuth oxychloride and silica.8, 16 and 17 This system uses a self-etching primer and also comprises Resilon (Resilon Research LLC, Madison, CT, USA), which is a thermoplastic synthetic material that contains bioactive glass, bismuth oxychloride and barium sulfate.8, 17 and 18 Some authors reported that the Epiphany/Resilon system creates a monoblock that tightly adheres to dentine.8, 15, 16 and 18 In vitro17 and in vivo19 studies have demonstrated that monoblock has good resistance to bacterial infiltration. Schfer et al.8 verified an increase in fracture resistance of teeth with root canals filled with Real Seal sealer. The purpose of this in vitro study was to assess the influence of different endodontic filing materials (Endofill, Sealer 26, AH Plus and Epiphany combined with gutta-percha cones, and Epiphany/Resilon system) on root fracture susceptibility. 2. Materials and methods Seventy-two human mandibular incisors10 and 13 were selected from University of Ribeiro Preto Dental Research Laboratory according to these criteria: (a) absence of fractures or fissures, checked with a 20 stereomicroscopy (Stemi 2000C; Carl Zeiss, Germany), (b) presence of a single root canal without calcifications or resorptions, checked with radiographical exam, (c) root thickness at 12 mm from apex between 3.5 3.8 mm in buccal face and 2.9 3.1 mm in lingual face, both at mesiodistal direction; and 6.3 6.5 mm in buccolingual direction, ntschecked with a digital pachymeter (Digimess; Shiko Precision Gaging Ltd., China). The teeth were sectioned transversally 1 mm below the cementoenamel junction, leaving a standard root length of 12 mm. A #10 K file (Dentsply Maillefer, Ballaigues, Switzerland) was introduced into each canal until it appeared at the apical foramen. The working length was determined by subtracting 1 mm from this measurement. The cervical third was prepared with #70.12 instrument from GT system (Dentsply Tulsa Dental, Tulsa, USA) until 5 mm depth. Roots were then submitted to chemomechanical preparation with the rotary instruments of Profile system (Dentsply Tulsa) in the following sequence: #30/.06, 25/.06, 20/.06, 30/.04, 25/.04, 20/.04, 30/.06, 35/.06 and 40/.06. The canal was irrigated with 2 ml of 1% sodium hypochlorite during instrumentation using disposable plastic syringe and NaviTip needles (Ultradent Products Inc., South Jordan, USA). Final irrigation was done with 2 ml of 17% EDTAC solution for 5 min followed by 5 ml of distilled water20. The canals were aspirated with silicon tips (Ultradent) and dried with paper points (Dentsply Herpo, Petropolis, Brazil). The roots were randomly distributed into six groups (n = 12) according to the filling material: GI, without obturation (control); GII, Endofill (Dermo Lab. Ltda, Petropolis, Brazil) and gutta-percha; GIII, Sealer 26 (Dentsply Herpo, Petropolis, Brazil) and gutta-percha; GIV, AH Plus (Dentsply De Trey GmbH, Konstanz, Germany) and gutta-percha; GV, Epiphany (Pentron) and gutta-percha; GVI, Epiphany (Pentron) and Resilon. The ideal proportions and setting time of each endodontic sealer were determined according to previous studies.21 and 22 Root canals of all teeth were obturated using the lateral condensation technique. Heated pluggers ntswere used to remove up to 2 mm of the obturation and vertical compaction was accomplished. Epiphany primer (Pentron) was inserted into the root canals of GV and GVI before filling. The excess primer was removed with paper points (Dentsply Herpo), Epiphany sealer was placed with a lentulo spiral (Dentsply Maillefer) and light-cured for 40 s (Ultralux; Dabi Atlante, Ribeiro Preto, Brazil). Root canal entrances were swabbed with alcohol and sealed with a non-eugenol temporary material (Coltosol; Vigodent, Rio de Janeiro, Brazil). Each root was checked with radiographical exam to ensure the quality of the obturation. Roots were stored in distilled water at 37 C and 95% humidity until the sealers setting time. All sealers were totally set. A 2 mm wear was done in the lingual portion of the root using a #57 HP diamond cylindrical bur (KG Sorensen, Barueri, Brazil) to prevent traversal root fracture at the acrylic resin.7 and 12 Roots were centralized in a parallelepiped-shaped base (16.5 mm width and 31.0 mm length) with wax in the apical portion, so they were kept in vertical position. The root part projected out of the matrix presented 6 mm length. After that, the specimens were embedded in autopolymerized acrylic resin (Classic JET, So Paulo, Brazil) and the set remained untouched for 1 h to ensure