Alginates can be used to create study casts, preliminary impressions, provisional crown or bridge impressions, opposing arch impressions, and fabricate orthodontic casts, sports mouth guards, occlusal splints, and bleaching trays. IndicationsĪlginate is one of the most frequently used materials in dentistry and is the impression material of choice when accurate detail reproduction is not paramount. Some studies advocate that a damp paper towel should not be placed in the impression if it can be poured within ten minutes to avoid water absorption by the material. This environment can be created by wrapping the impression in a moistened paper towel before being shipped to the dental laboratory or stored in a container with some water, which will evaporate. If it is not feasible to pour the impression immediately, it must be stored in a humid environment. Imbibition and evaporation processes decrease when the impression is poured as soon as possible. Imbibition is fluid absorption by a colloid resulting in swelling, and syneresis is the expulsion of liquid from a gel. Alginate impressions can undergo imbibition, evaporation, and syneresis, affecting their dimensional stability. However, the dimensional stability of alginate impressions decreases with longer storage time. Īn ideal impression material would have sufficient dimensional stability over time to allow for pouring whenever convenient. Alginates provide a less accurate reproduction than elastomers they have low tear strength and are likely to tear when removed from deep undercuts, such as interproximal and subgingival areas they can only be poured once, producing only one plaster model and they have poor dimensional stability when pouring is delayed. However, several downsides of dental alginates have been described. Some dental alginates have added features such as the ability to change color to signal the phases of the chemical reaction and different flavors. Alginates are easy to manipulate, affordable, and have rapid setting times. When freshly spatulated, alginates have low viscosity and record the soft tissues without compressing them. Īlginates are mucostatic impression materials. The water-to-powder ratio also affects the setting reaction the hardening reaction is faster with more powder. Warmer water speeds up the setting reaction, and colder water slows the reaction down. The setting reaction time of dental alginates also depends on the water temperature used for the mixture. Type I is a fast set that hardens within 1 to 2 minutes, and type II is a standard set that hardens within 2 to 5 minutes. The retarder can slow the setting reaction, giving rise to dental alginates with different working times. After all the retarder is consumed, the remaining calcium sulfate reacts with the alginic salt to form insoluble calcium alginate in gel form. When the powder is mixed with water, the calcium sulfate reactor initially combines with the sodium phosphate retarder, allowing for adequate working time. This biphasic chemical reaction has a slowing phase and a setting phase. The setting mechanism of alginate is a chemical reaction between the salt sodium alginate and the reactor calcium sulfate. The powder contains sodium or potassium alginates, filler particles, calcium sulfate (reactor), fluoride (accelerator), and sodium phosphate (retarder). Dental alginates are available as a powder designed to be mixed with water. Alginic acid is a polysaccharide extracted from brown algae, a member of the Phaeophyceae family found primarily in America. Alginates are salts produced from the combination of alginic acid with either sodium, calcium, potassium, or magnesium. Anatomy and PhysiologyĪlginate is an irreversible hydrocolloid material that can reproduce soft and hard tissue details when in the presence of water. Alginate is an elastic, irreversible hydrocolloid that offers lower costs, improved patient tolerance, ease of manipulation, reduced execution times, and the possibility of obtaining a detailed impression in a single step. While the impressions deform upon removal, they later adapt to the original shape due to their elastic properties. Hydrocolloids were the first elastic materials used in the dental field. Hydrocolloids produce an imprint providing high-definition details despite undercuts. Non-elastic or rigid impression materials include impression compounds, zinc oxide eugenol, and impression waxes. Elastic materials comprise reversible and irreversible hydrocolloids, addition and condensation silicones, polysulfides, and polyether. Elastic materials are capable of stretching, compressing, and recovering after deformation. Impression materials are classified as either elastic or non-elastic based on mechanical properties.
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