Dental Materials PDF

DENTAL MATERIALS OLFU- COLLEGE OF DENTISTRY  INTRODUCTION TO DENTAL MATERIALS  Introduction The study of dental materials will enable members of the dental health profession to understand the properties of these materials and how best to use them. The correct selection and manipulation of...

DENTAL MATERIALS OLFU- COLLEGE OF DENTISTRY  INTRODUCTION TO DENTAL MATERIALS  Introduction The study of dental materials will enable members of the dental health profession to understand the properties of these materials and how best to use them. The correct selection and manipulation of dental materials largely determine the service a restoration will give to the patient.  Definition Science of Dental Materials is a basic science which deal with the physical, mechanical and biological properties of dental materials.  HISTORY  Seashells, Ivory, Bone, Wood, Metal wires, Animal & Human teeth, stones iron, precious metals, & alloys.  700 - 800 B.C. – Etruscans: partial dentures  600 B.C. – Mayans: implants & inlays  2500 B.C. – Phoenicians: gold wires & bands  3000 B.C. – Egyptian: tooth doctors  HISTORY  Pierre Fauchard (1678 - 1761) “Father of Modern Dentistry” – published a treatise of resto materials (1728)  Pfaff (1756) – wax impressions & plaster models  de Chamant (1792) – patented “mineral paste” porcelain teeth  1800: Porcelain inlays  1895: G.V. Black - pioneered restorative dentistry  HISTORY  1915: effects of fluoride were noted in Colorado  1919: NIST set up specifications for evaluation and selection of amalgam for US govt. use  1928: Dental Research Fellowship by Dr. W. Souder was absorbed by the ADA  1935: polymerized acrylic resin denture base  1944: fluoridation started in the US (1 ppm) IMPORTANCE OF STUDYING DENTAL MATERIALS 1. For the knowledge to make optimal selection of materials. 2. To understand the behavior of the materials, use, handling and manipulation 3. Safety considerations of the materials 4. Patient‟s education 5. Understanding the professional literature Importance of Dental Materials Science The sceince of dental materials has two main benefits: 1. Selection of the Materials 2. Evaluation of the Materials 1. Selection of the Materials  2. Evaluation of the Materials Most manufacturers of Dental materials operate an extensive quality assurance program and the materials are thoroughly tested before being released to the general practitioner. 1. Standard Specifications 2. Laboratory Evaluation 3. Clinical Trials  2.1 Standard Specifications (ADA) (FDA) (ISO) American Dental Federation Dental International Association Association Standard Organization  2.2 Laboratory Evaluation Performed initially for testing a new material. It is carried out outside the human body. This evaluation may include some animal tests for systemic toxicity.  2.3 Clinical Trials Manufacturers carryout extensive clinical trials of new materials in group of peoples, normally in cooperation with a university or hospital department, prioe to releasing a product for use by practitioners. Dental Materials may be classified as: 1. Preventive Dental Materials 2. Restorative Dental Materials 3. Auxiliary Dental Materials  Preventive Dental Materials Preventive dental materials are used to prevent disease in the oral cavity. - Pit and Fissure Sealants - Liners, bases, cements and restorative materials that are used primarily because they release fluoride. - Chemotherapeutic agents like dentrifices, mouthwashes and cavity varnish - Chlorhexidine or other therapeutic agents used to prevent or inhibit the progression of tooth decay.  Restorative Dental Materials It consists of all synthetic components that can be used to repair or replace tooth structure, including: - Primers - Bonding agents - Liners - Cement bases - Amalgam - Resin-based composites - Compomers - Cast metals  Restorative Dental Materials Restorative materials may further be classified as…. 1. Direct Restorative materials Use intra-orally to fabricate restorations or prosthetic devices directly on teeth. 2. Indirect Restorative materials Made extra-orally in which the materials are formed indirectly on casts or other replicas of the teeth.  Auxiliary Dental Materials Substance that are used in the process of fabricating dental prostheses and appliances but DO NOT BECOME part of these devices. These include: -Acid- etch solutions - Impression materials - Casting investments - Gypsum cast and model material - Dental Waxes - Acrylic resins for impression and bleaching trays - Finishing and polishing abrasives  Properties of an Ideal Restorative Material 1. Biocompatible 2. Bond permanently to tooth structure or bone 3. Match the natural appearance of tooth structure and other visible tissues 4. Exhibit properties similar to those of tooth enamel, dentin, and other tissues 5. Capable of initiating tissue repair or the regeneration of missing or damaged tissues General Categories of Biomaterials  PROPERTIES OF DENTAL MATERIAL An understanding of the physical, electrical and mechanical properties of materials used in dentistry is of tremendous importance. These are the basis for the selection of materials to be used in particular dental procedures and restorations. It is also important in the selection of materials to have knowledge of their effect on the oral tissues and of possible toxic effects if they are ingested.  