When you're trying to decide whether or not to use a Web site, try looking at the following criteria:
So let's apply these criteria to Wikipedia articles, such as the article on Xylitol.
Author: None listed. Wikipedia is edited by anyone who creates an account.
Presentation: Very attractive presentation. Authors refer us to other sources where they got their information.
As you can see, Wikipedia is a good place to find citations to other sources, and to get an idea of how people talk about Xylitol, but it's not a good site to cite for your professors.
Now let's try these criteria on a Web page about teeth-whitening products on the Crest site.
Author: Unnamed; presumably works for Crest.
Is s/he a licensed hygenist or assistant or dentist?