| http://www.w3.org/ns/prov#value | - The embodiments of the present invention also overcome the prior art limitation of loss of friction fit where at least one component such as the cushion is made of a material that tends to lose its frictional quality over time, such as with silicone which material tends to become ???greasy??? due to chemical change and its own absorption of environmental pollutants, such as the patient's skin oil.
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