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Biomedical subjects

A J Goldberg

Publications and source records attributed to A J Goldberg.

At least 19 recordsLinked to original sources
PubMed2005

Autologous chondrocyte implantation. Culture in a TGF-beta-containing medium enhances the re-expression of a chondrocytic phenotype in passaged human chondrocytes in pellet culture.

An increasing number of patients are treated by autologous chondrocyte implantation (ACI). This study tests the hypothesis that culture within a defined chondrogenic medium containing TGF-beta enhances the re-expression of a chondrocytic phenotype and the subsequent production of cartilaginous extracellular matrix by human chondrocytes used in ACI. Chondrocytes surplus to clinical requirements for ACI from 24 patients were pelleted and cultured in either DMEM (Dulbecco's modified eagles medium)/ITS+Premix/TGF-beta1 or DMEM/10%FCS (fetal calf serum) and were subsequently analysed biochemically and morphologically. Pellets cultured in DMEM/ITS+/TGF-beta1 stained positively for type-II collagen, while those maintained in DMEM/10%FCS expressed type-I collagen. The pellets cultured in DMEM/ITS+/TGF-beta1 were larger and contained significantly greater amounts of DNA and glycosaminoglycans. This study suggests that the use of a defined medium containing TGF-beta is necessary to induce the re-expression of a differentiated chondrocytic phenotype and the subsequent stimulation of glycosaminoglycan and type-II collagen production by human monolayer expanded chondrocytes.

Adolescent↗
PubMed2003

Shear in flexure of fiber composites with different end supports.

The integrity of fiber-reinforced composite (FRC) prostheses is dependent, in part, on flexural rigidity. The object of this study was to determine if the flexure behavior of uniform FRC beams with restrained or simply supported ends and various length/depth (L/d) aspect ratios could be more accurately modeled by correcting for shear. Experimental results were compared with three analytical models. All models were accurate at high L/d ratios, but the shear-corrected model was accurate to the lowest, more clinically relevant, L/d values. In this range, more than 40% of the beam deflection was due to shear.

Composite Resins↗
PubMed1999

An innovative pre-impregnated glass fiber for reinforcing composites.

This article summarized the development of pre-impregnated, fiber-reinforced composites. Previous efforts with various reinforcement materials for splinting are cited. The benefits of pre-impregnation are explained. The clinical procedure for placing a fiber-reinforced composite splint is described.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1998

Development and clinical applications of a light-polymerized fiber-reinforced composite.

STATEMENT OF PROBLEM: After 0 years of intermittent reports in the literature, the use of fiber reinforcement is just now experiencing rapid expansion in dentistry. PURPOSE: This article describes the development and use of a continuous, unidirectional fiber reinforced composite as a framework for the fabrication of fixed prostheses. METHODS: By using various matrix materials and fibers, a number of fiber-reinforced composite formulations were evaluated with the goal of creating a system with optimized mechanical properties and handling characteristics. Fiber-reinforced composite based on a light polymerized BIS-GMA matrix has been used clinically to make 2-phase prostheses comprised of an internal glass fiber-reinforced composite substructure covered by a particulate composite. The clinical and laboratory procedures required for the fabrication and use of reinforced composite fixed prostheses are described for laboratory-fabricated complete or partial coverage fixed prosthesis and chairside prosthesis. RESULTS: Although additional clinical experience is needed, fiber-reinforced composite materials can be used to make metal-free prostheses with excellent esthetic qualities.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1998

Preimpregnated, fiber-reinforced prostheses. Part II. Direct applications: splints and fixed partial dentures.

This article is the second in a series that describes the development, physical properties, and clinical applications of fiber-reinforced composite materials. The development of fiber-reinforced composite technology has opened new avenues for fabricating direct tooth replacements and splints that are esthetic and simple in design and execution and have the potential for excellent durability. Splinting techniques for hypermobile dentitions or postorthodontic retention and the replacement of anterior and posterior teeth using a groove preparation, a denture tooth, and a fiber-reinforced composite framework will be described.

Composite Resins↗
PubMed1998

Preimpregnated, fiber-reinforced prostheses. Part I. Basic rationale and complete-coverage and intracoronal fixed partial denture designs.

