DENTAL-2417; No. of Pages 7

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 4 ) xxx–xxx

Available online at

ScienceDirect journal homepage:

High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties Pekka K. Vallittu ∗ Department of Biomaterials Science and Turku Clinical Biomaterials Centre – TCBC, Institute of Dentistry, University of Turku, Turku, Finland

a r t i c l e

i n f o

a b s t r a c t

Article history:

Objectives. To present an overview of fiber-reinforced composites (FRCs) that are a group of

Received 21 June 2014

non-metallic dental biomaterials used in several fields of dentistry.

Received in revised form

Methods. A range of relevant publications from the past half century are surveyed, with

11 July 2014

emphasis upon recent publications.

Accepted 14 July 2014

Results. FRCs vary according to the type of fiber fillers and orientation of fibers, the latter being

Available online xxx

responsible for several properties which can vary from isotropic to anisotropic. The length of the fibers, i.e. the aspect ratio of the filler, is another factor or variable that contributes


to the properties and the development of new types of composite resins for restorative and


prosthetic dentistry, as well as to reconstructive medicine.


Significance. Understanding the anisotropic nature of FRCs from the perspective of dental

Fiber-reinforced composite

applications has increased in recent years. This review describes some fiber orientation


related anisotropic properties of FRCs which contribute to the increased use of FRCs in


clinical dentistry. © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.



Using high aspect ratio fillers in composite resins can significantly change the resin’s physical properties in comparison to using particulate fillers which provide isotropic properties for the material. High aspect ratio fillers have a high ratio of the length of the filler to its cross-sectional diameter. In composites, high aspect ratio fillers are fibers but shorter filament like fillers of whiskers can be also considered high aspect ratio fillers [1]. Different types of fibers with various orientations and lengths have been utilized for decades in engineering applications to construct devices with high strength and fracture toughness. The first glass fiber-reinforced boat was

produced in 1937 in Russia and since then the anisotropicity of fiber-reinforced materials has been utilized in everyday life and recently in dentistry and medicine. In natural constructs, reinforcing fibers of cellulose can be found, e.g. in wood, where the length of the oriented polysaccharide based cellulose fibers and shorter branched hemicellulose fibers is between 0.8 and 2.3 mm [2]. Chiral and crystalline cellulose fibers in wood are embedded in the lignin matrix, which is a natural biopolymer of aromatic alcohols. Other examples of natural systems that contain high aspect ratio components include bone and dentin [3]. Osseous tissue of bone and dentin is composed of a hard, lightweight composite, where mineral calcium phosphate in the chemical arrangement of hydroxyapatite forms the inorganic matrix for

Correspondence to: Institute of Dentistry, University of Turku, Lemminkäisenkatu 2, FI-20520 Turku, Finland. Tel.: +358 2 333 8332. E-mail address: [email protected]fi 0109-5641/© 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Please cite this article in press as: Vallittu PK. High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties. Dent Mater (2014),

DENTAL-2417; No. of Pages 7


ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 4 ) xxx–xxx

the protein origin collagen fibers, which are formed from thinner type I fibrillar collagen. The collagen fibers with a diameter of 20–400 nm consist of collagen molecules, which are stabilized by four cross-linking covalent bonds per molecule [4]. The length of collagen fiber is around 23 ␮m [5]. High aspect ratio fibers in collagen provide high tensile strength and fracture toughness for bone and dentin, whereas hydroxyapatite is responsible for the compressive properties. Both collagen fibers and crystals of hydroxyapatite are oriented best to withstand physiological loading conditions. Mineralized collagen fibers provide toughness through crack-tip shielding through osteons, especially with lower strain rates [6]. Man-made high aspect ratio fillers have been used since ancient times to reinforce bricks and buildings [1]. Modern fiber-reinforced composites (FRCs) are used in applications where high static and dynamic strength and fracture toughness, especially in relation to weight, are desired properties. For example, dental and medical devices are typically subjected to hundreds of thousands of loading cycles by the masticatory system or the weight of the body during physical exercise [7]. FRCs are typically designed to have the highest possible reinforcing efficiency against the direction of stress, and thus, they often represent anisotropic material in terms of mechanical properties. However, some other properties, such as optical properties, surface physical properties, thermal properties and polymerization contraction properties are related to the orientation of the fibers in the FRC. From the point of view of high fatigue resistance and toughness, FRC is part of a group of choice materials for dental and medical needs. FRCs in dentistry were first developed in the early 1960s but an increase in the number of published scientific papers occurred in the early 1990s [8–15]. Currently, FRCs are used in fixed prosthodontics, restorative dentistry, periodontology, orthodontics and in repairs of prosthetic devices [16–26]. There are also cranial implants made of glass FRCs and attempts to develop oral and orthopedic implants are ongoing [27,26,28,29]. This is a review of the current status of knowledge of some anisotropic properties of FRCs used in dentistry.


