Dental Materials Impression Mat(1).pdf

DENTAL IMPRESSION MATERIALS IMPRESSION MATERIALS  The function of an impression material is to accurately record the dimensions of oral tissues and their spatial relationships.  In making an impression, a material in the plastic state is placed against the oral tissues...

DENTAL IMPRESSION MATERIALS IMPRESSION MATERIALS  The function of an impression material is to accurately record the dimensions of oral tissues and their spatial relationships.  In making an impression, a material in the plastic state is placed against the oral tissues to set. IMPRESSION MATERIALS  After setting, the impression is removed from the mouth and is used to make a replica of the oral tissues.  Impression is refer to a negative reproduction of tissues.  Model or Cast is the positive reproduction of tissues. It is obtained by pouring dental stone or other suitable material into the impression allowing it to harden.  Die cast is a positive reproduction of the form of a prepared tooth. Properties for an ideal impression material: 1. Ease of manipulation and reasonable cost 2. Adequate flow property 3. Appropriate setting time and characteristics 4. Sufficient mechanical strength not to tear or permanently deform during removal 5. Good dimensional accuracy Properties for an ideal impression material: 6. Acceptability to the patient 7. Safety (not toxic or irritating) 8. Compatible with die or cast materials 9. Good keeping qualities (no deterioration / longer shelf-life) IMPRESSION MATERIALS Methods / Types of Impression making A. Preliminary - initial impression, the purpose of which is to construct a study cast for diagnosis and fabrication of the individual tray. Preliminary impression IMPRESSION MATERIALS B. Secondary/ Final/ Wash impression - corrective impression, the purpose of which is to construct a master cast or a working cast for the fabrication of the prosthesis. Secondary/ Final/ Wash impression  Classification of Impression materials 1. According to their uses in dentistry - Restorative dentistry - never use modeling compound IM - Prosthodontics - Orthodontics 2. According to manner of hardening: - Thermoplastic IM - materials that set as a result of change in temperature; soften under heat and solidify when cooled, with no chemical change taking place; examples are modeling compound, agar, waxes - Thermoset IM - materials that harden by chemical reaction; examples are Type I dental gypsum, alginate, rubber IM (polysulfide, silicon, polyether), zinc oxide eugenol pastes,  Classification of Impression materials 1. According to their uses in dentistry - Restorative dentistry - never use modeling compound IM - Prosthodontics - Orthodontics 2. According to manner of hardening: - Thermoplastic IM - materials that set as a result of change in temperature; soften under heat and solidify when cooled, with no chemical change taking place; examples are modeling compound, agar, waxes - Thermoset IM - materials that harden by chemical reaction; examples are Type I dental gypsum, alginate, rubber IM (polysulfide, silicon, polyether), zinc oxide eugenol pastes, 3. According to Dr. McCracken: – Rigid - IM that harden at the time of removal from the mouth; restricted to applications in areas where no undercuts exist, edentulous mouth. Ex. Modeling compound, impression plaster, zinc oxide eugenol paste. – Elastic - IM that are flexible at time of removal, can be used in areas with or without undercuts. Ex. Alginate, agar, RIM – Thermoplastic - change of one state to another because of change in temperature  Impression Materials Impression Materials Inelastomeric Materials Elastomeric Materials Zinc Oxide Eugenol Pastes Aqueous Materials Nonaqueous Materials (Hydrocolloids) (Elastomers/Rubber Bases) Impression Compound Agar Polysulfides (Reversible) Alginate Condensation Silicones (Irreversible) (Polysiloxane) Polyethers Additional Silicones (Polyvinyl Siloxanes) Impression Trays: 1. Stock trays - non-perforated for use with modeling compound Rim-locked tray - added retention for IM Perforated tray - for added retention of IM and release or pressure during impression making 2. Individual tray - self-made tray of acrylic or shellac base plate; specific for one patient 3. Water-cooled tray - specifically for agar IM IMPRESSION PLASTER Other names: Type I dental gypsum, soluble plaster Description: Rarely used these days to take impressions, since it is rigid and fractures easily. However because of its short setting time and accuracy, it is primarily used to mount casts on an articulator or to record occlusal bite registration. Impression plasters are plasters of Paris to which regulators have been added to regulate the