This is the first of two articles describing the development and use of a continuous fiber-reinforced composite as a framework for the fabrication of fixed partial dentures and splints. The chemical composition and physical structure of the fiber-reinforced composite, along with the progression and development of a variety of fiber-reinforced composite materials, are discussed. Criteria for case selection, tooth preparation, and the clinical and laboratory procedures required for partial- or complete-coverage fixed partial denture fabrication and delivery are described.

Composite Resins↗
PubMed1997

Extent of conversion and its effect on the mechanical performance of Bis-GMA/PEGDMA-based resins and their composites with continuous glass fibres.

The reaction mechanism of bisphenol A bis(2-hydroxy propyl) methacrylate (Bis-GMA) and polyethylene glycol dimethacrylate (PEGDMA) was characterized by differential scanning calorimetry (DSC) and infrared (IR) spectroscopy. Composites of S2-glass fibres with different formulations of Bis-GMA/PEGDMA were fabricated by filament winding. The mechanical properties of neat resins and composites were investigated by dynamic mechanical thermal analysis (DMTA) and a three-point-bending flexural test.

Journal Article↗
PubMed1997

Continuous fiber reinforced composite materials as alternatives for metal alloys used for dental appliances.

Two types of uniaxially oriented long S2-glass fiber reinforced composites were prepared for use in various dental appliances. Matrix polymers were polycarbonate (PC) and bisphenol A bis (2-hydroxy-propyl) methacrylate (Bis-GMA) based copolymers. Flexural tests were conducted on the composites using a procedure which simulates clinical usages. To evaluate the adhesion between the composites and the adhesive, the single-lap shear test was conducted. Mechanical properties of the small cross-sectional composite strips were superior to those used previously in clinical studies.

Dental Alloys↗
PubMed1996

Utility of the routine chest X-ray after "over-wire" venous catheter changes.

The Seldinger technique is commonly used to change central venous access catheters in the Intensive Care Unit. These catheters are routinely being changed to prevent septic complications. Some of these changes are performed by an "over-wire" technique. To assess the utility of postprocedural chest X-rays on critically ill patients after an over-wire catheter change, we followed 68 patients after they had 80 catheter changes. This study assesses catheter position by use of a postprocedural X-ray. During the study, we found no misplaced catheters and minimum symptomatology in 80 patients. The trauma/critical care fellows performing the procedures rated them as easy in 97.5 percent of the changes. The conclusion of the study is that, if the catheter change is technically easy and the patient has no symptoms, a postprocedural X-ray is not necessary.

Bacterial Infections↗
PubMed1994

Screening of matrices and fibers for reinforced thermoplastics intended for dental applications.

Plastics reinforced with continuous fibers (FRC) are being developed for dental applications, such as prosthodontic frameworks and orthodontic retainers. Flexure properties, stress relaxation and hydrolytic stability of FRC based on six thermoplastic matrices, three types of fibers, and three fiber volume fractions were evaluated. Samples with clinically relevant dimensions were tested. Polycarbonate was the preferred matrix material. Polycarbonate reinforced with 42 volume percent glass fibers exhibited the highest combination of flexure modulus (17.9 +/- 2.6 GPa), flexure strength (426 +/- 40 MPa), reinforcing efficiency (0.79), and resistance to stress relaxation. No statistically significant difference was observed between E and S2 glass reinforced composites under the experimental conditions used. Kevlar reinforced materials exhibited a low flexure modulus and strength. The apparent flexure moduli of all composites decreased with span length in the range of clinical interest. Generally, the prevalent mode of failure for all FRC investigated was brittle failure under flexure loading. Relatively large sample-to-sample variation in both composition and properties indicated that improved fabrication methods will be needed in future studies. The combination of good flexure properties, formability, and translucency suggests that novel appliance designs for dentistry are feasible with FRC, but further studies of its properties and particularly the effects of fiber/matrix interfacial quality are needed.

Dental Materials↗
PubMed1994

Longitudinal clinical evaluation of fiber-reinforced composite fixed partial dentures: a pilot study.

This report describes a clinical pilot study that monitored a group of 12 patients who have received 14 single tooth replacement experimental restorations made with prefabricated continuous fiber-reinforced composite (FRC) frameworks. Because these restorations represent a purely adhesive restorative system, tooth preparation was not performed. The Kaplan-Meier survival probability at 12 months was approximately 50%. The restoration with the longest service life was a mandibular molar replacement that has remained in service 24 months. With improved survival times, bonded FRC definitive restorations should be plausible.

