Dental Materials Used In Prosthodontics Introduction
Various dental biomaterials are used in prosthodontic procedures. One should identify and know their use as dental material. This chapter gives brief idea about various dental biomaterials used in prosthodontic clinical and laboratory procedures. Dental materials are broadly divided here into three categories for easy understanding as gypsum products, impression materials, processing materials, etc.
Table of Contents
Dental Biomaterials
Dental Plaster (Type-I Gypsum Product) Impression plaster is modified dental plaster used for making impression of edentulous arch. Not in used widely. It has low strength. Water-powder ratio is 0.50–0.75.
Read and Learn More: Preclinical Prosthodontics Notes
Dental Plaster (Type-II Gypsum Product):
Dental plaster is used for making primary cast/diagnostic cast. It is used for mounting casts on articulator and also used for flasking procedure. It consists of irregular, porous beta hemihydrate particles of calcium sulfate. It has low strength compared to dental stone. Usually white in color. Water-powder ratio is 0.45–0.50.
Dental Stone (Type-III Gypsum Product):
It is used for making master casts and for flasking procedures. It consists of regular, crystalline alpha hemihydrate particles of calcium sulfate. It is available in various colors. Water-powder ratio is 0.28–0.30.
Die Stone (Type-IV Gypsum Product):
It is widely used die material. Used for making die of prepared tooth/teeth. It has high strength and abrasion resistance. It has finer particle size. It is available in various colors. Water-powder ratio is 0.22–0.24.
Investment Material (Type-V Gypsum Product):
It is used for investment of wax pattern and casting them into metal. It consists of powder and silica suspension. It has high strength and high expansion. It can withstand high temperature. Water powder ratio is 0.18–0.20
Note: Water-powder ratio: This indicates recommended proportion of gypsum product to be mixed with water. It indicate required amount of water per 100 g of powder (gypsum product). For dental plaster, it is 0.45–0.50. This means 45–50 mL of water is needed to mix 100 g of dental plaster to achieve optimum mix and properties.
Impression Materials
Impression Materials In Dentistry
Variety of impression materials are available to be used in dentistry.
Impression Compound:
It is used for making primary impression of edentulous arches. It is rigid impression material. It is thermoplastic in nature, changes consistency according to change in temperature. It consists of wax, resin, fillers, and coloring agent. It is available in various colors. The American Dental Association (ADA) specification number is 3.
Zinc Oxide Eugenol Paste:
It becomes rigid after set. It is used for making final impression of edentulous arches. It is also used for bite registration. Thermosetting in nature, there is no effect of temperature
once it is set. It is available in two pastes system. It sets by chelation reaction and forms chelate as zinc eugenolate. It contains eugenol which causes burning sensation and allergic reaction in some patients. ADA specification number is 16.
Agar-agar (Reversible Hydrocolloid):
It is elastic impression material. It is reversible hydrocolloid. For making impression of dentulous and partially edentulous arches. It is also used for duplication of cast. Specially designed trays called as rim locked watercooled tray are used for agar impression. Special equipment called as “conditioning unit” is required for manipulation of agar.
Alginate (Irreversible Hydrocolloid):
It is elastic impression material. It is irreversible hydrocolloid. For making impression of dentulous, partially edentulous, and complete edentulous arches. It is natural product generated from seaweed. Main ingredient is sodium alginate, potassium alginate, or triethanolamine alginate. Manipulation is done with rubber bowl and curved spatula. Chromatic alginate is also available which indicates color changes at different working and setting stages. Water-powder ratio is 16 mL water and 38 g of powder. ADA specification number is 18.
Addition Silicone Impression Material:
It is nonaqueous elastomeric material. It is hydrophobic in nature but can be converted in hydrophilic by adding surfactants. It is also known as polyvinyl siloxane or vinyl polysiloxane. It is available as reactor and base. It reacts by addition reaction. It gives most accurate surface reproduction. It is available in various consistencies like putty consistency, light body consistency, etc. Light body consistency has less filler particles and more flow. Putty consistency has more filler particles and less flow. Used for making impression for fabrication of fixed prosthesis. It can be used for border molding also. ADA specification number is 19.
Dental Waxes – Modeling Wax
It is also known as baseplate wax. It is widely used in prosthetic work for making wax rims, trial denture bases, making maxillofacial patterns, and for bite registrations. It can be used for spacer and blocking the undercut on the cast. It is available in three types as type-I soft, type-II medium, and type-III hard. Consist of paraffin wax, resins, and carnauba wax. ADA specification number is 24.
Sticky Wax
It is made up of beeswax, paraffin wax, and resin. The resin gives the sticky wax its adhesiveness and hardness. It is very sticky when heated. It is used to join broken parts of prosthesis before repair. Become firm and brittle when cooled. It is also used to stabilize components while soldering. It should break under pressure rather than bending or distort.
Prefabricated Patterns For Cast Partial Denture
Wax patterns in preformed shapes are available as ready to use for making pattern of cast partial dentures. Available as various component patterns as major connector, minor connector, circumferential clasps, and bar clasp.
