[A reliable method for evaluating the masticatory function in complete denture wearers, concerning a masticatory function evaluation chart based on food hardness].

The purpose of this study was to construct an evaluation chart to objectively and simply determine the extent of the masticatory function of complete denture wearers in daily clinical practice, and to describe the chart's clinical application. 58 different types of food were selected according to two criteria: their frequency of ingestion by complete denture wearers, and their convenience for determining the masticatory function. Then an anatomical artificial porcelain set of dentures was used to bite each food item, using only bicuspids and molars. Dentures were installed on an Instron Universal Testing Instrument to compression-cut the food. Food requiring the highest pressure was considered the hardest food. Then the masticatory function evaluation chart was constructed by using the hardness of the food as an index of relative masticatory difficulty. Using this chart, 95 complete denture wearers were tested to determine the masticatory function of their dentures. The following results were obtained: 1. The mean hardness of the 58 food items tested was 7.85 +/- 11.29 kg. The mean hardness of the 38 food items frequently ingested by complete denture wearers was 5.24 +/- 5.41 kg. 2. The differences in hardness of the foods tested were statistically processed, and the 58 food items were classified into 5 groups (I-V). This five-fold classification was used as a range for determining masticatory function. 3. A correlation coefficient of -0.697 (p less than 0.01) was found between the hardness of the food and the ease of eating the food. 4. A correlation coefficient of 0.548 (p less than 0.01) was found between the hardness of the food and the frequency of ingestion. 5. The masticatory function was determined on a 5-point scale from A to E according to the total number of food types that the subjects said that they could eat easily. The masticatory function increased progressively from A to E. The results of determining the masticatory function of the 95 complete denture wearers were as follows: Rank A 1.1%, B 10.5%, C 34.7%, D 29.5% and E 24.2%. 6. Persons who evaluated their own dentures positively comprised 86.0% of ranks D and E. On the other hand, persons who evaluated their own denture negatively were widely distributed from rank A through E, indicating that there were considerable individual differences. 7. It was concluded that the masticatory function evaluation chart was a reliable means of objectively and simply determining the masticatory function of complete denture wearers.