Fiber-Reinforced Composites in Fixed Prosthodontics: A Comprehensive Overview of Their Historical Development, Types, Techniques, and Longevity

Abstract

Background: Fiber-reinforced composites (FRCs) have emerged as transformative materials in restorative dentistry, particularly for managing partial edentulism through fixed partial dentures (FPDs). Their superior aesthetic, mechanical, and adhesive properties offer a minimally invasive alternative to traditional metal–ceramic restorations. Objective: This review aims to evaluate the historical evolution, clinical applications, technological advancements, and prospects of FRCs in prosthodontics, emphasizing their potential to deliver durable, aesthetic, and cost-effective treatment solutions. Methods: This narrative review follows the SANRA guidelines. A comprehensive literature search was conducted across PubMed, ScienceDirect, and Google Scholar for studies published between January 1995 and January 2025. Search terms included “fiber-reinforced composite”, “fixed prosthodontics”, “fixed partial dentures”, “adhesive restorations”, and “implant-supported restorations”. Only English-language studies addressing the clinical applications, mechanical properties, technological innovations, or survival outcomes of FRCs were included. Data were extracted from original research papers, systematic reviews, and narrative reviews. Results: Advancements in fiber architecture, resin matrices, and polymerization techniques have enhanced the strength, aesthetics, and longevity of FRC-based FPDs. Their high flexural strength, fatigue resistance, and compatibility with adhesive restorative techniques provide clinicians with versatile treatment options. Clinical studies demonstrate favorable survival rates and long-term success, positioning FRC FDPs as reliable alternatives to conventional restorations. Emerging technologies such as CAD/CAM and 3D printing further broaden their scope and precision. Conclusions: FRC FPDs have evolved from interim solutions to predictable, long-term restorations. With ongoing technological innovations and clinical validation, they are poised to become a mainstream treatment choice in prosthodontics. FRC FPDs offer a durable, aesthetic, and cost-effective solution aligned with minimally invasive dentistry, reducing tooth preparation while improving patient-centered outcomes.

1. Introduction

Fiber-reinforced composites (FRCs) are advanced materials engineered by integrating a matrix material with high-strength fibers, significantly enhancing the mechanical properties of the composite. The use of dental FRCs began in the early 1960s with glass fibers and in the early 1970s with carbon or graphite fibers. These materials were originally developed to strengthen denture base polymers such as polymethyl methacrylate (PMMA) [1,2]. Over the past three decades, clinical acceptance grew alongside improvements in resin systems, design principles and clinical expertise. These materials are employed to address various clinical challenges posed by traditional bulk metals, ceramics, and polymers, meeting stringent regulatory standards for medical devices and biomaterials globally [1,3]. FRC materials significantly enhance dentistry by offering excellent mechanical properties. The high elastic modulus fibers within a flexible matrix ensure an optimal strength-to-weight ratio, exceptional durability, flexural strength, and resistance to corrosion and wear [4]. In dental applications, FRCs have facilitated the creation of better dental resin composites with tailored mechanical properties suitable for high load-bearing capacities and robust substructures [5].

Partial edentulism, the condition where some but not all natural teeth are missing in a dental arch, poses significant challenges for achieving effective prosthetic restoration due to the loss and deterioration of alveolar bone, adjacent teeth, and supporting structures [6]. Traditional solutions, such as removable partial dentures, teeth-supported fixed partial dentures (FPDs), and implant-supported prostheses, have been widely used. However, conventional metal-based crowns and FPDs often require extensive removal of tooth structure, while all-ceramic FPDs introduced to mitigate these issues still face limitations [7]. Recently, FRC FPDs have emerged as a promising alternative, offering less invasive procedures and better aesthetic outcomes. Early clinical applications of dental FRCs faced challenges, particularly in denture base polymers [2]. However, the introduction of pre-impregnated glass fibers and systems like everStickC&B (GC Corporation, Tokyo, Japan) in the late 1990s revolutionized the direct fabrication of customized FPDs [8]. Modern advancements in CAD/CAM and 3D printing technologies have further expanded the clinical applicability of FRCs, enabling their use in a wide range of dental disciplines, including orthodontics, periodontics, endodontics, prosthodontics, and restorative dentistry [9]. Particularly in prosthodontics, FRC materials have been instrumental in fabricating FPDs and removable devices, showcasing advantages in minimally invasive preparations, enhanced aesthetics, and cost-effective fabrication methods.

The dual composition of FRC prostheses include fiber composites for the framework made from glass, carbon, polymers and hybrid or microfilled composites for the veneer surface. The framework structure, designed to support vertical loads and enhance resistance to dislodgement, consists of continuous, unidirectional fibers. Additional fibers may be incorporated to support the pontic and counteract delamination [10,11]. Veneer materials used in these prostheses often involve light-cured hybrid or microfilled composites often based on resinous substances like A-glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate (UDMA), encasing the fibers, with laboratory-fabricated prostheses potentially undergoing an additional heat polymerization step to improve mechanical properties like flexural strength and wear resistance [12,13].

To address the biomechanical demands of the oral environment, FRC FDPs must fulfill several key requirements [14]. The framework must provide sufficient flexural strength and stiffness to withstand occlusal forces without fracture, which is achieved by placing a high volume of continuous unidirectional fibers in the connector areas [15]. The design must also prevent delamination between the fiber framework and the veneering composite, often requiring specific fiber orientations and adequate veneer thickness [15,16]. Furthermore, the prosthesis must effectively transfer and dissipate functional loads to the abutment teeth, which dictates the design of the retention elements (e.g., bonding wings, inlays) to ensure they are placed on the non-load-bearing surfaces or within adequately prepared cavities to resist dislodgment [16,17].

Despite early concerns about the lack of clinical evidence, subsequent studies have demonstrated improved survival rates and positive clinical outcomes for FRC when used as FPDs both on natural abutment [18,19,20,21,22], and as both partial and complete fixed dental prostheses (P-FPDs) on implants [23,24]. Moreover, FRC prostheses offer superior aesthetics, reparability, and chemical adhesion to resin cement. The ability to bond effectively to abutment teeth without extensive preparation, combined with a strong foundation for adhesive cementation, enhances the longevity and functionality of dental restorations. These features make FRC FPDs a balanced choice in terms of functionality, aesthetics, and affordability in dental care [25,26].

The scope of this narrative review encompasses a comprehensive analysis of fiber-reinforced composites (FRCs) in fixed prosthodontics. It traces the historical development, material properties, and diverse clinical applications of FRCs for fixed partial dentures (FPDs). The review critically examines the technological advancements that have improved their performance, including innovations in fiber architecture and fabrication techniques like CAD/CAM. Furthermore, it synthesizes clinical evidence on the survival rates and long-term outcomes of FRC FPDs, ultimately discussing their evolving role from interim to definitive restorations and their future potential in minimally invasive, aesthetic dentistry.

