ENDODONTOLOGY. Evaluation of root canal sealers on the fracture resistance of root canal treated teeth - An in vitro study INTRODUCTION

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1 Original Research Evaluation of root canal sealers on the fracture resistance of root canal treated teeth - An in vitro study K. K. WADHWANI * SARITA GURUNG ** ABSTRACT Objectives : To compare the fracture toughness of the instrumented roots after obturating it with three different sealers and comparing it with the control group (where the roots were first instrumented but not restored). Study Design: Forty freshly extracted human maxillary central incisor teeth were selected. Crowns were removed at cemento-enamel junction and the length of the roots were adjusted to 13 mm. Following canal preparation roots in group I were filled with using Resilon with Epiphany sealer. Ten in group II were filled using guttapercha and AH plus sealer. Similarly group III were filled with gutta-percha and Endomethasone sealer. Ten canals were left unrestored to be used as control group. Tests for fracture toughness were performed under Instron Machine and force at the time of fracture was recorded in Newtons. The results were evaluated with ANOVA and Tukey Honestly significant difference tests. Results : The mean force of fracture values recorded were N, N, N and N respectively. There was a significant difference (p<0.001) between the three experimental groups to that of the control group. But no significant differences were found among the three experimental groups. Conclusions: All the materials used for the study reinforced the prepared root canals. Key words: Fracture resistance, root canal sealers, Resilon, Epiphany, AH Plus Sealer, Endomethasone sealer. INTRODUCTION There is a clinical impression that endodontically treated teeth are more friable and fracture easily thus may have to be removed (Steele and Johnson, 1999). Similarly many studies have suggested that as removal of tooth structure increases fracture resistance decreases. Vertical root fractures are severe complications that are seen in root filled teeth, which often leads to extraction (Fuss et al., 2001). The incidence of vertical root fracture was higher in root filled teeth than teeth without filling (Chan et al., 1999). Cohen et al., 2003 observed that vertical root fracture results largely from operative procedures performed in the root canal after the root canal treatment. Similarly Lert Chirakarn et al., (1999) reported fractures results from excessive lateral compaction forces during the root filling. But the root canal instrumentation is an unavoidable step in endodontic therapy. Therefore any material that can compensate for this weakening effect could be useful. Thus to reinforce the instrumented teeth against fracture sealers are used in conjunction with a core filling material. As gutta-percha with various sealers has been the best combinations available till date but along with the old, experiment with the new should also be done. In the present study gutta-percha and AH plus sealer (epoxy resin based * Professor & Head, ** P. G. Student, Department of Operative Dentistry & Endodontics, Chhatrapati Shahuji Maharaj Medical University, Lucknow. 53

2 K. K. WADHWANI, SARITA GURUNG sealer), gutta-percha with endomethasone sealer (zinc oxide eugenol based sealer) and recently introduced new obturation material Resilon with Epiphany sealer was used (Resilon is synthetic polycarplactone polymer based polyster and epiphany sealer contains methacrylate or HEMA). According to the manufacturer the epiphany sealer bonds both to the Resilon cores and root dentin creating a Mono block that has good adaptation to the canal walls. The aim of the present study was to evaluate the fracture resistance of root canals filled with Resilon and Epiphany, gutta-percha and AH plus, gutta-percha with Endomethasone sealer and instrumented but unrestored control group. MATERIALS AND METHODS Forty freshly extracted human maxillary central incisor teeth that were approximately of similar dimension were selected, cleaned and stored in physiological normal saline until required. The crowns were removed at cemento-enamel junction and all the roots were adjusted to 13 mm. The patency of the apical foramen was determined with a size 15 k file (Dentsply). The working length was established 1 mm short of apical foramen. Root canals were instrumented to a size 40 K file and flared using 2, 4, 6 Gates-Glidden drills. Throughout the instrumentation 1 ml. of 5.25% sodium hypochlorite was used and a final rinse with 1 ml of 17% EDTA was done in order to remove the smear layer. And finally root canals were flushed with 1 ml of saline solution and dried with paper points and divided into four groups of ten teeth each. Group-I Ten root canals were filled with Resilon and Epiphany sealer. The sealer was placed using Lentulo spiral filler. A master Resilon cone was placed into the root canal and with cold lateral compaction technique filled using accessory Resilon points. The excess was seared off with the help of plugger 1 mm below the canal opening and coronally cured for 40 seconds and canal opening was sealed with cavit. Group-II Ten root canals were filled using gutta-percha with AH plus sealer. The master cone was dipped in the sealer and placed in the canal and filled with gutta-percha of smaller sizes. Excess gutta-percha was seared off and condensed 1 mm below the canal opening with a plugger and the opening was sealed with cavit. Group-III Likewise here also ten numbers of root canals were filled using gutta-percha with Endomethasone sealer rest is similar as done in group II. Group-IV Here ten root canals were left unrestored. Only the canal opening was sealed with cavit and was used as control group. Then cylindrical moulds of 20 mm in diameter and 20 mm in length were prepared using elastomeric impression material (Provil P Soft, Heraeus Kulzer, Domagen, Germany) and then self cure acrylic was placed in the mould and apical 6 mm of the root were embedded individually with 7 mm remaining exposed. The acrylic blocks including the specimen was placed on the lower plate of the machine (Universal Testing Machine, Instron), the upper plate of the machine included a round tip that had a diameter of 4 mm. This round tip contacted the coronal surface of the specimen and was subjected to slowly increasing vertical force 54

