thanks for sharing your concern.
don't worry at all.
how old r u?which jaw,which tooth is RETAINED? I need to know this before answering you.
anyways, no problem you can just visit your dentist
and ask for an INTRA ORAL PERIAPICAL XRAY (IO PA).
THIS WILL CLEARLY SHOW YOU THE PERMANENT TOOTH, ITS ROOT DEVELOPMENT, AND AMOUNT OF BONE COVERING IT.
this will give you an approximate time during which the tooth must appear in the oral cavity.it will also help you to understand why it hasn't come yet in oral cavity?
coming to your worry regarding RETAINED DECIDUOUS(baby) tooth, if there is permanent tooth underlying, it can be very well extracted.
a simple xray should solve your problem,so visit your dentist and get the baby tooth out if said so by your dentist.
also be sure that it will be painless because the roots are already in the process of resorption.
hope this helps.
take care, thanx.