Smart materials in dentistry

Most dental materials are designed to have a relatively 'neutral' existence in the mouth. It is considered that if they are 'passive' and do not react with the oral environment they will be more stable and have a greater durability. At the same time, it is hoped that our materials will be well accepted and will cause neither harm nor injury. This is an entirely negative approach to material tolerance and biocompatibility and hides the possibility that some positive gains can be achieved by using materials which behave in a more dynamic fashion in the environment in which they are placed. An example of materials which have potential for 'dynamic' behaviour exists with structures which are partly water-based or have phases or zones with significant water content and for which the water within the material can react to changes in the ambient conditions. Such materials may even be said to have the potential for 'smart' behaviour, i.e. they can react to changes in the environment to bring about advantageous changes in properties, either within the material itself or in the material-tooth complex. The controlled movement of water or aqueous media through the material may cause changes in dimensions, may be the carrier for various dissolved species, and may influence the potential for the formation of biofilms at the surface. Some of these issues may be closely interrelated. Clearly, materials which do not have the capacity for water transport or storage do not have the potential for this sort of behaviour. Some materials which are normally resistant to the healthy oral environment can undergo controlled degradation at low pH in order to release ions which may prove beneficial or protective. It is doubtful whether such behaviour should be classified as 'smart' because the material cannot readily return to its original condition when the stimulus is removed. Other materials, such as certain alloys, having no means of transporting water through their structure, can display smart behaviour by undergoing predictable changes in structure in response to applied mechanical or thermal stimuli. It has been difficult to harness such behaviour to the benefit of patients but progress in this area is slowly being made.     

Chronic obstructive parotitis. Report of ninety-two cases.

Clinical, sialographic, and sequential quantitative scintigraphic characteristics of 92 cases of chronic obstructive parotitis (in 117 diseased parotid glands) are reported, and the treatment investigated. The cardinal feature of this disease is obstruction or retarded salivary flow resulting in recurrent swellings and retrograde infection. The main characteristic seen in sialograms is irregular dilation of the main and branching ducts. On the basis of sialographic findings, the ducts are classified into four types. This classification reflects the severity of the disease and can also be used as a guide to treatment.     

The effect of simvastatin on remodelling of the alveolar bone following tooth extraction

Suppression of residual ridge resorption after tooth extraction is a hot spot in dental research. Recently, simvastatin was reported to influence bone turnover by stimulating bone formation. In this study, the effect of simvastatin application on residual ridge resorption following tooth extraction was investigated. Sixty male Wistar rats were randomly divided into experimental and control groups (n=30). Polylactic acid/polyglycolic acid copolymer carriers, with or without simvastatin, were implanted into extraction sockets of right mandibular incisors. The rats were killed at 1, 2, 4, 8 or 12 weeks after implantation. The relative height of the residual alveolar ridge was significantly greater in the experimental compared to the control group at 2, 4, 8 and 12 weeks. The bone mineral density in the experimental group was significantly higher than that in the control group at 4, 8 and 12 weeks. A larger newly formed bone island was observed in the experimental group at 4 weeks, and higher bone formation rate and quality were found than in the control group at different time points except 1 week. The findings indicate that local application of simvastatin would effectively preserve the residual alveolar bone by promoting bone formation in the extraction socket.     

Association of vitamin D receptor gene polymorphisms in Chinese patients with generalized aggressive periodontitis

Background and Objective:  The clinical features suggest that genetic factors may have a strong influence on susceptibility to aggressive periodontitis. The aim of this study was to investigate the association of vitamin D receptor gene polymorphisms with generalized aggressive periodontitis in Chinese patients.
Material and Methods:  A restriction fragment length polymorphism (RFLP) for 10,438,141 C to T (rs1544410, Bsm I), 10,382,063 A to G (rs731236, Taq I), 10,382,143 C to A (rs7975232, Apa I) and 10,416,201 A to G (rs2228570, Fok I) of vitamin D receptor gene was analysed by polymerase chain reaction, followed by digestion with restriction enzymes and gel electrophoresis. The genotypes of 51 generalized aggressive periodontitis patients and 53 periodontally healthy control subjects were analysed. The genotypic and allelic frequencies of each polymorphism site for the patients and control subjects were compared.
Results:  The distribution of vitamin D receptor Fok I genotypes and alleles between the two groups was significantly different ( p =  0.043 and p  = 0.012, respectively). The F allele seemed to increase the susceptibility of aggressive periodontitis (odds ratio = 2.02, 95% confidence interval = 1.16–3.50) in Chinese patients. There was no significant difference in the genotype distribution or the allele frequencies of vitamin D receptor Bsm I, Apa I and Taq I between two groups.
Conclusion:  The study indicates that Fok I polymorphism of vitamin D receptor gene might be associated with generalized aggressive periodontitis in Chinese patients. In addition, the carriage of F allele increases the risk of developing generalized aggressive periodontitis.     

In vitro antifungal susceptibility to six antifungal agents of 229 Candida isolates from patients with diabetes mellitus

The most common antifungal drugs in current clinical use for the treatment of oral candidosis are polyenes and azoles, mainly used topically. Poor glycaemic control in association with other local factors, such as the presence of oral dental prostheses, salivary pH, salivary flow rate and tobacco habits, may lead to the development of oral candidosis. Topical antifungal agents are frequently used to prevent the development of candidal infections in patients with poor metabolic control, particularly in the elderly wearing dentures. The aim of this study was to assess the antifungal susceptibility of Candida isolates to six antifungal agents using a commercially available kit, Fungitest. The isolated were collected from patients affected by diabetes mellitus from two different geographic localities (London, UK, and Parma, Italy) and from a group of healthy non-diabetic subjects. No differences in antifungal susceptibility to the six agents tested were observed between Candida isolates from diabetic and non-diabetic subjects. However, differences were observed between the two geographically different diabetes mellitus populations. Oral yeast isolates from diabetes mellitus patients in the UK more often displayed resistance or intermediate resistance to fluconazole (P=0.02), miconazole (P<0.0001), and ketoconazole (P=0.01) than did isolates from diabetes mellitus patients in Italy. In addition, more C. albicans isolates were found in diabetic and non-diabetic subjects that were susceptible to fluconazole (P=0.0008 and P=0.01, respectively) than non-albicans isolates. The difference in the antifungal resistance of isolates from the two populations of diabetes mellitus patients may be related to differences in the therapeutic management of candidal infections between the two centres.     

