RESTORATION OF PARTIAL TOOTH ARCH DEFECTS USING ADHESIVE BRIDGES

16 Journal of science. Lyon №71/2025 MEDICAL SCIENCES RESTORATION OF PARTIAL TOOTH ARCH DEFECTS USING ADHESIVE BRIDGES Kerimova G. Candidate of Medical Sciences, Associate Professor Ashrafov D. Department of Orthodontics ,assistent Rustamov E. Doctor of Philosophy in Medicine,Assistent Zeynalova N. Doctor of Philosophy in Medicine Department of Orthopedic Dentistry Chief laboratory Assistant Azerbaijan Medical University Baku, Azerbaijan https://doi.org/10.5281/zenodo.17533487 Abstract Adhesive bridges fabricated directly in a single patient visit allow for the restoration of single partial defects in the tooth arch with minimal preparation of the abutment teeth. The review discusses the issues of strength and aesthetics of the resulting structures depending on the type of fiber reinforcement and the composite material used. Keywords: partial tooth arch defects; adhesive bridges; fiber-reinforcing elements; composite materials In clinical practice, it is common to encounter cases where replacement of a single tooth arch defect is required. This is especially relevant for young patients, since the absence of even one tooth visible when smiling presents a serious aesthetic problem [1, 2]. To address this issue, in the late 20th century, fixed adhesive bridges (ABs) were developed. Their fabrication does not require significant time or financial costs and, most importantly, is a less invasive procedure compared to traditional prosthetic treatment using conventional bridge constructions [3]. Initially, ABs were considered temporary prostheses; however, as dental materials have improved, the strength and durability of these constructions have significantly increased, allowing other restorative treatment options to be completely avoided or postponed [4]. According to various authors, the longevity of ABs ranges from 3 to 5 years, during which 75% to 95% of constructions remain functional. This largely depends on the design type, materials used, fabrication technology, and other factors [5–7]. The main structural feature of ABs is the shape of the retention elements and the type of their stabilization on the abutment teeth. This type of prosthesis may have supporting elements in the form of adhesive overlays or inlays. The choice of supporting elements for ABs in the molar region generally depends on the condition of the hard tissues: if the abutment tooth has already undergone restoration, the inlay serves as the supporting element, placed at the site of an existing cavity or filling [8–10]. One of the advantages of ABs is the minimal processing of the abutment teeth compared to traditional crown preparation. According to the study by S. Yu. Grishin, the loss of hard tissue in abutment teeth during preparation for an adhesive prosthesis with overlay elements averages 5%, while cavity preparation for inlays (MO or OD) results in an average loss of 15% of enamel and dentin, and preparation for cast crowns results in an average loss of 44% of the coronal portion of the abutment tooth [11]. A significant advantage of ABs is the possibility of their fabrication using the direct method in a single visit, without the need for an additional laboratory stage. As the missing tooth, one may use stock plastic teeth for removable dentures, or the coronal portion of the patient’s extracted tooth after forming a cervical part from composite material, but most often, the tooth is restored entirely from composite material [12]. Over the past decades, numerous experimental and clinical studies have been devoted to finding optimal types of supporting and reinforcing constructions for adhesive bridges. Reinforcement has included cast elements made of metal alloys, porcelain, glass, plastic, and various fiber structures. Over the thirty-year history of adhesive bridge (AB) use, the techniques for fabricating fiber-reinforced composite structures have been refined, gradually replacing prostheses with metal substructures, as the former are not inferior in strength [13]. Fiber reinforcement ensures the stability and rigidity of ABs. In turn, the mechanical characteristics and effectiveness of the reinforcing elements in ABs depend on the type of fiber (polyethylene, glass, carbon, aramid), the thickness of the reinforcement, fiber quality, fiber structure, the orientation of individual strands (unidirectional, bidirectional, or randomly oriented), water absorption capacity, and the degree of adhesive impregnation [14–18]. Various fiber materials differing in origin, chemical composition, structure, and properties are used as reinforcement for AB fabrication [19, 20]. Natural fi- Journal of science. Lyon №71/2025 17 bers (silk, cotton, linen, jute, etc.) are rarely used because they lack sufficient strength and resistance to the oral environment. Organic fibers are industrially synthesized and represent the largest group of materials (polyethylene, polypropylene, polyester, polyacrylic, polyamide, aramid, carbon