Dental Impression Materials PDF

DENTAL IMPRESSION MATERIALS BY DR/ BASMA FAYAD  I. Introduction  The set impression is a negative reproduction of the oral tissues. To obtain a positive reproduction; (used to reproduce the form of the teeth and surrounding tissues )the set impression is poured by a suitable model or...

DENTAL IMPRESSION MATERIALS BY DR/ BASMA FAYAD  I. Introduction  The set impression is a negative reproduction of the oral tissues. To obtain a positive reproduction; (used to reproduce the form of the teeth and surrounding tissues )the set impression is poured by a suitable model or die material.  The impression material is introduced to the mouth in an unset (plastic) condition and is maintained in position against the oral tissues until it set, and then it is removed from the mouth.  When the impression is poured with dental stone, a positive replication of the mouth, which is called a “dental cast  This procedure provides a tridimensionality and accurate mouth replica ,allowing dental work even in the absence of the patient. THE DENTAL CAST (DENTAL MOULD OR DENTAL MODEL) IS THE POSITIVE REPRODUCTION OF A PATIENT'S TEETH AND SURROUNDING TISSUES OBTAINED FROM A DENTAL IMPRESSION (WHICH IS A NEGATIVE IMPRINT OF TEETH AND SOFT TISSUES) To study a case What is To diagnose a case the purpose of To educate our patients about making their dental needs models To treatment plan To construct indirect restorations including (inlays ,onlays ,bridges ,crowns ,dentures) II. Desirable 1. Adequate shelf life properties for impression 2. Acceptable odor and taste. materials: 3. Biologically acceptable: Not toxic or irritant constituents 4. Easily manipulated: Easy to use with the minimum of equipment II. Desirable 5. Setting characteristics that meet properties for clinical requirements: impression materials  Suitable working time and setting (Cont.): time (reasonable working and setting time)  THE IDEAL MATERIALS GIVE LONGER WORKING TIME FOR DENTAL PROFESSIONALS AND MINIMIZE SETTING TIME FOR PATIENTS  Readily wets oral tissues.  Not affected by the oral fluids. Does not release gas during setting. II. Desirable 6. Properties of the set properties for material: impression Sufficient mechanical strength so materials  that it will not break or tear on (Cont.): removal from the mouth.  Elastic properties with no permanent deformation after strain.  Good dimensional accuracy.  Dimensional stability over temperature and humidity ranges met in clinic and lab. II. Desirable properties for impression materials (Cont.): “No impression material fulfills all the requirements” The selection of the material best suited for a particular clinical situation and technique rests with the dentist III. Classifications of impression materials 1- Method of setting: A. Hardening by chemical reaction: (thermoset) e.g. Plaster of Paris, Alginates, and Rubber impression materials.(irreversible) B. Softening and hardening by heat: (thermoplastic) These are reversible substances. e.g. Impression compounds. III. Classification of impression materials (cont.) 2- Behavior after setting: impression materials are commonly classified by their elastic properties once set. A. Non-elastic impression materials: They are used only when no undercuts exist. e.g. Plaster of Paris, and Zinc oxide Eugenol. B. Elastic impression materials: They can be used when undercuts exist.e.g. Hydrocolloids, and Rubber impression materials.  Waxes Plaster Non-Elastic Zno-Eugenol Compound Impression Material Alginate Hydrocolloid Agar Agar/Alginate Elastic Polysulfide Condensation Rubber base Silicone (Elastomers) Addition Polyether A. Non-elastic Rigid when set and therefore exhibit very little elasticity and any significant deformation to the impression results in permanent deformation The rigid materials are usually used to record impressions of edentulous arches Inability to sustain a substantial amount of elastic deformation without fracture A. NON-ELASTIC IMPRESSION MATERIALS A. Wax B. Impression Plaster (Plaster of Paris) C. Impression compound D. Zinc oxide-Eugenol impression material A. NON-ELASTIC IMPRESSION MATERIALS  Impression compound: must be Non elastic heated in a water bath and then molded onto the impression tray. It doesn’t flow well and can't record fine detail. It is therefore used for impression primary impressions of edentulous arches. Zinc oxide eugenol: Impression paste is materials a modified form of zinc oxide eugenol.. It comes in two tubes: one containing a white zinc oxide mixture and the other containing a red eugenol mixture. After mixing ,the mix be loaded into a special tray for secondary impressions of the edentulous arch. The advantage of impression paste is an improved fit ,accuracy can be improved by retaking the impression ,by adding fresh paste and inserting into the patient mouth until set But unfortunately it cant reproduce undercuts , and the material tends to stick to the patients hand and mouth ,and some patients may be sensitive to materials containing eugenol B. Elastic impression materials  B. Elastic impression materials Elastic impression materials can be divided into the following types: 1. Hydrocolloids – These include reversible hydrocolloids like agar agar and irreversible hydrocolloids like alginates. 