<prompt> A 33 year old female patient complains of decayed tooth. IOPA reveals dentinal caries with 46 not involving the pulp. A composite restoration has been planned for the tooth. Following etching, how much time should the operator wait before the patient is allowed to rinse?10 seconds15 seconds20 seconds30 seconds  <response>: Once the tooth is etched, the acid should be rinsed away thoroughly with a stream of water for about 20 seconds, and then rinsed water must be removed.When enamel alone is etched and is to be bonded with a hydrophobic resin e.g. bisphenol A glycidyl methacrylate based resin, it must be dried completely with warm air until it takes on a white, frosted appearance.Dentin, in contrast, cannot withstand such aggressive drying, which would cause bond failure because of the formation of impermeable, collapsed collagen fibers.In the total-etch technique, a dentin bonding agent and primer must be used that are compatible with both moist dentin and moist enamel.Reference- Sturdevant 6th ed Pg-310 