Properties of Dental Materials 01 02 03 Before Mixing During Mixing and After Setting (Unmixed state) Setting 01 BEFORE MIXING (UNMIXED STATE) 1. SHELF LIFE:  It is the length of time a dental material can be stored without deterioration. 2. STORAGE  Must be stored as per manufacturer‟s instructions.  Over storage should be avoided.  02 DURING MIXING AND SETTING 1. Mixing Time 2. Working Time 3. Setting Time 1. MIXING TIME: The recommended time for mixing a material until the required consistency / homogenous mixture is achieved. It’s the time from the addition of powder to water until mixing is completed. 2. WORKING TIME: It’s the time during which a material can be mixed/manipulated ideally with no thickening effect. Time available to use a workable mix. 3. SETTING TIME Time required for a material to reach a certain level of rigidity/elasticity. Starts when the mixing begins until the material hardens (Setting reaction is complete)  03 AFTER SETTING 1. Biological properties 2. Chemical properties 3. Electrical properties 4. Thermal properties 5. Physical properties 6. Mechanical properties  Biological Properties of Dental Materials - Dental material should be non toxic, non irritant, non allergic, non carcinogenic & non mutagenic to oro-dental tissues. - Primarily the dental material must be harmless to manufacturer, assistant, dental surgeon, patient and any other relevant person.  Biological Properties The material is said to be “biocompatible” when it possesses the property of being non destructive (non toxic/non irritant) in a biological system. Biocompatibility is defined as, “The ability of a material to elicit an appropriate biological response in a given application in the body.”  Chemical Properties of Dental Materials 1. Sorption 2. Adsorption 3. Absorption 4. Diffusion 5. Osmosis 6. Solubility 7. Erosion 8. Adhesion 9. Cohesion 10. Surface energy 11. Wetting 12. Contact angle of wetting 13. Leaching  Chemical Properties of Dental Materials 1. SORPTION: The taking up and holding of one substance by another. Sorption is used especially as a general term for absorption and adsorption. 2. ADSORPTION: The process in which liquid or gas molecules adheres firmly to the surface of solid or liquid. 3. ABSORPTION: The process in which a liquid or gas molecules penetrate into the solid material.  Chemical Properties of Dental Materials 4. DIFFUSION: The process by which molecules intermingle as a result of their kinetic energy of random motion. 5. OSMOSIS: The diffusion of solute from the region of low concentration to the region of high concentration through semi permeable membrane is called osmosis.  Chemical Properties of Dental Materials 6. SOLUBILITY: It is the measurement of the extent to which a material will dissolve in a given fluid. e.g. saliva or water.  Chemical Properties of Dental Materials 7. EROSION: The process which combines the chemical process of dissolution with a mild mechanical action. In dentistry erosion is used to describe the destruction of natural hard tissue by acids (either occurring naturally or present in food/drinks)  Chemical Properties of Dental Materials 8. ADHESION: Force of attraction between molecules of different substances. 9. COHESION: Force of attraction between molecules of same substance.  Chemical Properties of Dental Materials 10. SURFACE ENERGY/SURFACE TENSION: The increase in energy per unit area is called as surface energy or surface tension. Interfacial tension that exists between the two surfaces due to unbalanced intermolecular forces. For adhesion to exist the surfaces must be attracted to one another at their interface  Chemical Properties of Dental Materials 11. WETTING/WETABILITY: Interfacial tension between a liquid and a solid resulting in a contact angle of less than 90°. Adhesion is negligible when the surface molecules of the two materials are separated by a distance greater than 0.7nm.  Chemical Properties of Dental Materials 12. CONTACT ANGLE OF WETTING: The extent to which an adhesive can wet the surface of adherent can be determined by measuring the contact angle between the adhesive and the adherent. If the molecules of adhesive are attracted more to the molecules of the surface, the adhesive will spread completely over the surface of the solid  Electrical Properties of Dental Materials 1) Conductor 2) Insulator 3) Electric conductivity 4) Galvanism  Electrical Properties of Dental Materials 1) CONDUCTOR: A conductor is a material that allow the flow of electrical current in one or more directions. A metal wire is a common electrical conductor. 