Although the effects of sustained jaw-closing activities on somatosensory sensitivity and fatigue have been investigated, the effects of sustained jaw-opening activities on somatosensory sensitivity in the masticatory muscles remain unclear. Therefore, this study aimed to investigate the effects of sustained jaw opening（e.g. during dental treatment）on fatigue, pressure pain sensations, and stiffness in the masticatory muscles. A total of 35 healthy volunteers performed 30 minutes each of two jaw motor tasks, with a 1-week interval between tasks: unassisted jaw opening and jaw opening assisted by a mouth prop set at the right tooth. The pressure pain threshold（PPT）and muscle stiffness of the left masseter were measured before and after both jaw motor tasks（at 0 and 30 minutes）. Masticatory muscle fatigue was measured every 10 minutes（at 0, 10, 20, and 30 minutes）during each jaw motor task. No significant differences in the PPT were found between before and after the assisted jaw-opening task, but the PPT was significantly lower after compared with before unassisted jaw opening（P < 0.05）. No significant differences in left masseter muscle stiffness were found between any measurement point in either jaw motor task. Masticatory muscle fatigue was significantly higher after 10, 20, and 30 minutes of each jaw motor task compared with that at baseline（0 minutes）. However, no significant differences in masticatory muscle fatigue were found at any measurement point between both jaw motor tasks. The present results suggest that sustained jaw opening during dental treatment may affect pressure pain sensations in the masticatory muscles. In addition, masticatory muscle pain due to sustained jaw opening seems to be affected not only by jaw-opening but also jaw-closing muscle（masseter muscle）.
The purpose of this study was to compare and clarify the differences in pit formation between two modes of free-electron laser（FEL）irradiation with different beam cur rents and pulse structures and how the effects of these modes vary with the tissue structure of human teeth. FEL irradiation using the full-bunch mode（Fm）and burst mode（Bm）. The beam current was carried out at 200 mA for Fm and 2 A for Bm. The micro-pulse interval within the macro-pulse structure was 350 ps for Fm and 22.4 ns for Bm. The wavelength of the FEL was adjusted to 2.94 µm, and macro-pulse energy was adjusted to 6.0 mJ/macro-pulse by polarizing plate. The macro-pulse irradiation was set to 1 or 5 times for both modes. As the number of macro-pulse irradiations increased, the pits became deeper in Fm than in Bm, regardless of the site on the tooth. On the other hand, the bulge height was lower for Bm than for Fm, regardless of the site on the tooth or the number of macro-pulse irradiations. No scorch marks were observed in the pits for either mode. It was concluded that the differences in the pit including bulge formation were the macro-pulse structure between Fm and Bm. The intensity of the FEL irradiation caused plasma evaporation in the tooth hard tissue, and the tooth substance was ablated before thermal conduction occurred. The relation with the thermal relaxation time also confirmed that pits were formed without visible scorch marks.
Individuals with Down syndrome（DS）are prone to periodontitis. No studies have focused on mRNA expression of a pro-inflammatory cytokine, IL-1β and an anti-inflam matory cytokine, IL-37 in gingival fibroblasts（GFs）derived from individuals with DS （DGFs）. We cultured GFs derived from non-DS individuals（NGFs）and DGFs with outer membrane vesicles from Porphyromonas gingivalis（P-OMVs）. IL-1β and IL-37 mRNA expression was quantified using real-time PCR. Extracellular signal-regulated kinase（ERK）1/2 phosphorylation was performed by western blotting. We also analyzed the effect of an ERK1/2 inhibitor on IL-1β and IL-37 mRNA expression in GFs. Furthermore, we examined the influence of recombinant IL-37（rIL-37）on the cellular response of GFs. We quantified mRNA expression of IL-8 using real-time PCR and measured IL-8 productions in culture medium by an enzyme-linked immunosorbent assay. IL-1β mRNA expression and phosphorylated-ERK1/2 expression were significantly higher in P-OMVs-stimulated DGFs than in NGFs. In contrast, IL-37 mRNA expression was significantly lower in P-OMV-stimulated DGFs than in NGFs. P-OMVs-induced IL-1β and IL-37 mRNA expression in NGFs was reduced by an ERK1/2 inhibitor, while P-OMVs-induced IL-37 mRNA expression was not reduced by an ERK1/2 inhibitor in DGFs. P-OMVs-induced IL-8 mRNA expression and protein production were decreased by rIL-37 in both NGF and DGFs. It is considered that the imbalance of pro- and anti-inflammatory responses via ERK1/2 in DGFs may cause severe periodontal inflammation in DS. In addition, IL-37 may be a key mediator of the anti-inflammatory response in DGFs. These results provide insights into the therapeutic potential of targeting anti-inflammatory factors for severe periodontal inflammation in DS.
To clarify the effects of dental implant treatment on oral and physical function, chronological change between before and after treatment for six years was investigated in this study. In particular, the relationship between age at first visit and changes after treatment was focused. Eighty-two subjects who had four occlusal support areas restored by dental implant treatment. Four examinations were performed at baseline and during the follow-up periods. The test items were gum masticatory performance assessment, hand grip strength, and body component. To evaluate the effect of intervention with dental implant treatment, Friedman’s and post-hoc tests were used. Hand grip strength and mastication performance were significantly maintained during follow-up period in under and over 65 years. In over 65 years, a few items were significantly lower than at baseline. No significant difference was observed about skeletal muscle mass（%）, fat mass（%）, fat-free mas（%）, and leg（%）in under and over 65 years. These results indicated that hand grip strength and mastication performance were improved over a long period after dental implant treatment. It was speculated that the improvement in hand grip strength was associated with the recovery of systemic functions, especially in under 65 years old group.
