cavity lining materials

• composite resin • glass ionomer • amalgam • precious metal • ceramic

• may not make intimate contact with the tooth surface (especially dentine) = gaps allow ingress of fluids and bacteria • heat is released during curing/setting reaction • release of chemicals = may cause pulpal irritation and lead to pain or pulpal damage, often happens if not cured well • micro leakage = when doesn’t bond well and gaps form

• intermediate restorative material - a lining material = prevents gaps, acts as a protective barrier

• below the restorative material at the base of the cavity, protects the pulp

• a thick lining (lining and base are the same thing)

• a thin base (lining and base are the same thing)

• 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

• 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

• pulpal protection • therapeutic • palliative • want something bond to surface of tooth and be impenetrable

• chemical stimuli = form unreacted chemicals in the filling material or the initial ph of the filling • thermal stimuli = exothermic reaction of composite or heat conducted through metal fillings • bacteria and endotoxins = micro leakage, the penetration of oral fluids and bacteria and their toxins between restorative material and the cavity walls

• to calm down inflammation within the pulp and promote pulpal healing prior to or at the same time of a permanent restoration being placed

• to reduce patient symptoms prior to definitive treatment being carried out • most commonly in patients with reversible pulpitis

• easy to mix = if it was made difficult then a mess would be made of it • working time should be long enough to allow easy placement • setting time is short = but ideally would want on command set which we don’t have yet

• should be low • denture bases should be high, restorative material should be low, cavity lining as low as possible • want as little heat as possible going to pulp (especially under metal restoration)

how well heat is transferred through a material • heat flow through a cylinder of unit cross-sectional area and unit length, with a temperature difference of 1 degree between the ends • units are W/m-1/oC-1

change in length per unit length for a temperature rise of 1oC - units are ppmoC-1

• ideally a liner should match the thermal coefficient of the tooth • enamel = 8.3 ppmoC-1 • dentine = 11.4 • GIC = 11 • RMGIC = 20 • composite and amalgam = 25 (not very good)

similar to conductivity - measured in cm2/second

• similar to dentine or lower • ideally at least as low as tooth - enamel = 0.0042, dentine = 0.0026 • all commercially available liners have a similar or lower thermal diffusivity than tooth enamel • amalgam is 1.7cm2/sec (500 x more than dentine)

• high compressive strength = needs to be as filling going to packed on top so needs to not break (dentine around 275MPa) • modulus similar to dentine = around 15GPa, if material bent too much bond would eventually break and restoration would fracture

yes

• should be easy to see difference between lining and tooth - makes it easier to see if there if any leakage or secondary caries

• ideally lining should form a chemical bond to dentine - bond should be permanent and impenetrable

low