Short communicationMechanical properties of polymer-infiltrated-ceramic (sodium aluminum silicate) composites for dental restoration
Introduction
Because of the polymerization shrinkage and low mechanical properties of direct dental restorative composites, indirect restorative materials emerged recently as initials for patients and doctors. Especially, over the last few years, indirect restorative materials underwent great revolutions. As the significant developments of indirect restorative materials were made under the backgrounds of computer-aided design and computer-aided manufacturing, these restorative materials were also called CAD/CAM blocks. Indirect restorative materials can be classified into two groups, ceramics and ceramic-polymer composites. The ultimate aim of restorative composites would be to replace the lost part of the tooth. And therefore the restorative materials must mimic the natural tooth in structure and properties. Mechanical properties, aesthetic properties, biocompatibilities and anti-bacterial properties are among the most important performances.
CAD/CAM composites can be obtained simply by polymerizing direct restorative composites filled with inorganic particles. However, the mechanical properties of this kind of composites are often low because of the low inorganic filler loading ensuring the fluidity during restoration. High filler loadings often bring about high mechanical properties. And polymer infiltrated ceramic network (PICN) is an ideal method for high inorganic loadings. PICNs are categorized into phase interpenetrating composites with two continuous phases. Ceramic-metal interpenetrating composites and ceramic-glass interpenetrating composites have been reported before PICN. Different from ceramic-metal and ceramic-glass, interpenetrating composites, PICNs possess dual networks. The dual networks possess the properties of both ceramics and polymers. The ceramic parts provide hardness, strength and wear resistance, while the polymer parts provide flexibility and machinability. Lava Ultimate and Vita Enamic are two representative commercial composite CAD/CAM blocks. While Vita Enamic could be classified as PICN, Lava Ultimate is essentially filled composite with ultrahigh filler loading.
The main aim of this paper was to fabricate a PICN that could best imitate the natural tooth in mechanical properties. However, as mechanical properties of dentin and enamel are of gradient characteristics and are different from samples to samples, the true values are difficult to be determined. A series of literatures are summarized, and some mechanical properties of two parts (dentin and enamel) of human tooth are listed in Table 1.
In this paper, the flexural strength, flexural modulus, elastic modulus, hardness, fracture toughness and brittleness index were compared with respect to the sintered temperature of the green body.
Section snippets
Fabrication of the samples
Sodium aluminum silicate (SIPERNAT 820A, Degussa AG, Germany) was used to fabricate ceramic networks. The partially sintered sodium aluminum silicate blocks were infiltrated with monomer mixtures containing bisphenol-A-dimethacrylate, BisGMA, and triethylene glycol dimethacrylate, TEGDMA (Aladdin Reagents Company, Shanghai, China). TEGDMA was used as a diluent because the viscosity of BisGMA was rather high. The mass ratio of BisGMA and TEGDMA was 50:50. Dibenzoylperoxide, BPO (J & K Scientific
Results
The results of mechanical properties including flexural strength, flexural modulus, elastic modulus, Vickers hardness and fracture toughness for composites (with the sintering temperature of the green bodies from 550 °C to 850 °C) were illustrated in Table 2. The effects of sintering temperature on mechanical properties were indicated.
Flexural strength values were affected by sintering temperature. When the sintered temperature was 700 °C, the flexural strength attained a maximum of 214.91 ± 6.51
Discussion
The present work was mainly devoted to the production of a novel PICN with high mechanical properties. The ideal situation is that dental restorative materials could mimic the natural tooth in mechanical and aesthetic properties. The results suggested that this kind of polymer infiltrated ceramic networks is a promising candidate for CAD/CAM applications.
The flexural strengths vary from 130.41 ± 20.65 MPa to 214.91 ± 13.94 MPa, which are the results of two phase (polymer and porous ceramics)
Conclusions
Based on our experimental results, the following conclusions could be drawn:
- (1)
The dual networks could possess the properties of both ceramics and polymers.
- (2)
The contribution of ceramic networks is more on modulus and hardness than flexural strength; a slight increase in density of the porous ceramic could bring about an obvious rise in modulus and hardness.
- (3)
This experimental PICN composite which highly mimics the natural dentin can be a promising kind of indirect dental restorative material, and can
Acknowledgements
This work was financially supported by National Science Foundation (51532003, 51221291, 51328203 and 81671026).
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