A male 45 years old wants his missing teeth to be replaced. Intraoral examination reveals Kennedy class 4 edentulous maxillary arch. Impression is made with alginate. The setting time of the material is affected by all of the following except:
Correct Answer: Insufficient spatulation
Description: Clinicians, however, can safely influence the setting time by altering the temperature of the water. The higher the temperature, the shorter is the setting time. The temperature of the mixing water should be controlled carefully within a degree or two of a standard temperature, usually 20 °C, so that a constant and reliable setting time can be obtained. In hot weather, special precautions should be taken to provide cool water for mixing so that premature gelation does not occur. It may even be necessary to precool the mixing bowl and spatula, especially when small amounts of impression material are to be mixed.
Tap water naturally contains certain levels of metallic ions, primarily calcium and magnesium. It has been shown that compared with distilled water for mixing of alginate impression material, the use of tap water with a high hardness may accelerate the setting of the alginate. If one observes that the setting time has decreased in a new office or clinic location, the effect of the hardness of the tap water on setting time should be considered as a possible cause.
Insufficient spatulation results in failure of the ingredients to dissolve sufficiently. This leads to decrease in strength of the mix.
Reference: Phillips’ science of dental materials / Kenneth J. Anusavice, Chiayi Shen, H. Ralph Rawls.—12th ed. Page no 174
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