Die-spacing technique by diffusion precipitation

Abstract – The present study has shown that it is possible by utilizing the principle of diffusion to precipitate on stone dies an adequate resin spacer of uniform and desirable thickness. Details and variables of the technique are described. The precipitation technique is simple and requires a minimum of time and equipment. This spacer technique opens up gateways for a new and improved casting technique cleared of most of the variables affecting the precision of the methods employed up till now. A new gypsum bonded investment for the new casting technique is being developed.     

Finite Element Stress Analysis of IMZ Abutment Designs: Development of a Model

Purpose This article describes the development of a model system for use in finite element stress analysis of three different IMZ abutment designs: original threaded Intra-Mobile Element (IME), Abutment Complete (ABC), and Intra-Mobile Connector (IMC). Materials and Methods A three-dimensional model simulating a cast gold crown restoration attached to an osseointegrated IMZ implant fixture was generated for each abutment design. Each model was discretized into axisymmetric finite elements representing the crown, the various implant system components, and supporting structures. A convergence test was performed to optimize the mesh. Convergence test mesh refinement for the IME, the IMC, and the ABC abutment models resulted in 818 elements, 2,566 nodes; 738 elements, 2,362 nodes; and 663 elements, 2,051 nodes, respectively. Progressive tightening of the retaining screw (preload) was simulated; the degree of screw tightening necessary to prevent opening of the crown-abutment interface in extreme loading (500-N occlusal load at 45°) was determined individually for each system. Conclusions Models of three IMZ abutment designs have been refined and the appropriate relative screw preloads determined. This model system is to be used subsequently in stress analysis comparison for the three systems.     

Deflection and Stress Distribution in Three Different IMZ Abutment Designs

Purpose The purpose of this study was to compare the stress distribution in the resin element and the retaining screw for three different IMZ prosthetic systems: 1) original threaded Intra-Mobile Element (IME); 2) Abutment Complete (ABC); and 3) Intra-Mobile Connector (IMC). This stress distribution comparison was then related to variations in deflection of the prosthetic superstructure. Materials and Methods Employing the finite element method, a three-dimensional model simulating a cast gold restoration attached to an osseointegrated IMZ implant fixture was generated for each system. The representation of the implant fixture, the supporting structures, and the external contours of the crown were identical in the three models, while the configuration of the abutment varied to characterize the individual systems. Each model was discretized into axisymmetric finite elements representing the crown, the various implant system components, and supporting structures. A series of harmonic functions was written to define non-axisymmetric loads of 100 N and 500 N evenly distributed over the entire occlusal surface of the crown. Each load was applied individually to the models, first in a vertical direction, and then at a 45° angle to the median plane. Predicted deflection and stress distributions were computed and plotted for each loading condition of each model. Results Deflections measured at the buccal cusp tip ranged from 0.002 mm (100-N load applied vertically to the ABC model) to 0.802 mm (500-N load applied at 45° to the IME model). Maximum effective stresses in the retaining screw ranged from 129 MPa (100-N load applied vertically to the ABC model) to 1,315 MPa (500-N load applied at 45°C to the IMC model). A correlation was observed between the peak stresses in the screw and the deflection of the superstructure. Conclusions Deflections and stress concentrations with the IMC were predicted to be in the same range as with the IME, but much greater than with the ABC.     

牙本质处理剂对粘结影响的扫描电镜观察

应用扫描电镜观察使用两种不同牙本质粘结系统的树脂与牙本质粘结情况，结果发现：粘结界面有广泛密集的树脂突形成，树脂突又有旁侧分枝，彼此相加成网状，产生良好的机械固位，讨论分析了牙本质处理剂的作用，对于是否去除玷污层，应视牙本质处理剂的种类与性质而定。     

江苏省水厂源水中有机物污染现状研究

对江苏省12个水厂的源水浓集物用气相色谱/质谱仪进行了有机物分析,共检出229种次有机物,并对其中133种次主要有机物进行了定量。结果表明,苏南水厂源水中检出的有机物总数、优先监测污染物数及它们的检出浓度一般高于苏北水厂源水中的检出结果,说明苏南水厂源水受有机物污染比苏北更为严重。     

用大孔离子交换树脂从人尿中提取尿激酶

筛选得到一种大孔离子交换树脂（ＨＤ－２），用于从新鲜人尿提取尿激酶，树脂用量为０．１２％（ｗ／ｖ），收率为８５．０％，所得粗酶比活为５７３．０ＩＵ／ｍｇ。整个提取工艺简单、快速，成本低，有较大的推广潜力。     

SEM study of surface characteristics and marginal adaptation of anterior resin restorations after 3–4 years

SEM replica technique was. used to study surface characteristics and marginal adaptation of278 anterior resin fillings. 3-4 yr old. The fillings showed degradation of surfaces and margins with eroded areas and exposed macro- and microfiller particles. Cohesive failures were seen as chip fractures and marginal fractures parallel to the cavity margins. Microfiller resin fillings showed less rough surface characteristics than the conventional and hybrid composite resins in spite of a higher frequency of fillings with surface degradation. The microfiller resin fillings activated by visible light, in particular, showed relatively smooth surface characteristics with less surface degradation and less porosity. About 50% of the conventional and hybrid composite fillings showed marginal defects. The two chemically cured microfiller resin fillings showed marginal defects in 66% or 88%, whereas for the visible light cured microfiller resin fillings defects were observed in 44%.     

In vivo abrasion of Profile and Adaptic composite resins

Abstract – Thirty-six Class I cavities in mandibular molars from 18 schoolchildren were filled with Profile or Adaptic using the acid etch technique. Impressions were taken at 6-month intervals and abrasion was recorded by measuring the increasing height of the exposed cavity walls on cast models. The mean abrasion for Adaptic was 61.4 μm per yr and for Profile 28.7 μm per yr.     

Clinical evaluation of six composite resins in posterior teeth

Six different composite resin restorative materials were placed in posterior Class I and Class II cavities and evaluated at one and two years after placement for colour, marginal discoloration, and wear. Wear was determined by comparison with standard models and by SEM. All materials darkened over the study period but remained an acceptable match. Marginal discoloration increased. The trend of relative wear was in accordance with predictions from fracture mechanics. Insufficient restorations in one material were available at two years for it to be included in the results. The microfine materials used in this study suffered surface damage (micro-chipping) in high stress areas, again consistent with fracture mechanics predictions.