Reinforcing efficiency of fibers

The majority of dental FRCs are presently produced from glass fibers due to their surface chemistry, which allows for their adhesion to the resin matrix via silane coupling agents, and to the transparency of their fibers [30–32]. Glass fibers do not cause severe problems related to the appearance of the restoration. Out of the several different types of fibers (carbon/graphite, aramid, polyethylene), glass fibers have been adopted for use in dentistry and medicine. The most common glasses, namely E-glass and S-glass, and their behavior as components of dental FRCs were recently reviewed in more detail in another publication [33]. FRC is a material which contains at least two phases, one of which is characterized by its high aspect ratio, i.e. ratio between the length and diameter (l/d). Among many parameters (interfacial adhesion, elongation of fibers, fiber volume fraction) which contribute to the reinforcing efficiency of fibers, length and orientation of fibers are important in terms of the isotropicity–anisotropicity of the material [1]. FRCs are

Fig. 1 – Influence of the aspect ratio (l/d) of fibers and their orientation to the tensile stress ( t ) and modulus of elasticity (E) with the same volume fraction of fibers (Vf ) [34].

classified as short discontinuous and long continuous FRCs; which have different mechanical properties although the fiber volume fraction could remain the same [34]. By changing continuous unidirectional fibers to longitudinally oriented discontinuous short fibers of lower aspect ratio, ultimate tensile strength of the composite is reduced (Fig. 1). In this case both continuous and discontinuous FRCs are anisotropic. Changing the orientation of short fibers so they lay randomly causes the tensile strength to reduce even more, and the FRC material becomes isotropic. Consequently, strength, unlike stiffness of continuous FRCs, cannot be attained by discontinuous short fiber systems even with high aspect ratios [34]. Failure types of discontinuous short FRCs including cracking of the polymer matrix, debonding of the fiber and fracture of the fiber (Fig. 2). Depending on the length of the fiber, aspect ratio of the fiber, interfacial fracture energy (adhesion of fibers to the matrix) and fiber volume fraction, some of the failure types are more common. Dependence between the orientation and length of the fibers is also described by Krenchel’s factor, in which the reinforcing efficiency factor for fiber reinforcement goes against the known direction of stress [35]. Reinforcing fibers in the direction of the stress provides the highest reinforcing efficiency and finally axial failure of the fibers and polymer

Fig. 2 – Schematic presentation of the types of failures (crack of the matrix, debonding of the fiber, fracture of the fiber) of discontinuous short fiber-reinforced composite (Xo = embedded fiber length which as debonded, d = diameter of fiber, L on fiber length, f = volume fraction of fibers). Arrows show the direction of load.

Please cite this article in press as: Vallittu PK. High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties. Dent Mater (2014),

DENTAL-2417; No. of Pages 7

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 4 ) xxx–xxx


Fig. 4 – Schematic presentation of alternatives to bond particulate filler composite resin (PFC) to the surface of fiber-reinforced composite (FRC) (upper row) and bonding fiber-reinforced composite (FRC(bidir)) = bidirectional fibers, FRC (rand) = randomly oriented fibers, FRC(vert) = vertical unidirectional fibers) to the surface of enamel (E) and dentin (D). Bonding values are shown in Fig. 5.