materials), though not all of them are suitable for dental applications. Polyethylene-based fiber materials have gained the widest use in creating splinting structures and adhesive prostheses, such as Ribbond (Ribbond, USA), Connect (Kerr, USA), and DVA (Dental Ventures of America). Inorganic fibers are made from glass, basalt, quartz, aluminum oxide, boron, and other elements. Among these, glass fibers are the most commonly used reinforcing materials in dental practice, including GlasSpan (GlasSpan, USA), FiberSplint (Polidentia, Switzerland), and Fiberkor (Jeneric/Pentron). According to manufacturers, these fibers are characterized by bioinertness, high strength, low water absorption, and excellent optical properties. To further increase the strength of adhesive-fiber constructions, reinforced glass fibers with the addition of alumino-borosilicate oxides of alkali metals — known as E-glass fibers — have been developed. Recent studies by Zhang M. and Matinlinna J.P. have shown that such fibers are capable of maintaining their properties under a wide range of conditions, are relatively insensitive to moisture, and exhibit high chemical resistance [21]. Along with improvements in chemical composition, the structure of fiber materials is also continuously evolving: fiber bundles are twisted or interwoven into ropes, ribbons, or meshes. Bundles of parallel fibers behave strictly anisotropically, demonstrating the highest strength values along their longitudinal axis. Therefore, when such materials are used as reinforcement, the main requirement is that the applied load acts parallel to the orientation of the fibers; if the load is applied perpendicularly, the bond between the composite matrix and the fiber may fail [6]. A slight twisting of the fibers increases their strength, whereas excessive twisting deteriorates their properties: under high tensile load, the twisted fiber compresses again, compromising the rigidity and strength of the structure. When the direction of load vectors is difficult to predict, it is preferable to use fiber materials in the form of cords with diagonal or randomly oriented fibers [22]. For planar structural elements, ribbon materials with various weaving patterns have been developed. A modern representative of this group is Ribbond THM, made from ultra-thin fibers 3–5 μm in diameter, interwoven into a ribbon. Plasma treatment of the fibers significantly improves their adhesive impregnation, promoting a strong bond with the composite, while the knot-weaving method of the Ribbond ribbon provides flexibility and elasticity, preventing the formation of microcracks in the resulting structures. The structure of glass fiber materials has also been improved: they are now produced not only as ribbons and cords of various diameters, but also as multi-ribbon blocks stitched together with glass fibers for the creation of high-strength constructions, as well as in the form of ultra-thin mesh that can be used to reinforce restorations in the smile zone, where special aesthetic requirements apply. The choice of fiber used for AB fabrication, as well as its related properties and characteristics, depends on the design type. The use of glass fibers as a reinforcing element not only increases strength but, due to their optical properties, provides high aesthetic quality, making them suitable for the replacement of missing teeth in the anterior regions of the jaws [18, 23]. Clinical practice shows that nearly all fiber materials degrade in the oral environment if they are left uncovered by composite. The literature describes cases where polyethylene or glass fiber reinforcements within a structure became frayed and softened, eventually leading to complete disintegration [5–7]. One possible reason for the degradation of fiberreinforced constructions in the oral cavity is that coating the fiber with adhesive immediately before application does not ensure full impregnation. To address this problem, a technology for pre-impregnation of glass fibers with an adhesive agent under industrial conditions has been developed. Representatives of this generation of glass fiber materials include Splint-It (Pentron Corp., USA), EverStick (Stick Tech, Finland), and Dentapreg (Advanced Dental Material, Czech Republic). According to manufacturers, such fibers are much more resistant to acids and alkalis and remain stable in the oral environment. Complete infiltration of the glass fiber with adhesive throughout its thickness provides a structure with greater strength. It should be noted that the thickness of the glass fiber used determines the depth of tooth preparation. Pre-impregnated fibers are thinner, which allows the reduction of the preparation depth to about 1 mm. However, despite their stability and strength, it is not recommended to leave the reinforcing elements uncovered by composite material. In addition to the properties of the fiber reinforcement, the physical, mechanical, and