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
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.
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.
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
how much does one coat of varnish cover the surface?
How about two coats?
one coat - 55 % of surface
two coats about 80-85% of the surface.
The use of varnishes have decreased a lot since the late 90’s because of the use of bonding
is thermal protection better offered by bases or liners?
bases. They are thicker. This is also why they harden by either chemical or light curing.
______ can also offer relief of pulpal inflammation and stimulate dentinal bridging
liners
what is Eugenol
what is ZOE
in low concentrations, Eugenol eases discomfort from mild to moderate pulpal inflammation.
It can be combined with zinc oxideto form ZOE which is very common in liners, bases, and cements. Zoe liners and bases were used for moderatly-deep preps close to the pulp in the past. Now we use glass ionomers instead.
setting of ZOE liners and bases is accelerated by what?
moisture
When and why would we use Calcium Hydroxide?
Use when microscopic pulpal exposure is suspected. When ionized in low concentrations, it stimulates fomation of reparative dentin.
CaOH liners are formulated to set quickly, then allow small amounts of CaOH to be released and stimulate reparative dentin. Unfortunately the liners can degrade, at which point they do not provide adequate mechanical support for the restoration.
Can you use CaOH and ZOE together?
remember this one peeps, it will be on the exam.
NO!!! Use one or the other. Eugenol chelates the calcium in a strongly exothermic reaction… bad news bears.
it appears that ____ is more important than_____ for the purposes of pulpal protection
sealing is more important than medicating for pulpal protection
during these time periods, what has been used for pulpal protection?
prior to 1960
1970
1985-1994
1994-present
prior to 1960 - zinc phosphate and resin reinforced ZOE
1970- polycarboxylate cement bases
1985-1994 - glass ionomers
1994-present - highly modified glass ionomer cements provide chemical adhesion, good mechanical strength and potential fluoride release.
see image of glass ionomer cement
clinical judgement about when to use liners and bases are linked to?
the remaining dentinal thickness
why do we usually use Ca OH as a liner rather than Eugenol wiht a composite tooth prep?
Because eugenol has the potential to inhibit polymerization of layers of bonding agent or composite that is in contact with it.
What is the long term survival of liners and bases like? When should we replace them?
long term survival is not well understood, it is a good idea to replace them when we replace a restoration
