Problems of the Free End Saddle Denture

• Free end saddle dentures:

  • Kennedy class 1 or 2
  • Can also be referred to as:
  • Distal extension bases
  • Distal extension saddles
• Mandibular free-end saddle dentures tend to have more problems than maxillary ones; the palatal tissues provide some additional support.
• Problems of free end saddle dentures - denture support differential:

  • Mesial portion of saddle is tooth supported
  • Distal portion mucoperiosteal support
  • Differential in degree of tissue resilience from mesial to distal
  • Increased mucocompression of distal aspect of saddle leads to more rapid resorption and exacerbation therefore of saddle rotation
• Problems of free end saddle dentures - patients find them uncomfortable:

  • Dentures lack firm support
  • Pressure leads to 'denture bouncing'
  • Pts notice difference between forces transmitted through periodontal membrane and mucoperiosteum
  • Bucco-lingual and antero-posterior movement
  • Food stuck under denture
• Problems of free end saddle dentures - abutment teeth more at risk:

  • Unfavourable occlusal loading
  • Plaque retentive factors
• Abutment teeth: all loads on the base (even vertical), are transmitted to the abutment teeth as torque (tilts last standing abutment tooth in a distal direction)

  
• General principles for overcoming problems:

  • Avoid the use of free end saddle dentures where possible
  • Accept shortened dental arch
  • Alternative management of free end saddle dentures
  • Recall, maintenance and good oral/dental hygiene
  • Regular checks for continued ridge resorption and rebase when necessary
  • Maximising mucosal support and stabilisation
  • Maximum tissue coverage ie as for complete dentures
  • Functional impression (altered cast technique)
  • Correct bucco-lingual tooth position and polished surface shape, ie, within neutral zone
  • Correct occlusal scheme
  • Careful design
• Occlusal scheme:

  • Maximise natural tooth contacts
  • Narrow occlusal table
  • Shorten functional occlusal table
  • Eliminate interferences in excursive movements
• Altered cast technique = mucocompressive impression of saddle area, taken after framework construction

  • When framework seated mucoperiosteum already compressed and therefore on loading no further compression takes place and therefore no rotation/torque
• Design - path of insertion:

  • Determined by distal guide planes on abutment teeth
  • Preparation of 2-3mm long guide planes
  • Other considerations = aesthetics, dead spaces
• Design - abutment selection:

  • Currently we often use single abutments
  • Only when a canine is the prime abutment should it be used alone
  • When the first premolar is the prime abutment the canine should also be used
  • When the second premolar is the prime abutment then both premolars should be used
• Design - rest seat position:

  • Photoelastic studies show distal occlusal rest and occlusally approaching clasp results in greater load on abutment - abutment teeth tend to be tipped distally
  • Mesial rest tends to tip tooth mesially where it will gain support from other teeth - "wrench-like action" of distal seat and occlusally approaching clasp
  • Rest seat position is immaterial provided the denture is well-maintained
• Design - clasping:

  • An inflexible clasp system may be detrimental to supporting structures of abutment
  • Occlusally approaching/circumferential clasp alters natural contour of tooth and predisposes to plaque accumulation more so than a gingivally approaching clasp
  • Ideal design = infrabulge I-bar with tip placed at greatest convexity of tooth
• Design - connectors:

  • Maximum amount of soft tissue left uncovered
  • Lingual bar preferred to lingual plate - if remaining anteriors have limited prognosis, plate is favourable as additions can be made more easily
• Design - indirect retention:

  • Concept of denture components functioning through lever action on opposite sides of a fulcrum
  • Fulcrum = rest/clasp axis
  • Ideal position for location of indirect retainer - maximum distance from perpendicular bisector

  
• RPI system:

  • R = mesial rest
  • P = distal guiding plate
  • I = infra-bulge clasp
  • Minor connector carrying mesial rest seat acts as reciprocation along distal plate

  
• Stress breakers:

  • Saddle component able to move more than tooth supported component
  • More load transmitted to ridge tissues
  • More even load distribution
• Stress breakers vs rigid design:

  • More complex
  • More costly
  • Needs greater plaque control
  • May be less well-tolerated
  • Easier to design
  • More amenable to good plaque control
  • Tend to favour rigid design, but:
  • More extension
  • Decrease size of occlusal table
  • Flexible clasp system
• Treatment strategy for free-end saddle dentures:

  • Avoid if possible
  • Decrease occlusal load
  • Distribute load widely as possible between tooth and mucoperiosteum
  • Design aspects
  • Maintenance