Effect of Ridge Shape on the Fit of Denture Bases

The objective of this study was to determine the accuracy of heat cured acrylic base plates on simulated edentulous ridges with different configurations. Edentulous ridges of the maxillae were simulated by attaching parallel trapetsoidal rods simulating ridges to a flat plate simulating the palate. The slope of the palatal ridges was always 45 degrees, while the outside slopes were either 85 degrees, 75 degrees or 60 degrees. The sagital ridge convergencies were 5 degrees, 10 degrees or 15 degrees for each ridge shape. No ridges were simulated in the anterior regions. Two micrometers were attached to the aluminum base that mounts the simulated ridges. One measured the space between the metal palate surface and the base plate, and the other displaced the base plates in sagital anterior direction. PVS impressions of the simulated ridges were made. They were poured in type IV stone. A total of 54 acrylic base plates with 1 mm thickness were fabricated (n=6 per experimental condition). The acrylic base plates were placed on matching ridge models and the palatal-base plate distances were measured at each 1.000mm as the base plates were displaced in an anterior direction. The x and y values were plotted showing the vertical palate-base plate distance (y) as a function of anterior displacement (x). All results followed third degree polynomials. In conclusion, the best fit at zero displacement was for ridges with an anterior convergency of 15 degrees and an outside slope 60 degrees. Furthermore, it can be concluded from this study that the steeper the outer angles of the ridges, the worse the fit of the acrylic base at zero displacement. Also, the anterior displacement of a relatively well fitting acrylic base plate causes the fit to become poor because of the influence of the inner slopes of the simulated ridges. ( en )