Inlay Wax
It is available as type-I medium wax and typeII soft wax. Used for making inlay pattern by direct and indirect method. Medium wax is used for direct technique and soft wax is used for indirect technique.
Pattern Wax
Available as body wax, margin wax, and occlusal wax, all three have different flow and consistency. It is used to make wax patterns for crown and bridge. Margin wax is usually red in color with good flow and hard in consistency. Body wax has medium flow and occlusal wax is soft that is desired property to carve occlusal anatomy.
Denture Base Resin Introduction
The acrylic resins used in prosthodontics are polymers. The process by which they are processed is known as “polymerization”. Acrylic resin can be classified by its method of processing or curing. According to processing/curing method, they are classified as heat-cured acrylic, self-cured acrylic, and light-activated acrylic resin.
Self-Cure Acrylic Resin
It is available as powder and liquid. It is also known as cold cure or autopolymerizing resin. It is used to make denture base, custom tray, relining, temporization, denture repair, and orthodontic appliance. Activator is dimethylpara-toluidine.
Heat-Cure Acrylic Resin
It is available as powder and liquid. Activator is heat supplied in water bath. Mainly used for making removable prosthesis. Available as clear, pink, fiber reinforced, and high impact material. Appreciate fibers in fiber reinforced acrylic.
Light-Cure Acrylic Resin
It consists of urethane dimethacrylate matrix with an acrylic copolymer, silica filler, and camphorquinone-amine photoinitiator system. It is supplied as premixed sheets. Unpolymerized material has clay-like consistency. It is supplied in tight opaque packages. Polymerization is done by blue light of 400–500 nm wavelengths.
Note: Microwave-cured denture base resin: This type of material is polymerized by microwave energy. It requires special plastic flasks which can be used with microwave. Polymerization time is only 3 minutes. Polymerization can be done in household microwave ovens.
Alloys And Dental Ceramic
Nickel-Chrome Alloys
These are used for making all metal restorations. Altering the metal, like cutting,
finishing, and polishing is difficult and time consuming due to hardness of this alloy. It has passivation property making it resistance to tarnish and corrosion. Melting temperature range is 1,100–1,304°C. Nickelchrome alloys are available as pellets.
Cobalt-Chromium Alloys
It has excellent corrosion resistance. Used for porcelain fused to metal restorations. It is also used for fabrication of framework of cast partial dentures. White in color. The fusion temperature range is 1,250– 1,450°C.
Dental Porcelain Or Ceramic
This is material of earthen origin with added material to achieve strength and shade. It is used for porcelain denture teeth,
inlay, onlays, laminates veneers, all ceramic crown and bridge, and porcelain fused to metal restoration. It is available in various types and shades. According to fusion temperature, it can be classified as high fusing (more than 1,300°C), medium fusing (1,100°C–1,300°C), low fusing (850°C–1,100°C), and ultra-low fusing (less than 850°C).
Finishing And Polishing Agents
Sand Paper
Sand or any other form of quartz is used for finishing purpose. It is available in various particle size (grit). Sand is bonded to paper to use as finishing agent. It can be
used manually or with sandpaper mandrel. Available in different grit sizes.
Emery Paper
It consists of natural oxide or corundum. It is bonded with paper to make emery paper. It is used manually or with mandrel for finishing the acrylic resins as well as for metal surface.
Pumice
Pumice is siliceous material of volcanic origin. It can be used as abrasive or polishing agent depending on its practical size. It is available as powder form and cake.
Pumice can also be used for polishing of enamel, amalgam.
Separating Medium Introduction
A coating applied to a surface and serving to prevent a second surface from adhering to the first surface. It is used for easy separation of two surfaces. It prevents seepage of monomer from resin when packed in mould and also prevent water to integrate with the resin.
Separating Medium Types
Tin Foil:
It is adapted on surface of object to prevent adhesion. It requires time and manipulation skills. Widely used in the past. Not in use nowadays. It is replaced by some newer separating medium known as “tin foil substitutes”.
Tin Foil Substitutes:
Variety of separating materials are available. They are used instead of tin foil, so known as tin foil substitutes. Some of the tin foil substitutes are listed here.
- Aqueous solution of sodium silicate
- Cellulose lacquers
- Soap solutions
- Starch
- Calcium oleate
- Water soluble alginate (sodium alginate solution)
- Petroleum jelly.
Sodium alginate solution is most popular and widely used separating medium. It is also known as “cold mould seal”. Composition: 2% sodium alginate, water, glycerin, sodium phosphate, and alcohol preservatives.
Tin Foil Mode of action: When cold mould seal is applied on surface of gypsum products, sodium alginate of cold mould seal reacts with calcium sulfate of gypsum products and forms insoluble film of calcium alginate. This thin film will act as separating film between two surfaces.
Note: Sodium alginate + Calcium sulfate → Calcium alginate
Tin Foil Application: It is applied with soft bristle brush in single direction. One or more coats can be applied. Cold mould seal should be applied in unidirectional only otherwise it may disturb the formation of thin film. It should be applied in even coating.
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