aesthetic properties of adhesive bridges (ABs) are influenced by the characteristics of the composite materials themselves. The reinforcement serves as a substructure that distributes the stresses arising during mastication, while the composite surface provides the anatomical integrity and aesthetic appearance of the AB [24, 25]. It should be emphasized that ABs alter the tooth shape and create retention zones, which significantly worsen oral hygiene. Moreover, during clinical use, the surface roughness increases, allowing the formation of pores, defects, and microcracks that enhance bacterial adhesion. Such drawbacks depend on the brand of composite material and the technology used in its application (polymerization type—light-cured, chemically cured, or dual-cured) [12]. For direct-fabrication techniques, light-cured composites are considered the most suitable materials. Despite their high strength and aesthetic properties, modern composites still have disadvantages such as polymerization shrinkage, a high modulus of elasticity, and water absorption. Since the primary load during 18 Journal of science. Lyon №71/2025 function falls on the composite that bonds the fiber to the tooth, internal stress accumulates over time, leading to microcrack formation. Consequently, this results in fracture of the structure and its detachment from the tooth surface [12]. Hypothetically, if the composite contains a higher volume fraction of filler, polymerization shrinkage is reduced, thereby generating less stress at the bonding interface [26]. However, attempts to improve the physical and mechanical properties of composites by adding glass fibers and ceramic particles as fillers—although increasing the overall strength and wear resistance— have not significantly improved such an important property as flexural strength [27, 28]. To reduce deformation caused by polymerization shrinkage, nanohybrid composites can be used. These materials exhibit high flexural strength, excellent surface hardness, good marginal adaptation, resistance to masticatory loads, and are easily polished. Despite the high volume fraction of nanoparticles in the organic matrix, this does not lead to a significant increase in material viscosity [29]. However, the filler-to-matrix ratio is also important for the polymerization process; an excessively high filler content can hinder light penetration during curing [30], preventing the composite from achieving its ultimate strength. Sharafeddin F. et al. (2013) analyzed the flexural strength of specimens made from three types of composites combined with glass fiber and polyethylene reinforcement to determine which combinations yielded the best mechanical properties. The results showed that composites combined with glass fibers demonstrated higher flexural strength than those combined with polyethylene fibers. According to the authors, one of the reasons for the increased strength was the use of industrially preimpregnated glass fibers. Preliminary impregnation improves the adhesive properties of the fibers and creates a more homogeneous structure with the composite, which in turn increases its strength by 2–3 times [26]. In this study, no dependence was found between the strength of polyethylene fiber–based constructions and the type of composite used. At the same time, a significant increase in flexural strength was observed when glass fiber was combined with the Z250 composite, which contains 60% filler particles of silicon and zirconium with an average size of about 0.6 μm. The improvement in adhesion between the Z250 composite and glass fiber may be related to the silica content of the fiber and the resulting strong bonds with the filler particles within the composite’s organic matrix, thereby increasing flexural strength [31]. To some extent, the high flexural strength of the glass fiber–Z250 composite combination can be explained by the strong chemical bonding between glass fibers and polymers such as methyl methacrylate, BisGMA, and UDMA [32], which enhances compressive strength and may also affect flexural strength. According to N. Eronat et al., the flexural strength of a hybrid composite combined with glass fiber is significantly higher than that of a glass fiber–microfilled composite combination. Furthermore, the degree of fiber impregnation influences its performance. When infiltration is insufficient, voids form within the polymer matrix, reducing mechanical characteristics such as flexural strength. This also promotes water absorption and, over time, negatively affects the survival rate of adhesive bridges (ABs) in the moist oral environment [33]. In a study by S. Tsushima et al., it was also found that flexural bond strength increases when pre-impregnated fibers are used. The adhesive ensures a strong bond between the fiber and the composite, which is a crucial factor affecting flexural strength [34]. Laboratory studies have shown that most AB fractures occur at the interface between