Relationship between impacts attributed to malocclusion and psychological stress in young Japanese adults

Problematic internet use among people with dentofacial deformity: a preliminary study

Objective

Class III malocclusion represents one type of anterior malocclusions, characterised by a longer face and a more prominent chin. Class III malocclusions are a type of malocclusion related to the relationship between the maxilla and mandible. They are often characterized by mandibular protrusion relative to the maxilla, and in some cases, features such as elongation of the lower facial third or a more prominent chin may also be present. Due to their appearance, patients experience a range of psychosocial and emotional difficulties, which have also been identified as risk factors for problematic internet use (PIU), including depression, negative body image, and lower self-esteem.

Methods

A cross-sectional study was conducted and 170 fully completed questionnaires were obtained, 85 from people with Class III malocclusions aged between 18 and 42 years, and 85 from individuals without Class III malocclusions aged between 18 and 40 years.

Results

Participants with Class III malocclusions obtained statistically significantly more PIU points than participants without Class III malocclusions (p < 0.001). Among people with Class III malocclusions 45.9% showed a high or very high risk of Internet addiction, while in the comparison group, it was only 9.4% (p < 0.001). Among participants with Class III malocclusions, there was a statistically significant, although weak, correlation between the PIU score and feeling uncomfortable when being the centre of attention (rho = 0.284; p < 0.01), and between the PIU score and concern with appearance (rho = 0.272; p < 0.05).

Conclusion

Individuals with Class III malocclusion are at a much higher risk of problematic Internet use than people without the disorder. This problem especially concerns patients who feel discomfort when being the centre of attention and are more concerned about their appearance. Therefore, it seems that people suffering from disorders that cause changes in appearance should have access to extensive psychological support, including the prevention of problematic Internet use.

Mental Health and Malocclusion: A Comprehensive Review

The purpose of this study is to comprehensively review the relationship between malocclusion and anxiety and depression. While the physical implications of malocclusion are well documented, recent scholarship has shifted focus to examining the direct relationship between malocclusion and both anxiety and depression. It has been hypothesized that individuals with skeletal or dental malocclusion experience a range of psychological sequelae, including diminished quality of life (QoL), reduced oral-health-related quality of life (OHRQoL), increased vulnerability and appearance-related bullying, and impaired body image. Furthermore, these factors are postulated to collectively contribute to overall mental health, with malocclusion potentially serving as a contributing etiological factor in the development of elevated levels of anxiety and depression. Contemporary scholarship has established a complex relationship between dentofacial deviations and the psychological well-being of affected individuals. Evidence shows that malocclusion may contribute to increased depression and anxiety levels in some individuals, influencing their social functioning and treatment-seeking behavior. Dentofacial disharmony has also been associated with altered self-perception, potentially impacting an individual's OHQOL and overall quality of life. While the findings exhibit some inconsistency, a modest body of evidence indicates a possible correlation between pronounced skeletal or dental malocclusion and anxiety and depression. These adverse psychosocial impacts, in turn, contribute to an elevated risk of anxiety and depression, underscoring the far-reaching consequences of malocclusion beyond oral health. Therefore, clinicians need to consider these issues in their treatment plans, incorporating interdisciplinary approaches that address both orthodontic and psychological aspects of patient care.

Non-coding RNA alterations in occlusal disharmony-induced anxiety-like behaviour

BACKGROUND

Occlusal disharmony (OD) may induce anxiety-like behaviours; however, the underlying mechanism remains unclear. Herein, we explored the expression profiles of non-coding RNAs (ncRNAs), along with their biological function and regulatory network, in anxiety-like behaviour induced by OD.

MATERIALS AND METHODS

Occlusal disharmony was produced by anterior crossbite of C57BL/6 mice. Behavioural tests, corticosterone (CORT) and serotonin (5-HT) levels were used to measure anxiety. In addition, RNA sequencing was used to screen all differentially expressed (DE) ncRNAs. Moreover, the RNA-binding proteins interacting with ncRNAs were predicted by the ENCORI database and confirmed using western blots.

RESULTS

The significant differences in behavioural tests and CORT suggested the successful induction of anxiety-like behaviour by OD. In OD mice, ncRNAs were significantly dysregulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggested that the DE ncRNAs were enriched in anxiety-related pathways. CircRNA10039 was upregulated, and PTBP1 was predicted to interact with circRNA10039. In addition, KEGG pathway analysis showed that PTBP1 may be associated with messenger RNA biogenesis and spliceosomes.

