You can claim if a patient needs more work during an open CoT under some circumstances.
If the patient goes to the practice the open CoT is with, any additional treatment is considered as part of the existing CoT.
The only exception to this is detailed in DH factsheet 7b Gateway Reference 6990.
The situation is different if the patient sees a clinician working under a different contract. The clinician must claim for an Unscheduled Care CoT, charge the patient as normal if appropriate and they'll receive the appropriate units of dental activity (UDA).
When submitting a claim for Unscheduled Care, it cannot be claimed under the continuation rule.