Biomedical subjects

T Dérand

Publications and source records attributed to T Dérand.

At least 19 recordsLinked to original sources

PubMed2000

Effect of distance on the power density from two light guides.

PURPOSE: This study determined the effect of distance on the power density from standard and Turbo light guides (Demetron/Kerr, Danbury, Connecticut). MATERIALS AND METHODS: Power density was measured from 0 to 10 mm away from the tip of standard 8-mm curved light guides and 13/8-mm Turbo curved light guides. To determine the effect of distance on power density, a polynomial regression line was fitted. The Kolmogorov-Smirnov (K-S) statistic and the Wilcoxon rank sum (WR) tests were used to determine if there was a difference in the rate at which the power density decreased for the standard and Turbo light guides as the distance from the tip increased. Photographs of the light dispersion from each tip were also taken. RESULTS: At 0 mm, the mean (+/- SD) power density from the two standard light guides was 743 +/- 6.1 mW/cm2 and from the four Turbo light guides was 1128 +/- 22.1 mW/cm2. As the distance from the tip of the light-guide tip increased, the power density decreased, but the rate of decrease was greater from the Turbo light guides than from the standard light guides. At 6 mm the power density from the standard light guides fell to 372 mW/cm2 (50% of the original value) and the power density from the Turbo light guides fell to 263 mW/cm2 (23% of the original value). Both the K-S statistic and the WR sum test indicated that the distribution of light intensities was significantly different from the two light guides (WR p-value = .0246, K-S p-value < .0001). The two estimated polynomials intersected at 3.66 mm, and the 95% prediction intervals intersected at about 2.8 and 4.8 mm. Therefore, beyond 5 mm away from the tip of the light guide, the standard light guides gave higher power density readings than the Turbo light guides. Photographs showed that the light dispersed at a wider angle from the Turbo light guides than from the standard light guide. CLINICAL SIGNIFICANCE: The design of the light guide of a light curing unit affects light dispersion, power density, and ultimately the dentist's ability to properly cure composite. For these reasons, manufacturers should report the power density at the tip of the light guide and 6 mm from the tip of the light guide, since significant differences exist between light guide designs.

Dental Cavity Preparation↗

PubMed2000

Light energy transmission through cured resin composite and human dentin.

OBJECTIVE: This study determined the amount of light energy transmitted through various densities of cured resin composite and human dentin when 2 different light intensities were used. METHOD AND MATERIALS: The maximum light energy (mW/cm2) transmitted through disks (0.46 to 5.85 mm thick) of 7 resin composites and human dentin was measured when either a Standard or a Turbo light guide was attached to a curing light. The effects of the 2 light guides, the specimen thickness, and type of specimen dentin on light energy transmission were determined. RESULTS: The mean light energy reading at the surface of the specimens was 682.1 mW/cm2 with the Standard light guide and 1,014 mW/cm2 with the Turbo light guide. For all the specimens, there was an exponential decrease in light energy transmitted as the specimen thickness increased. The analysis of covariance showed that the specimen, thickness, and light guide all had a statistically significant effect. Significantly more light energy (about 42%) was transmitted through the specimens when the Turbo light guide was used. CONCLUSION: When the Turbo light guide was used, about 42% more light energy was transmitted through the cured composite specimens. There was an exponential decrease in the light energy transmitted through 7 resin composites and dentin as the specimen thickness increased.

Analysis of Variance↗

PubMed2000

Fracture strength of In-Ceram all-ceramic bridges in relation to cervical shape and try-in procedure. An in-vitro study.

Investigations were performed on the strength of dental porcelain depending on whether it was exposed to saliva before or after the final firing. Forty porcelain specimens were fabricated and subjected to different treatments. A three-point flexural test was performed. In a second study investigations were performed to compare how the cervical shape of the preparation influenced the fracture strength of fixed partial dentures made of glass-infiltrated aluminium oxide. It was concluded that short-term exposure to saliva could have a negative effect on the strength of porcelain and that all-ceramic bridges luted with non-adhesive luting techniques should be supported by abutments with shoulder preparations.

