In a meta-analysis the results of two different trials on posterior re
sin-bonded bridges (PRBBs) were combined. The common experimental vari
able 'preparation form' and the variable 'location' were combined for
this analysis. The meta-analysis showed a highly significant effect fo
r the variable 'location' (P < 0.001). Although the experimental varia
ble 'preparation form' had no significant influence in the separate tr
ials, the combined study revealed a significant effect for this variab
le on the retention of PRBBs (P = 0.03).