AO self-drilling and self-tapping screws in rat calvarial bone: an ultrastructural study of the implant interface.
OBJECTIVE
The purpose of the present study was to compare the bone-to-screw interface of both AO self-drilling screws (SDSs) and self-tapping screws (STSs) using scanning electron microscopy.


METHODS
The calvaria from Sprague-Dawley rats were harvested, and the periosteum was removed. The samples were stored in saline until use. AO STSs and SDSs were then inserted into the outer surface of the calvaria without irrigation. All screws were 4 mm in length and were inserted until their tips protruded to the endosteal side. A total of 6 screws, 3 of each type, were placed. The dimensions of the screws were 1.3, 1.5, and 2.0 mm. All STSs were placed with an appropriately sized predrilled hole. Samples were then examined and digitally photographed using scanning electron microscopy.


RESULTS
No damage was noted to any of the implants (STSs or SDSs). Excellent adaptation of the STSs to host bone was observed for all specimens. On the other hand, the endosteal surface of the SDSs demonstrated large voids adjacent to the screw threads at the interface. These appeared to represent microfractures of the bone at the bone-implant interface.


CONCLUSIONS
These data suggest a greater amount of bone damage during placement of the SDSs compared with the STSs. These results point to the need for further investigation into the use of SDSs in clinical practice.
Sowden
David
D
The University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.
Schmitz
John P
JP
D000818:Animals; D001863:Bone Screws; D001842:Bone and Bones / Q000473:pathology / Q000648:ultrastructure; D004867:Equipment Design; D008855:Microscopy, Electron, Scanning; D010521:Periosteum / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012886:Skull; D013718:Tensile Strength; D019415:Torque