What effect does over trituration have on working time and setting contraction?

Over trituration refers to the process of mixing dental materials, such as amalgam or composite, for an extended period of time or at an excessively high speed. This process alters the physical and chemical properties of the material, which directly affects working time and setting characteristics.

When over trituration occurs, the working time of the material decreases. This is because the excessive mixing initiates the setting reaction prematurely. Thus, the operator has less time to manipulate the material before it begins to harden. Additionally, over trituration affects the setting time, causing it to also decrease. The faster onset of the setting reaction results in the material hardening more quickly than it would under optimal mixing conditions.

Moreover, over trituration can lead to an increase in setting contraction, which is the dimensional change that occurs as the material sets and hardens. This increase in contraction can happen because the excessive energy introduced into the material can lead to a denser matrix with less space for expansion during the setting process.

In summary, over trituration reduces the working time and setting time while simultaneously increasing the setting contraction, making it crucial for dental professionals to be cautious with mixing techniques to ensure optimal material performance.