2. Elastomers – These are materials that demonstrate a similar elastic behavior to natural rubber. Depending on their chemical composition, elastomers can be divided into the following types: polysulfides, condensation silicones (C- silicones), addition silicones (A-silicones) and polyethers. Let us look in greater detail at the characteristics, applications and potential disadvantages of all these types of material. 1. hydrocolloid Definitions:  Hydro means water  Colloid means gelatin substance  Materials used to obtain preliminary and final impressions A colloid is a substance that is microscopically dispersed uniformly throughout another substance if the dispersion phase of a colloid system is water , its called a hydrocolloid Characteristics of hydrocolloids impression materials: During impression making ,the material sets from a flowable state to a solid state , this change of state associated with hydrocolloid is called the sol-gel transformation. A Sol is a colloidal dispersion of very small particles in a continuous liquid medium. Gel is a suspension that behaves like an elastic solid. Reduction in Chemical temperature Reaction Agar Alginate impression impression material material  Dimensional effects by Syneresis Imbibition Loss of water Absorption of water Shrinkage Expansion  The hydrocolloid gel may loose water by exuding of fluid ,and the prothesis is known as syneresis Imbibition is the process of Syneresis gaining of water when immersed and in water imbibition Both the phenomenon can cause dimensional changes and produce inaccurate casts. To avoid this impression should be poured immediately A. IRREVERSIBLE HYDROCOLLOIDS 1. Alginate Material that can’t return to a solution state after it becomes a gel(irreversible hydrocolloid ) Most widely used for preliminary impressions Alginate Advantages: impression 1. Easy of mixing and manipulation. material 2. Minimum equipment. 3. Flexible. 4. Accuracy is there if properly handled. 5. Low cost..  Disadvantages: 1. Restrict the model & die material to only gypsum. 2. Not accurate in reproducing fine details(not recommended when high degree of accuracy is required ex FPD 3. Poor dimensional stability –it cannot be store for a long time 4. Poor tear strength 5. Alginate impressions must not be soaked for too long in a water-based disinfectant and should be cast up as soon as possible to avoid shrinkage leading to inaccurate dental work.  Classification Normal set alginate : working time of 2 mins and a setting time of up to 5 mins after mixing fast set alginate: working time of 1 min and a setting time of up to 1-2 mins after mixing Working time: the time allowed for mixing the alginate , loading the tray and positioning the tray in the patient mouth Setting time : the time required for the chemical reaction to be completed Altering Cooler water can the setting increase the setting time time of if additional time is alginate needed for the procedure Warmer water can reduce or shorten the setting time of the process  Alginate impression material (cont.) Uses Preparing Preparing study cast gypsum models Removable Athletic partial mouth denture protector NOTE: Not recommended for impression of cavity preparations Alginate Storage: impression material It should be stored in 100% (cont.) relative humidity to avoid syneresis/imbibitions and thus avoid shrinkage/expansion. Alginate Manipulation: impression material  Equipment needed: (cont.) a. A powder-dispensing cup. b. A water-dispensing cup. c. A rubber mixing bowel. d. A spatula with ALGINATE IMPRESSION MATERIAL (CONT.)  B.Reversible hydrocolloids Agar: reversible hydrocolloidal impression material. It gives good detail reproduction than any other material. However, it has been replaced by rubber-based impression materials because of the costly armamentarium required and prolonged chair time.  Excellent detail reproduction Can record Agar undercut areas correctly impression Advantages materials Well tolerated by the patient. Distortion on removal is prevented due to elastic recovery Agar impression materials Special armamentariu (cont.) m required Disadvantages Gypsum harder required Patient discomfort of thermal shock  AGAR IMPRESSION MATERIALS (CONT.) chamber conditioning unit  2. Elastomers (Rubber base impression materials) Definition: Non aqueous elastomeric impression materials, that are rubber-like, and are made-up from long chain coiled molecules.  