DS5101 - Fixed-fixed conventional bridge Flashcards
Aims and Objectives
Sequence of treatment plan
- clinical exam, identification of patient’s needs
- special investigations, wax ups, mounted casts, radiographs
- correction of existing disease and stabilisation of conditions
- prevention of future disease - OHI, F
- evaluate outcome of preventative phase
- restore function, improve appearance
- review and maintenance, reinforce OHI and prevention
What to investigate regarding abutments
Radiographic, pulp, dental hard/soft tissue, occlusal evaluation
- structurally sound
- abutment abutments in alignment/position
- previous restorations/RCT satisfactory (not recommended for abutment)
- abutment root and supporting alveolar bone are functionally adequate
- adequate alveolar bone of edentulous ridge in quality and quantity
- adequate soft tissue of edentulous ridge in quantity and quality
What do you need to communicate with the patient when tx planning
- current conditions and management of any ongoing problems
- extent of intervention and logical sequence of proposed treatment
- time and cost
- level of home care required for favourable long-term outcomes
- level and cost of maintenance/repairs/replacements
- possible alterations before any irreversible procedures are undertaken
Considerations during history and examination
- patient factors: OH, parafunctional habits, past dental history
- mouth condition, extent of problem
- restorative status of tooth/teeth in question
- availability of interocclusal space and occlusion
- possible technical and clinical challenges
- patient wishes and expectations
- feasibility and prognosis of treatment
Advantages/disadvantages of fixed-fixed bridges
Advantages
- alternative to implant when bone quanity/quality suboptimal
- predictable/aesthetic results with good planning/patient selection
- allow stresses to be distributed more evenly
- various designs can be used in different parts of arch
- can be used in anterior/posterior long spans/periodontal splinting
Disadvantages
- destructive of tooth structure, can cause endodontic issues in abutments
- needs meticulous planning and design of bridge framework and occlusal features
- pulpal death common in abutments
- after RCT, remake normally needed
- costly and requries excellent OH and maintenance
Advantages/disadvantages of hybrid bridges
Advantages
- fixed solution for edentulous space
- no/minimal prep on one abutment
- good for transitional phase to keep the space and avoid loss of interocclusal space
- can be bonded adhesively
- good patient satisfaction
Disadvantages
- high probability of debonding of metal retainer
- can lead to caries under debonded retainer
- technique sensitive/requires excellent planning and moisture control
- needs regular check-ups to evaluate the retainers and their bond
- not enough clinical evidence
Advantages/disadvantages of cantilevered bridges
Advantages
- good aesthetic can be achieved
- more conservative and less complications due to simpler desig
- lesser chance of developing caries under retainer
- good option for single tooth replacement
- mostly non-castostrophic failure
Disadvantages
- risk of debonding and failure
- especially on RCT teeth
- metal base can make tooth look darker
- pulpal death of abutment possible
- not ideal for load bearing area
Advantages/disdavantages of fixed-movable bridges
Advantages
- allows for flexure of the bridge, reduced load on weaker retainer
- allows for partial coverage of retainers and less prep required
- compensates for abutment malalignment
- allows individual movement of sections during function
- units should eb cemented as individual sections in right order
Disadvantages
- destruction of tooth structure as room for dove-tail joint needs to be created
- metal may show on the site of moveable joint
- wear and mechanical failure of joint can happen
- try in and cementation can be challenigng
- technically challenging for technician and requires framework try-in
What is an intracoronal precision attachment? And the 2 types
- Dove tail attachments are incorporated entirely within the contour of the crown
- female component in crown and male in prosthesis
- prefabricated by manufacturer - usually made of precious metal
- plastic attachments (castable) - simple, precise and indicated for fixed bridges - CUSTOM MADE, better
Advantages and disadvantages of intracoronal attachment (3,3)
Advantages:
- reduced stress on abutment compared to conventional
- all stress is directed along the long axis of the tooth
- allows for individual movement of abutment teeth
Disadvantages:
- extra prep to create room for dove tail joint
- attachment is subject to wear as a result of friction between metal parts