3 EVALUATION OF ROOT CANAL SEALERS ON THE FRACTURE RESISTANCE OF ROOT CANAL TREATED TEETH - AN IN VITRO STUDY of 1 mm per minute until the fracture occured and the values were recorded in Newtons. RESULTS Table I : Graphical Presentation of fracture resistance of specimens from Group I to IV The mean forces of fracture was N, N, 98.40N for Resilon and Epiphany, Gutta-percha with AH plus, gutta-percha with Endomethasone sealer respectively. For the control group the mean force was N. There was a significant difference between group I and the control group ( p <0.001), group II and the control group ( p <0.001) and group III and the control group ( p <0.001). But no statistical differences were found amongst the three experimental groups. Table II : Descriptive statistics of the Fracture Resistance to the Force of Fracture of Four different Experimental groups Group Sample size Maximum Minimum Mean SDS Resilon with Epiphany Sealer (Group I) N N N N Gutta percha with AH Plus sealer (Group II) N N N N Gutta percha with Endomethasonse sealer (Group III) N N N 200. N Control Group (Group IV) N N N N 55

4 K. K. WADHWANI, SARITA GURUNG DISCUSSION As root canal therapy has become well established as a viable clinical treatment to retain a tooth where by the dental pulp has become necrotic, irreversibly inflamed or infected. But it is generally accepted that several endodontic procedures such as access preparation, instrumentation and even irrigation with sodiumhypochlorite lead to reduction in fracture resistance of instrumented teeth (J.C. Knowles, J. Shelton et al., 2001, Cobankara et al., 2002). As Zandbiglari et al.,(2006) and E. Schafer et al.,(2007) expressed Enlarged but unfilled roots are significantly weaker than filled roots thus more susceptible to fracture. Therefore, there is a general trend of restoring Endodontically prepared teeth to reinforce them against fracture (Ausiello et al., 1997, Pilo et al., 1998). For the current study to create uniformity of the samples and hence to avoid difficulty in obtaining uniform fracture strength, all the controllable factors like length and size were standardized i.e. roots were kept at 13 mm and enlarged upto size 40. Although many differences exists between fracture occurring intraorally and those induced by a testing machine because forces generated intraorally during function vary in magnitude, speed and duration. Therefore in several studies tests of fracture strength was done using the cyclic loading (Heydecke et al., 2001, Eakkinga et al., 2005) i.e. applying the forces from different direction thus to simulate the clinical conditions. But again in many studies it has been reported applying the forces vertically to the long axis of the tooth transmits the force uniformly (Chen et al., 2000, Lindemuth et al., 2002,Dias De Souza et al., 2002). Hence for this study also force applied was vertically like for other studies that evaluated the effect of root canal sealer on the fracture resistance of root filled teeth (Apicella et al., 1999, Cobankara et al., 2002, Lertchirakarn et al., 2002, Teixiera et al., 2004 a,b). For the current study the ability of different sealers to reinforce the root canal treated teeth was evaluated. AH plus sealer is epoxy resin based sealer hence reported to have highest bond strength to dentin and gutta-percha (K.W. Lee et al., 2002, Cobankara et al., 2003). Endomethasone sealer is zinc oxide eugenol based sealer having good flow and recently introduced 56