2) INSULATOR: The materials that offer high resistance to the flow of electric current. Are called insulators.  Electrical Properties of Dental Materials 3) ELECTRICAL CONDUCTIVITY: The ability of a material to conduct an electric current is called electric conductivity. 4) GALVANISM: Galvanic action occurs when two electrochemically dissimilar metals are in contact and a conductive path occurs for electrons and ions to move from one metal to the other.  Thermal Properties of Dental Materials 1. Boiling point 2. Melting point 3. Freezing point 4. Dew point 5. Heat of fusion 6. Heat of vaporization 7. Thermal conductivity 8. Thermal diffusivity 9. Specific heat 10. Coefficient of thermal expansion.  Thermal Properties of Dental Materials 1. BOILING POINT: The temperature at which a liquid boils and turns to vapor. 2. MELTING POINT: The temperature at which a given solid will melt. 3. FREEZING POINT: The temperature at which a liquid turns into a solid when cooled.  Thermal Properties of Dental Materials 4. DEW POINT: The atmospheric temperature (varying according to pressure and humidity) below which water droplets begin to condense and dew can form. A higher dew point indicates more moisture in the air. Dew point greater than 20 °C (68 °F) is considered uncomfortable and greater than 22 °C (72 °F) is considered to be extremely humid.  Thermal Properties of Dental Materials 5. HEAT OF FUSION: Heat of fusion is the energy required to change a gram of a substance from the solid to the liquid state at melting temperature. 6. HEAT OF VAPOURIZATION: Heat of vaporization is the energy required to change a gram of a liquid into the gaseous state at the boiling point Is called the "heat of vaporization"  Thermal Properties of Dental Materials 7. THERMAL CONDUCTIVITY: It is the measure of the ability of a material to allow the flow of heat. 8. THERMAL DIFFUSIVITY: Thermal conductivity of a substance divided by the product of its density and its specific heat capacity.  Thermal Properties of Dental Materials 9. SPECIFIC HEAT: The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. 10. COEFFICIENT OF THERMAL EXPANSION: Change in length per unit original length per degree rise in temperature is called coefficient of thermal expansion.  Physical Properties of Dental Materials A. OPTICAL PROPERTIES B. RHEOLOGICAL PROPERTIES 1) Colour 1) Viscosity 2) Hue 2) Creep & Flow 3) Value 3) Viscoelasticity 4) Chroma 4) Newtonian behavior 5) Transparency 5) Pseudoplastic behavior 6) Translucency 6) Thixotrophic behavior 7) Opacity 7) Dilatant 8) Fluorescence.  Physical Properties of Dental Materials A. OPTICAL PROPERTIES 1. COLOUR: Combined intensities of the wavelengths present in the beam of light determine the property color. 2. HUE: The property associated with colour of an object (i.e. Red, Green, Blue) 3. VALUE: The amount of lightness or darkness of a colour is called value (i.e. from bright to dull) 4. CHROMA: Degree of saturation of a particular hue. Higher the chroma = more intense the colour.  Physical Properties of Dental Materials A. OPTICAL PROPERTIES 5. TRANSPARENCY: The property of a material that allows the passage of light in such a manner that the object may be clearly seen through. 6. TRANSLUCENCY: The property of a material that permits passage of light but disperses the light so the object cannot be seen through. 7. OPACITY: The property of a material that prevents the passage of light.  Physical Properties of Dental Materials A. OPTICAL PROPERTIES 8. FLUORESCENCE: The phenomenon of emission of light by a substance that has absorbed light or other electromagnetic radiations. It is an emission of light (photons) by a substance that has absorbed light of higher energy.  Physical Properties of Dental Materials B. RHEOLOGICAL PROPERTIES - Rheology is the science of flow and deformation of matter and describes the interrelation between force, deformation and time. - It is the study of the manner in which materials respond to applied stress or strain. - The term comes from Greek „rheos‟ meaning to flow.  Physical Properties of Dental Materials B. RHEOLOGICAL PROPERTIES  Physical Properties of Dental Materials B. RHEOLOGICAL PROPERTIES 1. VISCOSITY: Resistance of a liquid to flow. Viscosity is dependent upon interatomic bonding. Water molecules has weak interatomic bonding thus flows easily as compared to oil/honey  Physical Properties of Dental Materials B. RHEOLOGICAL PROPERTIES 2. CREEP AND FLOW : Creep is defined as the time dependent plastic strain of a material under static load or constant stress. Flow implies a greater deformation produced more rapidly with a smaller applied stress. “Flow describes the rheology of the amorphous materials in dentistry”  Physical Properties of Dental Materials B. RHEOLOGICAL PROPERTIES 3. VISCOELASTICITY: The behavior that is intermediate between viscous liquid and elastic solid. e.g. Elastomeric impression materials. The more rapidly the material is loaded or unloaded the more elastically the material will behave.  