2. Methodology

This narrative review adheres to the guidelines outlined by the Scale for the Assessment of Narrative Review Articles (SANRA) standards [27]. It aims to comprehensively analyze the latest literature on the role and clinical applications of fiber-reinforced composites (FRCs) in fixed prosthodontics. In this review, three electronic databases—PubMed, ScienceDirect, and Google Scholar—were systematically searched for relevant research articles published between January 1995 and January 2025. A combination of keywords and Boolean operators was used, including: “fiber-reinforced composite” OR “composite resin” AND “fiber-reinforced composites” AND “fracture resistance” OR “glass fibers” AND “fiber-reinforced composite” OR “fixed prosthodontics” AND “resin-bonded bridge”, as well as broader search terms such as “Dental Prostheses”, “Fixed Partial Dentures”, “Adhesive Restorations”, and “Implant-Supported Restorations”. The search was restricted to English-language publications. Regarding inclusion criteria, studies were considered eligible for inclusion if they were published in English, focused on the clinical application, mechanical properties, technological innovations, or survival outcomes of FRCs in fixed prosthodontics, and included either in vitro or in vivo and clinical data relevant to FRC-based prostheses. Studies were excluded if they were not related to dental applications of FRCs, lacked original data or clinical relevance, or were review articles that did not demonstrate methodological transparency. The selection of studies was conducted in two distinct stages. In the first stage, titles and abstracts were screened, and duplicate entries were removed. In the second stage, full-text articles were reviewed for relevance and quality. Studies were included if they addressed the use of FRCs in fixed prosthodontics, discussed fiber types, fabrication techniques, or evaluated the longevity of FRC-based prostheses. Data extraction was independently carried out by two authors (M.A.M. and B.M.E.A.), and the accuracy of the extracted data was verified by a third reviewer (M.A.F.) to ensure consistency and reliability. It is acknowledged that narrative reviews inherently lack the statistical rigor and structured methodology of systematic reviews. The studies included in this review vary in design, sample size, and duration of follow-up, and most of them are observational or retrospective in nature, with limited availability of randomized controlled trials. After refining the inclusion criteria, articles were included if they presented evidence on the clinical applications, technological advancements, mechanical properties, or survival outcomes of FRCs in dental prosthetics. To ensure comprehensive coverage, data were extracted from original research papers, review articles, meta-analyses, and systematic reviews.

3. Historical Development and Evolution of FRC Materials

The use of dental FRCs began in the early 1960s with glass fibers and in the early 1970s with carbon or graphite fibers (Figure 1). These materials were originally developed to strengthen denture base polymers such as polymethyl methacrylate (PMMA) [1,2]. However, early attempts did not yield clinically viable methods until the late 1980s and early 1990s, when ultra-high modulus polyethylene, glass, and aramid fibers were experimented [28,29,30].

Technical feasibility for reinforcing denture base polymers was achieved with partial fiber reinforcements of PMMA pre-impregnated glass fibers [31]. Subsequently, FRC frameworks were evaluated for a range of uses, including indirect FPDs, implant-supported FPDs, fixed orthodontic retainers, and periodontal splints [32,33], and FRC root canal posts were introduced [34].

Although early commercial attempts with FRC materials such as Vectris (Ivoclar Vivadent AG, Schaan, Liechtenstein) and Fibrekor (Pentron Clinical Technologies, Orange, CA, USA) showed promise, they were hindered by failures related to poor bonding between the veneering particulate filler composite (PFC) and the FRC framework. In the late 1990s, a new approach was introduced with the everStickC&B brand, which combined the characteristics of Polymethyl methacrylate (PMMA) with light-curable monomers [8]. This innovation allowed for easier handling and curing, making it suitable even for direct intraoral applications. everStickC&B (was mainly used for custom-fabricated FPDs, root canal posts, and splints placed directly in the patient’s mouth. More recently, the development of short fiber-reinforced composites has helped overcome some of the shortcomings of traditional composites (Figure 1). When fibers with high aspect ratios are properly distributed, aligned, and securely bonded to the polymer matrix, they offer significant reinforcement, enabling the construction of strong substructures capable of withstanding high functional loads under veneering PFCs [5,35].

Currently, FRCs are primarily utilized in direct restorative and prosthetic dental treatments, while more complex restorations are typically fabricated indirectly in dental laboratories. Additionally, FRCs are employed in the repair of existing metal-based FPDs, porcelain veneers, traditional removable partial and complete dentures, as well as implant-supported overdentures [36,37,38,39,40]. Newer applications include fabricating indirect FPDs using CAD/CAM and 3D-printing prostheses [9,41]. Clinical experiences with FRC FPDs have shown good functionality [21,42,43], and FRC reinforcement of removable dentures has improved fatigue resistance and reduced recurrent fractures [44,45,46]. Nevertheless, the application of FRC reinforcement in removable dentures is still relatively limited, primarily because dental laboratory technicians lack adequate information and guidance on its use.

Figure 1. Timeline Diagram: Historical Evolution of Dental FRCs.

Figure 1. Timeline Diagram: Historical Evolution of Dental FRCs.

The integration of CAD/CAM technology has significantly enhanced the construction and clinical performance of FRC-based prostheses. Industrially produced FRC discs, made under controlled temperature and pressure, exhibit reduced voids, defects, and internal stress, thereby improving structural reliability and fiber alignment [47]. Precise CAD design and milling that take fiber orientation into account can improve the biomechanical properties of both the framework and the veneering material, thereby minimizing the risk of fractures [48]. CAD/CAM FRC technology also allows for the precise production of post and core systems in various angulations, diameters, and shapes [49,50,51].

4. Types of Fiber-Reinforced Composites

FRCs have evolved significantly since their inception. These composites, made from reinforcing fibers such as Glass fibers and carbon Fibers. Kevlar (Aramid) Fibers, Vectran Fibers or Organic Fibers encapsulated within a polymerized resin matrix (bisphenol-A-glycidyl dimethacrylate (bisGMA) and triethyleneglycol dimethacrylate (TEGDMA), provide a range of unique properties suitable for various dental treatments.

4.1. Types of Fibers Used in Fiber-Reinforced Composites

Several types of fibers have been investigated in the literature for dental applications (

Table 1. Classification of Glass Fibers Used in FRCs.

Sub-Classification	Composition/Properties	Advantages	Disadvantages/Limitations	Applications in Dentistry	Reference
Glass A	Alkali-based glass; low chemical resistance	Low cost, useful as filler in plastics	Poor strength and water resistance	Rarely used; mainly as filler	[49,50,51]
Glass C	High corrosion-resistant glass	Strong chemical protection	Lower mechanical strength compared to E-glass	Surface layers needing enhanced chemical durability	[49,50,51]
Glass E	Electric glass; superior electrical and mechanical properties	Most commonly used; high strength; good water resistance	Contains volatile substances like fluorine	Widely used in dental composites and reinforcement	[49,50,51]
Glass R	Calcium alumino-silicate reinforcement glass	High strength and acid corrosion resistance	Higher cost than E-glass	Applications requiring durability and strength	[49,50,51]
Glass S	High-strength, flexible glass produced via specialized manufacturing	Exceptional flexibility and tensile strength	Very expensive; limited dental applications	Rarely used in dentistry; mainly aerospace	[49,50,51]

and Table 2). Among them, glass fibers are the most widely used in dental FRCs, primarily because of their transparent appearance, high tensile strength, and low elongation at break [52], and high modulus of elasticity. These characteristics, along with the ability to bond glass fibers to the dimethacrylate polymer matrix through coupling agents, make them a suitable material for dental use [5].

Glass fibers are classified according to their chemical composition (Table 1). While E-glass fibers are not the most durable type, they are the most frequently used in both the dental field and the broader composite industry [53]. S-glass fibers offer higher tensile strength but are costly to process and limited in availability. R-glass fibers, with an aluminosilicate glass structure free of MgO and CaO, offer increased acid corrosion resistance but are less popular [54]. Less common types include A-glass and C-glass fibers used as reinforcing fillers for plastics. Radio-opacity, essential for dental FRCs, depends on the glass composition. Specially designed AR-glass fibers provide high x-ray visibility in composites. Typical fiber diameters for dental glass fibers range from 15–18 μm, with 5–6 μm being used in FRCs with discontinuous short fibers.

