ORIGINAL RESEARCH |
https://doi.org/10.5005/jp-journals-10019-1452 |
Comparison of Fracture Resistance and Mode of Fracture of Ultraconservative and Conventional Fiber Posts: An In Vitro Study
1–6Department of Conservative Dentistry, Karnavati School of Dentistry, Karnavati University, Gandhinagar, Gujarat, India
Corresponding Author: Janki K Prajapati, Department of Conservative Dentistry, Karnavati School of Dentistry, Karnavati University, Gandhinagar, Gujarat, India, Phone: +91 8200489593, e-mail: jankiprajapati2910@gmail.com
Received: 25 February 2024; Accepted: 20 May 2024; Published on: 29 June 2024
ABSTRACT
Purpose: The fracture resistance and mode of fracture in maxillary incisors restored with the ultraconservative post (size 0) and conventional fiber posts (sizes 1 and 2) subjected to 45° stress.
Materials and methods: A total of 60 extracted human permanent maxillary central incisors were decoronated, instrumented, and obturated using the sectional obturation technique. Six groups (n = 10 samples each) were created—group I (size 0 Hi-Rem post), group II (size 1 Hi-Rem post), group III (size 2 Hi-Rem post), group IV (size 0 EasyPost), group V (size 1 EasyPost), and group VI (size 2 EasyPost). Post space was prepared in each root, preparing posts for cementation and core buildup. The specimens were tested for fracture resistance using a universal testing machine at a 45° angle and 1 mm/minute. The mode of failure was visually determined. The paired t-test was done to analyze the difference in fracture resistance within the groups, and the unpaired t-test was used to compare the groups.
Results: The mean fracture resistance of EasyPost and Hi-Rem posts with size 0 was higher (618.30 and 624.40 N, respectively) than sizes 1 (544.80 and 561.20 N, respectively) and 2 (464.40 and 479.70 N, respectively). There were statistically significant mean value differences between the two groups for size 1 post (p = 0.008). In all three sizes, Hi-Rem showed a higher mean fracture resistance value than EasyPost.
Conclusion: This study found that ultraconservative posts (size 0) of Hi-Rem and EasyPost had greater fracture resistance than conservative posts (sizes 1 and 2). Furthermore, size 0 Hi-Rem posts performed marginally better than size 0 EasyPost. Favorable fractures are most common with both Hi-Rem and EasyPost.
How to cite this article: Prajapati JK, Joshi C, Thumar SJ, et al. Comparison of Fracture Resistance and Mode of Fracture of Ultraconservative and Conventional Fiber Posts: An In Vitro Study. Int J Prosthodont Restor Dent 2024;14(2):114–120.
Source of support: Nil
Conflict of interest: None
Keywords: EasyPost, Fiber post, Fracture resistance, Hi-Rem post, Unconventional post
INTRODUCTION
As a result of caries activity, prior restorations, trauma, and/or the endodontic treatment itself, endodontically treated teeth (ETTs) typically suffer substantial tooth structure loss, which weakens the tooth.1 Before a crown or cast partial denture can be put in place, these teeth must first be restored using a post and core to prevent further decay and provide retention to the core.2
A suitable post system must meet the needs of both the restoration and the tooth. However, the process of preparing the post space inevitably results in the removal of dentin from the root, compromising the structural integrity of the remaining tooth.3 Consequently, highly conservative fiber posts such as EasyPost and Hi-Rem, featuring smaller diameters, have recently emerged in the market. These posts claim to preserve radicular dentin while simultaneously enhancing the fracture resistance of the tooth.4
EasyPost (Dentsply, Ballaigues, Switzerland) utilizes a high density of unidirectional glass fibers to provide strength and flexibility for restorations, replicating the stress distribution found in healthy teeth.5 This characteristic helps to prevent fractures and fissures. On the other hand, the Hi-Rem post (Overfibers, Bologna, Italy) has been introduced and reported to possess strong bond strength. It incorporates soft polymer microfibers within the zirconia glass fiber post, offering additional reinforcement to the tooth structure.6
The longevity of survival in endodontically treated teeth (ETTs) with post and cores relies on various factors, including ferrule design, post placement, and substance loss. A lot of research has been done on the mechanical properties, effects of resin luting agents, post design, post length, and performance of different fiber-reinforced composite (FRC) post core systems.7
Prior studies8-10 have highlighted the significant influence of altering the diameter of the post on the fracture resistance of metal-post-restored teeth. Barjau-Escribano et al.8 and Santos-Filho et al.9 reported that modifying the post’s diameter had a substantial impact on fracture resistance. Additionally, a study by Sinha investigated the fracture resistance and failure patterns of size two fiber posts, known as EasyPosts.10 The results suggested that EasyPosts should not be considered a straightforward and effective solution for restoring and reconstructing teeth. The study looked at how well premolars that had been treated with EasyPosts after endodontic treatment held together when force was applied at a 90° angle using only size two easy fiber posts.10 Further research was deemed necessary to determine the full extent of the impact of dimensional variations on teeth restored with posts with mechanical properties similar to dental structures. Consequently, this experiment employed posts with an elasticity modulus similar to dentin.