Physical Properties of Dental Materials B. RHEOLOGICAL PROPERTIES 4. NEWTONIAN BEHAVIOR: When shear strain rate is proportional to shear stress, the behavior is called Newtonian behavior. 5. PSEUDOPLASTIC BEHAVIOR: Material is called pseudoplastic when viscosity decreases with increase in shear rate. 6.THIXOTROPIC BEHAVIOR: Material is called thixotropic when it exhibit a different viscosity after deformation. 7. DILATANT: Behavior seen in liquids that show higher viscosity with increase in shear rate.  Mechanical Properties of Dental Materials 1. Stress 11. Hardness 2. Strain 12. Relaxation 3. Proportional limit 13. Permanent deformation 4. Yield point 14. Ductility 5. Modulus of elasticity 15. Malleability. 6. Poision’s ratio 7.Toughness 8. Brittleness 9. Strength 10. Resilience  Mechanical Properties of Dental Materials Defined by the laws of mechanics. The physical science that deals with energy and forces and their effects on the bodies. Mechanical properties need to be considered collectively. Intended application of a material is important. Failure or success potential of any prosthesis / restoration is dependent upon the mechanical properties of the material.  Mechanical Properties of Dental Materials Generally, the force applied may be : 1. Axial (tensile or compressive) 2. Shear (sliding, rubbing) 3. Torsional (twisting movement) 4. Bending (bending movement)  Mechanical Properties of Dental Materials TENSION : Tension results when a body is subjected to two sets of forces directed away from each other in a straight line. Causes the material to elongate/Stretch.  Mechanical Properties of Dental Materials TORSION: Torsion results from the twisting of the body. BENDING Bending results by applying bending movement.  Mechanical Properties of Dental Materials TORSION: Torsion results from the twisting of the body. BENDING Bending results by applying bending movement.  Mechanical Properties of Dental Materials STRESS When a force acts on the body, a resistance is developed to the external force applied which is equal in magnitude/intensity and opposite in direction to the applied force and is called as “STRESS” Denoted by “S” or “σ” Designated as force per unit area (σ=N/m²) Pascal = 1 N / m².  Mechanical Properties of Dental Materials STRAIN Relative deformation of an object due to stress. It is change in length per unit length. It may be elastic, plastic or both elastic and plastic. It is denoted by “ε” Designated as ∆L / L.  Mechanical Properties of Dental Materials PROPORTIONAL LIMIT It is the maximum stress at which the stress is equivalent/proportional to strain and above this limit the plastic deformation of a material occurs. The material may be subjected to any type of applied force.  Mechanical Properties of Dental Materials YIELD POINT The point beyond which stress causes a material to undergo permanent deformation. Yield point is always slightly higher than proportional limit. Eg: Gold alloy (Proportional limit = 276 Mpa & Yield point = 324 Mpa) Material does not recover elastically when stress is removed.  Mechanical Properties of Dental Materials MODULUS OF ELASTICITY It is relative stiffness or rigidity of a material. Unaffected by the amount of elastic or Measured by the slope of the elastic region plastic stress induced in the material. Also called as Young „s modulus. Independent of ductility of a material. It is measured by the slope of stress strain The lower the strain for a given stress, curve. greater will be the elastic modulus. If a tensile or compressive stress (below the E.g. two wires of same shape and size. proportional limit) is divided by corresponding Polyether impression materials. strain value, a constant of proportionality will Unit is Giganewtons/m² (GPa). be obtained.  Mechanical Properties of Dental Materials STRESS STRAIN CURVE For materials in which strain is independent of the length of time that a load is applied “ STRESS STRAIN CURVES“ are important.  Mechanical Properties of Dental Materials ANALYSIS FOR A STRESS STRAIN CURVE TOUGHNESS & STIFFNESS & FLEXIBILITY BRITTLENESS 1) If longitudinal portion of 1) If material fractures after the curve is closer to the long a long concave portion axis the material is stiff & not of the curve, it donates flexible. that the material is 2) If it is away from the long tough & ductile. axis the material is flexible. 2) 2) If elastic portion of the curve is minimal, it shows the brittleness of the material.  Mechanical Properties of Dental Materials ANALYSIS FOR A STRESS STRAIN CURVE STRENGTH & WEAKNESS If longitudinal portion of curve is longer, means that the material is strong. If longitudinal portion is short the material is weak.  Mechanical Properties of Dental Materials POISION’S RATIO If a cylinder is subjected to a tensile or compressive stress, there will be simultaneously an axial or lateral strain. Within the elastic range, the ratio of letaral to axial strain is known as Poision‟s Ratio.  