For an upper denture I would consider using at least 6 mini implants. If there is poor quality of bone then your dentist may consider not adding the snaps to the inside of your denture that day and will delay loading the mini implants.
This will allow more time for the mini implant to integrate into the bone. He or she may also not remove the roof of the mouth portion of the denture.
Best regards,
Paresh B Patel DDS
mini dental implant upper denture