The research on the fracture resistance of maxillary incisors after endodontic treatment, specifically when force is applied at a 45° angle to the long axis, remains limited. Furthermore, the mean fracture resistances of different fiber-reinforced post core systems have also been extensively studied. In the meantime, no literature article has documented the fracture resistances of the ultraconservative post (size 0) and conventional fiber posts (sizes 1 and 2). To address this gap, this study examines the fracture resistance and mode of fracture in maxillary incisors restored with the ultraconservative post (size 0) and conventional fiber posts (sizes 1 and 2) subjected to 45° stress. Therefore, the null hypothesis (H0) states that there is no difference in fracture resistance of teeth and mode of fracture regardless of fiber post diameter.
MATERIALS AND METHODS
This in vitro study was conducted at the Department of Conservative Dentistry, Karnavati School of Dentistry, Karnavati University, Gandhinagar, Gujarat, India. The university’s ethics committee reviewed and approved the research design. In this study, extracted teeth sourced from the oral surgery department were chosen for their accessibility and standardized conditions. Utilizing these teeth ensures a uniform sample with diverse dental conditions, minimizing confounding variables. Additionally, their use alleviates ethical concerns associated with human subject research, contributing to the study’s reliability and integrity.
In this study, a sample size of 60 was selected to investigate the fracture resistance of ETTs restored with various sizes of fiber posts. By allocating 10 samples to each of the six groups, the adequate statistical power (80%) was achieved to detect significant differences between the groups.
Selection of the Specimens
The study included maxillary central incisors that met specific criteria, such as having a single canal and root, no cracks or fractures, no internal absorption, and having at least two-thirds of the remaining root length. The measurements of the coronal and root lengths, as well as the faciopalatal and mesiodistal root widths at the cementoenamel junction (CEJ), were conducted using a digital caliper (Mitutoyo, Kawasaki, Japan). The maximum height of the coronal portion was constrained to a range of 10 ± 1 mm, while the length of the root was confined to a range of 12.5 ± 1 mm. The dimensions at the CEJ were found to be restricted to a range of 6.75 ± 0.25 mm for the faciopalatal dimension and 6.25 ± 0.25 mm for the mesiodistal dimension. The study did not include teeth with fractures, internal structural defects, grossly carious teeth, or previously treated teeth. All the teeth were cleaned, kept for 2 weeks in a disinfecting solution with 0.1% thymol (F. Maia Industrial Company, Cotia, Brazil), and then placed in a saline solution at room temperature.
Endodontic Protocol
After using round burs #1012 and #1013 (KG Sorensen, Cotia, Brazil) and an Endo-Z bur (Dentsply Maillefer, Ballaigues, Switzerland), endodontic access cavities were prepared. A 10 K-file (Mani Inc., Tochigi, Japan) was passed through each canal. Utilizing a magnification tool such as a dental operating microscope at 10× magnification, the canal was visually magnified to provide a detailed and enlarged view of the canal anatomy. With the canal magnified, the operator visually identified the apical constriction. The distance from the designated reference point to the magnified apical constriction was meticulously measured, and the actual working length was recorded. All the teeth were instrumented using the ProTaper Next rotary file system (Dentsply Sirona, North Carolina, United States of America). The last file utilized was the ProTaper Next X3 file (0.30 mm tip with 7% taper). A 2.5% sodium hypochlorite (NaOCl) solution was used to irrigate the root canals following each instrumentation. Once the root canal had been instrumented, a 1-minute application with a 17% ethylenediaminetetraacetic acid (EDTA) solution was carried out. To eliminate any leftover EDTA, the canals were flushed further for 1 minute with 2.5% NaOCl and normal saline solution before being dried with paper points. After this, sectional obturation was done with 5 mm of gutta-percha in the apical third of all the teeth. The access cavities were temporarily filled using Cavit temporary filling material (3M ESPE, Minnesota, United States of America) and kept at 37°C with 100% humidity for 24 hours.11
Sectioning of the Crown
After that, the teeth were prepared for crown sectioning. A diamond disk and low-speed handpiece were used for sectioning the crown at a distance of 17 mm from the tip of the root; this allows for a ferrule effect of 2 mm, a post length of 8 mm, and leaving behind 5 mm of gutta-percha.
