An In Vitro Evaluation of Fracture Resistance Strength of Different Post Systems in Endodontically Treated Teeth

Abstract

Aim:

This study aimed to evaluate the fracture resistance strength of different post systems in endodontically treated teeth.

Materials and Methods:

Freshly extracted 60 single-rooted first premolars were selected for this study. Conventional step-back technique was used to prepare a canal for all the teeth. Obturation was carried out and post space was created using a Peeso reamer. All teeth were randomly divided into three groups of 20 samples in each group: Group I, teeth inserted with prefabricated carbon posts; Group II, teeth inserted with prefabricated zirconia posts; and Group III, teeth inserted with prefabricated everStick posts. Core buildup was performed using light-cured composite resin. Compressive load required to fracture the tooth was measured using a universal testing machine.

Results:

The compressive strength of zirconia posts was highest with a mean of 796.10 ± 20.78 followed by carbon posts (628.22 ± 18.11) and lower compressive strength was exhibited by everStick posts (534.13 ± 19.98). An analysis of variance revealed a statistically highly significant difference (P < 0.005) among the different posts used, and a statistically significant difference between carbon posts vs. zirconia posts, carbon posts vs. everStick posts, and zirconia posts vs. everStick posts (P < 0.05).

Conclusion:

Zirconia posts show the maximum fracture resistance than the carbon posts and everStick posts.

INTRODUCTION

Root canal–treated teeth with less tooth structure are often restored with the crowns. In teeth with substantial hard tissue loss resulting from cavities or trauma, posts are often necessary for providing sufficient retention for the core material. Although posts have been recommended to strengthen the teeth, several investigators have cautioned that posts with inadequate resistance to rotational forces can weaken the teeth.[1]

The prime objectives of post and core procedure are to build missing coronal structure and to provide sufficient retention and resistance form to final restoration. In earlier days, custom-made post and core restoration was one of the popular methods to restore endodontically treated teeth. Later on, prefabricated posts gained importance due to reduced time and feasibility.[2]

In cases where most of the coronal portion is lost, a common method to restore such teeth is the use of a post and core, onto which a full crown is cemented.[3] The dowel is a post or other relatively rigid, restorative material placed in the root of a nonvital tooth also retaining the core. The post functions primarily to aid the retention of the restoration and to protect the tooth by dissipating or distributing forces along the tooth.[4]

The clinical decision is difficult when the situation occurs with open apices, overprepared teeth for previous post-retained restorations, caries, fracture, or internal resorption. These flared root canals with thin dentin walls may require reinforcement and restoration using dentin-bonding agents and composite, posts and cores.[5]

Hence, this study was conducted to evaluate and compare any significant difference in the fracture resistance of endodontically treated teeth restored with three different post systems.

MATERIALS AND METHODS

The present in vitro study was conducted in the Department of Conservative Dentistry and Endodontics, Sree Anjaneya Institute of Dental Sciences, Kerala, India.

For this study, freshly extracted 60 single-rooted first premolars that were free of caries and with approximately the same root length were selected. All teeth were carefully examined using a stereomicroscope under ×10 magnification to confirm that they were free of cracks.

To standardize root canal lengths for the experiment, the roots were cut to a uniform length of 14 mm. Conventional step-back technique was used to prepare a canal for all the teeth. All canals were cleaned and shaped with hand instrumentation to an ISO K-file size 30 (Dentsply, Ballaigues, Switzerland) as the master apical file to standardize all teeth. During the preparation, all canals were irrigated with 2 mL of 5.25% sodium hypochlorite solution and dried with absorbent paper points. A sealer was coated with gutta-percha points and was placed into the root canals using a lentulo spiral. Canal entrances were sealed with glass ionomer cement and teeth were stored in a saline at 4°C. All teeth were mounted in acrylic resin blocks, with the long axis of the block, midfacial extent of each tooth parallel to the long axis of the block and the midfacial extent of the cementoenamel junction located 2 mm coronal to acrylic resin. After 48 h, the gutta-percha was removed using a size 2 Peeso reamer (Mani, Japan) until a depth of 10 mm, leaving 4 mm of gutta-percha at the apex. For standardization, post spaces were perpared using size 2 Tenax post drills in all the roots.

All teeth were randomly divided into three groups of 20 samples in each group: Group I, teeth inserted with prefabricated carbon posts; Group II, teeth inserted with prefabricated zirconia posts; and Group III, teeth inserted with prefabricated everStick posts.

Core build up

Light-cured composite resin, which consists of hybrid BISGMA composite resin of particle size 2–5 mm and weight of 80%, was used for core build up.

