title: Three-dimensional analysis of the casting accuracy of one-piece, osseointegrated implant-retained prostheses.
abstract: The three-dimensional distortions of implant frameworks of two designs, reflecting the early "Toronto" U-shaped design and a current L-shaped design, were measured. A conventional commercial laboratory one-piece casting method, using a silver-palladium alloy, was used. Distortion was defined by five displacement variables for the centroids of each of five gold cylinders incorporated in each casting: three orthogonal translational displacements (dx, dy, and dz) and two rotational displacements (d theta x and d theta y). A computerized coordinate measuring machine was used. Overall translational displacements measured were -17.4 +/- 15 microns for dx, 6.1 +/- 7.1 microns for dy, and -0.1 +/- 1.7 microns for dz. The overall global translational displacement, dR, was 20.2 +/- 14.5 microns. Overall rotational displacements were -0.098 +/- 0.109 degrees for d theta x and -0.020 +/- 0.097 degrees for d theta y, giving an average absolute angular change, d theta R, of 0.158 +/- 0.077 degrees. No significant differences were found between U- and L-shaped castings, except for dy values for cylinders 2, 3, and 4, and d theta x values for cylinder 1. Cylinder location within the arch was associated with a specific direction and magnitude of translational and rotational displacement. Even small rotational displacements may manifest large gap appearances with the one-screw test because of the "moment arm" effect. However, other rotational displacements may be hidden, depending on the direction of tilt and the moment arm length.
authors.affiliation: Department of Restorative Dentistry, National University of Singapore.
authors.forename: K B
authors.initials: KB
authors.lastname: Tan
authors.forename: J E
authors.initials: JE
authors.lastname: Rubenstein
authors.forename: J I
authors.initials: JI
authors.lastname: Nicholls
authors.forename: R A
authors.initials: RA
authors.lastname: Yuodelis
mesh_terms: D000704:Analysis of Variance; D003735:Dental Casting Technique / Q000592:standards*; D015921:Dental Implants; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis; D006047:Gold Alloys; D008954:Models, Biological; D010165:Palladium; D017755:Prosthesis Fitting; D015203:Reproducibility of Results; D012399:Rotation; D012834:Silver
chemical_list: D015921:Dental Implants; D006047:Gold Alloys; D012834:Silver; D010165:Palladium