Several non-glass fibers have been investigated for dental FRCs (Table 2). Carbon fibers (carbon content ~30–70%) provide high strength, fatigue resistance and toughen composites, but their dark color reduces aesthetics and their use in dentistry is limited; research on graphene-reinforced composites is noted. Kevlar fibers (aromatic polyamide derived from nylon) offer high impact and abrasion resistance and excellent fatigue resistance, but have poor aesthetics and limited dental use. Vectran fibers (aromatic polyester-based) provide high abrasion and impact resistance but are expensive and hard to manage. Organic fibers (polyester, acrylic, nylon, polypropylene, aramid, UHMWPE, PBO, PBI, M5, PI) are lightweight and versatile with some variants highly aesthetic, though some exhibit low bonding with resins. Aramid fibers (high-crystallinity organic fibers) have high strength but poor off-axis bonding with resins and their surface inertness limits effectiveness. Polyethylene fibers (high-strength organic fibers) can improve flexural strength, modulus, and aesthetics but are limited by cost and specific handling requirements [55].

Table 2. Classification of other types of fibers used in FRCs [55].

Fiber Type	Composition/Description	Advantages	Limitations	Applications in Dentistry
Carbon Fibers	Carbon content ~30–70%; higher content increases strength	High strength, fatigue resistance, toughens composites	Dark color reduces esthetics	Limited use; ongoing research on graphene-reinforced composites
Aramid Fibers	Aromatic polyamide (nylon-derived); high-crystallinity organic fiber	High impact and abrasion resistance; excellent fatigue resistance	Poor esthetics; limited bonding with resins due to surface inertness	Used when enhanced toughness is needed; bonding can be improved with surface treatments
Vectran Fibers	Aromatic polyester-based synthetic fibers	High abrasion and impact resistance	Expensive, difficult handling	Used in high-performance dental and medical materials
Polyethylene Fibers	High-strength organic fibers (e.g., UHMWPE)	Exhibit excellent toughness, impact resistance, and flexibility; enhance crack resistance in composites	Cost and handling limitations	Ideal for esthetic composite reinforcement
Other Organic Fibers	Includes polyester, acrylic, nylon, polypropylene, PBO, PBI, M5, and PI fibers	Lightweight, versatile, some variants highly esthetic	Some exhibit weak resin bonding	Alternative reinforcement options

Table 2. Classification of other types of fibers used in FRCs [55].

Fiber Type	Composition/Description	Advantages	Limitations	Applications in Dentistry
Carbon Fibers	Carbon content ~30–70%; higher content increases strength	High strength, fatigue resistance, toughens composites	Dark color reduces esthetics	Limited use; ongoing research on graphene-reinforced composites
Aramid Fibers	Aromatic polyamide (nylon-derived); high-crystallinity organic fiber	High impact and abrasion resistance; excellent fatigue resistance	Poor esthetics; limited bonding with resins due to surface inertness	Used when enhanced toughness is needed; bonding can be improved with surface treatments
Vectran Fibers	Aromatic polyester-based synthetic fibers	High abrasion and impact resistance	Expensive, difficult handling	Used in high-performance dental and medical materials
Polyethylene Fibers	High-strength organic fibers (e.g., UHMWPE)	Exhibit excellent toughness, impact resistance, and flexibility; enhance crack resistance in composites	Cost and handling limitations	Ideal for esthetic composite reinforcement
Other Organic Fibers	Includes polyester, acrylic, nylon, polypropylene, PBO, PBI, M5, and PI fibers	Lightweight, versatile, some variants highly esthetic	Some exhibit weak resin bonding	Alternative reinforcement options

4.2. Types of Polymers Used in Fiber-Reinforced Composites

Synthetic polymers used in FRCs can be classified based on the structure of their polymer chains. Following the polymerization of monomers during the setting process, the resulting polymers may form either linear (thermoplastic) or cross-linked (thermoset) structures [56]. Thermoplastic matrices include polymers such as polyamide (PA, nylon), polycarbonate (PC), polyurethane (PU), poly (ethylene terephthalate glycol) (PETG), polyetheretherketone (PEEK), and polypropylene (PP) [57,58]. In these materials, adhesion to glass fibers is mainly based on physical interactions rather than chemical bonding between the resin and the fiber surface. However, thermoplastic polymers are generally not used in dentistry. These materials are rigid at room temperature but become soft, flexible, and moldable when heated to their glass transition temperature.

In contrast, thermoset polymers undergo an irreversible chemical curing process that results in a cross-linked covalent network. This structure remains stable under high temperatures and is resistant to most solvents, although partial breakdown can occur through transesterification reactions [59].

The FRCs used in dental applications, the resin matrix polymerizes and bonds to glass fibers simultaneously using thermoset copolymer monomers such as bisphenol-A-glycidyl dimethacrylate (bis-GMA), triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA). These are typically activated by a blue light-sensitive initiator system [60]. The polymerization process results in a densely cross-linked polymer matrix, which can be challenging to bond later with dental adhesives and luting cements.

To improve both clinical handling before curing and subsequent adhesion, linear polymethyl methacrylate (PMMA) polymers are incorporated into the matrix. This creates a semi-interpenetrating polymer network (semi-IPN) [61,62]. During curing, the dimethacrylate monomers primarily form a cross-linked structure interwoven with PMMA phases. This cross-linked network gives the FRC a higher modulus of elasticity compared to those made with thermoplastic or purely semi-IPN matrices [63]. However, thermoplastic and semi-IPN matrices generally provide superior toughness compared to fully cross-linked thermoset FRCs.

The semi-IPN matrix offers advantages over purely cross-linked dimethacrylate or epoxy systems in terms of improved handling and enhanced bonding with resin luting cements and veneering composites—particularly for indirectly fabricated restorations and root canal posts [64,65,66].

4.3. Resin Impregnation of Fibers

Proper adhesion between reinforcing fibers and the resin matrix is essential for effective fiber-reinforced composites (FRCs). This process, known as resin impregnation, depends on the fiber surface wetting properties, fiber spacing, and resin viscosity [67,68]. Tightly bound fiber weaves and ribbons are more difficult to impregnate with resin [69].

Powder-liquid type denture base polymers, composed of PMMA powder beads and MMA monomers, present particular challenges for impregnation due to the large size of PMMA particles. This often results in reduced fiber volume and internal voids that inhibit polymerization [31]. The high polymerization shrinkage of MMA further complicates this process [70]. To address these issues, a preimpregnation method using a PMMA-solvent solution was developed, allowing better impregnation and control over polymerization contraction and dimensional changes [71]. In thermoset monomer systems, higher fiber loading is achievable since these systems lack powder bead fillers [72]. Melt thermoplastics have also been tested for fiber impregnation, though not widely adopted [58]. Mixing thermoset monomers with thermoplastic polymers improves handling and bonding properties, creating a semi-IPN resin matrix for FRCs (everStick products, Stick Tech-GC Group), with an enriched PMMA surface layer.

4.4. Glass Fiber Adhesion to the FRC Polymer Matrix

For effective adhesion of glass fibers to a polymer matrix, strong chemical bonds must form during resin polymerization, which is facilitated by silane coupling agents on the glass surface. Thermoset polymers create irreversible cross-linked structures during curing, which are stable despite high temperatures or solvents [59].

Effective load transfer in FRCs is dependent upon a well-established adhesive interface. This is achieved through hydroxyl groups present on silicate-based glass surfaces, which chemically interact with thermosetting monomers via silane coupling agents such as 3-trimethoxysilylpropyl methacrylate [73,74]. During production, glass fibers are treated with antistatic compounds and silane agents to form a stable, hydrolysis-resistant polysiloxane network [75,76]. Durable FRCs require not only strong fiber-matrix adhesion but also a dissolution-resistant glass composition [77]. For indirect restorations or prefabricated FRC root canal posts, adherence of dental adhesives or resin luting cement to the FRC surface is essential.

