| Abstract|| |
Aim: The aim of this study was to evaluate retention & fracture resistance of different fibre posts.
Methodology: 90 extracted human permanent maxillary central incisors were used in this study. For retention evaluation, after obturation, post space preparation was done in all root canals and posts were cemented under three groups. Later, the posts were grasped & pulled out from the roots with the help of a three-jaw chuck at a cross-head speed of 5mm/min. Force required to dislodge each post was recorded in Newtons. To evaluate the fracture behavior of posts, artificial root canals were drilled into aluminium blocks and posts were cemented. Load required to fracture each post was recorded in Newtons.
Results: The results of the present study show the mean retention values for Fibrekleer Parallel post were significantly greater than those for Synca Double tapered post & Bioloren Tapered post. The mean retention values of the Double tapered post & the tapered post were not statistically different. The Synca Double tapered post had the highest mean load to fracture, and this value was significantly higher than those of FibreKleer Parallel & Bioloren Tapered post. The mean fracture resistance values of Parallel & tapered post were not statistically different
Conclusions: This study showed parallel posts to have better retention than tapered and double tapered posts. Regarding the fracture resistance, double tapered posts were found to be better than parallel and tapered posts.
Keywords: Fiber post; fracture; parallel post; retention; tapered posts
|How to cite this article:|
Pruthi V, Talwar S, Nawal RR, Pruthi PJ, Choudhary S, Yadav S. Evaluation of retention and fracture resistance of different fiber reinforced posts: An in vitro study. J Conserv Dent 2018;21:157-61
|How to cite this URL:|
Pruthi V, Talwar S, Nawal RR, Pruthi PJ, Choudhary S, Yadav S. Evaluation of retention and fracture resistance of different fiber reinforced posts: An in vitro study. J Conserv Dent [serial online] 2018 [cited 2019 Aug 25];21:157-61. Available from: http://www.jcd.org.in/text.asp?2018/21/2/157/228271
| Introduction|| |
Esthetics plays a major role in patient satisfaction. With the increase in the popularity of all ceramic dental restorations, there has been an increased demand for endodontic post and core materials that provide superior esthetics.
Conventional cast post and core procedures were expensive, time-consuming, required more than two appointments, with a potential for post and root fracture and a high risk of corrosion, when different metals were used. Consequently, it was desired to have a less time-consuming approach to coronoradicular stabilization of pulpless teeth and a simplified procedure to replace arduous custom-cast post and core. The expeditious features such as rigidity, retention, resistance, and passivity of prefabricated posts combined with cost-effectiveness have stimulated considerable interest.
Common prefabricated postdesigns included the tapered, threaded, and parallel designs. Tapered post follows the prepared canal shape and conserves the tooth structure; however, they are less retentive and have shown to cause nonrestorable fractures. Parallel-sided posts provided superior retention; however, more dentin from apex of root canal must be removed. This may result in higher incidence of perforation failure and greatest stress generation at apex of canal preparation. Threaded posts are most retentive and distribute stresses better in short roots, but the incidence of vertical fracture is increased with the use of these posts. In addition to postdesign, dowel retention is also influenced by length and diameter of post.
Until recently, all the prefabricated posts consisted of metal alloy that resulted in final combination of heterogeneous interfaces of dentin, metallic post, cement, and core material. However, the stress concentration pattern of these post systems sometimes resulted in irreparable root fractures. In addition, metal posts lead to unfavorable esthetics such as gray discoloration of translucent all-ceramic crowns and the surrounding gingiva.
A nonmetallic “Carbon-fiber” postsystem was introduced in the year 1990 by Duret  The combination of fiber post, resin core, and resin cement results in interfaces having nearly similar modulus of elasticity and hence give a homogenous monoblock effect.
Although considered as having significant advantages as compared to metal post, especially with respect to mechanical properties, the carbon fiber post showed limitations of material's radiolucency and masking difficulties under all ceramic and resin composite restorations because of its gray color. This drawback of carbon-fiber posts leads to the introduction of glass/quartz fiber posts. The mechanical properties of these posts are similar to those of carbon posts and provide an additional esthetic benefit. Fiber posts appear to be biocompatible, are easy to insert, and are time and cost-effective.
Even though there is a body of published evidence on fiber-based posts, there is little consensus relating the fracture resistance and retention of newer posts designs. Hence, the aim of this study was to evaluate retention and fracture resistance of different fiber posts.
| Materials and Methods|| |
Ninety extracted human permanent maxillary central incisors were used in this study. Collection, storage, sterilization, and handling of extracted teeth to be used in this study followed the occupational safety and health administration and the Centre for the Disease Control and Prevention recommendations and guidelines.
