Biomedical subjects

J Vaidyanathan

Publications and source records attributed to J Vaidyanathan.

12 recordsLinked to original sources

PubMed2001

Flexural creep deformation and recovery in dental composites.

OBJECTIVES: Three different popular composite resin systems for dental restorative applications are microfilled, minifilled and midifilled types in which deformation under stress and recovery after stress removal may be strongly influenced by filler parameters and resin formulation. The purpose of this in vitro study was to evaluate these differences in selected composite resins. MATERIALS: Three composites, Clearfil (midifill), Charisma (minifill) and Durafill (microfill), were evaluated. Elastic, viscoelastic and viscous deformation of the composites under a constant stress and the subsequent recovery on removal of stress were measured. Dynamical mechanical properties of these materials were also characterized. RESULTS: The mean values (and SD) of elastic, viscoelastic and viscous components of overall deformation (mm), respectively, under a constant stress of 45(5)KPa were as follows: Clearfil, 0.17(0.03), 0.06(0.02), 0.03(0.05); Charisma, 0.34(0.1), 0.09(0.04), 0.14(0.03); Durafill, 0.68(0.06), 0.14(0.03), 0.23(0.03) The results show that there are significant differences (P<0.0001) between the different composite resins in the elastic, viscoelastic and viscous segments of deformation. The microfilled system deformed significantly more than the minifilled, and the minifilled system more than the midifilled. Storage modulus values evaluated by dynamic mechanical analysis were also significantly different (P<0.0001). The observed differences were readily explained by the differences in the type and volume fraction of the filler content in the composites. CONCLUSIONS: Differences in time dependent deformation and recovery as well as dynamic mechanical properties of dental composites were strongly influenced by filler parameter differences. The clinical performance of restorations may be strongly influenced by the observed differences.

Analysis of Variance↗

PubMed2000

Microleakage of compomer class V restorations: effect of load cycling, thermal cycling, and cavity shape differences.

STATEMENT OF PROBLEM: Microleakage is an important problem with direct filling restorations and an understanding of the factors that contribute to it is of critical importance. PURPOSE: This study investigated the effect of thermal and occlusal load cycling, and limited cavity preparation on microleakage of compomer Class V restorations in vitro. MATERIAL AND METHODS: Class V cavities were randomly prepared on the buccal and lingual surfaces of 32 recently extracted molars and premolars and restored with Dyract compomer restorative system as per the manufacturer's directions. Teeth were randomly assigned to 1 of 4 treatment groups with 8 teeth in each group: (I) thermocycling only; (II) load cycling only; (III) both thermocycling and load cycling; and (IV) no treatment. All teeth were then immersed in 2% basic fuchsin solution for 24 hours. Dye penetration was measured linearly using color photographic prints. ANOVA, comparisons between means, and correlation were used to analyze the results. RESULTS: Thermocycling and cavity preparation had a significant effect on microleakage, but load cycling did not. Occlusal margins leaked more than the gingival margins. CONCLUSION: Class V restorations demonstrated increased microleakage under the conditions of thermal cycling and nonretentive cavity design. More microleakage occurred at occlusal margins than at gingival margins. The effect of load cycling is complicated by considerations of the types of stresses applied and the restorative material response to such stresses.

Compomers↗

PubMed1999

Measurement of submucosal forces transmitted to dental implants.

Early loading of dental implants after placement is believed to be a major cause for premature implant failure. If a transitional denture or partial denture is used during the healing period, occlusal forces may be transmitted to the submerged implant, leading to poorly differentiated growth of bone cells and/or potential inhibition of osseointegration at the bone-implant interface. The objective of this study was to develop an experimental model to measure the force transmission and to characterize the effect of selected loading conditions and relief methods on the forces transmitted to the implant. The loading conditions studied included unilateral and bilateral loading of the prosthesis. Forces were measured at two different relief conditions (relief with and without soft liner) and were compared against a control with no relief. The results show that fabrication of the prosthesis with a proper relief at the implant-denture junction can eliminate the submucosal force transmission to the implant on loading the denture both under unilateral and bilateral loading conditions. When a soft liner is used at the relief site, the transmitted force is small, but a finite value is reproducibly recorded. With no relief, the submucosal force transmission is high and may adversely affect the healing process or osseointegration. The experimental model is valuable in measuring and understanding the submucosal forces that are transmitted to the implant by loading the transitional prosthesis, and such measurement may assist in the proper design of the prosthesis for improved clinical durability and for other uses.

Alveolar Process↗

PubMed1998

Color stability of dental composites as a function of shade.

STATEMENT OF PROBLEM: The selection of shade of composites for restorative applications may have a significant effect on color degradation through environmental exposure. PURPOSE: This study characterized the color changes in composites as a function of shade through environmental effects such as ultraviolet light exposure. MATERIAL AND METHODS: Five shades of two composites were subjected to ultraviolet light exposure at 37 degrees C for 24 hours after initial storage for 24 hours in distilled water at 37 degrees C. The lightness and chromaticity values of color were measured both before and after ultraviolet light exposure with a Minolta Chromameter. The total color change as well as changes in the lightness and chromaticity values were measured in the CIE L*a*b* scale and analyzed to monitor color degradation, if any. RESULTS: Color degradation was a significant function of shade and occurred primarily as an increase in yellowness. Color changes increased with the lightness of the shade in both composite systems. CONCLUSION: The lighter shades of composites were likely to be subject to higher color degradation through environmental effects of ultraviolet light exposure.