Fig. 3 – Schematic presentation of types of failures (from top to bottom: axial tensile failure, transverse tensile failure, shear failure) of a continuous unidirectional fiber-reinforced composite. Arrows show the direction of force.

matrix will occur (Fig. 3). If stress is applied perpendicular to the fibers, the fibers do not reinforce the FRC, and transverse failure of the polymer matrix occurs. The effect of the aspect ratio of fibers is also related to “critical fiber length”, which can be defined as the minimum length of the fiber. It allows for the development of sufficient stress to cause the fiber to fail at its midpoint. Interfacial fracture energy of the adhesive interface between the fibers and polymer matrix versus the tensile strength of the fiber has an impact on the critical fiber length. It has been concluded that for advanced FRCs, the critical fiber length could be as much as 50 times the diameter of the fiber. To eliminate fiber debonding under tensile stress, FRCs with longer fibers could exhibit strength similar to the corresponding continuous FRC [36]. The diameter of glass fibers presently used in dental FRCs is 15–18 ␮m and the critical fiber length should be, therefore, between 750 and 900 ␮m [37]. A recently introduced short fiberreinforced composite for filling applications has fiber lengths within this range [38,39].

3. Fiber-reinforced composite as an adhesive substrate Use of FRCs in dental applications requires covering the fiber-rich part of the construction by some other resin system in order to adhere (adhesives and luting cements) the fiber-rich FRC to the dental tissues. This also protects the fibers and provides a polishable surface for the FRC device (veneering composites, filling composites, removable

dentures) [17,19,40,41]. In these applications, the orientation of fibers in the load-bearing part of the construction is selected according to the loading conditions of an FRC system, which can best resist the mechanical stresses of the masticatory system. The surface of the substrate onto the adhesive resin, luting cement or veneering composite resin is adhered and can have different orientations of fibers as shown in Fig. 4. In the case that the surface of the substrate is ground, and the reinforcing glass fibers are exposed, an average of 50% of the surface area of the substrate is composed of the polymer matrix and 50% are glass fibers. The exposed glass fibers are those which have lost the surface silanation due to the grinding. This can occur with prefabricated FRC root canal posts and frameworks in fixed dental prostheses, which are polymerized and mechanically shaped before veneering. Repairs to FRC constructs also expose the fibers to the surface. Bonding mechanisms and bonding efficiency to the cross-linked polymer matrix and interpenetrating polymer matrix have been reported [42]. When the orientation of exposed fibers is considered, the highest bonding strength to the FRC surface is obtained with perpendicularly exposed fibers (Fig. 5). Fibers ina-plane, which were along the direction of debonding stress, reached almost the same value of bonding strength as perpendicularly oriented fibers, whereas the in-a-plane fibers, which were opposite to the debonding stress, gave the lowest bonding strength [43] (Figs. 4 and 5). Discontinuous short fibers can be used to reinforce dental fillings [39]. A layer of discontinuous short FRC, which replaces the missing part of dentin, is covered with a layer of particulate filler composite resin to achieve a wear resistant and polishable surface. FRC layer substructures and the particulate filler composite resins form a bilayered composite structure in which randomly oriented and slightly protruded discontinuous fibers reinforce the interface of the composite layers.

Please cite this article in press as: Vallittu PK. High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties. Dent Mater (2014),

DENTAL-2417; No. of Pages 7



d e n t a l m a t e r i a l s x x x ( 2 0 1 4 ) xxx–xxx

Fig. 5 – Shear bond strength (MPa) of material combinations described in Fig. 4 [43–45].

In direct applications of FRCs, e.g. during fabrication of direct fixed dental prostheses or periodontal splints, the fibers are adhered directly to the surface of the dentin or enamel. In direct applications, the orientation of fibers can vary from bidirectional weaves to veils of randomly oriented fibers to continuous longitudinal fibers (Fig. 5). Bonding efficiency of FRCs with different orientations of fibers varies only slightly from each other (Fig. 5) [44,45].


Fig. 6 – Anisotropic linear polymerization contraction strain (microstrain) of fiber-reinforced composites (FRC) with various orientations of fibers and the direction of measuring the strain in relation to the long axis of the fiber. Control material is isotropic particulate filler composite resin [53].

