liners and bases Flashcards
why do we use liners and bases?
because a lot of restorative materials don’t adequately protect the pulp against thermal or chemical insult
what kind of protection do liners and bases provide?
chemcial, electicla, thermal, mechanical proteciton and pulpal medication
concern for pulpal health increaes as______
tooth prep extends closer to the pulp. usually the dentin is a pretty good insulator, but not if it is really thin
![](https://s3.amazonaws.com/brainscape-prod/system/cm/161/145/643/a_image_thumb.png?1443553329)
so what is a liner or base?
material placed between dentin (and sometimes the pulp) and the restoration to provide pulpal protection.
what is a liner?
a relatively thin later of material used primarly to provide a barrier to the dentin from residual reactants diffusion out of the restoration or oral fluids that can penetrate leaky tooth restorations. contribute to initial ELECTRICAL and THERMAL insulation. provide some pulpal treatment.
![](https://s3.amazonaws.com/brainscape-prod/system/cm/161/145/645/a_image_thumb.png?1443553330)
For what materials are liners usually needed?
They are needed most with deep metallic restorations that do not bond to tooth structure such as amalgm and cast gold.
They are not usually used for composite and ceramic restorations because they are bonded to tooth structure.
what are two types of liners?
thin film liners (1-50 um) (examples of these are solution liners and suspension liners)
and cement liners (200-1000um), used for pulpal medication and permal protection)
what are cement bases
provide thermal protection for pulp and mechanical support for the restoration.
Also protects the pulp during the condensation of the amg
what is a solution liner? What is a suspension liner?
solution liner - any liner based on nonaqueaous solvents that rely on evaporaiton for hardening
suspension liner - liners based on water that have many constituents suspended rather than dissolved in them
most varnish coatings are produced by ____
drying solutions of copal or other resin dissolved in a volatile solvent
tooth preps cut with rotary instruments produce debris, some of which is compacted into a layer called the ______. When is this debris left in place? Why is it left in place?
smear layer
left in place for unbonded amalgm restorations. If you are doing something with bonding then you remove the smear layer
If left in place it provides some sealing of the dental tubules. though it is still about 25% porous.
![](https://s3.amazonaws.com/brainscape-prod/system/cm/161/145/651/a_image_thumb.png?1443553331)
how is flow through tubules related to diameter?
flow is proportional to the fourth power of diameter of the lumen. Therefore, blocking the opening by 50% (x2) decreases flow by a factor of 16.
the smear layer is a protective barrier, but is it good for long term protection
heck no.
so for amg restorations that can leak along margins, the smear layer should be sealed to provide chemical protection
is a dentin and amg bond a good liner?
yes, it can produce the same or better effect when compared to traditional liners
what is the most widely used varnish?
copalite. drying happens in first 8-10 seconds, no need to dry. a thin film is left over the smear layer. moisture is in smear layer and varnish is hydrophobic, so don’t wet it.
see image of coplilite varnish partially occluding the tubules
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