Comprehensive genomic profiling of salivary gland carcinoma: Analysis of the Center for Cancer Genomics and Advanced Therapeutics database in Japan.

Comprehensive information on genetic alterations in salivary gland cancer (SGC) is limited. This study aimed to elucidate the genetic and clinical characteristics of patients with SGC using the Center for Cancer Genomics and Advanced Therapeutics (C-CAT) database, a Japanese national genomic database. We analyzed data of 776 patients with SGC registered in the C-CAT database between June 1, 2019, and June 30, 2023. Adenoid cystic carcinoma was the most common histologic type, followed by salivary duct carcinoma (SDC) and adenocarcinoma not otherwise specified. Genetic data of 681 patients receiving FoundationOne® CDx were analyzed. We identified specific features of the combination of TP53 and CDKN2A alterations among the histological types. Specific LYN amplification was mainly detected in carcinoma ex pleomorphic adenoma and myoepithelial carcinoma. For SDC, the frequency of ERBB2 and BRAF alterations were higher in cases with metastatic lesions than in those with primary lesions. Although 28.6% patients were offered recommended treatment options, only 6.8% received the recommended treatments. This study highlights the differences in genetic alterations among the histological types of SGC, with comprehensive genomic profiling tests revealing lower drug accessibility. These findings could contribute to the development of personalized treatment for patients with SGC.

Subsite-specific trends in mid- and long-term survival for head and neck cancer patients in Japan: A population-based study.

Advances in diagnostic techniques and treatment modalities have impacted head and neck cancer (HNC) prognosis, but their effects on subsite-specific prognosis remain unclear. This study aimed to assess subsite-specific trends in mid- and long-term survival for HNC patients diagnosed from 1993 to 2011 using data from population-based cancer registries in Japan. We estimated the net survival (NS) for HNC by subsite using data from 13 prefectural population-based cancer registries in Japan. Changes in survival over time were assessed by multivariate excess hazard model of mortality. In total, 68,312 HNC patients were included in this analysis. We observed an overall improvement in 5-year NS for HNC patients in Japan. However, survival varied among subsites of HNC, with some, such as naso-, oro- and hypopharyngeal cancers, showing significant improvement in both 5- and 10-year NS, whereas others such as laryngeal cancer showed only a slight improvement in 5-year NS and no significant change in 10-year NS after adjustment for age, sex and stage. In conclusion, the study provides insights into changing HNC survival by site at the population level in Japan. Although advances in diagnostic techniques and treatment modalities have improved survival, these improvements are not shared equally among subsites.

Efficacy of dupilumab for severe chronic rhinosinusitis with nasal polyps and asthma: A prospective study.

BACKGROUND: Dupilumab exerts clinical effects, including improved sinus opacification, olfactory function, and quality of life, in patients with severe chronic rhinosinusitis with nasal polyps (CRSwNP). Meanwhile, only a few studies have reported its effects on nasal airway resistance and olfactory function, particularly in the Japanese population. Predictors of response remain unclear. OBJECTIVE: In this prospective, observational study, we assessed the comprehensive efficacy and therapeutic response to dupilumab in severe CRSwNP patients with comorbid asthma. METHODS: In 16 adult severe CRSwNP patients with comorbid asthma, the efficacy of 48-week dupilumab treatment, including olfactory function measured by a T&T olfactometer, nasal airway resistance measured by rhinomanometry, nasal polyp score, Lund-Mackay computed tomography score (LMS), and 22-item Sinonasal Outcome Test (SNOT-22), was assessed. Regarding asthma, the annualized rate of exacerbations, 7-item Asthma Control Questionnaire (ACQ-7), and spirometry were assessed. Treatment responsiveness was analyzed. RESULTS: With 48-week dupilumab treatment, olfactory function, nasal airway resistance, nasal polyp score, LMS, and SNOT-22 scores improved significantly. Regarding comorbid asthma, the rate of exacerbations decreased, and ACQ-7 scores and lung function improved significantly. According to the European Position Paper on Rhinosinusitis and Nasal Polyps 2022/European Forum for Research and Education in Allergy and Airway Diseases criteria, 15 patients (94%) were moderate-to-excellent responders at 48 weeks of treatment. Patients with higher SNOT-22 scores, ACQ-7 scores, rates of asthma exacerbation in the previous year, and blood eosinophil counts benefited more from treatment. CONCLUSION: Dupilumab improved upper and lower airway outcomes especially in severe CRSwNP patients with comorbid, poorly controlled asthma.

