no special care is necessary, other than common sense hygiene. you can wipe the tooth with a washcloth once or twice a day. i never did. cavities are caused by bacteria. some ppl get it some dont. my sis and i were formula fed. i brush and floss regularly, she walks around with green slime on her teeth. i have had so many cavities i lost count and she has never had one.
she and i nursed all of our kids til age 2, 4, and 5. all of our kids have had cavities. its not breastmilk, though. all three kids nursed through the night for at least 2 yrs, but the cavities came later. no bottle-rot from bm.
just clean the teeth 1-2x daily and dontn worry about night nursing. you may want to learn about s mutans, though, and maybe traditional foods and teeth, if you arent already into TF.