the fiber reinforcement and the polymer matrix [35]. When glass fiber is used as reinforcement, fractures most often result in complete separation of the structure into two parts. In contrast, the use of polyethylene fiber reinforcement prevents full separation, and the connection between the fiber and the composite is maintained throughout testing. This finding is supported by the study of C.L. Pereira et al., which demonstrated the strength and stability of polyethylene-based reinforcing structures [5]. Conversely, in the study by Sharafeddin F. et al., the average fracture strength of specimens made from three types of composites combined with polyethylene fibers was 203, 188, and 203 MPa, respectively—significantly lower than those made with E-glass fibers, which showed fracture loads of 243, 331, and 500 MPa. According to the authors, the inconsistency of these data requires further laboratory testing as well as longterm clinical studies [26]. E.V. Mokrenko and O.V. Semikozov presented data on the successful clinical application over seven years of adhesive reconstruction of dental arches with partial tooth loss using various fiber compositions (Fiber Splint, GlasSpan, Ribbond, FibreKor, Connect, etc.), including in patients with periodontal diseases. The authors used both surface and subsurface fixation methods for the supporting and reinforcing structures, and in devitalized teeth, deep embedding of the reinforcement elements into the hard tissues of the abutment teeth was employed [36]. S.Yu. Grishin recommends, for the direct fabrication of ABs, the use of filled unbraided glass fibers of the FibreKor type, with the total cross-section of the final modeled beam consisting of 36,000 unidirectional fibers for the posterior teeth and 24,000 fibers for the anterior group. The pontic part of the future adhesive bridge (AB) is recommended to be made from high-strength composites such as Alert, Filtek P-60, or QuixFil, or from reinforced composites like Build-it FR. The veneer layer of the prosthesis should be made from a highstrength nano-hybrid or microfilled composite with good polishability, such as Simile, Esthet-X, or Filtek Supreme XT [11]. Fiber reinforcement is necessary to increase the flexural strength and elastic modulus of splints made from composite materials. However, the reinforcing component may act as a stress concentrator at the interface zone with the composite. Partial debonding of Journal of science. Lyon №71/2025 19 adhesive bridges in clinical conditions is also caused by the natural autonomous micromobility of abutment teeth. This micromobility leads to the emergence of compressive and tensile forces at the contact points of adhesive overlays with the abutment teeth, which promotes the formation of microcracks in the adhesive cement, its fatigue, and, as a result, the debonding of the prosthesis [35, 37]. M.A. Freilich et al. evaluated 39 fixed partial dentures made of light-cured composite, fabricated with substructures of pre-impregnated unidirectional fibers veneered with a hybrid composite. Each prosthesis was evaluated for surface integrity, anatomic contour, marginal strength, and structural integrity. The results showed that the strength of the structures was primarily related to the volume and design of the substructure. The survival rate was 95% for prostheses fabricated with large-volume substructures. This study demonstrates that a bridge based on unidirectional, pre-impregnated fibers can be successfully used for 4 years or more when large substructures are employed [16]. W. Li et al. conducted an experimental study examining the causes of failure in directly fabricated adhesive bridges. It was found that the combined interface area is indeed the weakest point of composite bridges. In addition, it was shown that composite materials reinforced with high-modulus polymer fibers, as well as the presence of stable adjacent teeth, can significantly increase the structural strength and stiffness of the bridge and thus enhance its clinical performance [38]. Experimental results demonstrated good consistency with clinical observations [19]. T.C. Matheus et al. used optical coherence tomography, scanning electron microscopy, and optical microscopy to evaluate the propagation of microcracks and final fracture at the junctions of composite materials with fiber reinforcement after cyclic loading. The results showed that deformation in both the dental composite layer and the fiber occurs in the direction of the applied force [40]. A review of the literature indicates that despite the availability of advanced materials developed for adhesive-fiber prosthetics, certain complications still occur in clinical practice. These include fracture of the structure during use, fiber unraveling, and composite chipping leading to undercuts that trap dental plaque. Additionally, fibers not fully covered by composite may irritate the soft tissues. 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