Fixed Pros Flashcards
Indications for coring vital teeth
Vital tooth lost substantial amounts of tissue
RCT unnecessary + unlikely req. in near future
PD condition + hard tissues stable
What material is first choice for constructing core?
Amalgam
Dis/advantages of amalgam for cores
Adv
- easy
- cheap
- good longevity
- high compressive
Disadv
- colour
- nonadhesive
- environmental issues
Discuss comp as core material
H2O inclusion over T (8% expansion)
Initial polymerisation shrinkage
Bonds tooth tissue: longevity questionable
- doesn’t bond metal pins/posts
Hard to pack; flowable easier
Aesthetics: good, makes difficult to distinguish b/w tooth + matieral
Types of dentine pins + associated problems
Types
- cemented: least stress + retention
- friction: high stress + retention
- self tapping: medium stress + retention
Problems
- stresses in dentine: microcracks-> microleakage -> failure
- no bond to amalgam or comp
- 2mm deep = close to pulp (exposure)
- only reach 50-70% of hole prep: bacterial accumulate in space
Types of additional retention for amalgam cores
Slots + grooves: 2x2mm, 1mm from EDJ
Amalgapins: 2mm deep, large enough to use small instrument to pack
Adhesives
Discuss amalgam adhesives
Do not use
Unsuccessful: cause leakage = catastrophic failure
Never use w/ slots/grooves/amalgapins as fills space
Potential pooling around margin = inc. microleakage
Dis/adv of additional retention methods for amalgam cores
Adv
- less stress on dentine (no binding force)
- less corrosion: all same material
- strength = to pin retained amalgam
Disadv
- potential for exposure / perforation
- req. rigid matrix otherwise # on removal
Problem w/ posting post. teeth + solutions
Problem
- Divergent, curved roots
— prep. for rigid cast/wrought post system = perforation
- Weakened by RCT access; weakened further by thick, rigid post
Solution
- plastic restoration + pins: potential for perforation
- plastic restoration within root canal system
— filled as continuum of support
- metal castings: custom for each pt
What is a Nayyar core?
Core for crown which extends into root canal system
Drill 4mm into canals w/ rose head or GG
Root canals + chamber packed w/ amalgam/comp and crown built up
Importance of carving amalgam/comp to full contour for cores
If flat opposing tooth may over-erupt!!
Check occlusion
- cusp-to-tip relationship: tripod contacts
- light ICP contacts, no excursive contacts
Easy to construct provisional
Problem associated w/ using comp for nayyar core
Dimensional stability: unable to prep immediately
- polymerisation shrinkage then expand thus crown wouldn’t fit
Cannot use eugenol containing cement
Compare tapered and parallel sided posts
Tapered
- follows shape of tooth
- more stresses
- can # teeth
Parallel
- good retention
- red. stress
- difficult to provide sufficient diameter for whole post length in narrow teeth
- expensive
Compare passive and threaded posts
Passive
- red. stress + retention
Threaded
- high stress (worse w/ tapered) + best retention
Discuss importance of length of post
Longer = better
> 50% canal length
than height of crown
Extend well below crest of bone
Leave 4mm GP @ apex
Effect of diameter of post
Wider = more bending resistance
However = red. tooth tissue, inc. chance #
Leave at least 2mm tooth tissue around
<1.25mm req. wrought post as gives cross sectional strength
What is a RBB?
Minimally invasive fixed prostheses which relies on comp for retention
- FPD luted to etched tooth for resin retention
Indications for replacing missing teeth
Aesthetics: ant.
Function: chewing, speaking, pt discomfort
Prevent OE/movement
Psychological comfort
Components of RBB
Wing: attached to BA
Connector: attaches BA to BP
Pontic: artificial teeth
Discuss RBB wing
Non-precious metal cast in thin section
Tx’d to inc. micromechanical adhesion
- protheses + comp
Ni-Cr/Co-Cr sandblasted 50micro Al
Dis/advantages of RBB
Adv
- min. invasive; relatively reversible
- cheap cf implants
- less clinical T
- less demanding prep + fit
- failure less catastrophic
- aesthetic
- predictable
Disadv - aesthetics depend on BA tooth — quality + thickness of enamel — porcelain of Pontic — extent of soft tissue defect in BP region — management of soft tissue - de-bond; re-bond less successful + predictable - longevity + success cf implant
Principles of RBB design
Simple as possible
Cover as much BA poss + min. thickness (0.7mm)
Rigid: connector + wing
Hygienic pontic
Permit control of O contacts (BP not in excursion)
Types of RBB
Cantilever
Fixed-Fixed
Fixed-Moveable
Hybrid
Discuss design, dis/adv of cantilever bridges
Design
- simple; 1 retainer
- BA: M or D; D better longevity
Adv
- simple
- cheaper
- good longevity
- carious failure less likely
- differential tooth movement = less stress on bond
- higher success rate
Disadv
- limited to 1 BP
- most mechanically unsound; all stress transmitted to 1 BA
Compare fixed-fixed and fixed-moveable bridges
Fixed-Fixed Design - retainers: 1/+ either side BP - connectors: rigid Indications - excursive movements unavoidable on BP - long spans - cross midline Adv: load distributed more equally Disadv: differential BA movement = failure
Fixed-Moveable
Design
- connectors: 1 fixed (D) + 1 moveable
— allows some differential movement (vertical)
- 2 parts, keyed together by non-rigid attachment
Indication: where proximal walls BA can’t be prepped parallel
Adv: stress breaking action
Discuss hybrid bridges
Design: combination of conventional + RBB
- fixed-moveable: w/ resin retainer carrying moveable connector
- fixed-moveable: w/ conventional retainer carrying moveable connector
- fixed-fixed: 1 conventional + 1 RB retainer
Indication: 1 BA min. prepped so RB retainer used to conserve tooth tissue
Adv: allows variety of designs + retainers
Factors affecting success of RBB
Design: cantilever best BA surface coverage: complete best Connector height: long as poss BA prep Metal surface Tx Framework rigidity Occlusal considerations Span length Operator experience
Contra/indications of RBB
Indications
- BA: sound, non-restored
- good OH
- occlusion well controlled
- hypodontia
- U+L I
- single post.
Contraindications
- BA: heavily restored, lack clinical crown height
- bruxism or parafunction
- extensive bone loss