All the samples were randomly divided into six groups (n = 10 for each group):
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Group I: Size 0 Hi-Rem post with point diameter—0.7 mm; maximum diameter—1.20 mm.
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Group II: Size 1 Hi-Rem post with point diameter—0.8 mm; maximum diameter—1.40 mm.
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Group III: Size 2 Hi-Rem post with point diameter—0.88 mm and maximum diameter—1.60 mm.
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Group IV: Size 0 EasyPost with point diameter—0.8 mm; maximum diameter—1.35 mm.
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Group V: Size 1 EasyPost with point diameter—0.8 mm; maximum diameter—1.47 mm.
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Group VI: Size 2 EasyPost with point diameter—1 mm; maximum diameter—1.67 mm.
Post space Preparation
The samples were taken out of the saline water to prepare the post space. According to manufacturer guidelines, size 0 PD100 drills were used to prepare the post space for size 0 Hi-Rem posts (Overfibers, Bologna, Italy), size 1 PD101 drills for size 1 Hi-Rem posts, and size 2 PD102 drills for size 2 Hi-Rem posts. According to the manufacturer’s specifications, precision drills number 1, 2, and 3 were used to prepare the post area for size 0 EasyPost (Dentsply, Ballaigues, Switzerland), size 1 EasyPost, and size 2 EasyPost. Using a silicone stopper on the drill, each root was reliably drilled down to 5 mm of gutta-percha, which is present in the apical third of all the roots (Fig. 1A). The length and fit of the chosen glass fiber posts in the prepared canal were examined. To verify the exact position of the post in the canal, an intraoral periapical radiograph was performed.
Figs 1A and B: (A) Post space preparation; (B) Post insertion
Post Cementation
A 5% solution of NaOCl was used to clean the root canal walls; following this, the canals were dried with paper points before the post cementation procedure was carried out. The fiber posts were air-dried after being washed with a 75% alcohol solution. The cementation procedure was conducted using RelyX self-adhesive resin cement (3M, Maplewood, Minnesota, United States of America). It consists of a base and a catalyst paste. The cement base and catalyst were mixed in equal parts and applied to both the post and the canal. The posts were inserted into the canal and held there while being exposed to light for 40 seconds using a light-emitting diode curing light (Bluephase, Ivoclar Vivadent, Schaan, Liechtenstein) with a radiant emittance of 800 mW/cm² (Fig. 1B).11
Similar procedures were used to secure each position across all groups.
Core Buildup
Tetric Ceram, an Ivoclar Vivadent hybrid composite with fine particles (Ivoclar Vivadent AG, Schaan, Liechtenstein), was used for core buildup across the board. On the post, the light-cured composite was applied in parts that were 1–2 mm thick. As per the manufacturer’s instructions, each increment was meticulously applied to the surface of the post and then cured for 20 seconds on each side. The teeth were prepared to have a total height of 6 mm from the CEJ, while the roots were embedded in auto-polymerizing acrylic resin that extended 2 mm below the CEJ. A necessary adjustment had been made on an acrylic resin block with a lathe-cut machine to give the block a dimension of 4 × 2 so that this acrylic block could accurately fit into an inclined metal base.
