B) Self or cold or chemically cured acrylic resin

Dr. Waseem Bahjat Mushtaha

Specialized in prosthodontics

The chemistry of this resin is similar to that of the heat cured acrylic resin, except that the activation is by tertiary amine (e.g. dimethyl – Para – toluidine) rather than heat.

Polymerization reaction:

PMMA (polymer) + benzoyl peroxide (initiator)

+MMA (monomer) + dimethyl – para-toludin

) activation(

Additional polymerization

Polymer + heat

Heat cured acrylic Self cured acrylic

resin resin1(Activation By heat By chemical activator

) dimethyl-para-toludin

2(Residual (Less) 0.5% (More)

Monomer. (advantage)

3(Tissue Less (advantage) More

Irritation .

4(Molecular More Less

Weight(M.W)

5)Degree More LessOf polymerization

(D.P).

6)Strength. More (advantage) Less

7)Color stability More (advantage) Less, due to the presence of the

tertiary amine activator that effect

color stability.

8)Uses 1( Denture bases 2)Artificial teeth special trays.

Relining Repairing Rebasing

Manipulation and processing is the same as the heat cured type except that after packing and pressure for 2 hours, the dough is allowed to polymerize at room temperature rather than in a hot water bath

Recent advances in acrylic bases:

1(Pour type (fluid resins):

These have a composition similar to the chemically cured acrylic resin. The difference is that the pour type of denture resin have powder particles that are much smaller, and when they are mixed with monomer the resulting mix is very fluid. The mix is quickly poured into the mould and allowed to polymerize under pressure. Centrifugal casting has also been used to inject the fluid mix into the mould.

2(High impact strength resin

These materials are poly(methyl methacrylate) reinforced with rubber. The rubber particles

are grafted to methyl methacrylate so that they bond well to the heat cured acrylic resin. These materials are supplied in a powder – liquid form similar to the heat cured acrylic resins. They have greater impact strength than the conventional acrylic resins.

3(Rapid heat cured resins:

These are acrylics that are polymerized for 20 minutes in boiling water immediately after being packed in to a denture flask. The initiator is formulated to allow for rapid polymerization without the porosity than

one might expect .

4(Light – activated denture base resins:

These materials consist of a urethane dimethacrylate matrix with an acrylic copolymer and micro fine silica as fillers, and a photo initiator system. The photo initiator is activated by the same visible light source that is used for curing light – activated composites. For final polymerization, a special high energy light source is used. These materials are supplied in premixed soft sheets. The light activated denture base materials are an alternative choice for those patients who are sensitive to methyl methacrylate monomer.

Non Metallic Denture Base Materials

Introduction: a denture consists of:

a) Denture base.

b) Artificial teeth

A) Denture base: different materials have been used to construct denture base

Non metallic

1 (Old:I-Bakelite (phenol+formaldehyde).

It is too difficult to construct.II-Vinyl resin. It is weak.

III- Valcanite. It is of bad aesthetic.

Metallic

I- Gold alloy type IV.II-Cobalt chromium alloy

2 (Conventional:

Acrylic resins are the non metallic material of choice.

3 (Recent:

i-Visible light cured resin.

ii- Pour (fluid) resin.

iii- high impact strength resin.

iv-Rapid heat cured resin.

Advantages:

a) Good thermal conductivity.

b) Thinner.

c) Stronger.

Disadvantage:

a) Bad appearance.

b) Expensive.

c) High density.

b) Artificial teeth:

1 -Acrylic teeth:

More resilient, lighter in weight, better bonding to acrylic denture base and easily finished and polished.

2-Porcelain

The criteria of an ideal denture base material:

1 -Natural appearance.2 -High, strength (P.L., U.S., impact strength

and fatigue strength), stiffness and hardness.

3 -Good thermal conductivity to maintain healthy tissues.

4 -Low density to help denture retention.5 -Dimensionally stable and reproduce

surface details.

6 -Absence of odour, taste or toxic products.

7 -Good retention to other polymers, porcelain and metals.

8 -Radio-opaque to be seen in x-ray if swallowed.

9 -Easy to repair.

10 -Easy to manipulate.

11 -Good shelf life

12 -Inexpensive.

Acrylic resins are the most popular because they meet many of the required criteria, especially dentures made from acrylic resin as they are of natural appearance and of low density. More over, they are easy to process, inexpensive and easy to repair.