Overview
The Sheffield test, also known as the single-screw or one-screw test, is the gold standard method for evaluating passive fit of implant dental frameworks. Developed at the University of Sheffield, this elegant protocol isolates dental framework accuracy by eliminating the masking effect of multiple screws drawing a misfit dental framework into position. A dental framework that passes the Sheffield test will seat without inducing stress on the implants or supporting bone.
What You'll Need
- Implant dental framework or dental verification jig
- Hex driver compatible with dental prosthetic screws
- Calibrated torque wrench
- explorer
- Magnification (2.5x minimum, higher preferred)
- Good illumination (headlight or operatory light positioned optimally)
Step-by-Step
Prepare the dental framework
Clean the dental framework's implant interfaces thoroughly with alcohol. Remove any debris, stone, or residue that could interfere with seating. Inspect each interface for manufacturing defects, burrs, or damage. The dental framework should be free of any obstruction to full analog/implant engagement.
Position the dental framework
Seat the dental framework over the implants, allowing it to rest passively without any screw engagement. The dental framework should drop into approximate position guided by the implant connections. Do not force or press the dental framework—observe its natural seating tendency.
Select the First Test Position
Choose the most distal implant on either side as your first torque point. This position maximizes the lever arm, making any anterior discrepancies more apparent. The longer the span from the torqued screw, the more obvious any misfit becomes.
Apply Torque to Single Screw
Thread the dental prosthetic screw into the selected position and apply full seating torque (typically 15-35 Ncm depending on manufacturer specifications). This is the only screw tightened during this test phase. The dental framework is now fixed at one point only.
Evaluate All Other Positions
Systematically examine every non-torqued implant-dental framework interface. Using your explorer, probe the junction between the dental framework and each implant platform. Under magnification, assess for any visible vertical gap, angular lift, or horizontal displacement.
Interpret Your Findings
True passive fit means zero detectable gap at any non-torqued position. The explorer should not catch or pass between the dental framework and implant. Under magnification, interfaces should appear as continuous contacts with no light transmission through potential gaps.
Repeat from Opposite Side
Release the torqued screw and repeat the test using the opposite distal implant as the reference point. This evaluates the dental framework from a different anchor position. Consistent results from both directions confirm accuracy; inconsistent results indicate complex distortion.
Optional: Test from Anterior Position
For comprehensive evaluation, perform an additional test with torque applied to an anterior implant. This configuration stresses the dental framework differently and may reveal discrepancies missed by posterior-anchored testing.
Tips & Best Practices
- Use magnification for all interface evaluation—the naked eye cannot reliably detect clinically significant gaps
- Perform the test before any dental occlusal adjustment; modifying the dental framework after discovering misfit is preferable
- Document which positions pass or fail for dental laboratory communication
- Consider radiographic verification as an adjunct to clinical examination
Common Mistakes to Avoid
Tightening multiple screws
Each additional screw draws the dental framework into position, masking misfit. Only one screw may be tightened during Sheffield testing.
Inadequate magnification
Gaps under 100 microns are clinically significant but invisible to the naked eye. Use loupes or microscope.
Accepting "close" fit
Any detectable gap indicates misfit. Passive means zero perceivable gap, not "minimal" gap.