Polymerization contraction

Polymerization contraction is one of the shortcomings related to dental composite resins, which contributes to the longevity of restorations [46–48,50,51]. Reinforcing fibers not only improve mechanical properties of the composites but can also control the polymerization contraction. Polymerization contraction strain of FRCs has been measured by conventional strain gauges and optical Bragg grating sensors [49,52]. Both strain gauges and Bragg sensors have shown the dependence of the polymerization contraction on the direction of the reinforcing fibers. Fig. 6 summarizes isotropic polymerization contraction strains of particulate filler composite resin and FRCs with varied orientations of fibers. Hygroscopic expansion of resin composites is also dependent to the fiber orientation (Fig. 7) [49,53]. FRCs with longitudinal fiber orientation demonstrate no contraction in the direction of fibers; minor thermal expansion can be found, which is caused by an increase in temperature due to exothermic polymerization reactions. Anisotropicity in polymerization contractions can be beneficial in tailoring the properties of filling composite resins in order to minimize gaps between fillings and tooth substances. An observation was published recently on the use of individually formed FRC root canal posts, i.e. FRC material, which is directly polymerized in a root canal with a high configuration factor (c-factor = 953) [54]. It was expected that the higher polymerization contraction in the transverse direction to the fibers of the FRC could have caused debonding and gap formation between the FRC material and root canal dentin [55]. However, the results showed

Fig. 7 – Anisotropic hygroscopic expansion of the fiber-reinforced composite (FRC) compared to isotropic expansion of particulate filler composite resin and unfilled resin [49].

the opposite: direct polymerization of the FRC in the root canal with the composite resin luting cement demonstrated better adaptation and sealing between the post and root canal compared to the posts, which were polymerized chairside before cementation. This was explained by the elastic properties of the FRC post interpenetrating polymer network (IPN) polymer matrix. The lower modulus of elasticity of the IPN polymer matrix was assumed to be able to absorb polymerization contraction stress during polymerization and cause less stress to the cement–tooth interface [42,56].

5. Effect of fiber orientation on optical properties Optical properties of FRCs are also fiber direction related; they are utilized in fiber optics of communication systems and in transmission of light in illumination applications. Fiber

Please cite this article in press as: Vallittu PK. High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties. Dent Mater (2014),

DENTAL-2417; No. of Pages 7

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 4 ) xxx–xxx

optics can also be used in sensor technology, for instance in Braggs grating sensors to measure dimensional changes with high precision [57]. Optical fibers have a transparent core, which is covered with a transparent cladding material with a lower index of refraction in order to keep the light in the core by total internal reflection. Applications in dentistry, which are utilizing optical properties of fibers can be found in restorations of root canal treated teeth [58–61]. There are some prefabricated FRC root canal posts available which transmit the polymerization light through the post and enables lightinitiated polymerization to occur in the composite resin luting cement [59,60]. In the case of individually formed FRC root canal posts, the resin matrix of the post needs to be polymerized as well as the resin based luting cement. Transmission of light to the resin system surrounding the fibers and to the fiber-rich area in general is based on reflectance and the scattering of the light. Scattering of light includes the deflection of a ray of the light from a straight path. The deflection of light can be caused by irregularities in the propagation medium, at the interface between two media, or from differences in the refraction indices of light transmitting fibers in the surrounding resin system. Scattering of this type is referred to as diffuse reflection. There are studies related to the optical properties of dimethacrylate resin systems in the context of lightinitiated polymerization of resin systems. It has been shown that polymerization reactions of bisphenol-A-dimethacrylate (bisGMA)–triethylene glycol dimethacrylate (TEGDMA) resin systems increase the refraction index from 1.515 to 1.550 with a bisGMA–TEGDMA ratio of 50:50, and to 1.580 with bisGMA–TEGDMA ratio of 99:1 (Fig. 7) [62]. This is due to the reorganization of the molecular structure during polymerization. At the same time, the extinction coefficient at the 470 nm wavelength of the resin system decreases due to reducing the amount of initiator camphorquinone until the extinction coefficient is dominated by the copolymer only. Simultaneous changes in the refraction index and extinction coefficient of the resin system, and the refractive index of E-glass fiber (1.556) and boron free E-glass fiber (1.547) [63], enhance light to scatter out from the glass fibers once the polymerization of the resin system has started and proceeded to a particular stage (Fig. 7). This is according to the Snell’s law of relationship between the angles of incidence and refraction of light passing through a boundary between two isotropic media; Eglass and resin system of bisGMA–TEGDMA. In practice, this phenomenon is utilized in the polymerization of continuous unidirectional E-glass fiber composite prepreg with an optimized bisGMA–TEGDMA ratio inside the root canal when an individually formed root canal post is prepared. It is known that surface irregularities of the fibers enhance scattering. It has been demonstrated in vitro that the depth of lightinitiated polymerization of the bisGMA–TEGDMA resin matrix of FRC root canal post is 18 mm for the degree of monomer conversion of 55%. This exceeds the length of the suggested individual FRC post (ca. 5 mm), which has shown to provide the highest load-bearing capacity for a root-post-crown system [64]. Optical properties of glass FRCs also play a role in the appearance of FRC-reinforced restorations. A recent study showed that continuous unidirectional and bidirectional Eglass fibers should be veneered with a layer of particulate