CONCLUSION

OD induced by anterior crossbite can lead to the anxiety-like behaviours. During this process, ncRNA also changes. CircRNA10039 and PTBP1 may play a role in OD-induced anxiety-like behaviours.

Effects of the angiotensin-converting enzyme inhibitor captopril on occlusal-disharmony-induced cardiac dysfunction in mice

Occlusal disharmony is known to affect not only the oral cavity environment, but also the autonomic nervous system in the heart. Since the renin-angiotensin system (RAS) inhibitor captopril (Cap) is one of the first-line drugs for preventing cardiac remodeling in patients with heart failure, we hypothesized that Cap might prevent cardiac dysfunction induced by occlusal disharmony. Here, to test this idea, we used our bite-opening (BO) mouse model, which was developed by cementing a suitable appliance onto the mandibular incisor. Mice were divided into four groups: (1) Control, (2) BO, (3) Cap, and (4) BO + Cap. After 2 weeks, we evaluated cardiac function by echocardiography and confirmed that cardiac function was significantly decreased in the BO group compared to the control, while Cap ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and oxidative stress-induced myocardial damage in the BO group were significantly increased versus the control, and these increases were suppressed by Cap. Cardiac dysfunction induced by BO was associated with dual phosphorylation on PKCδ (Tyr-311/Thr-505), leading to activation of CaMKII with increased phosphorylation of RyR2 and phospholamban. Our results suggest that the RAS might play an important role in the development of cardiac diseases induced by occlusal anomalies.

Occlusal Disharmony-A Potential Factor Promoting Depression in a Rat Model

Objectives: Patients with occlusal disharmony (OD) may be susceptible to depression. The hypothalamus−pituitary−adrenal axis, 5-HT and 5HT2AR in the prefrontal cortex (PFC), amygdala, and hippocampus are involved in the modulation of emotion and depression. This study investigated whether OD affects the HPA axis and 5-HT system and, subsequently, produces depression-like behaviors in rats. Materials and methods: OD was produced by removing 0.5 and 0.25 mm of hard tissue from the cusps of the maxillary molars in randomly selected sides of Sprague−Dawley rats. CUS involved exposure to 2 different stressors per day for 35 days. OD-, CUS-, and OD + CUS-treated groups and an untreated control group were compared in terms of behavior, endocrine status and brain histology. Results: There were significant differences among the four groups in the behavior tests (p < 0.05), especially in the sucrose preference test, where there was a significant decrease in the OD group compared to the control group. ACTH and CORT concentrations were significantly higher in the OD + CUS group than the control group (p < 0.05). Expression of GR and 5-HT2AR in the PFC, amygdala and hippocampal CA1 was significantly higher in the OD, CUS and OD + CUS groups than the control group (p < 0.05). Conclusion: OD promotes depression-like behaviors through peripheral and central pathways via the HPA axis, GR and 5-HT system.

New Method of Avoiding Underestimation of Caries Incidence and Its Association with Possible Risk Factors in Japanese University Students: A Prospective Cohort Study

The objective of this three-year prospective cohort study was to investigate the association between a new definition of an increase in dental caries and risk factors in Japanese young adults. Data of Okayama University students who volunteered to undergo oral examinations and answer questionnaires in 2015 and 2018 were analyzed. The status of filled teeth and the status of occlusal/proximal surfaces of filled or decayed teeth were recorded. An increase in dental caries was defined as a change in the status of filled teeth and/or an increase in dental caries of occlusal and proximal surfaces. A total of 393 participants (18.2 ± 0.8 years) were analyzed. First and second molars showed a high prevalence of dental caries. Of the participants, 144 (36.6%) showed an increase in dental caries. In all the participants and in the females, the decayed, missing, and filled teeth (DMFT) score and history of orthodontic treatment at baseline were significantly associated with an increase in dental caries (p < 0.05) in logistic regression analyses. In the males, the DMFT score and the daily frequency of snacking (≥2) at baseline were significantly associated with an increase in dental caries (p = 0.04). The DMFT score and history of orthodontic treatment at baseline can be risk factors for an increase in dental caries using the new definition in young adults.

Patients' perceptions of orthodontic treatment experiences during COVID-19: a cross-sectional study

BACKGROUND

COVID-19 has impacted the care of patients undergoing orthodontic treatment. We aimed to provide an overall view of patients' perspectives, concerns, and expectations towards their treatment throughout the clinic lockdown during the pandemic; and to assess patients' levels of mental distress and its association with their confidence in resuming care.