Elastomers :Elastomers comprise a group of synthetic polymer-based impression materials that are chemically cross-linked when set and that can be stretched and yet rapidly recover to their original dimensions They are used where a high degree of accuracy is needed, especially in crown and bridge work They have two main advantages over hydrocolloids ,good tear resistance and dimensional stability Four types of elastomeric impression materials are available in the market based on the backbone of polymer chains: : A. polysulfide B. SILCONES 1. Condensation silicone 2. Addition silicone, also known as polyvinyl siloxanes (PVS) C. D. polyether Fluid impression materials (ELASTOMERS) These materials have a very soft ("runny") consistency when placed inside impression trays. After setting, they become hard and elastic. Their fluidity combined with specific features makes them the most accurate impression materials. The fluid materials are used in the second stage of the wash technique impression after an initial impression taken with a more viscous material. Materials in this category: polyether, polysulfide, fluid silicones Types of Impression Trays: 1. Stock Trays: Stock trays are pre-made and come in a range of standard sizes (small, medium, large) to fit different mouth shapes. They are often divided into upper and lower arch trays and can be made from plastic or metal. Although convenient, they may not fit every patient perfectly, leading to the use of custom trays for more precise impressions. 2. Custom Trays: Custom trays are individually crafted for a specific patient’s mouth. These trays are made using a preliminary impression to ensure the perfect fit, making them ideal for cases where high accuracy is crucial, such as in the creation of crowns, bridges, or dentures. they are produced specifically for an individual patient. Having an impression tray that accurately reflects the anatomy of the patient’s arch is a great advantage as the material used to take the impression will be distributed more accurately and more evenly over the relevant areas. REPRESENTATIVE COMMERCIALLY AVAILABLE ELASTOMERIC IMPRESSION MATERIALS. Rubber base Main advantage of elastomers impression are: materials (Elastomers) High accuracy. (C0nt.) More dimensional stability than Agar & alginate. Ease of manipulation. Can be used with undercuts. Can be electroplated. Rubber base 1-According to viscosities impression 1. Light bodied (Syringe materials consistency /wash). (Elastomers) 2. Medium (Regular). (C0nt.) dispensed in two collapsible tubes as base and catalyst 3. Heavy body (Tray consistency ). 4. Very heavy (putty consistency ). two jars containing base and catalyst Rubber base 2-Mixing systems: impression materials 3 types of mixing systems are (Elastomers) available: (C0nt.) I. Hand mixing II. STATIC Auto-mixing III. Dynamic mechanical mixing Rubber base 3-Impression techniques: impression Simultaneous dual viscosity materials technique. (Elastomers) (C0nt.) Single viscosity (mono- phase) technique. Putty wash technique. Rubber base impression materials (Elastomers)(C0nt.) Types of Elastomeric impression materials A. Polysulfides. B. Silicones: 1. Condensation Silicone 2. Addition silicone C. Polyethers. Types of Elastomeric impression materials A. Polysulfides POLYSULFIDES THESE ARE THE FIRST ELASTOMERS TO BE INTRODUCED ARE HYDROPHOBIC ELASTOMERS OF NATURAL ORIGIN AND ARE THEREFORE RELATIVELY CHEAP. THEY ALSO AFFORD EXCELLENT TEAR RESISTANCE, VISCOSITY AND ELASTICITY. IT IS USEFUL WHEN A LONG WORKING TIME IS NEEDED. THEIR EXTENDED CURING TIMES MAKE THEM SUITABLE FOR TAKING SECONDARY, MUCODYNAMIC IMPRESSIONS FROM TOTALLY EDENTULOUS PATIENTS AND WHEN IMPRESSIONS ARE BEING TAKEN OF MULTIPLE PREPARATIONS,’’ BUT A DISADVANTAGE WHEN ONLY ONE OR TWO TEETH HAVE BEEN PREPARED. ITS DISADVANTAGE OF A LONG SETTING TIME IN THE MOUTH INDUCES POOR PATIENT ACCEPTANCE (ESPECIALLY IN VIEW OF ITS UNPLEASANT SULFIDE ODOR). THEIR LIMITED DIMENSIONAL STABILITY, HOWEVER, OBLIGES DENTAL TECHNICIANS TO CAST IMPRESSIONS WITHIN 30 MINUTES OF REMOVAL FROM THE ORAL CAVITY Consistencies: Light body Regukar body Heavy body Mode of supply: It is available in a two- paste system: base and accelerator. THE POLYSULFIDE PREPOLYMER REACTS WITH LEAD OXIDE, FORMING POLYSULFIDE RUBBER AND WATER(REACTION BYPRODUCT). LOSS OF THIS SMALL MOLECULE FROM THE SET MATERIAL HAS A SIGNIFICANT EFFECT ON THE DIMENSIONAL STABILITY OF THE IMPRESSION.; THEREFORE, THE IMPRESSION SHOULD BE CAST IMMEDIATELY. POLYSULFIDE IS THE MOST FLEXIBLE OF ELASTOMERIC MATERIALS, AND IT CAN BE EASILY REMOVED FROM UNDERCUT AREAS  Polymerization of polysulfide impression material. SH groups interact with oxygen released from lead dioxide (left). Completion of the condensation reaction results in water as a by-product (right). Pendant −SH is for cross-linking and terminal −SH is for chain lengthening of the polymer.  