Here are the completed sentences:

48. The dentist and your parents show you the best way to get your teeth clean without damaging your gums.

49. Make sure your toothbrush has soft bristles, and some toothbrushes come with bristles that change color when it’s time to change them.

50. You also need to be careful about what you eat and drink; eat lots of fruits and vegetables and drink water instead of soda.