Evaluation of physical properties of fiber-reinforced composite resin
Graphical abstract
Introduction
In recent years, restorative treatments for preserving sound tooth structures with minimal intervention to the dentin have become important, based on the concept of minimal intervention dentistry (MID) [1]. Composite resin have been widely used to achieve the MID concept. Hybrid resin developed for restoring molars has been clinically successful. These positive results have expanded the indications of composite resin in a wide range of restorations, such as fixed partial dentures and full-mouth rehabilitation [2], [3]. Subsequently, various attempts have been made to improve the mechanical properties of composite resin to meet this clinical demand.
In the industry, fibers have been used as reinforcement of resin, called as the fiber-reinforced plastic (FRP) [4]. FRP is also used in dentistry. The representative examples of FRP in dentistry are hybrid resin for crown restoration, fiber post, high strength composite resin bridge, and CAD/CAM glass fiber reinforced resin. In all these materials, the fiber contained in FRP should be able to bear the tensile and bending stress and need to firmly adhere to resin matrix [5].
There are three patterns of fiber forms in FRP; random short fiber reinforced type (RSFRT), unidirectional continuous fiber reinforced type (UCFRT), and textile laminate reinforced type (TLRT). RSFRT is reinforced by short fibers randomly arranged in the matrix resin. UCFRT is reinforced by continuous fibers arranged unidirectionally in the matrix resin. TLRT is reinforced by tailoring fiber bundles into mesh fabrics. However, contributions of these fibers in improving the mechanical properties of FRP have not been clearly demonstrated. In particular, the effects of forms and directions of the fibers on reinforcing restoratives need to be comprehensively investigated.
Recent developments in digital technologies have significantly progressed the production of a restorative crown, especially CAD/CAM systems. A CAD/CAM crown can be made now by a simple process of milling a hybrid composite or a ceramic block without using complex technical procedures.
In this study, a glass fiber reinforced resin disc, TRINIA (SHOFU, Kyoto, Japan), was used, which was composed of 55 wt% glass fibers and 45 wt% epoxy resin matrix. A TRINIA disc, with fibers aligned as meshes and layers in a disc, seems to have good potential to produce various kinds of restorations by CAD/CAM system [6].
The purpose of this study was to evaluate flexural strength (FS), fracture toughness (FT), and water absorption of CAD/CAM glass fiber reinforced resin – TRINIA – by regulating the directions of fiber layers.
Section snippets
Materials
Materials used in this study are presented in Table 1. A glass fiber-reinforced resin disc (TRINIA, SHOFU, Kyoto, Japan) was composed of 45 wt% epoxy resin matrix and 55 wt% multi-directionally interlaced glass fibers, which aligned woven layers parallel to the top surface of the disc. Exposed fiber size was not disclosed. By SEM observation, the width and thickness of E-glass fibers were 1.2–1.5 mm and 0.1–0.4 mm, respectively. A fiber-reinforced composite resin (everX Posterior, GC, Tokyo, Japan)
Results
FS and flexural modulus (FM) of the materials tested are presented in Fig. 3. TRINIA longitudinal and longitudinal-rotated groups, which had the multi-directional glass fibers layered longitudinally parallel to the specimens, demonstrated significantly high FS (254.2 ± 22.3 and 248.8 ± 16.7 MPa, respectively). Those were approximately 2.5 times higher than those of TRINIA anti-longitudinal (96.9 ± 2.9 MPa), everX posterior (98.0 ± 15.9 MPa), and Beauti core flow paste (96.8 ± 3.3 MPa) groups. TRINIA
Discussion
Fiber reinforced materials have become popular in dental restorations, especially in post-core for restoring pulpless teeth [9], [10], [11] and in constituting the framework for bridge restoration [12], [13], [14]. Superior mechanical properties of fiber-reinforced composite resin have been reported [15]. Fiber-reinforced composite resin, containing randomly distributed short glass fiber (0.2–0.3 mm), have been demonstrated to have higher FS, elastic modulus, and FT compared to conventional
Conclusion
TRINIA demonstrated distinct anisotropy. TRINIA can be used as a superior restorative material when specifying directions of its fiber mesh layers.
Funding sources
This study was supported by the Grants-in-Aid for Scientific Research (17H04382, 17K19907 and 16K20454) from JSPS and SECOM science Technology Foundation Grant (2019).
Conflict of interest
None declared.
Acknowledgements
The authors are grateful to SHOFU for kindly providing some of the materials used.
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FDI, statement
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