Clinical Background

In All-on-4 Immediate Loading treatment, it is not common to observe a Provisional fracture within few months after surgery. When this occurs, the visible break in the prosthesis is often only the surface finding. The more important clinical question is whether the functional load within the system has already exceeded what the temporary restoration can tolerate.

This patient had previously experienced multiple implant failures and later underwent full-arch reconstruction. At the 2-month follow-up, examination showed that the preload of the NB new temp screw (direct to MUA screw) had clearly decreased, so it was retightened to 15 Ncm according to protocol. Two weeks later, the patient sent a photo showing fracture of the maxillary provisional prosthesis. A newly printed provisional was delivered and replaced the following day.

The most interesting aspect of this case was the timing. The prosthesis did not fail at the moment the screw preload had decreased. Instead, the fracture became evident only after preload had been re-established. This shifted the clinical question away from simply asking whether the screw had loosened, and toward understanding how force was redistributed once the connection became stable again.

Intraoral view showing fractured maxillary provisional prosthesis at approximately 2.5 months postoperatively.
Figure 1. Intraoral view at approximately 2.5 months postoperatively. The maxillary provisional prosthesis had separated into two segments, with a relatively symmetrical fracture pattern.

Findings

After removal of the prosthesis, several features were noteworthy. The fracture pattern was highly symmetrical, and three screws were positioned on either side of the fractured area. Clinically, the prosthesis had not demonstrated obvious mobility, and the screws were not completely loose at the time of inspection.

These findings suggest that this event did not follow the classic pattern of screw loosening, prosthesis mobility, and secondary fracture. A more reasonable interpretation is that even though preload had previously decreased, the system regained a meaningful degree of rigidity after retightening, while the resin provisional prosthesis became the first component to fail under continued cyclic functional stress.

Preoperative and postoperative panoramic radiographs showing full-arch implant reconstruction.
Figure 2. Preoperative and postoperative panoramic radiographs. The postoperative image demonstrates the immediate loading configuration and highlights the need to evaluate the occlusal system as a whole.

Discussion

From a biomechanical perspective, preload does more than simply hold a screw in place. It determines the stability of the implant-prosthesis interface. When preload is lost, microscopic movement may occur at the connection. This is not desirable and should still be corrected, because it may increase the risk of additional mechanical complications.

However, those tiny micromovements may also dissipate a small amount of energy. Once preload is restored, the implant-prosthesis complex becomes more rigid, and force transmission becomes more direct. Stresses that were previously absorbed, masked, or partially dispersed may then be delivered more completely into the resin Provisional.

If the patient also presents with strong bite force and heavy anterior guidance, the anterior segment and midline of the prosthesis may continue to receive repeated bending stress. Under those conditions, the provisional fracture may not represent a complication caused by preload itself. Rather, restoration of preload may simply reveal the true functional overload that was already present in the system.

Clinical takeaway: This case is better understood not as “the screw loosened, so the provisional fractured,” but as “once preload was restored, the real source of overload became visible.”

Clinical Management

Management included immediate replacement of the fractured temporary prosthesis and careful occlusion adjustment, especially reduction of excessive anterior guidance. Because the patient had a tendency to chew forward, the protrusive contacts were also made lighter to reduce concentrated load in the anterior region and midline of the provisional.

Patient education was equally important. The patient was instructed to use the anterior teeth only to lightly incise food, then transfer the food to the posterior dentition for chewing, rather than allowing the anterior segment to carry the main functional load for prolonged periods.

In high-force patients, simply replacing a fractured prosthesis is rarely enough. What matters more is close follow-up, periodic review, and ongoing monitoring of load distribution, guidance, and functional risk patterns.

Clinical Pearls

  • In All-on-4 cases, fracture of a temporary prosthesis does not always indicate treatment failure; it may be an early sign of force imbalance.
  • Screw loosening should be addressed, but prosthesis fracture is not always a direct consequence of screw loosening alone.
  • When preload is restored, system rigidity increases and force may be transferred more directly to the Provisional.
  • Excessive occlusion and heavy anterior guidance often deserve more attention than the fracture line itself.
  • For high-force patients, close maintenance, follow-up, and functional monitoring are essential for long-term stability.

Q&A

Would you retighten the screw again at the second month?

Yes. If the preload has clearly decreased, retightening is still the correct clinical decision. A loose screw is not a stable or acceptable long-term condition. It may lead to micromovement, interface instability, screw fatigue, and additional mechanical complications.

If I do not retighten it, could the provisional avoid fracturing?

Possibly in the short term, but that would not mean the problem has been solved. Without retightening, the connection may remain slightly unstable and temporarily absorb part of the force, making the provisional appear less likely to fracture. But this only hides the problem. It does not remove the true overload.

The real question is not whether to retighten the screw, but whether the overload itself was corrected at the same time.

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