title: The effect of investment material and ceramming regime on the surface roughness of two castable glass-ceramic materials.
abstract: OBJECTIVE
  To assess the surface roughness (R(a)) of two castable glass-ceramic materials, cast using four different investment materials and employing different ceramming regimes.
  
  
  METHODS
  Forty discs, each 12 mm diameter and 2 mm thick were produced from two castable glass-ceramic materials, one a glass ionomer derivative based on 1.5SiO(2)-1Al(2)O(3)-0.53P(2)O(5)-1CaO-0.67CaF(2) (LG112), the other a fluorcanasite material based on 0.60SiO(2)-0.05K(2)O-0.10Na(2)O-0.15CaO-0.10CaF(2) (SG3). The discs were made using four dental investments, two gypsum-bonded (Whip-Mix Cristobalite (WMC), Degussa California (DC)) and two phosphate-bonded (Fujivest Super (FS), Techceram Glass (TG)). A Ni-Cr metal/ceramic alloy (Wiron 99) was also used as a control. Each investment was used to produce 10 discs for each glass-ceramic material, five left in the as-cast, glass state, the other five cerammed. Ceramming was carried out either within the investment mold or after de-vesting from the investment mold. The discs had their surface roughness values measured using a stylus, surface contact measuring instrument.
  
  
  RESULTS
  For the Ni-Cr alloy the phosphate-bonded investments produced discs significantly smoother than those produced by the two gypsum-bonded investments (p<0.05). The FS investment produced the smoothest discs (p<0.05), but there was no significant difference between the discs produced by the two gypsum-bonded investments (p>0.05). For the SG3 material no significant differences were seen between the as-cast glass and cerammed discs (p>0.05), with the WMC investment producing the smoothest discs (p<0.05), and the TG investment the roughest (p<0.05). The LG112 material showed a significant difference between glass and cerammed discs for the gypsum-bonded investments (p<0.05) but not when using phosphate-bonded investments (p>0.05). With LG112 the WMC investment produced smoother discs than the DC and TG investments (p<0.05). The DC investment produced rougher discs than the two phosphate-bonded investments (p<0.05).
  
  
  CONCLUSIONS
  The selection of investment material can have a significant effect on the as-cast surface finish of castable glass-ceramic materials. A gypsum-bonded investment material gave smoother surface finishes compared to phosphate-bonded investments. The ceramming process significantly increases surface roughness.
authors.affiliation: Department of Restorative Dentistry, School of Clinical Dentistry, University of Sheffield, Claremont Crescent, S10 2TA, Sheffield, UK. a.johnson@sheffield.ac.uk
authors.forename: A
authors.initials: A
authors.lastname: Johnson
authors.forename: R
authors.initials: R
authors.lastname: van Noort
authors.forename: P V
authors.initials: PV
authors.lastname: Hatton
authors.forename: J M
authors.initials: JM
authors.lastname: Walsh
mesh_terms: D000704:Analysis of Variance; D002133:Calcium Sulfate / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D002858:Chromium Alloys / Q000737:chemistry; D003460:Crystallization; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique; D003764:Dental Materials / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D013499:Surface Properties
chemical_list: D002858:Chromium Alloys; D003734:Dental Casting Investment; D003764:Dental Materials; D016876:Metal Ceramic Alloys; D010710:Phosphates; D002133:Calcium Sulfate