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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 31  |  Issue : 1  |  Page : 84-88

Push-out bond strength of four different Post systems: An in vitro study


Department of Conservative Dentistry and Endodontics, Sardar Patel Postgraduate Institute of Dental and Medical Sciences, Lucknow, Uttar Pradesh, India

Date of Web Publication19-Jun-2019

Correspondence Address:
Dr. Sanjeev Srivastava
Department of Conservative Dentistry and Endodontics, Sardar Patel Postgraduate Institute of Dental and Medical Sciences, Lucknow, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/endo.endo_70_18

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  Abstract 

Introduction: Endodontically treated teeth in most cases are left with the extensive loss of coronal tooth structure; hence, the salvaging of such teeth requires the use of an “intracanal retainer” such as post. The long-term success of any restorative or prosthetic rehabilitation of endodontically treated teeth depends on the quality of the restoration, clinical adaptation, and on the health of the supporting tissues.
Materials and Methods: A total of 60 maxillary central incisors teeth were endodontically treated and Post space was prepared. The obturated teeth were randomly divided into four groups as follows: custom-made cast metal post, biological post, everstick post, and biological post. The consecutive posts were luted in each sample and sections were made. Push-out test was performed. The values were noted at bond failure and were subjected to statistical analysis.
Results: Custom-made cast metal post showed the highest bond strength followed by prefabricated and everstick post. The least push-out bond strength was shown by prefabricated fiber post.
Conclusions: The push-out values differed significantly according to posts systems used custom-made cast metal post showed the highest and prefabricated fiber post the least.

Keywords: Biological post, custom cast metal post, everstick post, fiber post, intracanal retainer, push-out bond strength


How to cite this article:
Srivastava S, Khan SZ, Chhabra H, Dubey S, Singh A, Bhardwaj K. Push-out bond strength of four different Post systems: An in vitro study. Endodontology 2019;31:84-8

How to cite this URL:
Srivastava S, Khan SZ, Chhabra H, Dubey S, Singh A, Bhardwaj K. Push-out bond strength of four different Post systems: An in vitro study. Endodontology [serial online] 2019 [cited 2019 Nov 20];31:84-8. Available from: http://www.endodontologyonweb.org/text.asp?2019/31/1/84/260535


  Introduction Top


Constant emergence in the field of dentistry has led to inventions of newer approaches toward the conservation of tooth structure. With the advent of modern endodontic and restorative procedures, it is possible to recover and rehabilitate grossly mutilated teeth to its normal form and function.

The long-term success of any restorative or prosthetic rehabilitation of endodontically treated teeth depends on the quality of the restoration, clinical conditions of the supporting hard and soft tissues.[1]

For the long-term prognosis of a restored tooth, it is pivotal to evaluate the physical properties and bonding of the posts to the tooth structure. Most frequently used research protocols for the bond strength of different posts systems or adhesive systems are pull-out and push-out methods.

In push-out bond strength method, a compressive load is applied to the apical aspect of the root slice in an apical-coronal direction to push the post toward the coronal direction. The stress pattern in the push-out test is more uniform; hence, it provides a better estimation of the bond strength as it mimics debonding in smaller sections of the root as per the clinical conditions.[2],[3]

Based on these considerations, the present study was carried out to comparatively analyze the push-out bond strength of newer posts systems such as everstick (GC Fuji, Finland, Europe) and biological with the traditional custom-made cast post and prefabricated fiber posts (EasyPost, Dentsply Maillefer, Switzerland) using same dual-cure resin adhesive cement.


  Materials and Methods Top


All the experimental teeth used in the present in vitro study were collected from the Department of Oral and Maxillofacial Surgery of the institution, extracted due to periodontal reasons. After thorough cleaning, they were sterilized by autoclaving at 240°F, 20 psi for 40 min. Access cavity for all 60 maxillary central incisors was prepared, and working length was established using no #10 K-file. Apical preparation up to no 40 K-file was performed with step-back technique, using 17% ethylenediaminetetraacetic acid and 10 mL of 3% sodium hypochlorite as an irrigant. Final rinse was done with 10 mL of 0.9% normal saline. All canals were dried with sterile paper points, and radiographs were taken using no 40 master cone. After application of sealer (AH Plus, Dentsply, Germany), obturation was done by lateral condensation technique using Gutta-percha points. The samples were kept at 37°C temperature and 100% humid conditions for 1 week to allow the setting of the sealer.

