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The purpose of the present study was to clarify the long-term effects of frequent chewing of unflavored and odorless gum (hereafter, gum base) on oral hygiene and mental health. This single-arm study, which started with a 4-week control and ended with a 4-week intervention period, was conducted in two phases: one in 2017 and one in 2018. The participants comprised 36 dental hygiene students (17 in 2017, 19 in 2018). During the intervention period, all participants were required to chew a piece of gum base 7 times a day for 10 min each time. The unstimulated salivary flow rate and masticatory efficiency were measured and chewing number counted. Two questionnaires -the Profile of Mood States, second edition (POMS2) and the 30-item General Health Questionnaire (GHQ-30)-were administered to assess mental health. In both phases, the unstimulated salivary flow rate showed a significant increase after the intervention period (p<0.05). In 2017, the GHQ-30 scores and masticatory efficiency showed a tendency toward a negative correlation after the intervention period (r=-0.4647, p=0.06). In 2018, a significant negative correlation was observed between chewing number and the POMS2 scores after the intervention period (r=-0.6296, p<0.01). These findings suggest that frequent chewing of gum base increases unstimulated salivary flow rate. However, no significant change was observed in the mental health.

The aim of this randomized-controlled, single-blinded study was to compare the effects of mechanical tooth cleaning (MTC) and ultrasonic debridement (UD) on oral hygiene status in healthy young adults. Thirty-seven participants (mean age: 20.3±0.62 years) were divided into 3 groups after pre-examination: group A, receiving MTC; B, receiving MTC+UD using a universal insert (UDUI); and C, receiving MTC+UD using a probe-shaped insert (UDPI). All participants were required to abstain from oral hygiene for 24 hours after the allocated intervention, after which they were examined. A masked examiner determined the Quigley-Hein plaque index (PlI) and Silness and Löe gingival index (GI) scores before the interventions and after 24 hours of non-brushing. A significant increase in the PlI score was observed in group A (p<0.001) in comparison with that in group B (A: 0.311±0.26; B: −0.01±0.33; C: 0.13±0.27; p<0.05). A significant decrease in the GI score was observed in groups B and C (p<0.05), and the change in this score in group C significantly differed from that in group A or B (A: −0.04±0.25; B: −0.13±0.17; C: −0.33±0.2; p<0.05). Only MTC was insufficient to prevent plaque formation over a 24-hour period of non-brushing and decrease the GI score. Ultrasonic debridement was more effective in preventing plaque formation and decreasing the GI score, regardless of the type of insert used. The present results suggest that UD should be included as an important procedure in the provision of professional oral prophylaxis and that UDPI is as efficient for cleaning as UDUI.

Saliva is an ideal biofluid for monitoring oral and systemic health. Repeated mastication is a typical physical stimulus that improves salivary flow and oral hygiene. Recent metabolomic studies have shown the potential of salivary metabolomic components for various disease monitoring systems. Here, we evaluated the effect of long-term mastication on salivary metabolomic profiles. Young women with good oral hygiene (20.8 ± 0.3 years, n = 17) participated. They were prohibited from chewing gum during control periods (4 weeks each) and were instructed to chew a piece of gum base seven times a day for 10 min each time during the intervention period. Paired samples of unstimulated whole saliva collected on the last day of the control and intervention period were compared. Liquid chromatography–time-of-flight mass spectrometry successfully quantified 85 metabolites, of which 41 showed significant differences (p < 0.05, Wilcoxon paired test corrected by false discovery rate). Except for a few metabolites, such as citrate, most metabolites showed lower concentrations after the intervention. The pathways related to glycogenic amino acids, such as alanine, arginine, and glutamine, altered considerably. This study suggests that long-term mastication induces unstimulated salivary component-level changes.