Fracture Resistance Test
A specialized mounting jig with an inclined metal base (Fig. 2) was used to place the specimens exactly at their desired position to conduct a fracture resistance test. The teeth-containing acrylic block was securely attached to a specially designed inclined metal base at a precise 45° angle. This ensured that the palatal surface of the tooth and the loading tip, which had a 2-mm spherical head, were in perfect alignment. The mounted specimen was then placed on the platform of a universal testing device (Lloyd Instruments, Fareham, Hants, United Kingdom) and subjected to a compressive force at a speed of 1 mm/minute until it fractured. After the test, a visual assessment was conducted to determine the location, type, and extent of the fracture. They were classified as either favorable (fracture above the CEJ or if it is an oblique fracture that crosses below the CEJ with enough coronal dentin and ends in the cervical one-third of the root) or unfavorable (fracture below the CEJ and there is no coronal tooth structure left).11
Fig. 2: Fracture resistance test on the universal testing machine using a specialized mounting jig
A flowchart for the selection process is presented in Figure 3.
Fig. 3: Flowchart showing the stepwise procedure followed
Statistical Analysis
Using the Shapiro–Wilk normality test, the data distribution was determined. For the comparison of the fracture resistance data between two related groups, the paired t-test was conducted, and for within-group comparison, an unpaired t-test was employed. The statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, New York: IBM Corp.).
RESULTS
The mean fracture resistance values of size 0 Hi-Rem and size 0 EasyPost were higher than those of sizes 1 and 2. Significant differences were found in fracture resistance within the groups of Hi-Rem and EasyPost (p = 0.001) (Table 1).
| Post and size | Mean | N | Standard deviation | Standard error mean | Mean difference | p-value | |
|---|---|---|---|---|---|---|---|
| Hi-Rem | Size 0 | 624.40 | 10 | 12.97 | 4.10 | 63.20 | 0.001* |
| Size 1 | 561.20 | 10 | 13.24 | 4.19 | |||
| Size 0 | 624.40 | 10 | 12.97 | 4.10 | 144.70 | 0.001* | |
| Size 2 | 479.70 | 10 | 11.99 | 3.79 | |||
| Size 1 | 561.20 | 10 | 13.24 | 4.19 | 81.50 | 0.001* | |
| Size 2 | 479.70 | 10 | 11.99 | 3.79 | |||
| EasyPost | Size 0 | 618.30 | 10 | 9.38 | 2.97 | 73.50 | 0.001* |
| Size 1 | 544.80 | 10 | 11.49 | 3.63 | |||
| Size 0 | 618.30 | 10 | 9.38 | 2.97 | 153.90 | 0.001* | |
| Size 2 | 464.40 | 10 | 20.53 | 6.49 | |||
| Size 1 | 544.80 | 10 | 11.49 | 3.63 | 80.40 | 0.001* | |
| Size 2 | 464.40 | 10 | 20.53 | 6.49 | |||
*, p < 0.05 is considered statistically significant
The mean fracture resistance values for size 0 Hi-Rem and EasyPost were 624.40 and 618.30 N, respectively, and the difference was statistically insignificant (p = 0.615). The mean fracture resistance values for size 1 Hi-Rem and EasyPost were 561.20 and 544.40 N, respectively, and the difference was statistically significant (p = 0.008). The mean fracture resistance values for size 2 Hi-Rem and EasyPost were 479.70 and 464.20 N, respectively, and the difference was statistically insignificant (p = 0.057). However, the Hi-Rem group had higher mean fracture resistance values than the EasyPost group in all three sizes (Table 2). The H0 was, therefore, rejected.
| Group | N | Mean | Standard deviation | Standard error mean | Mean difference | p-value | |
|---|---|---|---|---|---|---|---|
| Size 0 | Hi-Rem | 10 | 624.40 | 12.97 | 4.10 | 6.10 | 0.244 |
| EasyPost | 10 | 618.30 | 9.38 | 2.97 | |||
| Size 1 | Hi-Rem | 10 | 561.20 | 13.24 | 4.19 | 16.40 | 0.008* |
| EasyPost | 10 | 544.80 | 11.49 | 3.63 | |||
| Size 2 | Hi-Rem | 10 | 479.70 | 11.99 | 3.79 | 15.30 | 0.057 |
| EasyPost | 10 | 464.40 | 20.53 | 6.49 | |||
*, p < 0.05 is considered statistically significant
Root fracture failure was the worst among the common failure types in terms of the specimens’ failure types, as shown in Table 3. Six samples from each size of Hi-Rem post (sizes 0, 1, and 2) showed favorable fractures. The number of favorable fractures seen in EasyPost size 0 and size 1 was 7; however, six samples of size 2 EasyPost showed favorable fractures (Fig. 4A). Favorable fractures were more common compared to unfavorable fractures in all three sizes (size 0, 1, and 2) of Hi-Rem and EasyPost (Fig. 4B).
