title: Influence of investment type and sprue number on the casting accuracy of titanium crown margins.
abstract: BACKGROUND
  Titanium offers biocompatibility and adequate mechanical properties for fabricating dental prostheses; however, casting difficulties can compromise the accuracy of titanium crown margins.
  
  
  OBJECTIVE
  The aim of this study was to evaluate the influence of investment type and number of sprues on accuracy of crown castings made with commercially pure titanium.
  
  
  METHODS
  The casting accuracy was evaluated indirectly by determining the deficiency of titanium crown margins cast using the lost-wax technique. Crown margins were recorded in a silicone impression material. The degree of marginal rounding was measured and margin deficiencies were calculated. Seventy-five acrylic resin crown patterns with wax margins were prepared on a stainless steel stylized crown die having a 30-degree beveled finish line. Fifteen patterns were selected for the control group, and the degree of wax margin rounding was determined (group W, control). The remaining 60 were divided into 4 groups of 15 each, and cast using 2 different titanium investments: a monoammonium dihydrogenphosphate-bonded investment (Rematitan Plus; groups PI and PII), and a magnesium oxide-bonded investment (Rematitan Ultra; groups UI and UII). Each pattern was cast with either 1 (groups PI and UI) or 2 (groups PII and UII) sprues. Margin configurations for both wax pattern and cast specimens were measured and recorded with the same method, using silicone impressions of the margins. After polymerization, the silicone material was sectioned precisely in 8 locations through the margin area so that cross-sections of the margins could be observed. Marginal deficiency was determined using microscopic measurements from the silicone patterns and calculations. Data were subjected to 2-way analysis of variance (alpha=.05).
  
  
  RESULTS
  Specimens from group W presented a mean marginal deficiency of 19 +/- 6 microm. The analysis of variance indicated a significant difference for the main factors, investment (P<.01) (P=91 +/- 28 microm and U=78 +/- 17 microm) and sprue number (P<.001) (I=97 +/- 23 microm and II=72 +/- 16 microm), as well as for interaction (P<.05) (PI=109 +/- 25 microm; PII=73 +/- 17 microm; UI=85 +/- 15 microm; and UII=71 +/- 16 microm).
  
  
  CONCLUSIONS
  Within the limitations of this study, investment U provided better casting accuracy than investment P. Two sprues provided more accurate results than 1 sprue; however, this effect was more notable for investment P, as it produced similar results between groups PII and UII.
authors.affiliation: Department of Dental Materials and Prosthesis, School of Dentistry of Ribeirao Preto, Brazil.
authors.forename: Monica Barbosa
authors.initials: MB
authors.lastname: Leal
authors.forename: Silvana Maria
authors.initials: SM
authors.lastname: Paulino
authors.forename: Valeria Oliveira
authors.initials: VO
authors.lastname: Pagnano
authors.forename: Osvaldo Luiz
authors.initials: OL
authors.lastname: Bezzon
mesh_terms: D000704:Analysis of Variance; D003442:Crowns; D003722:Dental Alloys; D003734:Dental Casting Investment; D003735:Dental Casting Technique / Q000295:instrumentation*; D018772:Dental Marginal Adaptation; D008277:Magnesium Oxide; D008422:Materials Testing; D003765:Models, Dental; D010710:Phosphates; D014025:Titanium
chemical_list: D003722:Dental Alloys; D003734:Dental Casting Investment; D010710:Phosphates; C024788:ammonium phosphate; D008277:Magnesium Oxide; D014025:Titanium