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BACKGROUND: The study researched the structure of the OHIP-20 DG questionnaire, which was compiled from the questions of the validated international special questionnaire OHIP-49, to assess the patients quality of life depending on their mouths organs and tissue with the help of сategorical principal component analysis. PURPOSE OF THE STUDY: Reduce the original set of variables to an uncorrelated variables that carry the bulk of the information contained in the original set. MATERIAL AND METHODS: To determine the connections between the scales of the quality of life (QoL) questionnaire OHIP-20 DG and to assess the factor validity of the latter, data reduction with generalization procedure was conducted by the method of nonlinear principal component using the CatPCA algorithm. RESULTS: All scores from 0 to 4 were smoothed by a second-degree polynomial spline with three internal knots and ranking as a discretization method. To determine the number of necessary and sufficient components, Cattells scree plot and broken stick criteria were used. Calculations were performed using the IBM SPSS Statistics package (version 20), graphical constructions in the KyPlot (version 6.0), and PAST (version 4.06) packages. CONCLUSION: The factor structure of the questionnaire was explored using CatPCA algorithm of nonlinear principal component analysis. The analysis confirmed the factor validity of the OHIP-20 DG questionnaire, but found two weak structural elements that are not related to the QoL, but most likely have a connection with the psychosocial aspects of patients health. Comparison of the questionnaires initial scores with their quantification values revealed the nonlinearity of patients perception of most of the questionnaire items. Which allows for a broader interpretation of the patterns of patients perception of QoL and further improvement of the questionnaire.