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Questions and Answers
Which material is considered strong even when thin?
Which material is considered strong even when thin?
What is generally true about zirconia and its aesthetic qualities?
What is generally true about zirconia and its aesthetic qualities?
What thickness is recommended for lithium disilicate to ensure optimal strength?
What thickness is recommended for lithium disilicate to ensure optimal strength?
Which area is not accepted for equigingival margins in aesthetic restorations?
Which area is not accepted for equigingival margins in aesthetic restorations?
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When should full coverage restorations be preferred over partial coverage?
When should full coverage restorations be preferred over partial coverage?
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What is a common characteristic of class 3 and class 5 restorations regarding oral hygiene?
What is a common characteristic of class 3 and class 5 restorations regarding oral hygiene?
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What is a benefit of using glass ceramics like lithium disilicate?
What is a benefit of using glass ceramics like lithium disilicate?
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What happens to zirconia's properties when it is glazed and polished?
What happens to zirconia's properties when it is glazed and polished?
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Study Notes
Retainers in Fixed Prosthodontics
- Retainers are components of a fixed partial denture (FPD)
- They provide support from abutments and retention to the prosthesis.
Types of Retainers
- Classified by tooth coverage:
- Extracoronal (covers all surfaces)
- Conservative (less extensive, covers less)
- Intracoronal (inside the tooth)
- Resin-bonded
A) Full Coverage Retainer
- Covers all five surfaces of the tooth.
- Advantages:
- Best retention and resistance.
- Best protection against fracture (for endodontically treated teeth).
- Modifies tooth contours.
- Disadvantages:
- Extensive reduction is needed.
- Pulp vitality cannot be conducted (in non-metallic retainers).
Telescopic Retainers (Full Coverage)
- Used when the prosthesis insertion path does not align with the abutments' long axis.
- Common indications: tilted molars, RPD construction.
- Design:
- Primary coping cemented to the abutment, modifying its morphology.
- Secondary coping fitted over the primary coping along the new insertion part.
B) Partial Coverage Retainer
- Does not cover all surfaces of the abutment tooth.
- Can be constructed from metal or porcelain.
- Advantages:
- Conservative preparation (less reduction than full crowns).
- Suitable for esthetic areas, preserving the labial surface.
- Visible margins aid in caries detection.
- Disadvantages:
- Less retention and resistance.
- Common insertion path is harder to achieve.
- Abutments need longer clinical crowns.
- Limited for short span FPDs.
- Examples: 3/4 crown, reverse 3/4 crown, 7/8 crown, half crown, pin-ledge.
B) 3/4 Crown
- Covers most tooth surfaces except the labial/buccal areas.
- Labial/buccal surfaces must be intact.
- Fair esthetics.
- Low retention and resistance.
B) 1/2 Crown
- Covers half the abutment.
- Options: mesial-half or distal-half crown.
- Suitable for cases with non-parallel abutments (e.g., tilted molars).
### B) Pin Ledge Crown
- Uses parallel pins and grooves on the lingual/palatal surfaces to improve retention.
Reverse 3/4 Crown
- Lingual wall is left intact.
- Common in mandibular molars with lingual tilting.
7/8 Crown
- Surfaces besides the mesio-buccal cusp are covered.
- Common in maxillary molars (esthetic reasons).
Conservative Retainers
- Inlay-retained FPD:
- Conservative approach to replace missing teeth.
- Only inlay preparation on abutment teeth
- Bonded with resin cement
- Suitable for patients with good oral hygiene, long clinical crowns
- Constructed from metal, PFM, zirconia, and fibre-reinforced composite.
- Onlay-retained FPD
- Resin-bonded FPD
Inlay-retained FPD: Disadvantages
- Limited to short spans
- Prone to fracture with high loads
- Cannot be used with short abutments
Resin-Bonded FPD
- Minimal preparation on abutment teeth, suitable for single anterior teeth.
- Bonded with resin cement.
- Types:
- Maryland bridge
- Rochette bridge
- Cast mesh
- Virginia bridge
Maryland Bridge
- Micromechanical retention (wings bonded to abutments).
- Wings are thin and resist bending.
- Metal is acid-etched to improve bond
Rochette Bridge
- Macromechanical retention (funnel-shaped metal perforations).
- Increased mechanical retention from bonding with resin cement.
- Disadvantages: less surface bond area.
- Wear of exposed composite resin
- Weakening of metal retainers
Cast Mesh
- Macromechanical retention.
- Casted wings with tiny holes.
- Nylon mesh incorporated in wax pattern.
- Eliminates need for etching.
Resin-Bonded FPDs - Virginia Bridge
- Variation of the Maryland bridge
- Casted metal wings with roughened surface (lost-salt technique).
- The salt crystals in the wax pattern give a rough surface.
f) PMMA
- Not durable.
- Mostly used provisionally during healing period.
- Low strength.
Criteria for Selecting Retainer
- Abutment Alignment: Parallel abutments are best for full veneers.
- Abutment Condition: More damaged teeth often require full veneer retainers.
- Patient's Age: Younger patients sometimes require partial coverage for larger pulps.
- Caries Index: Higher caries indexes are treated with complete coverage.
- Opposing Dentition: Natural teeth are better for metal retainers due to wear.
- Esthetic Demands: All-ceramic > Zirconia > PFM> Metal
- Length of Edentulous Span: Longer spans need stronger materials (full coverage).
- Patient Musculature: Strong muscles means higher masticatory force requiring full coverage.
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Description
Test your knowledge on the types and functions of retainers in fixed prosthodontics. This quiz covers full coverage and telescopic retainers, including their advantages and disadvantages. A great way to reinforce your understanding of fixed partial dentures!
