Elastomeric Impression Materials PDF

ELASTOMERIC IMPRESSION MATERIAL ELASTOMERIC “Having elastic or rubber-like qualities” Ability to remove the impression after it has been set without distorting or tearing it. Elastomeric impression materials: A group of flexible po...

ELASTOMERIC IMPRESSION MATERIAL ELASTOMERIC “Having elastic or rubber-like qualities” Ability to remove the impression after it has been set without distorting or tearing it. Elastomeric impression materials: A group of flexible polymers materials that can be easily stretched and rapidly recover their original dimensions when applied stresses are released. ELASTOMERIC IMPRESSION MATERIAL Characteristics of EIM Self curing Supplied as a base and a catalyst (accelerator) Paste in a tube Paste in a tube Paste in a cartridge Paste in a cartridge Putty in a jar Liquid in a bottle with a dropper top Materials are supplied in three forms – light bodied, regular, and heavy-bodied. Elastomeric Impression Materials Advantages of elastomeric impression materials over the hydrocolloids Elastomeric impression materials have higher tear strength than hydrocolloid. Tear strength – resistance to fracture of an elastomeric material measured N/m where N = maximum force needed to pull specimen apart and m = thickness of the specimen. Elastomers have no synersis or imbibition like hydrocolloids. They are more dimensionally stable on storage. Most of the elastomers can be electroplated. ELASTOMERIC IMPRESSION MATERIALS GENERAL PROPERTIES Excellent reproduction of fine detail Excellent tear strength High coefficient of thermal expansion Electroplating can be done They are generally hydrophobic except polyether which is hydrophillic Hydrophobic – materials that naturally repel water causing droplets to form Hydrophillic – materials that have an affinity for water(spreads across maximizing contact) ELASTOMERIC IMPRESSION MATERIALS Properties cont’d Has a shelf life of approximately two (2 years) – cool condition increase shelf life. Dimensional changes occur: Curing shrinkage Incomplete elastic recovery Amount of filler content- less filler = more shrinkage; more filler = less shrinkage Loss of water (polyether) Thermal contraction when transferred from mouth to room temperature Time of pouring impression ELASTOMERIC IMPRESSION MATERIAL 1. Light-bodied (syringe type, wash-type) – ability to flow into and around the details of the prepared tooth. A special (extruder) is used to apply light-bodied material immediately around prepared teeth. 2. Regular and heavy-bodied material (tray-type) 1. Thicker than light bodied impression materials 2. Used to fill the tray 3. Stiffness helps to force light bodied material into close contact with prepared teeth and surrounding tissues. ELASTOMERIC IMPRESSION MATERIAL Curing of EMI Polymerization (curing reaction) is initiated as soon as the base and catalyst come in contact. This reaction takes place in three stages: 1. Initial set - paste stiffens without appearance of elasticity. 2. Final set - paste appears elastic and proceeds through a gradual change to a solid rubbery mass 3. Final cure - occurs within 1 – 24 hours Types of Elastomeric Materials Types of EMI most often used in dental practice are: 1. Polysulphide 2. Polyether 3. Silicone 4. Polysiloxane – polyvinyl siloxane Polusulphide First elastomeric impression material used for final impression in dentistry Rubber or rubber-based materials Also known As mercaptan or thymol Polysulphide is available in light-bodied, regular and heavy-bodied forms. Composition of polysulphide The material is supplied as two pastes in two tubes – one tube is dark brown; the other is white and larger. Base (white) paste contains: mercaptan polysulphide inorganic filler(Titanium oxide, silica, zinc sulphate). The brown paste (accelerator paste) contains: lead dioxide Dibutyl phthalate an oily chemical (magnesium stearate) sulfur to promote polymerization reaction. Use of polysulphide impression material Used for impressions of crowns and bridges – a light bodied material is injected around the preparation and a heavy-bodied material is used in the tray. Used with custom trays to increase accuracy of the impression Light and medium-body material s are used for full denture impressions Properties of polysulphide Accuracy – much more accurate than alginate; not as accurate as other elastomeric materials Excellent reproduction of details Lowest viscosity High tear strength Hydrophobic –tissue should be thoroughly dry Does not have a pleasant smell Of all the elastomeric materials it has the longest working time – 4 to 6 minutes. The working and setting times are accelerated by heat and humidity Dimensional stability: Water lost through evaporation may result in distortion. Good flexibility; allows for elastic recovery of the material Can be electroplated with copper Advantages and disadvantages of Polysulphide ADVANTAGES DISADVANTAGES More accurate than alginate Offensive odor and taste Long working time Must be poured with dental (4 – 7 mins.) stone immediately High tear resistance Stains clothing Long shelf life Significant distortion – loss of water Inexpensive to use Long setting time (7 – 10 mins.) High flexibility Not as accurate as other EMIM Mixing Polysulphide Impression The two pastes are dispensed in equal lengths on a paper mixing pad. The two pastes are mixed together with an impression material spatula – pastes are swirled and stropped together until a homogenous mix is obtained. The slide of the spatula is used to scrape unmixed material off the pad and then to incorporate it into the rest of the material Mixing may take 30 to 90 seconds s depending on the amount and viscosity of the material Polymerization starts when mixing begins and proceeds slowly. POLYETHER ELASTOMERIC