Thanks for asking the query,
Delayed erruption of teethin preterm baby can be due to,
Vitamin and calcium deficiencies,
under nutritions or malnutrition
that is low levels of T3 & T4 hormones and elevated levels of TSH
so please get the blood examination done for this hormones.
Genetic predisposition may also lead to delayed erruption .
Complete clinical evaluation by a Pedodontist will help us in diagnosis and deciding the treatment plan.
Hope this helps out.