- lack of RCTs and high quality data from SRs
Types of stress on fixed bridge (3)
Tensile stress: internal induced force that opposes elongation of a material parallel to direction of the stress, it is generated when structures are flexed, like deformation of a bridge
Compressive stress: internal induced that opposes shortening of material parallel to the direction of the stress, associated with compressive strain
Shearing stress: internal induced force that opposes the sliding of one plane of material on adjacent plane in direction parallel to the stress - tends to resist sliding or twisting of one portion over another. Can be produced by twisting action on a material e.g. force applied along surface of enamel-RBB retainer interface by sharp-edged tooth - the RBB. may debond by shear stress failure of resin luting agent
Things to consider in framework design
- dental porcelain is weak in tension/shear but strong in compression
- design should avoid/minimise tensile and shear stresses
-> especially at framework-porcelain interface/within the porcelain veneer - weakest part in posterior bridges is the fixed joint due to high concentration of tensile and shear stresses
- increased depth of connector increases its strength (atleast 2.5mm occluso-gingivally and bucco-lingually)
- doubling depth from 1.5mm to 3mm increases strength by a factor of 8
- doubling width of a connector doubles the strength
- doubling length of span allows 8x as much deflection for a given force (but more biological failure)
PFM vs Layered Zirconia
What is a Pier abutment?
- ## tooth in the middle of a bridge span
Disadvantage of Pier abutment design
Used in long span bridges around the dental arch
> functional/physiological tooth movements vary across dental arch
(due to shape of arch, movements are in different directions - anteriors tend to move labially, posteriors tilt mesialy)
> unfavourable forces put constant stress on restoration and luting material
> in a fixed bridge, the abutment fails at weakest interface
> leads to leakage/development of caries
In which case may Pier abutments/long span bridges be okay, as opposed to in sound teeth
in perio compromised teeth w some degree of mobility - long span splinting effect may be beneficial
but in sound abutments, will often lead to loss of restorative seal
Whats wrong with this
double abutments
- uneven distibution of stress
- fracture of cement lute of the weakest retainer
- leads to leakage/caries/debonding of bridge
General design considerations
- periodontal support
- occlusal loading (magnitude and direction of force)
- conservation of tooth tissue
- cleansability
- appearance
- rigidity
- no. of abutments
- choice of luting cement
Tooth Preparation - General Principles for fixed bridge
- diagnostic wax-up for all bridgework
- conservative prep with putty index from the final form
- abutments parallel to eachother
- maximum resistance/retention form
- supragingival finish line
- need to modify/replace old restos for better bonding
- IDS on freshly prepared abutments for better bonding
What is a malpositioned abutment. How does it differ from M and D?
- when abutment is tilted (might be due to adjacent exo), occlusal surfaces are non-parallel to occlusal table - may not need to reduce occlusal surface to achieve clearance
Image 1: tipping of distal abutment brings a change in the O plane as mesial cusps of distal abutment have no antagonistic contact and require less occlusal reduction to achieve the clearance
Implication of malposition abutment for bridge. Give solution. Whats the most conservative option? (3)
teeth deviated from normal long axis - no common path of insertion
can be managed by recontouring, orthodontics, 3/4 crowns or telescopic crowns
-> 3/4 crowns on tilted abutment plus a hybrid/fixed-moveable design are the most conservative option
Bridges in patients with advanced perio (Lindhe study)
- severe reduction of perio support doesnt influence perio status during observation period
- loss of retention occured in abutments w partial crowns - reduced resistance to deformation
- need maximum length and minimal taper prep and parallelism between abutments is imperative
- fracture of abutment occured more frequently in RCT fitted w posts and serving as terminal abutments for free-end segments
Occlusal considerations
- share load equally between abutments and pontics
- first achieve desired occlusal contacts on provisional
- avoid loading pontic in lateral and protrusive movements
- light contact in ICP on pontics
- proper planning using mounted study casts and well-fitted temporary will help achieve desired occlusion
- consider group function to avoid exceesive load on canine
