Which material undergoes a volume shrinkage of approximately 21% when polymerized?

Methyl methacrylate monomer is known for its significant volume shrinkage of about 21% when polymerized. This high level of shrinkage occurs because the polymerization process involves the transformation of a liquid monomer into a solid polymer, resulting in a reduction in the material's volume. The degree of shrinkage is critical to consider when using this material in dental applications since it can affect the fit and marginal integrity of restorations or prosthetics.

In contrast, gold alloys and wax patterns are materials that do not exhibit such high levels of volume shrinkage during their respective setting or cooling processes. Gold alloys tend to expand slightly when heated and contract minimally upon setting, while wax patterns are often used in their unpolymerized states and will usually undergo melting and solidification without dramatic volume changes. Self-cured resin, while it does experience some level of shrinkage, typically does not reach the same extent as methyl methacrylate monomer. This makes understanding the shrinkage characteristics of these materials essential for ensuring the quality and longevity of dental restorations.