Leached components from dental composites in oral simulating fluids and the resultant composite strengths

The aim of this study was to analyse the leached moieties of dental composites after storage in ethanol and organic acids of plaque and further evaluate the resultant effect on the diametral tensile strength (DTS) of the composites. Three commercial composites were used: Bis-GMA-based Z100, Bis-GMA/UDMA-based Heliomolar, and Bis-MPEPP-based Marathon One. The solutions used were: 99·9% acetic acid, 99% propionic acid and 75% ethanol. Specimens (4 mm diam. × 2 mm thick) were stored at 37°C in 3 mL of solution for up to 30 days. Gas chromatography/mass spectrometry was used to characterize the leached moieties and DTS of the specimens after immersion was evaluated. Data were analysed using ANOVA and Tukey LSD test. The eluted substances were not all the same in different solutions and composites but mostly increased with immersion time, and included diluents (TEGDMA and decamethacrylate) and some additives, such as an ultra-violet stabilizer (TINUVINP), plasticizers (dicyclohexyl phthalate and bis(2-ethylhexyl) phthalate), initiator (triphenyl stibine), coupling agent (γ-methacryloxypropyl trimethoxysilane), and phenyl benzoate. The chief polymerizing monomers were not found. More kinds of components were found in the acetic acid and ethanol groups studied. The fewest kinds and quantities of leached moieties were found for Bis-GMA specimens and then Bis-GMA/UDMA ones, most of which are diluent agents. Bis-MPEPP specimens leached the most substances, which were composed mostly of a short phenyl group chain structure. The BisGMA composite showed the highest DTS (54·8 ± 5·7 MPa), which was not greatly affected by the length of storage. Bis-GMA/UDMA (36·2 ± 6·8 MPa) and Bis-MPEPP (26·1 ± 4·5 MPa) composites were significantly reduced (P < 0·05) after 30 days storage in the ethanol (35–50%), in the propionic acid (25–30%), and in the acetic acid (40–60%). Irreversible processes such as the leaching of components occur in fluids simulating an oral environment, which may contribute to irreversible material degradation, especially for non-Bis-GMA-based composites.     

Resinous perforation-repair materials inhibit the growth,attachment, and proliferation of human gingival fibroblasts

The choice of repair material is one of the important factors in the prognosis of the endodontically treated tooth with a perforation defect. The cytotoxicity of perforation-repair materials must be investigated to ensure a safe biological response. The aim of this in vitro study was to evaluate the effect of resin-modified, glass-ionomer cement, compomer, and resin on human-gingival fibroblasts. Human gingival fibroblasts from crown lengthening surgery were cultured by using an explant technique with the consent of the patient. Cytotoxicity was judged by using an assay of tetrazolium bromide reduction. The results showed that resin-modified, glass-ionomer cement Fuji II LC, compomer Compoglass, and resin SpectrumTPH (TPH) were cytotoxic to primary human gingival fibroblast cultures by inhibiting cell growth and proliferation. TPH alone had an effect on cell attachment. It was found that TPH was the most cytotoxic repair material among those tested in all cultures. The toxicity decreased in the order of TPH>FLC>CG.     

The application of mini-implants for orthodontic anchorage

The aim of this study was to explore the use of mini-implants for skeletal anchorage, and to assess their stability and the causes of failure. Forty-five mini-implants were used in orthodontic treatment. The diameter of the implants was 2mm, and their lengths were 8, 10, 12 and 14mm. The drill procedure was directly through the cortical bone without any incision or flap operation. Two weeks later, a force of 100-200g was applied by an elastometric chain or NiTi coil spring. Risk factors for the failure of mini-implants were examined statistically using the Chi-square or Fisher exact test as applicable. The average placement time of a mini-implant was about 10-15min. Four mini-implants loosened after orthodontic force loading. The overall success rate was 91.1%. The location of the implant was the significant factor related to failure. In conclusion, the mini-implants are easy to insert for skeletal anchorage and could be successful in the control of tooth movement.     

Metal ion release from new and recycled stainless steel brackets

As orthodontic appliances can corrode with time in the oral environment, the aim of this study was to compare the release of metal ions from new and recycled brackets immersed in buffers of different pH values over a 48 week period. To simulate commercial recycling, the stainless steel brackets were divided into two groups: new and recycled. The bases of the latter were coated with adhesive and the brackets were heat treated before being immersed in the test solution for 48 weeks. The release of nickel, chromium, iron, copper, cobalt and manganese ions was analysed by atomic absorption spectrophotometry. Differences were compared using one-way analysis of variance. The results showed that recycled brackets released more ions than new brackets (P < 0.05). Brackets immersed in solutions of pH 4 released more ions than those immersed in solutions of pH 7, and the total amount of ions released increased with time over the 48 week period (P < 0.05). This study demonstrates that both new and recycled brackets will corrode in the oral environment. To avoid clinical side-effects, metal brackets should be made more resistant to corrosion, and recycled brackets should not be used.     

