Volumetric changes in acrylic denture base material

Aims of this study are to determine:a-Three dimensional chances (Volumetric changes) of the internal surfaces of twenty four maxillary acrylic resin complete denture bases in relation to their corresponding master casts, were determined among six patients by using three dimensional measuring machine {Cordimet 1200}.b-The maximum dimensional change of the acrylic resin denture that can be allowed to avoid displacement of the tissue.c-The effect of muco-static impression technique on the tissue displacement.Three maxillary dentures A, B, and C were constructed in the conventional way. Dentures B, and C were designed by increasing the space between the internal surface of the denture and the tissue surface of themaster cast by using tinfoil (0.2)mm, and (0.3)mm except the periphery region respectively.By the aid of computer, three special programs were designed for this study to, calculate the surface area,volumetric changes in acrylic denture base, and to draw any section of the tissue surface of the oral cavity in relation to the tissue surface of the denture every (5)mm longitudinally, and (2)mm horizontally.The results of this study showed that maximum tissue displacement was found in the midline region toward the posterior part of the denture base (27.465 mm).The area of tissue displacement was reduced toward the periphery, away from the midline of the maxillary arch. While in the post-dam region, tissue displacement was found in the middle part of the palate.In the periphery region there was a convergence of buccal flanges toward the middle of the denture base.A positive volumetric change in denture base was found in moral region (0.072 mm3). The results of muco-static impression technique was a pressure on the tissue to 0.3 mm vertically lead to have negative volume equal to (0.00 mm3).