Aluminum Oxide↗

PubMed1999

The CrescoTi Precision method: description of a simplified method to fabricate titanium superstructures with passive fit to osseointegrated implants.

Casting distortion and inadequate handling in the dental laboratory are 2 factors that can cause misfit between a cast framework and the implant analogs in the master cast. This article describes the CrescoTi Precision procedure, which has been developed for correction of misfit between cast titanium frameworks and supporting dental implants. The simplicity and accuracy of the procedure appear to demonstrate technical progress toward obtaining optimal precision of fit of the superstructure components, thereby eliminating stress forces that may be transformed to the peri-implant bone.

Dental Alloys↗

PubMed1999

Effect of margin design, cement polymerization, and angle of loading on stress in porcelain veneers.

STATEMENT OF PROBLEM: The clinical failure of porcelain veneers may result from stresses induced in the porcelain during mastication. PURPOSE: This study investigated whether applied stresses were large enough to cause porcelain fracture, examined the influence of the margin design, and examined whether a lack of bond in the middle, cervical, or incisal area would have any influence on stress distribution. MATERIAL AND METHODS: A 2-dimensional finite element model was made. Location and magnitude of maximum compressive and tensile stresses were calculated in porcelain veneer. RESULTS: Small differences in stress were observed in the margin portion for various cervical designs under the same conditions. An increase in stresses appeared for all situations and in all reading points with a more transverse angulation of load. A significant difference appeared between full bonding and a lack of adhesion in the middle portion, or cervical and incisal areas, of the veneer. CONCLUSION: A chamfer or shoulder preparation is recommended for porcelain veneer preparations. Careful evaluation of occlusal forces and how these forces affect the facing is indicated. It is important to receive a full bonding between the tooth and facing.

Bite Force↗

PubMed1998

Shear stresses in the adhesive layer under porcelain veneers. A finite element method study.

A finite element study was made investigating the shear stresses in the composite cement layer and the enamel bond under loaded porcelain veneers. The maximum shear stresses were calculated under various conditions concerning loading angle, laminating extension, and cervical design. The result of the study was that maximum shear stresses did not exceed the stress level for debonding, but that great differences in maximum shear stress appeared with varying loss of bond and different loading angle. The fully laminated facing showed stress levels in the composite cement only 1/5 of those in the facing with a lack of adhesion in the periphery, and 1/15 in the enamel bond. The maximum stresses increased about 4 times when the load angle was 30 degrees as compared with 0 degrees, and increased about 1.5 times from 30 degrees to 60 degrees. The importance of getting a full lamination of the veneer and avoiding unfavorable loading conditions is emphasized in this study.

Dental Bonding↗

PubMed1997

Solubility control of thin calcium-phosphate coating with rapid heating.

The thin calcium-phosphate (Ca-P) coatings produced by the ion-beam-mixing method instead of the plasma-spraying method have been found to be amorphous, resulting in films that easily dissolved in simulated body fluid. These coatings crystalized with conventional heat treatment in an electric furnace but tended to crack easily. Therefore, the purpose of this study was to find a suitable heat treatment that controls the solubility of Ca-P coatings without weakening their adhesion to titanium (Ti) substrate. Thin coatings (approximately 1 microm) were coated onto Ti substrates, followed by heat treatment in a conventional furnace and rapid heating by infrared radiation and laser radiation. X-ray diffraction analysis revealed untreated films to be amorphous but to become crystalline after being heated in a furnace at 500 degrees C, heated rapidly with infrared radiation higher than 600 degrees C and with laser radiation at output power of 10W. We evaluated solubility by estimating the film thickness after immersion in simulated body fluid for 5 weeks: Untreated films dissolved within 1 day. Coatings treated with infrared radiation at 600 degrees C dissolved minimally. Cracks were observed in coatings subjected to infrared radiation at 800 degrees C and furnace-heated at 500 degrees C. Coatings treated with laser radiation tended to dissolve easily, with non-uniform surface degradation. X-ray photoelectron spectroscopy analysis at the interface between the coating and the Ti substrate showed that cracks were the result of decreased Ca-implanted layers and too much growth of Ti-P compounds. No difference was recognized in the Ti-oxidation state among specimens. These data indicate that rapid, homogeneous, and comparatively low-temperature heating, such as defocused infrared radiation, controls Ca-P solubility and ensures the adherence of the coatings to the substrate.

