title: Some aspects of the formulation of alginate dental impression materials--setting characteristics and mechanical properties.
abstract: OBJECTIVE
  To study the role of the various components of alginate dental impression materials.
  
  
  METHODS
  Experimental materials were formulated and their physical properties characterized and compared to commercially available counterparts (Neocolloid, Palgat Plus and Blueprint Cremix). Properties examined were: dimensional stability and weight change in water and artificial saliva; setting behavior; Shore A hardness and tear energy. The role of magnesium oxide was also investigated.
  
  
  RESULTS
  Weight changes in water and artificial saliva can be attributed to an initial thermodynamic potential owing to the ionic content of the alginate, causing water to diffuse into the material. Water is then driven back out following a reversal of this potential. Hardness results for experimental materials were within the range obtained from the commercial materials. The hardness value for an experimental formulation that did not contain magnesium oxide was lower than values from the other experimental materials that did. Tear energies for all three experimental materials were greater than those of the commercial products. There were statistically significant differences between the two experimental materials that contained magnesium oxide and one that did not. With regard to setting time, statistically significant differences were seen between commercial materials and two of the experimental materials. The experimental material that did not contain magnesium oxide had a considerably longer setting time than all of the other materials tested.
  
  
  CONCLUSIONS
  The key role of magnesium oxide in the setting reaction and the effect on hardness have been demonstrated and discussed.
authors.affiliation: Dental Physical Sciences, Institute of Dentistry, Barts and the London School of Medicine and Dentistry, Queen Mary, University of London, London, United Kingdom. n.a.nallamuthu@qmul.ac.uk
authors.forename: Navina A
authors.initials: NA
authors.lastname: Nallamuthu
authors.forename: Michael
authors.initials: M
authors.lastname: Braden
authors.forename: Mangala P
authors.initials: MP
authors.lastname: Patel
mesh_terms: D000464:Alginates / Q000737:chemistry*; D002627:Chemistry, Physical; D003760:Dental Impression Materials / Q000138:chemical synthesis* / Q000737:chemistry; D006244:Hardness; D008277:Magnesium Oxide / Q000737:chemistry*; D008422:Materials Testing
chemical_list: D000464:Alginates; D003760:Dental Impression Materials; D008277:Magnesium Oxide