|Year : 2013 | Volume
| Issue : 2 | Page : 60-65
A comparative evaluation of different restorative technique using polyethylene fibre in reinforcing the root-filled teeth: An in vitro study"
Shailja Singh1, Anil Chandra2, Aseem Prakash Tikku2, Promila Verma2
1 Department of Conservative Dentistry and Endodontics, Career Dental College, Lucknow, Uttar Pradesh, India
2 Department of Conservative Dentistry and Endodontics, King George Medical University, Lucknow, Uttar Pradesh, India
|Date of Web Publication||3-Aug-2013|
Department of Conservative Dentistry and Endodontics, King Georges Medical University, Lucknow, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Aim: The purpose of any restorative material is not only to restore the decayed of defective tooth and provide an effective seal between the restoration and the tooth, but also to strengthen it. Endodontic treatment removes the vital contents of the canal, leaving the tooth pulpless and resulting in teeth with calcified tissues that contain significantly less moisture than that of vital teeth. The restorative material should be as much as strong, which support the endodontically treated tooth against the occlusal forces. Thus, the present study was undertaken to evaluate different restorative technique using the polyethylene fiber in reinforcing the root-filled teeth. Materials and Methods: 50 freshly extracted maxillary premolar human teeth were taken. All teeth were divided into 2 groups, the control and experimental group), sub group I (had unrestored mesial occlusal distal [MOD] cavities), sub group II (where MOD cavities were filled with composite), sub group III (where polyethylene fiber placed occlusally on the composite restoration) and sub group IV (had polyethylene fiber inserted under the composite the restorations). The specimens were then placed into a universal testing machine. A vertical compressive force was applied at a crosshead speed of 0.5 mm/min and the force necessary to fracture. Results: Fracture resistance was significantly highest in sub group III as compared to sub group IV, sub group II and sub group I. Conclusion: This study concluded that use of polyethylene fiber inserted over or under the restoration significantly increased the fracture strength of the root canal treated teeth and when the fiber was placed on the occlusal surface of the restoration from a buccal to lingual direction significantly higher fracture resistance was observed.
Keywords: Cuspal fracture, flexural strength, polyethylene fiber
|How to cite this article:|
Singh S, Chandra A, Tikku AP, Verma P. A comparative evaluation of different restorative technique using polyethylene fibre in reinforcing the root-filled teeth: An in vitro study". J Res Dent 2013;1:60-5
|How to cite this URL:|
Singh S, Chandra A, Tikku AP, Verma P. A comparative evaluation of different restorative technique using polyethylene fibre in reinforcing the root-filled teeth: An in vitro study". J Res Dent [serial online] 2013 [cited 2020 Jun 4];1:60-5. Available from: http://www.jresdent.org/text.asp?2013/1/2/60/116037
| Introduction|| |
The ultimate goal of endodontic and restorative dentistry is to retain natural teeth with maximum function and esthetics. Restoration of endodontically treated teeth maintains function and esthetics and protects the tooth against fracture and infection. Successful endodontic debridement and apical sealing are essential underpinnings for restoration of non-vital tooth.  Likewise, sealing of the coronal restoration and underlying components is crucial final step for long-term survival of the tooth. 
Endodontic treatment removes the vital contents of the canal, leaving the tooth pulpless and resulting in teeth with calcified tissues that contain significantly less moisture than that of vital teeth. Hence, endodontically treated teeth are structurally different from unrestored vital teeth and require specialized restorative treatment. The major changes include (1) loss of tooth structure (2) altered physical characteristics and (3) altered esthetic characteristics. 
Restorations for endodontically treated teeth are designed to compensate for these changes. All these changes that accompany root canal therapy influence the selection of restorative materials and procedures for endodontically treated teeth important consideration include: The amount of the remaining tooth structure, the anatomic position of the tooth, the occlusal forces on the tooth and the restorative and esthetic requirements of the tooth. 
Traditionally, many root-filled teeth have been restored in conjunction with a post in the belief that they were reinforced; although, there is little evidence to support this procedure.  In fact, restoration of a tooth with a post has been shown by various authors that weaken the tooth rather strengthen it. ,
A number of new denting bonding systems have been developed recently. These bonding system were introduced to increase the bond strength of composite resin to dentin as well as to produce leak free restoration. It is assured that these bonding systems improve the adhesive capability and bonding strength of resins to tooth structure by promoting penetration impregnation and entanglement of the coupling agent into dentinal substract where they polymerized in situ and create zones of resins reinforced dentine layers.