Mature dendritic cells enriched in regulatory molecules may control regulatory T cells and the prognosis of head and neck cancer.

We previously reported that regulatory T (Treg) cells expressing CTLA-4 on the cell surface are abundant in head and neck squamous cell carcinoma (HNSCC). The role of expanded Treg cells in the tumor microenvironment of HNSCC remains unclear. In this study, we reveal that the tumor microenvironment of HNSCC is characterized by the high expression of genes related to Treg cells, dendritic cells (DCs), and interleukin (IL)-17-related molecules. Increased expression of IL17A, IL17F, or IL23A contributes to a favorable prognosis of HNSCC. In the tumor microenvironment of HNSCC, IL23A and IL12B are expressed in mature dendritic cells enriched in regulatory molecules (mregDCs). The mregDCs in HNSCC are a migratory and mature phenotype; their signature genes strongly correlate with Treg signature genes in HNSCC. We also observed that IL17A was highly expressed in Th17 cells and exhausted CD8+ T cells in HNSCC. These data suggest that mregDCs in HNSCC may contribute to the prognosis by balancing Treg cells and effector T cells that produce IL-17. Targeting mregDCs may be a novel strategy for developing new immune therapies against HNSCC.

Imaging manifestations on sequential magnetic resonance imaging in pharyngolaryngeal involvement by varicella zoster virus.

Clarifying temporal changes in magnetic resonance imaging (MRI) offers a good chance to understand the pathology of neural lesions; however, such information is scarce in varicella zoster virus (VZV) neuropathies for the glossopharyngeal and vagus nerves. Here, we present the changes in sequential MR images of such a pathology over a period of 12 months from symptom onset.A 27-year-old woman with difficulty in swallowing and hoarseness due to a palatal palsy and arytenoid fixation on the left presented 2 days after onset. MRI revealed a lesion which largely filled the left jugular foramen on T2-weighted images (T2-WI) with high diffusion-weighted imaging (DWI) signals, which has never been previously described, on the 3rd day after onset. The DWI signals were highest on day 3, then deteriorated over 2 months until the signal was only detectable at the intracranial level, but not in the jugular foramen. The glossopharyngeal nerve had returned to normal by 2 months.The time course of the glossopharyngeal and vagus nerve swelling detected on T2-WI suggests that nerve swelling reduces over several months, even though the paralytic symptoms persist. Furthermore, the high DWI signal suggests that nerve swelling was caused by edematous swelling of the nerve fibers, rather than fiber disruption with water displacement in the extracellular space. These findings may provide good clues to speculate on the dynamically changing pathology of VZV neuropathies of the glossopharyngeal and vagus nerves.

Cervical Vestibular Evoked Myogenic Potentials That Are Absent at 500 Hz But Present at 1000 Hz Are Characteristic of Endolymphatic Hydrops-Related Disease.

OBJECTIVES: It remains unclear whether the dominance of 1000 Hz responses over responses at 500 Hz in cervical vestibular evoked myogenic potentials (cVEMPs) are characteristic of endolymphatic hydrops (EH), due to the presence of patients with absent responses at both frequencies. The purpose of the present study is to examine whether the dominant cVEMP responses at 1000 Hz over 500 Hz are characteristic findings of EH-related diseases among patients who show various cVEMP findings. DESIGN: We retrospectively reviewed the medical records of 470 consecutive patients who underwent cVEMP testing with short-tone bursts at both 500 Hz and 1000 Hz. We categorized the cVEMP responses of these 470 patients into the following five groups: (group 1) present responses at both frequencies bilaterally, (group 2) present responses at 500 Hz but absent at 1000 Hz on at least one side, (group 3) absent responses at 500 Hz but present at 1000 Hz on at least one side, (group 4) absent responses at both frequencies on one side and present at both frequencies on the other side, and (group 5) absent responses at both frequencies bilaterally. We compared the proportion of EH-related diseases between each group and the other four groups and then investigated any increased or decreased disease incidence in each group. RESULTS: In group 3, the proportion of EH-related disease was significantly higher (p < 0.01), and the incidence of an EH-related disease was greatly increased (standard residual value > 3). CONCLUSIONS: cVEMPs that are absent at 500 Hz and present at 1000 Hz may be characteristic of EH-related disease.

