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Biomedical subjects

D Nathanson

Publications and source records attributed to D Nathanson.

At least 37 records · Page 2Linked to original sources
PubMed1993

Advances and current research in ceramic restorative materials.

Ceramics are currently the most widely used material for veneering crowns and bridges. Newer applications, such as bonded inlays, onlays, and veneers, are steadily gaining in popularity. A new generation of metal-free, all-ceramic systems for crowns became available during the 1980s. More recently, other all-ceramic systems with improved mechanical properties affording a variety of uses have been introduced. Also, a computer-assisted design-computer-assisted manufacture method of fabricating ceramic inlays has become a routine treatment entity with favorable 5-year clinical data. Research is leading to a better understanding of conventional ceramic systems as well as providing information on laboratory manipulation and clinical methodology for optimal results.

Crowns↗
PubMed1993

The significance of retention in post and core restorations.

Endodontically-treated, pulpless teeth tend to become brittle and loose their natural resistance to intraoral functional stress. To retain the core to the root, posts are placed in such teeth. This article presents the rationale for placing the posts, reports past results, and discusses the current materials and implementation procedures. Understanding those principles is the learning objective of this article.

Acrylic Resins↗
PubMed1992

Effects of cement, cement space, marginal design, seating aid materials, and seating force on crown cementation.

An evaluation of the effects of a die spacer, the seating force, the marginal design, seating aid materials, and the cement type during cementation was conducted. Two stainless steel dies were used: one with a 1 mm shoulder and the other with a shoulder and a 65-degree bevel. Ten stone dies were produced from each metal die and half were painted with four layers of die spacer. The crowns were waxed on the dies and cast in a nonprecious alloy, and the seating of crowns was measured with a micrometer before and after cementation. Comparisons were made between zinc phosphate and glass ionomer cements under two seating forces of 5 and 30 lb using an orangewood stick or E-Z-bite seating aid. ANOVA and the Newman-Keuls test revealed that the use of a die spacer, a heavier force of 30 lb, and glass ionomer cement significantly improved crown seating. The beveled preparation led to superior crown seating when the heavier force or glass ionomer cement was used. The orangewood stick and bite device had a similar effect on crown seating.

Cementation↗
PubMed1992

Effects of temporary cementation on permanent cement retention to composite resin cores.

This in vitro study compared the effects on retention of base metal cylindrical retainers placed on composite resin cores when pretreated with eugenol and noneugenol temporary cements. Sixty composite cores and base metal cylindrical retainers were tested. The cores were pretreated with eugenol and noneugenol temporary cements before eventual cementation with resin and zinc phosphate cements. Cemented core retention was measured by application of a compressive force to the cores in an Instron machine. Differences were found between the two permanent cements. Pretreatment with eugenol cement reduced retainer retention with resin cements, but had no effect with zinc phosphate cement. Pretreatment with noneugenol cement did not reduce retainer retention.

Cementation↗
PubMed1992

Effects of moisture content and endodontic treatment on some mechanical properties of human dentin.

The objective of this study was to determine whether significant differences exist between the mechanical properties of human dentin from treated pulpless teeth and dentin from normal vital teeth. Dentin specimens (n = 262) were obtained from 54 freshly extracted normal vital human teeth and 24 treated human pulpless teeth. These specimens were subjected to different experimental conditions (wet, air dried, desiccated, and rehydrated). Compression, indirect tensile, and impact tests were conducted to measure the mechanical properties of those specimens. All data obtained were analyzed with t tests. The results showed that the dehydration of dentin increases the Young's modulus, proportional limit (in compression), and especially the ultimate strength (in both compression and tension). Substantial dehydration changes the fracture characteristics of dentin specimens under static compressive and indirect tensile loadings. The measurements of impact-breaking energies of desiccated dentin were not found to be significantly decreased. The compressive and tensile strengths of dentin from treated pulpless teeth obtained in this study do not appear to be significantly different from those of normal dentin (p > 0.05), while the mean values of Young's modulus and proportional limit in compression tests appear to be lower. Fifty percent of the dentin specimens from treated pulpless teeth exhibit greater plastic deformation than normal dentin in compression. The results of this study do not support the theory that dehydration after endodontic treatment per se weakens dentin structure in terms of compressive and tensile strengths. Other mechanical properties of treated pulpless teeth, however, may not be the same as those of normal vital teeth.