Fig. 8 – Index of refraction and extinction coefficient of a monomer system of bisGMA–TEGDMA in volume ratios of 50:50 and 99:1 plotted against the light curing time. The gray area demonstrates the refraction index of E-glass fibers with different compositions [62,63].

filler composite resin with a thickness of more than 2 mm in order to eliminate the risk of color shade mismatch [65] (Fig. 8).

6. Other anisotropic properties and conclusions Research on man-made FRCs demonstrates that they mimic structurally constructs of biological systems. Natural anisotropic systems are not only anisotropic in their final constructs. Natural systems function anisotropically during the creation of tissues and structures from cellular activity. Anisotropic substrates for cells can direct cell morphology and growth. Studies related to continuous unidirectional Eglass FRC in implant applications have shown that surface wettability, surface energy and cellular responses are also dependent on the direction of the exposed glass fibers [66,67]. Microscopic investigation has shown fibroblast cells to orient themselves parallel to the direction of E-glass fibers. This was likely due to the hydrophilic surface of the glass fiber when compared to the polymer matrix. Approaches of tailoring fiber-containing scaffolds for tissue engineering applications are ongoing. One promising alternative could be to add fibrous scaffold to the surface of the implant construction in order to enable anisotropic tissue growth to the implant. It can be concluded that FRCs with high-aspectratio fillers have several properties which relate to the direction of the fibers. In the case of unidirectional fibers, both continuous and discontinuous fibers provide anisotropic properties for the composite. Dependent on the application, anisotropicity should be carefully considered when designing FRC devices. More research is needed for detailed information on anisotropicity and its influence on the function of FRC devices in clinical applications.

Please cite this article in press as: Vallittu PK. High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties. Dent Mater (2014),

DENTAL-2417; No. of Pages 7


ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 4 ) xxx–xxx

Acknowledgements Author expresses gratitude to the researcher team of the BioCity Turku Biomaterials Research Program ( and principal financing partners of the FRC research: Finnish Agency for Technology and Innovation (TEKES), Academy of Finland and European Commission (Grant: NEWBONE NMP3-CT-006-026279-2).


