|Year : 2014 | Volume
| Issue : 3 | Page : 144-148
Comparison of fracture resistance of endodontically treated teeth with MOD cavity using different techniques of fiber insertion
Omer Kirmah1, Onur Sahin2, Fatma Aytac3, Fatih Sari4, Faik Tugut5, Alper Kustarci6
1 Department of Prosthodontics, Faculty of Dentistry, Akdeniz University, Antalya, Turkey
2 Department of Prosthodontics, Faculty of Dentistry, Bulent Ecevit University, Zonguldak, Turkey
3 Department of Restorative Dentistry, Faculty of Dentistry, Gaziosmanpasa University, Tokat, Turkey
4 Department of Prosthodontics, Faculty of Dentistry, Gaziantep University, Gaziantep, Turkey
5 Department of Prosthodontics, Faculty of Dentistry, Cumhuriyet University, Sivas, Turkey
6 Department of Endodontics, Faculty of Dentistry, Akdeniz University, Antalya, Turkey
|Date of Web Publication||29-Oct-2014|
Departments of Prosthodontics, Faculty of Dentistry, Akdeniz University, Antalya
Source of Support: None, Conflict of Interest: None
Objectives: The purpose of this study was to evaluate the effect of fiber by using different techniques on fracture resistance of endodontically treated molars with mesio-occlusal-distal (MOD) cavities. Materials and Methods: Forty extracted human molars were randomly assigned to four groups (n = 10). Teeth in Groups 2-4 received root canal treatment and a MOD cavity preparation. Group 1 served as control. Group 2 was restored with composite resin. In Group 3, the fiber was inserted into the cavities in buccal to lingual direction by coating the occlusal one-third of the buccal wall to the occlusal one-third of the lingual wall, and lastly, the teeth were restored with composite resin. In Group 4, the flowable resin was coated inside the cavities with the fiber, as Group 3 was before restoring teeth with composite resin. Compressive loading of the teeth was performed at a cross-head speed of 0.5 mm/min. Data were analyzed using one-way ANOVA and Tukey post-hoc tests. Results: Fracture resistance values of all the groups were compared; the differences between Groups 2 and 3 or Groups 2 and 4 were found to be statistically significant. Conclusions: As a result, use of the fiber under composite resin with a flowable resin increased fracture strength to MOD cavities.
Keywords: Endodontically treated, fiber, fracture resistance, mesio-occlusal-distal preparation
|How to cite this article:|
Kirmah O, Sahin O, Aytac F, Sari F, Tugut F, Kustarci A. Comparison of fracture resistance of endodontically treated teeth with MOD cavity using different techniques of fiber insertion
. J Res Dent 2014;2:144-8
|How to cite this URL:|
Kirmah O, Sahin O, Aytac F, Sari F, Tugut F, Kustarci A. Comparison of fracture resistance of endodontically treated teeth with MOD cavity using different techniques of fiber insertion
. J Res Dent [serial online] 2014 [cited 2020 Aug 15];2:144-8. Available from: http://www.jresdent.org/text.asp?2014/2/3/144/143598
| Introduction|| |
The teeth with healthy pulps are more resistant to fracture than endodontically treated teeth because of reduced dentinal elasticity, substantial loss of dentine,  and lower water content. , The loss of anatomical structures due to caries and tooth preparation is the key reason for the fracture. 
An ideal restoration for these teeth is able to preserve the remaining tooth structure, maintain the aesthetics and function, and prevent the microleakage. Following endodontic treatment, full cast crown restorations, , complex amalgam restorations, , composite materials, or aesthetic restorations for inlays/onlays (composites/ceramics) can be used for final restorations.
