Cavity lining materials
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What are disadvantages of restoratives
May not make intimate contact with the tooth surface (especially dentine) -Any gap may allow ingress of fluids and bacteria Heat released during setting/curing Release of chemicals -These may be pulpal irritants and lead to pain or pulpal damage
What can be used to prevent micro-leakage
Intermediate Restorative Material A lining material - Prevents gaps - Acts as a protective barrier
What is a cavity base
Thick mix placed in bulk Dentine replacement used to minimise the bulk of the material or block out undercuts More common in metal restorations (direct or indirect)
What is cavity lining
Thin coating (<0.5mm) over EXPOSED Dentine Van Noort ‘a dentine sealer able to promote the health of the pulp by adhering to the tooth structure or by an anti-bacterial action’
What is the purpose of a liner
Pulpal protection
What is the pulp needing protection from
Chemical Stimuli from unreacted chemicals in the filling material or the initial pH of the filling Thermal Stimuli. eg. exothermic setting reaction of composite or heat conducted through metal fillings Bacteria and Endotoxins. Microleakage – the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls.
Why is a liner placed
Therapeutic. To calm down inflammation within the pulp and promote pulpal healing. Prior to or 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 reversible pulpitis.
What is the thermal expansion coefficient
Change in length per unit length for a temprise of 1 degree
What is the thermal coefficient of enamel
8.3ppmdegrees
What is the thermal coefficient of dentine
11.4ppmdegrees-1
What is the thermal coefficient of amalgam and composite
25ppmdegrees-1
What is the thermal coefficient of GIC and RMGIC
GIC- 11 RMGIC - 20
How is thermal diffusivity measured
cm2/sec
What is the thermal diffusivity of enamel and dentine
E- 0.0042cm2/sec D- 0.0026cm2/sec
What is a marginal seal
The chemical bond of the lining to the dentine. Should be permanent and impenetrable
What are some properties of lining materials
Easy to mix Short setting time Low thermal conductivity Similar thermal expansion to dentine Lower or similar thermal diffusivity to dentine High compressive strength Radioplaque Low solubility
How do lining materials prevent secondary caries around the restoration
Cariostatic -fluoride releasing -antibacterial
What does biocompatible mean
Non-toxic Not damaging to the pulp -pH neutral -No excessive heat during setting Low thermal conductivity
Are lining materials biocompatible
yes
What materials are used as bases
Zinc Oxide based cements Glass Ionomer and Resin Modified Glass Ionomer cements Palliative cements
What materials are used for liners
Setting calcium hydroxide Glass Ionomer and Resin Modified Glass Ionomer cements
Who invented vitrebond
Sumita mitra
When should calcium hydroxide be used
Only when the cavity approaches the pulp (as a direct or indirect pulp cap)
What is the setting reaction for calcium hydrocide liner
a chelation reaction between the ZnO and the butylene glycol disalicylate