4.5. Dental Adhesives’ Adherence to FRC Construction

For FRC structures to effectively manage and transfer occlusal forces to the tooth, periodontal ligament, and jawbone, a strong bond to the tooth is crucial, achieved through both mechanical and adhesive methods [78]. The direct technique, in which FRC is polymerized and bonded directly onto the tooth, provides an optimal, unified construction. However, bonding prefabricated FRC components or root canal posts is more difficult because their highly cross-linked polymer matrices have limited reactivity with dental adhesives and resin luting cements. This can result in problems such as delamination and debonding [79].

To overcome these adhesion difficulties, the semi-interpenetrating polymer network (semi-IPN) matrix was developed for dental FRCs [40,80,81,82]. In these dental FRCs, ethylene glycol dimethacrylate (EGDMA) is replaced with light-curable bis-GMA/TEGDMA co-monomers, while a non-cross-linked PMMA phase remains soluble in the monomers found in dental adhesives and luting cements. This PMMA phase facilitates adhesion through dissolution and diffusion, forming a secondary interpenetrating polymer network (sec-IPN) at the interface [62].

The adhesion mechanism involves wetting, adsorption, and diffusion, with the degree of monomer diffusion and molecular chain involvement being critical for bond durability [83]. Factors like monomer solubility parameters, contact time, temperature, and semi-IPN polymer structure significantly affect the adhesion process [84]. Eliminating solvents from dental adhesives before polymerization is vital to avoid interference with the bonding process.

In a recent systematic review and meta-analysis, Escobar et al. studied the fracture resistance of FRC restorations and reported that FRC restorations exhibited significantly higher fracture resistance (976.0 N) compared to non-fiber-reinforced restorations (771.0 N; p = 0.008) and unrestored cavities (386.6 N; p < 0.001). However, their resistance remained lower than that of intact teeth (1459.9 N; p = 0.048). The findings underscore the reinforcing effect of glass and polyethylene fibers in enhancing the mechanical performance of composite restorations [85].

Khan et al. reported valuable insights into the adhesion mechanisms both within the components of glass fiber-reinforced composites, specifically between the fibers and the matrix and between the resin luting agent and the overall glass FRC structure. The findings of this review emphasize the role of adhesion science in the design, functionality, and clinical effectiveness of fiber-reinforced composite materials. Key processes such as surface treatment of glass fibers using antistatic agents and the application of silane coupling agents are essential for achieving optimal wetting and impregnation. These steps facilitate covalent bonding between the glass fibers and the resin matrix, thereby enhancing the FRC performance [86].

For direct restorations, an oxygen-inhibited layer on the freshly cured polymer matrix surface aids adhesion. However, this layer is absent in indirectly fabricated or mechanically ground restorations, necessitating alternative adhesion strategies [40,87]. Surface roughness of the FRC bonding substructure also plays a crucial role, providing additional surface area for micromechanical bonding, with the direction of fibers relative to debonding stress impacting bond strength [88,89,90].

5. Characteristics of FRC- FPD’ Structure

Fixed Partial dentures (FDPs) made from fiber-reinforced composites (FRCs) are classified into several types based on their method of retention: surface-retained FPDs, inlay/onlay-retained prostheses, full-coverage crown-retained prostheses, and hybrid designs (

Table 3. Structural Features of FRC-FDPs.

FRC-FDP Type	Fiber Framework	Key Structural Features	Veneering & Aesthetic Considerations
Surface-Retained [14]	High volume of continuous fibers in the connector [15].	Bonding wings placed incisally in wings to resist dislodging [17]. Requires large bonding area [17]. Fibers in bonding wings are protected with a polymerizable fluorinated resin (PFR) layer [17]. Connector thickness (palatal/lingual to buccal direction) is more critical than width for stiffness and durability [15]. Fibers should be positioned on the tension side of the prosthesis [15]. Minimal proximal preparations may be needed in anterior FPDs to optimize connector strength [15].	Veneering composite is applied over the framework. The thin, translucent nature requires careful masking to prevent graying (dark oral background) [17].
Inlay/Onlay-Retained [14]	Continuous unidirectional fibers run between cavities [16].	Box preparation depth > 1.5 mm in sound tooth structure is required for vertical support [16]. An extra bonding wing is advised for canine abutments in canine-guided occlusion [16]. Capable of withstanding high forces (up to ~2600 N) [16]. Requires adhesive cementation with composite resin luting cements for a secondary IPN bond [16].	Veneering layer on the occlusal surface should be at least 1.5 mm thick. Can be done with laboratory or direct restorative composites [16].
Full-Coverage Retained [14]	Woven copings connected by continuous unidirectional fibers [17].	The framework is built on full-coverage preparations, providing maximum retention and support. The design relies on the principles of a conventional fixed prosthesis [17].	The entire framework is covered with veneering composite for aesthetics and polishability [17]. An opaque layer is often necessary to mask the dark oral background and prevent show-through in the connectors [17].

) that combine multiple retention elements to meet specific clinical requirements [14]. While FRC FPDs can be fabricated either directly in the mouth or indirectly in a dental lab, the underlying design principles are generally consistent.

Single-unit composite crowns can be reinforced using woven bidirectional continuous fibers to form the coping, which is then layered with veneering composite. In multi-unit FPD designs, especially those involving pontics in both anterior and posterior regions, additional fiber reinforcement is essential to prevent delamination between the veneering composite and the underlying framework [15].

Surface-retained resin-bonded FPDs are bonded to the abutment teeth either from both ends or just one. The vertical placement of the bonding wing on the abutment tooth is critical fibers should be positioned near the incisal edge to counteract dislodging forces. The wing must also cover a substantial bonding area. Typically, wings are bonded to the lingual or palatal surfaces, though buccal or labial bonding is possible when space is limited. To protect the fibers in the bonding wings, a layer of polymerizable fluorinated resin (PFR) is applied [17]. In the connector areas, continuous unidirectional fibers should be arranged in a cross-sectional shape that can withstand occlusal forces effectively. Research shows that the thickness of the connector in the palatal/lingual to buccal direction is more critical than width for ensuring stiffness and durability. The connector typically contains the maximum fiber volume. If additional space is available, fibers should be positioned on the tension side to enhance strength, with the remaining space used for veneering composite. In anterior FPDs, especially in the upper jaw, optimizing connector thickness is vital, and in some cases, minimal proximal cavity preparations may be needed to improve connector strength [15].

Inlay/onlay-retained FPDs are constructed by running continuous unidirectional fibers between prepared inlay or onlay cavities (Table 3). They can be produced using direct or indirect techniques. For indirect restorations, cementation involves composite resin luting cements that contain conventional adhesive systems to activate bonding through a secondary IPN mechanism. Self-adhesive cements are less effective for bonding to FRC frameworks but may bond well to dentin. When bonding to canine teeth, it’s advisable to add an extra bonding wing (palatal or buccal) to prevent inlay loosening, especially in canine-guided occlusions. If existing restorations are present in abutments, they should be removed to create space for both the fiber framework and veneering resin. In posterior restorations (premolars and molars), sufficient vertical support is essential to resist biting forces. A box preparation with a depth greater than 1.5 mm in sound teeth can adequately support the prosthesis, provided fibers are accurately positioned within the cavity. These inlay FPDs can withstand forces up to 2600 N, well above the average masticatory load in the molar region (approximately 800 N). Veneering can be done using laboratory composites or direct restorative composites. The veneering layer on the occlusal surface should ideally be at least 1.5 mm thick [16].

