|Year : 2014 | Volume
| Issue : 3 | Page : 109-114
Evaluation of the flexural strength of carbon, quartz, and glass fiber-based posts
Sita Rama Raju1, Krishna Rao Kilaru2, Kidyoor Krishnamurthy Haridas3, Balaram Naik3, Krishnaprasad Shetty4, Satish Sarvepalli Venkata4
1 Department of Conservative Dentistry and Endodontics, Vishnu Dental College and Hospital, Bhimavaram, East Godavari District, Andhra Pradesh, India
2 Department of Restorative Dental Sciences, College of Dentistry, King Khalid University, Abha, Saudi Arabia
3 Department of Conservative Dentistry and Endodontics, SDM College of Dental Sciences and Hospital, Sattur, Dharwad, India
4 Navodaya Dental College and Hospital, Raichur, Karnataka, India
|Date of Web Publication||6-Aug-2014|
Krishna Rao Kilaru
Department of Restorative Dental Sciences, College of Dentistry, King Khalid University, Abha, Saudi Arabia
Source of Support: None, Conflict of Interest: None
Objectives: This study was done to evaluate the flexural strength of carbon, quartz, and glass fiber posts by means of three-point bending test. Materials and Methods: Thirty pre-fabricated fiber posts were used and divided into three groups. Group I carbon fiber posts (C-Post), group II quartz fiber post (Aestheti Plus), group III glass fiber post (Para Post White) Ten posts (N = 10) were used for each experimental group and were measured with digital caliper before test accomplishment. The fracture load of post specimens was measured, and flexural strength was obtained by the formula using S = 8FL/pd 3 . The values in Kgf/mm 2 were obtained and calculated to Mpa and submitted to ANOVA (a = 0.01) and to the Tukey's test. Results: The mean values of flexural strength show that group II quartz fiber posts (666 MPa) are significantly higher than group I carbon fiber (614 MPa) and group III glass fiber (575 MPa). C onclusion: Hence, this study concluded that quartz fiber post showed significantly higher flexural strength values. Further scope of this study lies in the evaluation and evolution of a restorative materials used for post and core preparation, which have modulus of elasticity in harmony with that of dentin and near-natural esthetic appearance.
Keywords: Carbon, flexural strength, glass fiber posts, quartz, three-point bend test
|How to cite this article:|
Raju SR, Kilaru KR, Haridas KK, Naik B, Shetty K, Venkata SS. Evaluation of the flexural strength of carbon, quartz, and glass fiber-based posts. Saudi Endod J 2014;4:109-14
|How to cite this URL:|
Raju SR, Kilaru KR, Haridas KK, Naik B, Shetty K, Venkata SS. Evaluation of the flexural strength of carbon, quartz, and glass fiber-based posts. Saudi Endod J [serial online] 2014 [cited 2019 Nov 20];4:109-14. Available from: http://www.saudiendodj.com/text.asp?2014/4/3/109/138136
| Introduction|| |
Endodontic treatment has provided dentistry with the ability to retain teeth, those which a few decades ago would have been extracted without hesitation. Improvements in instruments, techniques, and modern pharmacologic agents have led to a high success rate of 95% as reported by Ingle. , When the endodontic treatment has been completed, questions arise as how to restore and protect the tooth structure that remains.
The objective of post-endodontic restoration is to restore the normal tooth structure, function, and esthetics. These teeth need special considerations for their restoration as stated by various authors; endodontically treated teeth are weaker than vital teeth.  Extensive research showed that dehydration doesn't seem to be a significant reason. Instead, endodontically treated teeth are weakened due to cumulative loss of tooth structure due to caries, trauma and derangement of collagen network, restorative and endodontic procedures that increase the susceptibility of fracture. ,,, The restoration of endodontically treated teeth can be difficult both diagnostically and technically. In cases where tooth structure is intact, conservative approaches such as core build-up and full-coverage restorations are satisfactory. But, as most teeth show significant loss of coronal tooth structure, utilization of post and core and final restoration is necessary to achieve proper form and function. 