Relationship between cognition and the severity of chronic tinnitus: Validation of the Japanese version of the Tinnitus Cognitions Questionnaire.

OBJECTIVE: The Tinnitus Cognitions Questionnaire (TCQ) is a scale designed to assess the positive and negative cognitions associated with tinnitus. The purpose of this study was to validate the Japanese version of the TCQ and to analyze the relationship between cognition and the severity of chronic tinnitus. METHODS: This was a cross-sectional, multicenter study. Patients with chronic tinnitus persisting for longer than 3 months were included. Participants completed the TCQ, the Tinnitus Handicap Inventory (THI), and the Hospital Anxiety and Depression Scale (HADS). They also completed the TCQ a second time 3-7 days later. The questionnaire was translated into Japanese. A factor analysis was performed and the convergent and discriminant validity, internal consistency, and test-retest reliability were evaluated. RESULTS: The total sample consisted of 75 participants. We obtained high Cronbach's α coefficients for the total score and subscales, ranging from 0.933 to 0.974. The total score and subscale interclass correlation coefficients for test-retest reliability ranged from 0.631 to 0.963. The factor analysis yielded a two-factor structure: negative and positive subscales. The convergent and discriminative validity was sufficiently clear. The negative subscale of the TCQ was strongly correlated with the THI and the HADS. CONCLUSION: The Japanese version of the TCQ was validated here. It also exhibited a two-factor structure that was well matched with previous data. And it was a highly consistent and reliable measure that can be used to evaluate cognitions in patients with chronic tinnitus. Negative cognition for tinnitus was greatly related to handicap and psychological state.

Acceptance and commitment therapy combined with vestibular rehabilitation for persistent postural-perceptual dizziness: A pilot study.

PURPOSE: This study investigated the feasibility of acceptance and commitment therapy for persistent postural-perceptual dizziness and preliminarily verified the long-term effectiveness of the therapy. MATERIALS AND METHODS: This study implemented the within-group pre-post comparison design. We enrolled 27 adult patients who met the criteria of persistent postural-perceptual dizziness. They underwent a treatment program including acceptance and commitment therapy combined with vestibular rehabilitation once a week for a total of six sessions. The primary outcome was changes in the Dizziness Handicap Inventory score 6 months posttreatment. RESULTS: All 27 patients completed the acceptance and commitment therapy + vestibular rehabilitation program, and 25 patients (92.6%) could be followed for 6 months posttreatment. For 27 participants, the scores from pretreatment to 6 months posttreatment significantly declined (P < .001), and the Dizziness Handicap Inventory effect size was 1.11 (95% confidence interval = 0.80-1.42). At 6 months posttreatment, 11 patients (40.7%) achieved remission (the score ≤ 14), 16 (59.3%) achieved treatment response (reduction in the score ≥ 18), and 20 (74.1%) achieved remission and/or treatment response. CONCLUSIONS: Acceptance and commitment therapy is feasible for persistent postural-perceptual dizziness and might have long-term effectiveness. However, a randomized controlled trial is warranted.

Burnout and occupational stressors among non-medical occupational health staff.

BACKGROUND: The work required to assist individuals in improving their mental health is stressful and known to be associated with burnout. In Japanese companies, non-medical occupational health (OH) staff often take the role of maintaining and improving workers' mental health. However, few studies have examined burnout in this population. AIMS: To assess the relationship between burnout and occupational stressors among non-medical OH staff. METHODS: We conducted a cross-sectional study of OH staff who had participated in mental health seminars between 2016 and 2018. Occupational stressors were assessed using the Japanese version of the Job Content Questionnaire. Burnout was assessed using the Japanese version of the Maslach Burnout Inventory. RESULTS: We administered the survey to 230 non-medical OH staff, of which 188 completed the questionnaire. According to a hierarchical multiple linear regression analysis, high job demands were associated with greater emotional exhaustion, depersonalization and personal accomplishment. Greater job control was associated only with higher personal accomplishment. Lower job support was associated with greater emotional exhaustion and depersonalization. CONCLUSIONS: The present study found relationships between occupational stressors and burnout dimensions among OH staff. To avoid burnout among non-medical OH staff, it is important to take measures against occupational stressors, especially job demands and low levels of job support.