Testing procedure

All specimens were stored in artificial saliva for 24 h prior to the mechanical testing. Compressive load required to fracture the tooth was measured using a universal testing machine. Compressive load was applied at an angle of 130° to the long axis of the tooth, at a crosshead speed of 0.5 mm/min until fracture. Load was applied to a small sphere that was placed on the occlusal surface of the prepared teeth at the long axis of the root. Fracture loads were recorded.

Statistical analysis

Statistical analysis was carried out using one-way analysis of variance followed by Tukey post hoc test; 95% confidence interval with a P value of less than 0.05 was considered to be statistically significant.

RESULTS

Table 1 depicts the mean compressive strength of different post systems before fracture. The compressive strength of zirconia posts was highest with a mean of 796.10 ± 20.78 followed by carbon posts (628.22 ± 18.11) and lower compressive strength was exhibited by everStick posts (534.13 ± 19.98). An analysis of variance revealed a statistically highly significant difference (P < 0.005) among the different posts used.

Table 1.

Assessment of mean compressive strength of different post systems

Posts	n	Mean ± SD	F value	P value
Carbon	20	628.22 ± 18.11	41.122	0.0001***
Zirconia	20	796.10 ± 20.78
everStick	20	534.13 ± 19.98

***Highly significant

Table 2 reveals the multiple comparisons between the different post systems using Tukey post hoc test. This revealed a statistically significant difference between carbon posts vs. zirconia posts, carbon posts vs. everStick posts, and zirconia posts vs. everStick posts (P < 0.05).

Table 2.

Multiple comparisons between different post systems using Tukey post hoc test

Posts	Compared with	Mean difference	P value
Carbon	Zirconia posts	−167.88	0.0001*
	everStick posts	94.09	0.008*
Zirconia	everStick posts	261.97	0.001*

*Statistically significant

DISCUSSION

Success of post and core treatment depends on case selection, type of post and core used, adhesive resin cement, and operator caliber.[6] Post restoration depends on esthetic requirements, amount of remaining tooth structure, tooth position, and functional load on tooth.[7] Posts can be classified as custom made or prefabricated, metallic or nonmetallic, flexible or stiff, and esthetic or nonesthetic types. Post and core interface is the most common site for tooth fractures. Fracture resistance of restoration with post is directly related to post design, post length, post diameter, core material, and type of cement used.[8] It has been observed that the core structure provides stress transmission from crown to the post and core structure to remaining root dentin. Root fracture occurs when this stress transmission exceeds the withstanding resistance.[9]

The first fiber posts were made of carbon fibers due to their good mechanical properties. However, they were black and thus lacked cosmetic qualities. Although the flexural strength of fiber posts has been shown to be relatively high, large variations in the reported flexural modulus of carbon/graphite fiber posts can be found.[10]

In this study, the carbon posts showed better fracture resistance than everStick posts. One study reported that a carbon fiber–reinforced post had flexural modulus values comparable to a stainless-steel post.[11] Isidor et al.[10] suggested that teeth restored with carbon fiber posts have higher fracture strengths than those with prefabricated titanium posts or cast metal post restoration. A study conducted by Chakmakchi et al.[12] showed that the teeth receiving everStick posts were associated with the highest fracture resistance (1780.30 ± 155.2) in newtons.

Zirconia has attracted the maximum attention because it has the highest flexural strength and fracture toughness of all the existing ceramics. A spontaneous phase transformation occurs internally in zirconia upon the application of an external stress, which tightens the crack tip and prevents crack propagation, leading to an increase in the fracture toughness and flexural strength. The fracture strength of the self-adhesive resin cement is less than that of zirconia, the force that fracture of the zirconia crystals will cause a subsequent fracture throughout the entire self-adhesive resin cement.[13]

In this study, zirconia posts showed maximum fracture resistance followed by carbon posts and everStick posts. This result is similar to that obtained by the study conducted by Yang et al.,[14] which stated that cast post and core had a higher failure threshold including the teeth fracture in accordance with the study conducted by Torabi and Fattahi[15] on the effect of ferrule and bonding agent on the compressive fracture resistance of post and core restorations, and concluded that a ferrule preparation can increase the fracture resistance of teeth with little remaining tooth structure. Limitations of the present study were lower sample size and thermal changes in oral environment, masticatory forces not applied, and an in vitro study.

CONCLUSION

Within the limitations of this study it is concluded that zirconia posts show the maximum fracture resistance than the carbon posts and everStick posts.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.