Table 1. Risk of bias of the included trials.
| Study | Sequence generation | Allocation concealment | Blinding of participants and personnel* | Blinding of outcome assessment | Incomplete outcome data assessed | Selective reporting | Free of other bias | Overall risk |
|---|---|---|---|---|---|---|---|---|
| Lopez 2002 [39] | Low risk of bias. (Randomization by toss of coin.) | Unclear risk of bias.(No mention of concealment.) | High risk of bias.(No blinding strategy.) | Low risk of bias.(Obstetrician masked.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | High risk of bias. |
| Jeffcoat 2003 [40] | Low risk of bias. (Randomization accomplished by code.) | Low risk of bias.(Allocation concealment by use of double packet with coding information.) | Low risk of bias. (Mention about blinding in study design.????? Can this become more clear?????) | Low risk of bias. (Mention about blinding in study design.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | Low risk of bias. |
| Sadamansouri 2006 [41] | Unclear risk of bias.(No mention about how randomization was accomplished.) | Unclear risk of bias.(No information on allocation concealment.) | High risk of bias.(No mention about blinding.) | High risk of bias.(No mention about blinding | Unclear risk of bias.(Effects of covariates and confounders on outcomes are not examined.) | Low risk of bias. | Unclear risk of bias.(Imbalance in baseline characteristics.) | High risk of bias. |
| Offenbacher 2006 [42] | Unclear risk of bias. (No mention about how randomization was accomplished.) | Unclear risk of bias (No information on allocation concealment.) | Low risk of bias.(Mention about examiners being blinded.) | Low risk of bias.(Mention about examiners being blinded.) | Low risk of bias | Low risk of bias. | Unclear risk of bias. (Periodontal status imbalanced at baseline.) | High risk of bias. |
| Michalowicz 2006 [43] | Low risk of bias. (Block randomization.) | Low risk of bias. (Mention about telephone calls and central randomization.) | Low risk of bias.(Mention about blinding in study design.) | Low risk of bias.(Mention about blinding in study design.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | Low risk of bias. |
| Tarannum and Faiduzzin 2007 [44] | Low risk of bias. (Randomization by flip of coin.) | Unclear risk of bias. (No mention about allocation concealment.) | High risk of bias.(No information on blinding strategy is provided.) | High risk of bias.(No mention about blinding.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | High risk of bias. |
| Radnai 2009 [45] | Low risk of bias. (Block randomization by of random sequence of numbers.) | Unclear risk of bias. (No mention about allocation concealment.) | Low risk of bias.(Mention about blinding in study design.) | Low risk of bias.(Mention about blinding in study design.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | High risk of bias. |
| Newnham 2009 [46] | Low risk of bias. (Randomization accomplished by computer generated software.) | Unclear risk of bias.(No mention about allocation concealment.) | High risk of bias.(No information on blinding strategy is provided.) | Low risk of bias.(Assessors unaware of treatment.) | Low risk of bias | Low risk of bias. | Low risk of bias. | High risk of bias. |
| Offenbacher 2009 [47] | Low risk of bias. (Permutated block randomization.) | Unclear risk of bias (no mention about allocation concealment) | High risk of bias.(No information on blinding strategy is provided.) | Low risk of bias.(Dental examiners were blinded.) | Unclear risk of bias. (Unclear how missing data was treated.) | Low risk of bias. | Unclear risk of bias. (Baseline characteristics similar excepting for number of nulliparous pregnancies and self-reported alcohol use.) | High risk of bias. |
| Oliveira 2011 [48] | Unclear risk of bias. (Not clear how randomization was accomplished.) | Unclear risk of bias.(No mention about allocation concealment.) | High risk of bias. (No information on blinding strategy is provided.) | Low risk of bias.(Mention about blinding in study design.) | Low risk of bias. | Low risk of bias. | Unclear risk of bias. (Differences in periodontal status at baseline.) | High risk of bias. |
| Macones 2011 [49] | Low risk of bias. (Permutated block randomization.) | Unclear risk of bias. (No mention about allocation concealment). | High risk of bias.(No information on blinding strategy is provided.) | Low risk of bias.(Outcome assessors blinded.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | High risk of bias. |
| Pirie 2013 [8] | Low risk of bias. (Randomization accomplished by computer generated random number.) | Low risk of bias.(Allocation concealment accomplished by use of opaque sealed envelope.) | Low risk of bias. (Staff members were masked for treatment.) | Low risk of bias. (Staff members were masked for treatment.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | Low risk of bias. |
| Weidlich 2013 [7] | Low risk of bias. (Randomization accomplished by computer generated random number-block stratification.) | Low risk of bias. (Allocation concealment accomplished by use of sealed envelope.) | High risk of bias.(No information on blinding strategy is provided.) | Low risk of bias.(Independent examiners.) | Low risk of bias. | Low risk of bias. | Low risk of bias. | Low risk of bias. |
* Risk of bias stemming from not blinding participants or personnel was not used to decide a trial’s overall risk of bias.