middle ear prosthetics

my son was diagnosed and treated for congenital cholesteotoma 5 years ago.  he received a canal-wall-down procedure in which case the stapes and incus were removed because they were damaged from the cholesteotoma.  He's now 12 and things have been fine other than he's mostly deaf in that ear.   I'm interested in any perspective on (a) when is the right time to consider a prosthetic? (b) are there multiple types of prosthetics to consider? and (c) what expectations on hearing recovery should we expect assuming everything worked?

If anyone has personal experience with this, I'd enjoy hearing (pardon the pun) your perspective/experience.