Numerous techniques and materials for post and core restorations have been advocated, varying from custom-made cast-metal posts to pre-fabricated metal and non-metal, esthetic, and bonded posts are available, each having their own merits and demerits. Several studies have reported the failure rate of restorations with post and cores to be higher than that of restorations on vital teeth. The causes of failure include fracture or bending of posts, ,,, loss of retention, root fracture, corrosion of metallic posts etc., Research into post systems has continued to develop systems that are biocompatible, preserve root dentin, do not stress the root, retentive to dental cements, corrosion-resistant, and compatible with restorative materials. 
Fiber-reinforced composite root canal posts were introduced in the 1990's as an alternative. The biomechanical properties of these have been reported to be close to those of dentin.  Teeth restored with these posts are found to resist fracture propagation better than teeth restored with pre-fabricated titanium, ceramic, or cast-metal posts. 
The first fiber-reinforced composite posts were made of carbon/graphite due to their good mechanical properties. However, they are black in color and thus lack esthetic qualities. Hence, a further development led to the introduction of glass and quartz fiber posts, which were white and translucent and had thus fulfilled the high-esthetic demands, replacing the carbon-fiber posts. , Many studies concerning the mechanical properties of fiber-reinforced root canal posts have been done. Although the flexural strengths of fiber-reinforced composite posts have been shown to be relatively high, large variations are reported to be found in the flexural modulus of these fiber-reinforced posts. The present study compares the flexural strength of carbon, quartz, and glass fiber posts by means of the three-point bending test.
| Materials and methods|| |
In this study, 30 pre-fabricated posts were used and were divided into 3 groups (n = 10) based on the fiber used for manufacturing of the fiber post.
Group 1: Composipost/C-post (Bisco/RTD FRANCE) - Carbon fiber post
Group 2: Aestheti-Plus (Bisco/RTD FRANCE) - Quartz fiber post
Group 3: Para post fiber white (Coltene Whaledent) - Glass fiber post.
The carbon fiber post is made of carbon fiber of 64% volume and 36% volume Epoxy resin where the fibers are pre-tensed, unidirectional of 8 microns in diameter.  The Quartz fiber post consists of 60% volume of quartz fiber and 40% volume of Epoxy resin, and the fibers are pre-tensed, unidirectional of 8 microns in diameter. The glass fiber post consists of 42% glass fiber, 29% Epoxy resin, 29% Filler having a uni-directional fiber matrix.
All the above posts were parallel-sided, smooth surfaced with a diameter of 1.5 mm. The three-point bending test is performed to evaluate the flexural strength using Universal Testing Machine (Instron) [Figure 1]. All the posts were measured with a digital caliper with 0.01 mm accuracy before test procedure. The flexural testing of the posts was done by placing the posts in a custom-made metal mould with a span length of 6 mm. This mould was then mounted on to Instron testing machine where the test specimens were subjected to a constant load with a cross-head speed of 1 mm/min. Then, a three-point bend test was performed until the proportional limit of the posts were reached and recorded., The flexural strength is calculated using the following formula:
Flexural strength(s) =8 FL/pd 3
F = Force applied
L = Span length (6 mm)
d = Diameter of the post (1.5 mm).
| Results|| |
The results were analyzed using repeated measures of ANOVA and Turkey's pair-wise comparison. The comparative chart showing flexural strength values of all groups was listed in [Table 1]. A P value less than 0.01 was considered as significant. Quartz fiber posts showed higher flexural strength when compared to glass and composite-reinforced fiber posts, which was statistically significant. The mean flexural strength values of group II (Quartz fiber posts) were statistically higher (P < 0.01) than group I (Carbon fiber) and group III (Glass fiber) posts [Table 2]. The mean flexural strength values of group II (Quartz fiber posts) were statistically higher (P < 0.01) than group I (Carbon fiber) and group III (Glass fiber) posts [Table 3].