| Favorable fracture | Hi-Rem | EasyPost | |||
|---|---|---|---|---|---|
| Size 0 | No | 4 | 40% | 3 | 30% |
| Yes | 6 | 60% | 7 | 70% | |
| Size 1 | No | 4 | 40% | 3 | 30% |
| Yes | 6 | 60% | 7 | 70% | |
| Size 2 | No | 4 | 40% | 4 | 40% |
| Yes | 6 | 60% | 6 | 60% | |
Figs 4A and B: (A) Favorable fracture; (B) Unfavorable fracture
DISCUSSION
Dentistry has been extensively concerned with the repair of teeth that have undergone endodontic treatment. Retention of the prosthetic crown is essential when there has been a significant loss of tooth structure.12 Numerous studies have indicated that the quantity, quality, and anatomical structure of the dentin determine the tooth’s structural integrity.13-15 When the tooth is endodontically treated, both of these elements are affected, which means they might not execute their critical tooth function to the maximum degree; thus, a post and core are suggested.16
The decision to use extracted central incisors appears to be the best method for mimicking clinical situations for anterior teeth receiving endodontic therapy. Their use for the investigation of various post systems has been reported in earlier studies.17-19 The teeth in this investigation were carefully chosen to have a standard size because it was noted that this variation significantly affected the specimen’s resistance to fracture. Digital calipers were used to standardize the root length, faciopalatal dimensions, and mesiodistal dimensions of each specimen so that they were all the same size.20
In their evaluation of the literature on the ferrule effect, Juloski et al.21 noted that the presence of a 1.5–2 mm ferrule has a favorable impact on the fracture resistance of teeth that have undergone endodontic treatment. As a result, a 2 mm ferrule height was developed for the current investigation to simulate the situation that can be maintained with fiberglass posts.
The post length affects how the stress is distributed and how resistant the root is to fracture. According to research, ETTs are more likely to be successfully restored when the post length is at least as long as the crown length.22 According to a study by Shillingburg et al.,23 the maxillary central incisor’s post length measured 8.3 mm below the CEJ. However, for this study, the posts were placed 8 mm below the CEJ, leaving the post head exposed 3 mm above the ferrule to keep the core material in place.24
In this study, Rely X, a dual-cure self-adhesive universal resin cement, was used since it allows for single-step luting, which removes any procedural method sensitivity.25 In addition, RelyX cement’s modulus of elasticity is 18.6 GPa, which is comparable to dentin’s value of 18.2 GPa.26 Tetric Ceram, an Ivoclar Vivadent (United States of America) hybrid composite with fine particles, was used as a core buildup material. Accordingly, the materials used for core buildup did not make any significant difference in the fracture resistance of the ETTs, as shown in a study by Alshahrani et al.3 Furthermore, based on a study conducted by Izadi et al.,27 it has been shown that the fracture resistance of dental restorations is not influenced by the type of core material used. Additionally, none of the core materials examined in the study demonstrated superior performance compared to the others.
The test loads in this investigation were not applied to artificial crowns but rather directly to the cores. According to Asif et al.,28 the placement of a full crown with a 2 mm ferrule on a healthy tooth structure altered how forces were distributed between the root and the post and core complex. The outcomes of this study would have been different if full crowns had been included. The cores were not capped with crowns in order to rule out any external impact on the post and core material.25 As it is impossible to simulate a clinical setting without using crowns, this could be considered a study limitation.
The force was applied to the palatal aspect of the tooth at a 45° angle to its long axis. This was observed as a result of the lower anterior teeth making contact with the upper anterior palatal surface at an angle of 45° to the maxillary central incisor’s long axis. According to Santos Pantaleón et al.29 incisor loading angles were chosen to replicate class I occlusion contact angles between maxillary and mandibular anterior teeth at 45°.
