posts - indications for use?
- root filled teeth
- severely broken down coronal tooth structure: inadequate retention for restoration or core
- weakened remaining tooth structure
posts: can be? what is each made of?
- cast (indirect): metal
- prefabricated (direct): metal, non-metal
posts: 2 types? describe each
- active posts: threaded
- are tapered or parallel
- passive posts: smooth sided or serrated
- are tapered or parallel
cast (indirect) post and cores: how is GP root filling removed?
how does this allow the cast post system to be used?
- using non end cutting burs e.g. gates glidden
- the size is gradually increased and transferred to the appropriate size twist drill for the cast post system to be used
how does the cast post cool down?
what are the implications of this?
what could result?
- it cools from the outside. it contracts while solidifying, sucks molten gold from the core.
- this could create porosities at the junction of the post
- could lead to increased likelihood of fracture
coring: if the alloy cast is cooled quickly, how does the composition of the alloy change?
- what does this change lead to?
- how to improve the mechanical properties of the cast alloy?
- it varies at different sites due to premature precipitation of some components of the alloy
- different areas richer in one material to another, sets up electrolytic cells -> corrosion leading to a weaker structure
- it should be cooled slowly
which class of alloy is used for cast post and core?
- usually type IV (extra hard)
prefabricated (direct) metal posts: what materials can they be made of?
which one is stronger? but what does it have risk of?
- platinum-gold-palladium
- brass
- nickel chromium (stainless steel)
- pure titanium
- titanium alloys
- chromium alloys
- stainless steel. risk of adverse tissue response to nickel (for technician, unlikely for patient).
prefabricated metal posts: what has stimulated concerns about the use of these posts?
- excessive stiffness (modulus of elasticity)
- corrosion of the post
- post & root fracture?
prefabricated metal posts - active threaded posts:
- possible materials they are made of?
- reamers?
- square cross cut head - how is it beneficial?
- examples of other active posts?
- titanium, stainless steel, goldplated SS versions
- reamers screw post into root
- helps with retention of core
- self-threading posts: parapost XT (titanium alloy parallel), radix anchor (titanium alloy parallel)
prefabricated metal posts - passive: most are in what form?
interconnecting serrations help with?
- parallel
- parapost XH:
serrated pattern
titanium alloy
parallel
vented via interconnecting serrations - help luting cements set into pattern, provides mechanical retention
luting cements for metal posts: choice based upon?
ideal cements are?
what not to use?
- choice is based upon retrievability; metal posts are removed using ultrasonics meaning that the cements should be relatively brittle
- zinc phosphate, zinc polycarboxylate, GI, RMGI
- no adhesive resin luting cements e.g. panavia
prefabricated non-metal posts: name 3
- zirconia
- ceramic
- fibre reinforced resins: carbon fibre, glass fibre, woven polyethylene reinforced composite
prefabricated non-metal posts: zirconia and ceramic - issues with use?
- brittle
- high modulus of elasticity, may lead to fracture
- zirconia difficult to remove with USS
prefabricated non-metal posts - fibre reinforced posts:
advantage?
disadvantage?
- strong, but can flex
- absorbs and transfers forces similar to dentine
- dark color - cannot transmit light, not suitable for aesthetic restorations
prefabricated non-metal posts: glass (quartz) fibre posts - embedded where? made out of?
- embedded longitudinally in an epoxy resin (die?)
- 60% fibre 40% resin
advantages of fibre based posts?
- good flexural str
- less rigid than metal
- cement with adhesive resin cements
- white or transparent quartz fibre posts - translucent
- all ceramic bonded crowns
- easier to remove if required
- must be covered, will delaminate in moist environment
luting cements for non-metal fibre posts: choice based on?
- based on retrievability
- fibre posts drilled out, bond to post and dentine walls beneficial
- therefore luting cements needs to be resin based
- ideally self etching resin luting cements e.g. RelyX Unicem
