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Table of Contents   
ORIGINAL ARTICLE  
Year : 2019  |  Volume : 22  |  Issue : 4  |  Page : 376-380
A comparative evaluation of fracture resistance of endodontically treated premolar teeth reinforced with different prefabricated and custom-made fiber-reinforced post system with two different post lengths: An in vitro study


1 Department of Conservative Dentistry and Endodontics, Maharishi Markandeshwar College of Dental Sciences and Research, Mullana, Ambala, Haryana, India
2 Department of Conservative Dentistry and Endodontics, Vishnu Dental College, Bhimavaram, Andhra Pradesh, India

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Date of Submission11-Feb-2019
Date of Decision18-Mar-2019
Date of Acceptance10-Aug-2019
Date of Web Publication07-Nov-2019
 

   Abstract 

Aims: The aim of this study is to determine the mean failure load for each postsystem and the relationship between post lengths with the mean failure loads.
Materials and Methods: Ninety single-rooted decoronated mandibular premolar teeth were endodontically treated and randomly assigned to three groups with respect to their post length (2/3rd and ½ of the root length). The first two groups were randomly divided into four subgroups, restored with the following postsystem: polyethylene-woven fiber posts, glass fiber tape, prefabricated carbon, and glass fiber posts. A composite core with no post served as control. All posts were cemented using dual-cure resin cement, and the same was used for core buildup. The standard cores were formed in each group. All the specimens were tested in a universal testing machine, and the load was calculated.
Results: One-way analysis of variance (ANOVA) showed that prefabricated glass fiber post had significantly highest fracture resistance when compared to other prefabricated and custom fiber-reinforced composite posts. Two-way ANOVA demonstrated no significant difference among the post lengths.
Conclusion: The results of this study showed that glass fiber posts showed higher fracture load, but post length did not significantly increase the fracture resistance of endodontically treated teeth.

Keywords: Endodontically treated teeth; fiber-reinforced composite post; fracture resistance; post length; resin cement

How to cite this article:
Thakur A, Ramarao S. A comparative evaluation of fracture resistance of endodontically treated premolar teeth reinforced with different prefabricated and custom-made fiber-reinforced post system with two different post lengths: An in vitro study. J Conserv Dent 2019;22:376-80

How to cite this URL:
Thakur A, Ramarao S. A comparative evaluation of fracture resistance of endodontically treated premolar teeth reinforced with different prefabricated and custom-made fiber-reinforced post system with two different post lengths: An in vitro study. J Conserv Dent [serial online] 2019 [cited 2019 Nov 18];22:376-80. Available from: http://www.jcd.org.in/text.asp?2019/22/4/376/270500

   Introduction Top


The restoration of endodontically treated has been a challenge as these teeth loses significant part of tooth structure due to caries, previous restorative procedures, from endodontic access cavity preparation or due to loss of moisture supplied by dentin, which makes them weak. The restoration of such teeth is accomplished by using post and core, to prevent further destruction and provide retention for the core, before a crown or a fixed partial denture can be placed.[1]

Custom cast and prefabricated metal post are rigid, lack bonding ability, and modulus of elasticity was different from the tooth structure which induced stresses and results in root fracture; therefore, fiber-reinforced composite (FRC) posts have been preferred choice.[2] The FRC-posts contain a high percentage of continuous reinforcing fibers embedded in a polymer matrix of epoxy resins or others polymers with a high degree of conversion and highly cross-linked structure.[3],[4]

The FRC posts are available as prefabricated and chair-side custom-made FRC posts. The prefabricated FRC posts are made of a high volume percentage of continuous unidirectional reinforcing fibers in finally polymerized matrix. The prefabricated FRC posts are made of carbon, glass, and quartz fiber. Chair-side custom-made FRC posts use non-preimpregnated polyethylene fibers or glass fibers to form posts.[5]

With respect to post fit within the root canal system, custom-made polyethylene fibers and intertwined glass fibers allows adjustment of postgeometry to the anatomy of the root canal rather than adjustment of the root canal to the geometry of prefabricated posts. Furthermore, post and the restorative coronal segment can be fabricated using similar materials.[6],[7]

Various guidelines have been recommended regarding post length, which includes: (1) the post length should be equal to or longer than the clinical crown; (2) the post should end halfway between crestal bone and root apex; (3) the post should be half, two-third or four-fifth the root length; and (4) the post should be as long as possible without disturbing the apical seal. These statements were related to cast metal posts, which have high modulus of elasticity and only frictional retention in the root canal. The use of resin cements have improved the retention of fiber posts, but as we go apically the quality of bonding diminishes, and hence, increased post length may not provide any increase in predictable bonding area. Further, when the remaining root is curved or short it is not always possible to use longer posts.[8] As no consensus exists, so post length within the root canal still remains to be controversial.

