The screw shears! What's up?
- The screw is in soft dentine
- The screw thread is blunt
As to 1: the screw needs positioning in firm dentine
Mill the core of the root deep down into the apical third of the root with a round bur.
Open the visible root channel with the trephine and prepare with the Benex drill (often using the shaft extender).
Drilling should penetrate the root; this is clearly noticeable (the drilling resistance diminishes).
This enables the screw to be well and securely anchored in the apical, firm root fragment.
As to 2: the screw thread is blunt