Objective: The purpose of this investigation was to establish a connection between masticatory deficiency and pathomorphologic alterations of gastric mucosa in patients with dyspepsia. Method and Materials: In 40 dyspeptic, edentulous and partially dentate patients and in 40 dyspeptic control patients with good dental status, the Optosil masticatory function test was performed. Histopathologic changes of gastric mucosa and the severity of Helicobacter pylori infection were scored according to the updated Sydney Classification of Chronic Gastritis. Results: The comminution of Optosil particles after increasing the number of chewing strokes was significantly impaired in edentulous and partially dentate patients, indicating masticatory deficiency in this group. This masticatory deficiency group was subdivided into groups with a lower (subgroup 1) and higher (subgroup 2) degree of masticatory deficiency according to median X50 in the Optosil test. The endoscopic appearance of gastric mucosa in masticatory deficiency patients and in the control group suggested chronic gastritis. Higher inflammatory and infection scores were noted in subgroup 2 than in the control group and subgroup 1, especially in the antral part of the stomach. The differences between the antral part and the body of the stomach were significant only in subgroup 2. Conclusions: Masticatory deficiency in patients with dyspepsia was connected with more severe chronic inflammatory changes and H pylori infection of gastric mucosa, especially in the antrum of the stomach. Higher values of inflammatory and infection scores in the subgroup with a higher degree of masticatory deficiency suggest its causal role in the promotion of gastritis and H pylori infection. Keywords: chewing, gastritis, Helicobacter pylori, masticatory deficiency, Optosil test