METHODS

An anonymous, validated, in-person paper questionnaire was distributed to adult orthodontic patients' post-lockdown at an academic institution. The survey focused on the clinical aspects and patients' perspectives regarding orthodontic treatment during the pandemic. The Kessler Mental Distress Scale (K10) was used to evaluate their psychological status. Survey responses were descriptively summarized and confidence in resuming care was compared between normal patients and patients with mental distress using Mann-Whitney tests.

RESULTS

One hundred fifty-four patients were surveyed from July to October 2020. Mean age of the participants was 29.30 (SD = 12.01) years and 62% were females. Emergencies during the closure (21%, 32/154) involved primarily irritation with protruding wires. Patients were neutral regarding tele-dentistry and preferred their current fixed appliances over clear aligners. Upon resuming care, 80.51% were extremely pleased with the restrictive protocols and with high level of confidence in resuming treatment. The average level of anxiety was low, and a modest association was found between mental distress and reduced confidence in resuming treatment.

CONCLUSIONS

Few numbers of minor emergencies occurred during the clinic closure. Despite the rising interest in tele-dentistry, patients were neutral on considering this option to monitor treatment and were content with fixed appliances. Patients had high confidence levels to resume their care based on the protocols established upon reopening. The association of mental distress and confidence in resuming care is suggestive and needs further investigation.

Association between Household Exposure to Secondhand Smoke and Dental Caries among Japanese Young Adults: A Cross-Sectional Study

The long-term effects of secondhand smoke (SHS) on dental caries among Japanese young adults remain unclear. The purpose of this cross-sectional study was to evaluate whether household exposure to SHS is associated with dental caries in permanent dentition among Japanese young adults. The study sample included 1905 first-year university students (age range: 18-19 years) who answered a questionnaire and participated in oral examinations. The degree of household exposure to SHS was categorized into four levels according to the SHS duration: no experience (-), past, current SHS < 10 years, and current SHS ≥ 10 years. Dental caries are expressed as the total number of decayed, missing, and filled teeth (DMFT) score. The relationships between SHS and dental caries were determined by logistic regression analysis. DMFT scores (median (25th percentile, 75th percentile)) were significantly higher in the current SHS ≥ 10 years (median: 1.0 (0.0, 3.0)) than in the SHS-(median: 0.0 (0.0, 2.0)); p = 0.001). DMFT ≥ 1 was significantly associated with SHS ≥ 10 years (adjusted odds ratio: 1.50, 95% confidence interval: 1.20-1.87, p < 0.001). Long-term exposure to SHS (≥10 years) was associated with dental caries in permanent dentition among Japanese young adults.

Effects of occlusal disharmony on cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage in mice

Occlusal disharmony leads to morphological changes in the hippocampus and osteopenia of the lumbar vertebra and long bones in mice, and causes stress. Various types of stress are associated with increased incidence of cardiovascular disease, but the relationship between occlusal disharmony and cardiovascular disease remain poorly understood. Therefore, in this work, we examined the effects of occlusal disharmony on cardiac homeostasis in bite-opening (BO) mice, in which a 0.7 mm space was introduced by cementing a suitable applicance onto the mandibular incisior. We first examined the effects of BO on the level of serum corticosterone, a key biomarker for stress, and on heart rate variability at 14 days after BO treatment, compared with baseline. BO treatment increased serum corticosterone levels by approximately 3.6-fold and the low frequency/high frequency ratio, an index of sympathetic nervous activity, was significantly increased by approximately 4-fold by the BO treatment. We then examined the effects of BO treatment on cardiac homeostasis in mice treated or not treated with the non-selective β-blocker propranolol for 2 weeks. Cardiac function was significantly decreased in the BO group compared to the control group, but propranolol ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but propranolol blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as inhibition of Akt/mTOR signaling and autophagic flux. These data suggest that occlusal disharmony might affect cardiac homeostasis via alteration of the autonomic nervous system.

Is there association between dental malocclusion and bruxism? A systematic review and meta-analysis

OBJECTIVES

Given that current literature largely dissociates dental malocclusion and bruxism, the objective of this study was to gather, through a systematic review, scientific evidence to support their relationship.