Later, to standardize, maxillary central incisors were measured 14 mm in length from the apex with the help of a Vernier caliper and decoronated apical to the cementoenamel junction with carborundum disk.

Postspace for each sample was prepared of similar size up to number 3 Peeso reamer and 10 mm length leaving 4-mm apical Gutta-percha to prevent the variations in dimension which may influence the push-out bond strength values. Final flushing of the postspace was accomplished using distilled water, and the canals were dried with paper points. The presence of any residual Gutta-percha in the root canal walls along the postspace was checked by radiographic evaluation.

For the preparation of biological post, after preparation of postspace in maxillary central incisors, the direct wax pattern was formed. This wax pattern acted as a reference for orienting the shape, thickness, and length of the dentinal post. Then, the crown portion of canine which is to be used for the biological post was separated from the root using a diamond disk, and the root was sectioned mesiodistally along the long axis of the tooth. Each part of the root was cut in such a way so that it simulates the wax patterns for each canal. The final adaptation of the biological post was checked using a radiograph.

All the 60 teeth were divided into four groups each containing 15 samples (n = 15):

  1. Group A: Custom cast metal post (Ni–Cr alloy)
  2. Group B: Biological post
  3. Group C: Everstick fiber post
  4. Group D: Prefabricated fiber post.


Cementation of these posts in the postspace was done using the RelyX Unicem U200 (3M, ESPE, USA) resin cement as per the manufacturer's instructions. Each specimen was sectioned horizontally at low speed using carborundum disk under water cooling to produce 1 ± 0.1 mm thick postdentine sections at the coronal end of the specimen. Each slice of the sample was mounted onto an acrylic mold.

Push-out force was applied from apical to coronal end using a 0.76 mm diameter custom stainless steel cylindrical plunger [Figure 1] mounted on an Instron universal testing machine with crosshead speed of 1 mm/min until bond failure. The bond strength at failure was noted in Newton (N). The raw data thus collected were subjected to statistical analysis.
Figure 1: Custom-made plunger tip

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  Results Top


Data were summarized as mean ± SE (standard error of the mean). Groups were compared by one-way analysis of variance and the significance of mean difference between the groups was done by Tukey's honestly significant difference. A two-tailed (α = 2) P < 0.05 was considered statistically significant. Analyses were performed on SPSS software (Windows version 17.0). The bond strength of the four postsystems is depicted by the bar graph.

The push-out bond strength of Groups A–D ranged from 65.70 to 89.20, 58.50 to 70.20, 49.80 to 57.80, and 44.70 to 51.30, respectively, with mean ± SE 77.09 ± 1.51, 63.71 ± 0.87, 53.90 ± 0.59, and 47.46 ± 0.54, respectively [Table 1], and median 78, 63, 54, and 48, respectively.
Table 1: Observed push-out bond strength (n) of four groups

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After statistical analysis and data interpretation, the push-out bond strength of Groups A–D ranged from 65.70 to 89.20, 58.50 to 70.20, 49.80 to 57.80, and 44.70 to 51.30, respectively, with mean ± SE 77.09 ± 1.51, 63.71 ± 0.87, 53.90 ± 0.59, and 47.46 ± 0.54, respectively [Figure 2], and median 78, 63, 54, and 48, respectively [Table 2].
Figure 2: Graph showing mean values of bond strength

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Table 2: Summary of push-out bond strength (n) of four groups

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The mean push-out bond strength of Group A (77.09) was the highest followed by Group B (63.71), Group C (53.90), and Group D (47.46) the least [Table 3]:
Table 3: Comparison of mean push-out bond strength of four groups by analysis of variance

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Group A > Group B > Group C > Group D.


