Dental Materials Lecture 3 PDF

Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar Lecture 3 Impression Materials A dental impression is a negative record of tissue of the mouth; it is used to reproduce the form of teeth and surrounding tissues. A pos...

Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar Lecture 3 Impression Materials A dental impression is a negative record of tissue of the mouth; it is used to reproduce the form of teeth and surrounding tissues. A positive reproduction is obtained by pouring dental stone or other suitable material into the impression and allowing it to harden. The positive reproduction of a single tooth is described as a die, when several teeth or a whole arch is reproduced; it is called a cast or model. The impression material is carried to the mouth in a tray which is either stock tray or special tray. Classification of Impressions Preliminary impressions. Final impressions. Bite registrations. Impression Trays Quadrant tray: Covers one half of the arch. Section tray: Covers the anterior portion of the arch. Full arch tray: Covers the entire arch. Perforated tray: Holes in the tray create a mechanical lock to hold the material in place. Smooth tray: Interior of the tray is painted or sprayed with an adhesive to hold the impression material.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar Requirements of an ideal Impression Material: 1. Accurate reproduction of surface details; depend upon: Low viscosity; should be sufficiently fluid upon placement to prevent displacement of soft tissue). The material should be compatible with moisture and saliva (hydrophilic not hydrophobic). 2. Dimensional accuracy and stability; depend upon: Type of tray. Shrinkage of impression material. Permanent set. Storage stability. Impression technique. 3. A placement taste and odor and esthetic color. 4. Freedom from toxic or irritant constituents. 5. Adequate shelf life for requirements of storage and distribution. 6. Easy of manipulation and reasonable cost. 7. Appropriate setting time and characteristics. 8. Adequate strength so that it will not break or tear on removal from mouth. 9. Compatibility with cast and die material. 10. Easily disinfected without loss of accuracy. *** No single material is ideal for all applications and none of the current materials completely satisfies the requirements. Key Properties Accuracy = ability to replicate the intraoral surface details. Dimensional Stability = ability to retain its absolute dimensional size over time. Tear Resistance = ability to resist tearing in thin sections.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar Classification of impression materials 1. According to elasticity: A-Elastic material: Show the properties of elasticity that will return to its original shape and dimensions after removal from the patient’s mouth. This materials can engage undercuts, used in partially edentulous and may be used in fully edentulous patients. B- Rigid material: Show the properties of non-elastic and cannot engage undercuts. Their use is restricted to edentulous patient. Impression Materials Non-elastic Elastic Hydrocolloids Elastomers Polysulfide Silicones Polyether Condensation Addition Agar (reversible) Alginate (irreversible) Plaster Compound ZnO - Eugenol Waxes ‫اﻟﻤﺨﻄﻂ ﻣﻬﻢ‬  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar 2. According to setting reaction: A- Physical reaction ( reversible, thermoplastic material): Means when we apply heat upon it will become soft, and when we remove it becomes hard. E.g. impression compound, agar and wax. B- Chemical reaction (irreversible): When the setting is by chemical reaction like most of other impression materials. This includes a change within the material structure; so can be used once. E.g. impression plaster, Zinc-oxide eugenol, alginate Polysulphide, Silicones, Polyether. 3. According to reaction with saliva: A- Hydrophilic: The impression material is compatible with moisture and saliva, this means that the impression material will completely absorb saliva from the patient’s mouth and we get full adherence between the tissue and the material. B- Hydrophobic: Means the impression will not absorb saliva and repeal it; this means also any drop of saliva within the surface of patient’s mouth will make a slight depression or concavity on the material, so the patient’s mouth must be completely dried before taking impression. 4- According to viscosity before setting: A- Mucostatic: Not compress tissue during setting of impression. B- Mucocompressive: Compress tissue during setting of impression, the material more viscous. C- Pseudo-plastic: Material fairly viscous, whilst under low stress conditions may become fluid during recording of impression.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar Methods of making impression 1. Stock tray with pressure (Mucocompressive). This technique used in primary impression for complete denture works using impression compound. 2. Resin custom tray without pressure (Mucostatic). This technique used in final impression for complete denture works using Zinc-oxide eugenol or impression plaster. 3. Stock tray (rim-lock, perforated or with adhesive) to taking the impression for partially edentulous ridge using hydrocolloids or elastomers (heavy body only). 