Full-coverage crown-retained FPDs are created by layering woven FRC on prepared abutments to create copings (Table 3). Continuous unidirectional fibers are used to connect these copings from one occlusal surface to the other. Additional fiber segments placed perpendicular to the main framework help support pontic cusps. Veneering is performed with laboratory-applied PFR, and the entire FRC framework is covered with veneering composite to ensure a smooth, tooth-colored, and polishable surface. Special attention is needed in interproximal areas for aesthetic reasons. If the FRC framework isn’t fully masked by veneering composites or an opaque layer, the dark oral background may show through the connectors, compromising esthetics [17].

FRCs can also reinforce provisional FPDs during the fabrication of conventional FPDs. In provisional FPDs, provisional automix or powder-liquid acrylic resins are reinforced with glass fibers.

6. Mechanical Properties and Load-Bearing Capacities of FRCs

Biomechanically, the loading conditions in the oral cavity are demanding, as has been described previously [91]. Prosthodontic and restorative devices must be designed to resist the same magnitude of forces as intact natural teeth.

The direction of biting force needs to be considered carefully because FRCs are generally not isotropic (independent of direction of applied load), but rather are often anisotropic (different depending on the direction of the applied loads) [17].

The mechanical strength of FRC materials is often measured using the three-point flexural strength (bending strength) test. The homogeneity and location of the fiber-rich layer significantly influence strength values, with fibers providing the highest reinforcement when located on the side of highest tensile stress [92]. Continuous unidirectional FRCs exhibit four failure types: axial tensile failure, transverse tensile failure, shear failure, and fiber buckling, depending on the applied stress. Static strength depends on fiber content, with optimal properties seen at approximately 68 vol% fiber content [34]. Water sorption can reduce the strength and modulus of elasticity of the FRC by about 15% within 30 days due to polymer matrix plasticization [93,94]. Testing conditions, including specimen dimensions and span length, significantly affect the strength and modulus of elasticity values, which are given in MPa and must be interpreted in the context of these factors [95].

Long continuous fibers in FRCs exhibit the highest anisotropic mechanical properties due to their large surface area, which enhances bonding with the polymer matrix. Discontinuous short fibers offer reinforcing efficiency between long continuous fibers and low aspect ratio particulate fillers. The critical fiber length (lc) is the minimum length required for a fiber to achieve ultimate strength and maximum matrix shear strength [96]. This can be determined by a single fiber fragmentation test and is influenced by the elongation at break and adhesion to the matrix [89].

When continuous fibers are cut into discontinuous fibers for applications like fillings and core-build-ups, the FRC behavior changes. Discontinuous short fibers exhibit properties influenced by their direction and length [97,98,99]. Replacing continuous unidirectional fibers with longitudinally oriented discontinuous fibers reduces ultimate tensile strength, making the FRC anisotropic. Randomly oriented fibers further reduce strength, resulting in isotropic FRC. The aspect ratio (fiber length-to-diameter ratio) plays a key role in determining the efficiency of stress transfer in fiber-reinforced composites. The critical fiber length, defined as the minimum fiber length required to enable effective stress transfer from the resin matrix to the fiber, must be substantially greater than the fiber diameter. For dental E-glass fibers with diameters of 15–18 µm, the critical fiber length typically ranges from 0.5 to 1.5 mm, depending on the quality of the fiber–matrix interfacial adhesion [89]. Orientation of discontinuous fibers can be three-dimensional or two-dimensional. Packing in tooth cavities orients fibers two-dimensionally, enhancing mechanical interlocking and reducing curing shrinkage. Discontinuous FRCs can fail through polymer matrix cracking, fiber debonding, and fiber fracture [17].

The load-bearing capacities of FRC FPDs with different pontic materials and thicknesses were evaluated by Perea et al. [9] in their study, 72 FPDs were fabricated using continuous unidirectional glass fibers (everStickC&B) [8]. The pontics were made from glass ceramics, polymer denture teeth, and composite resin, with varying occlusal thicknesses (2.5 mm, 3.2 mm, and 4.0 mm). The results indicated significant differences in load-bearing capacities depending on the material and thickness of the pontics. Ceramic pontics with a 4.0 mm thickness demonstrated the highest load-bearing capacity, while polymer denture teeth and composite pontics performed better at thinner dimensions. This suggests that increasing the occlusal thickness enhances the prosthesis’s strength, particularly with ceramic pontics [9].

7. Advantages and Challenges in FRC Prosthetic Application

The use of Fiber Reinforced Composite (FRC) prostheses presents notable advantages in terms of aesthetics and minimally invasive treatment (

Table 4. Advantages and Disadvantages of FRC FPD.

Advantages	Disadvantages/Challenges
Superior Aesthetics: Metal-free framework provides excellent, natural aesthetics [13,16].	Aesthetic Complications: Loss of surface shine and excessive translucency [13,16].
Minimally Invasive: Requires little to no tooth preparation, preserving natural tooth structure [26].	Fracture Risk: Potential for framework or veneer fracture if not designed correctly [13,16].
Biocompatibility: Does not wear opposing tooth enamel [13,16].	Technical Sensitivity: Success depends on correct framework design and the use of high-quality, pre-impregnated fibers to prevent issues [13,16].
Strong Adhesion: Achieves high bond strength to tooth structure, exceeding that of traditional dental alloys [25].	Reparability Required: While failures are often repairable, this requires careful analysis and skilled intraoral repair by the dentist [13,16].
Cost-Effective: Offers a balance between functionality, aesthetics, and affordability.	Reparable: Most failures can be repaired directly in the patient’s mouth using composite resin technology [13,16].

). FRC prostheses offer a strong metal-free framework and do not wear opposing tooth enamel [13,16].

FRC Fixed Partial Dentures (FPDs) are presented as a less invasive alternative to procedures like implants or traditional crown preparations. They require minimal preparation and offer excellent aesthetics. The preparation geometry of FRC FPDs enables a strong foundation for adhesive cementation, potentially enhancing the longevity of the restoration [26]. This minimally invasive approach not only preserves more of the natural tooth structure but also strikes a balance between functionality, aesthetics, and affordability.

One of the key advantages of FRC prostheses is their ability to bond effectively to abutment teeth, addressing both retention and resistance forms. Depending on the clinical requirements, the restoration can be retained on the abutment teeth surface without additional preparation. The adhesion is achieved chemically, relying on the bond strength between the luting cement and the enamel surface, as well as the specific occlusal conditions. Notably, the bond strength between the luting cements and FRC fixed dentures exceeds that of traditional dental alloys [25].

However, while FRC prostheses provide both functional and aesthetic advantages, several potential clinical challenges have been reported (Table 4). These include undesirable color show-through from the underlying tooth structure or fiber framework, loss of surface luster over time due to wear or inadequate polishing, excessive translucency leading to compromised shade matching, and susceptibility to fracture under high occlusal loads. Such issues can be effectively mitigated by using high-quality pre-impregnated glass fibers with uniform resin distribution, designing the FRC framework with proper support and thickness, and applying sufficient layers of veneering composite resin to enhance opacity and esthetics. Furthermore, a distinct advantage of FRC bridges is their repairability—most failures, such as minor fractures or debonding, can be managed intraorally using direct composite repair techniques, provided that the failure mode is accurately diagnosed and the correct repair protocol is followed [13,16].

8. Techniques of Fabricating FRC-FPDs

FRC-FPDs can be fabricated using direct (in-office), semi-direct (in-office on a silicon die) and indirect (laboratory) methods. Each method has its benefits and drawbacks (

Table 5. Techniques of Fabricating FRC-FPDs.