5 EVALUATION OF ROOT CANAL SEALERS ON THE FRACTURE RESISTANCE OF ROOT CANAL TREATED TEETH - AN IN VITRO STUDY Resilon with Epiphany sealer. Resilon is a synthetic polymer core material and epiphany is dual curable resin composite sealer which provides both mechanical and chemical adhesion (Nakabayashi et al., 1992). Here Resilon with epiphany sealer showed high resistance to fracture compared to control group. This may be due to mono-block created because of Resilon filling closely adapting to epiphany sealer and in turn epiphany sealer adhering to the dentin walls thus holds the root together and reduce microleakage as compared to gutta-percha fillings. This bond between polyester core material to dual cure methacrylate based sealer helps to keep Resilon filled roots to increase its fracture toughness. Supporting this observation is studies of (Teixiera et al., 2004 a,b) reported teeth filled with Resilon and Epiphany were more resistant to fracture. Similarly roots filled with gutta-percha with AH plus sealer also showed greater fracture resistance than control group. This may be due to its adhesive properties, as the epoxy resin based sealer is found to have good adhesion to dentin and gutta-percha and is characterized by low shrinkage and high dimensional stability. This finding was similar to the studies of (F.K. Cobankara et al., 2002 and B. Sagsen et al., 2007). They observed roots obturated with epoxy resin based sealers with lateral compaction technique was significantly stronger than just instrumented roots. The roots obturated with Endomethasone sealer also showed higher resistance to fracture than the just instrumented but unrestored roots of the control group. This maybe due to its flow and was able to penetrate into the dentinal tubules thus creating adhesion resulting in reinforcement of the weakened roots. Hence for the current study all the filling materials increased the fracture toughness of the prepared teeth but there was a significant difference between the restored roots to that of unrestored roots of control group. This result corroborate the previous studies by (J.C. Bakkel et al., 1985, F.K. Cobankara et al., 2002, T. Zandbiglari et al., 2006, and B. Sagsen et al., 2007). But the study of M.J. Apicella et al., 1999, found no statistical difference between the restored and unrestored groups using Ketac Endosealer. But the study of M. Trope et al., 1992 using the same material found restored group significantly stronger than the unrestored group. This may have resulted due to variables in sample selection because for the study of M.J. Apicella they had used randomly selected maxillary and mandibular incisors, molars and canines where as for the study of M. Trope they had tried to standardize the samples by using only the maxillary and mandibular canines of similar dimension of 7 to 8 mm. Similarly in the study of Teixeira et al., 2004 a,b they found no significant differences between the restored and just instrumented but unrestored control group. This may have resulted due to the length of specimen exposed to the force of fracture during mechanical testing. For the current study 7 mm of roots were exposed whereas in the study of Teixiera et al., 2004 a,b 9 mm of roots was exposed to the force. Further the high standard deviation values obtained in the present study may be due to the variations between the structure of root dentin of the tested samples related to age or dentinal sclerosis. CONCLUSIONS For the current study all the tested materials significantly increased the fracture toughness of the instrumented roots after obturation. Therefore the ability of these materials i.e., Resilon and Epiphany 57

6 K. K. WADHWANI, SARITA GURUNG sealer, Gutta-percha and AH plus sealer, guttapercha and Endomethasone sealer to reinforce the Endodontically treated teeth looks very promising but further long-term clinical studies are necessary to collect evidence based data thus to be able to support the confident use of these materials in day to day practice. REFERENCES 1. Zvi Fuss et al., An evaluation of endodontically treated vertical root fractured teeth : Impact of operative procedures. J.O.E. 2001; 27: Chiu-Po Chan et al., Vertical root fracture in endodontically versus non-endodontically treated teeth. A survey of 315 cases in Chinese patients. Oral Sur. Oral Med and Oral Path. 1999; 87: Stephen Cohen et al., Vertical root fractures. J.A.D.A 2003; 134 : Stephen Cohen, Ninth Edition. 5. Veera Lertchirakarn et al., Effects of root canal sealers on vertical root fracture resistance of endodontically treated teeth. J.O.E. 2002; 28 : Veera Lertchirakarn et al., Load and strain during lateral condensation and vertical root fracture. J.O.E. 1999; 25: Tannaz Zandbiglari et al., Influence of instrument taper on the resistance to fracture of endodontically treated roots. Oral Surg, Oral Med, Oral Patho Oral Radio. 2006; 1: E. Schafer et al., Influence of resin based adhesive root canal fillings on the resistance to fracture of endodontically treated roots. An in vitro preliminary study. Oral Surg, Oral Med and Oral Path. 2007; 3 : P.Ausiello et al., Fracture resistance of endodontically treated premolars adhesively restored. American Journal of Dentistry. 1997; : Guido Heydecke et al., Fracture strength and survival rate of endodontically treated maxillary incisors with approximal cavities after restoration with different post and core systems. An in vitro study. Journal of Dentistry. 2001; 29: W.A. Eakkinga et al., Ex-vivo fracture resistance of direct resin composite complete crowns with and without posts on maxillary premolars. I.E.J. 2005; 38 : M.J. Apicella et al., A comparison of root fracture resistance using two root canal sealers. I.E.J. 1999; 32: Fabrico. B. Teixeira et al., Fracture resistance of roots endodontically treated with a new resin filling material. JADA. 2004; 135 : B. Sagsen et al., Resistance to fracture of roots filled with three different techniques. I.E.J. 2007; 40: Martin Trope and Herbert L. Ray Jr. Resistance to fracture of endodontically treated roots. Oral Surg, Oral Med, Oral Patho. 1992; 73 : Martin Trope et al., Resistance to fracture of restored endodontically treated teeth. Endo-Dental Traumatology. 1985; 1: H. Nakabayashi et al., Morphology of root canal wall and arrangement of underlying dentinal tubules. I.E.J. 1993; 26: