Complex sentence: Enamel hypoplasia is a congenital defect of the teeth in which the enamel is hard but thin and deficient in amount, caused by defective enamel matrix formation with a deficiency in the cementing substance.
Split into simpler sentences: Enamel hypoplasia is the defect of the teeth in which the enamel is hard but thin and deficient in amount. This is caused by defective enamel matrix formation with a deficiency in the cementing substance.