title: Evaluation of the thermal shrinkage of titanium and the setting and thermal expansion of phosphate-bonded investments.
abstract: BACKGROUND
  There are few studies on titanium casting shrinkage, and phosphate-bonded investments for titanium casting have not produced appropriate marginal fit.
  
  
  OBJECTIVE
  The purpose of this study was to determine the thermal shrinkage of titanium and the setting and thermal expansion of 3 phosphate-bonded investments.
  
  
  METHODS
  The thermal shrinkage between the melting temperature and room temperature was calculated using a titanium thermal expansion coefficient. The thermal and setting expansion were measured for 3 phosphate bonded investments: Rematitan Plus (RP) specific for titanium, Rema Exakt (RE), and Castorit Super C (CA), using different special liquid concentrations (100%, 75%, and 50%). Setting expansion was measured for cylindrical specimens 50 mm long x 8 mm in diameter with a transducer. The heating and cooling curves were obtained with a dilatometer (DIL 402 PC). The total expansion curve was drawn using software, and temperatures to obtain expansion equivalent to titanium casting shrinkage were determined (n=5). In addition, the total expansion of the control group (RP at 430 degrees C) was measured, as well as the temperatures at which the other groups achieved equivalent total expansion (n=5). Data were analyzed by 1-way ANOVA and the Tukey HSD test (alpha=.05).
  
  
  RESULTS
  Titanium casting shrinkage was estimated as 1.55%. RP did not achieve this expansion. RE achieved expansion of 1.55% only with a special liquid concentration of 100% at 594 degrees C. CA with all special liquid concentrations attained this expansion (351 degrees C to 572 degrees C). Total expansion of the control group was 0.86%, and the other groups reached that expansion within the range of 70 degrees C to 360 degrees C.
  
  
  CONCLUSIONS
  Only RE and CA demonstrated sufficient expansion to compensate for titanium casting shrinkage. All groups reached total expansion equivalent to that of the control group at significantly lower temperatures.
authors.affiliation: Department of Dental Materials and Prosthodontics, School of Dentistry, Sao Paulo State University, Araraquara, SP, Brazil.
authors.forename: Anelise R
authors.initials: AR
authors.lastname: Ferreira
authors.forename: Gelson L
authors.initials: GL
authors.lastname: Adabo
authors.forename: Oscar Peitl
authors.initials: OP
authors.lastname: Filho
authors.forename: Sicknan
authors.initials: S
authors.lastname: Soares da Rocha
authors.forename: Renata Garcia
authors.initials: RG
authors.lastname: Fonseca
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D003080:Cold Temperature; D003734:Dental Casting Investment / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D008277:Magnesium Oxide / Q000737:chemistry; D008422:Materials Testing; D010710:Phosphates / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics; D014025:Titanium / Q000737:chemistry*
chemical_list: D003734:Dental Casting Investment; D005290:Ferric Compounds; D010710:Phosphates; C000499:ferric oxide; D008277:Magnesium Oxide; D012822:Silicon Dioxide; D014025:Titanium; D000537:Aluminum Oxide