Yes, they are fixed solutions, but in different ways.
The denture in case of All-on-4 can not be removed by you, but if you see your dentist he is able to remove it with special dental tools as the denture is attached to the implants by screws. It is very useful if it needs fixing or a tooth is chipped, as it is simple to solve these kind of problems.
All-on-6 has two versions. One of them is totally fixed it can not be removed either by you or your dentist as the complete bridge is bonded to the implants. For example a broken or chipped tooth can not be fixed separately only if the whole bridge is taken off the implants. There is another solution with All-on-6, which is similar to All-on-4, when screws are used to fix the bridge to the implants. It has a surcharge compared to the other All-on-6 solution but it provides quick and cheap fixing possibility in case of broken or chipped teeth.
You can read more about All-on-4 and All-on-6 solutions on the implant page.