setting time and to control the setting expansion. Classification: thermoset, rigid, for final or secondary imp. making Manner of dispensing - supplied as a finely divided powder added to water and sets as a result of hydration reaction. Color - light pink IMPRESSION PLASTER Use: For final impression making of edentulous arches. Composition: 1. CaSO4 2H2O (Plaster) 2. Potato starch - to render it soluble; after the cast has set, place in hot water  the starch swells & the impression disintegrates making it easy to remove from the cast 3. Chemical modifiers: a. accelerator (potassium sulfate) - to reduce setting time b. retarder (sodium citrate) - both will reduce setting expansion from 0.3 to 0.06. Should have low setting expansion so that the cast will not warp. 1. Coloring material - alizarin red 2. Flavoring material - peppermint IMPRESSION PLASTER Manipulation: Use a plaster bowl and spatula. W:P ratio of 0.6 - 0.7. Increase ratio to reduce exothermic heat so as not to injure the soft tissues in the mouth. Mix in a single rotary motion for 1 minute. Setting time is 3 - 5 minutes. Manner of withdrawal from patient’s mouth: with a teasing motion, slowly remove from the mouth to avoid fracture. Construction of casts and separation of casts from impression: Before pouring a gypsum material to make a cast, paint a coat of separating medium (colorgard) onto the impression plaster before pouring in the gypsum to facilitate easy removal. The cast should not be separated from the impression until it has thoroughly set. From 30 - 60 minutes, submerge in hot water for easy separation of cast from the impression plaster. IMPRESSION COMPOUND Description: Other name: Modeling plastic; Modeling compound Also called simply as impression compound, but actually there are 2 different types, identified as tray compound and impression compound. To avoid confusion, the term dental compound will be used to refer to the general class of materials and tray or impression compound will denote the specific type. IMPRESSION COMPOUND IMPRESSION COMPOUND Type I - Impression compound, low fusing compound, needs only 55o-65o C to soften the compound. - Used to make a final impression of a tooth preparation; more commonly it is used as a check impression to evaluate the adequacy of a cavity preparation. Type II - Tray compound, high fusing compound, 70oC to soften - Used in construction of a custom-made impression tray IMPRESSION COMPOUND Classification: thermoplastic, rigid, preliminary IM Manner of dispensing: cakes of different shapes and color; cones or stick forms Colors: pink, brown, maroon, white and black (in cake forms) and green (in stick form). Uses: 1. for edentulous impression Type I / impression compound 2. In restorative dentistry, to obtain impressions of single tooth 3. tray compound used to form tray to be used for other types of IM IMPRESSION COMPOUND Composition 1. Beeswax - one of the first substance to be used as an impression material; exhibits brittleness if used alone: lack of dimensional stability and a tendency towards tackiness. 2. Plasticizers - added in order to improve the plasticity and workability, i.e. burgundy pitch, shellac, gutta- percha, & kauri resin. Stearic acid may function as plasticizer, besides making the material less tougher and less brittle. IMPRESSION COMPOUND 3. Fillers - to strengthen materials; also decreases the flow of the material and reduces adhesiveness of the softened material to the oral tissues i.e. talc, chalk, iron oxide, various coloring pigments and flavoring materials. 4. Anti-microbial agents - to prevent bacterial growth during storage e.g. thymol & alkyl benzoic acid IMPRESSION COMPOUND Manipulation: There are two ways to soften the impression compound: 1. Dry heat method - A stick or cone impression compound is heated over a flame (Bunsen burner, alcohol lamp) until the material is thoroughly softened, then pressed into the area of the cavity preparation and held firmly until it cools thoroughly. A. direct flame B. oven 2. Moist heat method - The material is softened in a hot water bath (thermostatically controlled bath) *Whenever possible, compound should be softened with “dry” heat as in an oven or similar device. *When a direct flame is used, the compound should not be allowed to boil or ignite so that important constituents are not volatilized. *When large amount of compound is to be softened, softening is better accomplished in a water bath. IMPRESSION COMPOUND Disadvantages with the use of water bath: chief disadvantage – plasticity of the compound may be altered, if water is incorporated, it acts as a plasticizer if compound is heated in water for an excessive period, it may become brittle