Mechanical Properties of Dental Materials STRENGTH: Strength is the maximum stress that a material can withstand without sustaining a specific amount of plastic strain. OR Stress at the point of fracture. SHEAR STRENGTH: Maximum shear stress at the point of fracture. FLEXURAL STRENGTH: Defined as “force per unit area at the point of fracture when a material is subjected to flexural loading” Also called as “BENDING STRENGTH” or “MODULUS OF RUPTURE”  Mechanical Properties of Dental Materials FATIGUE STRENGTH: IMPACT STRENGTH Determined by subjecting a material to Impact is the reaction of a cyclic stress of maximum known value stationary object to a collision with a and determining the number of cycles moving body. required to cause failure of the material. Impact strength is defined as Maximum service stress (endurance energy required to fracture a limit) can be maintained without failure material under an impact force. over an infinite number of cycles. The energy units are joules. Endurance limit is lower for materials with brittle and rough surface.  Mechanical Properties of Dental Materials FATIGUE STRENGTH: IMPACT STRENGTH Determined by subjecting a material to Impact is the reaction of a cyclic stress of maximum known value stationary object to a collision with a and determining the number of cycles moving body. required to cause failure of the material. Impact strength is defined as Maximum service stress (endurance energy required to fracture a limit) can be maintained without failure material under an impact force. over an infinite number of cycles. The energy units are joules. Endurance limit is lower for materials with brittle and rough surface.  Mechanical Properties of Dental Materials TOUGHNESS : The energy required to fracture a material is called toughness. Also determined by the total area under stress strain curve. Toughness describes how difficult it is to break a material.  Mechanical Properties of Dental Materials BRITTLENESS It is opposite of toughness. When a material fractures at or near its proportional limit. Should not be confused with the lack of strength. Porcelain, Dental stone & Cements are examples of a brittle material.  Mechanical Properties of Dental Materials RESILIENCE (Springiness) It is the amount of energy absorbed by a material when it is stressed not to exceed its proportional limit. Measured in terms of modulus of resilience (amount of energy stored in the body) Modulus of resilience=Proportional limit/Modulus of elasticity  Mechanical Properties of Dental Materials HARDNESS In mineralogy, relative hardness of a substance is based upon its ability to resist scratching. In metallurgy and mostly in all other disciplines, hardness is defined as resistance to indentation. Higher hardness number = more hardness.  Mechanical Properties of Dental Materials RELAXATION Change in shape due to release of stresses is referred as relaxation. Example: Dental waxes & other thermoplastic materials.  Mechanical Properties of Dental Materials PERMANENT DEFORMATION After crossing the elastic limit with continuous stress the resulting change in strain (dimension) is permanent. For example: Elastic impression materials  Mechanical Properties of Dental Materials DUCTILITY Ability of a material to deform plastically under a tensile stress before fracture. e.g. metal drawn readily into long thin wires.  Mechanical Properties of Dental Materials MALLEABILITY The ability of a material to sustain plastic deformation, without fracture under compression. Gold is the most ductile and malleable pure metal, followed by silver. Platinum is ranked third in ductility. Copper ranks third in malleability -THE END- Gypsum Products  Gypsum Products ◆ Gypsum - is a rock mineral mined in various parts of the world. For dental purposes, it is nearly pure calcium sulfate dihydrate (CaSO4. 2H2O). ◆ All forms of gypsum are obtained from the mineral gypsum, which is the dihydrate form calcium sulfate (CaSO4. 2H2O). ◆ Calcination - during heating in the manufacturing process the, gypsum loses 1½ moles of water of crystallization and is converted to the hemihydrate form of CaSO4. ◆ The chemical formula of the hemihydrate form is CaSO4. ½ H2O; also written as (CaSO4)2. H2O.  Gypsum Products ◆ When CaSO4 in the form of plaster, dental stone, or high- strength stone is mixed with water, a chemical reaction takes place, and the hemihydrate is converted back to the dihydrate form of CaSO4. This reaction is exothermic, written as follows: ◆ CaSO4. ½ H2O + ½ H2O →→ CaSO4. 2H2O + Heat (Plaster) (water) (Gypsum)  Gypsum Products ◆ Types of gypsum: ADA classification 1. Impression plaster (Type I) - used to get a negative copy 2. Model plaster (Type II) 3. Dental stone (Type III) 4. Dental stone of high strength (Type IV) 5. Dental stone of high strength and high expansion (Type V)  Gypsum Products ◆ Methods of manufacturing: Calcination - heating the gypsum in order to remove the water of crystallization 1. Open Calcination - gypsum is heated in an open kettle at 110oC-120oC; production of steam with pressure which changes the rock to powder form, after cooling, the white powder is then called plaster or b-hemidydrate. 