  Discussion Top


A significant amount of coronal tooth loss after endodontic therapy presents challenges for the clinician in restoring such teeth. Endodontically treated teeth frequently require the placement of post inside the root canal, to retain a core for definitive full-coverage restoration. These teeth must be restored in a way that it can withstand vertical, lateral, and oblique forces without being fractured.[4]

Custom-made cast metal posts and cores have been the most accepted treatment mode to restore a grossly decayed teeth for many years because of their superior mechanical properties.[5] Major drawbacks of custom cast metal post being catastrophic root fractures have been attributed to its higher rigidity as compared to root dentin as it causes wedging effect resulting in stress concentration in the area. Sorensen and Martinoff stated that the anatomy of the post confirms the anatomy of the canal, hence, better adaptability, and increased bond strength.[6]

Fiber-reinforced composite posts, as an alternative to cast metal post and cores and metal dowels, were introduced in the early 1990s to restore endodontically treated teeth with an excessive loss of tooth structure.[7] Isidor et al. observed favorable fractures which are often reparable because fiber-reinforced composite posts distribute occlusal stresses more evenly in root dentin.[8] Kadam et al. reported that the most common failure for fiber-reinforced composite posts is debonding. Since the flexing of the bonding materials is different, the stress is generated at the dentin-cement-post interface causing bond failure.[9]

Kalkan et al. termed “electrical glass” since the posts are translucent, light transmitting and its chemical composition make it an excellent electrical insulator. These posts consist of continuous unidirectional glass fibers and the multiphase polymer matrix. This polymer matrix reveals a semi-interpenetrating polymer network (IPN) with both linear polymer phases, polymethylmethacrylate, and cross-link polymer phase. Due to its high flexibility and moldability, these posts adapt well to root canal anatomy. The dentin removal is minimal, and the angulation of the core can also be changed within limits.[10]

Several authors have suggested the use of natural tooth fragments as an efficient method for restoring fractured anterior teeth called “biological posts.” They are made of natural human donated extracted teeth and the adhesion provided among the biological post, cementing agent, and the dental structure attains a sole biomechanical system forming a “monobloc.”[11]

In the present study, customized cast metal post (Group A) exhibited the highest bond strength among tested groups which ranged between 65.7 N and 89.2 N with a mean value of 77.9 N. There was a significant difference between the bond strength shown by custom cast metal post (Group A) with the push-out bond strength of biological (Group B), ever stick (Group C), and fiber post (Group D) [Table 4]. The higher bond strength of custom cast metal post in the current study can be attributed to its high rigidity and its adaptation to shape of the root canal which imparts better retention to the post as they are fabricated through the direct wax pattern. The relatively superior fitting of the cast post enhances the frictional resistance between the post and tooth structure when compared with the other experimental groups. Türker et al. reported that cast metal post showed higher push-out bond strength. In the present study, since the cast posts were sandblasted, they exhibited higher push-out bond strength because of surface roughness.[12] According to Oilo and Jørgensen, surface roughness on the retentive ability of the post system showed that rough surfaces are more retentive than polished ones as they provide micromechanical interlocking with adequate bond strength.[13]
Table 4: Comparison of mean push-out bond strength between the groups by Tukey test

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Biological post (Group B), in the present study, showed bond strength values ranging from 58.5 N to 70.20 N with a mean value of 63.71 N which is higher than Groups C and D. The results showed a highly significant difference (P < 0.001) of bond strength values of these posts than ever stick (Group C) and glass fiber post (Group D). The results of this study are in agreement with the research conducted by Ambica et al. in which they concluded that biological posts showed higher bond strength as compared to carbon and glass fiber post which is in accordance to the current study.[14] This higher bond strength of biological post than the everstick and glass fiber post can be ascribed to the physiomechanical properties of the dentinal post. Dentin post made from roots of extracted teeth allow a juxtaposed adaptation to the root canals and do not cause stress to the dentin since they contain the same biomechanical behavior as the restored teeth. However, the bond strength values of biological post were lower than custom cast post which can be due to autoclaved procedure of the biological post as suggested by Parsell et al. in which they stated that autoclaving the tooth makes it brittle and leads to degenerative changes in the hard tissues of the tooth.[15]

Bond strength of Everstick post (Group-C)in the present study was between 49.80 N to 57.80 N. The mean bond strength of these everstick posts (53.90 N) was greater than prefabricated glass fiber post (47.46 N) but lower than that of cast post (77.09 N) and biological post (63.71 N). The everstick glass fiber post underwent separation of the fibers before the debonding took place while some fibers were still attached at the post-cement interface.