In this study, the fracture resistance of teeth that had undergone endodontic treatment was repaired with posts of three different diameters. The findings revealed significant differences in the groups of Hi-Rem and EasyPost for sizes 0–1, sizes 1–2, and sizes 0–2. As the fiber post size increased from size 0 to 2, the resistance to fracture decreased. When comparing the groups, it was discovered that there was no significant difference between sizes 0, 1, 2, Hi-Rem, and EasyPost. Size 0 Hi-Rem and Easy fiber posts had higher mean fracture resistance values, respectively, of 624.40 and 618.30 N. The reason behind obtaining higher fracture resistance with size 0 Hi-Rem and fiber posts might be the amount of remaining dentin thickness left after post space preparation.30 As per a study conducted by Rodriguez-Cervantes et al.,30 the findings were similar to the present study. That study concluded that the diameter of the post has a significant impact on the biomechanical performance of teeth that are restored with stainless steel posts.
Some researchers3,27,28 suggest taking a conservative approach to post space preparation by only minimally instrumenting the canal after removing the gutta-percha. The objective is to remove undercuts that hinder the withdrawal of post patterns.31 In a study by Robbins,32 they recommended using the most conservative post that could retain a tooth without compromising its resistance to fractures. Similarly, Potashnick et al.33 found that teeth with smaller-diameter posts were more resistant to fractures and suggested minimal flaring of the canal. It should be noted that teeth act mechanically like a cantilever when subjected to a 45° oblique force.33 In this scenario, the failure loads observed mainly represent the bending resistance of the cantilever.34 Posts having a higher elastic modulus, like metallic posts, and posts with a lower elastic modulus, like fiber posts, can both increase the bending resistance, but the failure pattern formed by FRC posts was easier to repair, as reported by Hayashi et al.35 It is important to note that posts with greater elasticity moduli could potentially induce unrestorable fracture patterns.34-36
Research has shown that the maximum force exerted on the anterior teeth during biting is usually <200 N.37 However, in this study, it was found that all groups had higher fracture loads (ranging from 728.5 to 895.9 N) than the average chewing force and even surpassed the maximum biting force. This suggests that front teeth that have been repaired with an FRC post and have a 2 mm ferrule are able to withstand normal biting pressure.37
In cases of fractures, the pattern of the fracture is very important, as it determines whether fractured teeth can be repaired or not. The present research supports previous findings that the use of FRC posts in restoring ETT can lead to favorable fracture patterns where the fractures can be repaired. This is according to research studies,20,22,30,36 which have shown that the use of FRC posts can result in reparable fractures. Recent studies20 have also found that this can be explained by the way stress is distributed to ETT, which has been repaired using FRC posts and composite cores.
In this study, a unidirectional load was applied, which may not accurately replicate the multidirectional masticatory forces experienced in the oral environment. The materials used to replicate periodontal ligament have reportedly had no impact on the bond strength and fracture resistance of teeth repaired using fiber posts and cores.34 As a result, in this investigation, actual clinical situations were not replicated by using artificial periodontal ligaments. It is recommended that more relevant test methods be developed to ensure that the results of in vitro tests more accurately reflect the failure mechanisms observed clinically in teeth. Therefore, further research and clinical investigations are recommended to verify the in vitro results while taking into consideration different sizes of fiber posts.
Even though the approach employed in this study did not precisely recreate oral conditions, it nonetheless offered useful guidance for choosing post systems of various sizes. In order to better understand the clinical survivability of fiber-reinforced post systems, it is recommended that a long-term clinical evaluation be conducted.
CONCLUSION
With the limitations of this study, it can be concluded that ultraconservative posts (size 0) of Hi-Rem and EasyPosts had greater fracture resistance than conservative (sizes 1 and 2) posts. Furthermore, size 0 Hi-Rem posts performed marginally better than size 0 EasyPosts. Favorable fractures are most familiar with both Hi-Rem and EasyPost.
ORCID
Janki K Prajapati https://orcid.org/0009-0004-3428-9233
Chintan Joshi https://orcid.org/0000-0002-5033-3191
Palak Ranpariya https://orcid.org/0009-0009-4032-0045
Mahima P Jain https://orcid.org/0009-0009-7673-8857
ACKNOWLEDGMENT
I would like to thank Dr Sagar Prajapati for constantly supporting me and helping me out with the photographic documentation.
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