Adhesiveness↗

PubMed1997

A 5-year evaluation of ceramic inlays (CEREC).

The intention of this study was to evaluate the clinical function of porcelain inlays made with the Cerec technique after 5 years. 115 inlays were produced in 46 patients and of these were 51 inlays evaluated. Epoxy models were made from impressions and the gap width and depth was measured in a microscope. SEM pictures were also produced to illustrate the ditching. The measured marginal defects showed a mean width and depth of (SD) 373 (147) and 111 (67) microns respectively. No significant differences of the ditchings could be detected between molars and premolars. Only 3 inlays were found to be fractured of all inlays produced.

Bicuspid↗

PubMed1996

The biocompatibility (cell culture and histologic study) of hydroxy-apatite-coated implants created by ion beam dynamic mixing.

Titanium implants were coated with hydroxyapatite by using a method of ion beam dynamic mixing. Coated and noncoated plates of titanium were placed in a growth medium with fibroblast cells. Implant screws, coated and noncoated, were inserted in rabbit bones and the animals were euthanized after 7, 27, and 122 days, respectively. The results from the cell culture test showed no visible difference between the specimens. Histologic examination of implant specimens indicated more new bone activity against coated screws at 27 days, and that was more pronounced at 127 days. Although the amount of new bone formation was not significantly different, certain signs of favourable new bone formation could be seen in contact with coated implants compared to the noncoated controls.

Animals↗

PubMed1995

Porcelain bond to laser-welded titanium surfaces.

OBJECTIVES: The purpose of this investigation was to determine if laser-welding titanium had an effect on the bond strength of porcelain to metal. This is an important consideration since the metal copings for many multi-unit porcelain restorations are fabricated as single units and then either soldered or welded. METHODS: The bond strength of porcelain to laser-welded titanium was measured with a four-point bending test and the interface was examined using SEM/EDX analysis. RESULTS: The result showed no statistically significant differences (p<0.05) in bond strengths between laser-welded surfaces and mechanically machined surfaces and neither were there any alterations in composition identified after the welding. The use of a special bonding agent did not improve the bond strength significantly. SIGNIFICANCE: Fusing porcelain to laser-welded areas in titanium fixed restorations implies no deterioration of bond strength.

Barium↗

PubMed1995

Photoelastic experiments on facings laminated to teeth.

The influence of various cervical designs of laminated facings was investigated. A variation in the attachment between tooth and facing was also investigated, to examine the influence of partly bad adherence of the resin. The facings were incisally loaded at three different angulations. The study was made in a polariscope, using an Na light source and quarter wave plates. Lack of adhesion of the laminate incisally or cervically created a higher fringe order than when the middle part suffered from insufficient bonding. The shape of the cervical part had only a minor effect on the stress distribution in the facing.

Birefringence↗

PubMed1994

Thin hydroxyapatite coating produced by the ion beam dynamic mixing method.

An ion beam dynamic mixing (IBDM) method was used to produce thin hydroxyapatite coatings on titanium substrates. Structure, solubility and bond strength of coatings were evaluated. The hydroxyapatite-type structure was obtained from heat-treated coatings. As-coated coatings seemed to be almost dissolved within 1 d in Hanks' solution. The thin layer of films, however, was recognized with a firm intermediate compound (such as Ti3P4) to the substrate by X-ray photoelectron spectroscopy, indicating the high tensile bond strengths from the as-coated films. Although slight reductions of the bond strength were observed in heat-treated specimens, the strengths were not reduced by immersion in Hanks' solution for 30 d.

Biomechanical Phenomena↗

PubMed1994

Reduction of cusp deflection resulting from composite polymerization shrinkage, using a light-transmitting cone.

