direct restorative materials

Question 1

what is a composite

Answer 1

2 or more materials combined

Question 2

phases of composites

Answer 2

3 phases of composites:
Organic matrix – plastic monomer that polymerises –BisGMA normally

Inorganic filler – particles spread in the matrix that reinforce it
Can be macrofillers (poor finish due to big bumps),
hybrid (good for mechanical properties),
or microfillers (can be polished so very smooth but are weaker)

Coupling agent– promotes adhesion between filler and matrix – e.g. silane

Question 3

composite pros and cons

Answer 3

Composite pros:
Aesthetics
Less tooth tissues removed compared to amalgam
Command set if light cured

Composite cons:
Uncured resin can leach out
Long time to place since incremental curing needed
Polymerisation shrinkage can increase risk of secondary caries
Doesn’t adhere intrinsically to enamel and dentine

Question 4

Bonding of Composites

Answer 4

Enamel bonding -> wetting of enamel is impossible so we need to etch (enamel surface tension is lower).
(wetting allows thin and uniform layer)
30-50% phosphoric acid opens prism areas and then resin can flow inside and form resin tags (this allows chemical bonding!)

Dentine bonding -> you need 3 things in this order to bond:
Conditioner – acid that clears the smear layer (but opens tubules)
Coupling primer – acts as an adhesive
Sealer – bond that seals dentine tubules

Smear layer = denatured collagen and debris contaminated with bacteria

Question 5

what is a cavity lining material

Answer 5

= an intermediate restorative material that lines a cavity. It is applied before the restoration and is permanent.

Question 6

types of cavity lining materials

Answer 6

Cavity varnish 2-5μm – seals dentine, decreases microleakage, no strengthening purposes

Cavity liner <0.5mm– seals dentine, promotes pulp health, antibacterial action

Cavity base >0.75mm – thick mix placed in bulk, acts as dentine replacement, minimises need for lots of resto material, insulator, high strength

Question 7

how do cavity lining materials set

Answer 7

These set by acid-base cement setting -> this reaction is never complete.

Question 8

factors affecting set of cavity lining materials

Answer 8

Factors affecting set:
Particle size
Smaller the particle size, the greater the specific surface area and the faster the setting reaction.

Powder/liquid ratio
A higher powder content will give a faster set

Temperature
Increasing the temperature will increase the setting rate
The setting reaction is exothermic so it may further accelerate set

Moisture

Question 9

options for cavity lining materials/ cements

Answer 9

1. zinc phosphate cements
2. zinc oxide eugenol cements ZOE
3. zinc oxide non eugonel cements
4. zinc polycarboxylate cements
5. calcium hydroxide cements CaOH
6. ethoxy benzoic acid

from QB->
1. Water-based: Zinc phosphate, zinc polycarboxylate, GIC, RMGIC
2. Resin-based: Composites, compomers, RMGIC, Panavia
3. Temporary: Zinc oxide eugenol (ZOE)

Question 10

cavity lining materials/ cements

zinc phosphate cements

setting reaction | properties | uses

Answer 10

ZnO and phosphoric acid, p+l, exothermic setting reaction

Good strength
Quick hardening
Cheap
Good thermal insulator
Low initial pH so pulpal irritation
Brittle
No chemical adhesion

Used for luting cement for restos and ortho, thermal insulator, temporary resto material

Question 11

cavity lining materials/ cements

Zinc oxide eugenol cements

setting reaction | properties | uses

Answer 11

ZnO and eugenol, 2 paste

Fast set
Easy to mix
Not irritant
Good thermal insulator and protects pulp from chemical irritation
Low strengths
Potential allergy to eugenol
Can’t be used under composites since it inhibits vinyl polymerisation

Used as thermal insulating base ( protects tooth from thermal sensitivity)

Question 12

cavity lining materials/ cements

Zinc polycarboxylate cements

setting reaction | properties | uses

Answer 12

ZnO and polyacrylic acid

Low irritancy
Good chemical adhesion
Gains strength quickly
Lower compressive strength
Short working time

Used for luting and thermal insulating bases, ortho band luting

Question 13

cavity lining materials/ cements

Calcium hydroxide cements

setting reaction | properties | uses

Answer 13

2 paste salicylate ester and Ca(OH)2

Alkaline so neutralises acid materials
Antibacterial
Easy handling and mixing
Good seal
Low strength
Weakened by moisture

Used for cavity lining, thermal insulating and in endo

Question 14

ethoxy benzoic acid vs ZOE as a cavitity lining material

Answer 14

similar to ZOE but poor handling characteristics

Question 15

cavity lining materials/ cements

when would zinc oxide non-eugonal cements be used

Answer 15

for pts that are allergic to eugonal

euogenol = clove oil

Question 16

Composition and setting reaction of GICs

Answer 16

Composition
Powder – ionomer glass
Liquid – polyacrylic acid in aqueous solution

Setting reaction:
Dissolution – H+ ions from PAA attack glass and free other ions
Gelation and hardening – ions cause polymer chain entanglement
Final maturation – increase in strength

Question 17

pros, cons and uses of GICs

Answer 17

GIC pros:
Fluoride release
No free monomer
Aesthetics
No shrinkage

GIC cons:
Weaker than composites/amalgam
Poor wear resistance at early stage

GICs are used for anterior restorations, cavity linings, luting cements, fissure sealants

Question 18

list the modified GICs

Answer 18

GICs can be modified to make cermets, RMGIC, giomers, PAMCs:

Question 19

properties of cerments, giomers, pamc

Answer 19

Cermets = more abrasion resistant and less brittle but worse F release and bond strength

Giomers = composite resin + glass ionomer particles as filler – still has fluoride release with the better properties of composites

PAMC (compomer)= polyacid modified composites, inferior mechanical properties to composite and undergoes shrinkage, but good handling properties

Question 20

pros, cons, use of RMGICs

Answer 20

Pros -> good compressive strength, longer working time, less brittle
Cons -> shrinkage, unpolymerized HEMA leaching, swell in water after curing

RMGICs used for cavity linings, luting cements, restorative for primary teeth

Question 21

amalgam compition and mechanical properties

Answer 21

Amalgams = when mercury is mixed with another metal

Amalgams can be low copper (3%) or high copper (20%)

Mechanical properties -> good compressive strength, wear resistance, mercury content must be less than 50% for strength to be good

Question 22

disadvantages of amalgams

Answer 22

Non-adhesive (mechanical retention only)
Conducts heat and electricity (galvanic effects)
Poor aesthetics
Weak in thin sections
Marginal leakage can occur

Rule for UK – no amalgam for under 15s

Question 23

compare GIC and RMGIC

Answer 23

RMGIC
has better aesthetics
has ability to use bonding agent
has better wear, polish, strength

BUT RMGIC shrinks and has a medium thermal expansion coefficient

whereas GIC TEC matches the tooth

both release fluoride

Question 24

compare compomers and composite

Answer 24

all have good aesthetics and require bonding agents
they all have minimal fluoride release

composites can have macrofillers (poor finish due to big bumps), hybrid (good for mechanical properties), or microfillers (can be polished so very smooth but are weaker)

compomers are just modified GICs
polyacid modified composites, inferior mechanical properties to composite and undergoes shrinkage, but good handling properties

Question 25

compare composite vs amalgam

Answer 25

composites have better aesthetics and don’t soley rely on mechanical retention ˙.˙ bonding agents available

but amalgams have better wear, polish and stregth
they also shrink less
but have contraindications in children, pregnant etc ˙.˙ mercury