What Is Passive Fit?
Passive fit means the restoration seats on all multi-unit abutments without introducing stress or tension. When a full arch restoration is not passive, the forces concentrate on specific implants, leading to screw loosening, framework fracture, or even implant failure over time.
At Master Design Center, every AOX case starts with passive fit planning. We do not begin design until we have verified that all implant positions are accurately captured and the restorative space is adequate.
The Verification Workflow
We use photogrammetry (ICam4D) as our primary verification method. This technology captures the 3D positions of implant scan bodies from multiple camera angles, then triangulates their exact positions. Studies show photogrammetry achieves accuracy within 5-30 microns for full arch cases, compared to 50-150 microns for conventional splinted impressions.
Key Steps:
1. Scan bodies are placed on all multi-unit abutments
2. Photogrammetry captures implant positions
3. Digital model is aligned with scan data
4. Bar or framework is designed on verified positions
5. Final restoration is verified with Sheffield test
Common Causes of Non-Passive Fit
- Inaccurate impression or scan
- Model distortion
- Framework misfit from manufacturing tolerances
- Screw tightening sequence errors
The cost of ignoring passive fit is high. A non-passive framework may feel acceptable at delivery but fail months later. We have seen cases where a single loose screw cascaded into multiple implant failures because stress was not evenly distributed.
Our design protocol includes a mandatory passive fit check at three stages: scan verification before design, model verification after milling, and final Sheffield test documentation. Every case ships with verification documentation included.