| Abstract|| |
Aim: Comparative assessment of fracture resistance of roots obturated with three hydrophilic systems - novel CPoint system, Resilon/Epiphany system, and EndoSequence BC sealer; and one hydrophobic gold standard gutta-percha/AHPlus system.
Materials and Methods: Ninety freshly extracted, human, single-rooted mandibular premolars were selected. The specimens were decoronated and standardized to a working length of 13 mm. The teeth were randomly divided into six groups (n = 15). In Group A, teeth were left unprepared and unfilled (negative control). Rest of the groups were prepared by using ProTaper system up to a master apical file F3; followed by which Group B was left unobturated (positive control); Group C, novel CPoint System; group D, Resilon/Epiphany system, Group E EndoSequence BC sealer, and Group F gutta-percha and AH Plus. Specimens were stored for 2 weeks at 100% humidity. Each group was then subjected to fracture testing by using a universal testing machine. The force required to fracture each specimen was recorded and the data was analyzed statistically using analysis of variance (ANOVA) test and Tukey's post-hoc test.
Results: The hydrophilic obturation systems have shown to exhibit significantly higher fracture resistance as shown by the values in Groups C, D, and E (P < 0.05) when compared with Group F. Within hydrophilic groups there was significant difference between Group D and Groups C and E (P < 0.05), while Groups C and E had no significant difference (P > 0.05).
Conclusion: In contrast to hydrophobic systems, hydrophilic systems showed higher fracture resistance in a single-rooted premolar.
Keywords: CPoint; hydrophilic systems; smart-seal system
|How to cite this article:|
Hegde V, Arora S. Fracture resistance of roots obturated with novel hydrophilic obturation systems. J Conserv Dent 2015;18:261-4
| Introduction|| |
An endodontically treated tooth is weaker and prone to fracture than vital teeth.  There are several factors that affect the strength of endodontically treated tooth including loss of tooth structure because of caries or trauma, dehydration of dentin, access cavity preparation, instrumentation and irrigation of the root canal, excess pressure during root obturation, and preparation of intraradicular post space. , Reinforcement of the tooth is a desirable characteristic that a clinician expects from a material. Adhesive dental materials might offer an opportunity to reinforce the endodontically treated tooth through the utilization of bonded sealers in the root canal system.  A dental material that can bond to the dentinal walls of the root canal will not only provide a good seal but also reinforce the tooth.  Gutta-percha with an epoxyresin-based sealer AH Plus has set a gold standard as an obturation system. Despite several advantages exhibited by the system, its hydrophobic nature and its inability to sufficiently reinforce the root canal remain its drawbacks. In the wake of this concept, introduction of hydrophilic materials utilized for obturation of root canals have led to an evolution. The mechanism of action involved in setting of hydrophilic materials is their ability to set utilizing the intrinsical moisture present in the dentinal tubules which allows the material to bond to the root canal wall and core, additionally reinforces bond strengths. Resilon is a polymer-predicated thermoplastic resin containing bioactive glass, bismuth oxychloride, barium sulfate, and radiopaque fillers. These advantages have been attributed to the monoblock concept, wherein the Resilon core is bonded to the sealer and the resulting intricate is bonded to root dentin by a resin-predicated primer. ,, Recently, an incipient bioceramic root canal sealer has been introduced; commercially known as EndoSequence BC sealer (Brasseler USA, Savannah, GA). EndoSequence BC sealer is a premixed and injectable endodontic sealer and its nanoparticle size allows it to flow into canal irregularities and dentinal tubules. The most recent advancement in endodontic obturating materials utilizes a hydrophilic polymer in the root canal, the CPoint system (Endotechnologies, LLC). The system consists of premade obturation points (CPoints) containing a polyamide core with an outer bonded hydrophilic polymer coating. The endodontic points are designed to expand laterally without expanding axially by absorbing residual dihydrogen monoxide from the instrumented root canal space and the naturally present moisture in the dentinal tubules.  The inner core of CPoints is composed of two proprietary nylon polymers: Trogamid T and Trogamid CX. The polymer coating is a cross-linked copolymer of acrylonitrile and vinylpyrrolidone, which is polymerized and cross-linked utilizing allyl methacrylate and a thermal initiator. The lateral expansion of CPoints is claimed to occur nonuniformly with the expandability depending on the extent to which the hydrophilic polymer is prestressed (i. e., contact with a canal wall will reduce the rate or extent of polymer expansion). The SmartPaste Bio sealer is composed of zirconium oxide, calcium silicate, calcium phosphate monobasic, and calcium hydroxide with similar setting properties as EndoSequence BC sealer. In the literature, negligible data is available regarding the accentuation on the hydrophilic nature of the sealers on the fracture resistance of a root canal.  Therefore, the purport of this study was to compare the hydrophilic obturating systems along with the gold standard gutta-percha/AH Plus system.
