Fit of direct retainers in removable partial dentures after 8 years of use.

In a cross-sectional study the fit of direct retainers was assessed after 8 years of use. A total of 101 metal frame removable partial dentures (RPD) were investigated, including 54 extension base prostheses without any tooth supported replacement and 47 tooth supported prostheses that replaced only premolars and molars. Of the frameworks studied, about 60% of the clasps showed a space between retainers and abutments. Logistic regression analyses demonstrated that the age of the RPD and the type of opposing dentition significantly influenced the fit of the clasps. The relative risks and a backward regression analysis revealed that the variable non-rigid extension base RPD had the greatest influence on clasp fit. It was concluded that in extension base RPDs a rigid design should be preferred.