In the present study, using an alternating technique, the effect of polyethylene fiber ribbon which was inserted over the occlusal surface was compared with the use of polyethylene fiber ribbon under the composite resin. The effect of these techniques on cuspal fracture strength in root-filled premolar teeth was evaluated.
| Materials and Methods|| |
A total of 50 freshly extracted human maxillary premolars were selected, cleaned and stored in physiologic normal saline until required [Figure 1]. The materials required were:
- Gutta-percha (GP) Cones
- AH plus sealer
- Self-etch adhesive system
- Hybrid composite resin
- Flowable composite resin (FCR)
- Polyethylene fiber: Ribbond - ultra-high molecular weight polyethylenefibre
| Preparation of the Samples|| |
Control group: (10 samples)
Samples did not receive any root canal treatment and cavity preparation.
Experimental group: (40 Samples)
Endodontic access cavity was prepared with the help of diamond bur in a high speed airoter hand piece and the pulp tissue was removed with barbed broaches. A size 15 K file was introduced in the canal and intraoral periapical X-ray was carried out to determine the working length. The canals were prepared to size 35 K file at working length with a step back technique. After irrigation with 5.25% NaOCl, canals were dried with absorbent points and filled with GP and AH plus root canal sealer using a cold lateral condensation technique [Figure 2]. Excess root canal filling materials were removed with Gutta Cut.
After obturation, all samples were subjected to standardized mesial occlusal distal (MOD) cavities preparation [Figure 3]. The floor of the MOD was placed on the pulp chamber floor of the samples. The teeth were then mounted in self-curing polymethyl methacrylate resin up to cervical third of the root. Only crown portion of teeth are visible. These samples are mounted into a model, which is square in shape and is 2 cm in length and width.
These samples were further subdivided-
Sub group I
Teeth were not restored by any restorative material coronally after MOD cavities preparation.
Sub group II
MOD cavities preparations were cleaned and dried. After priming for 20 sec, cavity surfaces are gently dried and self-etch adhesive system is applied to the cavity surfaces and cured for 20 sec. The cavities are then restored with a resin composite using a bulk technique and cured for 40 sec from occlusal surface. To standardize the curing distance, the tip of polymerization unit was applied to the occlusal surface of the teeth.
Sub group III
After finishing the restoration, a groove 3 mm wide and 1 mm deep was prepared on the occlusal surface of the restorations between the cusp tips from a buccal to lingual direction with a high speed bur under water coolant. The end of the grooves was on the occlusal one-third of the buccal or lingual walls of the teeth. The grooves were rinsed and dried before FCR is added to the floor of the groove cavities, but not cured. 2 mm wide polyethylene ribbon fiber was saturated with adhesive resin and after removing the excess adhesive resin with a hand instrument and then placed into the bed of un-cured FCR. This combination is then cured for 20 s from the occlusal surface using the same curing unit and the exposed fiber surface was covered with composite resin and cured for 40 s.
Sub group IV
After priming and bonding procedures, the cavity surfaces were coated with a FCR. Before curing a piece of polyethylene fiber (6-mm long, 2-mm width) was first saturated with adhesive resin. The excess adhesive resin was removed with the help of hand instrument. Then, it embedded inside the FCR from the occlusal one-third of the buccal wall to the occlusal one-third of the lingual wall. After curing for 20 s, the cavities were restored with composite and cured for 40 s.
After the completion of restoration sample of all groups and sub groups were stored at 37°C in 100% humidity for 24 h. The specimens were then placed into a Universal testing machine (Instron) [Figure 4]. A 5-mm diameter stainless steel bar is affixed to the upper stage of the Instron. The bar was parallel to the long axis of the teeth: The upper stage was positioned so that the bar was centered over the teeth until the bar just contacted the occlusal surface of the restoration and buccal and lingual cusps. A vertical compressive force was applied and the force n necessary to fracture each tooth was recorded as Newtons.
| Results|| |
In the present study, control group showed statically significant result with maximum fracture resistance 1674.01 as compared with experimental groups. In the experimental group, maximum fracture resistance was obtained in sub group III with fracture resistance 1236.82, which was restored with polyethylene fiber. The unrestored teeth (sub group I) showed statically lower fracture resistance (379.65) [Table 1].
Inserting a piece of polyethylene fiber from buccal to lingual direction under the resin composite restoration (sub group IV) significantly increase fracture strength of premolar teeth with MOD cavities when compared with the subgroup II, which is restored with dentin bonding system and composite resin. In sub group III, the preparation of a groove in the bucco-lingual direction after finishing the restoration and inserting poly ethylene fiber provided significantly higher fracture strength then sub group IV restored with the use of the fiber under the restoration [Table 2].
|Table 2: Analysis of variance of fracture resistance of the control group and different experimental sub groups|
Click here to view
Control group > experimental group sub group III>sub group IV>sub group II>sub group I.
| Discussion|| |
The strength of the teeth was significantly reduced after cavity preparation as supported by previous studies. Trope et al. (1986)  showed that the resistance to fracture of teeth increased significantly when MOD preparations were acid-etched before restoration with a composite resin. A significant increase in the fracture resistance of root filled teeth was observed when they were intracoronally restored with a resin composite material. Composite restoration and enamel plus dentin etch were almost as strong as the unaltered tooth, while enamel-etch-only yielded lower stiffness.  Root canal treatment should not be considered complete until the ﬁnal coronal restoration has been placed (Wagnild and Mueller 2002).  Teeth with large MOD cavities are severely weakened due to the loss of reinforcing structures, such as the marginal edging, and become more susceptible to fractures; they suggested that cast restorations with cuspal protection should be indicated for preparations in which the width of the occlusal isthmus is half or more of the intercuspal distance. 