METHODOLOGY

This study was performed according to the PECO strategy (where P = general population; E = dental malocclusion; C = no dental malocclusion; and O = bruxism). Literature searches were conducted without language or date restrictions in the following databases: PubMed, Scopus, the Web of Science, the Cochrane Library, LILACS/BBO via VHL and the grey literature. The search strategy included Medical Subject Headings/DECs, synonyms and free terms relevant to each database, with no age restrictions applied. Once the relevant data were extracted from the articles, the Fowkes and Fulton guidelines were followed to assess the quality and risk of bias. For quantitative analysis, dental malocclusions were divided into groups according to their type in order to perform odds ratio (OR) meta-analyses with 95% confidence intervals (CI) using the Review Manager software program (Cochrane, London, UK). The level of certainty of evidence was demonstrated through the Grading of Recommendations Assessment, Development, and Evaluation (GRADE).

RESULTS

After 1,502 studies found, 10 studies were included for qualitative analysis and nine for quantitative synthesis. Four studies presented high methodological quality. Five meta-analyses suggested a non-association between bruxism and Angle class I (OR: 1.05, 95% CI: 0.41-2.69; P = .92; I²  = 84%), Angle class II (OR: 1.49, 95% CI: 0.77-2.87; P = .23; I²  = 71%) or Angle class III (OR: 0.77, 95% CI: 0.31-1.93; P = .58; I²  = 0%). Bruxism was associated with children who did not present with a posterior crossbite (OR: 0.70, 95% CI: 0.51-0.96; P = .03; I²  = 27%) and present crowding (OR: 1.53, 95% CI: 1.03-2.26; P = .03; I²  = 0%). The GRADE analysis presented a very low quality of evidence.

CONCLUSION

Individuals who present with bruxism have a greater chance of crowding. However, bruxism is not associated with the presence of any of the other malocclusions evaluated.

Structural equation modeling to detect predictors of oral health-related quality of life among Japanese university students: a prospective cohort study

PURPOSE

This prospective cohort study of Japanese university students aimed to identify factors that might affect oral health-related quality of life (OHRQoL) and longitudinal relationships over a period of 3 years.

METHODS

Students (n = 487) provided complete data before entering and 3 years later (before university graduation) participated in the present study. Decayed, missing, and filled teeth (DMFT) scores, community periodontal index, ratios (%) of teeth with bleeding on probing, and malocclusion were determined during oral examinations. The questionnaire addressed age, sex, self-rated oral health, oral health behavior, subjective oral symptoms, and OHRQoL determined using the oral health impact profile (OHIP)-14. Associations were analyzed using structural equation modeling (SEM).

RESULTS

The OHRQoL significantly worsened according to OHIP-14 total score (p = 0.001). The final model in the symptoms of SEM analysis showed that OHRQoL at follow-up positively correlated with OHRQoL at baseline. Self-rated oral health was directly associated with the OHRQoL at baseline (p < 0.05).

CONCLUSIONS

This study determined that OHRQoL at baseline was a direct predictor, and that self-rated oral health were indirect predictors of OHRQoL at follow-up among Japanese university students.

Prevalence and factors related to malocclusion, normative and perceived orthodontic treatment need among children and adolescents in Bangladesh

OBJECTIVE

The purpose of the present study was to assess the prevalence of normative and perceived orthodontic treatment need in schoolchildren and adolescents, related risk factors, and children/parent's aesthetic perception, compared to orthodontist's opinion, in Dhaka city, Bangladesh.

METHODS

A random sample of 800 schoolchildren aging 11-15 years was selected from different schools in the city of Dhaka, Bangladesh. The Dental Health Component (DHC) and Aesthetic Component (AC) of the Index of Orthodontic Treatment Need (IOTN) were assessed as normative treatment need. The Decayed, Missing, Filled Teeth (DMFT) index was used to record caries experience. Children were interviewed on the perception of orthodontic treatment need. Parents also completed a questionnaire on the perception of their child's orthodontic treatment need, assessed by AC/ IOTN.

RESULTS

According to the DHC/IOTN, only 24.7% were in the category of definite need (grade 4-5) for orthodontic treatment. A significant difference was found between the clinician/children and clinician/parents perceived AC score of IOTN (p= 0.0001). Multiple logistic regression showed children with a higher DMFT were significantly more likely to need orthodontic treatment, according to the DHC of IOTN.

CONCLUSION

A low proportion of schoolchildren needs normative orthodontic treatment in the city of Dhaka, Bangladesh. Children with a higher DMFT score were significantly more likely to need orthodontic treatment, according to the DHC of IOTN.