Hence, the aim of this laboratory study was to compare the fracture resistance of endodontically treated teeth restored with prefabricated and custom-made FRC postsystems at two different postlengths.


   Materials and Methods Top


A total of 90 extracted human mandibular first premolars with single root were selected and stored in 0.9% saline solution. The teeth with visible cracks, caries, and developmental anomalies were excluded from the study. Teeth were decoronated horizontally at the cementoenamel junction (CEJ) with diamond disc at slow speed handpiece under water-cooling water cooling in order to standardize the length at 15 ± 1 mm.

Cleaning and shaping was completed using the stepback technique to ISO k-file size number 35 and 3% sodium hypochlorite as irrigant. The canal was obturated with laterally condensed gutta-percha and a resin sealer (AH26, Dentsply Maillefer, Ballaigues). Canal orifices were sealed with cavit and stored for 48 h in normal saline. The gutta-percha was removed using #2 gates Glidden drill (Manni Tochigi-Ken/JAPAN) to remove ⅔rd and ½th of gutta-percha apical to CEJ from each filled canals. The post-space preparation was standardized through flaring with No. #5 pesso reamer (Manni Tochigi-Ken/JAPAN). All posts were placed to the total depth of the prepared post spaces, i.e., to ½th or ⅔rd the root length and handled according to the manufacturers' instructions.

Ninety prepared roots were then randomly divided into two experimental groups with eight subgroups and one control group with ten samples each [Figure 1].
Figure 1: Schematic representation of experimental groups. *Polyethylene-woven fiber

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Post placement

Polyethylene-woven fiber posts

Custom-made polyethylene-woven fiber (Ribbond, Ribbond Inc. Seattle, WA, USA) was cut in excess of twice the post space so that 3 mm of post was available above the root canal to retain the composite core. The fiber was cut with the special scissors made of hardened stainless steel blades provided by the manufacturer to predetermine length as these scissors can cut fibers without leaving stray uncut fibers. Polyethylene-woven fiber was saturated with Ribbond wetting resin (Ribbond Inc., Seattle, WA, USA), was than formed into “V” shaped and introduced into the canal, leaving excess “ear” out of the canal. It was further condensed tightly into the canal space using an endodontic plugger.

Custom-made glass fiber post

Custom-made glass fiber (Angelus Rua Goias, Londrina, PR, Brazil) was cut excess of post space so that 3 mm of fiber is available above the root canal to retain the composite core. This predetermined fiber was then placed into the canal and further adapted to the cavity by gently pressing with the plugger.

Prefabricated posts

Prefabricated carbon and Glass (Reforpost, Angelus, Londrina, Brazil) fiber post was cut with a diamond disc to the desired length with excess of 3 mm to retain core.

Postcementation

Prior to cementation, the canals were rinsed with water for 30 s and then dried with paper points. Etching was done with 37% phosphoric acid for at least 20 s followed by rinsing with water for 15 s. Single component total-etch (SDI, Australia) was applied to then prepared canal to saturate all the internal surfaces. It was then gently blow-dried to keep surface moist and light cured for 10 s. Cementation of posts were done with Luxa core Z-dual-cure resin cement (DMG, Hamburg) according to the manufacturer's instructions. The control group had no coronoradicular reinforcement and thus, root canals were not prepared for post space, 2 mm of gutta-percha was removed from the root canal space and core buildup was done.

Core buildup

For standardization of coronal portion, in each group, crown portion was made using the prefabricated core formers (Parapost Paraform No. #5, Coltene Whaledent) of lower premolar shape. Here, core buildup was intentionally carried out using prefabricated core formers, as they duplicate the crown morphology of the mandibular premolars, still it has a limitation of not being able to replicate the exact crown inclination.

