T IS well recognized that the sensory mechanisms of the mouth fulfill protective and selective functions.' Oral sensations are obviously needed during mastication, as was observed in a study with a subject before and during mandibular block anesthesia. His chewing ability was diminished during anesthesia. Some fairly large particles of food were missed during the mastication. The subject stated that he was unable to sense the location of unchewed food, and hence could not bring it to the ocelusal surfaces of his molars for mastication.Persons who wear complete dentures lose tactile sensations which are derived from the periodontal membrane. It is possible that the sensory cues from food become impaired after the transition to dentures. Perhaps blunted sensations would cause manipulation of food to be less efficient, which would explain why the masticatory efficiency of denture wearers is only one-fourth that of the normal dentition on the average, and why it varies widely from one individual to another, without apparent cause.2This investigation is concerned with certain sensory processes mediated by natural or artificial teeth. The tests selected represent a compromise between those which can be estimated readily and those most likely to be related to masticatory function. Thresholds for the discrimination of thickness, hardness, light touch, and texture were studied in persons with normal and artificial dentitions. The purpose was to compare how well persons with natural and artificial dentition could discriminate these stimuli, in order to learn whether such discrimination among denture wearers is impaired. If there was any impairment, it might be partly responsible for low masticatory efficiency of some denture wearers. METHODSSize Judgment Between Anterior Teeth.-Rods of boilable lucite one inch in diameter were obtained from the Dupont Company. Disks were cut from these and machined and polished to thicknesses of 5.00, 5.25, 5.50, and 5.75 mm. ± 0.01 mm. During a test each disk was placed horizontally between the subject's incisor teeth and held by the examiner while the subject bit gently but firmly upon the disk. Each subject was given a familiarization trial with each disk, presented in the order of thinnest to thickest. During an actual test, subjects were presented disks in the following order: ADCB CABD DBAC DBCA BCAD CDBA DCAB CB. He indicated his response by writing plus on paper whenever he believed the disk was one the thicker two (C or D) and by writing minus in case the disks were perceived to be one of the thinner two (A or B).

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