Non-invasive intravital observation of lingual surface features using sliding oral mucoscopy techniques in clinically healthy subjects.

To investigate intravital morphological features of the broader area of the lingual mucosa in clinically healthy subjects, and to attempt to evaluate subclinical conditions, we evaluated detailed intravital morphological features of the lingual mucosa using our newly developed oral contact mucoscopy techniques. Clinically healthy subjects (female: 19-22 years, average age: 20.27 years, and n = 28) were enrolled. A position indicator stain was placed on the lingual mucosal surface, and sliding images were captured and then reconstructed. In addition, the lingual mucosa was divided into six areas, and morphometry of the fungiform and filiform papillae was performed. The results were statistically analyzed. There were two morphological features among clinically healthy subjects involving the filiform papillae: the length of the papillae and the degree of biofilm (tongue coat) deposition. We defined a modified tongue coat index (mTCI) with scores ranging from 0 (tongue coating not visible) to 0.5, 1, 1.5, and 2 (thick tongue coating) for six sections of the tongue dorsum. No subjects received a score of 2. Significant differences were found in the mTCI between the six sections of the tongue dorsum, especially between the posterior areas and the lingual apex. The fungiform papillae of some subjects exhibited elongated morphological changes. Our findings suggest that magnified lingual dorsum examination of a broader area is especially important in accurate screening for subclinical or transient conditions of potential lingual mucosal diseases. For this purpose, our new oral mucoscopy and non-invasive intravital observational techniques were especially effective.

The adhesion molecule cadherin 11 is essential for acquisition of normal hearing ability through middle ear development in the mouse.

Cadherin 11 (Cdh11), a member of the cadherin adhesion molecule family, is expressed in various regions of the brain as well as the head and ear. To gain further insights into the roles of Cdh11 in the development of the ear, we performed behavioral tests using Cdh11 knockout (KO) mice. KO mice showed reduced acoustic startle responses and increased thresholds for auditory brainstem responses, indicating moderate hearing loss. The auditory bulla volume and ratio of air-filled to non-air-filled space in the middle ear cavity were reduced in KO mice, potentially causing conductive hearing loss. Furthermore, residual mesenchymal and inflammatory cells were observed in the middle ear cavity of KO mice. Cdh11 was expressed in developing mesenchymal cells just before the start of cavitation, indicating that Cdh11 may be directly involved in middle ear cavitation. Since the auditory bulla is derived from the neural crest, the regulation of neural crest-derived cells by Cdh11 may be responsible for structural development. This mutant mouse may be a promising animal model for elucidating the causes of conductive hearing loss and otitis media.

Effect of thermal shrinkage during thermoforming on the thickness of fabricated mouthguards: Part 2 pressure formation.

BACKGROUND: The aim of this study was to examine the effect of thermal shrinkage, which occurs during thermoforming of ethylene vinyl acetate (EVA) sheets on the thickness of mouthguards fabricated by pressure formation. MATERIALS AND METHODS: Mouthguards were fabricated from 4.0-mm-thick EVA sheets by utilizing a pressure-forming machine. Two molding conditions were compared: The sheets were placed in the thermoforming machine with the sheet extrusion direction either vertical or parallel to the model's center line. The working model was trimmed to the height of 20 mm at the cutting edge of the maxillary central incisor and 15 mm at the mesiobuccal cusp of the maxillary first molar. The sheet was pressed against the working model for 2 min where the center of the softened sheet sagged 15 mm lower than the clamp. After fabrication, the thickness of mouthguard sheets was determined for the incisal (incisal edge and labial surface) and molar (cusp and buccal surface) portions, and dimensional measurements were made. Differences in molded mouthguard thickness with the sheet orientation of extruded sheets were analyzed by Mann-Whitney U-test. RESULT: In comparison with the parallel axis orientation, the sheets in vertical orientation with the model's centerline yielded significantly higher thickness measurements at the incisal edge, labial surface, and the cusp (P < 0.01, respectively). CONCLUSION: The results suggest that the EVA sheet produced by extrusion molding in vertical axis orientation with the model's centerline can effectively reduce loss of thickness in mouthguards after pressure formation.

Influence of continuous use of a vacuum-forming machine for mouthguard thickness after thermoforming.