Bonding systems, restorative materials, and conservative preparation techniques continue to evolve. The use of direct composite restoration in posterior teeth has become increasingly more popular. Cavity preparation procedures for all conservative restorations play an important role in the fracture of the cusps  and polymerization shrinkage of composite resins (CRs), especially for endodontically treated teeth. , This result facilitates microleakage, which could promote secondary caries and pulpal irritation in vital teeth.  The incremental placement techniques increase in importance to minimize the development of stresses. In addition, polymerization shrinkage is compensated for by flow of the composite. A rigid bond interface between the resin composite and tooth structure generates contraction stresses at the bonding interface.  These stresses can be reduced by several methods. One method is the application of low viscosity resin between the bonding agent and the restorative resin to act as a "stress breaker" that can relieve contraction stresses. ,
The use of CR materials in endodontically treated teeth with mesio-occlusal-distal (MOD) cavity is preferred because it is cheaper than other restorations. Furthermore, the procedure is a very conservative method and is less time-consuming. Of course, the development of fiber-reinforced composite (FRC) technology is particularly important for this reason. FRC has been used in the laboratory for fabrication of single crowns, full and partial coverage fixed partial dentures, , periodontal splints, and chairside fixed partial dentures; ,, the fiber must possess adequate modulus and strength to function successfully in the mouth. ,
Several researchers , have investigated the effect of FRC on the fracture resistance of endodontically treated teeth through different methods. Belli et al.  reported that the fracture resistance of molar teeth may increase if the insertion of a piece of polyethylene fiber into the cavity in the gingival and occlusal third method is used. Another study  showed that a ribbon of glass fiber in the occlusal third of the restoration was an effective method to fracture resistance. The purpose of this study was to evaluate the effect of fiber using different techniques on fracture resistance of endodontically treated molars with MOD cavity. The null hypothesis was that increased fracture resistance of molar teeth restored with different fiber locations.
| Materials and Methods|| |
Forty extracted human mandibular molar teeth were used in this study. All the teeth were scaled to remove the adhering soft tissue/calculus and stored in distilled water. Teeth received endodontic treatment, followed by preparation of MOD cavities without Group 1, and were randomly distributed into four groups of 10 teeth each. The teeth were prepared as follows:
Group 1. Ten intact teeth served as the control group. Access cavities were prepared using a high-speed bur and water spray, and the root canals were instrumented 1 mm short of the apical foramen with ProTaper NiTi rotary files (Dentsply Maillefer, Ballaigues, Switzerland) in experimental groups. Following the instrumentation, canals were filled with gutta-percha and AH Plus root canal sealer (Dentsply Maillefer, Ballaigues, Switzerland) using a lateral condensation technique. MOD cavities were prepared in such a manner that the thickness of the buccal wall of the teeth measured 2 mm at the buccal-occlusal surface, 2.5 mm at the cement-enamel junction (CEJ), 1.5 mm at the lingual-occlusal surface, and 1.5 mm at the CEJ [Figure 1]. The teeth were then embedded in acrylic resin cylinder to the level of the CEJ.
|Figure 1: Schematic view of procedures and dimensions of MOD preparation|
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Group 2. Cavities were cleaned and dried, and the Clearfil SE Bond (Kuraray Co., Osaka, Japan) two-step self-etch adhesive system was applied to the cavities according to the manufacturer's instructions. Primer was applied for 20 seconds and dried gently. Bonding agent was then applied and light cured using an LED (LEDition; Ivoclar Vivadent, Liechtenstein) at 600 m W/cm for 20 seconds. Cavities were then restored with CR (Gradia Direct; GC Corporation, Tokyo, Japan) using an incremental technique and cured for 40 seconds according to the manufacturer's instruction.
Group 3. After etching and bonding procedures, the cavity surfaces were coated with an FRC. Before curing, a piece of fiber (Ever Stick; Stick Teck Ltd., Turku, Finland) was prepared (12 mm long, 10 mm wide) and inserted into the cavities in a buccal to lingual direction by coating the occlusal one-third of the buccal wall to the occlusal one-third of the lingual wall [Figure 1]. After curing for 20 seconds, the cavities were restored with CR as described above.
Group 4. After the etching and bonding procedure, flowable resin (Natural Flow; DFL, Rio de Janeiro, Brazil) was coated inside the cavities with the FRC in a manner similar to Group 3 and cured from an occlusal direction for 20 seconds. Then, the exposed surface of the fiber was covered with CR as described above.
After all the specimens were stored in distilled water at 37 o C for 24 hours, the teeth were then mounted in a block of acrylic resin measuring 2 cm in diameter at CEJ. The specimens were placed in a universal testing machine (LF Plus; LLOYD Instruments, Ametek, England) for measuring the fracture resistance of teeth. A 5 mm diameter round stainless steel ball was positioned parallel to the long axis of the teeth and centered over the teeth until the bar just slightly contacted the occlusal surface of the restoration and the buccal and lingual cusps. Compressive loading of the teeth was performed at a cross-head speed of 0.5 mm/min, and the force necessary to fracture each tooth was recorded in Newtons. The results of the study were evaluated statistically using one-way ANOVA and Tukey post-hoc test. P values were computed and compared with statistical significance at the level of 0.05.
| Results|| |
The mean of the fracture resistance values and the standard deviation for each group are presented in [Table 1]. Statistically significant differences were found among the fracture resistance values between the tested groups. Fracture resistance value of group 1 (intact teeth specimens) was significantly higher than the other groups. Restored teeth with different FRC locations with or without a flowable composite (Groups 3 and 4) lining showed significantly more fracture resistance than Group 2. No significant difference was found between Groups 3 and 4. However, the mean fracture resistance value of Group 4 was higher than the mean value of Group 3.
|Table 1: Mean fracture resistance and standard deviation for each groups|
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| Discussion|| |
The results obtained in this study demonstrated that an increase in fracture resistance values was observed by using different fiber locations on endodontically treated molars with MOD cavity. Therefore the null hypothesis was accepted.
