Children often damage their front teeth. In approximately 6% of cases, the nerve inside the affected tooth dies (becomes 'non-vital') and natural root development stops. In these cases, the tooth requires a root canal treatment in order to prevent problems such as pain and dental abscesses from arising. However, because the roots of these young teeth are not fully formed, they are weaker and prone to fracture. In addition, root canal treatment is difficult because a root canal filling cannot be placed in a tooth which is not yet fully formed, due to the fact that the root has an 'open' end.

To enable root canal treatment to be carried out, a 'barrier' must be placed at the end of the 'open' root. This can be done using materials called Calcium Hydroxide or Mineral Trioxide Aggregate (MTA). These materials are placed inside the root and sealed into the tooth. However, although they help to provide a barrier, they do not help to strengthen the walls of the root. Treatment with these materials requires multiple visits to the dentist, over a period of up to 18 months.

There is evidence to suggest that an alternative treatment involving 'revascularisation' (recovery of the blood supply to the tooth) and the use of a triple antibiotic paste allows 'natural' root growth to restart, and also strengthens the walls of the root. Treatment can often be carried out in just two visits.

The aim of this study is to discover whether there is a difference between one of two methods of treating non-vital teeth with open ends. It is thought that there will be no significant differences seen between the results of the two techniques.

Children with teeth that fall into this category and require root canal treatment will be given one of two treatments, both of which aim to treat infection, close the root end and to allow healing to take place.

Teeth will receive one of the following methods of root treatment:

1. Revascularisation (recovery of the natural blood supply to the tooth) following placement of an antibiotic paste into the tooth root. The aim of this treatment is to allow 'natural' root growth to restart. Root growth will allow the tooth to form at barrier at the end of the root. No root canal filling will then be necessary.
2. Closure of the open root end by placement of an artificial barrier at the end of the root so that a root canal filling can then be placed. This will be done with a dental material called Mineral Trioxide Aggregate (MTA). Non-vital teeth with an open end are routinely treated in this way at Liverpool Dental Hospital.

Participants will be randomly allocated in to one of the above treatment groups. This means that neither the participants, nor the researchers, will be able to choose which group a participant will be allocated to.

In both techniques, in order to learn about the bacteria involved in non-vital teeth, the investigators will take samples of the bacteria within the root canal.

The outcomes of the study will provide us with further information about root growth, the bacteria involved in infection of non-vital teeth and the success of the different treatment methods that are available. This information will enable us to increase our understanding of the treatment of non-vital teeth with an open end and help us to explain our treatments to future patients.

All children presenting to Liverpool University Dental Hospital aged between 7 and 25 years of age and who are medically well and cooperative to receive prolonged treatment in the dental chair are eligible to take part in the study if they have a damaged upper front adult tooth in which the nerve has died and the root is open ended. Unfortunately, if there is dental decay in the tooth or a fracture of the root then these teeth are not suitable for this study. In some cases following damage to a tooth, the root of the tooth starts to dissolve and unfortunately these teeth are also not suitable for this study.

Suitable patients attend with their parent or carer for a consultation to the Paediatric Dentistry Clinic at Liverpool University Dental Hospital. Following this visit, if a suitable patient wishes to join our study the investigators will arrange two further visits during which the dental treatment will take place. Following completion of treatment, patients will be asked to return for four check ups over the next year so that the investigators can check that they are happy and that treatment has been successful.

There are no risks or disadvantages to taking part in this study. However, if the tooth does not respond to treatment, or if symptoms of infection arise, then alternative treatment methods may be initiated as necessary.

The study is being funded by the Royal Liverpool and Broadgreen University Hospitals NHS Trust and by the University of Liverpool.

Inclusion Criteria for participants:

• Between 7 and 25 years of age
• Have no significant medical history
• Cooperative in the dental chair
• Able to commit to the recall schedules prescribed by the study
• Have one or more traumatised non-vital permanent maxillary central incisors with incomplete root development

Exclusion Criteria for participants:

• Have a medical history that may complicate treatment
• Have a medical history for which the study procedures may place the patient at increased risk
• Have a diagnosis of avulsion or severe intrusion following dental trauma

Exclusion Criteria for Permanent maxillary central incisors:

• Less than half formed
• Have anatomical complexity (such as dens invaginatus)
• Have horizontal or vertical root fractures present
• Have evidence of root resorption