The bacterial content of a mouth full of cavities is very high. When the new permanent teeth start to erupt by the age of 6, these existing bacteria invade them leading to cavities in young erupting permanent teeth.
Cavities are caused by multiple reasons; poor oral hygiene and diet being the most common ones.
Small cavities need small fillings, big cavities need big fillings. Cavities close to nerve of the baby tooth should be evaluated for half or complete root canal treatments. The whole point of these treatments is to arrest the progressing decay, restore baby tooth and maintain infection free environment for the permanent teeth to develop.
Where there is lack of treatment of decayed primary teeth, bacteria continue to progress deeper into and through the root canals into the underlying bone. This may cause acidic environment around the developing permanent tooth, the response to which is related to the age of the child and status of development of the erupting permanent tooth.
Also, the bacterial content of a mouth full of cavities is very high. When the new permanent teeth start to erupt by the age of 6 years, these existing bacteria invade them leading to cavities in young erupting permanent teeth.
Decays in baby teeth should be diagnosed, treated and then maintained by good oral hygiene practice, dietary guidance and six-monthly regular appointments with the dentist.
Thus, cavities in baby teeth need not necessarily lead to cavities in permanent teeth if necessary, treatments, routines and prevention method are diligently being followed.