Analysis of Variance↗

PubMed1996

Development and evaluation of a new 3-D digitization and computer graphic system to study the anatomic tissue and restoration surfaces.

It is necessary to visualize and reconstruct tissue anatomic surfaces accurately for a variety of oral rehabilitation applications such as surface wear characterization and automated fabrication of dental restorations, accuracy of reproduction of impression and die materials, etc. In this investigation, a 3-D digitization and computer-graphic system was developed for surface characterization. The hardware consists of a profiler assembly for digitization in an MTS biomechanical test system with an artificial mouth, an IBM PS/2 computer model 70 for data processing and a Hewlett-Packard laser printer for hardcopy outputs. The software used includes a commercially available Surfer 3-D graphics package, a public domain data-fitting alignment software and an inhouse Pascal program for intercommunication plus some other limited tasks. Surfaces were digitized before and after rotation by angular displacement, the digital data were interpolated by Surfer to provide a data grid and the surfaces were computer graphically reconstructed: Misaligned surfaces were aligned by the data-fitting alignment software under different choices of parameters. The effect of different interpolation parameters (e.g. grid size, method of interpolation) and extent of rotation on the alignment accuracy was determined. The results indicate that improved alignment accuracy results from optimization of interpolation parameters and minimization of the initial misorientation between the digitized surfaces. The method provides important advantages for surface reconstruction and visualization, such as overlay of sequentially generated surfaces and accurate alignment of pairs of surfaces with small misalignment.

Computer Communication Networks↗

PubMed1992

Thermoanalytical characterization of visible light cure dental composites.

Selected commercial and experimental composites and resin systems have been evaluated by thermal analysis techniques of Differential Scanning Calorimetry, Thermogravimetric Analysis and Thermomechanical Analysis. Important thermal data such as heat of cure, coefficient of thermal expansion, dimensional changes over selected temperature ranges, filler weight percent, onset temperature of decomposition, etc. have been determined. Heat of cure, thermal expansion coefficient and dimensional changes appear to follow an inverse linear regression fit with filler fraction in the composite. Thermal expansion changes and exothermic reactions with temperature indicate secondary cure during postcure heating. The thermally-induced decomposition occurs in multiple stages indicating presence of different structural species in the resin matrix.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1991

Tarnish of dental alloys by oral microorganisms.

Five dental alloys, on exposure to blood and chocolate media with and without inoculated microorganisms, showed varying degrees of tarnish. The results indicated a composition-dependent tarnish behavior of alloys in microorganism-inoculated media, indicating a potential role for the oral microorganisms in inducing clinically observed tarnish of dental alloys. Actinomyces viscosus and periodontal pocket specimens show a similarity in their activity to induce tarnish in base metal-containing dental alloys.

Actinomyces viscosus↗

PubMed1991

Direct post and core pattern made with light-curing composite resin.

An unfilled Bis-GMA composite resin can be used advantageously for making an accurate cast post and core pattern. The technique is faster and easier than normal pattern fabrication methods using an unfilled acrylic resin, wax, or a combination of the two.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1991

Computer-controlled differential scanning calorimetry of dental composites.

In this paper, computer-controlled differential scanning calorimetry has been used to evaluate the heat liberated and the temperature rise associated with the light cure of selected dental composites. In addition, the effect of postcure heating and increased ambient temperature of light cure are examined in terms of potential secondary cure. The results indicate significant differences between the mean heats of cure of different composites, primarily reflecting the filler fraction variations of the composites. In addition, increased cure activity appears to result from both postcure heating as well as thermal activation due to higher ambient temperature of light cure. The results are analyzed and attributed to variations in resin phase composition and resin content per unit weight of composite as well as thermally induced enhancement of cure.

Calorimetry, Differential Scanning↗

PubMed1990

Interactive effects of etching and pre-oxidation on porcelain adherence to non-precious alloys: a guided planar shear test study.

Interactive effects of etching and pre-oxidation on porcelain adherence to non-precious alloys were studied by a guided planar shear bond test under non-cantilever conditions. The results indicated that electrolytic etching decreases bond strength, but that oxidation of etched surfaces restores the bond strength level. The results are explained by a hypothesis that depletion of critical elemental species occurs during etching. Potential replenishment of the lost elements during subsequent oxidation, although not confirmed, may assist in improving bond strength.

Acid Etching, Dental↗

PubMed1989

Evaluation of the ability of glass-ionomer cement to bond to glass-ionomer cement.

This study investigated the cohesive bond strengths of glass-ionomer cement at three setting and etching intervals and compared these bonds to the shear strength of the material itself. Bonded cylinders were created and then sheared using the Instron Universal Testing Machine. Analysis of bond values of glass ionomer added to glass ionomer indicate bond variability and low cohesive bond strength of the material. Bond values of unbonded glass-ionomer material indicate that the material itself is stronger than bonds established between bonded samples.

Dental Bonding↗

PubMed1984

Demineralization and ion binding action of polycarboxylate cement liquid on human dental enamel.

The demineralization and ion binding effects on dental tissues due to poly(acrylic) acid attack under different dilution conditions of the latter are studied by scanning electron microscope (SEM) and infrared (IR) spectroscopy. The results indicate that in addition to the general demineralization effects such as preferential prism core attack, prism periphery attack, and protruding prism rods, competing ion binding effects also occur. Using optimum dilution conditions, the microstructural effects of demineralization and ion binding are shown and the effects are related to IR spectral observations.

Dental Cements↗