Prosthodontic materials can be roughly divided into the following 8 groups.
(l) Impression
(2) Model materials (Gypsum, waxes)
(3) Investments
(4) Metals and alloys
(5) Ceramic and metal-bonded ceramics
(6) Synthetic polymers (Denture base polymers, denture lining materials, artificial teeth)
(7) Dental cements
(8) Abrasion and polishing materials etc.
Many dental appliances are constructed outside the patient' s mouth on models of the hard and/or soft tissues.
The impression stage is the first of many stages involved in the production of dentures, crowns, bridges, orthodontic appliances etc. Impression materials can be categorized as either rigid or elastic when set. The rigid or non-elastic materials include impression plaster, impression compound, and impression wax and zinc oxide/eugenol impression paste. The factor, which links these materials, is their inability to accurately record undercuts. Impression compound and impression waxes are thermoplastic materials. The elastic impression materials can be divided into two groups, the hydrocolloids and the elastomers. The hydrocolloid impression materials are best used for obtaining an accurate reproduction of tooth form, including the undercuts and interproximal spaces. The hydrocolloids can be sub-divided into the reversible, agar-based materials, and the irreversible, alginate-based materials. They are hydrophilic and do not recoil when they come into contact with pockets of saliva or blood. Reversible hydrococolloids are viscoelastic materials. The primary uses of agar impression are for denture and crown and bridges patients. Alginate impression materials are widely used for a variety of applications, such as edentulous and partially edentulous arches. Synthetic elastomers are commonly used for crown and bridge impressions, since they have better tear resistance and dimensional stability than hydrocolloids. Four types of elastomers are in general use, polysulphides, silicone rubbers (condensation curing type), polyethers.
After "setting", the impression is removed from the patient' s mouth, the morphology of the hard and soft tissues is recorded in the impression, then models and dies can be prepared using gypsum model and die materials. Gypsum products used in dentistry are based on calcium sulphate hemihydrate [(CaSO4)2.H2O].
Following the production of a stone model or die, the next stage in the formation of many dental appliances, dentures or restorations is the production of a wax pattern of the appliance on the model using pattern waxes (modeling and inlay waxes).
The next stage involves the investment of the pattern to form a mould. The commonly used investment materials can be referred to as gypsum-bonded or phosphate-bonded investments. Using the lost-wax technique, the wax is removed to leave a mould, which can be filled with an alloy, ceramic or a polymer.
The shaping of metal and alloys for dental use can be accomplished by casting, cold working or amalgamation methods.
Gold casting alloys, silver-palladium casting alloys are used for making crowns, inla，英语论文题目，英语论文 |