Technique	Description	Benefits	Drawbacks	Reference
Direct	No tooth preparation required; minimal enamel etching (micro-invasive). Composite is layered and completed in one workflow.	Minimal or no preparation. Single visit. Low cost.	Lower mechanical properties Rigid fibers and limited workspace. Challenging esthetics, finishing, and polishing.	[100,101]
Indirect	Teeth are prepared, impressions taken, and prosthesis fabricated in the laboratory.	Superior mechanical properties due to enhanced laboratory polymerization. Better esthetics and functional design.	Requires two visits. Preparation of cavities with parallel surfaces. Adhesion issues due to multiple polymerizations and potential dentin contamination.	[100,102,103]
Semi-direct	FRC-FPD fabricated chairside on a silicone cast and inserted in the same appointment.	Better esthetics and functional design than direct technique. Single visit.	Requires preparation of cavities with parallel surfaces. Longer chairside time.	[104]

).

8.1. Direct Technique

Direct FRC-FPDs provide a minimally invasive method for immediate aesthetic restoration, eliminating the need for significant preparation of abutment teeth [20]. However, the direct technique is difficult and prone to errors due to the constraints of working within the oral cavity and the challenges associated with shaping the pontic [101].

Digital tools, including intraoral and facial scanning, as well as additive manufacturing techniques, play a crucial role in supporting restorative treatments. In two recent studies by the same group, a digital workflow was outlined for treatment planning and crafting a direct FRC-FPD [105,106]. The digital workflow involved aligning facial and intraoral scans using scan bodies, followed by diagnostic waxing and the creation of a three- or four-piece additive manufacturing (AM) index to assist with the direct restoration process. This approach enabled the accurate transfer of the virtual diagnostic wax-up into the patient’s mouth, ensured precise control over the path of insertion for each index, allowed customization of the space and positioning of the restoration’s lingual wings, and helped minimize the overall clinical procedure time.

Another study outlines a technique for shaping the gingival surface of a pontic into an ovate form using a contoured metal matrix. Composite incorporation in this procedure contributes to enhancing the emergence profile of the pontic [107].

8.2. Indirect Techniques

Indirect FRC-FPDs can be supported by various retention methods, including crowns, inlays, onlays, surface-bonded wings, or a combination of these approaches, forming hybrid-type FRC FPDs [108]. Regardless of the definitive FRC FPD type, the load-bearing FRC framework is veneered with laboratory veneering resin composite [100]. Reconstruction using CAD/CAM technology is typically performed using prefabricated blocks made of porcelain, resin composite, hybrid materials combining resin composite and/or ceramic, or PMMA, which are then shaped through milling [109].

8.3. Semi-Direct Techniques

Semi-direct FRC-FPDs are fabricated chair-side on a silicone cast and inserted during the same visit. Like the indirect technique, this technique requires an invasive parallelizing preparation of the adjacent teeth, often involving proximal box preparations, to ensure precise positioning of the polymerized bridge [104].

9. Discussion

9.1. Clinical Performance and Longevity of Direct and Indirect FRC-FPDs

Direct and indirect Fiber-Reinforced Composite (FRC) fixed partial denture (FPDs) have demonstrated encouraging clinical outcomes, with multiple studies evaluating their mechanical performance and long-term survival.

Following 100 cases for up to nine years, a recent retrospective study investigated the durability of direct FRC FPDs for immediate rehabilitation in a general practice setting [21]. One hundred directly applied DFRC-FPDs were used. Preparation of the proximal cavity was restricted to abutment teeth that already had an existing filling (minimal-invasive approach), while all intact enamel surfaces were preserved (micro-invasive approach). The DFRC-FPDs were reinforced with fiber splints utilizing semi-interpenetrating polymer network matrices (everStickC&B) [8,21]. For a total of 100 direct protheses, the study exhibited high survival rates and moderate success rates. Over a period of up to 9 years, the annual failure rate (AFR) was 1.6% for survival and 8.3% for success.

Another study by Goguta et al. [110] used the same type of the FRC framework (everStickC&B) [8] has evaluated the survival rates of direct FRC anterior and posterior FPDs in 23 patients over a period of 6 years. The survival rates were satisfactory for the protheses that used inlays as retainers (94.7% out of 19), but significantly lower (25%) for the four protheses that used hybrid retainers (one inlay and one wing) [110].

Moreover, Wolff et al. [101] reported a functional survival rate of 73.5% over four years for direct and semi-direct FRC FPDs that were either surface-retained or embedded in minimal preparations on abutment teeth, with 17 out of 26 protheses still functioning. Of these, 12 were classified as “success” and 5 as “survival.” The overall survival rate was 53%, with six FRC FPDs failing completely. The study also found no negative effects on periodontal health over the observation period, although aging effects such as wear, and surface luster degradation were noted. This indicates a risk of disintegration over time, attributed to the composite nature of the FRCs, comprising a fiber framework and veneering composite resin [101].

In a systematic review by Ahmed et al. [20], nine cohort studies were included, involving placement of 592 FRC FPDs in 463 patients. Follow-up periods ranged between 2 months and 8 years. Kaplan–Meier overall survival probability was 94.5% (95% C.I: 92.5–96.5%) at 4.8 years but authors did not identify any randomized controlled trials involving the placement of FRC FPDs in comparison to conventional FPDs or RBBs. The results of the systematic review by Van Heumen et al. [19] estimated the overall survival of FRC FPDs to be 73% at 4.5 years [19]. The included studies involved the placement of 435 FRC FPDs in three hundred and forty patients. There was a clear and significant improvement in the overall survival of FPDs reported by Ahmed et al., (94.4% at 4.8 years), when compared to the previous systematic review (73% at 4.5 years) [19,20].

The studies included in the van Heumen et al. systematic review [19] mainly relied on inlay-retention 52% (n = 227/435), compared to surface retainers 20% (n = 87/435). The most commonly used materials were unidirectional R-glass fibers for the FPD framework (Vectris PonticTM, Ivoclar Vivadent AG, Schaan, Liechtenstein) and an indirect hybrid resin composite (Targis DentinTM, Ivoclar Vivadent AG, Schaan, Liechtenstein).

In contrast, studies included by Ahmed et al. [20] demonstrated a preference for using surface retainers in comparison to inlay retainers for retention of FPDs at 63% and 26%, respectively (

Table 6. Longevity of direct and indirect FRC-FPDs.

Study	Reference	No. of FPDs	Follow-Up Duration	Survival Rate (%)	Success Rate (%)	Type of FRC FPD	Notes
Perrin et al. (2020)	[21]	100	Up to 9 years	98.4%	91.7%	Direct	everStickC&B, minimal invasive
Goguta et al. (2019)	[110]	19	6 years	94.7%	Not reported	Direct	everStickC&B; Inlay retainers
Goguta et al. (2019)	[110]	4	6 years	25%	Not reported	Direct	Hybrid retainers
Wolff et al. (2018)	[101]	26	4 years	73.5%	46.2%	Direct & Semi-direct	17/26 functioning; 12 success
Ahmed et al. (2017)	[20]	592	Mean 4.8 years	94.5%	Not reported	Mixed	Systematic review
Van Heumen et al. (2009)	[19]	435	Mean 4.5 years	73%	Not reported	Mixed	Early materials
Pooled Survival Rate						86.2%
Pooled Success Rate						82.3% (based on limited data)

). Additionally, 64% of delivered FPDs replaced missing anterior teeth. Unidirectional pre-impregnated E-glass fiber bundles embedded in a PMMA/bis-GMA matrix (everStickC&B) and microhybrid veneering resin composite were the materials of choice for the fabrication of FPDs in the majority of included studies [8,19,20,21]. Indirect fabrication of FRC FPDs was the preferred fabrication technique in the majority of studies in both systematic reviews [19,20].