The purpose of the restorative material is not only to restore the decayed or defective tooth and provide an effective seal between the restoration and the tooth, but also to strengthen the tooth. The restorative materials should be as much as strong which support the endodontically treated tooth against the occlusal forces. ,,,
Extension of cavity preparation may reduce the fracture strength of a tooth. Recent reports have indicated that the fracture strength of root-filled teeth was reduced because of tooth structure loss. ,,,, An extensive MOD preparation in a root-filled tooth may cause cuspal fracture of the tooth if not restored adequately. ,,, The results of the present study also showed that restoration of a root-filled tooth is important to achieve an increased resistance to fracture.
Many differences exist between fractures occurring clinically and those induced by a testing machine. Forces generated intraorally during function vary in magnitude, speed of application and direction, whereas the forces applied to the teeth in this study were at a constant direction and speed and they were increased continually until the fracture occurred.  The results indicate that the use of a fiber under or over the final composite restoration significantly increase fracture strength. However, the clinical conditions and complexity of forces generated intraoral restoration techniques described in this study must be evaluated further in vivo.
Applications of composite with polymers provided dental researchers with bondable, fracture tough, esthetic, extremely manageable reinforcement materials that have the potential to be applied to dental restoration.  Since 1991, Ribbond bondable reinforcement ribbon has been used successfully for a variety of clinical techniques. ,,,
The successful performance of the polyethylene fiber is because of the properties of the fiber itself the degree of chemical bonding between the resin and fiber and the effect of the leno weave with regard to crack resistance and deflection as well as resistance to shifting within the resin matrix. 
Ribbond fiber used under filled composite resin in combination with flowable resin increased the fracture strength in root-filled teeth with MOD preparations. It was assumed that polyethylene fiber had the stress-modifying effect along the restoration and dentine interface. The other possible explanation of the results was that the bonding ability of fiber in combination with resin might have increased the fracture strength of the tooth by keeping both cusps together. 
In a study, it was found that flowable composite had no effect on fracture strength of root-filled teeth with MOD cavities. On the other hand, when fiber was embedded into a bed of flowable resin the fracture strength was increased.  This increase in fracture strength can be seen in [Table 3] and Graph 1 [Additional file 1]. In the bar graph means fracture resistance was maximum in control group (1674.01) and 1236.82 for group III in experimental group. In the present study, an alternative fiber insertion technique was evaluated. In this technique, the natural cusps were protected and a groove was prepared from a buccal to lingual direction and the fiber was inserted in this groove and covered with the composite resin. Extension of the fiber ends through the occlusal one-third of the buccal or lingual walls allowed the fiber to keep the cusps together and the additional bonding ability of the material provided a greater fracture resistance in root-filled teeth with MOD cavities when compared with the previously described technique. However, further in vitro and in vivo investigations are needed before materials can be recommended for routine use in clinical practice.
|Table 3: Comparison of fracture resistance of experimental|
groups with the control group and within the experimental
Click here to view
Use of flowable resin in root-filled premolar teeth with MOD cavities did not increase fracture strength on the other hand, when a polyethylene fiber was inserted into the bed of flowable resin fracture strength of teeth was increased. 
Endodontically, treated teeth can be restored with a wide range of techniques of varying complexity. Composite apparently offers adequate strength clinically, its ultimate strength being somewhat lower than that of an amalgam. Its resistance to leakage is almost totally dependent on the luting agent and the ability of dentin bonding agents to prevent leakage over the long-term is unproven. Burrow and others showed degradation of dentin bond strength in vitro over 3 years almost to the level of an unbonded restoration. The long-term ability of dentin adhesives to reduce leakage cannot be relied on, which means composite build-ups must rely on mechanical retention as do amalgam build-ups.
| Conclusion|| |
The present study it can be concluded that:
Our study is by no means a conclusive one, but within the limits of this study, it may concluded that polyethylene fiber place on occlusal surface of restoration from a buccal to lingual direction have significantly higher fracture resistance than other experiments group. Fracture resistances of untreated teeth are highest and the fracture resistance of root canal treated teeth without MOD restoration is least.
- Composite restoration increased the fracture strength of the root-filled teeth with MOD preparation because of interlinking of dentinal surface and restoration.
- Use of polyethylene fiber inserted over or under the restoration significantly increases the fracture strength of the root canal treated teeth.
- When the fiber was placed on the occlusal surface of the restoration from a buccal to lingual direction significantly higher fracture resistance was observed.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]