C19    Discuss the clinical significance of dimensional changes occurring in dental amalgams.

Excessive dimensional changes can result in amalgam expansion that causes cusp fractures and pain, or in shrinkage that results in leakage and pain.  Such problems are mainly due to delayed expansion caused by contamination of zinc-containing amalgams.

Because of the possibility that an amalgam can cause problems due to expansion-contraction, ADA will not certify any amalgam alloys that has an expansion/contraction exceeding 20 µm/cm (0.2%). This expansion-contraction value is substantially better than any of the existing polymer-ceramic composites. Just remember that the delayed expansion is not included in the ADA specification.