Indirect restorations Flashcards
What two ways can bridges be retained?
- Full coverage crowns - preparation of an abutment tooth is a full coverage crown e.g. FGC
- Adhesive retainers - the preparation of the abutment tooth is minimal and involves the proximal and palatal surfaces only
What are the two ways abutments can be used?
- Fixed-fixed - the bridge spans from one abutment to another with the pontic inbetween
- Cantilevered - the bridge is retained by one abutment only
What are the design criteria for a bridge?
- Periodontal support - abutment teeth need adequate periodontal support
- Occlusal loading - magnitude and direction of force vectors
- Conservation of tooth tissue
- Cleansability
- Appearance
- Rigidity (of retainer and connector)
- Quality of abutments
- Number of abutments
- Choice of adhesive lute
- Contingency planning
What is the design of choice for an adhesive bridge?
A single cantilevered bridge. It is more retentive than a fixed-fixed adhesive bridge. The pontic is allowed to move with the abutment. There are reduced shear forces on the pontic. Debond leads to cleansable surfaces and risk of caries is eliminated.
What two aspects of an adhesive bridge need to be designed?
- Framework (retainer thickness and configuration, bonding area, wrap around, occlusal extension of framework, connector design, length of span)
- Tooth preparation (axial tooth preparation, grooves, occlusal rest seats, intracoronal preparation)
What needs to be considered in terms of the bridge framework?
Retainer thickness and configuration:
- Retainer is 0.8mm thick for molars
- Greater if retainer is not joined over the occlusal surface
Bonding area:
- Retainer should extend as far occluso-gingivally and circumferentially as possible
Wrap around:
- Maximum wrap around is 180 degrees (mesial and distal groove)
Occlusal extension of framework:
- Full palatal coverage with no tooth preparation
- Reduced palatal coverage with tooth preparation (finish 1-3mm from incisal edge)
- Posterior occlusal coverage to resist displacement laterally or apically, increase rigidity of framework, greater surface area for bonding
Connector design:
- Significant height and width required
- Needs to resist bending of alloys
- Avoid putting adhesive lute under tensile loading
- Connector needs to be at least 50% height of pontic
Length of span:
- Ideally one tooth
- Longer spans not contraindicated but plan to reduce debonding stresses on retainer
What needs to be considered in terms of tooth preparation?
Axial preparation:
- Increases surface area for bonding, increases resistance and retention form
Grooves:
- Resist lateral displacement
- Increase retention form
- Increase structural rigidity of framework
- 2 grooves per tooth significantly increases resistance to debonding forces
Occlusal rest seats:
- Directs forces down the long axis of the tooth
- Resists lateral displacement
- Limit shear forces to the cement lute
Intracoronal preparation:
- Joining of mesial and distal rest seats of the retainer over the occlusal surface to form an occlusal bar to increase rigidity of retainer
- Increases resistance to deformation
- Improves resistance to lateral forces and increase surface area for bonding
What cements can be used for an adhesive bridge?
Always use an adhesive lute.
- Self cure composite lute e.g. rely x unicem - non-adhesive on its own so requires bonding system, requires an etched metal substrate
- Anaerobic adhesive lute e.g. Panavia - opaque so not aesthetic, specific adhesion to metal retainers
- 4 meta adhesive lutes e.g. calibra - specific bonding to metal and ceramic retainers
What alloys are used for adhesive bridges?
- Nickel chromium - can be etched, very rigid, works well with composite luting systems
- Gold alloys - cannot be etched, not as rigid at nickel chromium, requires sandblasting, need specific adhesive systems
- Ceramics - experimental
What affects the choice of abutment?
- Tooth position
- Crown shape
- Restorative status - proximal restorations
- Endodontic status and prognosis
- Periodontal status
- Retention and resistance form
What teeth make poor abutments?
- Maxillary lateral incisors
- Tilted incisor teeth - unfavourable pulp chamber morphology
- Root filled teeth
What is the survival rate of RBB?
- 87.7% for 5 years
- 80% for 10 years
How can RBB fail?