and grainy IMPRESSION COMPOUND Manner of withdrawal: teasing method Construction and technique of separation from cast: The gypsum cast material is mixed and poured in the same manner as described for the plaster impressions. The safest method for removal of the impression is to immerse it in warm water until the compound softens sufficiently to allow it to be separated from the cast. If the compound is overheated, it may adhere to the cast and cause a discoloration of the stone. IMPRESSION COMPOUND Properties 1. Flow - These compounds are hard at mouth temperature (37oC) but plastic and capable of recording an impression at 45oC. The flow requirement differs for tray and impression compounds IMPRESSION COMPOUND 2. Thermal conductivity - Dental compound has low thermal conductivity. During heating or cooling, the dental compound must be allowed to come to a uniform temperature. Since transfer of heat is slow, it is important to knead the material very well. 3. Dimensional stability – Relaxation can occur in a comparatively short time, especially with an increase in temperature, resulting in warping or distortion of the impression. IMPRESSION COMPOUND Causes of warpage: 1. premature removal of impression material from the patients mouth 2. cast material not poured onto the impression material as soon as possible. ZOE IMPRESSION PASTE Description: Two pastes that are homogenously mixed and is used in a custom-made tray to record impressions of completely or partially edentulous arches. The impression material sets to a brittle solid. When used as a thin layer in a tray, the impression is sometimes referred to as a wash impression.  Classification: Thermoset, rigid (not used to record undercuts); final/wash/corrective impression Manner of dispensing: 2-paste system in collapsible tubes 1 paste = base (white) 2 = catalyst (brown, amber) Uses of ZOE: 1. as final impression for an edentulous mouth (Type II, soft set) 2. as a relining material for ill-fitting dentures 3. for centric jaw registration 4. as a cementing medium, surgical dressing, temporary filling material, root canal filling material  Types: 1. Type I = Hard set; 3-6 minutes IST / 10 min. FST 2. Type II = Soft set; 3-6 minutes IST / 15 min FST Composition: 1. Base: a. zinc oxide – should be finely divided, French processed and it should contain a very slight amount of water b. inert oil – mineral /vegetable oil; acts as a plasticizer, to make into a paste, and it also aids in masking the action of the eugenol as an irritant c. hydrogenated rosin – imparts thermoplasticity to make zinc oxide more fluid; 2. Reactor / Catalyst - also called an accelerator a. Oil of cloves – contains 70-85% eugenol, used in preference over eugenol because it reduces the burning sensation in the soft tissues of the mouth. With a characteristic odor. Substitutes for eugenol are lauric acid or other alkoxy- substituted phenols b. Polymerized rosin - facilitates speed of reaction, and for a smoother, more homogeneous product c. Accelerators – for the setting time; calcium chloride, zinc acetate, primary alcohols, glacial acetic acid. The accelerator can be incorporated in one or both pastes d. Olive oil, linseed oil, cotton seed oil – plasticizers, reduces burning sensation to tissues e. Canada balsam, Peru balsam - often used to increase flow and mixing properties of the paste f. Fillers – if the mixed paste is too thin or lacks body before it sets; wax, or an inert powder (kaolin, talc, diatomaceous earth, etc) maybe added to one or both pastes g. Coloring material / flavoring material Manipulation and mixing technique The mixing of the two pastes is done on an oil-impervious paper, a glass slab could also be used. The proper proportion is 1:1 squeeze two ropes of paste of the same length. A flexible stainless steel spatula is used for mixing. The two ropes are combined with the first sweep of the spatula, then broad strokes in a sweeping motion, mixing is continued for 30-45 seconds to 1 minute or as directed by manufacturer or until a uniform color is observed. Load the impression material onto the tray and carry into mouth of the patient, hold firmly in position until it has thoroughly hardened. Setting time is 3-5 minutes. The principal difference between the two types is that the soft-set material is tougher and brittle. Hard-set has a more fluid consistency when mixed and a higher resistance to penetration when set. The soft-set has a buttery consistency when mixed.  