| Study | Reason for exclusion |
|---|---|
| Angle 2003 | Not a randomised controlled trial. |
| De Vries 2005 | Not a randomised controlled trial. |
| Henry 1999 | Not a randomised controlled trial. |
| Mathias 1993 | Not a randomised controlled trial. |
| Motarjeme 1996 | Not a randomised controlled trial. |
| Schillinger 2001 | Not a randomised controlled trial. |
| Sixt 2009 | Not a randomised controlled trial. |
| Westerband 2003 | Not a randomised controlled trial. |
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