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Abstract
Statement of problem
Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force.
Purpose
The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic.
Material and methods
Heat pressed ceramic (ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire (Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens (width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine (Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope (JSM-6360, JEOL, Japan) under platinum coating.
Results
The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics (P < .001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire.
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Fig. 4.
Fracture patterns of wireless ceramic (a) & wire inserted ceramics (b). The dotted line shows crack line.
Fig. 5.
Scanning Electron Microscopy (× 100) of cross-sectioned (left) and longitudinally-sectioned (right) specimen.
Table I.
Components of the IPS Empress 2 ceramic
| Components | wt% |
|---|---|
| SiO2 | 57 - 80 |
| Al2O3 | 0 - 5 |
| La2O3 | 0.1 - 6 |
| MgO | 0 - 5 |
| ZnO | 0 - 8 |
| K2O | 0 - 13 |
| Li2O | 11 - 19 |
| P2O5 | 0 - 11 |
| Additional components | 0 - 8 |
Table II.
Average and standard deviation of flexural modulus, flexural strength, strain and fracture toughness
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