Checking the margins of long-span dental bridges before cementation is critical. Mistakes here can lead to misfit, leakage, sensitivity, or even bridge failure. Here’s a step-by-step guide for predictably verifying margins during the try-in appointment:
1. Dry and Isolate the Field
• Use cotton rolls, cheek retractors, and possibly suction or isolation systems (e.g., DryShield, Isolite).
• Thoroughly dry the teeth and internal of the bridge with air—moisture hides misfit margins.
2. Use Visual + Tactile Inspection
• Visual: Look from all angles using magnification (loupes or microscope).
• Explorer Test: Gently run a sharp explorer from tooth to crown margin. A smooth transition suggests a good fit.
• If the explorer “catches” or dives into a gap, suspect an open or short margin.
• Tug-Back Check: A well-fitted bridge often gives some resistance when removing it from the abutments.
3. Use Disclosing Materials to Reveal Internal Binding
Binding inside will prevent full seating, especially on longer bridges. Use:
• Fit Checker (e.g., GC Fit Checker or PVS wash):
1. Place inside the bridge.
2. Seat on the abutments with firm pressure.
3. Let it set, remove, and inspect where material is thin/absent—this indicates binding spots.
• Occlude Spray (green/red aerosol):
• Spray inside the bridge, seat it, then check where it’s rubbed off. Those areas may need internal relief.
4. Sectional Seating Technique
• Rocking (suggests uneven fit or binding).
• Simultaneous seating is harder with long spans—watch each margin independently as you press down.
5. Radiographic Verification
Take a bitewing or periapical X-ray:
• Use orthoradial angle (perpendicular to tooth axis) to best visualize margins.
• You’re checking for gaps, open margins, or cement space issues.
• This is especially useful when visual access is limited (e.g., distal molars).
6. Shimstock and Floss Test (Optional for Seating Confidence)
• Use shimstock (8–12 μm) between bridge and opposing teeth:
• Should hold under light pull but not jam—helps confirm seating and occlusion.
• Use floss to check interproximal contacts—tight but passable is ideal.
7. Evaluate Each Abutment Margin Individually
• Sometimes one retainer is over-tapered or under-reduced and prevents full seating.
• If one margin is consistently open despite internal adjustments, consider whether the prep needs redoing.
Red Flags to Watch For
A. Issue – One or more open margins Internal binding, seating not complete. Cause – Rocking – One abutment too high or under-reduced.
B. Issue – Margins look short. Cause – Bridge not fully seated. Check intaglio surface.
C. Issue – Bridge lifts slightly after pressure. Cause – Over-tight contacts or high spots.
If You Find an Issue:
• Adjust internal areas using a high-speed handpiece with a fine diamond or lab bur.
• Recheck margins after each adjustment.
• If margins cannot be seated fully after multiple tries, consider re-impression or digital rescan — especially for long spans.