Patients with the most common weak D types 1, 2, and 3 can be safely considered D positive. We evaluated 1,113 Rh-negative Egyptian samples for weak D expression to propose a cost-effective strategy related to D variant testing. D variants were tested using polymerase chain reaction with sequence-specific priming. Fifty samples were D variants (4.5%): weak D type 4.2 (32%), weak D type 4.0/4.1 (16%), and weak D type 15 (2%). Fifteen (62.5%) of 24 samples were identified serologically as partial D. We also studied the probability of the development of anti-D in 52 Rh-negative children with thalassemia who were receiving units for which weak D was not tested. Anti-D alloimmunization was observed in 63.5% of patients with thalassemia. It is prudent to implement weak D typing in Egyptian donors. Weak D variants of Egyptians are significantly different compared with Caucasians. Ethnicity must be taken into consideration when developing clinical and prenatal strategies related to D variants.

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DATA SOURCES: Medline, Embase, Cochrane Oral Health Group's Trials Register and the Cochrane Central Register of Controlled Trials (CENTRAL). Unpublished data were sought by searching ClinicalTrials.gov, the National Research Register and Pro-Quest Dissertation Abstracts and Thesis database. There were no language restrictions.

STUDY SELECTION: Randomised and controlled clinical trials (including split mouth) directly comparing self-etch and acid-etch primers including patients with full-arch, fixed and bonded orthodontic appliances (not banded) with follow-up periods of at least 12 months were included.

DATA EXTRACTION AND SYNTHESIS: Two authors abstracted data independently, with disagreements being resolved by a third. The Cochrane Risk of Bias tool was used to assess study quality. A random effects meta-analysis was undertaken.

RESULTS: Eleven studies were included in the qualitative summary with five studies contributing to a meta-analysis. These five studies (n =3444 brackets, 1721 acid-etch, 1723 self-etch) had relatively low statistical and clinical heterogeneity. Meta-analysis demonstrated a tendency for a higher risk of failure (odds ratio 1.35; 95% CI, 0.99-1.83; P 5 0.06) with self-etch primers. The use of self-etch techniques was also associated with a small but statistically significant time saving (weighted mean difference 23.2 seconds per bracket; 95% CI, 20.7-25.8; P \0.001). There was insufficient evidence to assess the effect of bonding modality on demineralisation rates.

CONCLUSIONS: There is weak evidence indicating higher odds of failure with self-etch primer than acid-etch over 12 months in orthodontic patients, and there is strong evidence that a self-etch primer is likely to result in modest time savings (eight minutes for full bonding) compared with acid-etch.

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