Fracture resistance

The root portion of the specimen was wrapped twice with the polytetrafluoroethylene tape to simulate 0.2-mm thickness of periodontal ligament. All the specimens were embedded in ISO type 4 die stone at a distance of 2 mm from buccal CEJ. The specimens were submitted to the fracture resistance testing using (Hounsfield universal testing machine, S-series). The compressive load was applied on the buccal surface at 90° and crosshead speed of 1 mm/min to the long axis on a universal testing machine. Fracture strength value was recorded in Newton's (N). Failure threshold was defined as the point at which the loading force reached a maximum value either by fracturing the root, bending the post, or debonding the cement.

Statistical analysis

One-way and two-way analysis of variance (ANOVA) was used to analyze the data for significant differences. Bonferroni adjustment test was used for intergroup comparison. Significance for all statistical tests was predetermined at P < 0.05.


   Results Top


The mean and standard deviation of failure load are listed in [Table 1]. The effect of post type and post length on the failure loads using two-way ANOVA is shown in [Table 2].
Table 1: The Mean and Standard deviation of failure loads for all groups

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Table 2: Two-Way ANOVA based on post length and post type

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The highest failure load was found with prefabricated glass fiber post at ⅔rd postlength (250.33 ± 15.40 N). This group had significantly higher load compared to other groups. The composite core control group (with no post) had the lowest fracture load (57.34 ± 14.03 N) and was statistically different from other groups (Group I and II). The type of post placed (P < 0.001) had an effect on fracture resistance, but the length within the root (P = 0.0061) did not significantly influence the failure loads of the groups.


   Discussion Top


A comparative analysis of fracture resistance values between the control group and experimental group showed a high statistical significance (P < 0.001); hence, the placement of FRC post had a direct influence on the fracture strength of the endodontically treated teeth. It could be assumed that posts were able to transmit part of the loading stresses to the prepared root canals, thus distributing the load over a bigger surface area of the tooth structure resulting in higher fracture loads. The results of this study are consistent with Kantor and Pines, Robbins, who recommended post-and-core to increase the fracture resistance.[9],[10] The results, however, are in contrast with the other studies which stated that endodontically treated teeth without coronoradicular reinforcement demonstrated higher fracture load.[11],[12]

Higher mean load (N) is recorded in Group I-C followed by Group II-C, Group II-D, Group I-D, Group I-A, Group I-B, Group II-B, and Group II-A, respectively. The difference in mean load between the groups was found to be statistically significant (P < 0.001). A similar result was obtained by Newman et al. and Torabi and Fattahi in their study where they compared custom post with prefabricated FRC posts and found lower fracture resistance of custom-made FRC posts.[2],[11]

In the present study, for standardization, parallel posts space was prepared which probably deprived additional mechanical retention provided by small undercuts present in the canal therefore, prefabricated serrated parallel side posts (both carbon and glass fiber post) were used, which provided additional retentive features, as they get embedded into the resin luting cement and resist dislodging forces on pulling.[8],[13]

Another important factor concerning clinicians, with the increasing use of fiber and resin reinforced posts, is determining the proper length of the post. Early studies revealed that longer metal posts reduce stresses in the coronal third of restored roots compared to shorter posts. Accordingly, it has been suggested that post length should be at least equal to the crown height or two-thirds of the root length to facilitate even stress distribution and provide resistance to occlusal loads.[14],[15] In contrast, few studies have disputed the necessity of increasing metal post length, since the differences in fracture resistance of teeth with posts of various lengths were not significant. In addition, increasing post length is usually accomplished with additional root wall enlargement, which could decrease the root strength.[16],[17] Hence, there is still no definite consensus regarding the proper post length for metal posts and therefore these criteria's regarding post length cannot be used for nonrigid posts. Hence, post length was one of the parameters that was studied in the present study, and as the length of post increased the fracture resistance value also increased and lower fracture resistance was observed with shorter post. But no statistical difference was observed between two post lengths and a similar result was observed in a study performed by Nissan et al. and Chuang et al. who reported no significant difference in retention of posts at different lengths.[18],[19] Mode of fracture was not the focus of this study, but all samples showed favorable fracture, similarly to other studies on FRC posts.[2],[20]

Ferrario et al. assessed the bite force of teeth from 52 healthy young adults and reported that single-tooth bite forces ranged from 178 to 291 N in premolar teeth.[21] In the present study, fractures occurred under very high loads, which do not occur in clinical situation. Therefore, it is possible to infer that under normal conditions, the four systems tested in this analysis would present a favorable prognosis. In this study, resin sealer was selected to circumvent the potentially detrimental influence the eugenol-containing root canal sealers have on adhesion between root dentin, luting agent, and fiber posts.[22] Dual-cure resin material was used for both post cementation and core buildup to reduce the variability at the tooth core interface resin and creates a monoblock effect, which further reinforces the intraarticular tooth structure.[23]

