Which historical theory of periodontal disease proposes that disease results from a shift in the overall balance and proportions of the resident oral microbiota — rather than from a single specific pathogen?

The ecological plaque hypothesis (Marsh) proposes that periodontal disease results from an ecological shift in the proportions of microorganisms within plaque (driven by local environmental changes), rather than simple overall plaque accumulation (nonspecific plaque hypothesis) or a single specific pathogen alone (specific plaque hypothesis). Focal infection theory is an older, largely discredited idea that oral infections were a primary cause of distant systemic disease.