Below you can see a picture of a patient that has 2 dental implants with ball attachments on top of the implants. The ball attachments enable the patient to fit his denture on to the attachment and serve as a very strong and stable connection. This connection puts end to the use of denture adhesive and improves his quality of significantly. Read more about denture implants here.
This standard ball abutment is connected on top of a dental implant and is used usually as a retaining device for dentures. The ball snaps into a "socket" like connector (a retaining fixture) that is incorporated into the base of the denture.
The connection is achieved thanks to a rubber o-ring inside the socket connector providing adequate retaining force to hold the denture in place. By applying a bit more force the connection may be forced open, enabling the removal of dentures.