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Year : 2014  |  Volume : 2  |  Issue : 3  |  Page : 125-129

Comparison of the effect of three different post systems on root fracture

1 Department of Endodontics, Faculty of Dentistry, Sifa University, Izmir, Turkey
2 Department of Prosthodontics, Faculty of Dentistry, Sifa University, Izmir, Turkey
3 Department of Pediatric Dentistry, Faculty of Dentistry, Sifa University, Izmir, Turkey
4 Department of Prosthodontics, Faculty of Dentistry, Selcuk University, Konya, Turkey

Date of Web Publication29-Oct-2014

Correspondence Address:
Evren Ok
Department of Endodontic, Faculty of Dentistry, Sifa University, Izmir
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2321-4619.143595

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Aim: The aim of this in vitro study was to compare the effect of three different post systems cemented with different systems on root fracture. Materials and Methods: Seventy-five extracted human maxillary canines with single and straight roots were used in this study. After the crowns were removed, root canals were prepared with Reciproc R50 files. Smear layer of roots were removed using 17% Ethylenediaminetetraacetic acid (EDTA) followed by 5.25% NaOCl and distilled water. All the root canals were filled with cold lateral compaction technique using AH Plus root canal sealer and gutta-percha. Samples were stored at 37°C and 100% humidity for 1 week and then post space was prepared using fiber post drills. The roots were then randomly divided into five groups according to the luting cements and post systems: negative control, positive control, glass fiber post [Unicore® (Ultradent, Salt Lake City UT, USA)] + composite core [Grandio SO (Voco GmbH, Cuxhave, Germany)], glass fiber post [Unicore® ] + Rebilda® post-core system, individual cast post core. A load was applied on the crowns of all teeth at 135° to their long axis until fracture occurred. Data were analyzed using one-way analysis of variance (ANOVA) and post-hoc Tukey tests. Results: There was statistically significant difference between the groups. According to the post-hoc Tukey test, cast post core (1949.35 + 316 N) showed statistically significantly higher fracture resistance than all the groups except Unicore® + Rebilda® post-core systems (1722.48 + 144.0 N). Conclusion: Fiber post core system which is an alternative to cast post core systems increased the fracture resistance of the canines with root canal treatment. While irrepairable catastrophic fractures might be seen in cast post-core systems, separations between composite resin core, and root interfaces might be seen in teeth restored with fiber post-core systems.

Keywords: Cast post-core, fiber post-core, root fracture, self-adhesive resin cement, vertical root fracture

How to cite this article:
Ok E, Dilber E, Altunsoy M, Kalkan A, Demir N. Comparison of the effect of three different post systems on root fracture . J Res Dent 2014;2:125-9

How to cite this URL:
Ok E, Dilber E, Altunsoy M, Kalkan A, Demir N. Comparison of the effect of three different post systems on root fracture . J Res Dent [serial online] 2014 [cited 2020 Nov 30];2:125-9. Available from: http://www.jresdent.org/text.asp?2014/2/3/125/143595

  Introduction Top

Post-core systems are widely used for the rehabilitation of teeth with endodontic treatment which incurred excessive material loss. [1],[2] Vertical root fractures are mostly occured on post-applied teeth with endodontic treatment. [3] The 40-51.2% of the vertical root fractures are the teeth with canal therapy. [4],[5],[6],[7] Root fractures occur at the area where the tension stress is at the most critical values at the root of the tooth [8] and they are influenced by the post type that is applied to the tooth. [9] In the literature, it is stated that the cast posts have adverse effects on fracture resistance of the root as well [10],[11],[12],[13],[14] and many researchers state that especially during the placement of the post; due to the stress intensity occurred at the root, these cast posts cause root fractures. [15],[16],[17]

Restorations supported with cast post cores result in radicular fractures at teeth roots when they are compared with prefabricated posts. [18] According to many studies, as for the fiber post application on teeth with canal treatment, it increases the fracture resistance of the teeth substantially by exposing better stress dispersion on roots of teeth. [15],[19],[20] The proximity of elasticity module of fiber posts to elasticity module of dentin is an advantage. Moreover, coronal restoration functions as a mono-block structure by forming a homogeneous completeness with fiber post, resin cement, and composite material. It is thought that the mono-block structure decreases the fracture risk to minimum levels. [21]

Fracture resistance of restoration increased with post is directly related with the factors such as post length, post diameter, post design, conformity of post, core material, and adhesive cement. [22] Cementation with resin cements are mostly applied for the reinforcement of fiber post's unity and strength. Selection of an appropriate material and system at the restoration of canal-treated teeth with post core increases the lifetime of tooth structures and provides a long functioning duration.