BACKGROUND/AIMS: Mouthguards can reduce the risk of sports-related injuries such as tooth fracture or avulsion, but the sheet material and thickness have a large effect on their efficacy and safety. The aim of this study was to investigate the effect of the continuous use of a vacuum-forming machine on mouthguard thickness. MATERIALS AND METHODS: Ethylene vinyl acetate sheets and olefin copolymer sheets were used for thermoforming with a vacuum-forming machine. The working model was trimmed to a height of 23 mm at the maxillary central incisor and 20 mm at maxillary first molar. During molding, the model was placed at the center of the vacuum unit. Three molding conditions were investigated (i) molding was carried out after the sag at the center of the softened sheet was 15 mm below the clamp (control); (ii) sheet heating started 5 minutes after the control, and molding in the same way as the control (AF5); and (iii) sheet heating started 10 minutes after the control, and molding in the same way as the control (AF10). Under each condition, vacuum forming was conducted for 30 seconds. Sheet thickness after fabrication was determined for the incisal edge, labial surface, cusp, and buccal surface using a special caliper accurate to 0.1 mm. The differences of the molding conditions on the thickness in each sheet material were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. RESULTS: For both sheet materials, significant differences between the control and AF5 were observed at all measurement points (P<.01), but not between the control and AF10. Compared with the control, AF5 was thinner and AF10 was a similar thickness. CONCLUSION: The continuous use of a vacuum-forming machine led to a reduction in the thickness of the mouthguard. Intervals of 10 minutes are necessary to achieve consistent molding.

Shape change in mouthguard sheets during thermoforming - part 2: effect of the anteroposterior position of the model on mouthguard thickness.

BACKGROUND/AIM: Mouthguards can reduce the risk of sports-related injuries, but the sheet material and thickness have a large effect on their efficacy and safety. The aim of this study was to investigate the effect of model position in the molding machine on the reduction in mouthguard thickness. MATERIALS AND METHODS: Ethylene vinyl acetate sheets and olefin copolymer sheets were used for thermoforming by a pressure- or a vacuum-forming machine. The working model was trimmed to the height of 25 mm at the maxillary central incisor and 20 mm at maxillary first molar. For both pressure forming and vacuum forming, the model was placed with the anterior rim of the model positioned 40, 30, 25, 20, or 10 mm from the front of the sheet frame. An additional test was carried out at 50 mm for vacuum forming. The sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper. The difference of the model position on the reduction in thickness in each forming device and sheet material was analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. RESULT: The reductions in thickness at the incisal edge and labial surface were about -60% and -50%, respectively, for the distance of 25 mm from the front of forming table. That position was the same as the height of the anterior part of the model for each molding machine and sheet material. The anterior thickness after molding became greater as the distance between the model and the sheet frame became smaller. CONCLUSION: The results showed that the thickness reduction was large when the distance from the model to the frame was small. This demonstrates the importance of centering the sheet and the model to achieve the most stable molding when positioning the model in the forming unit.

Denervation of nasal mucosa induced by posterior nasal neurectomy suppresses nasal secretion, not hypersensitivity, in an allergic rhinitis rat model.

The posterior nasal nerve is the dominant source of the parasympathetic, sympathetic, and sensory fibers that innervate the nasal respiratory mucosa. Therefore, a posterior nasal neurectomy (PNN) is thought to induce denervation of the nasal mucosa and relieve the nasal symptoms of allergic rhinitis. However, the underlying mechanisms and therapeutic action of PNN remain unknown. To investigate the impact of PNN-induced denervation of the nasal mucosa on allergic rhinitis, we developed a rat model of PNN and examined the effects of PNN on allergic rhinitis in ovalbumin-sensitized rats. This rat model of PNN was characterized by the depletion of nerve fibers, choline acetyltransferase, and neuropeptides (eg, substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, and neuropeptide Y) in the nasal respiratory mucosa. These animals exhibited nasal gland and goblet cell hypertrophy in the septal mucosa and atrophy of the submucosal gland in the lateral nasal wall, as well as reduced nasal secretion due to deficient acetylcholine synthesis. In an ovalbumin-sensitized model of allergic rhinitis, PNN also induced the depletion of nerve fibers, choline acetyltransferase, and neuropeptides in the nasal mucosa and suppressed nasal secretion. However, PNN did not affect mucosal thickening, eosinophil and mast cell infiltration, interleukin-4 and interferon-γ mRNA expression, and allergic symptoms (ie, sneezing and nasal scratching). These results suggest that the peripheral nerves and corresponding neuropeptides regulate nasal secretion, but not hypersensitivity, in allergic rhinitis, and that allergic rhinitis-related mucosal reactions occur in a highly denervated mucosa after PNN. Posterior nasal neurectomy may be a therapeutic option for the treatment of hyperrhinorrhea, but not allergic rhinitis hypersensitivity.

