Maxillary complete denture rebase may be associated with slight occluding changes attributed to tissue displacement during impression making.
3-dimensional measurement system was used to compare displacements of the tissue/denture base interface of occluding and digital impression technique for complete denture rebase.
Methods:
10 completely edentulous subjects were included. For each subject, 3 maxillary casts were obtained: (1) a reference cast of the existing denture base, (2) a cast made with an occluding rebase impression technique, and (3) a cast made with a digital rebase impression technique.
With an optical 3-dimensional measurement system, the corresponding casts in a common coordinate system were analyzed geometrically. For each cast, the coordinates of the barycentric point and the high point were determined. For the same subject, the differences between the coordinates of the barycentric points of the 3 casts were calculated 2-by-2. The same calculation was performed for the high points. To determine whether these differences, which represent the displacements of the barycentric points and the high points, were statistically significant, Wilcoxon signed-rank test for paired group comparisons was applied (P<.05). Cartographic differences among casts from the same subject also were compared.
Results:
Cartography data showed that the greatest dimensional differences between the 2 impression techniques were located on the palate area, posterior palatal seal area and anterior third of the palate. Barycentric points displacements were essentially vertical and longer under digital than occluding impression (0.5mm). The highest point under occluding pressure is only 0.32 mm higher than reference, while the tissue denture base-interface at the anterior area sinks 1.2 mm vertically under digital pressure.
Conclusions:
Within the limitations of this 3-dimensional in vivo study, displacements of the tissue/denture base interface were significantly more important with the use of digital than with occluding impression technique, probably due to a more posterior loading point.