Castability and marginal fit of pure titanium castings
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Although titanium (Ti) has been used to cast removable prostheses, its use for fixed restorations is relatively new. The aim of this study was to determine whether pure (99.6%) Ti could be used to consistently cast crowns with precise marginal fit. First a pilot study was conducted. Thirty crown pattern were waxed on the Bureau of Standards metal die-wax assembly and invested with an Al-Mg non-silica investment (Titavest CB, J. Morita Co., Osaka, Japan). Castings were made with an arc type automatic casting machine in an argon atmosphere (Cyclarc, J. Morita Co., Osaka, Japan). Secondly, 80 wax crown patterns were made on the ADA die wax assembly and divided into five groups according to: (A) liquid/powder investment ratio (L/P), (B) burnout temperature (BOT), (C) Heat soaking time (HST), (D) casting moId-temperature (C M-T) and (E) sprue design (SD). Each group was then subdivided into subgroups of five castings each [GrA (L/P); 1:15, 2:14.5, 3:14, 4:13.5 and 5:13 cc/100g] [GrB (BOT); 1:950, 2:850 and 3:875Oc] [GrC (HST); 1:60, 2:70 and 3:65 minutes] [GrD (C M-T); 1:600, 2:700 and 3:550Oc] and [Gr E (SD): sprue designs I, II, III and lV]. Castings were visually (detail), microscopically (surface characteristics) and radiographically (density) analyzed. Marginal fit was measured with an optical microscope at four evenly spaced marginal positions of the castings to the metal die for each casting. Data was tabulated and statistically analyzed using a one way ANOVA followed by Duncan’s multiple range test. Mean discrepancy, standard deviations and comparison among subgroups were determined. It was concluded that consistently precise Ti crowns can be made under carefully controlled conditions using a commercially available casting system and its specially formulated investment for fixed restorations. Ti crowns were fabricated with optimum marginal fit and sharp detail.However, upon radiographic, visual and microscopic examination most castings revealed internal and external porosity when a flattened sprue was used. It is strongly suggested that radiographic examination be perfermed to analyze Ti castings for internal porosity prior to definitive clinical use.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact firstname.lastname@example.org.Thesis (M.Sc.D.)--Boston University. Henry M. Goldman School of Graduate Dentistry, 1990 (Prosthodontics)Includes bibliographical references.
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