The aim of this in vitro study was to compare the effect of various post and core systems cemented with different systems on root fracture. The null hypothesis is that the application of different post-core systems to canal treated canine teeth has no effect on fractural resistance.

  Materials and methods Top

Preparation of the Samples

Seventy-five single-canalled and single-rooted maxillary canine teeth were used in this in vitro study. After removing the residues on the teeth, they were stored in 0.1% sodium azide solution. The crowns of the teeth were removed by a diamond bur under water cooling in a way that the length of the roots remained 18 mm. The mesiodistal (MD) and buccolingual (BL) diameters of the teeth were measured by a digital measurement device (Mitutoyo Co., Tokyo, Tokyo, Japan) for standardization. Their weights were measured in a precision scale and the data were evaluated statistically. The root canals were prepared using Reciproc R50 rotary instruments (VDW, Munich, Germany), smear layer of roots were removed using 17% Ethylenediaminetetraacetic acid (EDTA) followed by 5.25% NaOCl and distilled water, and the canals were dried with paper points. All the root canals were obturated with cold lateral compaction technique using epoxy resin-based sealer [AH Plus sealer (Dentsply DeTrey, Konstnaz, Germany)] and gutta percha. Then the samples were stored at 37°C at 100% relative humidity for 1 week to allow the sealer to set. The roots were divided into five groups as listed below; (n = 15).

Negative control (Group NC): The root canals were prepared and left empty.

Positive control (Group PC): The root canals were filled with gutta percha and AH Plus sealer.

Glass fiber post [Unicore® ] + composite resin core [Grandio SO] (Group GCR)

Post space (5000 RPM) was prepared in 2/3 of the root canal length (1.75 mm diameter of the coronal section and 1.5 mm of the apex section) using the bur of the glass fiber posts (Unicore Ultradent, Salt Lake City UT, USA). The post was adapted using a diamond disc bur enough to support the core structure. After conditioning the prepared canals and the glass fiber post with 37% phosphoric acid (3M Espe, Seefeld, Germany), they were cleaned by air water spray, and then the canals were dried by paper points (80). Due to the instructions of the fiber post manufacturer, silane was not applied. After washing and drying the canal, the glass fiber post were cemented with dual cure resin cement (Bifix, QM, Voco GmbH, Cuxhaven, Germany), and the cement residues were removed. Then, they were polymerized using light-emitting diode light curing unit (LED) (Bluephase; Ivoclar Vivadent AG, Schaan, Lichtenstein) from 2 mm distance for 20 seconds. The coronal section of the teeth was restored with Grandio SO light cure composite resin (Voco GmbH, Cuxhave, Germany) by using layering technique, it was polymerized by applying light from 2 mm distance for 40 seconds, and tooth form was made up as prepared canine.

Glass fiber post [Unicore® ] + Rebilda® post-core system (Group GR)

The procedures in the previous group were performed during the preparation of the canals and posts. After preparing the canals available for post cementation and applying the post, self-etch adhesive resin system (Futurabond DC, Voko, Cuxhaven, Germany) was used. Finally, the posts were cemented with dual cure resin cement (Rebilda, Voko, Cuxhaven, Germany) to the root canals. They were polymerized using LED (Bluephase; Ivoclar Vivadent AG, Schaan, Lichtenstein) from 2 mm distance for 20 seconds. The core structure was provided with the same resin cement and tooth form was made up as prepared canine.

Individual cast post core (Group I)

The same procedure which was performed in the previous groups during the preparation of the canals. Then, impression was taken from the root canals with C-type silicone based impression material (Zeta Plus, Zhermack, Badia Polesine Rovigno, Italy) with the help of the headstrom canal instrument. Post-core modelling was completed on the plaster model in the dental laboratory and later post core was fabricated from cast cobalt chrome [Figure 1]. After applying the cast post to the root canals, the post was cemented with dual cure resin cement (Bifix QM) and polymerized using LED for 20 seconds. All samples were stored for 1 week for the complete setting of the resin cement.
Figure 1: Individual cast posts

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Fracture strength test

The samples were embedded in the trapezoid-shaped transparent acrylic blocks whose bases were flat and tops were 45° angled, perpendicularly to the surface. A notch was opened to the core parts of the teeth 2 mm below the incisal. The universal testing machine (Shimadzu Corporation, Kyoto, Japan) was used at the speed of 0.5 mm/min by a tip which was inserted into the groove that was opened 135° angle between the long axis of the root and the tip of the device [Figure 2]. The values measured at the moment of fracture were recorded in Newton (N). The samples were examined under a steromicroscope with x20 magnification for the evaluation of the fracture types.
Figure 2: Universal test device

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Statistical analysis

The statistical analysis of the data was performed using one-way analysis of variance (ANOVA) and post hoc Tukey tests (P = 0.05). The MD, BL diameters, and the weights of the teeth which were used in the study were evaluated by the Kolmogorov-Smirnov test for standardization. Whether there was a difference between the dimensions of the teeth was evaluated with one-way ANOVA and post hoc Tukey HSD tests.