2. Closed Calcination - uses a closed container (autoclave), at 120oC-130oC; the higher the temperature → the greater the pressure → the finer yellow powder particles are produced called dental stone of a-hemihydrate  Gypsum Products ◆ Type II: Plaster of Paris; Model Plaster ◆ Description: –Powder particles and crystals –Creamy white in color, in powder form; large, porous, spongy, irregular in shape –W:P ratio = 0.45-0.5 (45 ml H2O / 100 G. plaster –Other names: Alabaster, b- hemidydrate –Process of Calcination - open  Gypsum Products Type II constituents: ◆ CaSO4 ½H2O - principal constituent ◆ CaSO4 anhydrite ◆ KSO4 - an accelerator, increases the rate of reaction between powder and liquid; reduces setting expansion ◆ Borax - an effective retarder. Insoluble Ca borate is a product of its reaction with CaSO4. The Ca borate deposits on the nuclei of crystallization and thus effectively reduces the rate of crystallization.  Gypsum Products ◆ Uses: Medical uses – as an immobilizing casts in case of fractures, accidents, etc. ◆ Commercial use – figurine making ◆ Dental uses: 1. model or study cast 2. investing material 3. for mounting the upper and lower casts on the articulator  Dental Uses of Plaster Impression plaster Plaster study casts For mounting casts For investing casts on the articulator  Gypsum Products ◆ Type III: Dental Stone Class I ◆ Description: –Powder particles and crystals –Yellow color, powder form; small, dense, regular in shape –W:P ratio = 0.28-0.30 (28 ml of H2O / 100 gm powder) –Other names: Castone; Hydrocal, a-hemihydrate –Process of calcination - closed  Gypsum Products Composition: same as plaster except that there is an increase in the concentration of accelerator and the presence of pigments. ◆ CaSO4 hemihydrate – principal constituent ◆ Lignosulfonate - when added reduces water requirement ◆ Higher % of KSO4 - for faster setting ◆ Borax - retarder Dental Stone Class I crystals Powder particles Dental Stone Class I For final model / casts  Gypsum Products ◆ Type IV: Dental Stone Class II ◆ Description: – Powder particles and crystals – bright yellow/aqua in color, powder form – Finer, denser, more regular in shape than class I – W:P ratio = 0.22-0.24 (24 ml of water/100 gm powder) – Other names: Die stone, Dental stone of high strength, Densite, a-hemihydrate – Process of calcination: ◆ Closed – in an autoclave and gypsum is boiled in a 30% solution of Ca chloride ◆ Open calcination - with >1% Na succinate  Type IV: Dental Stone Class II Use: for constructing casts for dies that are used for fabricating gold restorations, inlays, crowns & bridges. This material is able to withstand most of the manipulative procedures involved in the production of appliances and restorations, and is more dimensionally stable.  Gypsum Products ◆ Type V: Dental Stone of higher strength and high expansion Description: – use colloidal silica and modifiers instead of water – W:P ratio = 0.18-0.22 (18 ml of H2O / 100 gm powder) – Manipulation of Mixing: 1. Equipment: rubber/plastic bowl & plaster spatula with a flexible and easy to grasp handle. 2. Precautions before mixing: Pour water into bowl first before powder to eliminate air bubbles during mixing. 3. Mixing procedures: In a single rotary motion – to prevent formation of air bubbles into the mix.  Gypsum Products ◆ 3 methods of mixing gypsum and water 1. Hand method – single rotary motion for 1 minute 2. Mechanical method – use of a mixer for gypsum products for 20-30 seconds; advantage - no entrapment of air bubbles 3. Hand-mechanical combination method – the rotary part is mechanical while you hold the bowl; for 1 minute; has a cover  Gypsum Products ◆ Properties of gypsum: – Setting Time - time from the start of mixing until the materials are blended and have hardened – The actual mechanism of setting or hardening is the result of a difference in solubility between the hemihydrate and dihydrate forms of calcium sulfate. – During setting, growth and subsequent locking of gypsum crystals occur. The interlocking contributes to the strength and dimensional change of the gypsum. – Manipulative procedures that influence the difference in solubility and the growth of the dihydrate crystals can influence the physical and mechanical properties of the gypsum mass.  Gypsum Products ◆ Types of setting: – Initial setting time (IST) is also called the working time the material can still be mixed and poured into the impression semi-fluid consistency - freshly mixed mass and can be poured into a mold of any shape As the reaction proceeds → more hemihydrate crystals react to form dihydrate crystals → the viscosity rapidly increases (and at some point the mass can no longer flow into the impression’s minute spaces. At this point the material has reached the final phase of the initial setting time and should no longer be manipulated.  