1. Liners & Bases

2. Purposes of liners & bases
Protect the pulp from:
chemical insult
leakage
electrical insult
thermal insult

3. Hydrodynamic theory of dentinal pain:
Cause of pain:
Hydrodynamic theory of dentinal pain:
flow of fluids within the dentinal tubules is the cause of pain.
Key point:
changes in temperature change the volume of the fluid: the fluid flows

4. Stopping fluid flow:
Completely seal the dentinal tubules
Completely seal the path to the external surface of the restoration

5. Thermal properties of dental materials
Conductors:
metals (amalgam, cast alloys)
Insulators:
enamel
dentin (except tubules)
all luting cements, resin composites, porcelains

6. How insulators affect thermal expansion:
Slow the rate at which dentinal fluid is heated or cooled - fluid changing volume slowly will move more slowly - less pain?
Reduce the heat conducted to or from the dentinal fluid; some of the heat will be conducted away by the surrounding tooth structure.

7. Therapeutic effects of liners & bases:
neutralizes acids
slows or stops increase in the number of bacteria
dulls pain (obtundent)
increases the resistance of adjacent tooth structure to dissolution in acids
stimulates the formation of reparative dentin

8. Classification of liners & bases:
thin liners (< 0.20 mm)
liners ( mm)
bases (> 0.75 mm)

9. Cavity Varnish

10. Thin liners – cavity varnishes
uses:
reduce leakage of amalgam restorations
protect cements from exposure to oral fluid while setting
coating to reduce electrical shock from freshly placed metallic restorations

11. Thin liners – cavity varnishes
natural gum: copal or rosin
solvent: acetone, chloroform, ether, benzene, polystyrene

12. Thin liners – cavity varnishes
manipulation:
avoid evaporation – do not use thickened varnish
apply with a cotton ball
remove excess from the ball
apply two layers, wait 15 – 20 s between layers

13. Dentin permeability: effect of a varnish
Two layers are
more effective.
Note: the end result is less leakage, not no leakage
D. Pashley, 1983

14. One Day - Leakage in Class III Restorations - Dispersalloy
Leakage into
axial wall
Initially, some products work better than others.
No leakage
Murray, G. A., J. L. Yates, et al. (1983). Oper Dent 8:

15. Seven Day - Leakage in Class III Restorations - Dispersalloy
Murray, G. A., J. L. Yates, et al. (1983). Oper Dent 8:

16. Six Months - Leakage in Class III Restorations - Dispersalloy
After 6 months, the liners make no difference. Corrosion has sealed the margins.
Murray, G. A., J. L. Yates, et al. (1983). Oper Dent 8:

17. filled cavity varnishes dentin bonding systems adhesive resin cements
Thin liners (< 0.20 mm):
cavity varnishes
filled cavity varnishes
dentin bonding systems
adhesive resin cements

18. Thin liners - filled cavity varnishes
Not recommended:
Fillers dissolve, leading to accelerated dissolution of the liner.

19. filled cavity varnishes dentin bonding systems adhesive resin cements
Thin liners (< 0.20 mm):
cavity varnishes
filled cavity varnishes
dentin bonding systems
adhesive resin cements
discussed
earlier in the bonding and luting cement slides

20. Classification of liners & bases:
thin liners (< 0.20 mm)
liners ( mm)
bases (> 0.75 mm)

21. Hard-setting calcium hydroxide
Liners ( mm):
Hard-setting calcium hydroxide
calcium hydroxide-containing resin composites
hard setting zinc oxide - eugenol
glass-ionomer cements
resin-modified glass-ionomer cements

22. Hard-setting Calcium Hydroxide Cements
Wt. %
Paste 1
Paste 2
calcium hydroxide
49%
salicylate esters
44%
ethylene toluene
sufonamides
37%
tricalcium ortho phosphate
30%
zinc oxide 9%
calcium tungstate
14%
titanium dioxide 4%
zinc stearate
0.5%
hydrophilic & dissolves in
in H2O – accelerates dissolution
of Ca hydroxide
weak acids that
attacks Ca hydroxide
& zinc oxide
chelates with Ca++
& Zn++ ions: gels

23. Hard-setting Calcium Hydroxide Cements : Advantages:
easy manipulation
rapid hardening – accelerated by water vapor
good sealing
stimulates reparative dentin
recommended for direct pulp capping
recommended for indirect pulp capping when close to the pulp

24. Hard-setting Calcium Hydroxide Cements: Disadvantages:
low strength
weakened when exposed to moisture
dissolves, especially under acidic conditions
Hard-setting calcium hydroxide washed out under an amalgam restoration

