|Year : 2012 | Volume
| Issue : 4 | Page : 305-309
Evaluation of resistance of teeth subjected to fracture after endodontic treatment using different root canal sealers: An in vitro study
SS Bhat, SK Hegde, A Rao, AK Shaji Mohammed
Department of Paedodontics and Preventive Dentistry, Yenepoya Dental College, Mangalore, Karnataka, India
|Date of Web Publication||19-Mar-2013|
S S Bhat
Department of Paedodontics, Yenepoya Dental College, Mangalore - 575 018, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aims: The aim of this study was to compare the ex-vivo effects of different root canal sealers on the fracture resistance of endodontically treated teeth. Materials and Methods: Seventy-five freshly extracted human mandibular premolars were used for the study. The length was standardized to 14 mm and all the teeth were biomechanically prepared and divided into five different groups based on the type of root canal sealers used. Group I:- Roeko seal + gutta percha, Group II: AH plus ® root canal sealer + gutta percha, Group III: PULPDENT root canal sealer + gutta percha, Group IV: Zinc oxide-eugenol sealer + gutta percha, Group V: Control (unobturated teeth). The teeth were embedded in acrylic resin blocks and compressive strengths were measured using universal testing machine (Instron). Statistical Analysis Used: One-way ANOVA, unpaired t- test Results: Data obtained were statistically evaluated using one-way ANOVA and unpaired t-test. All groups showed a statistically significant result (P < 0.05). Teeth obturated with Group I and Group II showed higher resistance to fracture than teeth obturated with other three Groups. It was seen that the teeth obturated with group III showed a better fracture resistance than Group IV and there was no statistical significance found between Group and Group V. Conclusions: From this study, it has been concluded that both the resin based sealers that were used in this study were equally effective compared to that of the zinc oxide-based sealers and the control group. However, no significant results were obtained when the comparison was made between zinc oxide-eugenol and gutta-percha and the control group.
Keywords: AH plus ® , fracture resistance, gutta percha, Instron, Pulpdent sealer, Roeko seal
|How to cite this article:|
Bhat S S, Hegde S K, Rao A, Shaji Mohammed A K. Evaluation of resistance of teeth subjected to fracture after endodontic treatment using different root canal sealers: An in vitro study. J Indian Soc Pedod Prev Dent 2012;30:305-9
|How to cite this URL:|
Bhat S S, Hegde S K, Rao A, Shaji Mohammed A K. Evaluation of resistance of teeth subjected to fracture after endodontic treatment using different root canal sealers: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2012 [cited 2020 Feb 28];30:305-9. Available from: http://www.jisppd.com/text.asp?2012/30/4/305/108926
| Introduction|| |
Root canal treated teeth are considered sensible to fractures than vital teeth, which then have to get extracted to avoid any further complications  and the prevalence being 10.9%.  The main causes may be due to over instrumentation inside the root canal, dehydration of dentine after endodontic therapy and also the uncontrolled pressure at the time of obturation.  All these factors interact one after other with an increase in the occlusal load which cumulatively influence and increase the possibility of a root fracture. Apart from that, a synergetic action by intracanal irrigants and medicaments may also regulate the physical and mechanical properties of the root dentin, leading to failure or fracture of the root canal treated teeth. Many studies have reported a decrease in the micro hardness of dentine specimens treated with NaOCl (Sodium hypochlorite) only, EDTA (Ethylene di-amine tetra acetic acid) only, or both. 
It has been mentioned in few studies that calcium hydroxide Ca (OH) 2 , an effective intra canal medicament which when used for a longer period inside the root canals can lead to an increase chance of root fractures. 
However contradicting reports have been published as whether the strength of roots could be restored after canal preparation and root filling with a core material and sealer. ,
The main aim of obturating a root canal is to strengthen the root canal wall to increase the resistance of the tooth to compressive stresses. Therefore, root canal sealers with additional quality of strengthening the root against fracture can be of obvious value.  The new research methodologies have put forward materials which facilitates more of adhesion to the root canal system.  It is thought that adhesion and mechanical interlocking may strengthen the remaining tooth structure, and thus reduces the risk of fracture.
