Dental acrylics 3 - Other room temperature cured acrylics

what dental acrylics are used in materials

why don’t we go

Don’t use propyl - too reactive

Further than butyl - (you want dentures to be rigid, longer CH2 chains the material becomes more flexible - used for soft lining material, want dentures to be rigid to replace the lost dentition the stresses from chewing on the bone - keeps the bone stimulated so less bone loss due to the pressure as you need bone to for dentures)

Methyl methacrylate is used because of its high Tg temperature

(Tg - going from rigid to soft material)

overall, RT have lower Tg than HC - need higher Tg than those enocuntered during use so it doesnt warm up adn flow

What are other cured acrylics? do we use PMMA/MMA?

These materials utilise another polymer powder in place of PMMA and a higher methacrylate monomer not MMA 

What is the polymer powder that is used?

the polymer powder used is a higher methacrylate - poly(ethyl methacrylate) PEMA - next relative to PMMA in the homologous series

How is it mixed with a higher molecular weight monomer?

it is mixed using the dough technique

What is the role of PEMA?

PEMA, like PMMA is used to reduce the shrinkage and exotherm of the final set material

What is PEMA formed from and how, does it take part in the reaction? 

it is a pre-polymerised ethyl methacrylate, - acts as a virtual filler - like PMMA and does not take part in the free radical polymerisation reaction - similarly to PMMA

What is important to note about the monomers that PMMA and PEMA can be mixed with?

• PMMA cannot be mixed with any other monomer - it can only be mixed with MMA - because it forms an incoherent gel and a poorly formed product 

• PEMA cannot be used with MMA monomer - results in an incoherently mixed product 

• PEMA can be used with several higher molecular weight monomers in place of MMA

(won’t get a paste)

PEMA can be used without a monomer in what situation?

tissue conditioners

What are the impacts of an incoherently mixed product?

• Detrimental effect on the physico-mechanical properties of the final product (appliance)

What is the Tg of PEMA  compared to PMMA?

Not used for making a denture - low Tg, only used in temporary appliances and not for making a full denture

What are some uses of PEMA? (7)

• Soft liners

• Tissue conditioners (RT)

  • Temporary crown and bridge materials

• Extension of impression trays and dentures

• Hard reline material 

• Denture lining (for allowing traumatised oral tissues to recover)

• Functional impression material

• Maxillofacial prothesis - obturator e.g

What are tissue conditioners?

temporary denture lining materials

what type of gel are tissue conditioners? what 2 properties do they have (hint in name)

Viscoelastic gels - exhibit both elastic and viscous behaviour on the application of stress 

What are the 3 components in a tissue conditioner?

PEMA powder (PMMA powder) + alcohol + plasticiser - no monomers

Tissue conditioners form a gel via what process?

Polymer chain entanglement and do not polymerise - remember no monomer is present

What is the main difference between a tissue conditioner and soft lining material ?

Soft liners contain a monomer while tissue conditioners don’t

Why is a soft lining material used?

a soft lining material is used to make the denture more comfortable for the patient

Dentures can cause patients persistence pain and discomfort, this is more common in which arch?

lower arch

Why ? (2)

The lower denture has a smaller surface area to distribute the load

also the patient could have sharp, thin or heavily resorbed alveolar ridges

What technique is used in soft lining material construction?

Dough technique to reduce overall shrinkage and exotherm of the material

What is the powder (4) and liquid (5) composition of RT cured soft lining materials based on PEMA?

Powder:

• PEMA powder (or butyl methacrylate/ethyl methacrylate - BMA/EMA)

• Benzoyl peroxide - initiator

• colour pigments

• opacifiers

liquid:

• Higher methacrylate monomers e.g ethyl, butyl, hexyl methacrylates

• phthalate or citrate plasticiser

• HQ - inhibitor

• DMPT - activator

• cross linking agent

Advantages of RT cured soft lining materials 

what type of material are soft liner

its adhesion to acrylic denture base?

what do plasticisers do?

(name 2 types of plasticiser)

how do they work?

• Soft lining material is soft, rubbery acrylic material

• it adheres well to the acrylic denture base since it contains acrylic groups

• Plasticisers reduce the glass transition temperature of the acrylic 

• aromatic ester or phthalate

plasticisers are an organic liquid that act as a lubricant, which seeps/flows between polymer chains and thus lowering/weakening the intermolecular forces between them - doesn’t take part in the free radical polymerisation reaction

Disadvantages of RT cured soft lining materials:

How much plasticiser should a soft lining material contain?

how does this impact the effectiveness of the soft lining material?