4. Resin custom tray with 2-4 mm spacing (perforated or with adhesive) to taking the impression for crown& bridge works or partial denture (single mix technique) using regular body elastomers. 5. Resin custom tray with 2-4 mm spacing (perforated or with adhesive) to taking the impression for crown& bridge works or partial denture using heavy & light body elastomers (Multi mix technique). 6. Stock tray (rim-lock, perforated or with adhesive) to taking the impression for crown& bridge works or partial denture (Two stage putty wash technique) using putty & light body elastomers. Rigid non – elastic impression materials 1.Impression plaster: ♦ Presentation: Present as powder mixed with water (w/p=o.6). ♦ Composition: 1. Calcium sulphate β-hemihydrate. 2. Potassium sulphate (K2SO4) to reduce the setting expansion & accelerate the setting reaction. 3. Borax, Pigments is added also like alizarin (pink); to distinguish it from other gypsum products also flavoring agent.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar 4. Starch is added for easier separation of impression plaster from the cast. After cast harden, starch grains will swell when hot water is applied on it making it easy to separate the cast from the impression. ♦Manipulation: Water is placed in to the rubber bowl and the powder is added, mix with spatula till the creamy mixture is formed the trey is filled and seated into the patients mouth where it is allowed to set. ♦Usage: Used in taking final impression for edentulous arches or wash impression, used to mount cast on an articulator and for bite registration. ♦Properties: 1. Setting time 3-5 min. 2. The mixed material has a very low viscosity so it is mucostatic. 3. It is hydrophilic (patients complain very dry sensation after having impression because of water absorption nature of this material) thus adapt readily to the soft tissues, recording their surface detail with great accuracy. 4. The material is best to be user in a special tray made of acrylic (1- 1.5 mm spacer). 5. The dimensional stability is very good (dimensional changes during setting 0.06%). 6. A separating medium must be used between the cast and the impression plaster (solution of sodium alginate or soap with water). 7. The material is rigid once set thus unable to record undercuts. bite registration mount cast on articulator special tray with spacer  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar 2- Impression compound: Non-elastic, thermoplastic, hydrophobic, mucocompressive impression material. Used mainly for complete denture (primary impression) and other uses depending on its type. ♦ Composition: 1. Waxes: usually bees-waxes. This material is brittle and must be soften to be workable. 2. Natural resin: give the material thermoplastic properties. These materials after mixing will stay weak with tendency to tackiness so we add. 3. Stearic acid (plasticizer): to overcome brittleness. 4. Filler: e.g. calcium carbonate and limestone which added to overcome tackiness, improve rigidity, control degree of flow and minimize shrinkage due to thermal contraction. ♦Types and uses: 1.TypeI Impression compound (lower fusing ) : Supplied in sheets, stick form or cones. Sheet form material used to take primary impression for edentulous ridges using stock tray, softened using water bath (55-60Cº). Storage in hot water should not be so long to prevents leacheing of important constituents. Such as Stearic acid. Over heating make the compound sticky and difficult to handle. Stick form material used for border molding of an acrylic special tray, softened over flame. The compound should not be allowed to boil, otherwise the plasticizer are volatilized. 2- TypeII Impression compound (higher fusing): It is stiffer and has less flow than regular impression compound. Used to make a special tray (now largely replaced by acrylic tray) into which another impression material is placed. This is done for complete dentures of edentulous arches.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar ♦Properties: 1.Thermoplastic property: So impression compound is softened when we heated it for 45Cº and becomes hard when it’s cooled to 37Cº. There is no chemical reaction but only a physical reaction, so the material is reversible and can be reused a number of times (for the same patient only) in case of errors. Inaccurate portions can be remade without having to remake the entire impression. 2.Poor dimensional stability: Material has a high value of coefficient of thermal expansion and undergo considerable shrinkage on removal from mouth (relaxation because stresses are introduced into the material during taking the impression or during removal of the impression- mucocompressive ). Then residual stress exists when cooling the impression. The gradual relief of internal stresses may cause distortion of impression so the impression should be chilled immediately in cold water to reduce the stress relaxation and poured as soon as possible (rigid once cooled). 3.Thermal conductivity: Impression compound is poor thermal conductors, so it needs thorough heating, and a water bath is preferred to soften the impression compound. We should wait for certain time in order that all the material is softened. When we introduce it into the patient’s mouth we should wait enough time till the outer and the inner portion of the impression compound is hard before we can remove it from the patient’s mouth. 