Manner of withdrawal: teasing method Setting time: is affected by mouth temperature and humidity Factors controlling setting time: 1. presence of water, high humidity and increase in temperature (heat of the mouth) - shortens or decreases the setting time 2. cool mixing slab or spatula - prolong setting time 3. if the paste sets too slow - addition of chemical modifiers, zinc acetate or a small drop of water or alcohol to the base or catalyst will decrease ST Factors controlling setting time: 1. when ST is too short - cool the spatula; addition of certain inert oils and waxes during mixing such as olive oil, mineral oil and petroleum 2. altering the ratio of zinc oxide paste to the eugenol paste - depends on where the accelerator is. Ex. If in the catalyst, decrease in amount of base will shorten ST. Will result to poor consistency and weak set material 3. time of mixing - longer mixing time (within limits) the shorter will be the ST Construction of casts: No separating medium needed. After the stone has set, it can be separated from the impression by immersion in hot water at 49C-60C for 5-10 minutes. The model materials used with ZOE impression materials are the gypsum type (Type II, III, IV) Properties a. Flow b. Consistency - a paste of thick consistency or high viscosity can compress tissues, whereas a thin, fluid material copies tissues in a relaxed condition with little or no compression c. Rigidity and Strength = the paste impression should be unyielding when removed from the mouth and should resist fracture; compressive strength of hardened ZOE impression pastes maybe as great as 70 kg./sq cm (1000 psi) 2 hours after mixing d. Dimensional stability = negligible shrinkage (< 0.1%) may occur during hardening Elastic Impression Materials Hydrocolloid Impression Materials Description: Impression materials that deform elastically when removed from the mouth and spring back to its original form will produce an accurate impression Flexible gel. Solids suspended in liquids Hydrophilic sols. All colloids are termed as sols. If gelatin or agar is dissolved in water, the gelatin particles attract the water molecules and swell in size thus forming a hydrocolloid. Hydrocolloid Impression Materials The sol may be changed to a gel or jelly, when the temperature is decreased. The temperature at which this change occurs is known as the gelation temperature. Types: A. reversible hydrocolloids: sol  gel  sol B. irreversible hydrocolloids sol  gel A. Reversible Hydrocolloids Agar - first successful elastic impression material used in dentistry. The flexibility of the material allows impression of undercut areas and fully dentulous impressions of the entire arch. Classification: 1. Thermoplastic 2. Corrective / Wash / Final impression Reversible Hydrocolloids Manner of dispensing: Gel in a collapsible tube = water cooled tray Gel in a glass jar = syringe Uses: 1. To make impressions of dentulous & edentulous mouths. 2. As a duplicating material for casts duplication. Agar impression material Reversible Hydrocolloids Composition: 1. Agar - basic constituent; an organic hydrophilic colloid (polysaccharide) from certain types of seaweed. Consists of a network of agar molecules, which holds the water in the intervening capillary spaces. When heated, the network breaks up and agar particles are dispersed in water, which is termed sol. The agar gel is converted to a sol by heating in water, usually boiling and becomes a gel again by cooling to 43.3oC The gel of the tray material: 12-15% agar; syringe material 6-8%. 2. Water - principal ingredient by weight 80%- 85% Reversible Hydrocolloids 3. 0.2% Borax - a borate is formed for improved strength, also increases viscosity of the sol, so that a filler is unnecessary. Also it retards the setting time of gypsum product poured into the impression. 4. 1-2% Potassium sulfate - ensures proper setting if the gypsum model and die materials against the agar 5. Fillers - for the control of strength, viscosity and rigidity; diatomaceous earth, clay, silica, wax, rubber and similar inert powders. 6. Coloring and flavoring materials 7. Anti-microbial agents - thymol 8. Plasticizer - glycerine 9. Preservatives - 0.1% benzoates Reversible Hydrocolloids Manipulation: 1. Single technique 2. Double impression technique: Syringe material first then tray material used as second. Syringe material has higher flow but weaker strength so it is followed with tray material for strength. Tray material contains more agar, but less water Double Impression Technique Reversible Hydrocolloids In a thermostatically controlled water bath. The tray material in a tube is placed in one of the water baths of a hydrocolloid conditioner at 100 C (212 F) for 10-15 minutes. After agar has been converted to sol, the tube is transferred to the 2nd water bath, maintained at 60-66 C. At these temperatures, the agar sol will remain fluid during the day. When an