| Abstract|| |
Aim: To investigate and compare the fracture resistance of resilon and realseal filled root canals with those that were obturated with thermoplasticized gutta-percha and AH-plus endodontic sealer.
Materials and Methods: Eighty extracted human mandibular single-rooted premolars stored in 10% formalin were used in this study. They were prepared by using a crown-down technique, debrided and irrigated with NaOCl, EDTA, and normal saline and divided into four groups. Group I = Negative control, canals prepared but no obturation was done; Group II = Positive control obturated with dual cure composite resin; Group III = Obturated with thermoplasticized GP and AH-plus; Group IV = Obturated with resilon and realseal. All root specimens were stored for two weeks in 100% humidity to allow for complete setting of the sealer. Each specimen was mounted in acrylic in a polyvinyl ring and tested for fracture resistance with a universal testing machine. The loading fixture of the machine was mounted with its spherical tip aligned with the center of the access opening of each root. A vertical loading force was applied until it fractured the root. The force values were subjected to statistical analysis: Kruskall-Wallis H-test and Mann-Whitney U-test.
Results: Group comparison revealed that Group II (positive control) had significantly higher values of resistance to fracture as compared to all the other groups. While Group IV (resilon with realseal) had significantly higher values of resistance to fracture as compared to Group I (negative control).
Conclusion: On the basis of our findings, it can be concluded that filling the root canals with resilon and realseal increased the in vitro resistance to fracture of single-canal extracted teeth. resilon and realseal demonstrated high fracture-resistance values and could be an alternative to the conventional gutta-percha.
Keywords: Resilon, realseal, thermoplasticized gutta-percha, AH-plus, fracture resistance
|How to cite this article:|
Kumar P, Kaur NM, Arora S, Dixit S. Evaluation of fracture resistance of roots obturated with resilon and thermoplasticized gutta-percha: An in vitro study
. J Conserv Dent 2014;17:354-8
|How to cite this URL:|
Kumar P, Kaur NM, Arora S, Dixit S. Evaluation of fracture resistance of roots obturated with resilon and thermoplasticized gutta-percha: An in vitro study
. J Conserv Dent [serial online] 2014 [cited 2019 Sep 15];17:354-8. Available from: http://www.jcd.org.in/text.asp?2014/17/4/354/136510
| Introduction|| |
American association of endodontists defined and characterized root canal obturation as a "three-dimensional filling of the entire root canal system as close to the cemento-dentinal junction as possible". So far as gutta-percha is the most popular and commonly used root canal filling material. It has been taken as the gold standard for root canal filling materials. Despite its many advantages gutta-percha still has its limitations like, its inability to strengthen the root as it does not bond to the dentine. 2 The concept of obturating root canals using injection-molded thermoplasticized dental gutta-percha was introduced by Yee et al. They found injected thermoplasticized gutta-percha could produce an effective apical seal, especially when used with sealer (Suheel Manzoor et al., 2010). If a dental material could be developed that ought to bond to the dentinal walls of the root canal, theoretically the material will not only provide a good seal but also reinforce the endodontically treated tooth (Williams et al., 2006). In 2004, a new obturating system resilon was introduced containing polycaprolactone core material with difunctional methacrylate resin along with resin-based sealer. The rationale behind the product was to create a monoblock consisting of a resin sealer with resin tags that enter into dentinal tubules and bond to dentine on canal walls as well as adhesively to the core material. Such a monoblock effect reduces ingress pathways and reinforces the strength of root canal system and the tooth per se. Vertical root fractures are one of the most common and serious complications of the root canal treated teeth. In 1999, Fuss et al., showed that vertical root fracture following endodontic treatment represented 10.9% of treated teeth (Williams et al., 2006). It has been reported that when the canals are filled with resilon in combination with epiphany oral bonding agent, it forms a monoblock within the canals that bonds to the dentinal walls. Because the resin core, sealant and dentinal wall all are "attached," it appears logical that they have the potential to strengthen the root against fracture (Teixeira et al., 2004).
| Materials and methods|| |
80 extracted mandibular single rooted first and second premolars collected from the department of Oral and Maxillofacial Surgery, Seema Dental College and Hospital, Rishikesh were used in this study.
