The invention provides structurally modified, pyrogenically prepared silicas obtained by reaction of pyrogenic silicas with cyclic polysiloxanes of the type —[O—Si(R2)]n—, where R is a C1 to C6 alkyl group and n is 3 to 9, and subsequent structural modification of the silanized silicas obtained. The invention further provides an adhesive comprising the structurally modified, pyrogenically prepared silicas.