- Debonding - failure of bond, lack of rigidity leading to peel effect
- Caries under retainer
- Aesthetic failure - show through of retainer
What types of RBB are not recommended?
- Double abutments - difficult to clean and not necessary
- Adhesive retainers with intermediate pontics, not recommended, exception is mandibular incisors where the peel dislodgement effect is less
Why are fixed-fixed adhesive bridges contraindicated?
Significant stresses placed on retainers due to different tooth movements between the abutments in functional and parafunctional movements. These forces tend to push one abutment away from the pontic. There is tensile stress on the cement lute and there is debonding and caries under the retainer.
What is restorative dentistry?
Eliminating disease and restoring function and aesthetics using appropriate materials and techniques.
What is the difference between RPD, bridges and implants?
Removable partial dentures replace the whole dento-alveolar complex. They are non-destructive and reversible. They provide an effective permanent or transitional option.
Implants replace the teeth. There can be replacement of bone/soft tissue with grafts. It is a surgical option with higher morbidity. It has a predictable success rate >90%.
Conventional bridges replace teeth only and are destructive. They have unpredictable long term prognosis.
What should be looked at in a clinical examination prior to bridges?
- Occlusal relationship – guidance
- Interocclusal space
- Centre line
- Lip smile line
- Position of teeth present
- Shape and position of potential abutments
- Restorative and vitality status of teeth
What should be looked at in a radiographic examination prior to bridges?
- Position of normal anatomical features
- Pathological conditions
- Periapical status of abutment teeth
- Alveolar support of abutment teeth
- Root remnants and foreign bodies
- Alveolar height and width
Periapical is best to check individual teeth and assess alveolar bone. OPT can be used but there can be distortion in horizontal place and shadowing of incisor region
What is important about periodontal support for bridges?
Disease history is not as important. Current and future periodontal health are critical and maintenance of periodontal health.
What occlusal loading is important for bridges?
- Functional
- Parafunctional loads
- Lateral excursive movements - canine guidance, group function, interferences
What materials are used for conventional bridges?
- All cast metal
- All ceramic
- Metal ceramic
What is the success rates of conventional bridges?
Fixed-fixed: - PFM 94% 5 years - All ceramic 88% 5 years - Sailer et al 2004 Cantilevered: - 5 years 82% - 10 years 63% - Pjetersson et al 2004
What are the two types of retention for indirect prostheses?
Mechanical and adhesive retention. Mechanical retention uses a luting cement e.g. metal-ceramic retained bridges. Read next bit of notes.
What should you check on the lab work before fit?
- Any doubts from technician - impressions, undercut, fit
- Check fit - marginal fit and quality of fit surfaces
- Shade
- Occlusion
- Pontic design
- Polish - ceramic glaze, metal polish
How is the temporary removed?
Assess if local anaesthetic is required but smile and speech can’t be evaluated with LA for anterior bridges. Add vaseline to temp bond to make removal easier. Can use crown and bridge removal forceps. Clean cement away using pumice and water/prophy paste. Use ultrasonic tips to remove firmly adhered cement. Remove resin bonded wing retainers with peeling forces.
When trying in what should be checked?
- Proximal contacts - floss, articulating paper
- Fit surfaces and retainer margins - can adjust
- Powder indicator inside fitting surface and adjust where surface is touching prep.
- Shade
- Occlusion
- Incisal position
- outline size and shape
- Proportions
- Contours
- Symmetry
Use try in paste. Adhesive bridges have to be held in place - difficult to check occlusion. Can request hooks on retainers to aid seating (cut off after bonding).
What are the signs of correct seating?
- Retainer crown margins closed
- Adjacent marginal ridges level
- Initial occlusion satisfactory
- Firm stop when bridge seated
- No rocking under lateral loading
Any open contacts require lab additions, reject open/deficient margins.
How can speech be checked?
- F and V for incisal edge
- T and S for cingulum shape
- Th for air escape under pontic
What is checked in occlusion?
- Check intercuspal interferences
- Adjust to harmonise with ICP
- Check lateral and protrusive contacts with two colours to distinguish ICP contacts
- Adjust non-ICP interferences
- Chairside polish or return to lab
