Dental Materials Lecture 1 PDF

Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim Types of impression materials Impression materials are used to register or reproduce the form and relationship of the teeth and oral tissues. Impression materials are used to make an...

Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim Types of impression materials Impression materials are used to register or reproduce the form and relationship of the teeth and oral tissues. Impression materials are used to make an accurate replica or mold of the teeth ,hard and soft oral tissues. The area involved may vary from a single tooth to the whole dentition, or an impression may be made of an edentulous mouth. The impression is a negative reproduction of the teeth and tissues and by filling the impression with dental stone or other model material, a positive cast is made. Usually the impression material is carried to the mouth in an instrument called (tray) and applied to the area under treatment. When the impression material has set, it is removed from the mouth with the tray. a b figure.1.a. impression(negative reproduction), b. dental cast (positive reproduction) The accuracy, detail, and quality of this final cast are of greatest importance as it used in the construction of dentures, crowns, fixed dental prostheses, and other restorations. Impression materials are supplied in a variety of forms. Some are powders that are mixed with water while others are paste-paste systems. However other materials are softened or melted by heating. Regardless of their form, impression materials are mixed (or heated) to make a thick paste or liquid. They are then loaded into an impression tray, placed in the mouth, and seated onto the tissues of interest. Impression trays: used to carry the impression material to the mouth and to support it until sets. Function of trays: 1.Carrier. 2.Support the set impression material 1  Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim #Types of impression trays: 1.Stock tray(prefabricated) 2.Custom tray 3.Bite registration tray 1-stock trays (prefabricated tray): Trays that come in different Materials (Plastic disposable trays And Metal trays) figure.2. stock trays 2-Custom trays: They are made on the model of the patient (cast) with acrylic or other resin. Figure.3.Custom tray 3-Bite registration trays: They record the occlusal surfaces of both arches and used to relate the upper and lower casts in the lab in the same manner as in the patient mouth. 2  Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim Figure.4.bite registration Ideal Requirements of an impression material 1.Non-toxic and non-irritant 2.Acceptability to the patient: a-setting time. b-Taste. c- Consistency. 3.Accuracy: a-Surface reproducibility. b-Dimensional stability 4.Use of materials: a-Ease of mixing. b- Good working time. c-Handling of the material 5.Economics of the materials: a- Cheep. b- Long shelf life. c- Save redoing impression 6.Elastic properties :easy removal of the set material from the mouth 7. Readily disinfected without loss of accuracy. Classification of impression materials According to the ability of set material to be withdrawn over undercuts. 3  Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim Figure.5.classification of impression materials Non-Elastic Impression Materials These materials are rigid and therefore exhibit little or no elasticity. Any significant deformation produces a permanent deformation. They are used when there are no undercuts and are mainly used for edentulous patient cases. The main non-elastic impression materials are: 1.Impression Plaster 2.Impression Waxes 3.Impression compound 4.Zinc Oxide Eugenol 1-impression Plaster -Uses: Mainly for complete denture impression. -Advantages: Rapid set. Inexpensive. -Disadvantages: Complexity of its technique. Hard and brittle. Unpleasant taste. 4  Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim Figure.6.impression plaster 2-Impression Waxes Is a thermoplastic material (that soften on heating and harden process when cooling). -Uses: primary impression for complete denture. Bite registration. To correct minor voids in impression of complete denture. -Advantages: Clean. Cheap. Easy to use. -Disadvantages: Very weak. Lack of accuracy. Distort easily. Figure.7.impression waxes 5  Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim 3-Impression compound Is a rigid thermoplastic material that soften when heated (by water bath or direct flame) and become firm at mouth temperature. -Uses: Primary impression for complete denture. To mold the peripheral borders of a custom tray for complete denture impression. -Advantages Non-toxic and Non-irritant Reusable (but with re-use the constituents are leached out( Can be reheated and readapted -Disadvantages Poor dimensional stability Poor surface details Distort when removed from the undercut Figure.8.impression compound 4-Zinc oxide-Eugenol -uses: Final impression of complete denture 6  Lecture 1 Dental Materials Assist. Lecture. Alaa Jasim -Advantages: application in complete denture. Does not require immediate pouring. -Disadvantages: unpleasant taste. irritate the tissues of some patients Figure.9.zinc oxide-Eugenol 7