Comparative study of two filling techniques using glass-ionomer (Ketac-endo) root canal cement on fracture resistance of endodontically treated roots (in vitro)

Forty freshly single rooted teeth were selected for this study. The coronal part of teeth were decapitated and the root canals were prepared by modified step-back technique with K-flex files to size 35# at the apex, five ml of 5.25% NaOCl was used as irrigating solution. According to the dentin thickness at the mesio-distal direction of the prepared roots, roots were divided into two groups: Group (I), dentin and cementum thickness from 1.5-2 mm, and Group (II), dentin and cementum thickness 1 mm. According to the filling technique used the teeth were subdivided into four subgroups each of five teeth; Subgroup (A) single gutta-percha cone and Ketac-endo root canal sealer, Subgroup (B) lateral condensation technique with gutta-percha and Ketac-endo sealer, Subgroup (C) laterally condensed gutta-percha with Roth 801 cement and Subgroup (D) teeth left unfilled as negative controls. The prepared roots were placed into acrylic resin so that 10 mm of the root was exposed. A slowly increasing force was applied vertically using a blunt punch with 1 mm tip thickness attached to Instron testing machine. The results showed that group (I) with 1.5-2mm dentin thickness required greater force to fracture in all experimental groups, than that of group (II) with 1 mm dentin thickness. So the amount of remaining dentin thickness significantly affected the resistance to fracture of the prepared roots.     

Histo-pathological study of a glass-ionomer/resin (Geristore) restoration system

The purpose of this experiment was to investigate histo-pathologically the pulpal reaction to a glass-ionomer/resin (Geristore) restoration system in human teeth. Black's class I cavities were prepared in 22 human teeth; these were divided into 2 groups, one with the Geristore after cavity was cleaned with 10% NaOCl solution and 3% H2O2 solution (Group G) and the other with the Geristore after the cavity was applied with Mirage-Bond (Group MG). The treated teeth were observed clinically over 90 days after operation. They were then extracted for histological examination. No unpleasant symptoms were noted. A few pathological changes were observed. No histo-pathological score differences were observed between groups G and MG. The average evaluation score of pathological results in both groups G and MG were excellent. Microorganisms observed in the cavity dentin of the group G was fewer than in group MG. In some cases, microorganisms were observed along the dentin walls. In conclusion, the pulpal injury due to this Geristore restoration system was slight, and the system was considered to be safe for the pulp and clinically useful.     

Effect of moisture protective coatings on the strength of a modern metal-reinforced glass-ionomer cement

The strength of a modern, low metal:glass ratio, metal-reinforced glass-ionomer cement was measured evaluating a number of protective barriers: one light-cured resin, two solvent-based dental varnishes and petroleum jelly. The cement was exposed to water at 10 and 60 min from start of mix. The results obtained with these protecting agents were compared with those obtained where no protection was applied. A comparison of uniaxial flexural strength and biaxial flexural strength showed the latter to be more discriminating. Proprietary dental varnishes were superior to petroleum jelly, producing similar strengths of 50 MPa. Petroleum jelly was, however, preferable to no protection. Moisture protection during the first 30 min was found to be beneficial, thereafter no further strength increase was found. A second material, a cement which has a high metal:glass ratio, was found to be more moisture resistant but weaker in strength than the modern material, with a biaxial strength of 39 MPa.     

Fluoride release process of (resin-modified) glass-ionomer cements versus (polyacid-modified) composite resins

The fluoride release of conventional and resin-modified glass-ionomers is reviewed and compared to that of fluoride-releasing (polyacid-modified) composite resins. Each formulation displays a typical fluoride release profile. The cumulative amount of fluoride released is described by [F]c = [F](I)t/(t + t1/2) + beta square root t for glass ionomers whether resin-modified or not, whereas for composite resins this quantity is given by [F]c = [F](I)t/(t + t1/2) + alpha t. Both equations indicate that two kinetic processes are responsible for the fluoride release profiles. The kinetic parameters [F](I), t1/2, beta and alpha depend on the formulation. On the basis of the exchange characteristics for fluoride, an attempt is made to explain the mechanisms responsible for these fluoride release processes.     

