Impression Materials PDF

Impression Material Presented by: Mustafa Razzaq And Ameer Ghzwan ❖ Impression : Is a negative production of the teeth and surrounding oral structures. ❖ Cast : It is the positive reproduction of the teeth and surrounding oral structure. Ideal Requirements Impression Material. 1.It should b...

Impression Material Presented by: Mustafa Razzaq And Ameer Ghzwan ❖ Impression : Is a negative production of the teeth and surrounding oral structures. ❖ Cast : It is the positive reproduction of the teeth and surrounding oral structure. Ideal Requirements Impression Material. 1.It should be accurate to produce fine details. 2.Biocompatible with oral environment,( not toxic or irritant to the oral tissues). 3.Easily manipulated. 4.Suitable working time. 5. Suitable setting time. 6. Acceptable taste and odor to the patient. 7. Good shelf life. Factors Affecting Accuracy of Impression Material 1.Flow: The material should have sufficient flow to record all fine details. 2.Hydrophilicity: The material should be hydrophilic to wet the oral tissues easily. 3.Dimensional accuracy: The material should not show any dimensional changes during setting (neither expansion or contraction).  Non-elastic Impression Materials 1. Plaster Impression Materials. 2. Impression Compound and Sticks. 3. Zinc Oxide eugenol. 4.Impression Wax. 1) Plaster of Paris ( IMPRESSION PLASTER) ⮚ Used for taking final impression for completely edentulous patient. ❖ Advantages ✔Very good dimensional stability. ✔Good accuracy. ✔Easy to mix. ✔Cheap. ❖ Disadvantages ✔Cannot be used in undercut ridge (rigid impression material). ♦PROPERTIES: 1. SETTING TIME 3-5 MIN. 2. THE MIXED MATERIAL HAS A VERY LOW VISCOSITY SO IT IS MUCOSTATIC. 3. A SEPARATING MEDIUM MUST BE USED BETWEEN THE CAST AND THE IMPRESSION PLASTER (SOLUTION OF SODIUM ALGINATE OR SOAP WITH WATER). MANIPULATION: WATER IS PLACED IN TO THE RUBBER BOWL AND THE POWDER IS ADDED, MIX WITH SPATULA TILL THE CREAMY MIXTURE IS FORMED THE TRAY IS FILLED AND SEATED INTO THE PATIENTS MOUTH WHERE IT IS ALLOWED TO SET. ♦USAGE: USED IN TAKING FINAL IMPRESSION FOR EDENTULOUS ARCHES OR WASH IMPRESSION, USED TO MOUNT CAST ON AN ARTICULATOR AND FOR BITE REGISTRATION. Mount on articulator Bite registration 2) Impression Compound ⮚ Two basic forms of impression compound: cake form and stick form. ❖ Uses ✔Cake form : Making primary impression for edentulous ridge. ✔Stick form : Border molding of special trays. Manipulation of the cake ✔Heated in a water path (55 – 60 °C),due to its lower thermal conductivity it should be immersed for sufficient time and kneaded. Manipulation of the sticks ✔They heated over a direct flame. ✔Avoid overheating as it will affect the properties. Border molding by stick compound 3) Zinc oxide- eugenol impression ⮚ Supplied in two tubes of different colors. ❖ Indications ✔secondary impression material for complete dentures. Manipulation ⮚ Dispense form both equal lengths on a glass slab ,mix using stainless steel spatula until homogenous color is obtained. 4) Impression waxes ✔Waxes are thermoplastic materials which are normally solid at room temperature but melt when heated to form liquid material. ✔Used to correct small imperfection (e.g. air bubble) in other impressions, especially zinc oxide impressions. Elastic Impression Materials 1) Hydrocolloids ( Agar and alginate impression material ). ❑ Irreversible Hydrocolloid (Alginate) ⮚ Most widely used impression material. ❖ Indications ✔Diagnostic casts. ✔Orthodontic treatment casts. ✔Master casts for R.P.D. ❖ Advantages ✔Hydrophilic. ✔Have acceptable taste and odor. ✔Nontoxic. ✔nonstaining. ✔Inexpensive. ❖ Disadvantages ✔Provide less surface details than other materials. ✔They are dimensionally unstable ,therefore they must be poured immediately. Properties of hydrocolloids ❖ They exhibit poor dimensional stability caused by: ⮚ Syneresis : If the alginate remains in the open air ,mositure will evaporate from material causing to shrinkage and distort. ⮚ Imbibition: If the alginate is remains in the open air ,will absorb additional water and expand. ✔Therefore hydrocolloid materials must be poured immediately. 2) Elastomers ( Polyether, Addition silicon , Condensation silicon, Polysulfide). ❖Indication ⮚ crown and bridge work. ❖ Properties ✔Accuracy. ✔Good tear resistance. ✔Dimensional stability. 1) Condensation Silicone ❖ Indications ✔ Crown and bridge. ✔Partial dentures. ✔Implants. ❖Properties ✔Odor free. ✔Poor dimensional stability. ✔Must be poured immediately. 2) Addition Silicones ❖ Indications ✔ Cobalt-chromium denture impressions. ✔ Crown and bridge impressions. ✔ Implant impressions. ❖ Properties ✔High accurate. ✔Good tear resistance. ✔Excellent dimensional stability. ✔ Pouring can be delayed up to 7 days. 3) Polysulfide ⮚ Mode of supply :Base and Catalyst. ❖ Indications ✔ Cobalt-chromium dental impressions. ✔ Crown and bridge impressions. ✔ Secondary impression for edentulous ridge. ❖Properties ✔Accurate. ✔High tear strength. ✔Unacceptable odor. 4) Polyether ⮚ Supplied in two pastes , Base and Catalyst. ❖ Properties ✔Accurate. ✔Odor free. ✔Good tear resistance. ✔Excellent dimensional stability. ✔Will absorb water but pouring can wait 24hrs.