Restoration of the teeth is an essential final step of root canal treatment. But to reinforce the tooth structure is an important aim, not only to repair tooth structure, but also to provide an effective seal between the canal system and mouth. Following the endodontic treatment, the clinician can select an alternative situation for a fracture risk to the restorations. A full crown is the most preferable situation. However, the conservative treatments for CR restoration, with or without FRC, may be desirable to others because adhesive restorations allow a more efficient transfer and distribution of functional stresses across bonding interface to the tooth structure. , Researchers , have evaluated fracture resistance of endodontically treated teeth using different techniques.
In the current study, the control group had a mean fracture resistance of 1648 N and Group 2 (only dentin bonding and CR applied) had a mean fracture resistance of 695 N, which were the highest and lowest values, respectively, and there was a significant difference between them. These results are in agreement with the previous studies. ,,,, In a previous study, Belli et al.  evaluated the reinforcement effect of polyethylene fiber in root-filled teeth using two restoration techniques; they found increased fracture resistance to use of polyethylene fiber before or after the restoration. Also, they reported that the resistance to fracture of teeth increased significantly when the fiber was placed on the occlusal surface of the restoration from a buccal to lingual direction. In another study, they evaluated to effect of fiber insertion on fracture resistance of endodontically treated molars with MOD cavity. As a result, they found that inserting a leno-woven ultra-high molecular weight polyethylene ribbon fiber in endodontically treated molars with MOD cavity significantly increased fracture strength.  In a similar study, Navimipour et al.  evaluated the effect of different methods of fiber insertion on fracture resistance of endodontically treated maxillary premolars, and they reported that glass fiber, inserted from the buccal to lingual aspect in the occlusal portion of the restoration, increased fracture resistance. Also, Oskoee et al.  found that the fracture resistance in the occlusal fiber group was significantly higher than in the other groups. In the present study, when the fiber was placed into the cavities in a buccal to lingual direction by coating the occlusal one-third of the buccal wall to the occlusal one-third of the lingual wall, with or without flowable resin, significantly higher fracture resistance was observed. However, Luthria et al. evaluated the effect of polyethylene fiber and composite-impregnated glass fiber on fracture resistance of endodontically treated teeth, and they found that the fracture resistance of the composite-impregnated glass fiber reinforced group was much higher. According to the results of these studies, the different techniques of using the fiber can be important for increased fracture resistance of the restorations.
On the other hand, Rodrigues et al. reported that the terms of fracture resistance of molar teeth with MOD cavity, with or without glass fiber, were not different, and the insertion of glass fibers into MOD cavities was not an effective technique to reinforce teeth. This result contrasts the result of the present study. This difference could be because the fiber was inserted into cavities by a different technique, and it was positioned over the adhesive system.
Hernandez et al.  reported some advantage of bonding, such as the high-bond strength to tooth structure and increased resistance to fracture, and Takada et al.  stated that the high viscosity bonding agents may release contraction stresses. Alhadainy et al.  reported that the high-viscosity bonding agents act as a stress absorber until restorations occur. The present study showed that inserting flowable composite into the cavities in a buccal to lingual direction before coating the cavity with fiber would provide an increase in fracture resistance. This was theorized based on the concept that the presence of the glass or polyethylene network would create a change in the stress dynamics at the restoration/adhesive resin interface. In agreement with the present study, Belli et al.  reported that fracture resistance increased when fiber was embedded into a bed of flowable resin.
As part of the results of this study, the use of different techniques to insert the fiber into cavities should be supported by clinical applications in order to strengthen the restorations and tooth structure. Also, the evaluation of the clinical effects of each technique will enhance the preferred variation of fiber locations.
| Conclusions|| |
Within the limitations of this study, the following conclusions were drawn:
- MOD cavities reduced fracture resistance of endodontically treated teeth
- Use of flowable composite with fiber under composite restoration significantly increased fracture resistance of endodontically treated teeth with MOD cavities
- The different techniques of using the fiber can be important for increasing the fracture resistance of the restorations.
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