3. Cavity Lining Materials Flashcards
Disadvantages of restorative materials (3)
May not make intimate contact with the tooth surface (any gaps may allow ingress of fluids and bacteria)
Heat released during setting or curing
Release of chemicals (pulpal irritants and lead to pain or pulpal damage)
Function of lining materials (2)
Prevents gaps
Acts as a protective barrier
Features of cavity base (3)
Thick mix placed in bulk
Dentine replacement used to minimise the bulk of the material of block out undercuts
More common in metal restorations
Features of cavity lining (2)
Thin coating (<0.5mm) over exposed dentine A dentine sealer able to promote the health of the pulp by adhering to the tooth structure or by an antibacterial action
Purpose of cavity liner (5)
Pulpal protection from chemical stimuli from unreacted chemicals in the filling material/initial pH of filling
Pulpal protection from thermal stimuli - exothermic setting reaction of composite or heat conducted through metal fillings
Pulpal protection from bacteria and toxins - micro leakage - the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls
Therapeutic - to calm down inflammation within the pulp and promote pulpal healing prior to/at the time of a permanent restoration being placed
Palliative - to reduce patient symptoms prior to definitive treatment being carried out. Most commonly in patients with irreversible pulpitis
Properties of lining materials (9)
Easy to use Thermal properties Mechanical properties Radiopaque Marginal seal Solubility Cariostatic Biocompatible Compatible with restorative materials
Ideal easy to use properties of lining materials (3)
Easy to mix
Long working time for easy placement
Short setting time - ideally command set
Ideal thermal properties of cavity lining materials (3)
Thermal conductivity should be low
Thermal expansion coefficient should be similar to dentine
Thermal diffusivity should be similar to dentine or lower
Definition of thermal conductivity
How well heat energy is transferred through a material (heat flow through a cylinder of unit cross-sectional area and unit length, with a temperature difference of 1C between the ends)
Units are Wm-1C-1
Examples of thermal conductivity (3)
Denture base should be high
Restorative material should be low
Cavity lining should be as low as possible
Definition of thermal expansion coefficient
Change in length per unit length for a temperature rise of 1C
Units are ppmC-1
Thermal expansion coefficient of enamel
8.3ppmC-1
Thermal expansion coefficient of dentine
11.4ppmC-1
Thermal expansion coefficient of GIC
11ppmC-1
Thermal expansion coefficient of RMGIC
20ppmC-1
Thermal expansion coefficient of composite
25ppmC-1
Thermal expansion coefficient of amalgam
25ppmC-1
Definition of thermal diffusivity
Similar to thermal conductivity but measured in cm2s-1
Thermal expansion coefficient of enamel
0.0042cm2s-1
Thermal expansion coefficient of dentine
0.0026cm2s-1
Thermal expansion coefficient of cavity liners
Similar/lower than enamel
Thermal expansion coefficient of amalgam
1.7cm2s-1
Ideal mechanical properties of cavity lining materials (2)
High compressive strength
YM/rigidity similar to dentine
Why is a high compressive strength required
To allow placement of filling without it breaking
Compressive strength of dentine
275MPa
YM of dentine
15GPa