CSAR 33, 34, 35 - Bridges Flashcards
What do you need to know about abutment teeth before any prep?
Angulation
Vitality
Crown-root ratio
When are articulated study models needed before tooth preparations?
Long bridge spans
Multiple extracoronal restorations
Reorganising occlusion
Why are bridges used?
Aid chewing and speech Distribute forces Prevent drift Aesthetic Maintain face shape
What is the retainer of the bridge?
Restoration that attaches the bridge to the abutment tooth/teeth
What do conventional bridges rely on when placed? And what 3 types are there?
Rely on crown principles for retention
Cantilever
Fixed-fixed
Fixed-moveable
How are RBB attached to tooth prep?
Resin-based cements for adhesion
What are advantages and disadvantages of conventional bridges?
+ Abutments may already be heavily restored
+ Can alter shape and colour of teeth
+ Retention better if crown principles applied correctly
+ Last longer than adhesive bridges
- Use crowns as retainers is very destructive
- Impression-taking more difficult = silicone used which is hydrophobic
- Longer preparation time
What shape are the tooth preparations of fixed-fixed bridges?
PARALLEL
What is the advantage of using a fixed-moveable bridge over a fixed-fixed bridge?
Has a stress breaker
Teeth don’t need to be parallel
What are the connections on a fixed-moveable bridge?
One side rigid support
Other side intra/extra-coronal attachments and small degree of movement
What movements are allowed and resisted by a fixed-moveable bridge?
Small amount of vertical movement
Resists lateral movement
What are advantages and disadvantages of adhesive bridges?
+ Preservation of sound tooth tissue
+ Little preparation
+ Impression taking very much easier
- Don’t last as long
- Cannot change shape of abutment teeth
- Can discolour abutments if they are thin
- Heavily restored abutments not ideal – need ENAMEL!
- Shine through of wing
- Hard to try-in
What is the difference between minor and major bridge retainers?
Major need full occlusal coverage and minor don’t
When planning for a bridge, what do you want to know about the edentulous ridge?
- Ridge shape (pontic selection)
- Alveolar bone loss (disguise or augment)
- Retained roots
- Unerupted teeth = need to let patient know that they are there and document it
- Lip line
When are conventional bridges more suitable than adhesive?
Heavily restored teeth when can not be bonded to enamel
Long spans
Repeated failure of adhesive bridges
Implants not possible
What is Ante’s law when treatment planning dentures?
THE TOTAL PERIODONTAL MEMBRANE AREA OF THE ABUTMENT TEETH MUST EQUAL OR EXCEED THAT OF THE TEETH TO BE REPLACED
When using an abutment tooth that has had endo, what should be known of the tooth?
The endo must be good, or redo it
What abutment teeth are preferred due to their root shape and angulation?
- Molars with divergent roots offer more support than those with straight conical roots
- Single rooted teeth with elliptic cross sections offer more support than those with a circular cross section
What is the optimum crown-root ratio and why?
Optimum crown-root ratio 2:3
Large root – coronal part may break
Small root – root may break
Official minimum is 1:1 = IF OPPOSED BY DENTURE
What happens to forces on a bridge with a longer span?
Increases load on abutment teeth
Less rigid and increased flexing, resulting in fractures/debonding
If there are small defects in the alveolar ridge due to bone loss when placing a bridge, what can be done to correct this?
Add pink porcelain
Why should a bridge with double abutments be avoided?
Central abutment acts as a fulcrum causing debonding of the peripheral retainer
What are advantages and disadvantages of fixed-fixed bridges?
+ Robust with maximum retention and resistance
+ Recommended for larger bridges
- Parallel preps = DIFFICULT
- Destructive
- Cementation is difficult
What are advantages and disadvantages of fixed-moveable bridges?
+ Preps do not need to be parallel
+ More conservative as prep for minor retainer less than major
+ Allows minor movements of teeth
+ Parts can be cemented separately
- Length of span limited
- Complex laboratory process
- Temporisation is difficult
- More expensive
What are advantages and disadvantages of cantilever bridges?
+ Most conservative easier prep
+ Anterior region where occlusion is favourable
- Limited to one pontic
- Rigid construction
- Occlusal forces can encourage tilting posteriorly if the pontic is distally positioned
- Occlusal forces can encourage rotation of abutment anteriorly if care not taken with occlusion
Why would a bridge fail?
One abutment loosens
Debond and fall out
Fracture
Why would an abutment fail?
Loss of vitality Endo failure Caries Periodontal disease Fracture of natural crown
After prepping a tooth for a RBB and not putting a temporary over it, what might the patient complain of?
Sensitivity
After prepping a tooth for a RBB why mustn’t fluoride varnish be placed on after?
Fluoride ion integrates with hydroxyapatite and changes the surface, affecting bonding
If can not get Pontic tooth out of guidance, what type of guidance is referred?
Group function
When doing a preparation for a RBB what should you do to ensure bonding success?
Have 180 degrees wraparound
Occlusal coverage posteriorly to increase surface area for bonding and reduce sheer stress
Minimum thickness of 0.7mm to reduce flexing
What type of margin is created with a RBB?
Chamfer margin, to help with seating the wing
Before bonding of RBB, what steps can aid success of bonding
Sandblast metal with alumina Silicate coating Tin plating Primer added Enamel surface etch
Why may a cingulum rest help adhesive with a RBB?
Resists sheer stress and acts as a locating device
How may you ensure you have adequate crown height for a bridge preparation?
Possible crown lengthening using electrocautery
When using a metal wing on a RBB, what cement would be best?
To stop grey shine through use an opaque cement
What is the process when cementing a RBB with panavia?
- Clean abutment
- Etch for 10s, rinse and dry
- Apply ED Primer II to entire abutment surface, leave for 30s, then dry
- Apply the mixed panavia paste to the wing
- Firmly seat the retainer and maintain finger pressure for 60s
- While maintaining finger pressure remove all excess with a microbrush/probe
- Light cure for 20s or Oxyguard and leave for 3 min then rinse off Oxyguard
- Remove any excess
Why would bond failure occur in a bridge? and how is this overcome?
- Inadequate moisture control
- Inadequate seating resulting in uneven cement layer
- Inadequate surface treatment of fit surface
- Cement out of date/ instructions not followed
What to do if it is a bond failure
• Remove all existing cement
• Sand blast
• Rebond
What is the bucket handle effect of anterior bridges?
Curve involved when placing Pontic teeth in their natural position, not straight line
Tilting forces on abutment teeth are greater
