Step 1: Use Pictures
Research how other ads (especially Newspaper ads) market their toothpaste. Usually they just show a picture of a tube of toothpaste with either their target demographic using it or the toothpaste squirting out.
Step 2: Accentuate the Good Stuff
Make sure your audience is aware of all the benefits and give them evidence so they can determine if it's the best choice for them, and be sure to list all ingredients and list all additional components that sets it apart from other brands. Think of this step as a resume for your toothpaste. Obviously don't lie about what your toothpaste can do, but you want your potential customers to consider buying it.
Step 3: Focus Group (Feedback)
Post some results of how well your toothpaste was received by a group of people. Keep it sweet and simple and straight to the point. (Gather a diverse group of people who are in your target demographic to try the toothpaste, and ask for their opinions, make tweaks if needed and test again until a good chunk of people like it, that's how you get support for your brand of toothpaste.)
Step 4: Spark the Press
Reach out to local newspapers/magazines and show them your portfolio of people's feedback on your toothpaste, and with whatever money you have, you'll be paying them to allow you to put your ad in their paper (sometimes it can be vise versa).
Hope this helps, this is just a short summery of what I learned in Entrepreneurship.