Prevention of tooth hypersensitivity caused by the hydrodynamic action of zinc phosphate and composite resin luting cements (SEM) study

This study was done to determine the role of cement liner as a reducing factor to the fluid movement in order to prevent tooth hypersensitivity according to the hydrodynamic theory during cementation of crowns. A total of fourty freshly extracted intact lower molar were selected for this study. After conventional tooth preparation the teeth were sub-divided into four equal groups to identify the role of cement liner in preventing the penetration of used cement into the dentinal tubules. Scanning electron microscopic study proved the efficiency of glass ionomer liner on preventing cement penetration into the dentinal tubules.     

The effect of pulpal fluid flow on tensile bond strength of a glass-ionomer cement: an in vivo and in vitro comparison

Previous studies of the bonding capabilities of glass-ionomer cements have concentrated on the use of in vitro testing conditions. Since early moisture contamination appears to have adverse effects on the physical properties of glass-ionomer cements, and with the probability of pulpally derived dentinal fluid being present under in vivo conditions, the objective of this study was to compare in vivo tensile bond strength with in vitro tensile bond strength of a glass-ionomer cement to dentin utilizing the same teeth under similar test conditions. A glass-ionomer lining cement was placed on freshly exposed labial dentin of the maxillary incisor on 10 Rhesus monkeys. Immediately following placement, an orthodontic button was placed over the cement and left undisturbed for 1 hour. The teeth were then extracted and stored in 100% relative humidity for 23 hours. An Instron testing machine was used to register in kilograms the force required to cause tensile bond failure of the cement. Identical methodology was then used on the same teeth for in vitro testing. The concluding results indicate that a statistically significant difference (P < or = 0.05) exists between in vivo and in vitro tensile bond strengths of the glass-ionomer lining cement and that the bond failure was cohesive in character for all cases both in vivo and in vitro. These findings suggest that clinically, tensile bond strengths of glass-ionomer cements to cut dentin can be expected to be weaker in vital teeth than in devital teeth.     

Evidence of alae in Aelurostrongylus abstrusus larvae examined by scanning electron microscope (SEM)

Aelurostrongylus abstrusus larvae lateral alae, previously noticed in cat lung sections, are described by SEM in larvae found in the faeces of an infected cat.     

Chemistry of glass-ionomer cements: a review

Genetic susceptibility to toxic chemicals is of major importance but most studies concentrate on candidate genes and searches for unknown susceptibility genes are uncommon. Human sporadic porphyria cutanea tarda is usually precipitated by alcohol, oestrogens, hepatitis viruses, HIV or haemodialysis. The mechanism is not known but there is a role for iron metabolism and an underlying genetic predisposition is suspected. A similar porphyria in humans has also been caused by hexachlorobenzene. These human porphyrias can be modelled in iron-loaded mice exposed to hexachlorobenzene, in which C57BL/10ScSn is a prototype susceptible strain whereas DBA/2 mice are extremely resistant. A search for susceptibility genes was undertaken using complex trait analysis with DNA microsatellite markers of 'high' and 'low' responders from an F2 intercross. Correlation of markers with susceptibility, defined as accumulation of uroporphyrin in the liver, was assessed by chi-squared test for the proportion of C57BL/10ScSn and DBA/2 alleles present. Susceptibility loci on chromosomes 12, 14 and 17 were identified. Further analysis of markers on chromosomes 14 and 17 by MAPMAKER/EXP and MAPMAKER/QTL gave LOD scores of 7.3 and 3.6, respectively. Typing of chromosome 12 for the Ahr gene, using a restriction fragment length polymorphism distinguishing between the b-1 and d alleles, gave significant but not perfect linkage. However, no strong association between alleles or expression of Cyp1a1/2 genes, regulated by Ahr, and susceptibility for porphyria was detected. The results demonstrate that the porphyria induced by hexachlorobenzene in C57BL/10ScSn mice is a complex trait determined by at least three genes, which may be of relevance to susceptibility in the development of sporadic porphyria cutanea tarda and unknown aspects of liver damage.     

