Fracture resistance and failure modes of endodontically-treated permanent teeth restored with Ribbond posts vs other post systems: a systematic review and meta-analysis of in vitro studies

Article information

Restor Dent Endod. 2025;50.e5

Publication date (electronic) : 2025 February 17

doi : https://doi.org/10.5395/rde.2025.50.e5

Meghana Aditya Vartak^,, Vibha Rahul Hegde, Sanitra Rahul Hegde, Ushaina Fanibunda^,

Department of Conservative Dentistry and Endodontics, Post Graduate Program, YMT Dental College and Hospital, Navi Mumbai, India

Citation: Vartak MA, Hegde VR, Hegde SR, Fanibunda U. Fracture resistance and failure modes of endodontically-treated permanent teeth restored with Ribbond posts vs other post systems: a systematic review and meta-analysis of in vitro studies. Restor Dent Endod 2024;50(1):e5.

^*Correspondence to Meghana Aditya Vartak, BDS, MDS Department of Conservative Dentistry and Endodontics, YMT Dental College and Hospital, Institutional Area, Sector 4, Kharghar, Navi Mumbai, Maharashtra 410210, India Email: meghanavartak@gmail.com

^*Correspondence to Ushaina Fanibunda, BDS, MDS Department of Conservative Dentistry and Endodontics, YMT Dental College and Hospital, Institutional Area, Sector 4, Kharghar, Navi Mumbai, Maharashtra 410210, India Email: ushaina@gmail.com

Meghana Aditya Vartak and Ushaina Fanibunda contributed equally to this work as corresponding authors.

Received 2024 July 31; Revised 2024 October 3; Accepted 2024 November 10.

Abstract

INTRODUCTION

Restoration of endodontically-treated teeth presents a persistent clinical challenge as they are frequently structurally compromised due to a variety of reasons, including caries, restorations, and endodontic access interventions [1]. The loss of tooth structure involving one or both marginal ridges or the loss of a facial/lingual wall of the tooth significantly increases the risk of fracture [2]. Root-filled teeth show a greater association with fractures as compared to vital teeth [3].

Determining the optimal type of post-endodontic restoration is influenced by the type of teeth and their position in the arch, forces of occlusion, and the remaining coronal tissue structure [4]. The quantity of the remaining tooth structure comprises the ferrule, which is defined as “a 360° collar of the crown that surrounds the parallel walls of the dentin and extends coronally to the shoulder of the preparation” [5]. An abundance of literature demonstrates increased fracture resistance of endodontically-treated teeth in the presence of at least 1 mm of ferrule height [5–7]. When the coronal structural loss is greater than 50%, the literature suggests the placement of an intraradicular post to reinforce structurally compromised teeth, increase their fracture resistance, and support the final crown restoration [8]. Posts do not directly increase the strength of endodontically-treated teeth but rather they facilitate the core retention [9,10].

Cast posts and cores have conventionally been employed to reinforce pulpless teeth. Metal posts have excellent rigidity and the ability to withstand loads without undergoing deformation. They are resilient to axial stresses whose intensity is along the post’s axis. However, they have poor stress distribution ability, and they exhibit a concentration of forces at the root apex [11,12] since they possess a high modulus of elasticity, much different from that of dentin. This also holds true for other post and core systems with a high modulus of elasticity, such as prefabricated zirconium or prefabricated metal posts. Employing posts with an elastic modulus closer to that of dentin reduces the chances of catastrophic radicular fractures [13]. Other than biological concerns, metal posts also present aesthetic problems, especially in anterior teeth.

This led to a shift in the trend from using more rigid posts to using prefabricated fiber posts which had greater elasticity and better esthetics [14]. Their lower elastic modulus leads to a uniform distribution of stresses along the post-dentin interface, thus avoiding critical stress concentration and catastrophic fractures of the root [15–18]. Prefabricated fiber posts are cemented with a dual cure luting agent. The thickness of the resin cement used affects the strength of the restoration at the post-dentin interface [19], thus suggesting the need for dowels that adapt to the canal anatomy and have a good intracanal fit.

