Which of the following contributes to periodontal issues due to restoration characteristics?

The correct choice highlights how a flat ridge causing no food deflection can lead to periodontal issues. In restoration design, the shape and contour of dental restorations play a crucial role in oral hygiene and periodontitis prevention. A flat ridge does not facilitate proper food deflection, which is essential in directing food away from the periodontal tissue. When food accumulates around the teeth and gum line without being deflected, it creates an environment conducive to plaque build-up and potential inflammation, thus exacerbating periodontal disease.

This contrasts with the other options. Deep occlusal pits can potentially trap food debris, which could be detrimental but are not the primary factor in restoration design influencing periodontal health. Highly polished surfaces are generally beneficial for reducing plaque accumulation, as they make it harder for biofilm to adhere. Inadequate flossing technique is related to a patient's oral hygiene practices rather than the restoration's inherent characteristics.