76 made with the elastomer materials (especially with the harder silicons). Thus the measurements one hour after production gave the smallest inaccuracies with the impressions made of Futar D ® , followed by those made of Ramitec Penta ® , Memosil CD ® “new”, Dimension Bite ® and Memosil CD ® “old.” Large and ever-increasing variations were shown (in order) in the impressions made of Memoreg C.D. ® , Futar ® , Registrado opak ® - hard, Omicron Topas ® , Silagum ® , Regisil PB ® , Registrado ® , 3M ® bite impressions, Regisil ® and Stat BR KERR ® . 24 hours after production, the impressions made of Memoreg C.D. ® and those made of Dimension Bite ® and Futar D ® stood out especially thanks to the comparatively small errors that they revealed. After these, increasingly large errors were found in the impressions made of Omicron Topas ® , Futar ® , Memosil C.D. ® , Ramitec Penta ® , Memosil C.D. ® “old,” Silagum ® , Registrado opak ® - hard, 3M ® bite registration material, Regisil PB ® , Stat BR KERR ® , Regisil ® , Kristall ® and Registrado ® . In addition, compared with one hour after production of the impressions, with the measurements taken again after 24 hours, there were greater inaccuracies, in particular with the impressions made of Registrado ® , followed by those made of Kristall ® . On the other hand, variations on a smaller scale were shown in particular with the impressions made of Memoreg C.D. ® . The other impressions made with elastomers showed relatively small or scarcely no differences in their variations between one hour and 24 hours after their production. In the second part of the test in the present study, elastomer bite impressions were tested under practical conditions, as is the case in technical dentistry laboratories. The errors discovered are no longer seen to be based only on the material-specific properties of the registration material used but they are also caused by the moulding technique, the model production and the materialspecific properties of the superhard plaster used with this.
77 The moulds of both the jaws were made with the corrective impression technique and the double-mix technique with casting with a superhard plaster. The accuracy of reproduction of the bite impressions used was tested after a storage period of at least 24 hours. Here greater inaccuracies appeared than under purely technical laboratory conditions in all ten of the tested impressions made of Kristall ® , Memosil C.D. ® “new” and in particular also in those made of Futar D ® – with which in itself good properties are to be expected. Somewhat smaller but surprisingly insignificant variations arose with the impressions made of Futar D ® in the test on jaw models with the corrective impression technique than with the impressions made of Memosil C.D. ® “new” and Kristall ® . Of the impressions tested on jaw models with the double-mix technique, however, the impressions made of Memosil C.D. ® “new” actually stood out with their smaller inaccuracies than those made of Futar D ® . The impressions made of Kristall ® , on the other hand, showed greater errors here too. An additional test with the cut impressions made of Futar D ® found no improvement in accuracy of reproduction. In conclusion it can be said that with hard registration materials such as Futar D ® , of which very good properties may be expected, greater errors may occur with plaster models than with impressions of an average consistency. On the other hand, with soft impressions such as Kristall ® , the error is great, as is expected. The moulding technique used for the production of the models plays scarcely any part here.