Recently, custom-made fiber post and core systems that employ polyethylene fibers (Ribbond fibers; Ribbond, Inc., Seattle, WA, USA) [20] have been introduced. Ribbond is an ultra-thin, leno-weaved, high molecular weight, reinforcement ribbon with excellent bondability and fracture toughness. Ribbond fibers are embedded in resin composite which are then condensed within the canal in the form of an endodontic post [21]. Ribbond posts are said to be biologic posts with improved esthetics and translucency, and relative ease of manipulation. They can also be placed in a single visit without the need for a laboratory phase [22].

Literature regarding the behavior and performance of Ribbond post and core systems in terms of their retentive ability, fracture strength, and fracture repairability as compared to that of conventional post and core systems needs further evaluation. Thus, this systematic review was undertaken to analyze the outcome of in vitro studies comparing the fracture resistance and mode of failure of Ribbond post and core systems with that of other post and core systems.

METHODS

The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol for systematic reviews and meta-analyses was undertaken and was registered on PROSPERO (CRD42023472726). Using the PICOS (Population; Intervention; Comparison; Outcome; Study Design) framework, a review question was composed as follows: “Does the use of a Ribbond post and core system influence the fracture resistance and failure modes of endodontically-treated permanent teeth as compared to those of other post and core systems?”

RESULTS

Search strategy and characteristics of the studies

A total of 597 records were obtained from searching electronic databases. After the removal of duplicates, a total of 407 records remained which were then subjected to title screening and abstract reading. A total of 389 records were excluded, and 18 articles underwent full-text evaluation. Of those, 12 articles met the eligibility criteria and were included in the present systematic review and underwent quality assessment and data extraction. Meta-analysis was performed with 11 of the 12 studies included. The search strategy and process of study selection are reported in Figure 1 along with the reasons for exclusion.

Figure 1.

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flowchart showing search strategy and selection of studies.

Characteristics of included studies

The chief characteristics of the 12 studies included are presented in Table 1. In comparison to Ribbond posts, all 12 studies tested prefabricated glass fiber posts [18,26–36], four studies tested custom glass fiber (EverStick; GC Europe N.V., Leuven, Belgium) posts [28,29,31,32], two studies tested cast metal posts [33,35], four studies tested prefabricated metal posts [18,31–33], and one study also tested zirconia and quartz post [27]. Nine of the 12 studies also assessed the fracture patterns in which three studies tested reattached fragment samples [29,32,36] whereas the other five studies tested a composite resin core build-up [26,30,31,33,35]. Amongst the three reattached fragment studies, two studies described the fracture patterns as repairable/nonrepairable [32,36] while the third study described it as a fracture at the original site/fracture at new sites [29]. One study did not provide an adequate description of the fracture patterns [18]. Amongst the five composite resin core studies, two studies described the fracture pattern based on restorability as favorable/unfavorable [31] or repairable/nonrepairable [35], while the other three studies described the fracture pattern based on fracture line propagation along the root [26,30,33]. Some additional characteristics are also mentioned in Table 2.

Table 1.

Main characteristics extracted from selected studies

Table 2.

Additional characteristics extracted from selected studies

Risk of bias of included studies

The risk of bias in the included studies is presented in Table 3, along with the overall risk of bias presented in Figure 2. All the included studies were largely comparable in methodological quality. All the included studies had a low risk of bias with all the respective domains. The highest risk of bias was seen for ‘sample size calculation,’ ‘implementation of sequence generation,’ and ‘blinded evaluation’ domains. As per the domains analyzed, all studies presented a low risk of bias.

Table 3.

Risk of bias assessment based on reporting of items according to the modified CONSORT guidelines for in vitro studies

Figure 2.