| Materials and Methods|| |
Ninety freshly extracted, human, single-rooted mandibular premolar teeth, recently extracted from patients between the ages 18 and 35 years for orthodontic reasons were selected and stored in 0.1% thymol until the beginning of experiment, but no longer than 30 days after extraction. Age group selected was considered as young permanent teeth of similar mechanical properties as the teeth were examined under an operating microscope to exclude any roots with immature apices, root caries, calcifications, cracks, or fractures. Preoperative radiographs were taken in the mesiodistal and buccolingual directions to confirm the presence of a single canal without previous root canal treatment, resorptions, or calcifications. The crowns of all the teeth were removed by using a slow-speed diamond precision saw with water cooling (Isomet 1000; Buehler, Lake Bluff, IL) to adjust the length of the roots to a standardized length of 13 mm. The buccolingual and mesiodistal diameters of the coronal planes were measured by using a digital caliper (Teknikel, Istanbul, Turkey). All the roots were of similar dimensions measuring 5 ± 1 mm buccolingually and 4 ± 1 mm mesiodistally; except for 15 randomly selected teeth that formed a negative control group (Group A, unprepared and unfilled). The working length was determined by subtracting 1 mm from the length of an inserted #10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) with its tip visualized at the apical foramen. Seventy-five teeth were instrumented up to a master apical file size of F3 with ProTaper rotary instruments (Dentsply Maillefer) by using a 16:1 reduction hand piece with a torque- and speed-controlled electric motor (X Smart; Dentsply Maillefer). The speed and torque values were set as recommended by the manufacturer. The canals were irrigated by using 3 mL 5.25% sodium hypochlorite (NaOCl) solution between each file size. After instrumentation, the smear layer was removed by flushing the root canals with 5 mL 17% ethylenediaminetetraacetic acid (EDTA) solution. The canals were finally rinsed with 10 mL distilled water and dried with ProTaper paper points (Dentsply Maillefer).
Obturation and distribution of specimens
Fifteen teeth were randomly selected to serve as a negative control group (Group A, unprepared and unfilled) and 15 teeth were randomly selected to serve as positive control group (Group B, prepared and unfilled). The 60 remaining teeth were then randomly assigned into four experimental groups (n = 15 for each group). In all the four groups, the canals were obturated with sealer by using the matched taper and single-cone technique.
In Group C, teeth were obturated with F3 taper master polyamide polymer cone using single cone technique with no accessory cones being used. The sealer used in this group was SmartPasteBio (Endotechnologies, LLC), which was inserted in the canal with the help of the intracanal tip provided.
In Group D, obturation was done using the Resilon/Epiphany system. A dry paper point was soaked with Epiphany primer and used to coat the root canal walls. The Resilon core material master point of size 30/.06 was then coated in Epiphany sealer and inserted into the canal. Once the obturation was completed, the coronal surface was light-cured for 40 s.
In Group E, EndoSequence BC sealer was introduced into the root canal via its intracanal tip. The tip was not inserted deeper into the canal than the coronal one-third. An F3 master gutta-percha cone (Dentsply Maillefer) with good tug-back was then coated with sealer and slowly inserted into the canal until the working length was reached.
In Group F, AH plus sealer was applied with the help of lentulospiral using slow-speed handpiece till the canal was coated thoroughly. An F3 master gutta-percha cone (Dentsply Maillefer) with good tug-back was then coated with sealer and slowly inserted into the canal until the working length was reached.
Mesiodistal and buccolingual radiographs were taken to confirm complete filling. After root filling, the coronal 1 mm of the filling materials was removed, and the spaces were filled with a temporary filling material (MD Temp). The teeth were stored at 37°C at 100% humidity for 14 days to allow the sealers to set.
To simulate a periodontal membrane, the apical 5 mm of all roots was covered with wax to obtain a 0.2-0.3-mm-thick layer before embedding the roots into acrylic resin. All the roots were then mounted vertically in copper rings (20 mm high and 20 mm diameter) and filled with self-curing acrylic resin (Imicryl, Konya, Turkey), exposing 8 mm of the coronal parts of the roots. As soon as polymerization of the acrylic resin started, the roots were removed from the resin and the wax was cleaned from the root surfaces by using a curette. The cleaned root surfaces were coated with a thin layer of polyvinylsiloxane impression material (Colten AG, Altstatten, Switzerland) and then they were again embedded into acrylic resin. A universal testing machine (Instron Corp, Canton, MA) was used for the strength test. The acrylic blocks were placed on the lower plate of the machine. The upper plate consisted of a spherical steel tip with a diameter of 3 mm. The tip was centered over the canal orifice and a slowly increasing vertical force was exerted (1 mm/min) until fracture occurred. The fracture moment was determined when a sudden drop in force occurred that was observed on the testing machine display. The maximum force required to fracture each specimen was recorded in Newton.
