First of all it seems to be better to request the blood test to determine infant's T 3&4 hormonal levels
Next Steps
old.Delay in tooth eruption was reported in infant with premature birth . After a few months waiting if the teeth do not erupt ,radiography can help us to diagnosis of probably reasons such as dental missing that it was reported in infant with premature birth.
Health Tips
I suggest you to do a clinical examination of the child's gingiva, if it has normal characteristics, ie, volume compatible with the presence of dental germs inside, I see no reason for concern.