Materials Used in the Management of Edentulous Patients.pdf

Materials Used in the Management of Edentulous Patients (Pt 1) General Requirements for Biomaterials Used to Make Complete Dentures The material must be biocompatible (i.e., with minimal harmful effects on the oral tissues) Non-toxic Non-irritating Non-allergenic Non-carcinogenic Chemically minimall...

Materials Used in the Management of Edentulous Patients (Pt 1) General Requirements for Biomaterials Used to Make Complete Dentures The material must be biocompatible (i.e., with minimal harmful effects on the oral tissues) Non-toxic Non-irritating Non-allergenic Non-carcinogenic Chemically minimally degradable or its degradation processes are biocompatible The material must fulfill clinical objectives by possessing appropriate optimal physical properties Adequate mechanical properties such as: o Hardness o Elasticity o Strength Adequate wear resistance Adequate thermal coefficient of expansion and conductivity properties (conductivity is in metals) Acceptable esthetic properties Ease of cleansing Ease of fabrication and manipulation Readily available and economical to use Easy and inexpensive maintenance such as repairs and additions Optimal Qualities for Prosthodontic Impression Materials Should have low viscosity to adapt to oral tissues but yet viscous enough to be contained in impression tray Adequate wettability of the oral tissues to allow for accurate adaptation and capturing of oral structures and tissues Pleasant taste and odor Should set into a rubbery/rigid solid in a reasonable amount of time in the mouth Set impression shows adequate elastic recovery with no permanent deformation, upon removal Adequate strength to avoid tears/breakage upon removal from the mouth Dimensionally stable after setting and until pouring of the cast Dimensionally stable to be repoured after removal from the cast Compatible with the cast material Biocompatible, nontoxic, and without irritant constituents Color and opacity that allows for proper evaluation of the impression by the dentist Readily disinfected without significant loss of accuracy or loss of mechanical properties Adequate shelf life for storage The materials, associated processing time, and equipment should be cost-effective Compound Type I and II (Composition and Manipulation) Type I (Lower Fusing Material) o As an impression material for completely edentulous patients o The material is softened by heat, inserted into the tray, and placed against the tissues BEFORE it cools to a rigid mass o Cakes: Compound preliminary impression using a stock metal tray o Sticks (compound): As a border molding material for the custom tray § Used BEFORE making the final impression § Compound is applied in sections around the borders of the custom tray § A wax spacer is kept in place during this procedure to maintain adequate space for the final impression TYPE II (Higher Fusing Material) o Used as a tray adaptation material, which requires more viscous properties. o Used for primary impression of soft tissues and then as a tray to support a thin layer of the second impression material (such as ZOE paste, hydrocolloids, or non-aqueous elastomers) DENTAL COMPOUND o A mixture of waxes and thermoplastic resins (principal ingredients that form a matrix) plus fillers that increase viscosity above mouth temperature and provide rigidity at room temperature o It also includes shellac, stearic acid, gutta percha, which contribute to plasticity and workability Zinc Oxide Eugenol (ZOE) Impression Paste Applications Mainly used for final impressions of edentulous ridges with minor or no undercuts As a wash impression with other impression materials, such as impression compound As an occlusal registration material As a temporary liner material for dentures As a surgical dressing Zinc oxide, in the presence of moisture, reacts with eugenol to form zinc eugenolate The setting reaction is accelerated by water, high humidity, or heat Some of these factors can be controlled to decrease or increase the setting time The eugenol containing pastes are classified according to their consistencies, hardness, and setting times o hard (10 minutes) o soft (15 minutes) o Initial setting time for both (3 to 5 minutes) Non-eugenol pastes, contain carboxylic acids NOT eugenol o Avoids stinging and burning sensation of eugenol experienced by some patients Impression compound is used to make an impression of the denture-bearing areas 1. Sufficient material is removed to allow space for ZOE paste to record all anatomic details ACCURACY 2. ZOE paste is applied to the relieved compound 3. The material flows easily to produce good surface details Zoe Paste Elastic Impression Materials Polysulfides introduced in 1950: first synthetic elastomeric material Condensation silicones followed in 1955 Polyethers in 1965 Addition