When Performing RCT Through a Metal Crown or Existing Amalgam Restoration
Avoid False Readings ⚡
✓ Establish Straight-Line Access
Make sure the hand file does not contact the cavity walls—such as the metal crown or amalgam restoration—while entering the canal.
✓ Keep the Irrigant at the Orifice Level and Away from the Metal Restoration
Remember: irrigants conduct electricity too.
How Does It Happen?
An apex locator works by measuring the electrical properties between the hand file and the lip clip.
If the hand file or conductive irrigant contacts the metal crown or amalgam restoration, it can create an alternative conductive pathway, resulting in:
- A premature or unstable reading
- A potentially inaccurate working length
Keep the hand file and irrigant isolated from the metal.
Clinical Case
#27 RCT through an existing metal crown
Working length was established using an apex locator while ensuring that the hand file and irrigant remained isolated from the metal restoration to avoid false or unstable readings.
File system: RC Blue
Date: 15 June 2026
Clinical case — #27 RCT through an existing metal crown, 15 June 2026.
Where Do You Establish Your Working Length?
Once you have a stable apex locator reading, the next question is: where do you choose to shape to?
Do you shape to “0” / the major foramen, or 0.5 mm short, towards the apical constriction?
What’s your approach? We’d love to hear how you determine working length in your clinical practice.
This article is intended for dental professional education and does not replace individual clinical judgement.
