Final answer:
The pH of plaque biofilm at rest is typically acidic, often below 7.0, which is favorable to acidophilic organisms and contributes to dental caries by demineralizing tooth enamel.
Step-by-step explanation:
The pH of plaque biofilm at rest is typically acidic, often falling below the neutral pH of 7.0. While the exact pH can vary, it is common for dental plaque to have a pH close to the values suitable for acidophilic organisms, which grow optimally at less than 5.5. Considering the environments in the human body, the pH of saliva is slightly acidic but can vary depending on various factors, including the presence of food and bacteria, which can produce acids as byproducts. The acidic environment of dental plaque contributes to dental caries as the acids demineralize the enamel of the teeth.