Contact of the tongue against the hard palate plays an important role in swallowing. This study aimed to clarify the pattern of contact between the tongue and hard palate by analyzing tongue pressure produced in swallowing 15 ml of water by healthy subjects wearing an experimental palatal plate with seven pressure sensors. Tongue pressure was generated initially by close contact with the anteriomedian part of the hard palate, then with the circumferential part, and finally softly with the posteriomedian part. Tongue pressure reached a peak quickly, then decreased gradually before disappearing almost simultaneously at each measured part of the hard palate. Magnitude and duration were significantly larger in the anteriomedian part compared to the other six parts measured, and was significantly smaller in the posteriomedian part. No laterality was found in tongue pressure produced at the circumferential parts of the hard palate. Our findings indicate that the order of tongue contact against each part of the hard palate as well as duration and magnitude of tongue pressure are coordinated precisely during swallowing. These findings could aid assessment of the tongue movement of dysphagic patients during rehabilitation.

Previous studies have identified various factors related to masticatory performance. This study was aimed to investigate variations and impacts of factors related to masticatory performance among different occlusal support areas in general urban population in Japan. A total of 1875 Japanese subjects (mean age: 66·7 years) were included in the Suita study. Periodontal status was evaluated using the Community Periodontal Index (CPI). The number of functional teeth and occlusal support areas (OSA) were recorded, and the latter divided into three categories of perfect, decreased and lost OSA based on the Eichner Index. Masticatory performance was determined by means of test gummy jelly. For denture wearers, masticatory performance was measured with the dentures in place. The multiple linear regression analysis showed that, when controlling for other variables, masticatory performance was significantly associated with sex, number of functional teeth, maximum bite force and periodontal status in perfect OSA. Masticatory performance was significantly associated with number of functional teeth, maximum bite force and periodontal status in decreased OSA. In lost OSA, masticatory performance was significantly associated with maximum bite force. Maximum bite force was a factor significantly influencing masticatory performance that was common to all OSA groups. After controlling for possible confounding factors, the number of functional teeth and periodontal status were common factors in the perfect and decreased OSA groups, and only sex was significant in the perfect OSA group. These findings may help in providing dietary guidance to elderly people with tooth loss or periodontal disease.

This position paper proposes a definition and naming standard for removable partial dentures (RPDs) using thermoplastic resin, and presents a guideline for clinical application. A panel of 14 experts having broad experience with clinical application of RPDs using thermoplastic resin was selected from members of the Japan Prosthodontic Society. At a meeting of the panel, "non-metal clasp denture" was referred as the generic name of RPDs with retentive elements (resin clasps) made of thermoplastic resin. The panel classified non-metal clasp dentures into two types: one with a flexible structure that lacks a metal framework and the other having a rigid structure that includes a metal framework. According to current prosthetic principles, flexible non-metal clasp dentures are not recommended as definitive dentures, except for limited cases such as patients with a metal allergy. Rigid non-metal clasp dentures are recommended in cases where patients will not accept metal clasps for esthetic reasons. Non-metal clasp dentures should follow the same design principles as conventional RPDs using metal clasps.

This system could be useful for evaluating tongue activity during oropharyngeal swallowing.

This position paper reviews physical and mechanical properties of thermoplastic resin used for non-metal clasp dentures, and describes feature of each thermoplastic resin in clinical application of non-metal clasp dentures and complications based on clinical experience of expert panels. Since products of thermoplastic resin have great variability in physical and mechanical properties, clinicians should utilize them with careful consideration of the specific properties of each product. In general, thermoplastic resin has lower color-stability and higher risk for fracture than polymethyl methacrylate. Additionally, the surface of thermoplastic resin becomes roughened more easily than polymethyl methacrylate. Studies related to material properties of thermoplastic resin, treatment efficacy and follow-up are insufficient to provide definitive conclusions at this time. Therefore, this position paper should be revised based on future studies and a clinical guideline should be provided.

An in vitro evaluation system of food texture was developed using artificial tongue and a conventional uniaxial compression apparatus to mimic the tongue-palate compression. Deformation behavior of agar gels on artificial tongues from silicone rubber with three levels of elastic modulus was observed during compression by a nondeformable plate. The results were compared with the oral strategy for size reduction from sensory evaluation by human subjects. Agar gels fractured upon compression when the strain of the gels was larger than that of artificial tongue, whereas they did not when the strain of the gels was equivalent to or smaller than that of the artificial tongue. When apparent elastic modulus of artificial tongue was approximately 5.5 ¥ 10 4 Pa, fracture profile of the gels corresponded well to human tests. Results suggest that the oral strategy for size reduction might be determined by sensing the relative strain of the gels to the tongue during compression to a somewhat small strain.

The tongue plays an important role in mastication and swallowing by its contact with the hard palate. Using an experimental palatal plate with 7 pressure sensors, and recording jaw movement using mandibular kinesiography, we assessed, in healthy subjects, the coordination of tongue and jaw movements during the entire masticatory sequence of solids, by measuring tongue pressure against the hard palate. Tongue pressure appeared during the occlusal phase, reached a peak near the start of opening, and disappeared during opening. Specific patterns in order, duration, and magnitude of tongue pressure were seen at the 7 pressure sensors in each chewing stroke. Magnitude and duration were significantly larger in the late stage of chewing (8 strokes before initial swallowing) than in the early stage (until 8 strokes after starting mastication). The normal pattern of tongue contact against the hard palate, control of tongue activity, and coordination with jaw movement during mastication is described.

Measurement of the magnitude of tongue pressure shows promise as a simple, non-invasive and quantitative method by which tongue activity in post-stroke patients, in whom swallowing ability is a concern, could be evaluated.