Dental Pulp Devitalization↗
PubMed1991

Retention between a serrated steel dowel and different core materials.

This in vitro study compared the retention of dowel posts using different core materials. Glass ionomer cements, composite resin, and amalgam core materials were combined with serrated dowel posts to form post and core assemblies. Individual post-core assemblies were mounted with a special jig in an Instron Universal testing machine. A tensile force was applied at a cross-head speed of 0.02 cm/min and the separation force was recorded. Glass ionomer cement core materials were weak in tension and metalized ionomers remained brittle and were not fracture resistant. Composite resin and amalgam were strong in tension and relatively fracture resistant.

Analysis of Variance↗
PubMed1991

Effect of aging on temporary cement retention in vitro.

Retention of restorations cemented with temporary cement varies. Some cements are adhesive and others are weak in retention. In addition, cement retention may vary over time. This study determined (1) the retentive properties of four temporary cements, and (2) the effects of aging on temporary cement retention. Cylindrical amalgam cores and mated stainless steel retainers with a 0.05 mm cement space were used in the study. Cores were cemented into the retainers and stored in 100% humidity at 37 degrees C until tested. Retention was measured by applying a compressive force to the cores through a rod in an Instron machine. Half the samples were tested after 1 week and half were tested after 6 weeks. The results indicate a significant difference in retentive value among the four cements, including a significant decrease in retention for one cement over the 6-week aging period.

Cementation↗
PubMed1991

Determining the accuracy of articulator interchangeability.

Twelve articulators (Denar D5-A and Mark II) were calibrated using the Denar Field Inspection Gage device. Silicone interocclusal records and the split cast method were used to test the positional accuracy of mounted casts transferred from one articulator to another. The interchangeability was performed by three independent observers. The results indicate that calibrated articulators can be used to transfer casts between articulators without a loss of positional accuracy.

Calibration↗
PubMed1991

Current developments in esthetic dentistry.

Current developments in esthetic dentistry center around new techniques and materials that improve the clinician's ability to provide esthetic services. These developments include the availability of improved composites for anterior and posterior use, a new generation of dentin bonding agents, bonded ceramic restorations, and more efficient and predictable ways to whiten teeth. There is a better understanding of factors contributing to the esthetic value of restoration as well as their longevity. New bonding techniques to dentin enable practitioners to perform difficult restorative procedures in a conservative manner, producing results that are highly esthetic and physiologically tolerable. The use of dental porcelains has expanded from the traditional applications in crowns and bridges to veneers, inlays, onlays and all-porcelain bridges that are directly bonded to teeth. Computer-designed and fabricated inlays and onlays are now an available treatment modality, with a reported 3-years follow-up looking very promising. The increasing public demand for esthetic dental procedures has made the discipline a significant part of dental practice and boosted interests and understanding of procedures, such as tooth bleaching and peridontal surgery, for improved esthetics.

Composite Resins↗
PubMed1990

New aspects of restoring the endodontically treated tooth.

It is common practice to 'reinforce' the endodontically treated tooth with a post-and-core combination (either custom or prefabricated) and ultimately restore it with a crown. Many studies have looked at the post, treatment of the post surface, the cements and other factors. It appears that, regardless of the treatment of the post surface, current post cementing technology enables the practitioner to achieve higher retention than previously possible.

Cementation↗
PubMed1989

Dentinal bonding after chemomechanical caries removal--effect of surface topography.

A study was carried out to determine whether or not the topography of the dentinal surface that is left after caries removal affects bond strength. The caries was removed either by a rotating instrument and a bur or by the chemomechanical method using D,L,2-aminobutyric acid. The bond strength appeared to be enhanced on those specimens treated by the chemomechanical removal since the surface was characterized by lack of a smeared layer and by open dentinal tubules and numerous undercuts.

Aminobutyrates↗
PubMed1988

Colour effect of denture base on denture tooth materials.

A study using a HunterLab colorimeter was conducted to determine the colour effect of denture base materials on denture tooth acrylics. The results show that denture base materials create a measurable change in the chroma of denture tooth acrylics and suggest that optimal shade selection of teeth should include a determination of the background effects of denture base materials.

Acrylic Resins↗