Evaluation of the hardness discrimination for elastic and viscous bodied

Objectives: The purpose of this study was to compare the range of hardness of elastic bodied and viscous bodied materials with partial denture or natural dentition subjects.

Materials and methods: Twenty three subjects with natural dentition ( 15males and 8 females; the average age =31.0) and 4 subjects with partial dentures (average age =67.0), participated in this study. The partial patients (using distal-extension removable denture), filled out a quality of life questionnaire (OHIP-16) before and after treatment. The materials used in this test were five thermoplastic polyurethane elastomers with compressive elastic moduli from 11.8 to 62.0 MPa (E1-E5) and five silicone impression material with coefficients of viscosity from 2.01x10^-2to 13.76x10^-2MPa・s(V1-V5).

Test1: The subjects compared 10 elastic bodied combinations with materials based on differences in elastic moduli by chewing a small amount for 10 seconds and judged which one was harder or softer.

Test2: They compared 10 viscous bodied combinations with materials based on differences in coefficients of viscosity in a similar way.

Results: In data of the partial denture subjects, correct answer ratios were low (<60%) in comparing 8 combinations ( E2/E3, E3/E4, E3/E5, E4/E5, V1/V2, V2/V3, V3/V4, V4/V5). We compared with correct answer ratios of partial denture subjects before and after treatment. Their correct answer ratios improved after new dentures were inserted, to the same level as natural dentition subjects, as did the results of the OHIP-16 questionnaires.

Conclusion: These results suggested that the prosthesis treatment improved the comparison in the hardness of foods and additionally in the improvement of the subject's QOL.