Cavity liners and bases
Liners and bases are materials placed between dentin (sometimes
pulp) and the restoration to provide pulpal protection or pulpal
Pulp protection against:
Protective needs for a restoration varies depending on the extent
and location of the restoration and the type or restorative material
Are relatively thin layers of materials (140pm) used to
provide a barrier to protect the dentin from residual reactants
diffusing out of a restoration and/or oral fluids, which may
penetrate leaky tooth-restoration interfaces.
• May provide pulpal treatment, some thermal and
• The need to liners is greatest with metallic restorations
that are not well bonded to the tooth structure such as
amalgam , while the composite and resin modified GIC
are bonded to the tooth so it eliminates the need to liners
UNLESS the cavity is very close to the pulp and pulpal
medication is needed.
Types of liners:
1.thin film liners:
A . Solution liners: varnishes, 2 - 5 µm thick.
B . Suspension liners: 20-25 µm.
also known as Cement liners: 200-1000 µm (0.2-1mm) used for
thermal protection, pulpal medication.
o Cement bases, typically 1-2 mm.
o Used to provide thermal protection for the pulp and
supplement mechanical support for the
Restoration by the stress distribution on the underlying
dentin surface e.g. forces of amalgam condensation.
Objectives of pulpal protection:
Reviewing the anatomy, physiology of dentin – pulp
Structure of dentin.
Reaction o pulp to different stimuli:
If the insult is strong and near to the pulp, the odontoblastic
processes are retracted rapidly and a thin local bridge of
hydroxyapatite crystals is formed at the site.
During cavity preparation with rotary instruments, some of
the cutting debris is compacted to the surface that material
known as smear layer…this layer is very effective barrier so
it is left when using a non-bonding restoration like amalgam.
However, it is partially porous 30 %, it can’t prevent slow
long term diffusion…that’s way the smear layer should be
sealed with a layer of liner.
Handling of smear layer (according to rest. mat. used):
With amalgam => leave it.
With composite => must be removed.
Traditional liners (varnishes) could be used with recent amalgam
restorations, but dentin and bonding systems can produce better
effect and replace the liners.
Solution liners (varnish)
Copal or natural resin dissolved in non-aqueous volatile solvent,
(ether, alcohol and acetone)upon drying it will produce a thin
ADVANTAGES: flexible – dry rapidly.
On the other hand, thick films tend to trap solvent during drying
and become brittle.
LAYERS OF VARNISH:
Single coating covers only 55% of the surface
because the smear layer is moist and the varnish is
hydrophobic..SO A SECOND LAYER IS NEEDED
Second coat covers 80-85%
N.B. use of varnishes decreased since 1990 due to using of DBS,
Same effect – dry slowly – give thicker films.
Constituents are suspended or dissolved in water.
Thermal protection thicker layer (20-25 µm)
Functions of Cavity liners:
1. Primary purpose protective seal of exposed dentin
2. Electrical insulation (with newly placed amalgam restoration)
from the electrical circuts with restorations in adjacent teeth.
3. Thermal insulation with metallic restoration
Degree of insulation depends upon
Thickness of remaining dentin
2mm of dentin or equivalent thickness of insulating
material should exist to protect the pulp.
4. Pulpal medication (dentin bridging)
Ca (OH)2 liner
Eugenol is slightly acidic, phenoloic compound that have an
obtundant action on the pulp at low concentrations with mild to
moderate pulpal inflammation.
N.B. high conc will be irritating to the pulp.
ZnO/E liner, base, cement
ZnO/liner for moderately deep cavities because it is
released during setting and over several days.
Now a days resin-modified glass ionomer cement is
Ca (OH)2 very deep cavities or microscopic
Exposure Ca (OH)2 Caustic (Alkaline, pH 12)
Stimulate secondary dentin formation
- Ca (OH)2 suspension
- Chemically set material
- Light-cured material
Ca (OH)2 dissolution or degradation overtime
Setting reaction of the ZnO/E and calcium hydroxide
accelerated by moisture.
Eugenol and calcium hydroxide cannot be incorporated is
the same formulation because eugenol rapidly chelates
with calcium ions in a strong exothermic reaction
the choice of eugenol-based versus
Calcium-hydroxide-based liner is based on the relative depth of
the tooth preparation.
Before 1960’s Zn phosphate cement
1970 polycarboxylate cement
LCGIC, compomers chemical adhesion,
Good mechanical properties, fluoride release, command setting
and rapid achievement of strength.
• Ca (OH)2 liner
• Base for mechanical support +stress distribution.
• Varnish on the base plus walls except when using
zinc phosphate cement the varnish must be
applied before the cement.
• Light cured Ca (OH)2 liner
• GIC base
For indirect restoration:
• A base is used to block undercuts
• Preferable to be bondable to dentin to prevent
temporization and impression taking.
- Composition, structure and properties of different
Clinical consideration with liners and bases
Clinical judgment depends upon:
1) Remaining dentin thickness (RDT)
2) Consideration of adhesive material
3) Type of restorative material use
* in amalgam: 1.5 mm depth => 2 layers of varnish +
* in composite: acid itch – primer – bonding agent>
THE AIM: to give chemical protection.
* eugenol can’t be used under
composite because it inhibits
* in case of very thin RDT use spherical amalgam
because it needs less forces of condensation.
Newer liners place less emphasis on pulpal medication and
focus more on chemical protection by sealing, adhesion and
Newer compositions rely on mechanically strong acrylic
resin matrices, and that choice makes the release of eugenol
or calcium hydroxide more difficult or impossible..