posts & cores Flashcards
purpose of post & core
gains interradicular support for restoration
- core provides retention for crown
- post retains core
- post DOES NOT strengthen / reinforce teeth
- prep of RCT for post weakens tooth
ferrule
dentine collar; 1-2mm of vertical axial tooth structure within the walls of a crown
prevents tooth # by placing crown margin on dentine instead of filling material
(may need ortho extrusion / crown lengthening to achieve this)
direct v cast post
direct = ferrule required
cast post & core = no ferrule needed; not ideal
guidelines for post placement (6)
- tooth type -
incisors & canines - if extensive coronal tooth tissue
avoid mandibular incisors due to thin, tapering, narrow roots
premolars - small pulp chambers & tapering roots if placing post put in widest canal
curved canals - do not place to avoid perforation - root filling - 4-5mm GP apically
- post width - should be no more than 1/3 of root width at narrowest point
- bone support - alveolar bone should be at least 1/2 of post length into root
- post length - MINIMUM 1:1 post : root
- ferrule 1-2mm
classification of posts
manufacture -> preformed / fabricated / custom made
material -> cast metal / zirconia / steel / carbon, fibre, glass
shape -> parallel sided / tapered
describe the ideal post (3)
- PARALLEL -> avoids ‘wedging’, more retentive than tapered
- NON THREADED -> smooth surface incorporates less stress to remaining tooth than threaded
- CEMENT RETAINED -> less retentive than threaded posts but cement acts as buffer between masticatory force & post / tooth
2 types of post
- prefabricated
- custom
prefabricated
post & core different materials
premade
only 1 visit
no imps / lab visit
chairside core build up
large selection of designs & materials present
custom posts
cast from direct pattern fabricated in pt mouth
post & core same material & come in 1 piece
imp of post hole & core then wax up in lab
2 visits required - 1 for imps and 2 for fit
temporisation required so risk of contamination of RC between
cast post made in type IV heat hardened gold
types of post material (3)
- METAL
e.g. type IV gold // SS
+ radiopaque on radiograph
- poor aesthetics (metal shine through)
- corrosion
- Ni sensitivity
- root # so failure - CERAMICS
e.g. alumina / zirconia
+ high flexural strength
+ # toughness
+ favourable aesthetics
- difficult retrievability
- root # common - FIBRE
e.g. carbon fibre / glass fibre
+ flexible
+ similar properties to dentine
+ aesthetics
+ retrievable
+ bonds to dentine with DBA
- radiolucent on radiograph (difficult to see)
- debonding at post / cement interface = caries
- flexing can cause 2ndary caries
- need substantial amount of tooth
tapered prefabricated post
conservative / high strength / high stiffness BUT less retentive than parallel or threaded
use - small circular canals
caution - avoid excessively flared canals
parallel pre fabricated post
high strength / good strength / comprehensive system BUT less conservative, precious metal post is expensive, corrosion of SS
use - small circular canals
caution - care during prep
threaded post
high retention BUT stresses in canal can cause #
use - only when max retention required
caution - care to avoid # when healing
custom cast post & core
high strength / better than prefab BUT less stiff than wrought, multiple appts, complex
use - elliptical or flared canal
caution - care to remove nodules prior to insertion
to remove GP for post placement
dental dam
soften using heat / solvent i.e. eucalyptus
gates glidden to min size 3 (only used in straight part of canal)
use rubber stopper & WL on GG
ensure 4-5mm GP left apically
measure using loupes / microscope / PA radiograph