25. Hard-setting calcium hydroxide
Liners ( mm):
Hard-setting calcium hydroxide
calcium hydroxide-containing resin composites
hard setting zinc oxide - eugenol
glass-ionomer cements
resin-modified glass-ionomer cements

26. calcium hydroxide direct pulp capping agent:
current product:
DYCAL® Radiopaque Calcium Hydroxide Composition
Caulk / Dentsply

27. Calcium Hydroxide-Containing Composite Liners
barium sulfate
fillers
urethane diacrylate
diluents
polymer matrix
activators & photoinitator
curable by light
Makes the cement radiopaque
Essentially a resin composite with a calcium hydroxide replacing glass as the filler.

28. Solubility of Calcium Hydroxide Liners
(wt. %)
hard-setting
resin
24 h in H2O
1.0 – 2.0
< 0.5
35% H3PO4 for 60 s
2.0 – 2.5
< 0.18
much more stable in water & acids

29. Properties of Calcium Hydroxide Liners
stronger
Properties of Calcium Hydroxide Liners
(MPa)
hard-setting
resin
compressive str (MPa) pH
9 – 10
9 - 10
both are basic; may be important to stimulating formation of reparative dentin.

30. Hard-setting calcium hydroxide
Liners ( mm):
Hard-setting calcium hydroxide
calcium hydroxide-containing resin composites
hard setting zinc oxide - eugenol
glass-ionomer cements
resin-modified glass-ionomer cements
Relatively weak & soluble. Does not stimulate reparative dentin as well as calcium hydroxide

31. Hard-setting calcium hydroxide
Liners ( mm):
Hard-setting calcium hydroxide
calcium hydroxide-containing resin composites
hard setting zinc oxide - eugenol
glass-ionomer cements
resin-modified glass-ionomer cements
Probably like RMGIs – more data is needed

32. Hard-setting calcium hydroxide
Liners ( mm):
Hard-setting calcium hydroxide
calcium hydroxide-containing resin composites
hard setting zinc oxide - eugenol
glass-ionomer cements
resin-modified glass-ionomer cements
Stronger than GIs; like GIs bond to dentin & enamel

33. Calcium hydroxide is associated with the most reparative dentin.
RMGIs are associated
with less reparative
dentin
Tertiary dentin is another term for “reparative dentin.”
Murray PE et al. (2001) Restorative pulpal and repair responses J Amer Dent Assoc132(4)

34. Calcium hydroxide liners have the least affect on the density of odontoblasts.
Remaining Dentin Thickness of 0.04 to 0.50 mm
Remaining Dentin Thickness of to mm
No cavity present.
Number of odontoblasts (mm2)
RMGIs reduce the odontoblast density
Murray PE et al. (2001) Restorative pulpal and repair responses J Am Dent Assoc132(4)

35. Hard-setting calcium hydroxide
Liners ( mm):
Hard-setting calcium hydroxide
calcium hydroxide-containing resin composites
hard setting zinc oxide - eugenol
glass-ionomer cements
resin-modified glass-ionomer cements
Less reparative dentin than calcium hydroxide; also reduces the number of odontoblasts

36. Classification of liners & bases:
thin liners (< 0.20 mm)
liners ( mm)
bases (> 0.75 mm)

37. zinc phosphate cements zinc polyacrylate cements glass-ionomer cements
Bases (> 0.75 mm):
zinc phosphate cements
zinc polyacrylate cements
glass-ionomer cements
resin-modified glass-ionomer cements
polyacid-modified composite resins
In the past, each of the above cements (and other cements too) has been used as a base under various restorative materials.

38. zinc phosphate cements zinc polyacrylate cements glass-ionomer cements
Bases (> 0.75 mm):
zinc phosphate cements
zinc polyacrylate cements
glass-ionomer cements
resin-modified glass-ionomer cements
polyacid-modified composite resins
Bases is rarely used today. Why?

39. Bases (why use has declined):
less need to protect pulp from restorative materials – materials are thought to be more biocompatible than in the past
experts now question the wisdom of placing a weaker material (the base) under a stronger material (the restorative material)

40. Bases (if you are going to use one) – desirable properties
strong immediately after placement
stronger when aged
stiff; does not flex

42. Compressive Strength at 7 Min
1.2 MPa needed to
resist condensation
stresses

43. Elastic Modulus
Zinc phosphate is the stiffest of these potential base materials. It is least likely to bend when the restorative material is under load.

44. End