Overview
Implant dental framework misfit stems from cumulative distortions throughout fabrication, making passive fit one of the most challenging goals in implant prosthodontics. While Brånemark originally specified misfit should not exceed 10 microns, current literature suggests misfits up to 150 microns may be clinically acceptable—though no definitive threshold has been established. Understanding the error sources enables systematic diagnosis and appropriate correction strategies.
What You'll Need
- verification jig that passed clinical Sheffield testing
- Hex drivers and calibrated torque wrench
- explorer and 20x magnification
- Fit checking material or articulating film
- Sectioning disc and slow-speed handpiece
- Access to laser welding services
Step-by-Step
Verify dental master cast Accuracy First
Before blaming the dental framework, confirm dental master cast accuracy. The dental verification jig that passed clinical testing must also pass Sheffield testing on the dental master cast. If the jig fits the patient but not the cast, the cast is inaccurate—remake the impression.
Perform dental framework Sheffield Test
Seat the dental framework and tighten ONE distal screw only. Examine all interfaces under magnification. Repeat from opposite side. Document gap locations and approximate magnitude. Systematic gaps suggest dental master cast error; localized gaps may indicate dental framework fabrication issues.
Evaluate CAD/CAM Error Sources
full-arch dental intraoral scans show accuracy values ranging from 21-816 microns, with accuracy decreasing as inter-implant distance increases. Check for dental scan body library mismatches, STL mesh approximation errors, and milling limitations (smallest bur ~1mm creates up to 0.5mm discrepancy on complex surfaces).
Consider Material Shrinkage
Cobalt-chromium casting shrinks approximately 2.3%. CNC-milled titanium shows only 3-80 microns 3D distortion. Milled dental frameworks achieve the most accurate fit—mean 50.1 microns versus 71.4 microns for additive manufacturing.
Apply Disclosing Medium
Use fit checking material on all implant interfaces. Seat the dental framework, tighten one screw, and examine contact patterns. Uniform contact indicates accurate fit; uneven or absent contact reveals positional error.
Determine Correction Approach
For correctable misfit: diagonal sectioning produces better passivity than transverse cuts. Ni-Cr casting misfit of 58.66 microns can reduce to 27.51 microns after sectioning and laser welding. Gas-air torch soldering shows the most consistent accuracy among joining methods.
Consider EDM for Precision Fit
Electrical Discharge Machining achieves surface finish of 2-5 microns and gap tolerance of maximum 5 microns. EDM can achieve gap-free, tension-free fit regardless of whether structures are cast or CAD/CAM milled. Combined laser welding plus EDM shows optimal results.
Make Go/No-Go Decision
Section and correct when misfit is localized, material is weldable, and marginal gap closes with light pressure. Remake when multiple areas show significant misfit, wax test shows buckling, visible rocking occurs, or CAD/CAM systematic error is identified.
Tips & Best Practices
- Milled titanium offers the best combination of accuracy and biocompatibility for dental full-arch dental frameworks
- Wax pattern deterioration causes significant fit degradation at 1 week to 1 month of storage
- Conventional lost-wax casting for one-piece dental full-arch dental frameworks is considered imprecise for passive fit requirements
- Always schedule dental framework try-in before final finishing—bare dental frameworks are easier to correct
Common Mistakes to Avoid
Skipping dental verification jig confirmation
Beginning correction without confirming dental master cast accuracy risks repeating the same error. Always verify the cast first.
Forcing the dental framework to seat
A dental framework requiring pressure to seat is not passively fitting. Forcing screws draws misfit dental frameworks onto implants, inducing harmful stresses.
Assuming CAD/CAM eliminates error
Digital workflows introduce their own error sources. Scan stitching errors, library mismatches, and milling limitations all affect fit.
Using transverse sectioning
Diagonal sectioning produces better passivity than transverse cuts. Plan section locations carefully before cutting.