Classification Of Denture Liners

Question 28. Classify denture lining materials and elaborate on permanent and temporary denture liners.
Answer:

Temporary denture liners The material may be classified as follows:

• Permanent lining materials

1. Heat-cured acrylics
2. Cold-cured acrylics
3. Light-cured acrylics
4. Plasticized acrylics
5. Silicones
6. Polyolefins
7. Phosphazines
8. Silastics

Read And Learn More: Complete Dentures Question and Answers

Temporary denture liners Temporary relining materials

1. Tissue conditioners
2. Functional impression materials.

Temporary denture liners Permanent Lining Materials

• Long-term soft lining materials distribute stress more evenly and absorb impacts that can arise from masticatory function. They can therefore be said to have a shock-absorbing or cushioning effect.
• Long-term soft lining to a complete lower denture improves the ability to bite and chew and provides a general improvement in comfort when compared with hard relines.

Temporary denture liners Indications for use

1. Persistent pain under a denture.
2. Thin atrophic mucosa.
3. Para function.
4. Replacing an existing denture, having a soft liner.
5. Sharp bony ridges or spicules on which the denture-bearing mucosa, in essence, becomes impaled.
6. Superficially placed mental nerve.

Temporary denture liners Types of Permanent Lining Materials

Silicone rubber or soft acrylic. The silicone materials may be cold-curing or heat-curing. Soft acrylics are heat-curing; cold-curing soft acrylics are only used as temporary soft liners.

Temporary denture liners Acrylic Resin Materials

Composition

Composition Polymer: Can be either poly (ethyl methacrylate) or poly (methyl methacrylate)/poly butyl methacrylate

Composition Monomer: Can be methyl methacrylate, N-butyl methacrylate or a combination of ethyl acetate and methyl methacrylate.

Composition Plasticizers: Butyl phthalate butyl glycolate, di-n-butyl glycolate, or 2 ethylhexyl-diphenyl phosphate.

Most of the materials use polymethylmethacrylate or polymethylmethacrylate as the basic polymer. The materials are heavily plasticized to create softness.

Composition Manipulation

Available as powder and liquid. A 2:1 or 1.5:1 polymer/monomer ratio is taken normally.

Composition Disadvantages

1. Water solubility is high.
2. Bacterial growth and fungal growth are prevalent.
3. Color changes are marked with these materials.

Composition Plasticized Vinyl Acrylics

The composition of vinyl acrylics is similar to acrylics except that the vinyl major function groups are present. They have a higher concentration of plasticizer that is in the range of butyl phthalate butyl glycollate in the concentration of about 58.8%.

Composition Properties

• Tensile strength: 20-37 kg/cm 2
• Percent elongation: 250-280
• Hardness shore A number: 35-55
• Tear resistance: 5-11 kg/ cm.

Composition Visible Light Cure Resins (VLC)

• Polymerization shrinkage for each of the three materials is nearly equal in value.
• The tensile strength for VLC resin was slightly higher than the values for HC and AP acrylic resin.
• The transverse deflection values at 3500 and 5000 g showed that the deflection of the VLC resin was less than that of the HC and AP acrylic resin materials, indicating that VLC resin is comparatively stiffer.
• The elastic modulus (bending) was slightly higher than in HC and AP acrylic resin.
• Dimensional changes were evaluated by fabricating VLC, HC, and AP bases on identical casts with metal markers in five locations. After 10 days in water, the AP resin shows a +0.05% expansion from ridge crest to ridge crest but no expansion was seen with HC or VLC.

Composition Phosphazines

These materials have higher bond strengths than other materials.

Composition Manipulation

Available as tube base and catalyst. Two equal lengths of catalyst and base are taken in a glass slab and mixed so that uniform color is obtained.

Composition Properties

• Tensile strength: 37 kg/cm 2
• Percent elongation: 240
• Hardness shore A number: 50
• Tear resistance: 9 kg/ cm.

Composition Cold-curing Silicone Rubber Materials

Composition

• Polymer Alpha dihydroxy end blocked poly (dimethyl siloxane) whereas the catalyst may be tri ethoxy silanol, ethyl polysilicate, Tetraethoxy silane, methyltriacetoxy silane, Acryloxyalkyl silane.
• Catalyst Dibutyl tin dilaurate, stannous octoate, moisture, or heat with benzoyl oxide. commonly used catalyst, dibutyl tin dilaurate, has been found to be a mucosal irritant.

Composition Manipulation

Available as tube base and catalyst. Two equal lengths of catalyst and base are taken in a glass slab and mixed so that uniform color is obtained.

Composition Properties

• Tensile strength: 25–44 kg/cm 2
• Percent elongation: 325–340
• Hardness shore a number: 25–45
• Tear resistance: 5–7 kg/cm.
• The abrasion resistance of these materials is poor.
• Heat-cure Silicone Rubber Materials

Composition

• Polymer Alpha dihydroxy end blocked poly (dimethyl siloxane)
• Catalyst Acryloxyalkyl silane.
• The adhesive used with this is gamma methacryloxypropyl trimethoxysilane.

Composition Manipulation

Available as tube base and catalyst. Two equal lengths of catalyst and base are taken in a glass slab and mixed so that uniform color is obtained.

Composition Properties

• Tensile strength: 25–48 kg/cm 2
• Percent elongation: 325–400
• Hardness shore a number: 25–50
• Tear resistance: 11–14 kg/cm.
• Water absorption of these materials is low.
• Dimensional stability is improved and the accuracy of fit is good.

Composition Recent Advances

A soft denture liner is made from an envelope covered with a polyethylene film which is filled with a viscous silicone liquid allowing continuous adaptation of the denture base.

Composition Temporary Lining Materials

Composition Tissue conditioners Plasticized acrylics

Tissue conditioners are soft elastomers used to treat an irritated mucosa supporting a denture. These materials will conform to the anatomy of the residual ridge, gel in that position, and continue to flow slowly after application. They are used only for short-term applications and should be replaced every 3 days. Supplied as powder/liquid or ready sheet forms.

Composition

Powder Polymethylmethacrylate or copolymers of polyethylene/methyl methacrylate. Liquid—A mixture of an aromatic ester, such as dibutyl phthalate which acts as a plasticizer, and Ethyl alcohol.

Composition Properties

• Hardness 13 to 49 shore A hardness units 24 hours after mixing.
• They show a loss in weight due to the loss of alcohol and become harder over a period of time.
• Easily deformed When a stress of 200 gm/cm 2 is applied 15 minutes after the set of the material, the compression will range from 60 to 83% of the original length.
• Those materials with a low alcohol content exhibit good dimensional stability for the first few hours after mixing.
• Viscoelastic and elastic behavior, cushions the cyclic forces of mastication and bruxism. Viscoelastic behavior can be modified by altering the powder/liquid ratio.