|Table 1: Comparative chart showing flexural strength values of all groups |
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|Table 3: Pair-wise comparison of groups by Tukey's multiple comparisons |
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| Discussion|| |
The endodontic restoration becomes a challenging task for the clinician due to extensive loss of coronal tooth structure owing to trauma, caries, restorative and endodontic procedures. The restoration of these teeth requires the use of a post and core as individual units or as abutment supports for fixed or removable restorations in a predictable long-term manner. ,,,,
A post is defined as the segment of restoration inserted into the root canal to aid in the retention of the core component. It is a rigid material placed in the root canal of the tooth. The main function of the post is to anchor the post and core complex within the radicular portion of the remaining tooth. , The post doesn't strengthen the tooth; to the contrary, the tooth is weakened if dentin is sacrificed to place a larger diameter post.  The post should have the following properties:  (A) Provide maximum protection to the root, (B) Have adequate retention between the roots, (C) Provide maximum retention of the post and core, (D) Should have pleasing esthetics. (E) High radiographic visibility, (F) Easy irretrievability, (G) Biocompatibility.
A core can be defined as a restorative material placed on the coronal portion of the tooth or can be thought of as a coronal extension of the post. Its main function is to provide visible and accessible platform for improving the retention as well as to strategically manage the transfer of forces from the final restoration. ,
Posts can be divided into two main groups depending on the manufacturing process as: (a) Custom-made, (b) pre-fabricated. The cast metal post and core have been the traditional, time-honored method of restoring endodontically treated teeth. Metal posts are commonly used because of their favorable physical properties and excellent bio-compatibility. Unfortunately, their metallic color leads to a grayish discoloration of the root and consequently of the gingiva (Paul. 1998).  This can be a disadvantage in anterior teeth. Certain other disadvantages of metal posts include frequent dislodgement and root fractures. Hence, to solve these problems, several types of non-metallic, esthetic, posts made of different fiber-reinforced composite systems have been proposed recently.
In 1990, Duret et al. reported the use of a non-metallic material for the fabrication of posts based on the principle of carbon-fiber reinforcement. These fiber-reinforced posts showed good mechanical properties with modulus of elasticity similar to that of dentin. ,,
Fiber-reinforced composite materials owe their mechanical properties not only to the characteristics of fiber and matrix but also to the strength of bond between these two components and the geometry of reinforcement, such as fiber length, orientation, and concentration. The addition of fibers to a polymer matrix leads to a significant increase in fracture toughness, stiffness, and fatigue resistance of the material. Since fibers represent the stiffer component in a post, as compared to the resin matrix, the posts that exhibit higher fiber loading would be expected to yield a greater fracture resistance than those with lower fiber densities. ,
The bio-mechanical properties of the fiber-reinforced composite posts are responsible for the success of their use in post-endodontic restorative treatment. The flexural properties of these fiber posts are responsible for preventing root fractures. Flexural strength can be defined as the force/unit area at a point of fracture of a test specimen subjected to flexural loading. 
The bending ability of a material is a function of the modulus of elasticity and the cross-sectional area of the material being tested (Deutsch, 2003).  Fiber-reinforced posts are able to absorb high impact without fracturing the tooth. This is said to be a direct result of their flexibility. A force applied to a metal post is said to result in a higher incidence of root fracture, than if the same force was applied to a non-metallic fiber-reinforced post (Musikant et al., 2000). 
In metal posts, stress concentrations may occur in the cervical area, leading to vertical fractures. These stresses may be transferred to the apex of the post, resulting in horizontal root fractures (Musikant et al., 2003).  The greater the transmission of forces to the remaining natural tooth, the greater is the likelihood of subsequent root fracture and thus, restorative failure.