Overall summary of the risk of bias assessment.

Results of meta-analysis

The meta-analysis of the review was performed on 11 studies [26–36]. The meta-analysis of the included studies evaluating the fracture strength values is presented as forest plots in Figure 3.

Figure 3.

Meta-analysis comparing fracture resistance of the Ribbond post (Ribbond, Inc., Seattle, WA, USA) groups and other experimental groups. (A) Ribbond posts and endodontically-treated teeth (ETT) without posts. (B) Ribbond posts and prefabricated metal posts. (C) Ribbond posts and prefabricated fiber posts. (D) Ribbond posts and custom e-glass fiber posts. CI, confidence interval; SD, standard deviation; SMD, standardized mean difference.

Mode of failure

Table 4 shows the fracture patterns and modes of failure of different post systems as compared to those of Ribbond posts. As evident from the incidence rate of catastrophic vs non-catastrophic fractures, Ribbond posts consistently showed a favorable mode of fracture across all the included studies. Cast metal posts showed the most unfavorable fractures followed by prefabricated metal posts, prefabricated glass fiber posts, and custom e-glass fiber posts in decreasing order.

Table 4.

Incidence rates of Modes of Failure (catastrophic vs non-catastrophic fractures) of Ribbond posts vs other post systems

Publication bias

No significant publication bias was reported according to the funnel plots generated on subgroup analysis using the random effects model presented in Figure 4.

Figure 4.

Begg’s Funnel plot with 95% confidence intervals demonstrating symmetric distribution with the absence of systematic heterogeneity of individual study compared with the standard error (SE) of each study, indicating an absence of any publication bias. SMD, standardized mean difference.

DISCUSSION

Teeth are susceptible to a variety of occlusal loads in the oral cavity during masticatory functions like chewing, biting, and sometimes parafunctional habits [37]. Endodontically-treated teeth are typically difficult to restore, and when they involve significant tissue loss, intraradicular reinforcements are sometimes required to keep the coronal restoration in place. This systematic review and meta-analysis comprised in vitro studies that assessed the placement of Ribbond posts as compared to other intraradicular posts based on the fracture strength and fracture patterns of structurally compromised endodontically-treated teeth.

The amount of coronal structural loss a tooth experiences dictates the type of post-endodontic restoration. According to Jotkowitz and Samet [38], the height and thickness of the remaining ferrule along with the lateral load a tooth undergoes directly affect the ‘risk of failure’ and the quality of the restoration. Dietschi et al. [39] recommended that weakened endodontically-treated posterior teeth can be restored functionally and aesthetically by direct and indirect adhesive techniques, avoiding an additional sacrifice of sound tissues and further stated that if there is less than half coronal residual tooth structure, post placement is indicated. The biomechanical properties of both, the remaining tooth structure and the material used for post and core, should be taken into consideration while restoring structurally compromised teeth.

Recently, Ribbond posts (custom polyethylene fiber posts) have been used to restore weakened endodontically-treated teeth [40]. Ribbond is made of leno-woven, ultra-high molecular weight polyethylene fibers [41]. Ribbond posts have several advantages over conventional post and core systems such as improved esthetics, excellent bondability, and a modulus of elasticity very close to that of dentin [40]. Polyethylene fiber-reinforced composites (FRCs) alter stress patterns, providing improved stress distribution [42]. According to a finite element analysis by Belli et al. [43], increased stress concentration was observed with an increase in the number of interfaces of the monoblocks created by the restorations. Ribbond fiber posts create a primary monoblock effect and thus dissipate the stresses along the long axis of the tooth [41]. Without necessitating structural alteration, Ribbond fibers can be cut and incorporated into dental composites. They adapt closely to the internal contours of the tooth and remain adhered to one another [40].

