Overdentures and Precision Attachments

• An overdenture = a prosthesis that derives support from one or more abutment teeth (or implant) by completely enclosing them beneath its impression surface - rather than an onlay denture, which sits on the occlusal surface of a tooth.
• Rationale for tooth-supported overdentures:

  • Maintenance of alveolar bone - by retaining the roots of teeth, you can preserve alveolar bone; periodontal ligament continues to stimulate bone
  • Edentate anterior mandible loses 9-10mm of height over 25 years (2.5-3mm in maxilla)
• Overdentures:

  • Alveolar bone height maintained
  • Bone maintained in adjacent areas - not just around roots, but between them too

  
• Maintained alveolar ridge height:

  • Increased resistance to antero-posterior, lateral and rotational displacement, ie improved stability
  • Increased denture bearing area ie potential for improved retention
• Other advantages of overdentures:

  • Roots can be used for inclusion of precision attachments to further improve retention
  • Improved sensory feedback (can feel food in their mouth better)
  • Decreased psychological trauma (because they haven't lost all their teeth)
• 30% of all partially edentate wear a complete maxillary denture opposing natural teeth (a complete maxillary denture, but keep some of their mandibular teeth, commonly the anteriors, leading to excessive wear on them).

  
• Problems with overdentures:

  • High degree of maintenance
  • Potential for caries and periodontal disease
  • Occasionally difficulty with undercuts
  • Occasional fracture of acrylic; less acrylic can be used in denture since trying to maintain alveolar ridge height
• Caries, perio disease, undercuts & intra-arch space:

  • Picture shows plaque accumulation around the roots, caries in the root on the right, bulge around that root difficult to manage in terms of a denture too
  • All the space taken up by those roots would normally be taken up by acrylic - therefore acrylic needs to be thinner

  
• Patient selection for overdentures (indications):

  • Single complete denture - trying to avoid rapid alveolar resorption
  • Cleft palate/surgical defect
  • Hypodontia - helps with teeth/alveolar ridge that might not have formed properly as a result of this
  • Severe tooth wear - if teeth are worn down to gingival margin
  • Potentially unfavourable complete denture
• Patient selection for overdentures (indications):

  • Teeth here are worn down to gingival margins - arrested caries seems to be present too
  • Precision attachment (stud) placed on canine that will help the overdenture to be retained
  • Overdenture will help them with function, increase face height and will preserve alveolar bone

  
• Patient selection for overdentures (contraindications):

  • Extremes of age (young - keep dentition for as long as possible ; old - may have problems with maintaining the abutments)
  • Severe debilitation
  • Poor co-operation
  • Mental handicap
  • Any condition which precludes RCT (root canal treatment)
  • Previous treatment and attitude
• Clinical stages of overdentures:

  • Exam/diagnosis/radiographs
  • Treatment plan including abutment selection (which teeth will be used as abutments)
  • Perio & endo (to decoronate the abutment teeth)
  • Denture construction
  • Preparation of abutments and insert
  • Review
• Overdenture abutment = modified crown or modified root structure of a natural tooth
• Overdenture abutment selection:

  • Crown to root ratio (canines often chosen; they have long roots)
  • No subgingival caries
  • RCT (root canal treatment) possible
  • Symmetrically distributed in the arch
  • At least 2 abutments required
  • Cleansable
  • Canines > premolars > molars > incisors
  • Canines most favourable; long roots, symmetrically distributed in the arch & good space between them so easy to clean
• Overdenture abutment:

  • Simplest preparation = doming
  • Doesn't allow use of precision attachments
  • Precision attachments provide additional retention - used for open face dentures, those with reduced palatal coverage, and they can improve retention for partial dentures
  • Simple & telescopic copings

  
• Disadvantages of overdenture precision attachments:

  • Cost (expensive + not provided on NHS)
  • More complicated maintenance
  • Weaken denture base
  • Oral hygiene requirements
  • Increase load to abutments (possible perio damage)
• Stud attachments:

  • Patrix (ball part) soldered onto coping
  • Patrix embedded within fitting surface of denture - 'O' ring made of resilient material (relatively easy to replace) - like a press-stud
  • Ball attachments/locators are the most common types

  
• Magnets:

  • Keeper = 'soft' magnet attached to root surface (either by use of a coping or with composite)
  • Magnet within denture
  • Preserves canines with  copings cemented on top - keeper soldered onto coping surface
  • Keeper only magnetic when in contact with denture

  
• Implant Supported Overdentures (ISODs):

  • For the restoration of the edentulous mandible with ISODs or complete dentures, there is an accumulating body of evidence
  • Pts are more satisfied with ISODs than complete dentures
  • Oral health related quality of life can be significantly improved using ISODs
• Implant supported (mandibular) overdenture:

  • Two implants
  • Intra-foraminal
  • Parallel positioning

  
• Implant supported (maxillary) overdenture:

  • Four implants at least
  • Parallel positioning

  
• Locators:

  • Clear are tightest, blue loosest
  • Green, orange, and red don't have the middle bit