title: Investment strength as a function of time and temperature.
abstract: OBJECTIVE
  The purpose of this investigation was to evaluate and compare the compressive strength characteristics of selected investments and to determine if these change as a function of time and temperature after mixing.
  
  
  METHODS
  Two phosphate-bonded investments and one gypsum-bonded investment were selected and 288 cylindrical specimens were fabricated (n = 9). Baseline compressive strength values were determined for each material at room temperature and compressive strength measurements were made for all materials at 700 degrees C, and at 872 degrees C only for phosphate-bonded investments. Each material was tested at 2, 6, 12, and 24 h after mixing. Specimens were heated at 15 degrees C/min and heat soaked for 5 min in a burnout oven at the applicable testing temperature. They were transferred to a preheated chamber on an Instron testing machine and subjected to a compressive load at a crosshead speed of 2 mm/min until failure. The resulting strength data are presented in MN/m2.
  
  
  RESULTS
  The gypsum-bonded investment did not exhibit marked differences in strength as a function of either time or temperature. The phosphate-bonded investments, on the other hand, demonstrated considerable changes in compressive strength and differed in compressive strength characteristics at 700 degrees C and 872 degrees C respectively.
  
  
  CONCLUSIONS
  At elevated temperatures, all materials approximated peak strength 2 h after initial mixing. At room temperature, the phosphate-bonded investments in this study were not significantly stronger than the gypsum-bonded investment material. However, they exhibited increased compressive strength as a function of time and temperature that was considerably higher than that exhibited by the gypsum-bonded investments.
authors: University of Singapore, School of Dentistry.
authors: C L
authors: CL
authors: Chew
authors: M F
authors: MF
authors: Land
authors: C C
authors: CC
authors: Thomas
authors: R D
authors: RD
authors: Norman
mesh_terms: D000704:Analysis of Variance; D002133:Calcium Sulfate / Q000737:chemistry; D019245:Compressive Strength; D003734:Dental Casting Investment / Q000737:chemistry*; D017616:Magnesium Compounds / Q000737:chemistry; D008422:Materials Testing / Q000379:methods / Q000706:statistics & numerical data; D010710:Phosphates / Q000737:chemistry; D000069877:Struvite; D013696:Temperature; D013997:Time Factors
chemical_list: D003734:Dental Casting Investment; D017616:Magnesium Compounds; D010710:Phosphates; C118503:cerafina; C118504:ceramigold; C118505:novocast; D000069877:Struvite; D002133:Calcium Sulfate