Traditionally, cast posts and cores have been employed due to their excellent strength and resistance to deformation [44]. Cast posts provide an accurate fit, eliminating the need for a thicker layer of cement thus contributing to its superior strength [44,45]. Likewise, in the present systematic review and meta-analysis, it was seen that cast metal posts had a significantly higher fracture strength when compared to Ribbond posts, but they resulted in catastrophic nonrepairable fractures. In the study by Sirimai et al. [33], it was seen that cast posts had the highest fracture strength while polyethylene fiber posts had the lowest fracture strength, but there was an unmistakable difference in the failure patterns for both groups. All of the teeth restored by cast posts suffered nonrepairable root fractures; 90% had a vertical root fracture pattern whereas 10% had a horizontal root fracture pattern at the junction of the middle and apical third of the root. Whereas, in the teeth restored with polyethylene fiber posts only 10% of the samples experienced a vertical root fracture and 80% of the samples had failure limited only to the composite core. Similar findings were seen in the study by Aggarwal et al. [35], with the cast post group having the highest fracture strength but nine out of 10 samples had a nonrepairable fracture pattern whereas the Ribbond post group showed a repairable fracture strength for all samples despite having the lowest fracture strength. Similar results were seen in the studies evaluating prefabricated metal posts (titanium posts). Ozcan and Valandro [31] reported that the fracture resistance of Paraposts (titanium posts; Coltene/Whaledent, Altstätten, Switzerland) was almost twice that of Ribbond posts, with no unfavorable fractures for either of the groups. The titanium post group reported core fractures whereas the Ribbond post group reported a loss of post retention. The possible reason for this could be that during the fracture test performed in the study, loading was arrested the moment core failure was observed and there was a high probability of root fracture if loading had been continued. Sirimai et al. [33] reported that although titanium posts have a higher fracture strength than Ribbond posts, 90% of the posts fractured with a nonrepairable fracture pattern, whereas only 10% of Ribbond posts had a nonrepairable fracture pattern. Ozcopur et al. [32] reported similar findings where despite a higher fracture strength, 60% of the posts fractured in a non-restorable fashion whereas Ribbond posts exhibited 100% fracture repairability. This could be attributed to the material properties that cast metal posts and prefabricated metal posts exhibit, such as high stiffness, high modulus of elasticity, and poor stress distribution ability with a critical concentration of stresses apically [11,12]. Due to the aforementioned properties, the posts tend to fracture at the expense of the root structure.

Prefabricated fiber posts have been gradually replacing metal posts due to their improved aesthetic properties, low modulus of elasticity, and greater dissipation of stresses [14]. Since fiber posts are prefabricated, a layer of luting cement surrounds the post, serving as the weakest point of the tooth-post-core complex [19,46]. This creates a secondary monoblock as opposed to the primary monoblock that Ribbond posts provide, thus the stress dissipation is lesser than in custom-made fiber posts [43]. The advantage of having primary monoblock over secondary monoblock is that the homogeneity of the tooth-post-core complex achieved in the former is greater, thus opposing forces as a single unit [43]. All studies comparing prefabricated fiber posts with Ribbond posts in the present meta-analysis showed that the former had a fracture resistance greater than that of the latter. The mode of fracture analysis revealed that in four out of the five studies [32,34–36], Ribbond posts had 100% fracture repairability whereas in one study [30] the fracture repairability was 75%. Prefabricated fiber posts had a fracture repairability of 80% or less in all studies, with one study showing fracture repairability even as low as 60%. Although prefabricated fiber posts have higher fracture resistance than Ribbond posts, the fracture mode is not exceedingly favorable, resulting in nonrepairable root fractures significantly more often than Ribbond posts. Depending on the thickness of the cement layer, a large portion of the prefabricated fiber post and core restoration comprises the luting cement. Thus, the quality of the luting cement has a direct influence on the biomechanical properties of the post and core restoration. Furthermore, prefabricated fiber posts require post space preparation which results in additional root dentin removal, whereas custom fiber posts do not necessitate the need for root dentin removal since they adopt the canal anatomy [40].

