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
what is a core build up
internal part of tooth built up with restorative materials to replace lost tooth tissue
provides retention & resistance for definitive rests
materials for core (3)
- COMPOSITE
most common
tooth coloured so aesthetics
technique sensitive (moisture control required)
used with fibre posts - AMALGAM
tend to avoid as retention poor
core cannot be prepared straight away - needs 24hrs to set
poor aesthetics - GI
absorbs water
core expands
prevents putting restoration on
design of core
6 degree taper
no undercuts
2mm below occlusal plane (allows clearance for crown)
purpose of anti rotation notch / groove
if sufficient coronal structure present - rotation prevented by vertical coronal wall
if coronal dentine absent - small vertical groove placed in canal serves as anti-rotational element; normally located in lingual as bulkiest area of the root
para post system
for indirect cast post
0.9mm narrowest
para post kit contains -> provisional post, para post drill, impression post
for post space prep & imp
lab prescription
please construct cast post & core
para post (colour)
core - 6 degree taper
please leave 2mm space in occlusion for crown
enclosed registration / opposing imp / shade / bite reg
try in
check post space for temp bond
irrigate 0.2% CHX
dry with paper points
ensure fits around prep
check if enough occlusal clearance
fit
care not to fill post space with cement as may prevent it seating
use firm apical pressure
get rid of excess
ensure no excess cement when taking crown imp or fitting MCC
reasons for post crown failure
restorative - 60% i.e. caries around margins, core#, post#, perforation (xla or repair via periradicular surgery)
perio - 32%
endo - 8% root crack or #
nayyar core
when we remove 2-3mm of root tx from root canals & pack amalgam into root canals as well as using it for a build up
tooth cannot be prepared for 24hrs until amalgam sets
potential use in posterior teeth as cannot place posts in posterior teeth (due to flared canals)
posts in premolars / molars
palatal in uppers
distal in lower 6/7
as these are the longest, widest, straightest canals
to remove posts
- ultrasonics
- masseran kit
- eggler
- moskito forceps
fibre posts
DT light
RelyX
etch & bond post hole
bond on post
cure these both
place cement - corecem on post
place in post hole and cure again
occurs at junction of post core crown - why
excessive lateral forces
inadequate ferrule
short / narrow / overtapered post
inadequate moisture control
bacterial interaction causing decay