粘液表皮样癌细胞中脆性组氨酸三聚体基因异常表达的研究

目的：检测粘液表皮样癌细胞中FHIT基因的异常表达。方法：应用逆转录巢式聚合酶链反应（RT－PCR）及DNA测序技术检测粘液表皮样癌和粘液表皮样癌细胞中FHIT基因表达情况。结果：粘液表皮样癌细胞系细胞中存在FHIT基因部分缺失，产生异常转录本，大小约247bp.FHIT基因mRNA异常转录本为多个外显子缺失所致，E1－E8全部缺失。结论：FHIT基因在粘液表皮样癌细胞中的异常表达可能在粘液表皮样癌的发生和发展中起作用。     

Effectiveness and dentin bond strengths of two materials for reinforcing thin-walled roots.

OBJECTIVES: To investigate the effectiveness of two restorative materials for reinforcing thin-walled roots and their microtensile bond strengths to root canal dentin. METHODS: Twenty-one decoronated maxillary central incisor roots were root filled and the canals enlarged to leave approximately 1.0 mm thick dentin walls. The roots were distributed randomly to three equal groups. Group 1 (control): a large tapered cast post-core was fabricated. Group 2 (BIS-CORE): a thick layer of dual-cured composite was placed in the post-hole before fabrication of a small-diameter tapered cast post-core. Group 3 (ChemFil Superior): a thick layer of glass-ionomer was placed, as before. Metal-ceramic crowns were fabricated for all teeth. Microtensile bond strength tests and optical and atomic force microscope observations were employed to examine adhesion between the two restorative materials and the root canal dentin. RESULTS: Mechanical loading (kN) demonstrated that composite 0.64 (S.D. 0.05), but not glass-ionomer 0.49 (0.05), significantly reinforced the fracture resistance of thin-walled roots, P<0.001. Microtensile bond strengths (MPa) were 21.7 (1.6) for composite and 12.9 (1.7) for glass-ionomer, P=002. SIGNIFICANCE: A thick intermediate layer of resin-bonded composite, sandwiched between the root dentin and a small-diameter cast Ni-Cr post or dowel, increased significantly the fracture resistance of the roots.     

载rhBMP2凝胶微球控释系统的设计与合成实验

目的:设计与合成rhBMP2新型控释载体,初步探讨其载药及降解性能。方法:用右旋糖酐 (dextran,dex)与甲基丙烯酸缩水甘油酯(glycidylmethacrylate,GMA)合成甲基丙烯酸缩水甘油酯右旋糖酐 (dex GMA),测定该凝胶微球溶胀系数Q,并对其载药、降解性能进行初步研究。结果:dex GMA在一定条件下可以成球,粒径与制备工艺密切相关;该凝胶微球溶胀参数 10. 9±5. 3;载药性能良好,在葡聚糖酶的作用下 20~40d内可以完全降解。结论:右旋糖酐基凝胶微球具有良好的溶胀性能,可生物降解,其粒径可控,作为生长因子载体,有望达到控释给药的目的,其制备工艺及理化性能有待进一步研究。     

错(牙合)患者β角的临床评价

目的推介一种新的准确评价上下颌骨矢状向关系的头影测量方法:β角.方法β角由A点、B点、髁状突中点三个骨性标志点构成,测量值反应上下颌骨在矢状方向的不调;样本选取137名患者,按照3项标准分三组,分别反应三种错(牙合)类型,并计算均数和标准差.结果安氏Ⅰ类错(牙合)β值为36.42°±3.33,安氏Ⅱ类错(牙合)的β值为26.88°±6.81,安氏Ⅲ类错(牙合)的β值为45.36°±3.68;各组β值在性别上没有显著性差异.结论β角能反应上下颌骨的矢状关系,β值在33°-39°之间为安氏Ⅰ类错(牙合)畸形,安氏Ⅱ类错(牙合)β角较锐,安氏ⅢⅡ类错(牙合)患者的β角较钝.     

Analysis of lateral tooth movement during forced orthodontic eruption

STATEMENT OF PROBLEM: Forced eruption is a prosthodontic procedure that enables the treatment of otherwise problematic restorative conditions. During the vertical orthodontic movement, the root may be moved laterally, affecting the position of a tooth in the arch. PURPOSE: This study quantified the degree of lateral movement possible during the eruptive procedure and addressed the significance of this movement from a theoretical and clinical standpoint. MATERIAL AND METHODS: A patient treatment, which demonstrated the movement in a single direction on the buccolingual axis, was isolated. On the basis of this theoretical model, a clinically relevant model was developed: A "worst-case" situation for each posterior tooth was calculated, from which clinical conclusions may be derived. RESULTS:. In a given extrusion angle of 30 degrees, a lateral movement/shift of 0.58 mm resulted per 1 mm of eruption distance. The lateral movement for every millimeter of eruption and the maximum extrusion angle for each of the maxillary and mandibular posterior teeth were calculated. CONCLUSION: The lateral movement that accompanies the forced eruption procedure may compromise or be used to esthetically enhance prosthodontic treatment.