Awareness of Clenching and Underweight are Risk Factors for Onset of Crowding in Young Adults: A Prospective 3-Year Cohort Study

Bruxism is a parafunctional activity that can seriously affect quality of life. Although bruxism induces many problems in the oral and maxillofacial area, whether it contributes to the onset of malocclusion remains unclear. The purpose of this prospective cohort study was to investigate the association between the onset of malocclusion and awareness of clenching during the daytime in young adults. Among 1,092 Okayama University students who underwent normal occlusion at baseline, we analysed 238 who had undergone a dental examination and had complete data after 3 years (2013⁻2016). We also performed subgroup analysis to focus on the association between awake bruxism and the onset of crowding (n = 216). Odds ratios (ORs) were calculated using multivariate logistic regression analyses. The incidences of malocclusion and crowding were 53.8% and 44.5%, respectively. In multivariate logistic regression, awareness of clenching was a risk factor for crowding (OR: 3.63; 95% confidence interval [CI]: 1.08⁻12.17). Moreover, underweight (body mass index < 18.5 kg/m²) was related to the onset of malocclusion (OR: 2.34; 95%CI: 1.11⁻4.92) and crowding (OR: 2.52, 95%CI: 1.25⁻5.76). These results suggest that awareness of clenching during the daytime and underweight are risk factors for the onset of crowding in young adults.

Influence of anthropometry, TMD, and sex on molar bite force in adolescents with and without orthodontic needs

PURPOSE

Bite force has been studied as representative of functional indices of mastication and its value may have diagnostic significance in disorders of the musculoskeletal system of facial bones. This study aimed to evaluate bite force in adolescents with and without orthodontic needs considering presence of temporomandibular disorders (TMD) as well as anthropometry: craniofacial dimensions and body mass index (BMI).

METHODS

A total of 80 subjects were screened (61 females, 19 males; 18 ± 3 years old). Unilateral molar bite force was measured using a digital dynamometer with a fork thickness of 12 mm. Direct anthropometry was used to quantify craniofacial measurements. Dental Health Component of the Index of Orthodontic Treatment Need (IOTN-DHC) and the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) were used to classify samples according to malocclusion and to TMD, respectively. Data were analyzed using normality tests, Mann-Whitney U test, and multiple linear regression analyses with stepwise backward elimination, controlling for the presence of malocclusion and TMD (p ≤ 0.05).

RESULTS

The cephalic index was greater in females with malocclusion and the longitudinal cranial diameter was reduced in females with malocclusion. BMI was not different between normal and malocclusion groups for either gender. Bite force was negatively related with vertical dimension of the face, and positively related with facial width and facial index. The model explained 32% of bite force variability, considering the sample size (coefficient of determination R ² = 0.324).

CONCLUSIONS

Even when orthodontic needs and TMD signs and symptoms are present, stronger bite force is still observed in males and in subjects with smaller anterior facial heights and wider facial widths.

Experimental occlusal disharmony - A promoting factor for anxiety in rats under chronic psychological stress

BACKGROUND AND PURPOSE

Clinically, patients under chronic psychological stress (PS) appear to be more susceptible to occlusal disharmony (OD) compared with those without PS. OD was proved to introduce anxiety-like stress. Therefore, the purpose of the study was to investigate whether OD would affect psychological stress-induced anxiety and its underlying mechanisms.

METHODS

Chronic PS was induced by a communication box, and OD was produced by bonding a 0.3mm-thick crown on the right maxillary first molar of male Sprague-Dawley rats. Sixty-seven rats were randomly divided into 8 groups: (A) chronic PS plus OD group (n=6); (B) chronic PS plus sham OD group (n=6); (C) chronic PS only group (n=6); (D) OD group (n=6); (E) sham OD group (n=6); (F) control group (n=6); (G) naive group (n=6); (H) foot-shock group (n=25). Open-field test (OFT) and elevated plus maze test (EPM) were conducted on the 7th, 21th, 35th day to measure the anxiety level of each group except naive and foot-shock group. In addition, corticosterone (CORT) level in serum, 5-hydroxytryptamine (5-HT) and 5-HT_2A receptor (5-HT_2AR) expressions in prefrontal cortex (PFC), hippocampal CA1 and dentate gyrus (DG) areas were measured on the 35th day to elucidate the mechanism(s) by which the exacerbation occurred.

