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While occurrences are extremely rare, UK-wide dental defence organisation MDDUS has dealt with cases where broken needles cannot be retrieved from the tissue.

MDDUS dental adviser Mike Williams says: 'Breakage and retention of dental needles within the tissues has become extremely rare due to the introduction of single-use, disposable needles made of modern, stainless steel alloys.

Nevertheless, it does happen and can be a stressful and upsetting event for both patient and clinician alike.

'It is invariably associated with bending the needle prior to insertion and then inserting the needle into soft tissues for its entire length. No local anaesthetic injection technique used in dentistry requires the needle to be bent for the injection to be successful.

'Dentists can reduce risk by using longer and larger gauge needles if significant depths of soft tissue are involved. Needles should not be forced against resistance or redirected into the tissues and dentists should consider changing needles if multiple injections are required.'

The problem occurs when needles break at the hub, which is the most rigid portion of the needle.

The needle should only be inserted into the hub if it is absolutely essential for the success of the technique. Broken needles that had not been inserted to the hub would not be a significant problem as any fragment of needle sticking out of the gum could be straightforwardly retrieved with a haemostat.

If, however, the needle is inserted to the hub and it breaks, the elasticity of the soft tissues produces a rebound, and the needle is buried. In routine dental practice, this would be most likely when giving inferior dental nerve blocks.

He adds: 'Needle breakage is more likely to occur when short needles are used, as they are more likely to be inserted to the hub, and when narrower needles are used (30 gauge instead of 27 or 25). It can be associated with sudden movement of the patient or changing direction of the needle when inserted into the tissues.

'First of all, the dentist should remain calm and tell the patient not to move and keep their mouth open. The dentist should ensure they keep the hand that has been retracting the soft tissues in place. If the fragment is visible, it can be retrieved with a haemostat.

'If the fragment is not visible, the dentist should not attempt any incision or probing. Needles that break off entirely within soft tissue cannot be readily retrieved. Usually they do not move more than a few millimetres and become encased in scar tissue.

'The dentist should inform and reassure the patient, asking them to avoid excessive jaw movements. Choosing to leave a needle fragment in the tissue instead of attempting its removal has been favoured in the past as it was thought to lead to fewer problems than having an extensive, surgical procedure, reliant upon plain radiographs to identify the position of the fragment.

'The use of CT scans can now give invaluable information and the availability of helical CT scanners has made this the investigation of choice. The technology, together with legal considerations has, more recently, tended to favour removal of the broken fragment.'

However, the procedure is usually done under general anaesthetic and must be carried out by an experienced oral surgeon or oral and maxilla-facial surgeon.

He adds: 'At the oral and maxilla-facial surgery department, an assessment will be made of the patient and the position of the retained needle fragment. Treatment options will be discussed and arrangements made for monitoring or surgery.

'Dentists must ensure they keep full and contemporaneous records during any incident involving needle breakage and contact their dental defence organisation. Ideally, they should retain the remaining needle fragment, ensuring it is not a cross infection or sharps injury risk.'

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