The higher bond strength values than prefabricated glass fiber post can also be because in everstick post both linear and cross-link phases are present. Dual-cure resin cements may also improve the bonding strength of everstick post as Khan et al. in their study concluded that could be due to the fact that the monomers of dual-cure RelyX Unicem U200 cement penetrated into the linear phase of the IPN polymer structure of everstick posts.[16]

In the present study, prefabricated glass fiber post showed appropriate bond strength ranging from 44.70 N to 51.30 N with the mean value of 47.46 N (P < 0.001) which was the lowest among all the experimental groups. Maccari et al. and Pereira et al. also found lower bond strength values for prefabricated posts when compared to everstick post which is in accordance to the findings of the present study. Since the prefabricated glass post is rigid than dentin, the stress is directed to the post-cement interface making the premature bond failure.[17],[18]

Makarewicz et al. stated that prefabricated glass fiber posts because of their highly cross-linked polymer matrix are difficult to bond with resin luting cements and core material.[19] This may be attributed to the lower bond strength of these posts.

A study conducted by Rosentritt et al. found contrast findings in their study where they reported higher bond strength values for prefabricated posts. This might be due to variations in methodology, chemical and physical properties of materials, and root canal morphology.[20]

Single-step self-adhesive dual-cure resin cement was used to lute all the posts to minimize variations in bond strength values as other systems involved multiple steps. This eliminates the errors of other multiple step adhesive systems.[21]

In the present study, degree of variation in the values of bond strength among the tested posts systems might be due to various reasons such as the degree of hydration of the root canal dentin, surface conditioning agent, luting agent, configuration factor and anatomic differences in density, and orientation of the dentinal tubules at different levels of the root canal space.

In the setup of the present study, the test methodology was limited to the root; the crowns were not included to exclude other variables such as ferrule design and remaining coronal dentin. In this way, we could solely test, the effect of the postdesign and type, while excluding any strengthening effect of the core buildup and the crown on the tooth.

The present in vitro study has some limitations in respect to its clinical relevance and cannot indicate precise results. Therefore, further evaluations, mainly clinical investigations and in vivo studies are required to support our results.


  Conclusions Top


Conventional custom cast metal post exhibited the highest bond strength followed by biological post, everstick electrical glass fiber post, and least by prefabricated glass fiber post. The push-out values differed significantly according to the posts systems used. The biological post has shown better push-out bond strength in this study, but further long-term studies are needed before its frequent use as post system in endodontically treated teeth. Studies should also be carried out to evaluate the changes in the extracted tooth used to make the post. The push-out bond strength of four different post systems is as follows:

Group A > Group B > Group C > Group D.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Sholapurmath SM, Anand S. Use of polyethylene fiber in pediatric esthetics clinical reports of two cases. J Int Oral Health 2010;2:99-101.  Back to cited text no. 1
    
2.
Drummond JL.In vitro evaluation of endodontic posts. Am J Dent 2000;13:5-8B.  Back to cited text no. 2
    
3.
Mitchell CA, Orr JF, Connor KN, Magill JP, Maguire GR. Comparative study of four glass ionomer luting cements during post pull-out tests. Dent Mater 1994;10:88-91.  Back to cited text no. 3
    
4.
Chan CP, Lin CP, Tseng SC, Jeng JH. Vertical root fracture in endodontically versus nonendodontically treated teeth: A survey of 315 cases in Chinese patients. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87:504-7.  Back to cited text no. 4
    
