Why are small teeth smooth at the top and the adult teeth bumpy at the top?

Small teeth, or primary teeth, are generally smoother at the top to facilitate easier chewing and to aid in the development of speech in young children. In contrast, adult teeth have bumpy surfaces, known as cusps, which provide better grip and efficiency for chewing tougher foods. The increased surface area and complexity of adult teeth help them withstand greater forces and enhance their functionality in a mature diet.