Placement of a crown ferrule is an important factor in increasing the fracture resistance of teeth. However, in this study, ferrules and crowns were eliminated from methodology as these features could introduce many more variables that could complicate interpretation of the results of load testing, as restoration with crowns, can cancel out the difference among various postsystems. Hence, these two variables were not considered in this experimental study.[24]

The polytetrafluoroethylene tape was used to simulate periodontal ligament as rigid reinforcement of the root is not found in nature and may alter the strength of the roots along with the pattern of failure.

The perpendicular angle of loading was used in this study because it has been shown to be the most traumatic to a post-and-core system and a likely manner in which many systems fail. The crosshead speed used in this study was within the range reported in the literature for static loading tests.[25]

Methodologically, the limitation of this study was that static loading testing was used to evaluate fracture resistance. Therefore, further research is suggested, using dynamic loading combined with thermocycling as well as further long-term follow-up in vivo survival studies of teeth restored with fiber-reinforced posts.

Based on this study, glass fiber posts showed higher fracture load, but post lengths did not significantly affect the fracture resistance of endodontically treated teeth. Hence, it can be concluded that FRC post and core shows a viable alternative to both custom cast and prefabricated metal posts.


   Conclusion Top


Hence, in clinical scenario, selecting a restorative option that allows higher fracture load and better stress distribution would implicate better clinical performance. Therefore, the higher fracture strength values observed for the FRC post restorations, the favorable restorable fractures associated with these restorations is a better option compared to rigid root canal reinforcement.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

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Adanir N, Belli S. Evaluation of different post lengths' effect on fracture resistance of a glass fiber post system. Eur J Dent 2008;2:23-8.  Back to cited text no. 1
    
2.
Torabi K, Fattahi F. Fracture resistance of endodontically treated teeth restored by different FRC posts: An in vitro study. Indian J Dent Res 2009;20:282-7.  Back to cited text no. 2
[PUBMED]  [Full text]  
3.
Maccari PC, Cosme DC, Oshima HM, Burnett LH Jr., Shinkai RS. Fracture strength of endodontically treated teeth with flared root canals and restored with different post systems. J Esthet Restor Dent 2007;19:30-6.  Back to cited text no. 3
    
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Robbins JW. Restoration of the endodontically treated tooth. Dent Clin North Am 2002;46:367-84.  Back to cited text no. 10
    
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Fernandes AS, Dessai GS. Factors affecting the fracture resistance of post-core reconstructed teeth: A review. Int J Prosthodont 2001;14:355-63.  Back to cited text no. 14
    
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Kishen A, Kumar GV, Chen NN. Stress-strain response in human dentine: Rethinking fracture predilection in postcore restored teeth. Dent Traumatol 2004;20:90-100.  Back to cited text no. 17
    
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Nissan J, Dmitry Y, Assif D. The use of reinforced composite resin cement as compensation for reduced post length. J Prosthet Dent 2001;86:304-8.  Back to cited text no. 18
    
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Kumar RV, Shruthi C. Evaluation of the sealing ability of resin cement used as a root canal sealer: An in vitro study. J Conserv Dent 2012;15:274-7.  Back to cited text no. 22
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23.
Kim YH, Lee JH. Influence of modification in core building procedure on fracture strength and failure patterns of premolars restored with fiber post and composite core. J Adv Prosthodont 2012;4:37-42.  Back to cited text no. 23
    
24.
Assif D, Bitenski A, Pilo R, Oren E. Effect of post design on resistance to fracture of endodontically treated teeth with complete crowns. J Prosthet Dent 1993;69:36-40.  Back to cited text no. 24
    
25.
Nam SH, Chang HS, Min KS, Lee Y, Cho HW, Bae JM. Effect of the number of residual walls on fracture resistances, failure patterns, and photoelasticity of simulated premolars restored with or without fiber-reinforced composite posts. J Endod 2010;36:297-301.  Back to cited text no. 25
    

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Dr. Anamika Thakur
House No 811-C, Trishla City, Zirakpur - 140 603, Punjab
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JCD.JCD_52_19

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