Tooth were decoronated with the help of a diamond disk mounted on a DFS mandrel in a straight hand piece at 30,000 rpm. Each root had a minimum length of 14 mm and a maximum buccolingual diameter of (5 ± 1) mm (measured with a vernier caliper). Patency of the canals was checked and the glidepath established.
Estimation of the provisional working length was made by placing size 15 K-file (Dentsply Mallefer) into the root canal until it was observed at the apex. The final working length was ascertained after subtracting 1mm from this length.
The canals were instrumented with ProTaper (Dentsply Tulsa Dental, Maillefer, OK) rotary instruments by using a 16:1 reduction handpiece (X-SMART; Dentsply Maillefer) at a speed of 250 rpm.
Shaping file S 1 was carried into the canal short of working length, followed by file Sx that was used with a brush stroke. File S 1 was then used up till the working length, followed by S 2. Next, finishing file F 1 was taken to working length and withdrawn. The size of the apical foramen was then gauged by using an ISO #20 hand K-File, after which finishing file F 2 was used. The size of the apical foramen was then gauged with an ISO #25 hand K-file, after which file F 3 was used to working length. Only those teeth that required finishing with file F 3 constituted the final sample of teeth.
Throughout the entire sequence of operations, irrigation was performed with an endodontic irrigating needle and syringe by using 3% sodium hypochlorite. Recapitulation was performed with an ISO #15 K-file, subsequent to the use of each ProTaper file. After completion of instrumentation, all specimens received a flush of sodium hypochlorite (Pyrex, 3%) followed by 17% ethylene diamine tetraacetic acid (EDTA) [PrevestDenPro] for 1 minute. All specimens were finally irrigated with normal saline. The canals were dried with paper points.
Distribution of groups
The selected teeth specimens (N = 80) were then randomly assigned into 4 experimental group (N = 20 for each group) by using a simple random sampling method.
Group I: This group comprised of 20 prepared teeth and was left unfilled. (Negative Control)
Group II:This group comprised of 20 teeth and were obturated with flowable, dual cure composite resin (Para Core Dual Cure, ColteneWhaledent. Switzerland) (Positive Control)
Group III: This group comprised of 20 teeth and were obturated with thermoplasticised gutta-percha (Calamus, Dentsply Maillefer, Switzerland) and AH-plus sealer (Dentsply Maillefer, Switzerland) (Experimental Group)
Group IV: This group comprised of 20 teeth and were obturated with resilon and realseal sealer (Sybron Endo) (Experimental Group)
All procedures for the 4 groups were performed according to manufacturer's instructions. The root canal openings of all specimens were sealed with a non-eugenol temporary filling material, cavit G (ESPE, 3M, St. Paul, MN).
Subsequent to obturation, all root specimens were stored for 2 weeks in an incubator (Obromax) at 37 0 C in 100% humidity to allow the sealer to set completely. Each apical root end was then embedded in a polyvinyl ring, leaving 9mm of the root exposed and 5mm embedded. Acrylic resin was poured into polyvinyl ring, on a stable and smooth base. Each root was mounted when the acrylic resin was in dough stage.
Evaluation of fracture resistance
Each polyvinyl ring containing a root specimen was mounted for evaluation of fracture resistance. A loading fixture was mounted with its spherical tip (r = 2mm) aligned with the center of the access opening of each specimen. A vertical loading force was applied at a crosshead speed of 1.25 mm per minute (for all samples) until it fractured the roots. Fracture was defined as the point at which a sharp and instantaneous drop greater than 25% of the applied load was observed. The test was terminated at this point, and the recorded force was measured on the dial gauge of the Universal strength-testing machine (Enkay, computerized universal testing machine) and was obtained as a micrograph. The mean load to fracture for all groups is given in [Table 1]. The statistics analysis is given in [Table 2].
