acrylics, liners and conditions

Question 1

formation of acrylics

Answer 1

PMMA polymer powder
+
MMA monomer liquid

mixed with dough technique (add powder to liquid slowly with no mixing until powder dissolves. then mix and leave to rest in screw top jar so it doesnt evaporate)
allows MMA to polymerise
polymerisation reduces shrinkage from 21 to 7%

acrylics can be heat cured or room temp cured

Question 2

storage of MMA

Answer 2

MMA stored in dark glass bottle to extend shelf life (stops spontaneous polymerisatoon by light)
volatile, highly flammable and distinct smell

Question 3

affect of powder: liquid ration on acrylics

Answer 3

If too much powder – weak + porous result

If too much liquid – increased shrinkage so alters denture fit

Question 4

components and use of heat cured acrylics

Answer 4

Components
Powder
PMMA
Benzoyl peroxide – initiator to activate the polymerisation when heated
Colour pigments
Opacifiers
Liquid

MMA monomer
Cross-linking monomer – improve crack resistance
Hydroquinone – inhibitor to extend shelf life

Uses – denture bases, artificial denture teeth, special trays, ortho appliances

Question 5

components and use of room temp cured acrylics (the main one)

Answer 5

Components
Powder
PMMA
Benzoyl peroxide – initiator
Colour pigments
Opacifiers
Liquid

MMA monomer
Cross-linking monomer – improve crack resistance
Hydroquinone – inhibitor to extend shelf life
DMPT (N,N-dimethyl-p-toluidine) – activator

Uses – soft liners, denture repairs

Question 7

advantages and disadv of RT over HC acrylics

Answer 7

Advantages of RT over heat cured
Cheaper
Less technician time
Can be done at chairside

Disadvantages of RT over heat cured
Physically weaker
More monomer so more leaching + hypersensitivity
Poor colour stability
Lower Tg
Porosity
More prone to water uptake

Question 8

list other rt cured acrylics

Answer 8

main one is PMMA/MMA -> soft liners, denture repairs

• PEMA/ Butyl methacrylate -> soft lining materials, tissue conditioners, temporary crown/bridges.
• light cured/RT dimethacyrlates -> one paste acrylic used for temporary crowns/bridges
• HEMA -> low viscosity liquid monomer that forms a hard resin when polymerised, unsuccessful as a soft lining materials but used in bonding agents and RMGICs.
• Cyanoacrylates -> used as general adhesive and some prostheses

Question 9

Advantages of PEMA/BM over PMMA/MMA

Answer 9

Lower exotherm
Less irritancy from residual monomer
Ductile
Good handling properties

Question 10

what is a long term soft lining material and its function

Answer 10

= material that can last in mouth for at least 4 weeks for patients who cannot tolerate rigid denture base material

Functions:
Distribute masticatory forces evenly
Absorb some of the masticatory forces
Relieve mucosa from this mechanical stress

Question 11

ideal properties of a SLM

Answer 11

Non-irritant
Adhesion to PMMA denture
Not support candida growth
Permanently compliant and resilient
Easy to clean
Not affected by denture cleaners

Question 12

disadvantages of using a SLM

Answer 12

expensive, difficult to modify or polish, more prone to fracture

Question 13

types of SLMs

Answer 13

Heat cured – addition silicone
RT vulcanised cured – condensation silicone
RT vulcanised cured – addition silicone
Heat cured – soft acrylic

Question 14

when are temporary SLM used

Answer 14

used to promote healing of irritated mucosa caused by ill-fitting dentures. It also absorbs some energy from masticatory forces.

Question 15

composition of temporary soft lining materials

Answer 15

soft rt cure acrylic used

PEMA/BMA or PMMA/MMA

Question 16

pros and cons of temporary SLM

Answer 16

Pros -> compliant/soft, bonds to PMMA base material, can be used chair side

Cons -> only last 2-3 weeks, residual monomer can cause irritation, difficult to remove from denture

Question 17

Difference between temp SLM and tissue conditioner

Answer 17

Similar composition to tissue conditioners but these are the differences:

Temp acrylics contain a polymerizable monomer
These set by free radical addition polymerisation
These last longer than tissue conditions

Question 18

what are tissue conditioners and its uses

Answer 18

Tissue conditioners = soft materials similar to temp soft cold cure acrylics

Tissue conditioners are used for
Treating denture related stomatitis
Denture liners
Impression materials (created as pt wears provisional denture)
Piezographs (impression of tongue/lips/cheeks)

Question 19

pros and cons of tissue conditioners

Answer 19

Pros -> compliant/soft, bonds to PMMA base material, can be used chair side
Cons -> only last 2-3 days, harden in mouth, difficult to remove from denture, possible leaching of plasticiser

Question 20

composition of tissue conditioners

Answer 20

powder
1. PEMA
2. BM/EM

liquid
1. Plasticiser
2. ethanol 6-15%

Question 21

how do tissue conditioners set

Answer 21

Tissue conditions set via gelation (alcohol swells the polymer beads, plasticisers lets polymer chains move, chains entangle and form a gel)

Things that will increase rate of gelation: more powder, higher temperature, lower molecular weight of polymer, more ethanol

Question 22

when do you use a tissue conditioner over a temp SLM

Answer 22

Which to use??
If mucosa will recover within a week -> use tissue conditioner
If lots of irritation and pt cannot come in every 3 days -> use temporary soft lining material