RESULTS

The significant differences in OFT and EPM tests on day 21 or day 35 between groups (p<0.01) indicated the successful establishment of animal model of PS or OD. And there was a significant increase in CORT concentration in serum (p<0.01), 5-HT expressions in PFC, hippocampal DG areas and 5-HT_2AR expressions in PFC, hippocampal CA1 areas (p<0.05) in group A, B, C, D compared with group F. Similar results were also found in group A, B, C, D when compared with group G (p<0.05) except 5-HT expression in DG area in group C and D (p>0.05), together with a gradual decrease in values of all the parameters mentioned above from group A to group G.

CONCLUSION

The significant changes in exploratory behaviors, serum CORT concentration, 5-HT and 5-HT_2AR expressions induced by OD in rats with or without chronic PS, and more obvious alterations in rats with chronic PS, may indicate that OD may be a promoting factor for anxiety through both peripheral and central pathways via the hypothalamus-pituitary-adrenal (HPA) axis and 5-HT system.

Associations among oral health-related quality of life, subjective symptoms, clinical status, and self-rated oral health in Japanese university students: a cross-sectional study

BACKGROUND

The present study aimed to elucidate the associations among self-rated oral health, clinical oral health status, oral health behaviors, subjective oral symptoms, and oral health-related quality of life (OHRQoL) in a group of Japanese university students.

METHODS

Of 2051 participants, 2027 (98.83%) students received an optional oral examination and answered a questionnaire including items regarding age, sex, self-rated oral health, oral health behaviors, subjective oral symptoms, and OHRQoL [The Oral Health Impact Profile (OHIP)-14]. On oral examination, the decayed, missing, and filled teeth (DMFT) score, Community Periodontal Index (CPI), the percentage of teeth showing bleeding on probing (%BOP), and malocclusion were recorded. Structural equation modelling (SEM) analysis was used to test associations.

RESULTS

The mean score (± SD) of OHIP-14 was 1.92 ± 5.47. In the SEM analysis, the final model showed that self-rated oral health, oral pain, malocclusion, and the DMFT score were directly associated with the OHRQoL, and subjective symptoms of temporomandibular disorders (TMD) and recurrent aphthous stomatitis were both directly and indirectly associated (p < 0.05). CPI, %BOP, and oral health behaviors were excluded from the final model.

CONCLUSIONS

OHRQoL was associated with self-related oral health, subjective symptoms of TMD, oral pain and stomatitis, DMFT, and malocclusion in this group of Japanese university students.

Novel stress increases hypothalamic-pituitary-adrenal activity in mice with a raised bite

BACKGROUND AND OBJECTIVE

In humans, occlusal disharmony may cause various physical complaints, including head and neck ache, stiffness in the shoulder and neck, and arthrosis of the temporomandibular joints. Occlusal disharmony induced by raising the bite in rodents, increases plasma corticosterone levels, which leads to morphologic changes in the hippocampus and altered hippocampus-related behavior. The paraventricular nucleus (PVN) of the hypothalamus regulates the hypothalamic-pituitary-adrenal system. Chronically stressed animals exposed to a novel stress exhibit higher adrenocorticotropic hormone levels than naive control animals. We hypothesized that there would be different response of the corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) to a novel acute stress with occlusal disharmony.

DESIGN

In order to investigate how exposure of mice with occlusal disharmony to a novel acute stress (restraint stress) affects the PVN, we induced occlusal disharmony by raising the vertical dimension of the bite (bite-raised condition) and examined the expression of corticotrophin releasing hormone (CRH) mRNA and arginine vasopressin (AVP) mRNA in mouse PVN.

RESULTS

CRH mRNA expression was increased in the PVN of the bite-raised group 90min after the bite-raising procedure, but the expression was recovered to the control level at 14days. AVP mRNA expression in the PVN was normal at 90min, and increased significantly 14days after the bite-raising procedure. Exposure to restraint stress in the bite-raised mice induced a significant increase in CRH mRNA expression in the PVN.

CONCLUSIONS

The bite-raising procedure induced a rapid CRH mRNA response and a slower AVP mRNA response in the parvocellular PVN of the hypothalamus. Exposure to a novel stress following the bite-raising procedure further reinforced the CRH stress response. Thus, occlusal disharmony, such as that induced by raising the bite, may be a risk factor for hypersensitivity to a novel stress.

Association Between Self-Reported Bruxism and Malocclusion in University Students: A Cross-Sectional Study

OBJECTIVES

Bruxism can result in temporomandibular disorders, oral pain, and tooth wear. However, it is unclear whether bruxism affects malocclusion. The aim of this study was to examine the association between self-reported bruxism and malocclusion in university students.

