When re-etching a contaminated tooth, how long should the acid be applied?

The recommended time for re-etching a contaminated tooth is typically between 10 to 20 seconds. This duration is sufficient to effectively remove any contamination and prepare the enamel surface for adhesive bonding. Etching with phosphoric acid creates a micro-retentive surface for subsequent materials, such as dental resins or bonding agents, ensuring a strong bond for restorative procedures.

Applying the acid for 10 to 20 seconds allows for efficient decontamination and enhanced bonding without risking over-etching, which could weaken the enamel or dentin. Over-etching might lead to a rougher surface than desired or even damage the tooth structure.

Using shorter etching times, such as 5 to 10 seconds, might not adequately facilitate the necessary structural changes to the enamel. Conversely, extending the etching time to 20 seconds or more, means potentially compromising the tooth structure and adversely affecting bond strength due to excessive removal of enamel. Therefore, the 10 to 20 second window is optimal for effective re-etching while protecting tooth integrity.