9.2. Factors Affecting the Success and Survival of FRC-FPDs

The influence of study design on failure rates was shown to be higher in practice-based studies compared to university-based randomized controlled trials [21]. Additionally, the construction of FRC-FPD directly is anticipated to be dependent on the type of technique that has been used [100]. Each case in Perrin et al. study [21] was managed by a single dentist, which could influence restoration survival [111]. Tooth type did not significantly impact failure rates in recent studies [20,21], unlike conventional bridges where tooth type influenced time until failure [112]. That might be attributed to the difference in follow-up time and the sample size [21].

The presence or absence of box-shaped cavities in direct FRC-FPDs showed no impact on survival or success times [21,113]. This suggests a micro-invasive approach for prompt esthetic treatment. A possible reason for the debonding observed in the hybrid type of retainer (one inlay and one wing) in the study by Goguta et al. [110] could be the occlusal forces during functions and bruxism, as the teeth with a wing-type retainer were involved in anterior guidance. The performance (fracture strength) of indirect FRC FPDs appears to be partially affected by the size and the method of cavity preparation for FRC FPD retainers [114,115].

The vital role of material compatibility in the survival of FRC FPDs was highlighted in several previous studies [20,72,116,117] Due to the possibility of the silane coupling agent bond failing [72], the Vectris Dentin system—which was frequently utilized in the studies reviewed by van Heumen et al. [19] —had drawbacks. The UDMA matrix-based micro-filled composite veneering material was found to have better compatibility with Vectris, thus resulting in fewer veneer fractures [116]. Micro-hybrid resin composite reinforcement with unidirectional pre-impregnated glass fibers demonstrated improved shear and flexural bond strengths [117], indicating advancements in material composition contributing to improved FRC FPD performance [20] as shown in

Table 7. Factors Affecting FRC Success and Survival.

Factor	Key Findings/Considerations	References
Study Location	Practice-based studies report higher failure rates compared to university-based randomized controlled trials, possibly due to stricter protocols and less routine in practice-based settings.	[118,119,120]
Dentist-Related Factors	Longevity of restorations may depend on operator skills and dentist profiles.	[111]
	FRC-FPD survival may also be influenced when treatment is provided by a single dentist.	[21]
Fabrication Method	Direct fabrication of FRC-FPDs is considered technique-sensitive, requiring higher clinical expertise.	[100]
Tooth Type	No significant survival difference was observed between anterior and posterior teeth; findings may be influenced by sample size and follow-up duration.	[20,21]
Cavity Design on Abutment	No significant difference found between no preparation (micro-invasive) and box preparation (minimally invasive).	[21,113]
Size & Method of Preparation	No significant difference between no preparation, shallow preparation, or deep preparation of abutment teeth.	[114,115]
	No significant difference between cavities prepared with conventional inlay burs versus ultrasonic tips.	[115]
Material Composition & Compatibility	Success depends on factors like adhesive protocols, chemical composition of FRC components, polymerization techniques/devices, and surface conditioning prior to adhesion.	[20,101,103,116,117,121]
Number of Pontics	Limited evidence is available; most studies focus on single-pontic restorations.	[20,21]

.

Indirect FRC RBFPDs commonly fail due to delamination of the veneering composite, fractures, or debonding [19,20]. Issues such as wear and discoloration are inherent to the veneering resins, not the FRC materials [121]. Studies show the most frequent failure modes are cohesive delamination within the veneering resin or adhesive detachment [54,115,122]. Failures may stem from polymerization methods and devices, which affect the degree of conversion and mechanical properties of the veneering resins [123]. Adhesion issues between prepolymerized veneer resin and luting cement could also contribute to debonding failures. The chemical composition of the veneering resin impacts the amount of remaining free monomers, influencing debonding [124]. Inadequate surface conditioning and dentin contamination during adhesion protocols further exacerbate debonding risks [103,125]. Lastly, unsupported areas of veneering resin may lead to veneer fractures [122].

9.3. Applications of FRCs in Dental Prosthetics

The primary use of FRCs in dentistry is in provisional or definitive prosthodontics. FRCs and veneers enable minimally invasive procedures by utilizing a combination of different adhesive and retentive components [126]. An FRC prosthesis may include inlays, onlays, surface-bonded wings, and crowns. FRC can be designed as surface-anchored, inlay-supported prosthetics or fully covered crown-supported dental prosthetics [14]. FRCs can also be used to repair existing conventional prosthetic devices. Repairs of porcelain-fused-to-metal restorations with resin composite veneers can be strengthened with woven glass fiber reinforcement [36,37], removable devices can be reinforced using FRCs [44]. FRCs are applicable in indirect pontic fabrication and can be combined with CAD/CAM-based technologies [9,127,128].

FRCs serve as a framework for crowns and bridges, offering a lighter yet durable alternative to traditional metals. FRC FPDs provide favorable aesthetic outcomes, biocompatibility, and affordability, meeting patient expectations in single-visit replacements for central maxillary teeth [129]. Moreover, FRC-FPDs are suitable for elderly patients and young individuals who cannot tolerate local anesthesia, offering minimal preparation and reduced chair-time compared to conventional FPD procedures [130,131]. In addition, it offers a conservative solution to close the diastema.

Furthermore, FRCs can stabilize periodontally compromised abutments, such as an FRC bridge replacing lower mandibular teeth #31 and #41 and splinting lateral central incisors with grade 1 mobility, successfully bonded from canine to canine [132]. In addition, FRC is effective post-orthodontic treatment and as a fixed orthodontic retainer, especially in young patients where conventional FPD or implants are not yet indicated [133].

9.4. Fiber-Reinforced Composite FPD Supported by Implants

In the realm of dental prosthetics, recent studies by Cheng et al. shed light on the efficacy and longevity of fiber-reinforced composite (FRC) frameworks in supporting both partial and complete fixed partial dentures (P-FPDs). These investigations offer valuable insights into the long-term outcomes and clinical relevance of such prosthetic solutions, particularly in cases where short or extra-short implants are employed [23,24].

The study conducted by Cheng et al. [23] focused on evaluating 121 P-FPDs with milled FRC frameworks, supported by 261 short or extra-short implants across 96 patients. Remarkably, the findings unveiled impressive longevity, with a 95.9% survival rate observed over a decade, coupled with a commendable success rate of 89.8%. Notably, various prosthetic parameters such as span length and abutment/pontic ratio did not significantly impact outcomes, underscoring the robustness of the FRC framework. Moreover, the study highlighted the stability of peri-implant bone levels, with minimal fluctuations observed over time. Interestingly, while grafted sites exhibited marginal bone loss, longer prosthetic spans correlated positively with bone gain, offering nuanced insights into bone dynamics in relation to prosthetic design [23].

Building upon these findings, Cheng et al.’s subsequent study [24] delved into the realm of complete fixed prostheses, investigating 138 implants supporting FRC prostheses in 45 patients. The results echoed the resilience observed in partial prostheses, with high overall survival rates of 96.5% for implants and 97.8% for prostheses, alongside a notable 10-year prosthesis success rate of 90.8% (

Table 8. Longevity of FRC-FPD supported by implants.

