Hi

There are many different options. Of course the options depend on –  is it for the upper or lower, amount of bone you have, type of bite you have, etc.

The possible options are
1. locators
2. magnets
3. studs
4. bars.

the following web page provides different videos which explain the different options in more detail – http://www.dental-suite.co.uk/dental_implants.htm
(just click on the video link on this page)

I personally tend to use locators or bars to provide denture retention.

Regards