Dental Impression Materials

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Dental Impression Materials by Mind Map: Dental Impression Materials

1. Elastic Materials

1.1. Hydrocolloids

1.1.1. Irreversible Hydrocolloids (Alginate) -Supplied as powder mixed with correct proportion of water -Increse the temperature of water during mixing will shorten working and setting time -Mixing time: 45 to 60 sec -Short setting time: 2 1/2 to 3 1/2 min -Straight forward technique -Low cost -Hydrophilic -Easy to manipulate -Poor accuracy and surface detail -Not a dimensionally stable material -Tear easily -Syneresis: the alginate rapidly loses water from surface with consequent shrinkage if it's left exposed in dry atmosphere -Imbibition: if water is left on the surface of the impression absorption will take place causing the alginate to swell -Only used for diagnostic casts, not suitable for definitive casts -Pour immediately within later 15 min while wrapped in a moist towel in a plastic bag (the towel should first be wetted with cold water and then sequeezed as dry as possible)

1.1.2. Reversible Hydrocolloids (Agar-Agar) -Colloidal gel in which the gelation is brought about by cooling and can be returned to the sol condition when the temperature is sufficiently increased -Multiple preparations -Supplied in a range of viscosities -Used for: full mouth impressions without deep undercuts and they can be used for FPD impressions -Hydrophilic -Long working time: 7 - 15 min -Low cost -No custom tray required -Excellent dimentional accuracy if poured immediately -Low tear resistance -Low stability (syneresis and imbibition) -Equipment needed -To avoid permanent deformation, impression should be removed with a quick jerk -Pour immediately for no longer than 1 hour -problem with moisture -Use only with stone -The accuracy is improved if the material has much bulk as possible (in contrast with elastomeric impression material)

1.2. Synthetic Elastomers

1.2.1. Silicons Condensation silicone -Available as a base and accelerator -Available in a variety of viscosities -The heavy consistency (called putty) used in customize a stock impression tray -Working time: 3 min -Mainly used for fixed partial denture impressions -Short sitting time: 6 to 8 min -Pleasant to use -Odorless -Hydrophobic, poor wetting -Low stability Addition silicone (poly vinyl siloxane) -Available in 2 pastes or 2 putty system (base and catalyst) -Available in a variety of viscosities - mainly used as 2 viscosity system (heavy and light bodied) -working time: 3 min -Short sitting time: 6 min -Pleasant to use -Odorless -Highly accurate -Dimensionally stable -Auto mix available -May be poured 1 week after taking the impression -Multiple pours are possible -Hydrophobic, poor wetting -Removal of the material from undercuts is difficult because of its stiffness, so caution must be taken with tissue undercuts (risky)! -Sulfur in latex gloves inhibit the setting reaction

1.2.2. Polysulfides -Commonly known as rubber base -Available as a base and accelerator -Available in a variety of viscosities (low, medium and high) -Supplied with adhesive (thin layer to custom tray must applied at least 10 mins before loading the tray) -Working time: 6 min -High tear strength -Good reproduction of surface detail -Its elastic properties facilitate impression making in sulcular areas, so it commonly used with removable denture impression where undercuts exist. (good elastic recovery) -High flexibility for easier removal around undercuts -Easier to pour than other elastomers -Messy -Unpleasant odor -Long setting time; 10 to 12.5 min -Stability only fair -Hydrophobic -Pour within 1 hr; allow 10 min to set -The slight contraction can be minimized with custom trays to reduce the bulk of the material and enable the impression to be withdrawn from undercuts without distortion -Unpolymerized product is sticky and should be handled carefully because it stains clothing permanently -The areas where finest details exist are needed to be clean and dry from any blood or saliva at the time of impression placement -Not recommended when hyper-salivation is a problem or for gagging patients.

1.2.3. Polyethers -Supplied as a base and catalyst -Supplied as light-, heavy bodied paste and catalyst -Should be used with adhesive -working time: 2 min -Used for accurate impressions of a few prepared teeth without severe undercuts -Excellent dimensional stability. -Good reproduction of surface detail -Accuracy -Short setting time: 5 min -Automix available -Accurate casts can be produced even when the material is poured more than a day after impression has been taking -If the impression kept dry, it will be dimensionally stable for up to 1 week -Sit material is very stiff -Short working time -Catalyst can cause skin irritation -Isolated cases of allergic hypersensitivity to polyether have been reported -Imbibition: absorbs moisture and undergoes significant dimentional changes -Care not to break teeth when separating cast -During removal of the impression from mouth, it should be pulled slowly to break the seal then removed in single stroke -Direct contact with catalyst should be avoided -Through mixing of the catalyst with the base should be accomplished to prevent any irritation of oral tissues -Should be stored dry without any contact with water to prevent any dimensional changes

2. Non-elastic Materials

2.1. Impression plaster

2.1.1. -Plaster of paris is seldom used as impression material. -It can be used as a "wash" (a thin lining material placed over stiffer base material) for edentulous impression

2.1.2. -Very rigid and will break rather than bend -Absorb water from air -Must be stored in an airtight container

2.2. Dental Impression Compound

2.2.1. -Thermoplastic material. when heated, the material become soft and flow readily to make imprissions, whilst on cooling to mouth temprature they revert to the solid state -2 Types I & II: Type I: for impression taking (full crown impressions and completely edentulous jaws) Type II: used for tray preparation when final impression is taken with another material -Poor conductors of heat. Initial softening and mouth hardening will take several minutes

2.2.2. -The imprission can be corrected, relived and modified (the bulk of the impression is chilled and the surface is repeated after flaming and tempering, also additions can be made where under extensions exist) -Easy to handle

2.2.3. -Cannot be used to record undercuts (not elastic) -Difficult to record details (not suitable as a final impression material) -Viscose material, which displaces sulcus tissues producing overextension of the border areas -The material shows some distortion when removed from mouth (lacking of stability) -The handling of this material is very technique sensitive -Should not be removed from mouth before it has cooled completely -Should be poured within one hour -During handling, care must be taken to avoid heating with excessive temperature or long period storage in water. -Care must be taken to prevent overheating and burning of tissues. Also, cooling water should not be too cold to avoid thermal shock

2.3. Zinc Oxide-Eugenol

2.3.1. -Supplied as 2 pastes, base (zinc oxide) and activator (eugenol) -The material of choice in complete edentulous when bony undercuts are absent -Also used as a bite regestration material -Mixing time: 45 to 60 seconds

2.3.2. -Short setting time: 3 to 5 min -Dimensionally stable -Accurate recording of tissue details because of its fluidity -Ease of separation from stone casts -Good shelf life

2.3.3. -Difficult to use in undercut areas (distortion when removed from undercuts) -Untidy to handle -Difficult peripheral control: induced gagging -Irritating to mucosa of some patients

2.4. Impression Waxes

2.4.1. -Thermoplastic material which flow readily at mouth temperature -Sometimes used as a final impression for complete edentulous cases -Might be used to correct other impressions such as ZOE or for placing a posterior palatal seal on a final impression

2.4.2. -Able to be corrected by addition of more wax then re-insertion -Non irritating to tissue -Excellent to determine proper border extension -Good to use with patient with hypertensive gag reflex

2.4.3. -Time consuming -Impression easy to be distorted upon removal or pouring -Does not provide accurate surface detail -Wax undergo a large dimensional change upon cooling -Should be left in the mouth a minimum of 8 min -Should be poured immediately

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