impression is to be made, the stored agar is squeezed into a perforated water-cooled tray metal impression tray. The tray, filled with agar sol at 60-66 C is tempered further to 43-46 C in the 3rd water bath, so that the impression material will not burn the oral tissues. When the tray has been properly positioned with the water hoses connected, water at 13 C is circulated through the tray, water may also be sprayed on the tray to facilitate jelling of the sol. Reversible Hydrocolloids Manner of withdrawal: Impression is removed with a single stroke, sudden jerk, with no side movements. Properties: 1. Strength - tray type has a tear strength of 4 lb/in2 (715 gm/cm2) and compressive strength of 116 lbs/ in2 (8000 gm/cm2). The syringe material has poorer mechanical properties. 2. Consistency and rigidity - agar gel is homogenous and free of lumps when used for impression, fluid enough to be easily transferred to the tray and can make impressions accurately. Upon setting it becomes a little stiff. Although the agar impression is flexible, it does not completely recover from being deformed during removal from undercut areas. That is why it should be removed with a sudden pull with no side movements. A slow removal is a common cause of inaccuracy. Reversible Hydrocolloids Properties: 3.Poor mechanical properties = Repeated stressing and unstressing of the gel increases stiffness, followed by brittleness  risk of fracture increases. 4.Shelf life - poor shelf life; storage is not recommended; usually results in dehydration (syneresis) and storage in water causes swelling of the impression (imbibition). Storage in 100% relative humidity results in shrinkage from syneresis. If storage is unavoidable, it should be limited to 1 hour in 100% relative humidity. Reversible Hydrocolloids Properties: 5. Dimensional changes - cast must be constructed within 15 minutes. When gypsum has set, agar impression must be removed promptly, since impression will dehydrate, become stiff and difficult to remove. Could cause fracture of cast. Prolonged contact of agar with gypsum will result in a rougher that normal surface on the model. 6. Hysteresis - the gelation of a hydrocolloid is in fact a solidification process, from sol to gel. The hydrocolloid gel does not return to the sol at the same temperature it is solidified. The gel must be heated at a higher temperature, known as the liquefaction temperature, to return to the sol condition. The temperature lag between the gelation temperature and the liquefaction temperature of the gel is known as hysteresis. Irreversible Hydrocolloid Alginate Description: From the „algin‟ dental compound; derived from a brown seaweed (algae) that yields a peculiar mucous extraction. one of the most widely used dental impression materials. Alginate Advantages: 1. Ease of mixing and manipulating 2. Minimum equipment necessary 3. Flexibility of the set impression 4. Accuracy if handled properly 5. Low cost 6. Comfortable to the patient Alginate Model and die materials are limited to gypsum types - one of the principal disadvantages Classification: Thermoset Preliminary / Final impression material Manner of dispensing: powder + water = sol  gel Powder are placed in a pre- weighed individual containers. Alginate Types based on setting time: 1. Type I – fast set ( must gel in not less than 60 seconds nor more than 120 seconds) 2. Type II – normal set (must gel between 2- 4.5 minutes) The overall simplified reaction is as follows: Paste  Gel Na alginate + CaS04 + H20 = Ca alginate + Na + S04 + H20 Alginate Uses: 1. for full mouth impressions - dentulous & edentulous 2. for quadrant impressions 3. as a duplicating material Alginate Composition: 1. Na or K alginate - soluble salts of alginic acid; main ingredient. Function: to dissolve in water to form sol, similar to the agar sol. 2. Ca SO4 - to react with dissolved alginate to form insoluble Ca alginate; acts as a reactor for conversion of sol to gel. 3. Na PO4 - to react preferentially with Ca SO4 for production of insoluble Ca alginate and serve as a retarder to have enough working time 4. Diatomaceous earth or silicate powder - fillers, can increase the strength and stiffness, produce a smooth texture, and insure a firm gel surface that is not tacky; controls consistency of mix and flexibility of impression. Alginate 5. K Ti Fluoride - added to assure a hard, dense stone cast surface. In proper concentrations, fluoride salts are accelerators for setting gypsum products. 