Implant Model Verification — When a Trial Index is Essential

A printed model may look perfect—and still have implant position errors exceeding fit tolerance. A verification index eliminates this problem before milling begins. This prevention costs less than a prosthesis remake.

What is a Verification Index and What Does It Check?

A verification index is a rigid CAD/CAM splint made from a patient scan. Its purpose: to check if the implant analogs on the printed model are seated in exactly the same positions as in vivo.

If the index passively seats on the model—without a gap—the model is accurate. If a gap or tension appears—the model contains a positional error and needs to be redone.

Errors detected by the index:

• Rotation of the analog during model printing
• Shrinkage of printed resin (up to 0.5% linearly)
• Displacement of the transfer during open tray scanning
• Loosening of the analog on the plaster model

When Verification is Mandatory

Case	Verification	Justification
Single implant crown, posterior	Optional	Greater tolerance
Bridge on 2+ implants	Mandatory	Errors accumulate
All-on-4/All-on-6	Mandatory	Requirement for passive fit
Zirconia framework	Mandatory	Zirconia does not tolerate tension

At deltalabs. we routinely perform index verification for multi-unit prostheses.

Verification Protocol — 7 Steps

1. Acquire scans (STL)
2. Design the index in CAD
3. Print/mill the index (PMMA, ±50 µm)
4. Seat the index on the model (without force)
5. Evaluate with 10× magnification — do all analogs fit tightly?
6. Measure tolerance: ≤0.05 mm (excellent), ≤0.1 mm (acceptable), >0.1 mm (redo)
7. Decision: proceed with milling or redo the model

Consequences of Skipping Verification

A framework without passive fit operates under tension:

• 3–6 months: patient feels poor fit
• 6–12 months: prosthetic screw loosening
• 12–24 months: screw fracture
• 24+ months: bone loss around the implant, framework fracture
• Repair cost: 3–10× higher than the cost of an index

What is a verification index?

A rigid CAD/CAM splint made from a patient scan. When seated on a model, it checks if each implant analog is in exactly the same position as in vivo. Passive seating = accurate model.

What tolerance is acceptable?

Up to 0.05 mm — excellent (All-on-x). Up to 0.1 mm — acceptable (bridges). Above 0.1 mm — model must be redone.

Does it apply to printed and cast models?

Yes. Printed models have up to 0.5% shrinkage, cast models have a risk of transfer displacement. The index is the only method for objective accuracy assessment.

How much time and cost?

Index print: 1 day. Evaluation: 30 minutes. Cost: ~200 PLN. Remake cost: 3000–10 000 PLN.