• Shrinkage of 21% occurs during the polymerization of the pure
• It is a hard resin with a Knoop hardness number of 18–20.
• Tensile strength is approximately 8500 pounds per square inch (600
• Modulus of elasticity is approximately 350,000 pounds per square
• It is soluble in organic solvents such as chloroform and acetone.
• Water absorption: 0.3% absorption is observed after 24 h, which is
reversible, if the resin is dried.
• Heat polymerization is preferred compared to autopolymerization
because of colour stability and also because of the presence of free
toxic tertiary amines in the latter.
• Compatible with most adhesive system and can be easily cleaned
• Duplicate prosthesis is not possible, because of mould destruction
• Water sorption – increased weight 0.5% after 1 week.
• Its use is doubtful in the movable tissue bed.
• Because of relatively high thermal conductivity, the patient may
complain of discomfort in cold climatic conditions.
Acrylic copolymers (palamed, polyderm)
These are soft elastic but are not widely accepted because of the
• These have poor edge strength.
• These are susceptible to degradation when exposed to sunlight.
• Processing and colouration is difficult.
• Completed restoration is often tacky and predisposing to dust
• J.M. Antonucci and J.W. Stansburry reported the new generation of
acrylic monomers, oligomers and macromers.
• These are thermal, chemical and photoinitiated.
• These can eliminate the shortcomings of traditional acrylic
PVC and copolymers (realistic, mediplast)
• It consists of a combination of PVC and plasticizer.
• PVC is a clear, hard resin. It is tasteless and odourless.
• Copolymers of vinyl chloride and vinyl acetate are more flexible but
less chemically resistant than polymethyl chloride.
• It darkens when exposed to UV light and heat.
• It requires heat and light stabilization to prevent discolouration
• Polyvinyl acetate is stable to light and heat but has an abnormally
low-softening point (35–40°C).
• It is a PVC compound and solidifies into a flexible material when
• It is easy to handle and is ideal for an inexperienced person using
• It is flexible and provides acceptable initial appearance.
• It is available in a wide variety of colours to match the patient’s skin
• Staining can be achieved both internally and externally. Ferrous
pigments incorporated into the mixture give the long life and the
• Migration of plasticizer leads to discolouration and hardening of
• These can be stained easily when exposed to UV light, peroxides
• These lack lifelike translucency and tend to absorb sebaceous
secretions, cosmetics and solvent.
• Edges, if thin, tear easily and may be reinforced with nylon fabric.
• These require metal moulds, as they polymerize at high
Chlorinated polyethylene (CPE)
• D.H. Lewis and D.J. Castleberry tested and found this material to
be similar to PVC in both chemical composition and physical
• The processing procedure involves high-heat curing with
pigmented sheets in metal moulds.
• The system consists of the industrial CPE which is blended with
additives – low-density polyethylene, calcium stearate and soya
• The mechanical properties of formulated material are good.
• No chemical reaction is involved in fabrication.
• Material is relatively cheap.
• Disadvantage: Metal moulds are required for fabrication, as they
polymerize at high temperatures.
Polyurethane elastomers (Epithane-3)
• Polyurethane elastomers contain a urethane linkage.
• In the presence of catalyst, isocyanate combines with a hydroxyl
• Varying amount of isocyanates will change the physical properties
• These have excellent properties such as elasticity and ease of
• Deficiencies are moisture sensitive leading to gas bubbles and cause
• Epithane-3 is a commercially available four-component system.
• These can be made elastic without compromising the strength at the
• Their flexibility made them to be used on movable bed.
• These can be coloured extrinsically and intrinsically.
• Superior cosmetic results can be obtained.
• These are durable and resemble the living tissue.
• These are difficult to process consistently.
• Isocyanate is moisture sensitive.
• Water contamination is difficult to control and leads to gas bubbles.
• These are not colour stable.
• These have poor compatibility with adhesive systems.
• Clinical usefulness is less than 6 months.
• Isocyanate is a toxic compound and can cause local irritation.
• Cleaning of adhesive from prosthesis can be difficult for the patient.
The silicones were introduced in 1946 and are one of the most widely
used materials for facial restorations.
• They consist of alternate chains of sodium and oxygen which can be
modified by attaching various organic side groups to the silicone
atoms or by cross-linking the molecular chains.
• G.W. Barnhart (1960) was the first to use silicone elastomers for
• These are a combination of organic and inorganic compounds.
• Chemically, polydimethyl siloxane (PDM) combines with water to
• These polymers are translucent, watery and white fluids, whose
viscosity is determined by the length of polymer chain.
• PDM is commonly known as silicone.
• Additives are added to give colour and fillers provide strength.
• Antioxidants and vulcanizing agents are used to convert the raw
mass from plastic to a rubbery resin during processing.
• The process of cross-linking of polymers is referred as
vulcanization. It can occur with or without heat and is dependent
on the catalyst or the cross-linking agent used.
On the basis of their application
(i) Class I: Implant grade, which requires the material to undergo
extensive testing and must meet the FDA requirements.
(ii) Class II: Medical grade, which is approved for external use. This
material is used for the fabrication of maxillofacial prosthesis.
(iii) Class III: Industrial grade, which is commonly used for industrial
HTV (heat vulcanizing silicones)
• These involve the use of a diorganopolysiloxane (e.g. PDM).
• The vulcanizing agent is benzoyl peroxide.
• The filler added to the polymer is finely divided silica with particle
• Amount of filler added to the polymer can be varied depending on
the requirement of strength, hardness and elongation.
• There is more intense mechanical milling of the solid HTV
elastomers compared with the soft putty RTV silicone.
• Silastic 370, 372, 373, 4-4514, and 4-4515 are white, opaque materials,
• Catalyst or vulcanizing agent of HTV is dichlorobenzoyl peroxide or
• These exhibit excellent thermal stability and are biologically inert
• PDM may be added to reduce the stiffness and the hardness of the
• Silastic S-6508 is in raw state which is similar to sticky modelling
clay. It must be vulcanized at high temperatures and is formed in
• Silastic 399 resembles white Vaseline in its raw state. It is easily
• Not adequate elasticity in function
RTV (room temperature vulcanization silicones)
• These are composed of comparatively short-chain silicone polymers
which are partially end blocked with hydroxyl groups.
• Filler: Diatomaceous earth particles.
• Cross-linking agent: Orthoalkyl silicate.
• These are available as clear solutions that enable the fabrication of
• RTV silicone is blended with suitable earth pigments to produce the
• These are biologically inert.
• These retain physical and chemical properties at wide range of
• These are easier to process.
• These have poor edge strength
• Cosmetic appearance of the material is inferior to other materials.
• Less chances of air bubble entrapment, because hand mixing of
catalyst with the elastomer is avoided.
• Increased tear strength, mechanical durability and chemical
It is a medical grade silicone rubber material.
• It is in the form of thick white liquid. When combined with
organometallic catalyst, it vulcanizes without the use of heat or
• Dibutyltin dilaurate will prolong the vulcanization time and will
cause skin irritation unless prosthesis is washed thoroughly.
• Working time varies from 2 to 60 min by adjusting the catalyst.
Thinner is added to the catalyst to increase accuracy (thinner can be
added 10% of weight without noticeable changes in the prostheses).
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