4. Reproduction of surface detail: It is mucocompressive and most viscous impression material used; the reproduction of surface detail is not very good, also not used to record undercut.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar ♦Disadvantages: The handling of dental impression compound is very technique sensitive. If it is not prepared properly, volatiles can be lost on heating, or low-molecular-weight ingredients can be lost during immersion in a water bath. Excessive wet kneading can incorporate water into the mix and change the flow properties of the compound. Due to a high coefficient of thermal expansion, the dimensions of the impression are not likely to be the same as the dimensions in the mouth. These materials are non-elastic and may distort on removal from the mouth. ♦Disinfection: Dental impression compound can be disinfected by immersion in sodium hypochlorite. The manufacturer's recommendations for proper disinfection should be followed. 3. Impression waxes: Impression waxes are rarely used to record complete impression but are used to correct small imperfection in other impression. These materials consisted from a mixture of low melting paraffin and bees waxes in ratio about 3:1. Waxes have high flow and larger coefficient of thermal expansion, so it will distort when removed from undercut area. It’s used in ranging consistencies soft, medium, hard, and extra hard. 4.Zinc oxide- eugenol: The reaction between zinc oxide (ZnO) and eugenol yields a relatively hard mass that has medical advantages, and also mechanical properties that make it usable in certain dental fields.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar ♦Uses: 1. A final impression for edentulous arches. 2. Bite registration paste. 3. Temporary relining material for dentures. 4. Temporary filling. 5. Surgical pack in periodontal surgical procedure. 6. Root canal filling. 7. Cementation and insulating medium. ♦Composition: Base paste: Zinc oxide 87% as a reactive component with vegetable and mineral oil 13% which act as a plasticizer and reduce the burning sensation of eugenol. Water essential either to Base or Accelerator Accelerator paste: Eugenol (oil of cloves) 12% (reactive component). Accelerators CaCl2. Filler (silica type) 20%. Gum or polymerized rosin 50% (speed the reaction). Lanolin 3%. Resinous balsam 10% (improves flow and mixing properties). Coloring agent 5%. ♦Chemical reaction: H2O ZnO + eugenol Zinc eugenolate +Unreacted ZnO The set material consists of a mixture of amorphous zinc eugenolate matrix which hold unreacted zinc oxide particles together. ♦Types of (ZnO-eugenol): According to ADA specification no. 16 Type I: hard, I.S.T = (3-6) minutes, F. S.T =10 minutes Type II: soft, I.S.T = (3-6) minutes, F. S.T =15 minutes  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar ♦Manipulation : two strips of equal length are squeezed from each tube on paper pad or glass slab , mixed by a spatula till the tow colors blend together. Mixing is for about (60 sec) the (2) strips are combined together from the 1st sweep of spatula. Then the mixture is filled into the special tray. After setting of the gypsum, the impression and the stone is placed in warm water for easier separation of zinc oxide from the cast. ♦Properties: 1. Setting time Factors controlling the S.T: a) Few drops of H2O to the eugenol paste shorten the S.T ,also zinc acetate or acetic acid shorten the S.T. b) Cooling the spatula and glass slab or adding small amount of oils or waxes prolong S.T. c) Varying the length of the two pastes, this results in either increase or decrease of S.T. d) Extent the mixing time (within limit) will shorten the S.T. e) High atmospheric temperature and humidity shorten the S.T. 2. Rigid non-elastic and should not be used for partially edentulous arches, its fractured when removed from undercut area. 3. Accurate registration for surface details due to good flow (mucostatic) property (recording tissue in uncompressed state). 4. The paste tends to adhere to skin, so that patient’s lips and cheek should be vazalined. It requires a special tray for impression making. 5. It has advantage of being dimensionally stable. A negligible shrinkage (less than 0.1%) may occur during hardening. 6. No separating medium is needed for making the cast. 7. Eugenol can cause burning sensation and tissue irritation. Non- eugenol paste was developed; here the zinc oxide reacts with a carboxylic acid.  Made with Xodo PDF Reader and Editor Dental Materials By: Assist.lect. Salah.M.alhar ♦Advantages: The advantages of zinc oxide-eugenol include high accuracy of soft tissue impressions due to its low viscosity. The material is stable after setting, has good surface detail reproduction, and is inexpensive. It also adheres well to dental impression compound. ♦Disadvantages:The disadvantages of this material are messiness and a variable setting time due to temperature and humidity. Eugenol is irritating to soft tissues. This material is non- elastic and may fracture if undercuts are present.