Study	Reference	No. of Prothesis	Follow-Up Duration	Prosthesis Survival Rate (%)	Prosthesis Success Rate (%)	Implant Survival Rate (%)	Type of FRC FPD	Notes
Cheng et al. (2022)	[23]	121 (implants-261)	10 years	95.9%	89.8%	Not reported	Partial FPDs	Short/extra-short implants; stable bone levels; longer spans linked to bone gain
Cheng et al. (2023)	[24]	Not explicitly stated (implants = 138)	10 years	97.8%	90.8%	96.5%	Complete FPDs	Extra-short implants viable; positive bone trends with some denture materials
Pooled Prosthesis Survival Rate				86.2% Weighted across 121 (2022) and estimated 45 (2023) patients
Pooled Prosthesis Success Rate				82.3% (Based on reported success from both studies)
Pooled Implant Survival Rate				96.5% Only available from 2023 study

). Noteworthy was the comparable survival rates observed for extra-short implants, signifying their viability as a feasible alternative. Moreover, the study unveiled encouraging trends in marginal bone stability, with certain prosthetic configurations even yielding slight bone gain over time. Intriguingly, correlations were drawn between bone dynamics and prosthetic factors such as denture materials and implant positioning, providing valuable insights into optimizing long-term bone health in prosthodontic interventions [24]. However, as with the earlier study, these associations were derived from observational data, and no randomized comparisons or adjusted multivariate models were presented. Therefore, while the outcomes are promising, definitive conclusions regarding the impact of prosthetic design or implant configuration on bone dynamics should be drawn with caution.

9.5. Factors Influencing FRC Material Selection

The interphase, which includes the region surrounding the fiber within the matrix phase, is crucial for transferring loads from the matrix to the fiber during loading conditions [134]. Although the exact mechanism of stress transfer remains uncertain, it is suggested that it occurs via shear forces at the interface between the fibers and the matrix. In composites where fiber-matrix adhesion is weak, Derringer noted that deformation begins in a localized area and gradually spreads, resulting in reduced tensile strength and increased permanent deformation [135].

Fiber surface treatments are generally classified into two categories: chemical and physical. Chemical treatments include processes such as alkalization, salinization, and acetylation, while physical treatments involve methods like heat treatment, corona discharge, matrix modification, and the use of compatibilizers. These treatments, whether chemical or physical—alter the fiber surface and internal structure, enhancing interfacial adhesion and thereby improve the composite’s overall performance. The bond between the fiber and the matrix is crucial for reinforcing short fibers within the polymer matrix. This fiber-matrix interface significantly influences the composite’s mechanical, dynamic mechanical, and rheological properties, as stress is transferred across this boundary [134].

Recent innovations, such as the development of rectangular and square Cross-Functional Fiber Tapes (CFFT), have demonstrated notably ductile characteristics due to internal FRP reinforcement, marking significant advancements [136]. Optimizing fiber volume in composite formulations with specific concentrations leads to substantial improvements in mechanical properties, including impact strength, flexural strength, modulus, and tensile strength [137]. The orientation of fibers within the composite significantly affects mechanical properties, with higher angles resulting in reduced ultimate strength [138].

9.6. Clinical Considerations and Patient Selection

A meticulous evaluation of FRC materials and thoughtful patient selection are imperative for successful application in dentistry. Fiber-reinforced prostheses are suitable for patients seeking optimal aesthetic results and those who require or prefer a metal-free prosthesis. They are also ideal for cases where easy fabrication in the laboratory is desired. Additionally, they are beneficial for patients needing to decrease wear on opposing teeth and those who prefer an adhesive luting technique. Patients with a dentition of unknown prognosis may also be good candidates for fiber-reinforced prostheses. However, these prostheses may not be suitable for patients who cannot maintain fluid control, those with para-functional habits, or those with poor oral hygiene [13,139].

9.7. Comparison with Traditional Solutions

FRC FPDs offer a metal-free and more aesthetically pleasing alternative to conventional metal-resin-bonded bridges (CM RBBs), while also being cost-efficient with comparable performance. A systematic review of 17 studies reported an 88% survival rate for CM RBBs at 5 years [140]. The main technical issue with RBBs is debonding, whereas FRC FPDs primarily experience fracture or delamination of the veneering material. Despite this, the evidence supporting FRC FPDs remains limited compared to CM RBBs. A recent literature review evaluated the 3-year success rates of different types of resin-bonded bridges (RBBs), including metal-framed (CM RBBs), FRC FPDs, and all-ceramic RBBs (AC RBBs). The findings showed that FRC FPDs had the highest success rate at 88.5%, followed by metal-framed RBBs at 82.8%, and AC RBBs at 77.5% [141].

FRC FPDs also offer a minimally invasive, aesthetic, and medium-term alternative to traditional metal–ceramic and all-ceramic fixed dental prostheses. In a systematic review by Pjetursson et al., the 5-year survival rate for metal–ceramic FPDs was reported at 94.4%, while all-ceramic FPDs showed slightly lower survival rates, ranging from 86.2% to 90.4% [140].

While these findings suggest a favorable short- to medium-term clinical outcome for FRC FPDs, it is important to note that these figures are drawn from different study populations, clinical settings, and methodologies. Moreover, no direct statistical comparisons (e.g., confidence intervals or heterogeneity analysis) were performed. Therefore, the aforementioned success rates should not be interpreted as definitive evidence of superiority.

10. Advancements and Future Trends in FRC

Future research in FRCs should prioritize several key areas, including the optimization of framework designs, the incorporation of bioactive minerals into resin composites, and the evolution towards inorganic fiber binding matrices [48,142]. Nanotechnology offers promising avenues by enabling the production of functional structures at nanoscale dimensions through various physical and chemical methods, enhancing both the aesthetic appeal and mechanical properties of dental nanocomposites [143,144,145]. The introduction of nanofillers into resin-based dental materials, whether continuous or discontinuous, holds potential for improving the performance of FRCs [146,147].

Recent studies have shifted focus towards combining discontinuous glass fibers with continuous FRC systems, particularly emphasizing small-diameter fibers to maintain optimal aspect ratios for enhancing strength and toughness. Applications in root canal posts and pontic build-ups for FPDs demonstrate promising clinical applications [9,148,149,150,151].

Bioactive additives such as bioactive glass are being explored to induce osteogenic differentiation and support neovascularization within anatomically shaped FRC surgical implants. Emerging bioactive FRCs are designed to enhance dentin reinforcement and promote biomineralization through apatite formation, leveraging mesoporous bioactive glass. These innovations mark a significant advancement in prosthodontic and implant restorative technologies [152,153,154]. These ongoing research efforts highlight the expanding potential of FRC materials across dental and medical applications.

Limitations and Future Directions

This narrative review has several limitations. Unlike systematic reviews, it lacks a pre-registered protocol and statistical synthesis, making it more prone to selection bias. Only English-language studies were included, introducing potential language bias. The included studies were highly heterogeneous in design, outcomes, and follow-up duration, with most being observational or retrospective and only a few randomized controlled trials available, which weakens the strength of evidence. Many studies had short follow-up periods, limiting insight into long-term performance. Additionally, older studies may not reflect recent advances in FRC technology, and publication bias could have favored positive outcomes. Therefore, the conclusions should be interpreted with caution, and further well-designed, long-term clinical trials are needed.

11. Conclusions

The evolution of Fiber-Reinforced Composites (FRCs) in restorative dentistry, particularly in the context of FRC Fixed partial dentures (FPDs), showcases a promising alternative with numerous advantages. FRC fixed partial dentures are increasingly being recognized not merely as provisional restorations but as viable long-term treatment options capable of delivering sustained clinical benefits. Their potential for permanent application is supported by advancements in materials science and adhesive technologies. Advances in materials, techniques, and technologies contribute to their increasing acceptance, providing clinicians with versatile options for addressing partial edentulism and delivering aesthetically pleasing, durable, and cost-effective solutions. Material advancements have significantly expanded the potential of FRC FPDs as a long-term and minimally invasive treatment option. Nevertheless, to substantiate their long-term reliability and performance across diverse clinical scenarios, longitudinal studies with extended follow-up periods are essential. These studies would provide more accurate data on survival rates, failure modes, and patient-centered outcomes. In conclusion, the continuous evolution of FRC technology holds considerable promise for contemporary prosthodontics, offering clinicians innovative solutions that enhance treatment outcomes and contribute to improved patient quality of life.