The data were analyzed statistically by using Statistical Package for Social Sciences (SPSS) version 16.0 and one-way analysis of variance (ANOVA) with Tukey's post-hoc test for multiple comparisons were performed. The level of significance was set at P < 0.05.
| Results|| |
The mean values and their respective standard deviations of the force required to fracture the roots are presented in [Table 1]. The strongest mean force required to fracture the roots was seen in the negative control group; whereas, the weakest force required was seen in the positive control group. There was a significant difference between Groups C, D, and E, which are the hydrophilic groups and the Group F, which is the conventional Gutta-Percha/AH Plus group (P < 0.05). Among the experimental groups, Groups C (CPoint system) and E (EndoSequence BC sealer) had the highest fracture resistance, followed by Group D (Resilon/Epiphany system) and then Group F (Gutta-Percha/AH Plus). The level of force required to fracture the roots between Groups C (CPoint system) and E (EndoSequence BC Sealer) was not found to be statistically significant (P > 0.05).
|Table 1: Descriptive statistics and significance of differences of six groups|
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| Discussion|| |
Shaping and Cleaning of root canals is an essential phase in endodontic treatment. During which, elimination of infected dentin tissue, uncontrollable force during the root canal obturation and prolonged exposure of the dentin to root canal irrigants may increase the root's susceptibility to fracture.  Various endodontic filling materials are advocated to augment the fracture resistance of endodontically treated teeth. , Most root canal filling methods utilize a root canal sealer as a complementary part of the obturation technique. It fills the voids between individual gutta-percha cones applied during obturation of the root canal system.  Secondary monoblocks are those that have two circumferential interfaces, one between the cement and dentin and the other between cement and the core material. In a root canal, the C factor can be more than 1,000. Hence, any polymerizing endodontic sealer would be subjected to sizably voluminous polymerization stresses during the setting process resulting in debonding and gap formation along the periphery of the root filling.  There have been varied outcomes from studies comparing the intraradicular sealing abilities between the two systems (Resilon system versus gutta-percha with AH Plus sealer). Some authors have reported lesser discrepancy between the two; , whereas, others have reported the later to be superior to the Resilon system.  In the present study, roots obturated with resilon were not significantly superior to the conventional gutta-percha system; whereas in comparison to the CPoint system and bioceramic sealer, its fracture resistance was significantly lower. Bioceramic technology has commenced to offer an alternative to the other filling materials in endodontic obturation. Koch and Brave  expressed that bioceramics have enhanced biocompatibility, incremented bond strength after obturation, high pH during the setting process (which is vigorously antibacterial), and have a sealing ability. Bioceramic root canal sealers additionally exhibit chemical bonding to root canal dentin walls.  Skidmore LJ et al.,  reported that chemical bonding enhances the fracture resistance of teeth with root canal filling. In the present study, this chemical bonding may have increased the fracture resistance of obturated teeth with EndoSequence BC sealer. In additament, the deep penetration of the sealer into canal irregularities and dentinal tubules as a result of the sealer's nanoparticles may be another factor associated with incremented fracture resistance.  In this study, 10% formalin was utilized for preserving teeth prior to experimentation. Formalin has been used to preserve human teeth prior to obturation with gutta-percha with AH Plus sealer.  Previous studies have reported no consequential time effect of formalin on dentin bond strength.  Jameson et al.,, found that covalently cross-linked type I collagen in dentin is not significantly affected by formalin storage. It has additionally been documented that teeth stored in formalin do not experience dihydrogen monoxide loss or dehydration for up to 12 weeks of storage. In the present study, the hydrophilic obturations have shown to reinforce the root, and thus increase the fracture resistance. The fracture resistance of Resilon group was lower as compared to the novel CPoint system and the bioceramic system; inspite of the fact it being a hydrophilic system itself. This result can be attributed to the polymerization shrinkage that may be involved along with the high C-factor associated with root canal. The novel CPoint system significantly amended the fracture resistance of the root which can be due to its self-expanding and hydrophilic nature of the composition of the system.
Due to a paramount result shown by the CPoint system, further investigations are required to know about its self-expanding nature and the forces it exerts on the root due to its expansion.
| Conclusion|| |
Hydrophilic obturations have shown to reinforce the strength of the root canal after instrumentation, and thus increasing the fracture resistance of the root to the stresses encountered.
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Dr. Shashank Arora
Department of Conservative and Endodontics, Yerala Medical Trust Dental College, Sector 4, Kharghar, Navi Mumbai - 410 210, Maharashtra
Source of Support: None, Conflict of Interest: None