If you scroll down in this brief review, http://www.llli.org/NB/NBSepOct05p211a.html, you'll find this paragraph:
"Cleaning children's teeth is not usually a favorite activity for either parents or children, but Enzor emphasized that it must be non-negotiable. Just as diapers must be changed and hands washed, teeth must be wiped or brushed. She recommended beginning at birth with a wet washcloth to accustom the child to the idea of something in his mouth. When the first tooth comes in, a soft toothbrush should be introduced. Dr. Enzor acknowledged that some children will resist and gave examples of using humor and novelty to encourage cooperation. She pointed out that insisting on cleaning a child's teeth is still much less invasive and forceful than the alternative: dental work to repair cavities."
One idea I've heard of is to wipe the teeth with a clean washcloth during bathtime. It can become part of the cleaning routine and and gets them used to the idea of something in their mouth.
The "humor and novelty" she speaks about would certainly vary by age of the child.