silicones in 1975 Silicones and polyethers are the majority of elastomeric impression materials used worldwide today Elastomeric indicated for making accurate final impressions for edentulous patients when used in custom trays REVIEW o Custom trays are border molded with a wax spacer in place o Seal around the borders is verified o Wax spacer is removed o Tray adhesive is applied and allowed to dry o Final impressions are taken Elastomeric materials are divided into four viscosity classes o light body o medium/regular body o heavy body o putty (extra heavy) Setting occurs through a combination of chain-lengthening polymerization and chemical cross-linking by either o condensation reaction o addition reaction ALL types of elastomers undergo SHRINKAGE upon polymerization o condensation type silicones undergo additional contraction due to reaction by-products Highest to lowest dimensional changes during setting Polysulfides and condensation silicones (highest) Addition silicones Polyethers (least) Polysulfide rubber Polysulfide impressions show excellent detail reproduction. However, the impressions need to be poured immediately to avoid distortion due to the loss of by-products and the continuous curing shrinkage that occurs The Base o Polysulfide polymer is the principal ingredient o Fillers: based on consistency of paste § Titanium oxide § Zinc § Strength provided by: ¾ Sulfate ¾ Copper carbonate ¾ Silica o Plasticizer: Dibutyl phthalate for viscosity The Accelerator/Reactor o Reactors: Lead dioxide, hydrated copper oxide, or organic peroxide o Promoter: Sulfur- accelerates the reaction o Retarder: Oleic or stearic acid- controls setting reaction o Working time: 5-7 minutes, the longest among elastomers o Setting time: 8-12 minutes o Impressions must be poured within 30 minutes to 1 hour Polyether Elastomer o The Base § Polyether polymer § Colloidal filler, such as silica § Plasticizer, such as glycol ether or phthalate o The Accelerator § Alkyl aromatic sulfonate, an initiator § Filler § Plasticizer § Working time: 2.5 minutes § Setting time: 4.5 minutes § The impression can be poured up to 1 week of storage Condensation Silicones (additional polymerization) Addition Silicones The Base Paste o The Base o High molecular weight polymer, such as § Polymethylhydrosiloxane (low molecular weight polymer) Plus fillers polydimethylsiloxane o The Accelerator o Fillers, such as silica or calcium carbonate § Fillers The Liquid Accelerator, a metal organic ester such as: ¾ Divinyl polymethyl siloxane o tin octoate ¾ Other siloxane prepolymers o Orthoalkyl silicate § Catalyst: Platinum salt – chloroplatinic acid o Oil-based diluents § Retarder: controls the working and setting times o As a paste, the accelerator has thickening agents § Working time: 2- 4.5 minutes added to increase viscosity § Setting time: 3-7 minutes Working time: 3 minutes § The cast can be poured up to 1 week after making the impression. Setting time: 6-8 minutes The impression must be poured as soon as possible in the first 30 minutes ELASTOMERIC IMPRESSION MATERIALS- COMPARISON OF THE PROPERTIES, ADVANTAGES, AND DISADVANTAGES Elastomer Polysulfide Rubber (Mercaptan) Condensation Silicones Addition Silicones Polyethers Properties/Advantages Mod elastic recovery Mod-high flow rate High flexibility High tear strength High elasticity Great Reproduction Cheaper (than silicone, polyether) Disadvantages Unpleasant odor, can stain Requires custom tray Low viscosity, flows down throat Low dimensional stability (high distortion) Hydrophobic (difficult to pour in stone) WT/ST/Pour High Elastic recovery Low Flow rates Stiffer than polysulfide Less to Mod tear strength Well accepted by pt No custom tray needed bc it is a putty wash method Shrinkage/distortion can occur Hydrophobic (difficult to pour in stone) Additional Polymerization shrinkage WT: 3 min ST: 6-8 min High elastic recovery Low flow rate Low dimensional change Low to Mod tear strength High Accuracy Pleasant taste, odor, color Can use stock/custom trays More rigid (than Cond. Silicone) Hydrophobic High Rigidity (hard to remove from undercuts) Latex gloves inhibit polymerization Expensive Can release H (causing stone imperfections so, WT: 2- 4.5 min ST: 3-7 min delay pour for 1hr) Multiple pour capable Mod elastic recovery Low Flow rate Low shrinkage High Accuracy Great Reproduction Least dimiensional change Easy to mix/pour Low Working/setting time High Stiffness (hard to remove) least flexible Low Tear strength Distort from water/humidity Damaged by disinfectants Bitter taste Expensive WT: 2.5 min (shortest) ST: 4.5 min WT: 5-7 min (longest) ST: 8-12 min Impressions must be poured ASAP within 30 min -1 hour Impression must be poured ASAP in the first 30 minutes Cast can be poured up to 1 week after making impression. Impression can be poured up to 1 week of storage