[Retention of three different luting cements (author's transl)].

Employing zinc phosphate, polycarboxylate and glass ionomer cements, effect of cement layer thickness on retention of crowns at their axial wall was investigated. Stainless steel preparations and occlusally perforated crowns having taper angles of 2.9 and 5.7 degrees were cemented, regulating the thickness at the axial wall from 5 to 60 mu. These dies were stored in a 100% relative humidity atmosphere at room temperature or in distilled water. After 48 hr, retention was measured, applying the load vertically to occlusal preparation surface through a plunger (Fig. 1). Due to the inclusion of unreacted powder particles in the set structure of all three cements, evidence of a critical value was always shown in the cement thickness-retention relationship (Figs. 2, 3 and 4). When the cement thickness was reduced below the critical value, the retention increased remarkably and was not affected by the environment. Above the critical value, however, the retention of these cements was relatively small and affected considerably by the environment. By water immersion, the increase in the retention was found for the two polyacrylate, but not for the zinc phosphate. Correlation between retention and mechanical strengths of the three cements in the respective environments was indefinite.