BDS4 Conventional Bridges Flashcards
What is meant by a conventional bridge?
The retainers are crowns
What are the different bridge designs you can get with conventional components?
- fixed-fixed
- fixed cantilver
- fixed moveable bridge
- hybrid (fixed and adhesive retainer)
- spring cantilever
What is a fixed-fixed bridge?
A bridge which has a retainer at each end with a pontic in the middle joined by rigid connectors
e.g. retainer-pontic-retainer
Fixed-fixed bridges aren’t generally used anteriorally, but when can they work? Why can they work in these situations?
- If pts have a class II incisor relationship (there isnt much contact between the upper and lower anteriors)
- Anterior open bite
Work because there is less force, and therefore less flex;
What are the advantages of fixed-fixed bridges?
- robust design
- max retention and strength
- abutment teeth are essentially splinted together (perio cases with mobile teeth)
- can be used in longer spans
- lab construction straughtforward
What are the disadvantages of conventional fixed-fixed bridges?
- prep difficult (parallel tooth preps needed)
- prep must be minimally tapered
- need a common path of insertion for abutments (parallel stuff)
- removal of tooth tissue which is a danger to pulp
Why must the prep for a fixed-fixed crown be minimally tapered?
Becasue if you over-taper then you reduce retention as the retainer can then slide off in a multitude of directions
(ideally want a 4-7 degree taper but can go to 10 degrees max)
What is an example of the problems that can occur when a fixed-fixed bridge prep is not parallel?
Can get overhanging marginal ridges from other teeth and the bridge won’t fit (see pic)
Note the 7 has a different path of insertion than the 5
What are the advantages of using a conventional cantilever bridge? (one crown)
- conservative design compared to fixed-fixed conventional design
- dont need to ensure the tooth preps are parallel
- lab construciton straightforward
What are the disadvanatages of using conventiona cantilevel bridge designs?
- short span of teeth only (single tooth replacement)
- are rigid to avoid distortion so may be more prone to fracture
- mesial cantilever is preferred to distal (aka abutment tooth behind the pontic/tooth being replaced)
Why is a mesial cantilever preferred for conventional cantilever bridges?
Because people are more liekly to occlude on more posterior teeth so would have a heavier occlusal contact on the pontic causing strain on it vs if there was heavier occlusal contact on the abutment tooth
How might you be able to fix the problem with a fixed fixed bridge where the tooth preparations are not parallel?
Use a fixed-moveable bridge
Describe a fixed moveable bridge
- The bridge is split into two and you only need one path of insertion
- On one crown there is a slot and on the bridge there is a dovetail which slots into the crown
- the rigid connector tends to be at the distal end of the pontic (crown with slot)
- the moveable connector is mesially (bridge with dovetail)
Note: it allows some vertical movement at the mesial abutment tooth
What are the advanatages of conventional fixed-moveable bridges?
- preps dont require a common path of insertion
- each prep is designed to be retentive independent of others
- more conservatuve of tooth tissue (not removing excess tissue to achieve a common path of insetion)
- allows minor tooth movement
- may be cemented in two parts
What are the disadvanategs of conventional fixed-moveable bridges?
- length of span limited (1 tooth really as decreased flexibility)
- lab construction more complicated
- Can be difficult to clean beneath the moveable joing (need a pt with good OH)
- Can’t construct a provisional bridge
What is a sprinf cantilever bridge? (these aren’t really done)
One pontic attached to the end of a metal ar that runs accross the palata to a rigid connector on the palatal side of a retainer