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Zalkind M, Hochman N. Esthetic considerations in restoring endodontically treated teeth with posts and cores. J Prosthet Dent 1998;79:702-5.  Back to cited text no. 5
    
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Sorensen JA, Martinoff JT. Intracoronal reinforcement and coronal coverage: A study of endodontically treated teeth. J Prosthet Dent 1984;51:780-4.  Back to cited text no. 6
    
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Rocha Rde O, das Neves LT, Marotti NR, Wanderley MT, Corrêa MS. Intracanal reinforcement fiber in pediatric dentistry: A case report. Quintessence Int 2004;35:263-8.  Back to cited text no. 7
    
8.
Isidor F, Odman P, Brøndum K. Intermittent loading of teeth restored using prefabricated carbon fiber posts. Int J Prosthodont 1996;9:131-6.  Back to cited text no. 8
    
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Kadam A, Pujar M, Patil C. Evaluation of push-out bond strength of two fiber-reinforced composite posts systems using two luting cements in vitro. J Conserv Dent 2013;16:444-8.  Back to cited text no. 9
[PUBMED]  [Full text]  
10.
Kalkan M, Usumez A, Ozturk AN, Belli S, Eskitascioglu G. Bond strength between root dentin and three glass-fiber post systems. J Prosthet Dent 2006;96:41-6.  Back to cited text no. 10
    
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Kathuria A, Kavitha M, Khetarpal S. Ex vivo fracture resistance of endodontically treated maxillary central incisors restored with fiber-reinforced composite posts and experimental dentin posts. J Conserv Dent 2011;14:401-5.  Back to cited text no. 11
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12.
Türker SA, Özçelik B, Yilmaz Z. Evaluation of the bond strength and fracture resistance of different post systems. J Contemp Dent Pract 2015;16:788-93.  Back to cited text no. 12
    
13.
Oilo G, Jørgensen KD. The influence of surface roughness on the retentive ability of two dental luting cements. J Oral Rehabil 1978;5:377-89.  Back to cited text no. 13
    
14.
Ambica K, Mahendran K, Talwar S, Verma M, Padmini G, Periasamy R, et al. Comparative evaluation of fracture resistance under static and fatigue loading of endodontically treated teeth restored with carbon fiber posts, glass fiber posts, and an experimental dentin post system: An in vitro study. J Endod 2013;39:96-100.  Back to cited text no. 14
    
15.
Parsell DA, Kowal AS, Singer M, Lindquist S. Protein disaggregation mediated by heat-Shock protein Hspl04. Nature 1994;6505:475-8.  Back to cited text no. 15
    
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Khan S, Pirvani M, Malik S. Evaluation of push out bond strength of a dual-cure self-adhesive resin-cement with fiber post systems and dentine. JPDA 2015;24:28-34.  Back to cited text no. 16
    
17.
Maccari PC, Conceição EN, Nunes MF. Fracture resistance of endodontically treated teeth restored with three different prefabricated esthetic posts. J Esthet Restor Dent 2003;15:25-30.  Back to cited text no. 17
    
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Pereira JR, de Ornelas F, Conti PC, do Valle AL. Effect of a crown ferrule on the fracture resistance of endodontically treated teeth restored with prefabricated posts. J Prosthet Dent 2006;95:50-4.  Back to cited text no. 18
    
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Makarewicz D, Le Bell-Rönnlöf AM, Lassila LV, Vallittu PK. Effect of cementation technique of individually formed fiber-reinforced composite post on bond strength and microleakage. Open Dent J 2013;7:68-75.  Back to cited text no. 19
    
20.
Rosentritt M, Fürer C, Behr M, Lang R, Handel G. Comparison of in vitro fracture strength of metallic and tooth-coloured posts and cores. J Oral Rehabil 2000;27:595-601.  Back to cited text no. 20
    
21.
Boscato N, Pereira-Cenci T, Moraes RR. Self-adhesive resin cement for luting glass fiber posts. J Esthet Rest Dent 2014;26:417-21.  Back to cited text no. 21
    


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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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