the resin setting. A stainless steel base (3 cm width 3 cm height 8.5 cm length) at an angle of 45 to the horizontal plan was specially developed for fitting the metal cylinders. The specimens were positioned in an Instron 4444 Universal Testing Machine (Instron Corporation, Canton, USA). The force was applied in the junction of the buccal wall and root canal ntsspace12 using a stainless steel tip at a crosshead speed of 1 mm/min until fracture.8 and 15 The “fracture moment” was determined when a sudden drop in force occurred that was observed in the testing machine display. The maximum force required to fracture each specimen was recorded in Newton (N) and the results were compared. After the fracture test, the fragments were analyzed at a 25 stereoscopic magnifying glass (Carl Zeiss) to assess the failure mode, which was considered adhesive (when occurred in the dentine/sealer interface or core material/sealer interface), cohesive (when the rupture happened in the filling material), and mixed (when combined both modes). Once the obtained data were normally and homogeneously distributed, the results were subjected to statistical analysis using one-way analysis of variance (ANOVA). The level of significance was 0.05. 3. Results The mean values and their respective standard deviations of the strength necessary to fracture the roots in different experimental groups are presented in Table 1. The mean forces ranged from 162.16 N (unfilled specimens control) to 193.11 N (filled with Epiphany/Resilon system). Table 1. Original data of statistical analysis Groups Mean values Standard deviations Median values Minimum values Maximum values Confidence intervals at 95% I. Unfilled 162.17 41.4 159.3 89.3 226.1 135. 188.ntsGroups Mean values Standard deviations Median values Minimum values Maximum values Confidence intervals at 95% a 9 5 II. Endofill + gutta-percha 168.46a 37.5 154.9 112.3 236.6 144.6 192.3 III. Sealer 26 + gutta-percha 164.83a 35.7 165.5 116.0 233.4 142.1 187.5 IV. AH Plus + gutta-percha 168.29a 38.7 170.9 105.8 223.8 143.7 192.9 V. Epiphany + gutta-percha 172.36a 20.6 177.5 144.9 198.7 159.3 185.4 VI. Epiphany + Resilon 193.11a 42.8 184.9 145.9 294.7 165.9 220.3 Same letter indicate statistical similarity (p .05) in the root fracture resistance of any filling material. The confidence interval analysis showed that the unfilled group had considerable variation between the minimum and maximum values. Conversely, when the roots were filled, a lower variation degree was observed (Table 1). After the fracture analysis, it was possible to observe a prevalence of adhesive failures in either the core materials (gutta-percha and Resilon) or dentine. It was also verified that the Sealer 26 and AH Plus presented a higher amount of adhesive fractures to the gutta-percha, respectively 55 and 54.5%. In the Epiphany/Resilon group, there was a predominance of ntsmixed failures (43.5%). The percentage of all fracture types recorded in each group is described in Table 2. Table 2. Fracture types in each group (%) Fracture type Gutta-percha Resilon Endofill Sealer 26 AH Plus Epiphany Epiphany Adhesive to the core material 43.0 55.0 54.5 26.0 21.4 Adhesive to the dentine 38.5 16.6 14.0 35.5 35.1 Mixed 18.5 28.4 32.5 38.5 43.5 4. Discussion The success of endodontic therapy is related to the appropriate execution of the different treatment phases. During chemomechanical preparation, the removal of dentine tissue is necessary to promote cleaning and disinfection, as well as to prepare root canal system to receive the filling material.1 and 7 This unavoidable loss of dentine may weaken the root and create an increased susceptibility to fracture.6, 7, 8 and 13 Resin-based materials have been proposed to reinforce teeth with root canal treatment through the use of adhesive sealers.8, 15, 17, 18, 19, 23 and 24 However, it is still controversial whether or not these sealers increase the strength of root dentine. The adhesion between dental structures and resin-based sealers is the result of a physicochemical interaction across the interface, allowing the union between filling material and root canal wall.21 and 24 This process is important in static and dynamic situations. In static circumstances, ntsthe adhesion eliminates spaces that allow the infiltration of fluids into the sealer/dentine interface. In dynamic situations, the adhesion is necessary to avoid the sealer dislodgment during operative procedures.25 Therefore, the endodontic filling materials may enhance the ability of root-filled teeth to