Evaluation of retention testing of fiber posts
The teeth were decoronated 1 mm coronal to cementoenamel junction with the help of a diamond disk using slow-speed handpiece under water cooling. All roots had a length of approximately 14.5 mm. Subsequently, the instrumentation phase of root canal preparation was performed at a working length of 14.0 mm, 0.5 mm short of the apical foramen, using ISO K-files (Dentsply Maillefer, Switzerland) through stepback technique. Apical enlargement was performed to size 0.02/60 with intermittent irrigation using 1 mL of 1% NaOCl solution after every change of file size throughout the cleaning and shaping of the root canal. Following this, the teeth were dried with paper points and obturated with gutta-percha and AH Plus sealer (DeTrey Dentsply, Konstanz, Germany).
After obturation, teeth were randomly divided into three experimental groups containing 30 teeth each. Standardized postspace preparation was done in all root canals to a depth of 10 mm, leaving 4 mm of gutta-percha apically.
- Group 1 – Fibrekleer Parallel Posts (Pentron clinical, CA) (n = 30)
- Group 2 – Bioloren-Tapered post (Bioloren S. r. l., Italy) (n = 30)
- Group 3 – Synca Double-Tapered Posts (Synca, USA) (n = 30).
After postspace preparation, each canal was rinsed with 17% ethylenediaminetetraacetic acid and distilled water and dried with paper points. Etching of the postspace preparation was done with 37% phosphoric acid gel followed by rinsing with distilled water and drying with paper points. Further, application of primer/adhesive system into the preparation and also to the fiber post was done followed by light curing for 10 s. A dual-cure- resin-cement (Calibra, Dentsply Detrey, Germany) was applied into the canal using lentulo spiral and posts were cemented to a length of 10 mm and then cured for 30 s. After half hour, specimens were placed in a high-humidity environment at 37°C for 48 h.
After 48 h, specimens were embedded in self-cure acrylic-resin blocks. The resin blocks with vertically aligned roots were placed in a holding fixture in Instron machine one at a time [Figure 1]a. Posts were grasped and pulled out from the roots with the help of a three-jaw chuck at a cross-head speed of 5 mm/min [Figure 1]b. Force required to dislodge each post was recorded in Newtons [Figure 1]c.
|Figure 1: (a) Vertically aligned roots in holding fixture and postgrasped with a three jaw chuck. (b) Postpulled out from the canal. (c) Schematic representation of the retention testing. (d) Posts seated in the aluminum blocks to a length of 10 mm. (e) Posts fractured at the 45° angle|
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Evaluation of fracture behavior of fiber posts
To evaluate the posts fracture behavior, the method described by Sahafi et al. was used. The total samples were divided into three groups:
- Group 1 – Parallel posts (n = 30)
- Group 2 – Tapered posts (n = 30)
- Group 3 – Double-tapered Posts (n = 30).
The artificial root canals were drilled into aluminum blocks corresponding to the size of the posts. Posts were seated to a depth of 10 mm and cemented in place using the same resin cement as above [Figure 1]d. Before placing the posts, they were adjusted so that in cemented state each protruded 5 mm from the canal. After hardening of the luting cement, posts were stored at 37°C for 48 h. The testing assembly was placed in Instron machine and each specimen loaded to fracture at a 45° angle at a cross-head speed of 5 mm/min [Figure 1]e. Load required to fracture each post was recorded in Newtons.
| Results and Statistical Analysis|| |
From the data collected in the study, the mean of retention and fracture resistance of different posts were calculated and statistically analyzed. The statistical package SPSS software was used for statistical analysis. The comparison for mean retention between the various types of fiber posts was assessed using the one-way ANOVA test. The post hoc comparison within the various types of posts was done using Tukey honest significant difference [Table 1] and [Table 2].
|Table 2: Mean fracture resistance values of different types of fibre posts|
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The results of the present study show that for both retention and fracture resistance testing; there is highly significant difference (P < 0.05) between the groups.
The mean retention values for Fibrekleer Parallel post were significantly greater than those for Synca Double-Tapered post and Bioloren Tapered post. The mean retention values of the double-tapered post and the tapered post were not statistically different [Graph 1].
Fracture resistance testing
The Synca Double-Tapered post had the highest mean load to fracture, and this value was significantly higher than those of FibreKleer Parallel and Bioloren-Tapered post. The mean fracture resistance values of parallel and tapered post were not statistically different [Graph 2].
| Discussion|| |
The present study investigated the retention and fracture resistance of three different designs of fiber posts, i.e., parallel, tapered, and double tapered. The purpose of this study was to evaluate the effect of designs of the different posts on their retention and fracture resistance. The length and the apical diameter of the posts were kept constant for all the samples used in this study.