Optimal heating condition of mouthguard sheet in vacuum-pressure formation: part 3 styrene-based thermoplastic elastomer.

BACKGROUND: The aim of this study was to identify suitable heating conditions of polyolefin-polystyrene co-polymer sheets in vacuum-pressure formation, monitor the sheet temperature during molding, and examine the thickness of the fabricated mouthguard. MATERIALS AND METHODS: Mouthguards were fabricated with polyolefin-polystyrene co-polymer sheets (4.0-mm thick) utilizing a vacuum/pressure-forming device, which was subjected to vacuum forming for 10 s and pressure molding for 2 min. Four heating conditions were compared, defined by the amount of sag distance of 5, 10, 15, or 20 mm from the center of the softened sheet below the clamp. The working model was trimmed to a height of 20 mm at the cutting edge of the maxillary central incisor and to a height of 15 mm at the mesiobuccal cusp of the maxillary first molar. The radiation thermometer was used to measure the sheet temperatures of the center of the heated and non-heated surfaces under each condition. The sheet thickness after fabrication was determined for the incisal and the molar portions, and dimensional measurements were obtained using a measuring device. The differences in the sheet thickness produced by the different heating conditions were analyzed by Games-Howell's multiple comparison tests. RESULTS: For condition of 5 mm sagged, the temperature on the non-heated surface did not reach a sufficient softening temperature and the thickness was smallest. Mouthguard thickness was largest in the order of 15 mm sagged condition, followed by 20 mm sagged condition and then by 10 mm sagged condition, but a statistical difference was not observed in the labial and the buccal surface among the three conditions. CONCLUSION: This study demonstrated that for sufficient softening, it was necessary to heat the sheet to obtain a sag of 10 mm or more, and that the mouthguard thickness decreased as the sag increased.

Thickness of mouthguard sheets after vacuum-pressure formation: influence of mouthguard sheet material.

The aim of this study was to investigate the thickness of mouthguard sheet after vacuum-pressure formation based on the mouthguard sheet material. Three mouthguard sheet materials (4.0 mm thick) were compared: ethylene-vinyl acetate co-polymer (EVA), olefin co-polymer (OL), and polyolefin-polystyrene co-polymer (OS). The working model was made by hard gypsum that was trimmed to the height of 20 mm at the cutting edge of the maxillary central incisor and 15 mm at the mesiobuccal cusp of the maxillary first molar. Where the center of the softened sheet sagged 15 mm lower than the clamp, the sheet was pressed against the working model, followed by vacuum forming for 10 s and compression molding for 2 min. The thickness of mouthguard sheets after fabrication was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface), and dimensional measurements were obtained using a measuring device. Differences in the change in thickness due to sheet materials were analyzed by one-way analysis of variance (anova) followed by Bonferroni's multiple comparison tests. The OL sheet was thickest at all measurement points. At the incisal edge and cusp, thickness after formation was highest for OL, then EVA and finally OS. At the labial surface and buccal surface, the thickness after formation was highest for OL, then OS and finally EVA. This study suggested that post-fabrication mouthguard thickness differed according to sheet material, with the olefin co-polymer sheet having the smallest thickness reduction.

Method for effectively maintaining the thickness of mouthguards fabricated using EVA sheets and a circle tray: influence of grooved sheet and heating conditions.