Gypsum Products ◆ IST occurs w/in 8-16 minutes from start of mixing. ◆ The IST can be detected clinically by a phenomenon known as loss of gloss. ◆ The IST is from the time of mixing until a certain increase in temperature. When loss of gloss occurs, further manipulation should be avoided → the surface appears dull.  Gypsum Products ◆ Final setting time (FST) - is defined as the time at which the material can be separated from the impression without distortion or fracture; the time at which the chemical reaction is complete → there is a second change, a decrease, in temperature. ◆ FST of many gypsum varies, but usually occurs w/in 20 minutes from the start of mixing. Common practice allows the gypsum mass to harden for 45-60 minutes before removing it from the impression  Gypsum Products ◆ Penetration tests to measure FST: 1. Gilmore needle: a. small needle (1/4 lb) from time of mixing until needle no longer penetrates surface → IST b. big needle (1 lb) no longer penetrates surface, is known as the FST. 2. Vicat needle - weighs 300 gm, 1 mm in diameter and 5 cm length - when needle no longer penetrates bottom of plaster → IST.  Gypsum Products ◆ Factors controlling setting time: - It is necessary for the dentist to control the ST. Theoretically, there are at least 3 methods by which such control can be effected. 1. The solubility of the hemihydrate can be increased or decreased. Ex. Increased solubility → greater rate of crystalline deposition. 2. The number of nuclei of crystallization can be increased or decreased. The greater the number of nuclei → faster gypsum crystals will form → the faster the setting. 3. If the rate of crystal growth can be increased or decreased, the ST can be accelerated or retarded respectively.  Gypsum Products ◆ Practical factors: A. Those governed by the manufacturer: 1. Process of Calcination – open or closed CaSO4. 2H2O (Ca sulfate dihydrate) 110oC 130oC 130oC with 200oC 200oC -120oC 30% CaCl –1000oC Plaster Hydrocal Densite Soluble Orthorhombic (CASO4 ½ H2O) anhydrite anhydrite 2. Impurities - if calcination is not complete so that the gypsum particles remain, or if the manufacturer adds gypsum, the setting time will be shortened because of the increase in potential nuclei of crystallization. - if orthorhombic anhydrite is present → induction period will be increased; if hexagonal anhydrite is present → it will be decreased  Gypsum Products 3. Particle size and shape - The finer the particle size of the hemihydrate, the faster the setting. Not only will the rate of solution of the hemihydrate be increased, but also the gypsum nuclei will be more numerous → more rapid rate of crystallization. 4. Addition of chemical modifiers - the most effective and practical method of controlling the setting time. 1. Accelerators - decreases the setting time; removes surface coating for easy water penetration - no more than 3% KSO4; less than 5% NaCl; & 3.4% NaSO4 2. Retarders - increases the setting time; adds surface coating and sometimes destroy some of the crystals - 20% NaCl, 12% NaSO4, & Borax  Gypsum Products B. Factors controlled by the dentist – 1. W:P ratio - method of manipulation should follow the correct W:P ratio. Not following the correct W:P ratio will have effect in 1. strength of casts 2. setting expansion 3. setting time - Increase W/P ratio: 1. thinner consistency & longer setting time 2. weaker casts - usually porous & will fracture and abrade easily - Decrease W/P ratio: 1. thicker consistency of mix 2. faster / inaccurate setting time 3. weaker casts  Gypsum Products 2. Creating air bubbles in the cast: a. reduces strength of casts b. increases surface inaccuracy c. unsightly cast 3. Temperature of water - should not be above 50oC → a gradual increasing retardation occurs - at higher temperatures, reaction 2 is reversed with the tendency for any gypsum crystals formed to be changed to the hemihydrate form.  Gypsum Products 4. Mixing time / spatulation - w/in practical limits, the longer and the more rapidly the plaster is mixed → the shorter the setting time. - the crystals are broken up by the mixing spatula and distributed throughout the mixture → more nuclei of crystallization→ faster ST. Importance of controlling the setting time: So that the setting occurs at a convenient time after mixing.  Gypsum Products C. Setting Expansion - all gypsum materials show a measurable linear expansion upon setting. The expansion results from growth of the CaSO4 · 2 H2O crystals and their impingement on one another. - the magnitude of expansion differs from one type of gypsum to another. - Setting expansion at 2 hours ◆ Type II Plaster = 0.30-0.40 ◆ Type III Hydrocal = 0.20 ◆ Type IV Densite = 0.10 ◆ Type V DS of high S & E = 0.30  Gypsum Products - if during the setting process the gypsum materials are immersed in water, the setting expansion will increase. - The Hygroscopic expansion of plaster, stone, & high-strength stone is approximately twice the normal setting expansion of these materials. ◆ Factors controlling setting expansion: - May be a source of error, so it should be controlled to obtain desired accuracy. 