Increased Young's modulus and hardness of Col1a2oim dentin

Mice harboring the Col1a2(oim) mutation (oim) express dentinogenesis imperfecta. To determine the effect of Col1a2 genotype on tissue mechanical properties, we compared Young's modulus and hardness of dentin in the 3 Col1a2 genotypes. Upper incisors were tested by nanoindentation. Genotype had a significant effect on Young's modulus, but there was not a simple mutant allele dosage relationship. The effect of genotype on hardness did not reach significance. Hardness and Young's modulus were greater near the dento-enamel junction than near the pulp chamber. Greater hardness and Young's modulus values near the dento-enamel junction reflected continued mineralization of the dentin following its initial synthesis. Analysis showed the mechanical data to be consistent with Fourier transform infrared and backscattered electron microscopy studies that revealed increased mineralization in oim bone. Analysis of the data suggests that clinical fragility of teeth in oim mice is not due to deficiencies of hardness or Young's modulus, but may be due to defects in post-yield behavior or resistance to fatigue damage.     

本科阶段口腔正畸教学模式与质量管理初探

口腔正畸学是口腔医学中专业性极强的分支学科,因而一直是口腔医学难教难学课程。本科生阶段正畸教学时数少,内容多,教学效果难以保证,理论与实践难以结合。医学院校的办学宗旨是培养掌握临床技能的创新人才,上海交通大学口腔医学院口腔正畸教研室为了更好培养适应社会需要,具有国际国内竞争力,适应不同层次要求的口腔医务工作者,坚持教学改革,加强质量管理,经过多年的教学实践,在教学改革和教学管理方面,取得了一些成绩。本文旨在分析正畸教学现状,探讨教学改革和教学质量管理的方法,为进一步深化教学改革、提高教学质量奠定基础。     

不同转流标准对颈动脉内膜切除术后脑梗死的影响

目的:颈动脉内膜切除术 (carotid endarterectomy, CEA)的麻醉管理要点是颈动脉阻断期间维持足够的颅脑灌注,放置转流管是外科常用方法之一,分析CEA手术不同转流标准对术后脑梗死的影响。方法:回顾收集2年内全身麻醉下接受CEA手术的443例患者,根据不同转流标准分为影像组 (以术前影像学资料作为是否转流的依据)和残端压组 (以术中残端压作为是否转流的依据)。分析患者术前人口学资料、既往病史、颈部血管狭窄程度、围术期各时间点血压情况、血管阻断时间、是否放置转流管、术后住院时间、住院期间脑梗死和其他不良事件,进行组间对比,在此基础上对组间差异有统计学意义的术前、术中情况进行倾向性评分匹配,分析不同转流标准对术后发生脑梗死的影响。结果:影像组患者268例、残端压组患者175例均接受全身麻醉下CEA手术,两组间基本情况和各时间点血压差异有统计学意义。经倾向性评分匹配后,匹配出影像组和残端压组各105例患者,两组患者的术前基本情况、各时间点血压差异无统计学意义。两组患者术后脑梗死发生率差异无统计学意义 (1.9% vs. 1.0%,P>0.999), 影像组术中转流率明显低于残端压组 (0 vs. 22.9%, P<0.001),影像组患者术后住院时间8 (7, 8) d明显长于残端压组5 (4, 6) d (P<0.001)。结论:依据术前影像学检查决定是否转流的患者组中,术中转流管使用率低于依据术中残端压决定是否转流的患者组,两组患者术后住院期间脑梗死的发生率差异无统计学意义,不同转流标准对患者脑梗死的影响有待于进一步深入研究。     

新型冠状病毒肺炎防控期间居家隔离人群心理健康状况调查及影响因素分析

目的 了解新型冠状病毒肺炎防控期间居家隔离人群心理健康状况并分析其影响因素,为进一步做好疫情防控工作,疏导不良情绪及心理恐慌提供依据.方法 选取2020年2月15 17日本研究团队7名研究生居住地为调查单位,采用自制一般情况调查表及12项一般健康问卷(GHQ-12)量表调查居家隔离的380人的心理健康状况.根据GHQ-12评分,将调查对象分为GHQ-12≥3分为阳性组(n=212)和GHQ-12＜3分为阴性组(n=168).采用Logistic回归模型分析居家隔离人群心理健康状况的影响因素.结果 两组在年龄、性别、是否独生子女、经济收入方面比较,差异无统计学意义(P＞0.05);而在居住地、婚姻状况、生育情况、担心感染、文化程度、职业方面差异有统计学意义(P＜0.05).多因素Logistic回归分析结果显示,居住地农村、初中及以下文化程度、已婚、学生、外出务工人员、担心感染是居家隔离人群心理健康的危险因素,年龄是其保护因素.结论 新型冠状病毒肺炎防控期间,居家隔离人群存在一定心理健康问题,其受多种因素影响.医院或社区卫生中心应针对不同人群进行心理疏导,改善其身心健康.