What is the correct constitution of acid etchant used during a restorative procedure with composite material?

The correct answer is based on the common use of phosphoric acid in dental procedures, particularly for etching enamel and dentin before the application of composite materials. A 33% concentration of phosphoric acid is typically used in dental etchants due to its effectiveness in creating a rough surface on the enamel, which enhances the mechanical retention of the composite resin.

In the context of restorative dentistry, the purpose of etching is to remove the smear layer and demineralize the surface of the tooth, thus improving the bonding capabilities of the composite material. Phosphoric acid effectively penetrates the hydroxyapatite crystals in the enamel, forming a microscopically roughened surface that promotes adhesion.

Other options presented do not fit the standard practice for dental etching. For instance, hydrochloric acid is too strong and not conventionally used for this purpose, while polyacrylic acid is used in certain applications but does not provide the same aggressive etching as phosphoric acid. Hydrogen peroxide, while it has oxidizing properties, does not serve the same function as an etching agent for composite bonding. Therefore, phosphoric acid at the specified concentration is the widely accepted choice for achieving optimal bonding in restorative procedures involving composite material.