Marginal leakage of amalgam restorations pretreated with various liners

PURPOSE: To evaluate and compare the microleakage of amalgam restorations lined with four different liners. MATERIALS AND METHODS: Cylindrical occlusal cavities were prepared in extracted human molars and the teeth were then divided into four groups and lined with one of four liners: Amalcoden, AM (glass-metal ionomer), FujiDuet, FD (glass ionomer), Amalgambond, AB (adhesive resin), or copal varnish, CV. Each cavity was then restored with a high-copper amalgam alloy and aged for 7 days in 37 degrees C distilled water. The specimens were then thermocycled for 300 cycles followed by immersion in 0.5% basic fuchsin dye solution for 24 hours. The teeth were then embedded in resin, sectioned, and dye penetration at the tooth/amalgam interface evaluated microscopically at x 100 and scored from 0 to 4 (0 = no leakage and 4 = greatest leakage). RESULTS: The median values were: AM = 1.0; FD = 0.5; AB = 1.1; and CV = 4.0. Statistical analysis using Kruskal-Wallis and Mann-Whitney U indicated no significant differences between AM and AB or FD and AB. CV was however, significantly worse at P < 0.01.     

Utilization of ceromer inlays/onlays for replacement of amalgam restorations

Fiber-reinforced Ceromer technology has been recommended for a variety of restorations, including inlays/onlays, crowns and bridges, and direct restorations. Ideal restorative dental materials must exhibit adequate physical properties and fit, as well as ease and predictability of fabrication and repair. The Ceromer restorative material combines the positive attributes of indirect composite restorations, feldspathic ceramics, and cast-gold restorations. This article reviews the material properties and aesthetic characteristics inherent to Ceromers, as well as the appropriate preparation and adhesive techniques for inlay/onlay restorations.     

The use of liners under amalgam restorations: an in vitro study on marginal leakage

OBJECTIVE: Marginal leakage of amalgam restorations may lead to secondary caries and pulpal damage. The purpose of this study was to determine the effect various cavity liners might have on microleakage. METHOD AND MATERIALS: Mesio-occlusodistal amalgam restorations with margins on enamel and dentin were treated with different liner materials (an adhesive system, a topical fluoride gel, a cavity varnish, and a glass-ionomer cement) in vitro. Following restoration, the teeth were submitted to thermocycling in a stained solution and sectioned to allow assessment of microleakage. RESULTS: On enamel, the control group (no liner) and the glass-ionomer-lined group had equivalent leakage scores and were superior to every other group. On dentin, only the glass-ionomer specimens had superior performance. The cavity varnish and fluoride-lined specimens exhibited the highest leakage scores. CONCLUSION: The use of liners does not reduce microleakage on amalgam restorations when the cavity margins remain on enamel. On dentin margins, a glass-ionomer liner can reduce microleakage.     

Corrosion and creep resistance of some dental amalgam alloys

Corrosion behaviour, creep values and phase transformation of conventional, admixed, unicompositional and two palladium-enriched amalgam alloys were investigated. Weight-loss method and solution analysis for dissolved metal ions were used. Creep values were determined after different immersion periods. X-ray diffraction was carried out to follow up phase transformation after different immersion periods and/or aging in dry air at 37 degrees up to one year. The results have shown that addition of palladium has improved corrosion and creep resistance and reduced gamma 1 to beta 1 phase transformation, and that gamma 2 did not appear again in high copper or palladium-enriched amalgam up to one year.     

Fracture resistance of low-carbon alloy irons

The temperature dependence of the critical stress intensity factor and of the fracture energy were measured on six low-carbon iron alloys, one containing 0.002 wt pct C and five containing 0.02 wt pct C. Either Ni, P, Si, or Si and Mn were added to four of the five 0.02C irons in quantities typically found in ferritic steels. The fracture tests were conducted at rapid (but less than impact) speed of 1 ips on fatigue cracked, three-point bend beam specimens. Each alloy was tested over a temperature range of —195° to 24°C in both furnace-cooled and quench-aged states. Both alloying and heat treatment produced wide differences in the fracture resistance of these alloys. The quench-aged 0.002C iron and furnace-cooled phosphorus alloy failed by intergranular separation, whereas the remaining alloys exhibited cleavage fractures. With the exception of 0.002C iron, an alloy in the quench-aged condition had higher fracture toughness than the same alloy in the furnace-cooled state. The transition temperature, however, was influenced by heat treatment only in the plain carbon irons. In this case the transition temperature was independent of carbon content but the furnace-cooled specimen had a lower transition temperature than the quench-aged specimens. D. C. A. R. COX, formerly Exchange Scientist at the Naval Research Laboratory     

Fracture resistance of various carburized steels

Fracture toughness and fatigue studies were conducted on various grades of car-burizing steels. The results indicate that similar or superior mechanical performance can be achieved using the alternate EX grades (EX24, EX29, and EX55) compared to the more commonly used grades (SAE 8620, SAE 4320, and SAE 4817). During the study of fatigue properties, various trends on the influence of surface carbon (re-tained austenite) and carbon gradient (hardness profile and case depth) were observed: 1) increasing the surface carbon to the extent that the hardness profile indicated a max-imum at 0.02 in. (0.5 mm) below the surface severely reduced the endurance limit, 2) changing the hardness profile such that the maximum hardness occurred within 0.010 in. (0.25 mm) of the surface improved the endurance limit, but lowered the impact fracture stress, and 3) increasing the case depth improved the endurance limit. This paper is based on a presentation made at a symposium on “Carburizing and Nitriding: Fundamentals, Processes and Properties” held at the Cincinnati Meeting of The Metallurgical Society of AIME, November 11 and 12, 1975 under the sponsorship of the Heat Treatment Committee.     

