The rate at which enamel returns to its normal appearance after acid etching was determined in patients of various ages. The incisal halves of mandibular right central incisors in four patients, ranging in age from 9 to 67 years, were etched with a commercial etching agent to determine rates at which enamel returns to normal appearance. The time for complete return to normal appearance increased with the patient’s age, from about 96 hours in the youngest to more than two weeks in the oldest. However, even in the older patients, the enamel had an almost normal texture after 48 hours. The rate at which enamel returns to its normal appearance after acid etching was determined in patients of various ages. The incisal halves of mandibular right central incisors in four patients, ranging in age from 9 to 67 years, were etched with a commercial etching agent to determine rates at which enamel returns to normal appearance. The time for complete return to normal appearance increased with the patient’s age, from about 96 hours in the youngest to more than two weeks in the oldest. However, even in the older patients, the enamel had an almost normal texture after 48 hours.