  Results Top

The MD and BL sizes, weights, and fracture strength values of the groups were given in [Table 1]. The results of the statistical analysis confirmed the standardization according to the MB and BL diameters and weights. The lowest fracture resistance (466.04 + 34.9) occurred in the group NC while the highest fracture resistance (1949.35 + 316.0) occurred in the group I. Groups PC and NC showed lower fracture resistance than the other groups (P < 0.05). Group I showed higher fracture resistance than the groups GCR, PC and NC (P < 0.05). While observing catastrophic fractures (vertical, oblique or horizontal type) in group I, group GCR, and group GR, fracture was observed in the cervical third of the crown.
Table 1: MD and BL sizes, weights, and fracture strength values of the groupsa

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  Discussion Top

This study compared the fracture resistance of the canal treated teeth which were supported by cast and glass fiber post-core systems. The null hypothesis was rejected because the different post-core systems affected the fracture resistance of the teeth.

The rigid cast posts which have high elasticity modulus did not absorb the energy under stress or transmitted oblique compressive forces to the dentin tissue which had less rigid structure. This condition increases the fracture risk of the root [23] . It was also stated by Hayashi et al.[23] that the root fracture of the teeth which were restored with cast post depended on the hardness of the post. In our study, the fracture occurred mostly obliquely and in the middle third.

Pereria et al.[18] applied four different post systems (cast post core, pre-fabricated stainless steel, carbon fiber, and glass fiber post) to the same root length of canine teeth and examined their fracture resistance. It was identified that the cast post showed higher resistance (750.6 N) according to the glass fiber post (461.35N), while catastrophic fracture was observed in all the teeth in the cast post group, root fracture was not observed in the other groups. Franco et al.[24] compared the fracture resistance of the cast posts (2/3) and fiber (1/3,1/2. 2/3) posts which were applied in different length and as a result they concluded that cast post (634.94 N) showed a higher fracture resistance value than the fiber posts (200.1, 212.17, 236.08 N). Verrisimo et al.[25] examined the three-dimensional finite element analysis and the in vitro stress distributions of the cast and fiber posts and it was determined that the glass fiber posts showed more homogenous stress distribution while the cast post created higher stress in the post-dentin interface.

In a study, Franco et al.[24] examined 40 maxillary canine teeth in terms of fracture resistance in four different groups. Gold cast post core was used in the control group and in the other groups composite resin core structure was applied to the glass fiber post which were in different lengths. Similarly to our study, even if the samples with the cast post core had high compressive resistance in all the samples catastrophic fracture was observed as in all the other studies. Observing very rare catastrophic root fracture in the fiber reinforced composite posts; the major clinical complication is the failure of the adhesive. Failure was observed in the joints of the composite resin core and the root in the sample to which glass fiber post was applied. The failure of the glass fiber post occurs due to the failure between the core structure and the remaining structure. This failure is a repairable failure like it is mentioned in many studies. [26],[27]

Cast post-core structures had higher elasticity module and rigidity in the control group, the coronal walls provided higher adhesion and stability to crown. However, the core structure provides more stress transmission from the crown to the post-core structure and to the remaining root dentin. When this stress exceeds the withstanding resistance, the root fracture occurs. Giovani et al.[28] studied on two groups (cast post core and glass fiber post) after they applied canal therapies on 60 canine teeth. Till the fracture was observed, the increasing compressing load was exerted. Alike to our study, glass fiber posts contributed higher fracture resistance to endodontically treated teeth than the cast metal post contributed.

The most important limitation of this study is a test method that imitates the in vivo clinical conditions was not applied. The other limitations of this study are the following: a wet condition that is exposed to chemical and thermal changes in oral environment and the masticatory forces could not be provided, only the maillary canine teeth were evaluated and cementations were achieved by finger press. The study designs where in periodontal ligaments are simulated and further studies should be done for the comparison of post-core systems.

  Conclusions Top

Within the limitations of this study, different fiber post-core systems as an alternative to the cast post-core systems enhanced the fracture resistance of canal therapy applied canine teeth. Besides irreparable catastrophic fractures observed in the cast post core, the core structure was fractured from the cervical part of the crown in the fiber post-core group.

  References Top

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  [Figure 1], [Figure 2]

  [Table 1]


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