6. Organic glycol - to coat the powder particles to minimize dust during dispensing 7. Quaternary ammonium compounds - provide self-disinfection 8. Flavoring and coloring materials Alginate Manipulation: A. W/P ratio = 15-18 grams : 40-50 cc water (1 pack of pre-weighed powder and about 50 cc of water) B. Technique = Water is added to the powder and with a figure eight motion is used to fold the powder and water together. A creamy consistency free of graininess in less than 1 minute mixing time must be produced. Mixing time for fast setting = 30- 45 seconds. C. Tray material = The proper size of tray should be selected before mixing, loading of the tray should be done quickly. Material is added to the posterior portion of the tray then pushed toward the anterior part, there should be less alginate in the posterior to prevent gagging by the patient. Alginate Making the impression: The tray is held gently but firmly in position until the alginate sets. Setting is determined by noting when the alginate is no longer tacky. Let alginate remain for additional 2 minutes to improve physical property, tear and permanent deformation. Removal of the impression: The seal between the impression and peripheral tissues is broken by moving the cheek or lips with the finger. Then the tray is removed with a single firm motion, sudden pull or sudden jerk. Alginate Stages during gelation: Chemical equation 1. When alginate is mixed with water 2Na3P04 + 3CaS04 = Ca3(P04)2 + 3Na2 S04 - main ingredient must first react with Na3P04, a retarder, until the latter is used up. 2. When alginate is already in the patient‟s mouth KnAlg + nCaS04 = nK2S04 + CanAlg soluble sol insoluble sol - before it reacts with soluble sol to produce insoluble gel Alginate Factor to control gelation time: Alter the temperature of the water for mixing, the higher temperature the shorter will be the gelation time. Shelf-life: Alginate impression materials will deteriorate rapidly at elevated temperatures. It is better not to stock more than 1 yr supply, and to store material in a cool dry environment. Rinse impression then pour cast material as soon as possible. If not, impression may be wrapped in a paper towel soaked with water and the excess squeezed out. A plastic bag is convenient for storing under humid conditions. In no instance should impressions be stored for longer than 1 hour. Properties: A. Dimensional stability = the accuracy of the impression material is of prime importance and alginates are no exception. A problem with alginate is loss of accuracy with increased time of storage. 1. When the water from inside the alginate evaporates, the impression shrinks syneresis (even under conditions of 100% relative humidity) 2. If the impression is placed in water, it absorbs water and expands, imbibition. Therefore storage is air or water results in serious changes in dimensions and a loss of accuracy. B. Strength = With proper manipulation, alginate may be greater than that of agar materials. Tear strength of alginates varies from 2-4 lbs/in (358-716 gm/cm), while with a compressive strength of 5000-7000 gm/cm2. C. Flow = good flow property so alginate can record the detail of oral tissues accurately and this detail must also be transferred to the model or die. D. Adhesive property = or the property for alginate to be tacky before setting. As mentioned, start of setting is determined by the loss of tackiness of the alginate material. Elastomeric (Rubber) Impression Materials RIM Description: A type of elastic impression material which is soft and rubber-like in nature, technically known as an elastomer. An elastomeric material must contain large molecules with weak interaction among them, tied together at certain points to form a 3- dimensional network. On stretching they uncoil, upon removal of stress, they snap back to their relaxed untangled state. In contrast to hydrocolloid gels, they are hydrophobic in character. The RIMs are two component systems, in that polymerization/ cross-linking occurs by (a) condensation or (b) ionic reaction in the presence of chemical reactors. Classification: Thermoset / Elastic IM / Final impression materials  Uses: 1. as a single impression 2. can be used for quadrant impression 3. for bite registration (addition silicone) Methods of dispensing: 1. 2-paste type (polysulfide & polyether) 2. Paste-liquid type (silicone) Types: 1. Polysulfide 2. Silicone 3. Polyether Polysulfide RIM = the first rubber impression material Composition: 2-paste system - base & catalyst/ reactor * The process of changing the rubber base product, or liquid polymer, to a rubber-like material is generally known as vulcanization or curing. 1. Base = 3 types or consistencies; actually an ADA classification for polysulfide RIM Type I soft or light-bodied Type II regular-bodied Type III heavy-bodied, depending on their viscosity and how easily they flow under load. The light-bodied class is used as a syringe material in combination with a tray material. The regular material is used alone. The light bodied is also used for denture impressions with a custom-made tray. Polysulfide RIM The base material consists of : 1. 