Which component of bacterial plaque is not always present in samples?

Bacterial plaque is a complex biofilm that typically consists of various bacteria, saliva, and oral debris. While food debris is a common component found in plaque, it is not always present in every sample. This is because food remnants can vary based on recent eating habits, individual oral hygiene practices, and timing.

On the other hand, microorganisms, oral debris, and saliva are consistently found in plaque formation. Microorganisms are fundamental to the very existence of plaque, as it is primarily made up of bacteria or other microorganisms. Oral debris encompasses a broader category, including dead cells and other materials that accumulate in the mouth, and saliva acts as a binding agent, providing a necessary medium for bacterial adherence and growth.

Thus, the variability of food debris, depending on diet and oral care routine, distinguishes it from the other components, making it the correct choice for this question.