Study of titanium screws as retrograde fillings using bacteria and dye

The tightness of retrograde titanium screw fillings and retrograde amalgam fillings was compared in 17 human, single-rooted teeth using Serratia marcescens bacteria in vitro. The root canals were subjected to instrumentation and irrigation, after which 2 mm was cut off from the apical end. Eight of the teeth were sealed using retrograde titanium screw fillings and nine using retrograde amalgam fillings. The teeth were suspended by means of wires in test tubes, with the crowns upwards and the roots immersed in trypticase soy broth. Suspensions of Serratia marcescens bacteria were placed in the root canals, and samples from the broth were plated daily. The bacteria penetrated the apical titanium screw seals in 2 to 7 days, and the retrograde amalgam fillings readily on the first day. Thus, the titanium screws seemed to provide a tighter seal. Staining with India ink showed that penetration had occurred at the tooth-filling margin and that the instrumentation had not caused any fractures to the roots.