Recently resin-based obturation material has been introduced which are promising and is proposed to strengthen the tooth by the use of adhesive sealers in the root canal system. Silicone-based sealers also evolved: Lee Endo-Fill ® , was an early attempt in utilizing the water repellent, chemical stability and adhesive properties of silicone materials in endodontics. Roeko-Seal is one of the most recent formulations which showed impressive biological performance, as documented by testing according to international standards including clinical follow-up studies. 
| Aims and Objectives|| |
The aim of this study was to compare the ex-vivo effects of different root canal sealers on the fracture resistance of endodontically treated teeth and the objective of the study was to evaluate the potential of endodontically treated tooth with different root canal sealers to withstand the facture tendency when they are subjected to vertical loads from a universal testing machine (Instron).
| Materials and Methods|| |
Seventy-five intact, non-carious, extracted human mandibular premolar teeth which were scheduled for orthodontic extraction were used for the study. All the selected teeth were debrided and cleansed using an ultra-sonic scaler to remove the periodontal fibres and the calculus flecks followed by examination under a stereo microscope to check for enamel cracks or craze lines. All the teeth were stored under normal temperature in normal saline and decoronated using a wheel diamond bur to a standard length of 14mm. A standard access cavity was prepared for all the teeth and the canal patency was achieved using a standard #no.10 K file. All the root canals were instrumented using a rotary Pro-taper system up to size F3. Irrigation was done in three steps between the successive filings, initially with 5 ml of 5.25% sodium hypoclorite, followed by 5 ml of 17% EDTA. The preparation was completed using 5 ml of normal saline. All canals were dried using paper points and divided into five experimental groups of 15 teeth each according to the obturating materials and the sealers used. Lateral compaction technique was used to obdurate the samples.
Group I: Roeko seal (Coltene-Whaledent, USA) root canal sealer and Gutta Percha (GP)
Group II: AH plus ® root canal sealer (Dentsply-DeTrey, Switzerland) and GP.
Group III: Pulpdent root canal sealer (PULPDENT Corporation, USA) and GP
Group IV: Zinc oxide-eugenol in a thin consistency as a sealer with GP
Group V: Unobturated teeth to serve as control.
All the excess material was removed from the canal orifice and the access cavity was sealed with temporary cement. The quality of root canal fillings was confirmed radio graphically. All the specimens were stored at 37°C in 100% relative humidity for 1 week.
A square-shaped plaster block of measurement 2 × 2 × 1 (l × b × h) cm 3 was used for each tooth to hold it vertically at the time of testing. The angulations of teeth to the plaster block were kept at right angle. Each root had an exposed length of 9 mm from the plaster block. Fracture resistance testing was done using a universal testing machine (Instron). A custom made metal indenter of 3 mm diameter was tightened to the upper arm jig and the tooth specimen was tightened on the lower platform jig. Continuous load was delivered to the canal orifice of the tooth until fracture occurred. A cross head speed of 1 mm/min was set and the load was applied perpendicular to the long axis of the tooth at the canal orifice. The force required to fracture each tooth was recorded in Newton (N). A vertical continuous fracture line was expected for a successful outcome. Data thus obtained were evaluated statistically using one-way ANOVA and the unpaired t-test to determine the significance of the difference between groups.[Figure 1], [Figure 2], [Figure 3] and [Figure 4]
| Results|| |
Results obtained were expressed in terms of mean ± SD. One-way ANOVA showed a significant difference among all groups at 5% level of significance (P0 < 0.05). Further unpaired t-test revealed that there was no significant difference between Group I and Group II but both the groups showed significant difference from Group III (P < 0.05), whereas Group III had a better fracture resistance than group IV, no significant difference was seen between Group IV and Group V (P > 0.05).
| Discussion|| |
Root canal treatment is the treatment of choice to save a grossly decayed tooth and to maintain its proper form, shape and strength in the oral cavity. Teeth which have undergone an endodontic treatment inevitably need an intracanal filing or instrumentation to prepare the cavity walls by removing some of the root dentine which there by weakens the root and may leads to an easy fracture of the tooth root. So any attempt or any materials which can be used to compensate this loss will be beneficial Johnson et al.  recommended the use of adhesive sealers in the root canal system to reinforce the root-filled teeth.
We have evaluated a resin-based sealer material, AH plus ® and Roeko Seal which is a two paste silicon-based sealer. AH plus ® has a good bioactive property, i.e. less shrinkage and a wide variety of radio opaque fillers AH plus ® has an added advantage in film thickness and adhesion to the dentinal walls. Due to its better adhesion properties to the root dentine, it forms a single unit within the root canals and bonds to the dentinal walls. Many studies have already shown that resin-based sealers are stable biocompatible and has good sealing abilities.  The polymer-based sealer materials are resilient and along with GP form a perfect seal with the dentinal wall, and so it appears that both the materials have a good potential to strengthen the canal walls against fracture.