Adult↗
PubMed1992

Direct and indirect evaluation of posterior composite restorations at three years.

The purpose of this study was to compare the use of direct (USPHS) and indirect (M-L) systems of evaluating the occlusal wear of posterior composite restorations. Additionally, this study has utilized the USPHS method to compare the in vivo performance of posterior resin composite restorations made from four different visible-light-cured materials. Of the 202 restorations placed for this randomized clinical trial, only those restorations that were scored by both direct and indirect evaluation systems were included in these comparisons. Restorations were evaluated by two calibrated examiners from baseline to 36 months. While there were some differences noted among the four materials, the majority (99%) of the restorations evaluated in this study received "alpha" or "bravo" scores for all USPHS parameters, indicating acceptable in vivo performance. The results of this study also indicate that there was a consistent relationship between the direct (USPHS) and indirect (M-L scale) scoring systems. For those restorations that changed anatomic form scores, the mean wear at the alfa/bravo transition was 100 +/- 80 microns. By the 24-month recall examination, the use of the USPHS evaluation system category of anatomic form enabled examiners to differentiate restorations and materials that had experienced little occlusal wear from those that had experienced greater amounts of wear.

Analysis of Variance↗
PubMed1992

The use of continuous fiber reinforcement in dentistry.

Fiber-reinforced composite (FRC) formulations were developed to serve as structural components for various dental appliances such as prosthodontic frameworks, retainers and splints. Poly(ethylene terephthalate glycol) and poly(1,4-cyclohexylene dimethylene terephthalate glycol) reinforced with continuous S-2 glass fibers were pultruded into continuous lengths with small rectangular cross sections. The microstructure was evaluated with SEM and optical microscopy. Fiber content and flexure properties were measured and compared to previous results by other authors. The present FRC contained 43-45 volume % fiber, which compared favorably with the 5-15 volume % fiber reported by all earlier investigators of dental FRC. The present materials achieved 65% of the theoretically expected modulus, in contrast to the typical value of 40% calculated in the earlier reports. The flexural strength and modulus of the experimental FRC were approximately 565 MPa and 20 GPa, respectively. The present FRC can be formed into individualized devices, and free fibers need not be manipulated by the operator. The improved properties and handling justify further study of these FRC as structural dental materials.

Carbon↗
PubMed1992

Three-year occlusal wear of posterior composite restorations.

The specific aims of this study were to: 1) measure the occlusal wear of four different dental composite materials placed in the posterior teeth of adults; and 2) evaluate the effect of the clinical parameters, cavity class and tooth type on occlusal wear. Four different visible light-cured composite materials were used to make the restorations in this study. The restorations placed for this randomized clinical trial were scored through the use of an indirect evaluation system (M-L scale). The total sample size per recall ranged from 90 to 142 restorations from baseline to 36 months. The mean wear at 36 months for Heliomolar, J&J Experimental (Adaptic II) and P-30 was 45-54 microns, which is rather low compared to the recently reported wear of other composite materials. Marathon exhibited significantly greater wear with a mean of 174 microns at 36 months. The data also showed that cavity class and tooth type had no significant effect on the occlusal wear of the restorations made with the three low wear-rate materials, while restorations composed of the high wear-rate material exhibited more wear in molars than premolars; this effect was again not statistically significant. These data support the hypothesis that the overall wear of a composite restoration is more dependent on the material's properties than clinical parameters such as cavity class and tooth type.

Acrylic Resins↗
PubMed1990

Deterioration of restorative materials and the risk for secondary caries.

This article reviews the literature related to marginal deterioration of amalgam restorations and the risk for secondary caries. Background information on this characteristic material failure is provided, including how it is measured clinically, its rate of progress with time, and the responsible microstructural mechanisms. The association between degree of marginal fracture and recurrent or secondary caries is reviewed in clinical and in vitro studies. Earlier clinical investigations and a more recent laboratory study demonstrated a strong correlation between gap size and recurrent caries for a caries-active environment, supporting replacement of defective restorations for preventive reasons. However, more recent clinical data show the complex and equivocal nature of this association. Poor specificity and validity for detection of recurrent caries with an explorer and mirror further complicate interpretation of some trials and decision-making in clinical practice. Improved methods of diagnosing recurrent caries and further studies of the factors influencing its initiation and progression are needed.

Dental Caries↗