[1] Murphy J. The Reinforced Plastics Handbook. Oxford, UK: Elsevier Advanced Technology; 1998. p. 11–26. [2] Ververis C, Georghiou K, Christodoulakis N, Santas P, Santas R. Fiber dimensions, ligning and cellulose content of various plant materials and their suitability for paper production. Indust Crops Prod 2014;19:245–54. [3] Yan J, Taskonak B, Platt JA, Mecholsky JJ. Evaluation of fracture toughness of human dentin using elastic–plastic fracture mechanics. J Biomech 2008;41:1253–9. [4] Toroian D, Lim JE, Proce PA. The size exclusion characteristics of type I collagen. J Biol Chem 2007;282:22374–447. [5] Chen X, Nadiarynkh O, Plotnikov S, Campagnola PJ. Second harmonic generation microscopy for quantitative analysis of collagen fibrillar structure. Nat Protoc 2012;7:654–69. [6] Zimmermann EA, Gludovatz B, Schaible E, Busse B, Ritchie RO. Fracture resistance of human cortical bone across multiple length-scales at physiological strain rates. Biomaterials 2014;(April 11),, pii:S0142-9612(14)00326-3. [7] Johnson W, Matthews E. Fatigue studies on some dental resins. Br Dent J 1949;86:252–3. [8] Smith DC. Recent developments and prospects in dental polymers. J Prosthet Dent 1962;12:1066–78. [9] Ladizesky NH. The Integration of dental resins with highly drawn polyethylene fibres. Clin Mater 1990;6:181–92. [10] Ladizesky NH, Chow TW, Cheng YY. Denture base reinforcement using woven polyethylene fiber. Int J Prosthodont 1994;7:307–14. [11] Freilich MA, Duncan JP, Meiers JC, Goldberg AJ. Preimpregnated, fiber-reinforced prostheses: Part I: Basic rationale and complete coverage and intracoronal fixed partial denture design. Quintessence Int 1998;29:689–96. [12] Loose M, Rosentritt M, Leibrock A, Behr M, Handel G. In vitro study of fracture strength and marginal adaptation of fiber-reinforced-composite versus all ceramic fixed partial dentures. Eur J Prothod Rest Dent 1998;6:55–62. [13] Meiers JC, Duncan JP, Freilich MA, Goldberg AJ. Preimpregnated, fiber-reinforced prostheses. Part II: Direct applications: splints and fixed partial dentures. Quintessence Int 1998;29:761–8. [14] Vallittu PK. Comparison of two different silane compounds used for improving adhesion between fibers and acrylic denture base material. J Oral Rehabil 1993;20:533–9. [15] Vallittu PK. Ultra-high-modulus polyethylene ribbon as reinforcement for denture polymethyl methcarylate. A short communication. Dent Mater 1997;13:381–2. [16] Rantala LI, Lastumaki TM, Peltomaki T, Vallittu PK. Fatigue resistance of removable orthodontic appliance reinforced with glass fibre weave. J Oral Rehabil 2003;30:501–6. [17] Le Bell A-M, Tanner J, Lassila LVJ, Kangasniemi I, Vallittu PK. Bonding of composite resin luting cement to fibre-reinforced composite root canal post. J Adhes Dent 2004;6:319–25.

[18] Vallittu PK. The effect of glass fiber reinforcement on the fracture resistance of a provisional fixed partial denture. J Prosthet Dent 1998;79:125–30. [19] Narva K, Vallittu PK, Yli-Urpo A. Clinical survey of acrylic resin removable denture repairs with glass-fiber reinforcement. Int J Prosthodont 2001;14:219–24. [20] Behr M, Rosentritt M, Lang E, Chazot C, Handel G. Glass-fibre-reinforced composite fixed partial dentures on dental implants. J Oral Rehabil 2001;28:895– 902. [21] Bergendal T, Ekstrand K, Karlsson U. Evaluation of implant-supported carbon/graphite fiber-reinforced poly(methyl methacrylate) prostheses. A longitudinal multicenter study. Clin Oral Impl Res 1995;6: 246–53. [22] Dyer SR, Lassila LVJ, Jokinen M, Vallittu PK. Effect of fiber position and orientation on fracture load of fiber-reinforced composite. Dent Mater 2004;20:947–55. [23] Özcan M, Breuklander MH, Vallittu PK. Effect of slot preparation on the strength of glass fiber-reinforced composite inlay retained fixed partial dentures. J Prosthet Dent 2005;93:337–45. [24] Garoushi S, Lassila LVJ, Tezvergil A, Vallittu PK. Load bearing capacity of fibre-reinforced and particulate filler composite resin combination. J Dent 2006;34:179–84. [25] Sewón LA, Ampula L, Vallittu PK. Rehabilitation of a periodontal patient with rapidly progressing marginal alveolar bone loss. A case report. J Clin Periodontol 2000;27:615–9. [26] Mannocci F, Ferrari M, Watson TF. Intermittent loading of teeth restored using quartz fiber, carbon-quartz fiber, and zirconium dioxide ceramic root canal posts. J Adhes Dent 1999;1:153–8. [27] Ballo AM, Akca EA, Ozen T, Lassila LVJ, Vallittu PK, Närhi TO. Bone tissue responses to glass fiber-reinforced composite implants – a histomorphometric study. Clin Oral Impl Res 2009;20:608–15. [28] Zhao DS, Moritz N, Laurila P, Mattila R, Lassila LVJ, Strandberg N, et al. Development of a biomechanically optimized multi-component fiber-reinforced composite implant for load-sharing conditions. Med Eng Phys 2009;31:461–9. [29] Aitasalo K, Piitulainen JM, Rekola J, Vallittu PK. Craniofacial bone reconstruction with bioactive fibre composite implant. Head Neck 2014;36:722–8, [30] Freilich MA, Karmarker AC, Burstone CJ, Goldberg AJ. Development and clinical applications of a light-polymerized fiber-reinforced composite. J Prosthet Dent 1998;80:311–8. [31] Cheremisinoff NP. Handbook of ceramics and composites. In: Ehrenstein GW, Schmiemann A, Bledzki A, Spaude R, editors. Corrosion phenomena in glass-fiber-reinforced thermosetting resins. USA: Marcel Dekker; 1990. p. 231–68 [chapter 9]. [32] Rosen MR. From treating solution to filler surface and beyond. The life history of a silane coupling agent. J Coat Technol 1978;50:70–82. [33] Vallittu PK. Glass fibers in dental fiber reinforced composites. In: Matinlinna J, editor. Handbook of oral biomaterials. Singapore: Pan Stanford Publishing; 2014. [34] Kardos JL. Short-fiber-reinforced polymeric composites, structure–property relations. In: Lee SM, editor. Handbook of composites. Palo Alto, CA: Wiley-VCH; 1993. p. 593. [35] Krenchel H. Fibre reinforcement [Ph.D. thesis]. Copenhagen: Technical University of Denmark; 1963. [36] Batdorf SB. Strength of composites. In: Kelly A, editor. Concise encyclopedia of composite materials. Oxford: Pergamon; 1994. p. 273.