With a deeper understanding of the biomechanics of the tooth system and improved material science and bonding protocols, aesthetic custom fiber posts have started coming into the limelight [28]. Custom FRC posts adapt to the internal anatomy of the canal system. They have a modulus of elasticity very close to that of dentin, which is advantageous due to excellent dissipation of stresses, with reduced incidence of root fractures [32]. Since custom fiber posts create a primary monoblock, stresses experienced during function and mastication get distributed more homogenously, thus avoiding critical stress concentration [32]. EverStick is a custom glass fiber post impregnated in unpolymerized resin which is pliable and can be condensed into the canal in the form of a post [47]. In the present meta-analysis, EverStick posts showed marginally higher fracture strength than Ribbond posts. This could possibly be attributed to the silanization of glass FRC posts which provides better adherence of the glass fibers to the resin, whereas the inherent difficulty to achieve silanization with polyethylene fibers leads to somewhat weaker adherence with the resin [28]. However, the mode of failure evaluation of EverStick posts when compared to Ribbond posts revealed that Ribbond posts have a higher fracture repairability than EverStick posts. This could be attributed to the differences in fiber orientation and intracanal adaptation. EverStick posts are unidirectional and congregate in the middle of the post space with a layer of resin cement around them, whereas polyethylene fibers are multidirectional and show close adaptation to the canal wall, minimizing the resin cement interface, possibly resulting in variations in the mode of failure [29].

Ribbond posts also present some added advantages over prefabricated fiber posts. Erkut et al. [48] studied the microleakage in overflared canals restored with adhesively luted posts and stated that Ribbond had the least amount of microleakage. Furthermore, custom Ribbond fiber posts have no shape memory and thus do not experience a “rebound” phenomenon once placed in the canal, whereas prefabricated glass fiber posts exhibit a significant memory and tend to revert to their original “straight” position. This gives Ribbond posts an edge while being placed in curved canals [49].

Clinical studies evaluating the survival rates of Ribbond posts are scarce. Despite having lower fracture resistance values, clinical survival rates of Ribbond posts have been promising, as seen in a clinical study performed by Piovesan et al. [50] which reported high survival rates of Ribbond posts after the 97-month follow-up period. This suggests that Ribbond posts may be advocated for long-term restorations.

Besides their lower fracture resistance, Ribbond posts also present another discernible drawback. They transfer stresses to the cervical third of the root [32], which could affect the retention of the post when there is a lack or absence of ferrule. The primary purpose of intraradicular post placement is not just retention of the core but to prevent the dislodgement of the tooth-core-post complex from the root at a level that is non-restorable [51]. When teeth are severely structurally compromised, with a ferrule of less than 2 mm, the need for a biologic post that does not compromise the tooth structure further or cause catastrophic failures is essentially heightened. Nilavarasan et al. [52] conducted a study on primary teeth with the remaining ferrule of only 1 mm and stated that Ribbond posts had a better fracture strength than prefabricated glass fiber posts. Further studies should be undertaken to evaluate the role of Ribbond posts in restoring severely structurally compromised teeth, with inadequate ferrule.

Although in vitro studies provide better standardization in terms of sample preparation and evaluation, well-designed randomized clinical trials with a long follow-up period are needed to eliminate the difference between in vitro and in vivo environments and reach a conclusive clinical opinion regarding the behavior and in vivo effectiveness of the Ribbond post and core system.

CONCLUSIONS

The focus of restoring teeth with compromised structure should shift to prevent the tooth from any harm during function in the long term. As seen within the limitations of the present systematic review, although Ribbond posts have less fracture resistance when compared to other contemporary post and core systems, they present the most favorable mode of failure. The fracture mode is almost never at the cost of the tooth-core-post complex, resulting in repairable non-catastrophic fractures. This makes Ribbond posts a suitable biomimetic restorative alternative for rehabilitating structurally compromised teeth.

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