Table 1 Inclusion and exclusion criteria of the studies

1. Observation studies (cross-sectional, case-control, retrospective cohort, or prospective cohort).

2. Studies assessing primary teeth.

3. Studies reported in the English language.

4. Studied having the following PECOs:

a. Population: children with primary or mixed dentition.

b. Exposure: black stains of any amount or extent related to primary teeth.

c. Comparators: children without dental black stains.

d. Outcomes: Occurrence of dental caries, number of teeth affected, number of surfaces affected.

1. Studies where caries parameters are not described in terms of the type of dentition.

2. Self-reported dental caries or black stains.

3. Studies that were conducted on medically compromised or institutionalized children.

4. Case-reports and case-series.

5. Editorials, and commentaries.

6. Secondary literature sources (such as books or reviews)