1 FIXED PARTIAL DENTURES

Dislodging forces on an FPD
FPD and Dislodging Forces
Shillingburg
• Occlusal force on pontics can cause M-D torque.
• Forces at an oblique angle or outside the center of the
restoration cause F-L torque (around M-D axis of rotation) .
• Grooves / boxes 8resistance to dislodgement.
• Place boxes / grooves in response to direction of anticipated torque.
• Use retainer with appropriate retention / resistance
– Wall length / occlusal convergence / geometric resistance form
Effect of Arch Curvature on FPD Deflection
Double abutments (splinting) can help problems
caused by poor crown-root ratio and long spans.
Shillingburg
• Pontics lying outside the inter-abutment axis act as a lever
arm → torquing movement.
• Additional resistance in opposite direction from lever arm;
distance = to length of the lever arm (2 o abutments)
• Double abutments help stabilize the prosthesis by
distributing forces over more teeth.
– Periodontally weakened teeth
Criteria for (splinted) secondary abutments:
Long-term periodontal splint
Shillingburg
• Root surface area and C:R must = 1 o abutments
• 2 o retainers must have ≥ retention of 1 o retainers
• Long crown length and adequate interproximal space for
connectors
• Bone loss and increased physiologic movement
• Deflection / torque → microleakage / debonding
• Caries involvement of abutment teeth
• Fracture of RCT abutment with large amount of missing tooth
structure
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