Four implants can carry a full arch — but bone density, bite force and grinding decide whether six is the safer engineering choice.
Two implants are placed vertically at the front and two angled up to 45° at the back. The tilt lets the rear implants engage dense bone in front of the sinus, which extends the support span without grafting — that geometry is the entire point of the technique.
If bone quality is good, the opposing arch is a denture or natural teeth without heavy bite force, and you do not grind, four implants distribute load safely and have twenty years of published follow-up behind them.
Patients who grind their teeth, have a strong natural opposing bite, or show soft bone on the CT scan get six implants. The extra two shorten the cantilever at the back, which is where a four-implant bridge is most stressed.
All-on-4 starts at €2,900 per arch including the fixed provisional bridge. Six implants add roughly €600–€900 per arch. Choosing on price alone is the wrong test; choose on the CT scan.
Yes, after the healing phase. During the first weeks a soft diet protects the provisional bridge while the implants integrate.