Final answer:
The black stain on children's teeth can be attributed to poor oral hygiene leading to fungal and bacterial accumulation in dental plaque, which, if not addressed, can calcify into tartar and cause dental caries and other oral health problems.
Step-by-step explanation:
The black stain found on some children's teeth may result from poor hygiene and the presence of fungi and bacteria in dental plaque. When clean teeth come into contact with saliva, a layer of proteins and carbohydrates forms, which attracts microbes, forming a sticky biofilm known as plaque. The main bacteria responsible for tooth decay within these biofilms is Streptococcus mutans. They metabolize sugars from food to produce acids such as lactic acid, which dissolves the tooth minerals, including the enamel, known as the hardest substance in the human body. If dental plaque becomes thick and calcifies, it turns into dental calculus or tartar. This can lead to dental caries (cavities) and other significant oral health issues, which emphasizes the importance of regular dental hygiene practices including brushing, flossing, and professional cleanings to maintain oral health and prevent decay.