For investigation of whether the use of a transparent plastic cone (Light-tip) influenced cusp deflection, as compared with a conventional method (control), the following experiments were performed. Mesiodistocclusal (MOD) cavities were prepared in 10 extracted premolars, and stainless steel pins were placed on the cusps. The cavities were bonded with Scotchbond Multipurpose, and the distance between the pins was measured. Control restorations using P-50 were placed in three increments, each increment having been polymerized for 40 s. For placing the test restorations, the Light-tip was fitted to the end of the curing wand and pressed into the resin in the proximal box, and the curing light was turned on. The next increment filled the recess created after the removal of the cone in the resin, and curing was performed with the plastic cone in the occlusal box. The third increment was cured without the cone. Each tooth was used for four restorations. In 16 of 20 cases, a significantly decreased cuspal flexure was found when the cone was used. The flexure decreased 24%, as compared with control.

Bicuspid↗

PubMed1993

Increase of in vitro curing depth of class II composite resin restorations.

Simulated class II cavity preparations were made in black Plexiglas acrylic, and various posterior composite resins were placed in the preparations and cured with and without a transparent cone-shaped "Light-tip" device. The transparent Light-tip device improved the curing depth approximately 2.2 mm, and this ability to illuminate the deeper portions of the restoration increases the potential to improve the curing of composite resin.

Acrylic Resins↗

PubMed1993

On functional strain in fixed and removable partial dentures. An experimental in vivo study.

Three rosette strain gauges were attached to a fixed bilateral cantilevered crossarch maxillary bridge and one linear strain gauge to an attachment-retained removable partial denture (RPD), to study the functional deformation pattern in this combined reconstruction. The deformation under clinical conditions at maximum habitual biting and at maximum unilateral loading was very complex, with both elongation and contraction in different parts of the fixed reconstruction. Even though this complexity in the functional deformation was found both with and without the RPD incorporated, the RPD seemed to provide a more even and favorable distribution of the masticatory forces in the fixed reconstruction.

Adult↗

PubMed1993

On functional strain in some fixed and removable partial dentures. An experimental in vitro study.

An 11-unit fixed maxillary reconstruction with 2 bilateral cantilever pontics in combination with a removable partial denture (RPD) with a palatal bar was fabricated. The RPD was retained to the fixed reconstruction with precision attachments. A laboratory model system was constructed in such a manner that the mechanical properties of the biologic supporting tissues involved were simulated by artificial materials. By means of a strain-gauge technique the deformation was studied in both the fixed and the removable partial denture. In different laboratory loading situations with and without the RPD the deformation in the fixed dental appliance was more extensive and more complex when the RPD was excluded.

Dental Stress Analysis↗

PubMed1992

Bond strength of porcelain on cast vs. wrought titanium.

The bond strength of porcelain fused to cast and wrought titanium surfaces was calculated from fracture loads in a 4-point bending test. Two different porcelain were applied (O'Hara and Duceratin). The surface of Ti-cast specimens was treated in two different ways to produce variations in the impurity level before porcelain veneering. Microhardness measurements as well as scanning electron microscopy with EDX analysis were conducted. The results showed no significant difference in bond strength between the two porcelains. Nor was any difference in bond capacity found between thoroughly blasted castings and wrought titanium. Significantly lower bond strengths were observed for lightly blasted specimens and for specimens treated with Gold bonding agent. Impurities in the surface region of the castings were found to be due to contact with the investment during solidification. This indicates that a thin surface layer (50-100 microns) of the casting should be removed before firing of the porcelain.

Aluminum Oxide↗

PubMed1992

Cytotoxicity of corroded gallium and dental amalgam alloys. An in vitro study.

The cytotoxicity of one gallium and three different dental amalgam alloys was assessed in a cell culture system. Two evaluation methods were used, the filter method and an extraction method. Before being tested, set specimens of the alloys were stored in 0.9% NaCl solution for 1 and 10 weeks, to corrode. The alloys showed various degrees of cytotoxicity, ranging from mild to marked. Differences were found between the two testing methods, but in most cases no major differences in cytotoxicity were found between the Ga alloy and the amalgams. The results encourage further study and development of the Ga alloy, which is mercury-free.

Biocompatible Materials↗