I am looking for images to be used for a Bingo type game for
preschoolers.  All the images must be related to dental care.  I need
about 20 of them, and they should be in a consistent style -- that is,
all cartoon type figures or all pictures of actual items. For example,
images might include a tooth, toothbrush, dentist, dental chair, and
so on.

Hi! Thanks for the question.

I was able to find the following free for use images of dental cartoons.

Clipsahoy (12 dental images)
http://www.clipsahoy.com/occupations/dental/dental1.htm
http://www.clipsahoy.com/occupations/dental/dental2.htm
http://www.clipsahoy.com/occupations/dental/dental3.htm

Discovery Channel Clipart (5 images)
http://school.discovery.com/clipart/clip/floss.html
http://school.discovery.com/clipart/clip/dentist.html 
http://school.discovery.com/clipart/clip/in-tooth.html
http://school.discovery.com/clipart/clip/toothgrn.html
http://school.discovery.com/clipart/clip/toothbrs.html 

EDU Pics (6 images)
http://www.edupics.com/cat83.htm

Cool Clips: Dentist Images (19 images)
http://dir.coolclips.com/Healthcare/Dentistry/Dentists_and_Patients/ 

Cool Clips: Teeth & Oral Hygiene (38 images)
http://dir.coolclips.com/Healthcare/Dentistry/Teeth_and_Oral_Hygiene/ 

Search terms used:  
dentist dental teeth clipart images

I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
                                                          
                              
Regards,                              
Easterangel-ga                              
Google Answers Researcher