Chinese Journal of Dental Research, 03/2017

Objective: To explore the effect of long-term stress on the temporomandibular joint (TMJ) condyle and its possible underlying mechanism. Methods: A 12-week, chronic unpredictable mild stress (CUMS) model was used to induce long-term psychological stress in rats. Rats were randomly divided into control group (CONT), chronic unpredictable mild stress group (CUMS) and chronic unpredictable mild stress with fluoxetine treatment group (CUMS + DT) (n = 30 per group). A 5 mg/kg dose of fluoxetine was intraperitoneally injected daily 0.5 h before stress. A sucrose preference test, plasma corticosterone test and open-field test were performed to verify the feasibility of the CUMS model. Histopathology was used to observe the pathological changes of condyle. The expression levels of inflammatory cytokines, matrix metalloproteases (MMPs) and extracellular matrix (ECM) were measured by real-time polymerase chain reaction, western blotting and immunohistochemistry. Results: At 8 and 12 weeks after exposure to CUMS, the rats showed higher plasma corticosterone than the control rats. Additionally, for the open-field test, the rats exposed to CUMS spent more time in the centre zone and moved a shorter distance than the control and drug treatment rats. In addition, pathological changes in the condylar cartilage occurred in the 8-week CUMS subgroup and were more obvious in the 12-week CUMS subgroup. The CUMS caused an increase in the secretion of inflammatory cytokines, imbalanced expression of MMPs and tissue inhibitor of metalloproteinase-1 and accelerated degradation of ECM in condylar cartilage in a time-dependent manner. Conclusion: Osteoarthritis-like lesions can be caused by long-term CUMS in the mandibular condyles, which suggests that the imbalance in chondrocyte-secreted regulatory factors within the cartilage of the TMJ may play an important role in cartilage injury induced by psychological stress. Keywords: chronic unpredictable mild stress, condylar cartilage, temporomandibular disorder (TMD), extracellular matrix, matrix metalloproteinase (MMP), tissue inhibitor of metalloproteinase-1 (TIMP)

Objective: To evaluate and compare certain mechanical properties and wear of five commercial short-fibre reinforced composites (Alert, EasyCore, Build-It, TI-Core, and everX Posterior), in relation to their microstructural characteristics. Methods: Fracture toughness, work of fracture, and flexural strength were determined for each material following ISO standards. The specimens (n = 6) were dry stored (37 °C for 2 days) before they were tested. A wear test was conducted with 15,000 chewing cycles using a dual-axis chewing simulator. Wear pattern was analysed by a three-dimensional (3D) noncontact optical profilometer. Scanning electron microscopy (SEM) was used to evaluate the microstructure of each composite material. The results were statistically analysed using ANOVA followed by post hoc Tukey's test. Results: everX Posterior exhibited the highest fracture toughness (2.4 MPa m1/2) among the materials tested (P 0.05). EasyCore presented the highest flexural strength (125.4 MPa), which was not significantly different (P > 0.05) from Alert (119 MPa) and everX Posterior (120 MPa). Lowest wear values were found for EasyCore and Build-It (19 and 22 µm). TI-Core showed significantly higher wear depth (45 µm) than all other materials (P 0.05). Conclusion: Significant differences between commercial short-fibre reinforced composites were found for fracture toughness and wear. Keywords: fracture toughness, short fibre composite, wear

Objective: To analyse the microbiome composition of health and gingivitis in Chinese undergraduates with high-throughput sequencing. Methods: Sequencing of 16S rRNA gene amplicons was performed with the MiSeq system to compare subgingival bacterial communities from 54 subjects with gingivitis and 12 periodontally healthy controls. Results: A total of 1,967,372 sequences representing 14 phyla, 104 genera, and 96 species were detected. Analysis of similarities (Anosim) test and Principal Component Analysis (PCA) showed significantly different community profiles between the health control and the subjects with gingivitis. Alpha-diversity metrics were significantly higher in the subgingival plaque of the subjects with gingivitis compared with that of the healthy control. Overall, the relative abundance of 35 genera and 46 species were significantly different between the two groups, among them 28 genera and 45 species showed higher relative abundance in the subjects with gingivitis, whereas seven genera and one species showed a higher relative abundance in the healthy control. The genera Porphyromonas, Treponema, and Tannerella showed higher relative abundance in the subjects with gingivitis, while the genera Capnocytophaga showed higher proportions in health controls. Porphyromonas gingivalis, Prevotella intermedia and Porphyromonas endodontalis had higher relative abundance in gingivitis. Among them, Porphyromonas gingivalis was most abundant. Conclusion: Our results revealed significantly different microbial community composition and structures of subgingival plaque between subjects with gingivitis and healthy controls. Subjects with gingivitis showed greater taxonomic diversity compared with periodontally healthy subjects. The proportion of Porphyromonas, especially Porphyromonas gingivalis, may be associated with gingivitis subjects aged between 18 and 21 years old in China. Adults with gingivitis in this age group may have a higher risk of developing periodontitis. Keywords: gingivitis, high-throughput sequencing, microbiome, undergraduates

