title: Crossover designs involving two treatments.
mesh_terms: D005782:Gels; D006801:Humans; D009911:Oral Hygiene Index; D010100:Oxygen / Q000627:therapeutic use; D010510:Periodontal Diseases / Q000628:therapy*; D010919:Placebos; D012107:Research Design
chemical_list: D005782:Gels; D010919:Placebos; D010100:Oxygen