Another important factor is whether the fibers are silanized prior to embedding in the resin matrix; it can affect both the resistance of these fiber posts to the fatigue tests and the structural integrity of these posts. Good interfacial bonding ensures load transfer from the matrix to the fibers and is a primary requirement for effective use of reinforcement properties. ,,, Many studies concerning the mechanical properties of fiber-reinforced composite root canal posts have been done wherein the flexural strengths of fiber-reinforced posts have shown to be relatively high.
The findings of the present study are consistent with the results of the study done by Mannocci et al. (2001).  They compared the flexural strength of carbon-fiber, quartz fiber, glass fiber, and silica fiber-reinforced composite posts in different storage conditions. Results showed that quartz-fiber showed greater flexural strength values than any other groups in any storage condition.
Graziela and Renata (2005)  compared the flexural strengths of carbon-fiber, glass-fiber, and quartz-fiber posts. The flexural strength test was done by subjecting the samples to a three-point bend test in an Instron testing machine. The results showed that quartz fiber posts were superior, showing higher flexural strengths than other fiber-reinforced composite post systems.
In another study, Lassila et al. (2004)  evaluated the flexural properties of five commercially available fiber-reinforced composite posts such as the Snowpost, Carbon post, Parapost, C-post, Glassir, Carbonate, and continuous unidirectional glass fiber composite, shaped in form of a post as control. Results showed that carbon-fiber posts have higher flexural strength values than glass-fiber posts.
Frank Seefeld et al. (2007)  studied the resistance to fracture and structural characteristics of 8 different fiber-reinforced post systems with glass and quartz fiber posts. The flexural strength was calculated by subjecting the test specimens to a three-point bend test until the posts fractured. The results showed flexural strength of DT light post, DT white posts (Quartz-fiber) to have a statistical difference when compared to other test groups. Bae et al. (2001)  studied the flexural properties of an elastic modulus of composite resin with and without reinforcing fibers and evaluated the reinforcing effect of various fibers. A polyethylene fiber (Ribbond), a polyaramid fiber (fiber flex), and three glass fibers (fibrekor, Glasspan, vectris) were used to reinforce the flexural strength of test specimens. Glass fibers were effective in reinforcing elastic modulus. Unidirectional glass and polyaramid fibers were effective in reinforcing both flexural strength and elastic modulus of composite resin.
Malferrari et al. (2003)  studied the acceptability of quartz-fiber posts (Aestheti-Plus) by evaluating 180 endodontically treated teeth restored with Aestheti-Plus posts, composite core, and a final restoration by all ceramic or metal ceramic crowns over a period of 30 months. The patients were re-evaluated at regular intervals of 6, 12, 24, and 30 months; follow-up showed one cohesive failure involving a margin of the composite core and two adhesive fractures. The failure rate was 1.7% over 30 months, and it was successful to replace the restoration in all failed cases.
The flexural strength of the unidirectional and braided fibers was found to be effective, in three-point bend test, because the load is applied only in one direction. Therefore, it is natural that unidirectional fiber perpendicular to the load is superior to the fibers of any other direction. Due to the different elastic modulus of glass, silica fibers, and matrix composites, stresses normally develop at the interface between the fibers and the matrix and propagate along the surface of the fibers when the posts are loaded. Therefore, it can be assumed that not only an increase of the fiber/matrix ratio but also an increase of the total interface area will lead to a higher elastic modulus and a higher stiffness. ,
The above results clearly elucidate and support the results of this study, which prove that the quartz fiber posts have a greater flexural strength. But, considering the direction of forces acting in-vivo, further studies need to be done to simulate the complexity of the functional loads in the oral environment.
| Conclusion|| |
Within the limitation of the present study, it may be concluded that the quartz-fiber posts had higher flexural strength than other fiber-reinforced composite posts. This property of fiber-reinforced composite posts makes them more resistant to fracture under the effect of masticatory and/or parafunctional forces. Further scope of this study lies in the evolution and evaluation of various other materials used for post and core preparation, which have modulus of elasticity in harmony with that of dentin and a near-natural esthetic appearance.
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[Table 1], [Table 2], [Table 3]