Manufacturers often claim that their particular toothbrush design is better than the competitors, but is it? As a result, engineers must consider the economic issues involved with selling the products they create, as well as their functionality: to produce the best possible toothbrush regardless of cost, or the toothbrush that will sell the most, or perhaps the toothbrush that costs the least to produce. This article describes a 5E learning-cycle lesson where students explore various manual toothbrush designs. (Contains 6 figures.)