Clinical results of the modular porous-coated anatomic (PCA) total knee arthroplasty with cement: a 5-year prospective study

Our study examines the clinical, radiographic, and patient satisfaction outcome of the cemented Modular Porous-Coated Anatomic (PCA) total knee arthroplasty with a minimum 5-year follow up. All data were gathered prospectively and consecutively. Patient satisfaction was assessed with a self-administered survey. Statistical analysis examined the effect of 17 patient factors, 19 surgical factors, and postoperative continuous passive motion use on range of motion (ROM) and HSS scores at 2 years. Seventy-eight Modular PCA arthroplasties performed by 9 orthopedic surgeons on 71 patients between January 1988 and November 1989 are reported in this study. Preoperative HSS scores averaged 51.2 and improved to an average of 89 at 1 and 2 years, and 86 at 5 years after surgery (90% good or excellent). ROM changed after surgery through improvement in preoperative knee flexion contracture, but not in increased knee flexion. One patient underwent reoperation for patellar instability, and one patient's arthroplasty was revised at 53 months for late instability. The total reoperation rate for any reason was 7.7%. Zonal analysis for progressive radiolucency at the bone-cement interface showed increasing frequency of narrow (< 1 mm) radiolucencies concentrated on the anterior and medial aspect of the tibial tray. Ninety-eight percent of patients responded to an outcome questionnaire, and 96% rated themselves improved. The Kaplan-Meier probability of an implant surviving without loosening at 5 years was 100%. The Modular PCA TKA has a low incidence of patellofemoral problems, is clinically successful, and results are stable at a minimum 5-year follow-up examination.     

SEM原位观察ZK60(0.9Y)镁合金板材的断裂行为

利用原位拉伸扫描电镜观察,研究ZK60合金及含稀土Y的ZK60(0.9Y)合金热轧板材动态拉伸过程中裂纹萌生和扩展情况,讨论合金的显微组织与断裂行为的相互关系.实验表明:在拉伸过程中,合金轧制态试样裂纹以撕裂的形式进行扩展,断口区域有解理、准解理断裂痕迹,ZK60(0.9Y)合金裂纹萌生所需载荷大于ZK60合金,且在拉伸过程中发生第2相的破碎,主裂纹沿第2相扩展,基体中的二次裂纹多萌生于第2相周围.     

Interfacial characteristics of resin-modified glass-ionomer materials: a study on fluid permeability using confocal fluorescence microscopy

The tooth interface with resin-modified glass-ionomer cements (RM GICs) is poorly understood. This study examined the interface, especially with dentin. Cervical cavities in extracted teeth were restored with Fuji II LC, Vitremer, Photac-Fil, or a conventional GIC, Fuji Cap II. Fluorescent dye was placed in the pulp chambers for 3 hrs before the specimens were sectioned. Examination of the tooth/material interface with a confocal microscope showed that dye uptake by the restoration varied among materials. A "structureless", non-particulate, highly-stained layer of GIC was observed next to dentin in Fuji II LC. This layer varied in width, was prominent where the dentin tubules were cut "end-on" and in areas closer to the pulp, and was not seen adjacent to enamel. Vitremer showed minimal dye uptake, and the "structureless" layer was barely discernible. Photac-Fil showed more uniform uptake and absence of this layer. Cracking of enamel was also noted with these materials. The conventional GIC did not show any dye uptake, presence of a "structureless" layer, or enamel cracking. We elucidated the potential mechanisms involved in the formation of a "structureless" interfacial layer in Fuji II LC by studying the variables of cavity design, surface pre-treatment, water content of the tooth, time for it to develop, early finishing, and coating of the restoration. This layer, the "absorption layer", is probably related to water flux within the maturing cement, depending on environmental moisture changes and communication with the pulp in a wet tooth. The "micropermeability model" was useful in this study of the interfacial characteristics of RM GICs.     

粉煤灰和木钙双掺用于胶结充填的正交组合试验

通过粉煤灰和木钙双掺用于尾砂胶结充填的交组合试验，提示了双掺的作用机理，建立了试验指标的二次回归程，得出了双掺时粉煤灰和木钙的最佳掺量。     

Variability in cytotoxicity and fluoride release of resin-modified glass-ionomer cements