80% polysulfide polymer or polyfunctional mercaptan (-SH) 2. 20% reinforcing agents - for strength, prevent tearing = titanium dioxide, zinc sulfate, copper carbonate, or silica 3. sulfur = promoter 4. plasticizer - dibutyl phtalate = controlling viscosity of the rubber The catalyst or accelerator contains a compound that causes the mercaptan groups to react to form a polysulfide rubber. 1. Lead dioxide = the most common catalyst; using it results in the paste being dark brown to dark gray 2. Copper hydroxide = and when mixed with the white base paste, a blue- green color results 3. Retarder = controls the rate of setting time ; oleic acid, stearic acid (controls polymerization of rubber) , castor oil (controls reaction of the 2 pastes) Manipulation: 2-paste type 1. Squeeze equal lengths of the base and accelerator onto a paper pad with a 1- inch interval. 2. A tapered stiff-bladed spatula is recommended. 3. The accelerator is mixed with the base for 5-10 seconds in a circular motion with the end of the spatula. 4. The mixing is continued with a wide sweeping motion until the mix is free from streaks and is uniform in color. 5. The mixing should be accomplished in 45 seconds. If the material is light-bodied, it is loaded on a syringe then ready for injecting into the cavity preparation. If regular- or heavy –bodied, it is placed on a custom-tray made of acrylic. The inside of the tray is painted with a rubber cement adhesive. Sometimes holes may be drilled to provide mechanical retention. Working time : 5-7 minutes Setting time: 25C = 8-12 minutes 37C = 4-6 minutes Silicone RIM The development of silicone RIM resulted from criticisms about polysulfide RIM, such as 1. Objectionable odor 2. Staining of linens and uniforms by lead dioxide 3. Amount of effort required to mix and long setting times 4. Moderately high shrinkage on setting 5. High permanent deformation Silicone RIM Composition: 2 types of silicone are used (according to polymerization reaction) 1. Condensation silicone 2. Addition silicone (sometimes called vinyl silicone) Silicone RIM Condensation type: The base material is a paste containing: 1. dimethylsiloxane, a low-molecular weight silicone liquid 2. reinforcing agents = silica, added to give the proper consistency to the paste and stiffness to the set rubber 3. The accelerator is supplied as a liquid which consists of: 1. tin organic ester suspension 2. alkyl silicate such as ortho-ethyl silicate = acts as a cross-linking agent Silicone RIM The silicone pastes have 4 types of consistency, same as the polysulfide pastes. As well as a very heavy consistency as Type IV called a putty. For light- bodied, reinforcing agents of 35%, while 75% for the putty consistency. Silicone RIM Addition type: The material is supplied as a two-paste or a two-putty system The base: 1. polymethyl hydrogen siloxane or divinyl polymethyl siloxane 2. reinforcing fillers 3. chloroplatinic acid catalyst. Manipulation: Paste-Liquid Condensation putty-type 1. The putty is dispensed with a scoop. Depressions are made in the surface of the putty and appropriate number of drops of catalyst is added. 2. Stiff spatula is used to mix the putty and liquid. Once well incorporated, mixing may be continued by hand for 30 seconds or until free from streaks. It is recommended that the hands be moist during mixing. 4. The putty is placed in a perforated tray and a preliminary impression is made. The impression tray is rocked to provide 1-2 mm of space for the wash material, then the putty is allowed to set. 5. The wash material is mixed as is any syringe material and injected into the impression area, held firmly until the wash material sets. * The putty-wash system increases the accuracy of the impression. Manipulation: Addition type Has four consistencies, so the same manipulation as mentioned above. Scoops are supplied for dispensing the putty base and catalyst. A retarder liquid is added, which extends the working time. The addition silicones are less viscous than polysulfides and can be mixed in 30-45 seconds to a streak –free mix. Latex gloves cannot be used, the rubber will retard the setting time. Vinyl gloves or bare hands are acceptable. o Setting Time: 25 C = 6-7 minutes o 37 C = 4-5 minutes Putty-Wash Technique (2 Steps) 1st Step: Primary Impression 1) Take equal amounts of base/ 2) Knead until color of mix is catalyst of putty using uniform color-coded measuring spoons Do not wear gloves. Putty Wash Technique 