Whiter teeth In an eff ort to make their teeth whiter,

Chapter 1, Problem 1.18

(choose chapter or problem)

Whiter teeth In an eff ort to make their teeth whiter, some people use whitening strips or bleaching gels. Are new light-activated bleaching techniques any more eff ective? Researchers carried out a study to help answer this question. Th ey gathered a small group of dental patients who were willing to participate. On one side of patients mouths, the researchers used bleaching gel alone. On the other side, they used light plus bleaching gel. Th e results? Th e patients teeth got whiter on both sides of their mouths; there was no real diff erence in whiteness between the two sides. (a) Was this study an experiment or an observational study? Explain. (b) Why did the researchers apply both possible treatments to each patient, rather than using bleaching gel on only half of the patients and light plus bleaching gel on the other half?