The vertical dimension of occlusion（VDO）must be correctly estimated when fabricating complete dentures to achieve efficient mastication and swallowing. The comfortable zone（CZ）method for VDO estimation is based on trichotomous subjective response. However, the difference in comfort level within and out of the CZ still needs to be determined. Therefore, this study aimed to examine the differences in subjective comfort on a 100-mm visual analog scale（VAS）when raising or lowering the VDO and to assess the relationship among the responses to the CZ method. Eight edentulous patients（five men and three women, with a mean age of 78.5±7.6 years）were recruited. The VAS score was obtained two times at the most comfortable position（MCP）and when it was raised from +1 to +7 mm（7VDO）. The VAS score was also obtained when the MCP was lowered from -1 to -3 mm（3VDO）. One-way analysis of variance and Bonferroni’s multiple comparison test were performed to analyze the differences in VAS scores at 11 VDOs. The VAS score significantly decreased when the VDO was raised by +3 mm from the MCP（p = 0.009）and continued to decrease in +4（p = 0.001）, +5, +6, and +7 mm（p < 0.001, respectively）. In addition, it significantly decreased when the VDO was lowered by -2 mm from the MCP（p = 0.048）. The results suggest that VDO estimates may be appropriate between -1 and +2 mm from the MCP when fabricating new complete dentures.
Tooth development is a multi-stage and multi-step process involving fate determination and morphogenetic patterning events, epithelial-mesenchymal interactions, and cell proliferation, differentiation, and migration. Animal model studies have shown that YAP and TAZ, effectors of the Hippo pathway, have a critical function in tooth morphogenesis. However, the function of YAP and TAZ in tooth development has not been well documented and its specific roles in tooth morphogenesis remain unclear. We used immunohistochemistry to examine the localization of YAP and TAZ in mouse mandibular first molar tooth germ. ICR mouse embryos on days E12, E14 and E18 were produced. Heads from these embryos were processed for paraffin embedding and prepared for immunohistochemistry. Immunostaining for YAP and TAZ showed different localization in tooth development. YAP was localized in the odontogenic epithelium from the early stages of tooth germ, but TAZ was not almost observed. YAP was also positive for pre-ameloblasts or inner enamel epithelium, which were high columnar cells. On the other hand, TAZ localized to odontoblasts and pre-ameloblasts or inner enamel epithelium. These results demonstrated functional differences between YAP and TAZ in tooth development, and suggested that these proteins were not only involved in cell proliferation, differentiation, and hard tissue formation, but also in three-dimensional cusp morphogenesis during tooth development.
Data on estimating the vertical dimension of occlusion（VDO）for fabricating a complete denture based on tongue pressure, which is related to masticatory and swallowing functions, are scarce. This study aimed to examine the changes in tongue pressure on raising or lowering of the VDO from the most comfortable position（MCP）. Ten edentulous, including Eichner C3, patients with existing dentures（six men and four women; mean age, 78.6±7.14 years）were recruited from a hospital setting. Twelve different height-positioning stimulus stainless-steel blocks were used（from +1 mm to 6 mm and +9 mm and from -1 mm to -4 mm）. VDO from the most comfortable position （MCP）and the tongue pressure at the respective height were measured. One-way analysis of variance（ANOVA）and Dunnett’s test were performed to analyze the differences in tongue pressure at different VDOs. There were no significant differences between the stimulus intervals（-1 to -4 mm, p = 0.99）on lowering VDO from MCP. Tongue pressure decreased marginally when the VDO was raised +5 mm from the MCP（p=0.054）; it continued to show a significant decrease at +6 mm（p=0.041）and +7 mm（p=0.035）from MCP. Tongue pressure did not change significantly when VDO was lowered and raised to +5 mm from MCP. These results suggest that VDO may be set to 5 mm from MCP when fabricating new complete dentures.
Oral Lichen planus（OLP）is a chronic autoimmune cell-mediated inflammatory disease. Most OLP patients complain of xerostomia/dry mouth due to changes in the oral mucosal protective barrier. Mucin 5B（MUC5B）is the predominate gel-forming mucin in the oral cavity that protects the underlying tissue from mechanical damage, chemical insult, and pathogenic microbes. This study aims to assess MUC5B in OLP subjects and correlate its role in etiopathogenesis. The study included 20 OLP subjects and 10 healthy controls. OLP subjects were divided further into 10 keratotic（reticular）and 10 non-keratotic（atrophic/erythematous）groups based on the clinical criteria. Dryness of mouth was confirmed by the subjective（Xerostomia Inventory, XI; Bother Index, BI）and clinical testing（Clinical Oral Dryness Score, CODS）method. Stimulated, unstimulated saliva and blood samples were collected from subjects. Samples were centrifuged and analysed for MUC5B level using an ELISA kit. The subjective and clinical testing methods which clinically define xerostomia are correlated with the age and sex of the OLP subjects. The stimulated and unstimulated salivary flow rate of OLP subjects was lower（p<0.05）than controls and was associated with the XI, BI, and CODS（p<0.01）. In contrast, the MUC5B level was increased in the serum of OLP subjects compared to controls（p<0.05）. OLP subjects with xerostomia, displayed lower salivary flow, decrease MUC5B in saliva and increase MUC5B in serum. Alteration of MUC5B in the saliva causes oral mucosal alterations affecting the protection of the oral cavity and increase xerostomia in OLP.