|Table 1: Mean and standard deviation of yield load of|
all the four groups
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|Table 2: Between group comparison of yield load for different group combinations (Mann-Whitney U-test)|
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| Results|| |
All the samples were subjected to fracture resistance measurement using Universal Testing Machine. The following physical property was noted:
Yield load (KN) = Force required for fracture of a specimen
| Discussion|| |
Root filled teeth are reported to be more prone to biomechanical failure. Most clinical failures can be ascribed to physiologic masticatory or Para functional forces when repeated over long periods of time, also known as fatigue stress. Stress is produced within a structure as a result of internal resistance generated to counter the applied force. The nature of the distribution of stress within the structural load changes because of the direction of the load applied and the shape of the structure. Concentrations of stresses from a biomechanical perspective indicate regions of potential failure. Therefore, biomechanical studies are necessary to highlight the behavior of a treated tooth to functional forces (Belli et al., 2011).
The aim of the present study was to investigate and compare the fracture resistance of resilon and realseal filled root canals with those that were obturated with thermoplasticised gutta-percha and AH-plus endodontic sealer. Endodontically treated teeth are widely considered to be more susceptible to fracture than the vital teeth. The reasons most often reported have been the dehydration of dentin after endodontic therapy, excessive pressure during obturation and removal of tooth structure during endodontic treatment (Teixeira et al., 2004). 
Amongst clinicians, the loss of dentin is commonly believed to create an increased susceptibility to fracture of endodontically treated teeth (Calt and Serper 2002). Study by Ekkasak et al., showed that a non-prepared root has a greater resistance to fracture than any current mode of restoration following endodontic treatment. Root canal instrumentation is an unavoidable step in endodontic treatment. However, it is understood that as dentine is removed during the instrumentation phase, a weakening effect on root is inevitable. Any material that can compensate for this weakening effect would be useful (Teixeira et al., 2004).
Calt and Serper in 2002 compared the smear layer removal capability and the structural effects of EDTA on root dentin with respect to duration of application. Their results showed that EDTA followed by NaOCl completely removed the smear layer in 1 minute. When EDTA was applied for 10 min, excessive erosive effects were observed with dissolution of peritubular and intertubular dentin. According to their findings, to inhibit the erosion on dentin, EDTA solution must not be applied for longer than 1 minute. Therefore in the present study EDTA was used for 1 minute to irrigate all the samples as a final rinse.
Gutta-percha has been considered as the "gold standard" filling material and for many years has been used as core material with zinc oxide eugenol based or Ca(OH) 2 based sealers (Patil et al., 2013). But, limitations of gutta-percha i.e. inability to reinforce endodontically treated roots and coronal micro leakage have lead to the development of alternatives. Because of absence of complete seal, it produces a poor barrier to bacterial micro-leakage and is considered to be one of the weakest points in root canal therapy (SV Ravi et al., 2014).
Few studies have evaluated the potential of using dentin bonding agents and resins as obturating material in non-surgical root canal treatment. Reasons for not using resin for root canal obturation have centered around questionable results, difficult and unpredictable methods of delivery into the root system and the inability to re-treat the canal if necessary (Baba et al., 2010). However, Mubashir et al., (2012) found that xylene, refined orange oil and tetrachloroethylene can be used for softening resilon during retreatment with various techniques. Xylene being the best solvent.
Resilon is a thermoplastic synthetic polymer. Resilon is based on polymers of polyester and contains bioactive and highly radiopaque fillers. The polymer has an improved flexural strength and when used in conjunction with a resin-based sealer offers improved bonding potential, as compared to gutta-percha.