New-generation glass-ionomer cements contain resin to improve their restorative properties. These resin-modified glass-ionomer cements vary considerably in their chemistry, which could result in corresponding variability in their physical and biological properties. This study investigated the cytotoxicity and the fluoride release of two resin-modified glass ionomers, a conventional glass-ionomer cement, and a resin composite. Samples were prepared and extracted in distilled water for 1, 4, and 7 days; eluates were filtered and tested by means of 3T3 mouse fibroblasts. Cytotoxicity (MTT assay) values were low for all materials and extraction times, indicating minimal cytotoxicity of all materials (less than 30% inhibition). Cytotoxicity of one resin-modified glass ionomer was significantly higher than for the other materials (p < 0.001). One resin-modified glass ionomer and the conventional glass-ionomer cement released significantly more fluoride at each time interval (p < 0.001) than the other resin-modified glass-ionomer cement and the resin composite. Fluoride release and cytotoxicity were correlated (r2 = 0.60; p < 0.001), although the fluoride release does not account for the cytotoxicity observed. Cytotoxicity and fluoride release suggest that one hybrid behaved more like a conventional glass ionomer, and the other like a resin composite. These differences may have implications for material selection in specific clinical situations.     

Early Stages of Recrystallization in Equal-Channel Angular Pressing (ECAP)-Deformed AA3104 Alloy Investigated Using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) Orientation Mappings

Early stages of recrystallization in alloys containing complex structure of second phase particles are of considerable practical interest. They were observed for the AA3104 alloy in which large particles occur against the background of randomly distributed dispersoids. The samples were deformed by equal channel angular pressing and then slightly annealed to obtain the state of partial recrystallization. The highly deformed alloy contained a structure of flat grains with the spacing between high-angle grain boundaries ranging from 100 nm to 1 ??m. On annealing, the structure coarsened and got transformed into nearly equiaxed grains by both discontinuous and continuous recrystallization. The nucleation of new grains was observed in statically recrystallized bulk samples using scanning electron microscopy, and during in-situ recrystallization in a transmission electron microscope. Special attention was paid to the nucleation of new grains in areas close to large second phase particles, where a relatively high stored energy was expected to stimulate nucleation. A particular role in the rise of nuclei is attributed to migration of low angle boundaries. During recrystallization at 623 K (350?°C), in most of the observed cases, the growth of grains occurred by coalescence of neighbouring cells and by migration of high-angle grain boundaries. These processes led to nearly equiaxed grains of similar size. Orientation mappings showed that although orientations of new grains were widely scattered, they were not completely random.     

Localization of the apical foramen using the newest electronic instruments: stereomicroscopy and SEM (scanning electron microscopy)

Introduction of double impedence as new parameter in root canal length electronic measurement allowed first and second generation electronic apical localizers main problems overcoming: precision failure in presence of conducting fluids. Our study's purpose was an in vitro evaluation of two third generation instruments (Apit-Osada and Root ZX-Morita Corp.) ability in apical foramen localization using sodium hypoclorite as irrigating solution. 40 human monorooted teeth with immature apex were studied. 20 samples were measured by Apit and 20 by Root ZX; measurements were recorded when apical foramen was reached. Samples were fixed for stereomicroscope observation before and after apical 3 mm worn and prepared for SEM observation. Evaluations about each system's precision were made by calculating difference between foramen position determined by electronic localizer and its real anatomical position determined by a computed image analizing system linked to SEM. All measurements were included between a minimum value of -0.45 mm and a maximum value of 0.26 mm. Mann Whithney U test was performed to compare average values of the two sample groups but his was not meaningful (p = 0.18) showing that there is no valuable difference in accuracy between Apit and Root ZX. According to most researchers, who consider a +/- 0.5 mm error range clinically acceptable, and considering that in vitro measurements never exceded this limit value we conclude confirming both instruments' safety.     

超低碳钢等温时效过程中析出物的电镜观察

采用扫描电子显微镜研究了超低碳钢在650 ℃经100 s、1000s、100 h、300 h等温时效过程的组织变化及铜的析出颗粒,探讨了时效时间与铜原子扩散对富铜析出颗粒的影响.研究结果表明,等温时效后的组织为多边形铁素体晶粒,富铜析出颗粒优先在铁素体晶界处析出,随着时效时间的延长,在铁素体晶粒内部也出现了富铜析出颗粒.计算表明在晶粒内部的铜原子完全可以借助位错和晶界的高扩散率通道,逐渐富集、长大并粗化.     

Finishing of the Blacksmith's products

Translated from Metallurg, No. 12, pp. 44–47, December, 1991.