1. W:P ratio = less W:P ratio and the longer the mixing time w/in practical limits, → greater setting expansion. Theoretically, the higher W:P → less nuclei of crystallization → bigger spaces between nuclei → follows less growth interaction of the dihydrate crystals with less outward thrust → less setting expansion.  Gypsum Products ◆ Factors controlling setting expansion: 2. Spatulation / Mixing procedure - w/in practical limits, an increase in the amount of spatulation will shorten the setting time. The setting expansion is also increased by increasing the time or rate of spatulation. 3. Temperature of mixing water - should not go beyond 50oC → longer setting time & lesser setting expansion. 4. Chemical modifiers - generally reduce setting expansion, makes crystals flat, less effective on outward thrust of crystals  Gypsum Products ◆ Strength – property wherein maximal stress required to fracture a material → directly related to the density of the set mass. Therefore, Type V, has the least amount of excess water making it the densest and therefore strongest of the gypsum products. ◆ Stress - is the force per unit area in a body which resists as external force designated as load. - For gypsum products, strength is always expressed as compressive strength. The strength of a plaster or stone increases rapidly as the material hardens after initial setting time. Two strengths of gypsum products are recognized. 1. wet strength - when water in excess of that required for the hydration of hemihydrate is left in the specimen. 2. dry strength - when the specimen is dried free of excess water. The dry strength is twice the wet strength.  Gypsum Products ◆ Minimum 1-hr compressive strength (psi /MPa) – Type II Plaster = 1300 psi / 2 MPa – Type III Hydrocal = 3000 psi / 4 MPa – Type IV Densite = 5000 psi / 34 MPa – Type V DS high S & E = 7000 psi / 49 MPa ◆ Factors controlling strength: 1. W:P ratio - the greater the W:P ratio → greater the porosity → the weaker the cast; the greater W:P ratio → lesser the dry strength. 2. Spatulation - increase in mixing time, increase strength, if w/in 1 minute. Overmixing has reverse effect. 3. Chemical modifiers - addition of both accelerator and retarder lowers both the wet and dry strength of gypsum products.  Gypsum Products ◆ Care of gypsum products: 1. Store in an air-tight container to prolong shelf-life. Shelf-life is the property to preserve life w/o deterioration of product. 2. Shake bottle first before getting powder. 3. Use a dry spoon or scoop when getting powder. 4. Always follow correct W:P ratio.  Gypsum Products ◆ Methods of constructing the cast 1. Boxing method - strips of soft wax, green boxing wax are wrapped around the impression to form a mold for the gypsum. The wax is extended ½ inch beyond the tissue side of the impression to provide a base for the model. The mixture is then vibrated so that the mixture pushes air ahead of itself as it fills the impressions of the teeth. 2. Inversion method - begins with filling the impression with stone the filled impression can then be inverted & place on a pile of freshly mixed plaster that has been placed on a glass plate. It must be of a thick consistency so it can stand when inverted, then it is practical to shape the base with a spatula before the gypsum sets finally. 3. Use of a rubber base former - also called a model former; the impression filled with stone is inverted and placed in a rubber mold in which freshly placed plaster has been vibrated. Before setting, the surfaces of the plaster is smoothed with a wet finger. Gypsum Products Boxing method Gypsum Products Inversion method  Gypsum Products ◆ Regardless of the method used to construct the model or cast, the gypsum should not be separated from the impression until it has thoroughly hardened. Gypsum materials are usually allowed to harden 45-60 minutes before the impression is removed and the model cast trimmed. ◆ Properties of a good cast 1. Must have high strength - reduces the chance of fracture 2. Should be hard - so that surface will have no scratches during carving 3. Accurately measured and stable - setting expansion should be controlled 4. Compatible with impression material 5. Good color contrast with other materials 6. Should be smooth and free of bubbles 7. Inexpensive and easy to use  Gypsum Products ◆ Disinfecting solution for model casts: Iodophore used according to manufacturer’s instructions or by immersion in 1:10 dilution of NaOCl (sodium hypochlorite) solution for 30 minutes. In a hospital dental clinic, a model poured from a non-disinfected impression can be aseptically wrapped and sterilized in ethylene oxide. 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