Patients suffering from Mucous Membrane Pemphigoid with desquamative gingivitis (MMPg) generally present a more degraded periodontal condition compared with controls. Bullous disease could represent a risk factor for plaque-induced periodontal disease, and vice versa. Indeed, the dysbiotic periodontal microbiota could aggravate the gingival damage specific to MMP, either directly by activating inflammatory pathways, or indirectly by degrading cellular and matrix components. On the other hand, areas of erosive gingiva generated by the autoimmune process could increase the virulent power of periodontal pathobionts, by representing accessible, nutrient-rich connective surfaces. Moreover, in recent years, bacterial studies based on a high-throughput metagenomic approach have suggested the existence of a relationship between the oral and intestinal microbiota in patients with degraded periodontal conditions and suffering from autoimmune inflammatory diseases (inflammatory bowel disease, acute graft-versus-host disease). This relationship can also be envisaged in MMPg patients who meet the conditions that allow this type of pathological process to occur: autoimmune disease; disruption of the gingival epithelial barrier in erosive gingival areas (increasing the risk of antigen exposure); large amounts of thick plaque; degraded periodontal condition with the presence of numerous periodontal pockets from which periodontopathogenic bacteria can translocate intra-tissularly and cause distant adverse consequences. The main aim of this observational, multicentre, case-control, matched study is to compare the composition of the periodontal microbiota between MMPg patients and control patients (arm 2 and arm 3). The secondary objectives are to compare the composition of periodontal and intestinal microbiota in cases and control patients (arm 2 and arm 3), to compare periodontal microbiota composition in cases and control patients (arm 2) according to periodontitis severity, and to compare gut microbiota composition between cases and control patients (arm 2 and arm3). To date, no such study exists.