Objective: To explore the relationship between single nuclear polymorphisms (SNPs) in ectodysplasin A receptor (EDAR) and EDAR-associated death domain (EDARADD) genes and non-syndromic tooth agenesis. Methods: Ten putative SNPs in EDAR and EDARADD were selected, and a case-control study was conducted in 112 subjects with non-syndromic tooth agenesis and 112 normal control subjects. DNA was obtained from peripheral blood samples. Genotyping was performed by Sanger sequencing. Results: Three SNPs (rs3749098, rs3749099, and rs10432616) in EDAR exhibited significant differences in the alleles and/or genotype frequencies between the case group (individuals with non-syndromic tooth agenesis) and control group (normal individuals). The T allele was identified in the SNP rs3749098 in 99.1% of the case group and in 96.0% of the control group (P = 0.0326). Regarding the SNP rs3749099, the C allele was identified in 99.1% of the case group and in 96.0% of the control group (P = 0.0326). Regarding the SNP rs10432616, the C allele was identified in 97.8% of the case group and in 100.0% of the control group (P = 0.0245). Conclusion: Our results suggested that SNPs in EDAR could be a pathogenic factor for non-syndromic tooth agenesis. Furthermore, EDAR can be regarded as a marker gene for the risk of tooth agenesis. Keywords: case-control study, ectodysplasin A receptor, non-syndromic tooth agenesis, single nucleotide polymorphism

Objective: To evaluate the effect of chlorhexidine and ethanol on microleakage of composite resin restoration to dentine. Methods: Class II cavities with dentinal margin were prepared on 96 premolar teeth. All specimens were acid-etched, rinsed and dried. Then the samples were randomly divided into four groups according to pre-treatment of the dentine: no treatment (control group); treatment with 100% ethanol for 60 s (group 2); treatment with 2% chlorhexidine for 60 s (group 3); 100% ethanol for 60 s and then 2% chlorhexidine for 60 s (group 4). After dentine treatment, each group was bonded and restored with a universal micro hybrid composite resin, according to the manufacturers' recommendation. Microleakage was evaluated by dye extraction method in two subgroups, immediately (24 h) and after 6 months in storage. Scan electronic microscope analyses for two samples of each group were also conducted. Data were analysed by two-way analysis of variance and Tukey test. Results: The lowest and the highest amount of microleakage were observed in the ethanol group and in the control group, respectively. There were significant differences in microleakage among the groups (P = 0.003) and between measurement times (P = 0.001). For each storage time, the control group showed significant differences from the other groups and there were no differences between the other groups. Conclusion: Ethanol-wet bonding and chlorhexidine application may have potential benefits in lowering the occurrence of microleakage in the long term. Keywords: chlorhexidine, ethanol, microleakage, surface treatment

Osteosarcomas are especially rare in the mandible and maxilla, representing 1.6% of all bony malignant tumours. In this article, we described a case of osteosarcoma of the mandible. Computed tomography (CT) image showed a well-circumscribed homogeneous mass, with nonhomogeneous contrast enhancement. T1-weighted magnetic resonance imaging (MR) image showed intermediate signal intensity on, and after administration the lesion showed signal intensity lower than muscle. T2-weighted MR image showed heterogeneous high signal intensity. Bone scintigraphy revealed monostatic involvement of the mandible with a homogenous intense uptake pattern. Ga-67 citrate scintigraphy revealed significantly increased uptake. Histopathological examination confirmed the diagnosis of osteosarcoma. Keywords: CT, MRI, osteosarcoma, scintigraphy

This report gives a brief introduction to the Virtual Simulation Teaching Centre of Fujian Medical University School of Stomatology (VSFMUSS), China. As one of the best dental simulation laboratories in China, the VSFMUSS aims to train dental students and clinicians to be professionals who are able to provide optimal oral health care by giving them the best virtual patient care experience possible in a nonclinical setting. The features, achievements and future directions of the VSFMUSS are addressed. Moreover, the role of the VSFMUSS was evaluated and discussed based on the students' and faculties' perceptions, rate of employment after graduation, and so on. Keywords: dental education, teaching centre, virtual reality