1st Step: Primary Impression 3) Place kneaded putty in stock Seat in mouth until set tray Putty-Wash Technique (2 Steps) 1st Step: Primary Impression 4) Remove some set putty around prepared teeth to provide space for final impression Putty-Wash Technique (2 Steps) 2nd Step: Final Impression 5) Hand mix wash material, or use Automix Catridge for: Uniform proportioning & homogenous mix Reduced mixing time & less wastage of materials Minimal air incorporation Putty-Wash Technique (2 Steps) 2nd Step: Final Impression 6) Inject mixed material into/around prep Putty Wash Technique (2 Step) 2nd Step: Final Impression 7) Put remaining wash material into putty-impression Putty Wash Technique (2 Steps) 2nd Step: Final Impression 8) Reseat tray into mouth & held until set Polyether RIM Polyether systems offer the possible combination of better mechanical properties than those of the polysulfides along with less dimensional change than those of condensation silicone materials. Disadvantages: short working time and high stiffness. Polyether RIM Composition: base & catalyst system The base material contains: 1. polyether polymer 2. colloidal silica as filler 3. plasticizer such as glycol ether phtalate The accelerator material contains: 1. alkyl-aromatic sulfonate 2. Filler 3. plasticizer Polyether RIM Manipulation: Equal lengths are extruded onto the paper mixing pad. Mixing is accomplished as with other RIM. It must be emphasized that a homogenous mix is essential for accuracy. Stock (rim-locked & perforated) / individual tray with an adhesive, butyl rubber cement. The adhesive will form a tenacious bond between the rubber material and the tray. Polyether RIM Methods of impression making: 1. Single impression technique: base and catalyst mixed and a single impression is taken. 2. Double impression technique: paste-putty system; preliminary impression using putty followed by a wash impression (thinner consistency) placed on top of putty as second or corrective impression. 3. Syringe technique = light-bodied + catalyst material injected into prepared tooth then followed by a secondary (regular body + catalyst) paste impression for a more accurate detailed impression with no bubbles. Ideal for laminates. Polyether RIM Single Impression Technique Polyether RIM Double Impression Technique Polyether RIM Syringe Technique Polyether RIM Manner of removal from patient‟s mouth: Remove with a steady force (a snap removal is not necessary). The material should be pulled slowly to break the seal then removed in a single stroke Rinse the impression with cold water disinfect, and blow dry before pouring cast material. The impression should not be stored in water or in direct sunlight, and the dies or models should be poured promptly. Polyether RIM Factors controlling setting time: 1.The ST can be controlled by temperature of the mixing slab or pad. - Increase in temperature - shortens ST - Decrease in temperature - prolongs ST A drop of water is a practical method for acceleration of curing. A drop or two of oleic acid will retard curing. A change in the ratio of accelerator paste to the base paste is not recommended for polysulfide RIM but OK for silicone materials. Delay of curing can be achieved by reducing amount of accelerator to base. RIM Properties: 1. Excellent elasticity - The polysulfide are allowed 4% & silicones 2% permanent deformation after a 12 % strain is held for 30 seconds. The elastic properties of the rubber impression materials improve with time of curing. The longer the impression can remain in the mouth before removal, the more accurate it will be after removal. 2. The tear strength of RIM are much superior to hydrocolloids, about 8X greater (22 lb/in – 4000 gm/cm) for polysulfide RIM; 17 lb/in (3000 gm/cm) for silicones. RIM 3. Dimensional stability - very low shrinkage in RIM which makes them much more stable dimensionally than hydrocolloids. Degree of contraction or shrinkage: - Polysulfide RIM = 0.3-0.4% during first 24 hours - Condensation silicone = 0.6% - Addition silicone = 0.1% - Polyether RIM = 0.2-0.4% 4. Excellent reproduction of detail 5. Compatibility with die and model materials Shelf life: Storage in a cool environment is advisable RIM Comparison of the 3 types of RIM: Polysulfide = long working & setting time, moderately high permanent deformation and flow, high flexibility Condensation / addition silicone = short working & setting time, moderate flexibility and tear strength; however addition silicones have very low shrinkage on setting flow, making them the most accurate impression material. Polyether = short working & setting time, low tear strength, and are very stiff. Types and causes of failures = in the book