What is a disadvantage of a type of plasticier and is being replaced by another type?

• a soft lining material should contain as little plasticiser as it tends to leach out in the oral fluids

• with time, the material hardens

• little amount - limits the life of the soft lining material

• biocompatibility of phthalate based plasticisers

• many products now contain citrate-based plasticisers instead

What are temporary crowns and why are they used?

where are they made?

• Temporary crowns are used to protect the tooth after being prepared for a permanent crown

• they perform the functions of a natural tooth

• it can take several weeks before permanent crowns are put in place

• they are made at the chair side and placed on the prepared tooth while the permanent crown is made by a technician in the lab

What is the powder and liquid composition of RT cured temporary crown and bridge/extension materials

Powder:

• PEMA

• BP - initiator 

• colour pigments

• opacifiers

Liquid:

• Butyl methacrylate

• HQ - inhibitor

• DMPT - activator

• (no plasticisers or cross linking agent)

dough technique is still used

Not heat cured so temporary - so has to be replaced by a permanent crown

The butyl methacrylate can be 2 forms?

• n-butyl methacrylate - straight chain

• Iso-butyl methacrylate - higher Tg

What are the monomers in TCBs for PEMA and PMMA?

PEMA - mixed with BM

PMMA - mixed with MMA

Advantages of PEMA/BM compared to PMMA/MMA TCBs? (5)

• lower exotherm than PMMA/MMA : less heat - more comfortable for patient when setting in their mouth

• Much less pulpal and soft tissue irritancy from residual monomer

• Good handling properties

• Not brittle, a ductile material - PMMA/MMA is a brittle material

• BM a non-volatile monomer, MMA is a volatile monomer

volatile - you could tell from the smell far away 

What are especial acrylic resins - how are they cured and what do they contain?

• dimethacrylates

• light cured or room temperature cured resins (remember - 2mm curing depth)

What are 3 uses of these special acrylic resins?

• composite filling material

• temporary crown and bridge material

• fissure sealant 

What are 2 examples of dimethacrylates that can be used?

2 other things that may be included in the formulation of special acrylic resins?

• Bis GMA or urethan dimethacrylate

  • Pigments 

• Agents for light cure/RT (CQ)

What are some properties of special acrylic resins? (30

• high modulus

• low exotherm

• adequate polymerisation shrinkage

how are the light or RT cured dimethacrylates for TCBs dispensed and what are the 3 main components?

Delivery gun not powder and liquid, cartridge and mixing tip - One paste

Dimethacrylate

filler - amorphous silica that is silane treated with

(similar to composite formulation)

What are the constituents of special acrylic resins (6)

• bis GMA/urethan dimethacrylate

• diluents (viscosity of materail)

• fillers - silane coated

• pigments 

• camphorquinone - light activated

• DMPT

-one paste-

What are dimethacrylates?

They have 2 methacrylate groups - hydrophobic

What type of liquid is HEMA?

bifunctional (hydrophobic and hydrophilic end) and has low viscosity liquid

hydroxyethyl methacrylate

(dissolved in a solvent and used in primer to adhere composite to dentine)

When it polymerises what does it form in the dry state?

hard resin in the dry state

In water?

it becomes a soft and rubbery hydrogel

it absorbs 10-100% of water

What are its (HEMA) uses? (2, unsuccessful in?)

• unsuccessful as a soft liner material

• RMGIC’s and dentine bonding agents 

What are cyanoacrylates?

how fast do they polymerise and why?

how was it used? (2)

Uses in dentistry? (2)

• general adhesive

• polymerises very quickly at body temperature - absence of inhibitor

• non-suture wound repair material, pre-fabricated surgical implants or prostheses

• Perio surgery

• adhesive for dentine - bonds to collagen, endodontic cements

What happens to the cyanoacrylate monomer for polymerisation reaction? 

• In presence of moisture (blood), the monomer polymerises to form a poly(cyanoacrylate)

Medical grades of cyanoacrylates include 2 ?

• butyl and octyl cyanoacrylates

what are some adv for tissue adhesion used for wound closure of cyanoacrylates? (3)

• stop bleeding

• waterproof

• prevents bacteria from entering wound

when is full strength achieved?

within 24 hours,

What 2 thing fasten the cure?

• the higher the humidity

• thinner the bond-line 

Different acrylates in dentistry?

which has much more improved physico-mechanical properties? (HC/RT/LT)

• HC will have more improved physico-mechanical properties

the amount of monomer released depends on what?

depends on the method of curing - LC and RT result in more residuals

remember: 

be specific