Cavity bases

Question 1

Define intermediate restorative materials (IRMs)

Answer 1

Materials applied to dentine to protect pulp prior to placing main restorative material

Question 2

What is a varnish?

Answer 2

A very thin polymer seal to dentine surface

Question 3

What is a cavity liner?

Answer 3

A layer of protective dentine sealer less than 500 um (0.5mm) thick

Question 4

What is a cavity base?

Answer 4

A dentine replacement intended to eliminate undercuts or minimise bulk of main restorative material

Question 5

What do IRMs do?

Answer 5

Most provide some form of protective function in addition to other functions to stop the pulp from getting damaged

Question 6

What might adversely affect the pulp?

Answer 6

Physical: e.g. T or mechanical forces
Chemical: e.g. acids
may be related to:
-caries, microbial ingress or contamination
-miscellaneous (e.g. thermal or electrical stimuli)

Question 7

Clinical need for IRMs

Answer 7

Intended to restore some of the protective barrier functions of enamel and dentine
-some direct restorative dental materials may themselves be irritant to the pulp

Question 8

Properties of an ideal cavity base or liner

Answer 8

• Safe and biocompatible
• Forms effective dentine seal against chemicals, bacteria and other stimuli
• Encourages reparative dentine
• Chemically and mechanically compatible with other restorative materials
• Tooth coloured, radiopaque and easy to place

Question 9

What materials are used as IRMs?

Answer 9

Varnishes
Calcium hydroxide cements
Zinc oxide cements
GICs
Resin modified GICs
Visible light cured resins

Question 10

What is a cavity varnish made out of?

Answer 10

Natural or synthetic polymer resins dissolved in a solvent

Question 11

How do you apply cavity varnish?

Answer 11

Applied to cavity floor with brush or cotton

Question 12

What happens after applying cavity varnish?

Answer 12

Solvent evaporates to leave thin layer of resin (process may be repeated)

Question 13

What is the function of a cavity varnish?

Answer 13

Acts as barrier against chemical penetration of tooth tissue
May protect against microleakage and secondary caries

Question 14

How are calcium hydroxide cements prepared?

Answer 14

Rigid self-setting material

Two pastes for mixing, chelation reaction forms zinc and calcium disalicyate and other compounds

Question 15

What pH are calcium hydroxide cements? What does this do

Answer 15

Alkaline nature due to free Ca(OH)2

May promote secondary dentine as well as provide antibacterial properties

Question 16

Calcium hydroxide cement properties

Answer 16

Low compressive strength (20MPa)
-sufficient to withstand condensation of amalgam
Initial pH > 11
-associated with tissue necrosis that may later mineralise –> reparative dentine

Question 17

What is the UK’s leading brand of calcium hydroxide cement?

Answer 17

Dycal
Mixing time 10s
Working time 2min20s
Setting time 2.5-3.5 mins
Radiopaque, ivory colour
Some say stimulation of secondary dentine

Question 18

How are ZOEs formed?

Answer 18

Generally by acid-base reaction between metal oxide and eugenol
Forms metal eugenolate chelate

Question 19

What are ZOEs used for?

Answer 19

Most commonly temporary restoration

Some developed for use as base/ liner

Question 20

Are ZOEs popular as bases or liners?

Answer 20

Increasingly unpopular
Risk of pulpal necrosis
Inhibition of composite resin polymerisation

Question 21

What is IRM (brand) used for?

Answer 21

Intermediate restoration designed to remain in place for up to 12 months
Or for use as base under non-resin restoration
ZOE

Question 22

Properties of GICs

Answer 22

Relatively durable (compressive strength >50 MPa)
Insoluble
Fluoride releasing
Aesthetic
Adhesion to mineralised tooth tissue

Question 23

What are GICs composed of?

Answer 23

Basic fluoroaluminosilicate glass
Polymeric acid
Water and
Tartaric acid

Question 24

How are GICs formed?

Answer 24

After mixing by acid-base reaction

Metal cations form salt bridges with ionised carboxylic acid gps on high molecular weight polyacids

Question 25

Phases of GIC reaction

Answer 25

Dissolution (acidic attack of glass surface)

Gelation (early cross-linking by CA++) Hardening (substitution of Ca++ by Al +++)

Question 26

Structure of a GIC

Answer 26

Composite biomaterial of acid-degraded glass particles set in a cross-linked hydrogel matrix

Question 27

What is a resin-modified GIC?

Answer 27

Like GIC but with addition of water miscible monomer (HEMA) and a photoinitiator

Question 28

How are RMGICs formed?

Answer 28

Acid-base reaction and photo-polymerisation

Shares chemical bond to untreated dentine

Question 29

What are unfilled resins used for?

Answer 29

Increasingly popular to seal dentine surface in a cavity

Question 30

How are unfilled resins formed?

Answer 30

Methacrylate monomers and photoinitiator to provide command set (via polymerisation)
May be layered to increase the thickness of resin seal

Question 31

Future trends for IRMs

Answer 31

Mineral trioxide aggregate increasingly considered for pulp capping
-claims to stimulate reparative dentine with good preservation of pulp vitality

Question 32

What is Biodentine from Septodont?

Answer 32

Portland cement which sets through complex dissolution and re-precipitation
-used in pulp capping

Question 33

What are the potential clinical benefits of Biodentine?

Answer 33

-Seal dentine = reduced microleakage = < sensitivity
-Thermal insulation = < sensitivity
Mechanical protection = better supported restoration
-Maybe reparative dentine formation