The posts chosen were evaluated for their retention property as post decementation is one of the most common causes of post failure. Further on, the fracture resistance of these posts was also evaluated as the fiber posts are more prone to fracture than previously used metal posts.
Various authors have claimed that fiber posts, having a modulus of elasticity similar to that of dentin, could achieve a tooth-post- core monoblock. This would help to distribute masticatory loads homogeneously and reduce stresses during function. This may also account for the better retention of the fiber posts when resin cements are used as a luting agent. However, the beneficial claims of the fiber post–root dentin monoblock could not be validated in independent in vitro and retrospective in vivo studies.
The retention of a post depends on its shape, size, and post length. There were three different designs of the posts used in this study, namely, parallel, tapered, and double-tapered. The postlength was set at 15 mm with 10 mm of post length cemented into the canal and 5 mm extending out for the purpose of standardization. The apical diameter of all the posts was standardized at 1.0 mm. For adequate retention of a post, its length should be equal to or larger than the crown length. Each prefabricated post system is manufactured in multiple widths and lengths to enable its ultimate selection for a given clinical situation. FiberKleer Parallel Post has a constant diameter of 1.0 mm throughout the postlength though characterized by a serrated head configuration for the core retention. The Bioloren-Tapered post is a constant-tapered post that varies in diameter from 1.00 mm at the apical end to 1.45 mm at the coronal end. Double-tapered post (Synca) is a double tapered post, and its diameter varies throughout its length. For the purpose of this study, size #2 Double-Tapered post was chosen which has a diameter of 1.0 mm at the apical end and 1.1 mm at the junction of apical and middle third of the post. This diameter reaches 1.8 mm at the junction of middle and coronal third of the post and remains constant thereafter.
All the posts used in this study were passive posts. The retention of passive posts relies mostly on the cement used for luting, especially in the case of tapered posts. It has been demonstrated that resin-based cements have greater bond strength than do conventional cements, such as zinc phosphate. Hence, resin cement was used as the luting agent for all samples in this study. The method of application of luting agent into the canal may also affect the bond strength of the fiber post. Placement of cement using lentulospiral is established as superior method compared to the other methods using hand instruments such as file or spreader.
The results of this study showed parallel posts to have better retention than tapered and double-tapered posts. Although the retentive strength of tapered post is inferior to parallel post, it has adequate retention for clinical use.,, Taper of the posts may have the same role as the conicity of the crowns to achieve friction. With crowns, as the taper of the preparation increases, the retention value decreases proportionately. This might be the reason for tapered posts showing comparatively lesser retention than the parallel posts.
According to manufacturers, double-tapered posts have increased retention because of the coronal portion of the post which is parallel in shape. However, in this study, double-tapered posts showed lesser retention as compared to the tapered posts, though the difference was not statistically significant. This result is in consensus with the previous studies. The reason for double-tapered posts showing lesser retention could be because only 10 mm intra canal length of the post was chosen, which is the tapered portion of this post. Hence, the parallel portion of the double-tapered posts did not contribute to any retention. In addition, the greater taper of the double-tapered posts could be the reason of these posts showing lesser retention than tapered posts.
The tensile force test was done in this study using the Instron machine which is a widely accepted method to estimate the retention of posts. This in vitro tensile force may not be similar to the exact clinical situation; however, the test would give us a good criterion for the comparison and evaluation of the retention of different fiber post designs.
For the fracture resistance testing, all the posts length were standardized at 15 mm with 10 mm of post cemented into the artificial canal of the aluminum blocks and the remaining 5 mm extending out. According to this study, double-tapered posts showed maximum fracture resistance followed by tapered and then parallel posts. At the length of 10 mm from the apical end (the point of fracture), parallel post has a diameter of 1.0 mm, tapered post 1.20 mm, and double-tapered post has a diameter of 1.50 mm. Hence, the maximum force required in the case of double-tapered post could be due to the increased diameter of this post at the point of fracture. Hence, the shape and design seem to have an important role in the mechanical behavior of fiber-reinforced posts. Numerous in vitro studies have shown that the strength of fiber-reinforced posts to be lower than that of metal posts. However, increasing the diameter of the fiber posts makes it stiffer and more resistant to fracture.
| Conclusion|| |
The results of this study showed parallel posts to have better retention than tapered and double-tapered posts. This observation is in compliance with the previous studies. The results also showed double-tapered posts to have greater fracture resistance than parallel and tapered posts. However, before some definite conclusion can be drawn, further studies need to be done to evaluate newer designs of the fiber posts with a large number of samples. Further research in laboratory and long-term, evidence-based clinical studies should be performed to determine its success at a significant level.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. Preeti Jain Pruthi
Department of Conservative Dentistry and Endodontics, 3rd Floor, Maulana Azad Institute of Dental Sciences, New Delhi - 110 002
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]