| Study | Reason for exclusion |
|---|---|
| Kapoor 2008 | This is a review. |
| Mahdavi 2011 | This is a review. |
| Mantegazza 2010 | This is a review. |
| Sakurai 1999 | This is a case series study without a control group. |
| Smith 2006 | This is a comment. |
| Waxman 2008 | This is a review. |
| Zhang 1999 | This is a case series study without a control group. |
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