CSAR Part2 Flashcards
Why we replace missing teeth. What are the options
appearance
ability to eat, distributes forces
quality of life, pyschological reasons
speech
occlusal stability
Maintaining face shape by supporting soft tissues
-options: denture, bridge, implant
[bridge definition: replaces teeth using natural teeth/implant for retention and support]
Criteria for abutment teeth for bridges
-PA radiographs and vitality tests - no PAP
-good crown-root ratio (2:3) (otherwise cause unwanted lever effect)
-good angulation
-no caries
-stable perio status, good bone level
-good OH
-not heavily restored
-not excessive tooth wear
-Abutments and pontics should have contacts in ICP
- [guidance is fine on abutments, just not on pontics]
-adequate tooth structure for bonding
-correct size to support pontic
-not rotated
-does not have a post (can be endo treated though)
-molars with divergent roots offer more support compared to straight conical
-oval single roots better than circular in cross section
Explain the following terms: 1) Pontic 2) abutment 3) retainer 4) connector 5) Span 6) Cantilever 7) Fixed-fixed bridge 8) Fixed-moveable
1) Pontic: the false tooth.
2) Abutment: tooth/teeth that support the bridge.
3) Retainer: restoration that attaches the bridge to the abutment tooth/teeth.
4) Connector: attaches the pontic to the retainer
5) Span: mesio distal length of the edentulous space
6) Simple Cantilever: attached on one side
7) Fixed fixed: Pontic supported by teeth on either side
Pros and cons of conventional bridges. What types are there
-cantilever, fixed-fixed or fixed-moveable
-getting retention from the prep (mechanical)
-Advantages: Abutments may already be heavily restored and needing crowns anyway. Can alter shape and colour of abutment teeth. Last longer (10 year average compared to 5 for adhesive) Better for larger spans as better support
-Disadvantages: Use crowns as retainers so more destructive. Impression-taking more difficult. Longer preparation time. Failure more destructive
Pros and cons of adhesive bridge work. What are the designs
-simple cantilever or fixed-fixed (not fixed-moevable)
-Advantages: Less destructive (minimal prep for wing) Simpler. Impression taking very much easier. Failure less destructive. Less expesnive
-Disadvantages: Don’t last as long. Cannot change shape of abutment teeth. Shine through of wing. Heavily restored abutments not ideal (need enamel). Cementation technique sensitive (needs isolation). Difficult to try in
Indications and contraindications for adhesive bridge
Abundant enamel
Caries-free abutment teeth
Single posterior tooth replacements
Incisor replacements
Periodontal splinting
Contraindications:
Extensive caries/restorations
Nickel sensitivity
Deep overbite (and therefore preparation through enamel)
Severe tooth wear (minimal enamel)
What is a fixed-moveable bridge. Is it a conventional or adhesive design
-conventional (mechanical)
-Pontic is rigidly supported on one side, (usually distal)
Other side has an intra or extracoronal attachment which allows a small degree of movement between the rigid component and the other abutment - stress breaking
Pros and cons of simple cantilever. Why spring cantilever no longer used
-conservative tooth prep on abutment tooth, easier prep, retrievability is favourable, easier to tell if de-bonded. Lab process simple
-but need to be careful of forces exerted on abutment. Tipping or rotation may occur.
-spring- Pontic is supported by a bar to an abutment tooth that is more posterior.
-limited use (anterior spacing, avoid damage to anteriors)
Pros and cons of fixed-fixed design
-Robust with maximum retention and resistance,
Recommended for larger bridges. Laboratory process straightforward (no moveable joints)
Cons: Parallel preps needed, Destructive, Cementation is more difficult than for cantilever. May be unaware if one side has debonded causing micro leakage- caries and perio issues
Pros and cons of fixed-moveable design
-Incorporates a stress breaker to allow minor movements. This also helps accommodate different paths of insertion.