IMPRESSION MATERIAL First elastomer to function as an impression material Material is supplied in different consistencies Light body (syringe, wash) Medium body (regular) Heavy body Material is supplied in tubes Base tube (large tube) accelerator tube (small tube) POLYETHER ELASTOMERIC IMPRESSION MATERIAL COMPOSITION Accelerator tube Sulphonic acid – initiate cross linking with the prepolymer Filler (silica) forms the paste Phthalite (plasticizer) Base tube Prepolymer – to form rubber Filler eg. Silica – gives body and control viscosity, control physical property Phthalite (plasticizer)- aids in mixing POLYETHER ELASTOMERIC IMPRESSION MATERIAL PROPERTIES Working time of 3 minutes Setting time of 6 minutes Good dimensional stability Good tear strength Least amount of distortion Biocompatibility – allergic hypersensitivity occur in some cases- contact dermatitis POLYETHER ELASTOMERIC IMPRESSION MATERIAL ADVANTAGES Accuracy Dimensional stability Shorter setting time Automix is available DISADVANTAGES Short working time Set material is very stiff Imbibition Allergic hypersensitivity in some instances Polyether Impression Material Recent advances Visible light cured polyether urethane dimethacrylate Introduced in 1988 – L.D. Caulk Supplied in two viscosities –light bodied; heavy bodied Composition Polyether urethane dimethacrylate Photoinitiators (camphoroquinone) Photoaccelerators (Diethyl amino ethyl methacrylate Filler (Silicone Dioxide) POLYETHER ELASTOMERIC IMPRESSION MATERIAL Properties of VLPUD Controlled working time Uses blue curing light and special transparent impression trays Has excellent properties Tear strength highest among elastomers Dimensional stability Detail reproduction Compatible with cast and die materials POLYETHER ELASTOMERIC IMPRESSION MATERIAL MANIPULATION of VLPUD Light bodied material is syringed into the sulcus and over the preparation Heavy bodied is loaded in the clear tray and seated over the light bodied material Both material are cured with visible light curing unit with 8mm or more diameter probe Curing time is approximately 3 minutes. Addition Silicone Condensation silicone SILICONE ELASTOMERIC IMPRESSION MATERIAL Silicone impression material consists of a base and catalyst in a putty consistency. They are available in a range of viscosities including light, medium, heavy and very high viscosity (or putty) material. Silicone material was developed after the polysulphide impression material. There are two types of Silicone material 1. Condensation Silicone/Conventional Silicone 2. Addition silicone https://www.slideshare.net/asdna505/12-elastomeric-imp-2010? SILICONE ELASTOMERIC IMPRESSION MATERIAL Condensation Silicone/Conventional Silicone First type of silicone impression material Settings occur at room temperature – RTV silicones Consists of a base and catalyst in a putty consistency. Supplied in various viscosities - light, medium, heavy and very high viscosity (or putty). SILICONE ELASTOMERIC IMPRESSION MATERIAL COMPOSITION - 2 paste system Base paste: Poly dimethyl siloxane polymer Filler : colloidal silica or titanium oxide Colour pigments Catalyst Liquid - Cross linking agent: alkyl silicate - Activator; Stannous Octoate or tin dilaurate) Paste - Cross linking agent, - Activator - Filler SILICONE ELASTOMERIC IMPRESSION MATERIAL Working time = 2.5 – 4 minutes Setting time = 6 – 8 minutes SILICONE ELASTOMERIC IMPRESSION MATERIAL AVANTAGES AND DISADVANTAGES OF CS Advantages Adequate working and setting time Pleasant taste and odour Disadvantage Low tear strength Hydrophobic Needs to be poured immediately Poor dimensional stability - High polymerization shrinkage Volatile alcohol bi product https://www.slideshare.net/asdna505/12-elastomeric-imp-2010? SILICONE ELASTOMERIC IMPRESSION MATERIAL Also known as polyvinyl siloxane Introduced after condensation silicone Improved properties over condensation silicone Available in low viscosity, medium viscosity and putty viscosity Mixing time 5.9 minutes Setting time 45 seconds SILICONE ELASTOMERIC IMPRESSION MATERIAL Composition of Addition Silicone A. BASE Poly methyl hydrogen siloxane Other siloxane prepolymers Fillers B. CATYLYST Divnyl polysiloxane Inert oils &fillers Platinum salt Palladium Retarders SILICONE ELASTOMERIC IMPRESSION MATERIAL Properties of Addition Silicone Highest dimensional stability among the elastomers Good tear strength Excellent surface detail reproduction Lowest curing shrinkage Low flexibility Exhibits the lowest permanent distortion Can be electroplated with copper and silver SILICONE ELASTOMERIC IMPRESSION MATERIAL Advantages and disadvantages Advantages Adequate strength High accuracy Short setting time High Dimensional stability Minimum distortion Disadvantages Hydrogen gas may cause dimensional stability Expensive Hydrophobic SILICONE ELASTOMERIC IMPRESSION MATERIAL Factors inhibiting the setting time of AS Sulphur contamination e.g. from latex gloves Materials used in gingival retraction cord e.g. aluminum sulphate Residues from acrylics, methacrylates and petroleum jelly may also interfere with setting reaction. SILICONE ELASTOMERIC IMPRESSION MATERIAL Disinfection Methods for Elastomers Polysulphide & Silicones Done by immersion More than 30 minutes not recommended Glutaraldehyde, chlorine component, iodophors. phenolics Polyether Immerse with caution Short-term exposure minimizes distortion Chlorine compounds and iodophers QUIZZIE What are the factors that affect dimensional stability of EMIMs? Give another name for Additional Silicone Which property refers to resistance to fracture of an elastomeric material? Name two disinfectants used to disinfect elastomers Which EMIM has the highest dimensional stability among the elastomers arunimaupendran/elastomeric-impression-materials-79811203