The shapes of ethylene vinyl acetate (EVA) sheets are mainly square or round. The aim of this study was to elucidate a fabrication method that effectively maintains the thickness of the round sheet. Mouthguards were fabricated using EVA sheets (diameter 125 mm, thickness 4.0 mm) and a vacuum-forming machine. The sheet was pinched at the top and bottom and stabilized by the circle tray. Two heating conditions were compared: (i) the sheet was molded when it sagged 10 mm below the level of the sheet frame at the top of the post under normal conditions (N); and (ii) the sheet frame was lowered to and heated at 50 mm from the level of ordinary use and molded when it sagged 10 mm from the sheet frame (L). Two EVA sheet shapes were compared: an ordinary sheet (O) and a sheet with a horizontal v-shaped groove 30 mm from the anterior end (G). The height of the working model was 20 mm at the incisor point and 15 mm at the first molar. The sheet temperatures of the heating and non-heated surface were measured by the radiation thermometer. Post-molding thickness was determined for the incisal and molar portion. Differences in the thickness were analyzed using two-way anova. The temperature difference among points was smaller under condition L than under condition N. Thickness after formation was higher in condition L than in condition N, and was higher in condition G than in condition O. At the labial surface and the cusp, L-G was thickest. With the present techniques, uneven softening during heating can be improved by lowering the sheet frame and consequently reducing the reduction in the thickness of the sheet. Additionally, the thickness reduction is reduced by creating a horizontal groove on the sheet, establishing the clinical efficacy of this method.

Shape change in mouthguard sheets during thermoforming.

BACKGROUND: The purpose of this study was to identify changes in sheet shape during thermoforming and the effect of the model position in the molding machine on fabricated mouthguard thickness. MATERIALS AND METHODS: Ethylene vinyl acetate mouthguard sheets (3.8 mm thick) were used that had cross-stripes (10 × 10 mm), and the anteroposterior and bilateral lengths were used for measurements. Two forming machines were used: a vacuum- and a pressure-forming machine, and two heating conditions were investigated that defined as the time when sagging of the softened sheet was 15 mm (H-15) and 20 mm (H-20) below the clamp, and the length of each cross-stripes was measured. The area of each lattice was calculated using Bretschneider's formula to compare changes in sheet shape for each condition. Next, mouthguards were molded by forming machine where the working model was positioned under two different conditions: with the model anterior centered in the forming unit and with the model centered. The sheet thickness after fabrication was determined for the incisal and the molar portion, and dimensional measurements were obtained using a measuring device. Differences in the thickness were analyzed by two-way analysis of variance (anova). RESULT: In both molding machines, the change in the area under H-20 was greater than H-15. While the increase in area tended to expand from the center of the sheet in concentric circles, the difference between the central and surrounding areas was only approximately 5%. For both molding machines, differences in thickness after molding due to setting position of the model were not observed. CONCLUSION: The results showed that shape changes of the sheet during thermoforming tend to concentrically and almost uniformly expand from the center and that it is important to center the sheet and the model when positioning the model in the forming unit.

Heating methods for reducing unevenness softening of mouthguard sheets in vacuum-pressure formation.

BACKGROUND: Unevenness in softening of the plastic sheet leads to a decrease in the mouthguard thickness during thermoforming. In this study, we examined the heating methods for reducing unevenness when softening mouthguard sheets during vacuum-pressure formation. MATERIALS AND METHODS: Ethylene vinyl acetate mouthguard sheets and olefin copolymer sheets (thickness: 4.0 mm) were used. The following three heating conditions were compared: condition A-the sheet was molded when it sagged 15 mm from the sheet frame (under normal condition); condition B-the heater was turned off when the sheet sagged by 10 mm from the frame, followed by the sheet molding when the sagging reached 15 mm below the frame; and condition C-the sheet was inverted after heating when the sheet sagged 10 mm and was molded when the sagging reached 15 mm below the frame. The sheet was heated and pressed over the model using a vacuum-pressure machine; then, 10 s of vacuum forming and 2 min of pressure molding were applied. The sheet temperatures were measured using a radiation thermometer. Thickness of the fabricated sheets was determined for the incisal and the molar portion using a measuring device. Thickness data for each condition were analyzed by one-way anova followed by Bonferroni's multiple comparison tests. RESULTS: On both sheets, condition B was smallest for temperature difference between the heated and the non-heated surface, and thicknesses after molding were greatest at all measuring portions. CONCLUSION: By comparing changes in sheet temperatures at molding and variation in thicknesses when applying the heating method using a vacuum-pressure molding machine, we found that reduced unevenness in sheet softening occurred when the heater was turned off when the sag distance of the sheet was 5 mm less than the conventional molding, and then, the sheet was pressed when the conventional sag distance was reached.