resist fracture.26 Bonding laboratory tests can be used as a screening mechanism for predicting clinical performance.9 and 25 Strength testing is the methodology that has been used to study the influence of filling materials on the fracture resistance of teeth submitted to root canal treatment1, 4, 11, 12, 13, 15 and 27, as performed in this experiment. The results of this study demonstrated no significant differences among groups, thereby the filling materials tested were not able to increase root fracture resistance. This outcome can be confirmed by the failure types that occurred after test, in which were observed the prevalence of adhesive mode, in either core material/sealer interface or dentine/sealer interface. Similar results were obtained by Apicella et al.4, Cobankara et al.12 and Stuart et al.27 However, in all the specimens that received the Epiphany sealer combined with gutta-percha or Resilon, the predominating type of fracture was mixed and the mean values were superior than those recorded in other groups, which may disclose the bond capacity of this sealer to dentine, although no significant statistical difference was observed among groups. The new generation of methacrylate resin-based sealers and self-etching primers increase the expectations of a better coronary and apical marginal sealing that could result in higher root fracture resistance.8,17 However, in this study, the adhesive system did not increase the root fracture resistance, probably due to the following factors: nts1. The polymerization of sealer/dentine interface was possibly affected by oxygen molecules presented into dentine tubules. According to Franco et al.23, the oxygen inhibits vinyl polymerization in composite resins and 40 60% of the carbon bonds remained insatured. Rueggeberg and Margeson28 observed that the oxygen produces a fine acidic polymeric layer with low polymerization degree that probably interferes with the sealer polymerization. Hiraishi et al.29 suggested the application of a dual-cured adhesive system just before bonding to create an oxygen inhibition layer on gutta-percha cones. 2. Limited creeping of the resinous sealer, which results in failure in dentine/sealer interface, since these cements were polymerized just after the insertion into radicular canal.14 The higher creeping would probably cause close contact of the methacrylate-based sealer with the self-etching primer, and consequently strong mechanical interlocking with the dentine. Tay et al.26, using SEM analysis, observed that primer was found in all the radicular canal portions (cervical, middle and apical), which reinforce the statement that failure recorded in sealer/dentine interface was related to the sealer and not to the primer application. 3. Incomplete photopolymerization of sealer in the whole extension of the specimens, which could produce residual monomers in root canal.22 The development of optic fibers for endodontic use and chemical polymerize bonding agents are possible future solutions to this problem.11 4. Low module of elasticity of Resilon and gutta-percha cones when compared to dentine, thus, these elastomeric polymers presented little capacity of reinforcing roots after canal treatment.30 nts5. Very high C-factor of root canals during polymerization of resinous endodontic sealers that may cause gaps along dentine/filling material interface. During photopolymerization, the volume of monomer is significantly reduced, promoting enough shrinkage stresses to debond the material from dentine, thereby reducing retention and increasing microleakage.18 and 31 Although Teixeira et al.15 concluded that Epiphany/Resilon system increased the resistance to fracture of root-filled teeth when compared to the Epiphany/gutta-percha filling, their results indicated that there was no statistical difference between the experimental and unfilled control groups. Theses findings are in agreement with our study. As regards to AH Plus and Sealer 26 cements, the literature has demonstrated that these materials have higher adhesion to dentine walls than glass ionomer- and zinc-eugenol-based sealers.21 and 22 The epoxy resin-based sealers penetrate better in the microirregularities due to their creep capacity and high polymerization time. Those properties facilitate the interlocking between sealer and dentine, which allied to the cohesion among molecules, promote larger adhesion and higher resistance to the sealer dislodgement from dentine surface.22 However, the bonding capa
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