Pulpdent sealer was the other material used in obturating one of the test groups. Pulpdent sealer is a zinc oxide-based sealer which can fill any irregularities and accessory canals for complete obturation as well as it provides proper strength to compensate the compromised internal canal walls Unlike the other two sealers, though it has a reduced physical property, it is tissue compatible and provides an adequate seal. Gutta percha has been used as a core material with ZNOE-based sealers for many years. The main disadvantage of Pulpdent is that it shrinks upon setting and dissolve over a period of time which compromises the quality and strength of the sealer. This may be one of the reason by which the sealer fail to give an adequate resistance to fracture. Also many studies have proved that no zinc oxide-based sealers bond to the root dentine and prevent the apical leakage in the root end,  which also can be a major cause for compromised strength of the root dentine.
Plain zinc oxide-eugenol sealer was also used with gutta percha as core material, as it was the most commonly and conventionally used material.
Extracted human permanent teeth were used for this study, but a large amount of variations were expected. So, proper care was taken to standardize all those controllable factors as much as possible. All the group of root specimens as done in previous studies were randomly selected from similar age group individuals.  A rotary instrumentation technique was used for biomechanical preparation in the current study. This can be explained as rotary instrumentation consumes less time and it has been mentioned in previous literatures about the effectiveness of cleaning and shaping of the canal walls when compared with hand Pro-Taper files.
To standardize the apical canal diameter of the root canal, each root was filed to Pro-Taper size F3, corresponding to an apical size ISO #no. 30. To achieve a satisfactory cleansing a standard three-step irrigation regimen, using EDTA, sodium hypochlorite followed by normal saline, was used to remove the smear layer as this regimen has shown better adhesion of the materials to the root dentine. 
In many studies fracture strength was performed using cyclic loading (Heydecke et al.)  by applying the load in different directions in order to simulate the exact oral conditions. But in few studies, it was reported that applying a force vertical to the long axis of the tooth transmits a uniform force all over (Dias de Souza et al.).  In our study a single load to fracture was delivered vertically parallel to the long axis of the tooth as in few other studies that compared the fracture resistance of root canal sealers (Apicella et al., Cobankara et al.). ,
The force in the present study was applied at a of 0 o angle, resulting in primarily a splitting stress applied over the access opening. This would result in smaller stresses because of decreased bending moments and maximum stresses located much more cervically. This study design is said to be more clinically relevant as it better simulates the support given to healthy teeth by alveolar bone, and results in less catastrophic stress build-ups caused by unrealistic bending movements. 
In this study, the highest mean fracture value was found in the teeth obturated with GP and AH Plus ® (Group II) as well as Roeko-seal and GP (group I) which was significantly greater than that seen in teeth obturated with any other group. The advantage of the resin sealers can be because of greater adhesion of these sealers to the root dentine as well as less volumetric shrinkage compared to the two other zinc oxide-based sealers. AH Plus ® has better penetration into the micro irregularities because of its creep capacity and long setting time, which increases the mechanical interlocking between the sealer and root dentin.
The results of this study can be correlated to the work done by Gesi et al.  who concluded that the Epiphany sealer and Resilon core combination showed lower bond strength values as compared to the AH Plus ® and GP core combination. This might be because of weak chemical coupling of the resin-based sealer to Resilon, due to the fact that amount or method of dimethacrylate incorporation in Resilon may not be optimized for predictable chemical coupling. This weak bonding between the Epiphany sealer and Resilon core was further substantiated by the work done by Tay et al. 
Also there was a slight increase in the fracture resistance of Pulpdent and GP (group III) when compared to the other two groups that is Group IV and Group V. As the reason is more evident that even though Pulpdent is a zinc oxide-based sealer, they have a variety of filler particles such as calcium phosphate and zinc sterate in them which may provide a better flow and more resilience. These properties imparts a shock reduction mechanism and add more resistance to fracture when obturated with a GP core but there was no significant result between Group III and Group IV to justify that Pulpdent has shown better fracture resistance when compared with ZNOE.
The fracture resistance of the zinc oxide-eugenol-gutta percha group (Group IV) was not significantly different from the control group (Group V). However, it is not wise option to leave an instrumented canal unobturated.
| Conclusion|| |
Within the limitations of this study, it has been concluded that both the resin-based sealers used were more effective compared to that of the zinc oxide-based sealers and the control group. However, no significant results were obtained when the comparison was made between ZNOE and GP and the control group. Hence, the use of an adhesive resin-based sealer will be more beneficial in obturating root canals when considering a long-term treatment prognosis.
| Acknowledgment|| |
The authors would like to thank Dr. Kishore, Department of Dental Materials, KMC, Manipal for his technical assistance and Dr.Vidya Bhat.S, Professor, Dept. of Prosthodontics, Yenepoya Dental College for help in the study.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]