Please cite this article in press as: Vallittu PK. High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties. Dent Mater (2014),

DENTAL-2417; No. of Pages 7

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 4 ) xxx–xxx

[37] Vallittu PK. Compositional and weave pattern analyses of glass fibers in dental polymer fiber composites. J Prosthod 1998;7:170–6. [38] Garoushi S, Vallittu PK, Lassila LVJ. Effect of short fiber fillers on the optical properties of composite resin. J Mater Sci Res 2012;1(2):174–80. [39] Garoushi S, Säilynoja E, Vallittu PK, Lassila LVJ. Physical properties and depth of cure of a new short fiber reinforced composite. Dent Mater 2013;29:835–41. [40] Fennis WMM, Tezvergil A, Kuijs RH, Lassila LVJ, Kreulen CM, Creugers NHJ, et al. In vitro fracture resistance of fiber reinforced cusp-replacing composite restorations. Dent Mater 2005;21:565–72. [41] Vallittu PK, Sevelius C. Resin-bonded, glass fiber reinforced composite fixed partial dentures – a clinical study. J Prosthet Dent 2000;84:413–8. [42] Vallittu PK. Interpenetrating polymer networks (IPNs) in dental polymers and composites. J Adhes Sci Technol 2009;23:961–72. [43] Lassila LVJ, Tezvergil A, Dyer SR, Vallittu PK. The bond strength of particulate-filler composite to differently oriented fiber-reinforced composite substrate. J Prosthod 2007;16:10–7. [44] Tezvergil A, Lassila LVJ, Vallittu PK. The shear bond strength of bidirectional and random-oriented fibre-reinforced composite to tooth structure. J Dent 2005;33:509–16. [45] Tezvergil A, Lassila LVJ, Vallittu PK. Strength of adhesive-bonded fiber-reinforced composites to enamel and dentine substrates. J Adhes Dent 2003;5:301–11. [46] Irie M, Tanaka J, Maruo Y, Nishigawa G. Vertical and horizontal polymerization shrinkage in composite restorations. Dent Mater 2014;30:189–98. [47] Shah PK, Stansbury JW. Role of filler and functional group conversion in the evolution of properties in polymeric dental restoratives. Dent Mater 2014;30:586–93. [48] Pitel ML. Low-shrink composite resins: a review of their history, strategies for managing shrinkage, and clinical significance. Compend Contin Educ Dent 2013;34:578–90. [49] Anttila E, Krintilä O, Laurila T, Lassila LVJ, Vallittu PK, Hernberg R. Evaluation of polymerization shrinkage and hygroscopic expansion of fiber reinforced composite using fiber Bragg grating sensors. Dent Mater 2008;24:1720–7. [50] Bicalho AA, Valdivia AD, Barreto BC, Tantbirojn D, Versluis A, Soares CJ. Incremental filling technique and composite material – part II: shrinkage and shrinkage stress. Oper Dent 2014;39(March–April),, 39(2):E83-92. [51] Fleming GJ, Cara RR, Palin WM, Burke FJ. Cuspal movement and micoleakage in premolar teeth restored with resin-based filling materials cured using a ‘soft-start’ polymerization protocol. Dent Mater 2007;23:637–43. [52] Feng L, Bi S. The effect of curing modes on polymerization contraction stress of dual cured composite. J Biomed Mater Res B: Appl Biomater 2006;76:196–202. [53] Tezvergil A, Lassila LVJ, Vallittu PK. The effect of fiber orientation on the polymerization shrinkage strain of fiber-reinforced composites. Dent Mater 2006;22:610–6.