Influence of finishing and polishing procedures on the decision to replace old amalgam restorations: an in vitro study

The purpose of this study was to establish the influence that finishing and polishing of existing amalgam restorations might have on the decision to replace them. Forty extracted teeth, in which amalgam restorations had been placed in vivo, were individually examined by 60 practitioners and students prior to and following standard finishing and polishing procedures. Examiners, who had not been informed of the study's methodology or objective, opted either for maintaining or replacing the restoration in question. The main reasons for replacement were also registered. Finishing and polishing significantly reduced the number of decisions to replace restorations in all groups and for all practitioners. "Appearance" (anatomic shape) was the most frequently cited reason for replacing restorations before finishing and polishing, followed by marginal defects and secondary caries.     

Fracture resistance of fiber-reinforced ceramic matrix composites

The influence of the properties of the fibers, the matrix and the interface on the mechanical properties of fiber reinforced ceramics is analyzed by a simplified method previously developed by the authors for cohesive materials. The method parts from the assumption that crack displacements are known a priori and furnishes, in a simple and easy way, the fracture resistance curves versus crack length. The numerical results from the model are compared with experimental data from the literature. Finally, the model is used to assess the influence of fiber strength, interface slipping shear stress, fiber radius and fiber defect distribution on the fracture resistance and ductility of fiber-reinforced ceramic composites.     

Interfacial bond strengths of amalgam bonded to amalgam and resin composite bonded to amalgam

A preparative method for the preparation of large peptides is described. An advantageous theoretical weight of peptide/weight of starting resin ratio (tPw/Rw) of about 0.3 was successfully experimented. The esterification of the first amino acid was realized with a racemization of less than 1%. The study of the coupling conditions led to the use of a diluted acylating mixture that allowed a 56% consumption of the amino acid derivatives (percentage use of amino acids) introduced in the synthesis. The cost analysis of the synthesis showed that the recovery of the amino acid derivatives was not worthwhile.     

Fracture resistance of endodontically treated roots after restoration

This study evaluated the shear strength resistance of endodontically treated roots that were restored by two different techniques. Twenty-seven recently extracted single-rooted teeth with similar anatomic characteristics were sectioned to obtain the same length for all specimens. Group I (GI) consisted of 14 roots restored with cast post-core (nickel-chromium alloy) and cemented using zinc phosphate cement; group II (GII) consisted of 13 roots restored with steel prefabricated posts (FKG) cemented with zinc phosphate cement and rotated with caution for anchorage. The crown portion of this group was made using a hybrid composite resin (Prisma APH). Results showed that on all specimens of GI the fracture occurred in the cervical root structure while in GII the composite resin fractured in all specimens. Statistical analysis showed a significantly higher resistance to fracture for GI than GII. The specimens were sectioned longitudinally for stereoscopic microscope analysis (63x) and did not show fracture lines in the dentin anchorage post area for any of the specimens.     

Indirect composite restorations in the anterior region: a predictable technique for complex cases

The indirect composite inlay technique demonstrates excellent aesthetic results in the posterior regions, achieved by reproducing the shape, color, and contour of the natural tooth on a cast model rather than using the free-hand composite restorative modality. The utilization of the indirect technique can be adapted for the anterior regions as well, and it offers a valid treatment alternative that is predictable with optimal restorative results. The evaluation, planning, and accuracy of implementation of the various phases of this methodology allow a more precise achievement of the result; any potential error in the restoration can be corrected prior to final cementation. This technique increases the quality of composite restorations that have always been considered unpredictable and extensively dependent upon the skills of the operator. The learning objective of this article is to familiarize the reader with the clinical and laboratory phases of this indirect treatment modality of the anterior dentition.     

Use of provisional restorations to enhance soft-tissue contours for implant restorations

The objective of restoring missing teeth with implant-supported restorations should not merely be achieving osseointegration with an implant and a biomechanically sound restoration. The objective must be the esthetic and functional restoration of the missing teeth. To achieve this, proper treatment planning is critical. Precise implant placement and delicate soft-tissue manipulation during surgery will allow the restorative dentist to enhance the peri-implant soft-tissue contours with the use of provisional restorations. Empirically, it seems that the earlier the provisional restoration is delivered in the treatment process the more ideal the esthetics. Several methods of using provisional restorations to enhance soft-tissue contours are presented. The concept of immediately delivering provisional restorations on placement of an implant is discussed.     

聚苯胺/氧化铈复合涂层的防腐性能

制备苯胺与氧化铈质量比分别为1:100,1:200,1:300的聚苯胺/氧化铈复合物,将制备的不同质量比的聚苯胺/氧化铈复合物与环氧树脂溶液共混制备防腐蚀涂料,通过测试该涂料在酸、碱、盐溶液中的交流阻抗谱与腐蚀电位,研究了聚苯胺/氧化铈/环氧树脂复合防腐涂料的防腐蚀性能.实验结果表明,以苯胺与氧化铈质量比为1:100聚苯胺/氧化铈复合粒子为填料的涂料抗腐蚀性能最好,所制备涂料抗酸腐蚀性能较差,而抗碱和抗盐腐蚀性能较好.