-Less destructive than fixed fixed so less risk exposing pulp
-Indicated when abutments are not parallel/poorly aligned
-Parts can be cemented separately
But, length of span limited, complex lab process, temporisation is difficult, more expensive
How much force can an abutment tooth take
-previously was thought that abutment teeth must equal or exceed that of the teeth to be replaced eg. Can use 6 as abutment for 5, but not other way round)
-but periodontal sensors, proprioception, MOM can reduce the load so pts can adapt to occlusal load applied to abutments
How does bending/deflection change with increasing span length. Consequences of this flexion
-larger the span= more deflection, less rigid
-Single pontic deflected = 8 times as much for 2 pontics = 27 times as much for 3 pontics
-flexion can cause fracture of abutment, debonding of retainer, and breakage of connector
-increasing the metal framework may counteract this
-longer span need fixed-fixed design
Is cantilever or fixed-fixed designs preferred for posterior or anterior teeth
-Posterior
Vertical forces
Fixed-fixed design preferred
-Anterior
Lateral forces
Cantilever design preferred
What is the optimum crown: root ratio for abutment teeth
2:3
Official minimum is 1:1
-reduces chance of harmful lateral forces
However, in certain circumstances less than 1:1 is possible but not recommended at undergraduate level
What factors affect whether you choose cantilever of fixed-fixed
-longer spans need fixed-fixed
-anterior teeth more likely cantilever, posterior fixed-fixed
How to deal with having a canine as a pontic
-They are the most challenging tooth to replace due to Abutment size and Canine guidance
-May require reorganising the occlusion into group function
How bridges can fail
-One retainer becomes loose (Fixed-fixed):
-Retainers(s) become loose and bridge falls out
-Porcelain fracture
-Fracture of connectors
-Distortion
-Occlusal wear and perforations
-Abutments: loss of vitality, caries, perio disease, fracture of natural crown
What to do if on fixed-fixed one retainer comes loose on one side. And why can it occur
-First try to find out why: bond failure, design failure, abutment selection, occlusion (excess loading)
-check if cement remains anywhere- a clue as to why
-Section to create cantilever, remove cement with USS, and crown the debonded abutment
-OR section and remove entire bridge, assess, reprep, replace
Why bond on abutment can fail
-Inadequate moisture control
-Inadequate seating resulting in uneven cement layer
-Inadequate surface treatment of fit surface
-Cement out of date/ instructions not followed
What does a bridge retainer look like usually, what material, how thick
-retainer is a metal wing usually made of Nickel chromium - 0.7 mm thick
-note, must still be in enamel for adhesive bridge
Adhesive bridges rely on resin bonding. What is done to to the metal and enamel to improve the bond strength
-Sandblasting with alumina
-Heat treatment and oxide formation
-Silicate coating
-Tin plating
-Application of primer
-The enamel surface is etched
-remove outer layer of enamel if not already (only tickle the surface with the bur)
-don’t apply fluoride varnish to help with any sensitivity experienced as this affects bond
Steps involved in making adhesive cantilever bridge. What tooth prep should be considered. What cement is used
-Replace existing restorations with composite
-Ensure adequate crown height (Crown lengthen using electrocautery)
-Tooth Prep – increase surface area for bonding, remove outer enamel to create consistent etch pattern for better bond, finishing margins for lab and seating, rests for support, guide planes for POI
-Choose shade (consider Grey shine through and Opaque cement)
-Impression and occlusal registration
-Lab prescription – explain components, draw
-No temporisation needed (as only in enamel)
-Check fit of bridge
-Good moisture control (dam not essential for anterior), etch, bond
-Cement with Panavia
-Check occlusion, expect it to be high on retainer - Dahl effect should sort this
Explain the bucket handle effect on anterior teeth
-refers to the curve to recreate natural tooth positions
-however it is better if the bridge is in a straight line to reduce tilting forces on the abutments
-A substantially curved arch generates a lever system at the incisor level.
Considerations for bridges in hypodontia cases. What bridge design is best
-These patients tend to be younger and therefore it is even more important to preserve tooth
-following ortho, adhesive cantilever bridges is provided. No prep is done to the abutments
-Essix retainer is given to prevent relapse
When is a face bow used for bridges
-when not using a patient’s ICP as opening up vertical dimension. And if the tooth you’re prepping will be in dynamic occlusion. (but you want to avoid doing this where possible)
-it locates the true hinge axis between the condyles, for replicating dynamic occlusion for more accuracy. It records the facial midline and aesthetic plane
How to record the face bow
-With Kois dento facial analyser, then it is mounted on semi-adjustable articulator
-Blob at posteriros, blod at centrals. Face into horizon. Insert into mouth and rest against upper teeth. Front teeth should rest against the notch. Once set, take out mouth, cavex, then trim the fissures
-ensure correct facial midline and aesthetic plane (parallel to floor when looking straight ahead)