Primary components of resilon are:
- Resilon core material containing bioactive glass, bismuth oxychloride and barium sulfate;
- Real seal, the resin sealer is a dual cure, resin based composite sealer. The resin matrix is composed of bisphenol-A-glycidyldimethacrylate (BisGMA), ethoxylated BisGMA, urethanedimethacrylate (UDMA), and hydrophilic difunctional dimethacrylates. It contains fillers of calcium hydroxide, barium sulfate, barium glass, and silica. The total filler content is approximately 70% by weight;
- Self-etch primer that contains sulfonic acid-terminated functional monomer, 2-hydroxyyethyl methacrylate (HEMA), water and a polymerization initiator.
HEMA enhances the bonding of resin to dentin (Baba et al., 2010). The penetration into dentinal tubule of the self-etching primer and composite sealer may prevent shrinkage of the resin filling away from the dentine wall and aid in sealing roots. These materials have been shown to be biocompatible, non-toxic and non-mutagenic and have been approved for endodontic use by the Food and Drug Administration of the United States (SV Ravi et al., 2014). Resilon/Epiphany showed better results of sealing ability than gutta-percha/AH-plus, when post space preparation was delayed (Dhanded et al., 2013).
There has been much controversy regarding the relative bonding power of the resilon system compared with AH26 and gutta-percha. Ozgur et al., 2007, in their study found a lower resistance with the Resilon system compared with the AH26 and gutta-percha group. Teixeira et al., reported that dual-curing resin-based root canal sealers increased the fracture strength more than AH26.
In the current study between group comparisons of yield load revealed that Group II (i. e. obturated with flowable, dual cure composite resin) had significantly higher values as compared to all the other groups. Group IV (i. e. obturated with resilon and realseal sealer) had significantly higher values as compared to Group I. There was not much difference in values of Group I and Group III.
Thus, it may be inferred that Resilon increased the fracture resistance of roots as compared to Thermoplasticized gutta-percha. This is in agreement with the results of study done by Jeanne Monteiro et al., 2011, Teixeira et al., 2004 and Baba et al., 2010 where filling the canals with Resilon increased the resistance to fracture of endodontically treated teeth when compared with gutta-percha root canal fillings.
The better performance of resilon in context with fracture resistance is attributed to its thermoplastic nature, which is because of incorporation of polycaprolactone, a bio-degradable aliphatic polyester that has a low glass transition temperature of 62 0 C. It is bondable to methacrylate based resin as it contains dimethacrylate resins. This radio-opaque root-filling material couples with resin based sealers like realseal or epiphany. The adjunctive use of self etch adhesives and methacrylate based resin sealer with resilon purportedly creates a monoblock between the intraradicular dentin and the root-filling material that is more resistant to both bacterial leakage and root fracture when compared with similar teeth that were root-filled with gutta-percha and conventional sealers (Teixeira et al., 2004).
The materials that constitute a monoblock should have the ability to bond strongly and mutually to one another, as well as to the substrate that the monoblock is intended to reinforce. Resilon is the only bondable root filling material that may be used for either lateral or warm vertical compaction technique. As resilon is applied using a methacrylate-based sealer to self etching primer-treated root dentine, it contains two interfaces, one between the sealer and primed dentin and the other between the sealer and Resilon, hence may be classified as a type of secondary monoblock (Tay et al., 2007).
Gutta-percha does not chemically bond to the dentinal wall, so they do not form the monoblock system (Hammad et al., 2007). According to Teixeira et al., gutta-percha does not form a monoblock even with the use of a resin-based sealer such as AH-plus, because the sealer does not bind to gutta-percha. The modulus of elasticity of gutta-percha points (ca.80 MPa) is 175-230 times lower than that of dentin (ca. 14,000-18,000 MPa), making them too plastic to reinforce root after endodontic therapy. (Franklin et al., 2007)
| Conclusion|| |
On the basis of the findings of present study, it can be concluded that filling the root canals with resilon and realseal increased the in vitro resistance to fracture of single-canal extracted teeth. Resilon along with realseal demonstrated high-fracture-resistance values, and could be an alternative to the conventional gutta-percha.
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Navsangeet Mangat Kaur
Mangat Nursing Home, Chandigarh Road, Katani Kalan, Ludhiana - 141 113, Punjab
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]