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This study aimed to determine changes in saliva secretion and subjective taste intensity during a sustained period with continuous gustatory stimulation.Twenty-two healthy adults participated in this study. The selected taste solutions were aspartame, sucralose, and acesulfame potassium, which are nonnutritive sweeteners. The concentrations of sucralose1 and acesulfame potassium were set to show the same sweetness intensity as aspartame. Sucralose2 was twice the concentration of sucralose1. The solution was continuously fed into the oral cavity at a flow rate of 0.04 mL / min through a neck-worn precise infusion system. The salivary flow rate (g/min) after 10 min of intraoral water supply from the device was used as the baseline. Salivary flow rate, subjective taste intensity evaluated by the visual analog scale (VAS), and salivary flow rate relative to the baseline were recorded at 10, 30, 60, and 120 min after the start of the test.In the aspartame, sucralose1, and sucralose2 groups, the salivary flow rate increased significantly from 10 min to 120 min after the start of the test when compared to the rate at baseline (p 0.05). The relative salivary flow rate increased and the VAS value decreased significantly over time and were affected by the time factor (p 0.001, p = 0.013, respectively) but not by the sweetener-group factor and the interaction effects.Continuous gustatory stimulation may maintain increased salivary production for a sustained period.

Objectives: The present study aimed to identify the effect of memory-related genes on male rats tested for spatial memory with either molar teeth extraction or its restoration by occlusal support using experimental dentures. Design: Memory-related genes were detected from hippocampi of male Wistar rats (exposed to teeth extraction with or without dentures, or no extraction (control)) (7-week old) after behavioural testing (via the radial maze task) using a DNA microarray. The time course of the expression of these genes was evaluated by quantitative real-time polymerase chain reaction (PCR) (on 49-week-old rats). Results: In preliminary experiments, to determine which memory genes are affected by spatial memory training, DNA microarray analysis revealed that thyrotropin-releasing hormone (Trh) and tenascin XA (Tnxa) were up-regulated and neuronatin (Nnat) and S100a9 were down-regulated after the maze training. The expression of Tnxa, Nnat and S100a9 of 49-week-old rats (during the time course) via quantitative real-time PCR was consistent with the results of microarrays of the preliminary experiment. Expression of Trh that was evaluated by quantitative real-time PCR did not agree with the results for this gene from the microarray for all groups. Therefore, expression of Trh may have increased in only young, trained rats. The expression of S100a9 prior to the maze task was down-regulated in only the extraction group. Conclusion: These results demonstrated that Trh, Tnxa and Nnat genes were affected according to the degree of memory in male rats. This study also indicated that S100a9 is a memory-related gene, which is affected by the presence of occlusal support.

Objective The study aims to investigate the dynamic perception of a force applied to the upper first molar for different rates of force increase. Design Six volunteers (four male and two female; mean age, 27.2 ± 2.4 years) with full natural dentition (except for the third molars) participated in this study. The psychophysical threshold for a force applied to the right maxillary first molar and the reaction time corresponding to each threshold were measured for rate of force increase of 103.74, 236.23, 354.58, 478.22 and 584.63 mN s −1 . The physical impulse, which is the integral of force over time, was calculated for each threshold. Results Psychophysical thresholds in the upper first molar increased with the rate of force increase. The reaction time corresponding to each threshold decreased with increasing force rate. Impulses corresponding to each threshold were independent of force rate. Conclusions In the present study, the psychophysical threshold for a force applied to a molar tooth was shown to change depending on the rate of increase of the exerted force. From the viewpoint of the impulse, the dissipated energy necessary to reach the psychophysical sensation threshold was almost constant, regardless of the rate of force increase.

Objective Intensive mechanical stress and/or inflammation are known to induce alveolar bone resorption. This study investigated whether a distribution of mechanical stress would reduce residual ridge resorption or improve ischaemia. Design Thirty rats were divided into six experimental groups (n = 5). The control group received no intentional stimulation, but rats in the experimental groups wore denture stimulators made of acrylic resin or a soft lining material. The stimulator transmitted masticatory pressure to the rats’ palates for four weeks. The four types of soft lining materials investigated in this study dispersed the applied pressure, with compressive stress ranging from 20.8 to 90.8 kPa. Volumes of blood flow and bone resorption of denture foundations were measured every week for 4 weeks. Statistical evaluation of these results was performed using two-way ANOVA and Holm–Sidak test within 5% error limits. Results Non-viscoelastic material clearly induced bone resorption and ischaemia of denture foundations, while viscoelastic materials reduced these phenomena to different extents according to their viscoelastic properties. Ischaemia in the alveolar ridge preceded residual ridge resorption, because the amount of residual ridge resorption and blood flow rate showed a simple linear regression. Conclusion Animal model of this study suggested that a distribution or reduction of mechanical stress could improve blood flow and decrease alveolar ridge resorption.