Full-arch fixed rehabilitation: immediate loading is decided on stability, not on the calendar

Full-arch fixed rehabilitation on four or six implants has changed the expectations of the edentulous patient, who now often asks to leave the practice with fixed teeth the same day.

Immediate loading is not, however, applicable to everyone. The decision is taken in the operating room, on the stability actually achieved, not at the planning stage on the calendar.

The most used parameter is insertion torque, with a threshold commonly cited around 35 Newton centimetres. It is a practical value but requires interpretation: high torque in dense bone may indicate excessive compression, which compromises vascularity and favours resorption.

Resonance frequency analysis provides a complementary figure less dependent on density: stability quotient values above 70 are generally considered compatible with immediate loading.

The biological principle is that micromovement at the interface must stay below a threshold of roughly 100 to 150 micrometres. Above that, fibrous tissue forms instead of bone and the implant fails within the first weeks.

Splinting the implants with a rigid framework is what makes immediate loading possible: it distributes forces and prevents any single implant from receiving eccentric load. An implant loaded singly in immediate function carries much higher risk.

The immediate provisional must therefore be rigid. Unreinforced acrylic resin flexes under load, and that flexion transfers micromovement to the implants: metal or fibre reinforcement is not a comfort detail.

The distal cantilever is the element most frequently causing mechanical complications. The prudent rule limits it to about one and a half times the anteroposterior spread between the most distal implants.

The angulation of posterior implants, characteristic of four-implant protocols, exists precisely to widen that spread: bringing the platform further distally shortens the cantilever required.

Transition from provisional to definitive requires a passivity check that admits no compromise. The single-screw test — tightening one screw and verifying the seating of the others — is simple and reveals tensions the eye does not see.

A non-passive framework generates permanent stress on the implants, and the consequences appear months later: screw loosening, framework fracture, marginal bone loss without inflammatory signs.

Home care must be designed together with the prosthesis, not explained afterwards. The fitting surface must be convex and polished, with spaces sufficient for interdental brushes: a concave framework is impossible to clean, however diligent the patient.

In summary, immediate loading depends on the stability achieved, on rigid splinting and on cantilever control. The timetable promised to the patient must never precede the assessment made at the moment of placement.