METHODS

Students (n = 1503; 896 men and 607 women) aged 18 and 19 years were examined. Malocclusion was defined using a modified version of the Index of Orthodontic Treatment Need. The presence of buccal mucosa ridging, tooth wear, dental impression on the tongue, palatal/mandibular torus, and the number of teeth present were recorded, as well as body mass index (BMI). Additional information regarding gender, awareness of bruxism, orthodontic treatment, and oral habits was collected via questionnaire.

RESULTS

The proportion of students with malocclusion was 32% (n = 481). The awareness of clenching in males with malocclusion was significantly higher than in those with normal occlusion (chi square test, P < 0.01). According to logistic regression analysis, the probability of malocclusion was significantly associated with awareness of clenching (odds ratio [OR] 2.19; 95% confidence interval [CI], 1.22-3.93) and underweight (BMI <18.5 kg/m(2)) (OR 1.89; 95% CI, 1.31-2.71) in males but not in females. In subgroup analyses, the probability of crowding was also significantly associated with awareness of clenching and underweight (P < 0.01) in males.

CONCLUSIONS

Awareness of clenching and underweight were related to malocclusion (crowding) in university male students.

Occlusal disharmony accelerates the initiation of atherosclerosis in apoE knockout rats

Background

Psychosocial stress is one of the risk factors for atherosclerosis. As occlusal disharmony induces psychological stress, we hypothesized that psychological stress by occlusal disharmony accelerates atherosclerosis. The aim of this study was to investigate the effects of occlusal disharmony on the initiation of atherosclerosis in apolipoprotein E (apoE) knockout rats.

Methods

Fourteen male apoE-knockout rats (age; 8 weeks) (Sprague–Dawley strain background) were divided into two groups of seven rats: the occlusal disharmony group and the no treatment (control) group. In the occlusal disharmony group, the maxillary molar cusps were cut off for the 8-week experimental period.

Results

In the occlusal disharmony group, the percentages of the area of total aortic lumen occupied by plaques and lipid were significantly higher than those in the control group (p < 0.05, t-test). The occlusal disharmony group also showed significantly higher serum levels of very low-density lipoprotein-cholesterol (VLDL) and low-density lipoprotein-cholesterol (LDL), plasma levels of corticosterone (1.9, 1.3 and 1.3 times, respectively), higher aortic protein expression levels of vascular cell adhesion molecule-1 (VCAM1) and intercellular adhesion molecule-1 (ICAM1) (1.5 and 1.4 times, respectively), and higher aortic gene expression of levels of VCAM1 and Toll-like receptor 4 (TLR4) (1.9 and 4.3 times, respectively), as compared to the control group (p < 0.05). However, there were no significant differences in serum levels of oxidized LDL, reactive oxygen metabolites and C-reactive protein between the two groups.

Conclusion

In apoE knockout rats, occlusal disharmony may induce VCAM1, ICAM1 and TLR4 expression and accelerate the initiation of atherosclerosis.

Soft-diet feeding after weaning affects behavior in mice: Potential increase in vulnerability to mental disorders

Mastication is one of the most important oral functions, and the period during which mastication is acquired overlaps with the term of rapid development and maturation of the neural systems. In particular, the acquisition period after weaning is related to the potential onset of mental disorders. However, the roles of mastication during this period for brain development remain largely unknown. Therefore, we used a series of standard behavioral analyses, assessment of hippocampal cell proliferation, and the expression of brain-derived neurotrophic factor (BDNF), TrkB, and Akt1 in the hippocampus and frontal cortex of mice to investigate the effects of post-weaning mastication on brain function. We fed 21-day-old C57BL6/J male mice either a hard or a soft diet for 4weeks and conducted a series of standard behavioral tests from 7weeks of age. Further, histological analysis with bromodeoxyuridine was performed to compare hippocampal cell proliferation at 7 and 14weeks of age. Real-time polymerase chain reaction was performed to compare BDNF, TrkB, and Akt1 expression in the hippocampus and frontal cortex of 14-week-old mice. Compared to mice fed a hard diet (HDM), soft-diet mice (SDM) showed behavioral impairments, including decreased home cage activity, increased open field test activity, and deficits in prepulse inhibition. These results were similar to those observed in mouse models of schizophrenia. However, no effects were observed on anxiety-like behaviors or memory/learning tests. Compared to HDM, SDM showed significantly decreased hippocampal cell proliferation and hippocampal BDNF and Akt1 gene expression at 14weeks of age. A soft diet after weaning may have resulted in histological and molecular changes in the hippocampus and influenced outcomes of behavioral tests related to mental disorders. Our findings suggest that soft-diet feeding after weaning may affect both physical and mental development of mice, and may increase vulnerability to mental disorders.