Advantages: Rubber base. Least rigid (most flexible of all the elastomers) Good tear strength impression Most biocompatible materials Excellent flow so good reproduction of details (Elastomers) Disadvantages: (C0nt.) Dimensional instability (water by-product). Must be poured within half an hour Hydrophobic. Bad odor (Sulfide odor). Staining of clothes. Relatively long setting time. custom-made rather than stock trays are needed because of the greater chance of distortion  Types of Elastomeric impression materials (CONT.) B. Silicones 1. Condensation Silicone 2. Addition Silicone  Condensation silicone: Types of Solve many problems of polysulphides Elastomeric impression more affordable than other elastomeric materials but have the disadvantage materials of being prone to shrinkage, requiring immediate pouring. 1. Condensation Advantages: 1-moderate working time Silicones 2-better odour and taste 3-less permnant deformation Disadvantages: 1-hydrophobic 2-dimensional instability (alcohol by-product)  Mode of supply: Consistencies: In collapsible tubes as base and catalyst Extra-low, (medium body)(two-paste system ) Low, In jars as base and catalyst (putty)(two putty system) medium, Syringes (ultralow and low) base paste and putty and a liquid catalyst C-silicone Putty/ light and catalyst POLYMERIZATION REACTION OCCURS WITH THE RELEASE OF ALCOHOL AS A BYPRODUCT THAT EVAPORATES AS FORMED. Advantages: 1-moderate working time 2-pleasant odor and taste 3-less permanent deformation(good elastic recovery) 4-The use of a putty-wash method improves accuracy and eliminates the need for a custom tray Disadvantages: Dimensional stability is affected due to reaction byproducts[(shrinkage on standing and should be poured within 1 hour) Hydrophobic (:requires a very dry field) poor wetting characteristics. The prepared teeth and gingival sulci must be completely free of moisture for a defect-free impression  Types of They are the most widely Elastomeric used impression materials impression materials in fixed prosthodontics. 2. Addition Have the least amount of Silicone shrinkage on setting (polyvinyl siloxane (PVS) making them the most or vinyl polysiloxane accurate class of rubber (VPS) impression material. MODE OF SUPPLY: AVAILABLE IN ALL CONSISTENCIES: ( EXTRA-LOW, LOW, MEDIUM, HEAVY, AND PUTTY) PUTTY/ CARTILAGE/ GUN SYSTEM Elastomeric Impression Materials. The image shows a loaded dispensing gun with cartridge and syringe, which is mostly used for light body elastomeric impression material (A); dispensing gun, cartridge, and unassembled syringe (B); and jars for putty elastomeric impression material, base and catalyst (C).  The poly(vinylsiloxanes) are characterized by excellent dimensional accuracy and long-term dimensional stability Their great stability means that accurate dies can be poured for up to a week after they have been removed from the mouth. If delay in pouring for making dies is anticipated, the addition silicones are the best choice of the rubber impression materials.  A secondary reaction can occur with the production of hydrogen gas which can result in pinpoint voids in the gypsum casts poured soon after the removal of the impression from the mouth. Epoxy dies should not be poured until the impression has stood overnight. Some products contain a hydrogen absorber (scavenger) such as palladium, and gypsum and epoxy die materials can be poured against them as soon as practical.  Sulfur contamination from natural latex gloves inhibits the setting of addition silicone. Thorough washing of the gloves with detergent and water just before mixing sometimes minimizes this effect. Vinyl and nitrile gloves do not have such an effect. Rubber base Properties: impression Accuracy: Highly accurate. materials Dimensional stability: Addition is more stable. (Elastomers) Flow: Is low. (C0nt.) Flexibility: Less flexible than Polysulfides. Elasticity: More elastic than Polysulfides (elastic recovery is 99.5%). Compatibility with die materials: Compatible with most types. Tear strength: Relatively low, but rapid rate of removal gives high tear strength. Can be electroplated. Can be disinfected by most disinfectants. Advantages Excellent dimensional stability - impressions can be stored or posted before casting. Elastic recovery Great accuracy Short setting time Good tear resistance Automix available Disadvantages: Hydrophobic - the impression area must be dry to prevent inaccuracies in the impression. The sulfur present in the latex gloves and rubber dam may interfere with the polymerization of the base and catalyst. Hydrogen gas may lead to pitting in the cast. Types of Elastomeric impression materials (cont.) C. Polyether Polyether: it has become popular because it only requires a stock tray and a single mix. Mode of supply: Available as light, medium, and heavy body consistencies. Polyether impression material (Cont). Properties :  Accuracy: Highly accurate.  