Principles of Attachment Selection for Implant Supported Overdentures
| Principles of Attachment Selection for Implant Supported Overdentures | Hamid Shafie, DDS* and George Obeid, DDS** |
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• The retention level of each color-coded female cap is listed in Table 11, and shown in Figure 20. • Verify the occlusion and perform any necessary occlusal adjustments. Zirconia Overdenture Implant Zirconium dioxide (ZrO2), commonly known as Zirconia, was discovered in 1789 by the German chemist M. H. Klaproth. However, it was only introduced into dentistry a few decades ago. It has since become a product of choice because of its high esthetic potential and strength compared to traditional |
metals. In dental implant manufacturing, titanium has been the mainstay; however, Zirconia has become a viable option because it possesses superior properties, including a higher tensile strength, compressive strength, and modulus of elasticity when compared to either titanium alloy or commercially pure titanium (Table 12).
The commercial grade Zirconia used in dentistry today has several modifications that enhance it compared to the zirconium dioxide discovered in the 18th century. Pure zirconium dioxide has a low shear strength and is very brittle, essentially making it useless as a dental material. The addition of small amounts of aluminum oxide and yttrium oxide increase the modulus of elasticity and help to stabilize the material. This combination of oxides is mixed in the powder state and placed in a sintering oven to produce a monocline crystal structure, with equally spaced, non-overlapping particles. (Fig. 21A) Although the monocline crystal is strong, cracks can propagate easily in it, making it less desirable for long-term implanted prostheses. In order to eliminate this issue, today’s Zirconia is also put through a process known as hot isostatic pressing (HIP). The high pressure causes condensation of the |
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