Fitness accuracy of Akers clasps fabricated from CAD/CAM patterns

Purpose: A CAD/CAM-precision modeling system can create a casting pattern with micron precision. This study evaluated the fitness accuracy of clasps fabricated from CAD/CAM resin and wax patterns. Materials and Methods: Using fifteen 18-8 stainless steel tooth dies (10.0-mm diameter, 8.0-mm height, 7.5-mm radius of curvature) simulating the first molar, 15 master casts were fabricated with extra-hard stone plaster (Fuji-rock, GC., Japan). After ten master casts were scanned with a 3D scanner (Rexcan DS, Solutionix Inc., South Korea), the clasps were designed using FreeForm (SensAble Technologies Inc., USA) and VR Mesh v3.5 Studio (VirtualGrid Company, USA). The wax and resin patterns of Akers clasps with 0.5-mm undercuts were molded using the 3D scanner R66 (CAD/CAM wax: Solidscape, USA) and ProjetDP3000 (CAD/CAM resin: 3D Systems Inc., USA). As a control, the patterns were waxed up on the refractory cast. All patterns were conventionally cast with a type IV gold alloy (PGA 3, Ishifuku, Japan). The gap distances between the clasps and the 18-8 stainless steel dies were recorded using silicone impression materials. After the silicones were perpendicularly sectioned at 3 regions (lower and upper area of the clasp arms and occclusal rest area), each silicone layer was measured using a digital microscope (VHX-200/100F, Keyence, Japan). The results (n=5) were analyzed by ANOVA/ Tukey's test (a=0.05). Results: The CAD/CAM wax pattern had a significantly thicker layer than control at the upper of the clasp arms and the rest (p<0.05). Of the CAD/CAM pattern, resin tended to demonstrate the thinner layer than that of wax. There were no statistical difference between CAD/CAM resin and the control except the rest section (p>0.05). Conclusions: Although control should the greatest fitness at the supporting area, CAD/CAM patterns system can be applied as a new laboratory procedure for making cast Akers clasps.