Susanna:

is it possible that the real culprit of your son's decay was amelagenesis
imperfecta? This is the condition that my daughter had and as soon as she
weaned at 31/2 years, she had massive tooth decay that required substantial
dental treatment including crowns.

her adult teeth are fine. they do not know what causes this disease and it
 manifested as wearing away of the enamel exposing the dentin underneath
making the teeth more susceptible to decay.

I often wonder if what dental researcher suggest id Baby Bottle Tooth decay
in breastfed babies actually this or a similar type of condition.

Linda Smith (are you out there, Linda?) has more information about this.

Alison