Relationships between self-rated oral health, subjective symptoms, oral health behavior and clinical conditions in Japanese university students: a cross-sectional survey at Okayama University

BACKGROUND

Self-rated oral health is a valid and useful summary indicator of overall oral health status and quality of life. However, few studies on perception of oral health have been conducted among Japanese young adults. This study investigated whether oral health behavior, subjective oral symptoms, or clinical oral status were associated with self-rated oral health in Japanese young adults.

METHODS

This cross-sectional survey included 2,087 students (1,183 males, 904 females), aged 18 and 19 years, at Okayama University, Japan. A self-administered questionnaire was distributed and an oral examination was performed.

RESULTS

In a structural equation modeling analysis, the score of decayed, missing and filled teeth (DMFT) significantly affected self-rated oral health (p <0.05) and the effect size was highest. Malocclusion, subjective symptoms of temporomandibular disorders (TMD) and stomatitis, and poor oral health behavior significantly induced self-rated poor oral health with small effect sizes (p <0.05). Clinical periodontal conditions and Oral Hygiene Index-simplified were not related to self-rated oral health.

CONCLUSION

Self-rated oral health was influenced by subjective symptoms of TMD and stomatitis, oral health behavior, the score of DMFT, and malocclusion. The evaluation of these parameters may be a useful approach in routine dental examination to improve self-rated oral health in university students.

Effect of incisor position on the self-perceived psychosocial impacts of malocclusion among Chinese young adults

OBJECTIVE

To evaluate the impact of the incisor position on the self-perceived psychosocial impacts of malocclusion among Chinese young adults.

MATERIALS AND METHODS

This cross-sectional study included a convenience sample of 17.1- to 22.3-year-old young adults (n = 1005). The five groups represented were normal occlusion as well as incisor Class I, Class II/1, Class II/2, and Class III malocclusion. For clinical assessment, the incisor relationship was evaluated according to the British Standards Institute Incisor Classification, and the self-perception of dental esthetics was assessed using the Psychosocial Impact of Dental Aesthetics Questionnaire (PIDAQ). Statistical analysis involved the analysis of variance and Tukey multiple-comparison post hoc tests.

RESULTS

Psychosocial impacts were different among the five groups for the four PIDAQ domains (P < .001 for all four domains). Statistically significant differences were found between the four malocclusion groups and the normal occlusion group in all four domains (P < .001 for all four domains). Furthermore, statistically significant differences were found between four malocclusion groups.

CONCLUSIONS

All four malocclusion groups had more severe psychosocial impacts than the normal occlusion group in the four PIDAQ domains. Statistically significant differences were also found between the four malocclusion groups; these malocclusion groups ranked by score, highest to lowest, were Class III, Class II/1, Class II/2, and Class I.

Occlusal disharmony increases amyloid-β in the rat hippocampus

Amyloid-β plays a causative role in Alzheimer's disease. Occlusal disharmony causes chronic psychological stress, and psychological stress increases amyloid-β accumulation. The purpose of the present study was to investigate whether occlusal disharmony-induced psychological stress affects the accumulation of amyloid-β and its related gene expressions in the rat hippocampus. Eight-week-old male Wistar rats (n = 18) were divided into three groups of six rats each: (1) a control group that received no treatment for 8 weeks; (2) an occlusal disharmony group that underwent cutoff maxillary molar cusps for 8 weeks; and (3) a recovered group that underwent cutoff maxillary molar cusps for 4 weeks followed by recovery for 4 weeks. Occlusal disharmony increased plasma corticosterone levels in a time-dependent manner. Levels of amyloid-β 40 and 42, glucocorticoid receptor (Gr) protein, and cleaved caspase 3 (Casp3) as well as gene expressions of amyloid precursor protein, beta-secretase, Casp3, and Gr in the hippocampus in the occlusal disharmony group were significantly higher than those in the control group (P < 0.016). These findings were significantly improved by recovery of occlusion (P < 0.016). These results indicate that psychological stress induced by occlusal disharmony reversibly induces amyloid-β 40 and 42 in the rat hippocampus through the glucocorticoid signal.