[54] Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentine bonding in root canals. A theoretical modeling approach. J Endod 2005;31:584–9. [55] Makarewicz D, Le Bell-Rönnlöf AM, Lassila LV, Vallittu PK. Effect of cementation technique of individually formed fiber-reinforced composite post on bond strength and microleakage. Open Dent J 2013;26:68–75. [56] Pastila P, Lassila LVJ, Jokinen M, Vuorinen J, Vallittu PK, Mäntylä T. Effect of short-term water storage on the elastic properties of some dental restorative materials – a ultrasound spectroscopy study. Dent Mater 2007;23(7 July):878–84. [57] Munendhar P, Aneesh R, Khijwania SK. Development of an all-optical temperature insensitive nonpendulum-type tilt sensor employing Bragg gratings. Appl Opt 2014;53:3574–80. [58] Dogar A, Altintas SC, Lavlak S, Guner A. Determining the influence of fibre post light transmission on polymerization depth and viscoelastic behaviour of dual-cured resin cement. Int Endod J 2012;45:1135–40. [59] Kim YK, Kim SK, Kim KH, Kwon TY. Degree of conversion of dual-cured resin cement light-cured through three fibre posts within human root canals: an ex vivo study. Int Endod J 2009;42:667–74. [60] Radovic I, Corciolani G, Magni E, Krtanovic G, Pavlovic V, Vulicevic ZR, et al. Light transmission through fiber post: the effect on adhesion, elastic modulus and hardness of dual-cure resin cement. Dent Mater 2009;25:837–44. [61] Galhano GA, de Melo RM, Barbosa SH, Zamboni SC, Bottino MA, Scotti R. Evaluation of light transmission through translucent and opaque posts. Oper Dent 2008;33:321–4. [62] Lehtinen J, Laurila T, Lassila LVJ, Tuusa S, Kienanen P, Vallittu PK, et al. Optical characterization of bisphenol-A-glycidyldimethacrylate-triethylene glycoldimethacrylate monomers and copolymers. Dent Mater 2008;24(10):1324–8. [63] Murphy J. Improving/modifying the mechanical properties – fillers. In: Murphy J, editor. The additives for plastics handbook. Oxford: Elsevier Advanced Technology; 1996. p. 62. [64] Hatta M, Shinya A, Vallittu PK, Shinya A, Lassila LV. High volume individual fibre post versus low volume fibre post: the fracture load of the restored tooth. J Dent 2011;39:65–71. [65] Chen D, Lassila LVJ, Vallittu PK. Effect of glass fiber-reinforced composite substructure on the color shade of composite restoration. Dent Mater 2014 [submitted for publication]. [66] Abdulmajeed AA, Walboomers XF, Massera J, Kokkari AK, Vallittu PK, Närhi TO. Blood and fibroblast responses to thermoset BisGMA–TEGDMA/glass fiber-reinforced composite implants in vitro. Clin Oral Implants Res 2014;25:843–51. [67] Abdulmajeed A, Lassila LV, Vallittu PK, Närhi TO. The effect of exposed glass fibers and particles of bioactive glass on the surface wettability of composite implants. Int J Biomater 2011:11, Article ID 607971.

Please cite this article in press as: Vallittu PK. High-aspect ratio fillers: Fiber-reinforced composites and their anisotropic properties. Dent Mater (2014),

High-aspect ratio fillers: fiber-reinforced composites and their anisotropic properties.

To present an overview of fiber-reinforced composites (FRCs) that are a group of non-metallic dental biomaterials used in several fields of dentistry...
2MB Sizes 0 Downloads 3 Views