This advertisement uses source credibility to appeal to it's audience. It uses an expert in the field (Dentist) to provide information on the health risks of our everyday diets and the benefits of using their product.
Evidence for this effect was demonstrated by Hovland & Weiss (1951) who found that students who read an article arguing that nuclear submarines were safe were more likely to believe it if the author was Robert Oppenheimer (scientist in charge of developing the atomic bomb and thus a credible source) compared to when the same article was attributed to a Soviet news agency (not a credible source).
Hovland, C. I. & Weiss, W. (1951). The influence of source credibility on communication effectiveness. Public Opinion Quarterly, 15, 635-650.