Dimensional stability: Polymerization shrinkage of 0.25% within 24 hours.  Flexibility: Least flexibility of all rubbers.  Elasticity: Viscoelastic with elastic recovery 98.9%.  Compatibility with die materials: Excellent  Tear strength: Better than Silicone, less than Polysulfide.  Can be disinfected by various antimicrobials. Advantages: Disadvantage: 1. Most rigid of all the 1. Hydrophilic elastomers makes it hard 2. Accurate and high dimensional stability to remove (newer - makes it possible to delay casting and polyethers are slightly more allow multiple pouring. flexible) 3. These materials are more accurate 2. May cause allergy due to than polysulfide or condensation silicone sulfonate acid esters( it impression materials. produces on allergic response in a significant 4. Good elastic recovery number of people) 5. Good compatibility with gypsum(easily 3. The cost of these poured with stone ) materials is high 4. working and setting 6. Good shelf life times are short It can be used as a single-phase material or with a syringe tray technique  VI. Impression techniques Single-viscosity or mono phase technique A. One-step impression (putty and wash are recorded simultaneously) Dual-viscosity or dual-phase technique B. Two steps impression ( putty is recorded first and after setting relined with thin layer of wash) It can be spaced or unspaced Single-viscosity or mono phase technique: A single-stage, one-phase impression technique. One impression material, usually of medium viscosity, is used for filling the tray and for syringing the prepared teeth. Addition-silicone and polyether impression materials are well suited for this technique because both have a capacity for shear thinning. When the medium viscosity material is forced through an impression syringe, the viscosity is reduced (because it is pseudoplastic material) whereas the viscosity of the same material residing in the tray is unaffected. In this manner, such materials can be used for syringing and for trays, as previously described for the simultaneous, dual-viscosity technique. Dual-viscosity or dual-phase technique: There are essentially three ways of recording a putty-wash impression A. One step impression (The simultaneous, dual-viscosity technique): putty and wash are recorded simultaneously. B. Two steps impression: 1. Unspaced: putty is recorded first and after setting relined with a thin layer of wash. 2. Spaced: a space is created for the light wash. A. ONE STEP IMPRESSION  low-consistency material is injected with a syringe into critical areas and the high- consistency material is mixed and placed in an impression tray. After injecting the low-viscosity material, the tray containing the higher-viscosity material is placed in the mouth. In this manner, the more viscous tray impression material forces the lower- viscosity material to flow into fine aspects of the areas of interest. Because they are both mixed at nearly the same time, the materials join, bond, and set together. After the materials have set, the tray and the impression are removed. B. Two steps impression 1. Two steps unspaced: putty is recorded first and after setting relined with a thin layer of wash. Disadvantages: Difficulty in reseating the set putty in the mouth. Contamination of the putty with saliva which may prevent light body adhering to it. 2. Two steps spaced: a space is created for the wash. Space can be made by: Polythene spacer over the teeth or putty prior to making putty impression. Removing a thin layer from the putty impression by scrapping  Optical impression RECENT ADVANCES OF IMPRESSION MATERIALS INTRA-ORAL SCANNING Intra-oral scanning allows you to take a scan of the natural teeth and gingiva. This saves you an extra work step and makes impression-taking more pleasant and time-saving than ever before. Demonstration of intra-oral scanning  Optical Advantages: impression No need for impression materials or trays. Impression can be transmitted & stored electronically. No mess. 3D, 360˚ view of preparation that can be moved & turned to every angle. Adjustments can be made to the virtual impression, no need for second impression. No disinfection required.  Optical Disadvantages: impression (cont.) Start up cost. Technique sensitive. More equipment required.