Under which condition are high copper amalgams considered superior?

High copper amalgams are considered superior primarily because copper within the amalgam can participate in a secondary reaction, leading to enhanced mechanical properties and corrosion resistance. The presence of copper allows for the formation of stable compounds, which improve the overall strength and durability of the amalgam. This reaction helps to strengthen the amalgam and reduces the likelihood of corrosion, making it a more reliable choice for dental restorations, especially in posterior teeth where greater strength is required.

When copper is available for this reaction, it can lead to better interparticle bonding and minimize the formation of gamma-2 phase, which is associated with lower mechanical strength and increased corrosion susceptibility. Thus, the capability of copper to undergo a secondary reaction is directly linked to the superior performance of high copper amalgams in clinical dentistry.