>I have two friends whose kids had some teeth that "rotted" as they came in.
> In both of these cases maternal illnesses with fever during the eighth month
>of pregnancy were implicated. Other breastfed kids  in the same families had
>nursed a lot at night yet had healthy teeth.

A few years ago, the national magazine of the Nursing Mothers' Association
of Australia had a discussion topic on the issue of breastfeeding and dental
health. A summary of the letters published:
1. 3 children all breastfed ad libitum, all with grossly decayed first
teeth. 2 dentists and orthodontist agreed breastfeeding not the cause.  All
3 suffered from measles and/or rubella before six weeks of age.  Febrile
nature of such illnesses believed to interfere with enamel leyering of
developing teeth.  In all cases, only upper a & b teeth affected, not molars.
2. 2 breastfed children who developed decay early, both introduced early to
cordial, the one who had it earlier showing decay earlier.
3. 4 children all with very different patterns of decay or lack of it.
Dentist said different acid levels in saliva can causes variation.
4. after starting solids, previously white 4 front teeth developed yellow
line. Diet low in sugear, teeth carefully cleaned. At eighteen months,
dentist felt either hereditary condition or in utero incident, and was
supportive of night breastfeeding.
5. 3 children, 8, 6 & 3, all fed at will around clock. Teeth carefully
cleaned, flouride supplements. No decay.
6. Mother dental therapist: children 4 & 1.5 (latter still feeding). No
decay. Teeth carefully cleaned. Mother suggests sickness, certain drugs or
medication (eg teetracycline) taken during pregnancy can affect developing
teeth.
7. ist child (night feeds till 2) developed white line across four front
teeth at 12 months.  School dentist blamed breastfeeding. Second child fed
as frequently to 18 months with no earlt decay. Mother points to sugars eg
honey on toast & iceblocks introduced early to first child and frequent
medications taken at bed time without teeth being brished afterwards, plus
infrequent tooth brushing before 9 months.
8. Breastfed child needed gum line fillings at 3, dental nurses suggested
pattern same as bottlefed babies going to bed with bottle of juice.
Frequently given sultanas as a reward - sweet & sticky. 2nd child now 3,
breastfed to sleep after teeth cleaned, no sultanas, no decay.
9. 4 children all breastfed (fed to sleep) for at least 2 years. 16 year old
has two fillings, possibly from diffulty cleaning teeth while wearing bands.
Only other decay child 2 developed bad decay on 4 teeth within months of
eruption. One dentist suggested antibiotics given to him as a baby, later
theory in-utero incident.
10. First 2 children (bottlefed) now aged 22 & 13 no fillings, brought up in
area with fluoridated water. Second husband, breastfed babies, 7 yr old has
three fillings, 5 yr old has 3 fillings, brought up in area with
nonfluoridated water.
11. 2rs 8 months fed to sleep every night of life. Diet low in sugar, teeth
carefully cleaned, no decay.
12. First child fillings at 2, mother living in area using bore water during
pregnancy. Child 2, pregnancy elsewhere, 1 filling at 4.
13. Child intensely breastfed 18 months. Decay started at 12 months of age
when getting back molars. Refluxing at night. Dentists agreed stomach acid
could cause decay.
14. Four children breastfed for short time, little sugar in diet, good
cleaning routines "fairly good first teeth". Child 5 breastfed on demand
till age 5, perfect set of first teeth. Now 21 no dental work.
15. Children aged 4 & 7, demand fed, mother took fluoride supplements late
in pregnancy, good cleaning routines, sugar restricted, high clacium diet,
no decay.
16. 4 daughters 18, 10, 8 & 5 have one filling between them.  All but one
breastfed constantly. Son at 3 has had 2 fillings and 1 extraction.  Same
diet, same care.
17. 3 children, 10, 7, 3, all frequent night feeders till about 2.5 yrs. 3
sets of perefect teeth.
18. 2 yr old twins, breastfed day & night for 14 months, same diet and care.
Son's teeth perfect, daughter had 3 molar cavities. Son had smooth, larger,
accessible teeth, daughter had small teeth with fine grooves, harder to clean.
19.Fully breastfed for 8-9 mths, at 12 months, enamel crumbled off teeth 3mm
from gum line.  Dentist at time blamed breastfeeding, later dentist
suggested genetic cause, said some babies are born with poor teeth that rot
for no apparent reason.
20. Letter from dentist, thinks it is theoretically possible for
breastfeeding to be implicated in nursing caries, but also thinks in reality
not very likely.
21. (me!) Both parents have shocking teeth, with mouths full of fillings
(husband has had many extractions). Two school age children, both cut out
night feeds early then resumed on demand for two years once teething
commenced. No decay. The first sucked 2 middle fingers & has required minor
orthodonty, also very attached to comfort object. 2nd no comfort object, no
digit sucking, developed 2 extra teeth (apparently genetic), one sideways,
and undergoing major orthodonty, which just goes to show that these things
are multi-factorial, and sometimes you just can't win!

Lesley McBurney, Brisbane, Australia, fascinated by this subject.