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Biomedical subjects

G Vanherle

Publications and source records attributed to G Vanherle.

107 records · Page 6Linked to original sources
PubMed1986

The impact of composite structure on its elastic response.

The non-destructive determination of Young's modulus of dental composites by means of the fundamental period was found to be reliable and accurate. Post-polymerization effects could clearly be detected. Exponential regression analysis showed a correlation coefficient of 0.92, after logarithmic transformation, with volumetric filler content. The high accuracy and reliability of the measurements themselves are reflected in low standard deviations. The results are in excellent agreement with those of other investigations. Furthermore, the ease and speed of operation make this new procedure a powerful laboratory tool for material-testing and practical large-scale investigations.

Chemical Phenomena↗
PubMed1983

Structural evidences of the microfilled composites.

The new composite concept of microfilled composites has certain advantages, such as polishability, permanent smoothness, and high abrasion resistance. In the mouth, however, these new materials are not perfect and they often fail in stress-bearing restorations. In the present study, the weak links and imperfections of these materials are determined by means of direct and indirect SEM techniques. The chemical adhesion between polymer blocks and polymer matrix is questionable; fractures occur most often at the filler-matrix interface. In vivo, there is still a certain preferential wear of the resin matrix. In Estic Microfill, rear weak zones with starlike condensations are observed, which could be related to a certain incompatibility of its composing resins and/or to incomplete and inhomogeneous polymerization. In a fractured Isopast restoration, the polymer blocks are clearly revealed, scattered in a three-dimensional polymerized matrix network.

Composite Resins↗
PubMed1982

Conventional and microfilled composite resins. Part II. Chip fractures.

Dentists are accustomed to advantages and disadvantages in the materials at their disposal. This article was concerned with one disadvantage of microfilled composite resins, namely, chip fractures. Probably due to their higher coefficient of thermal expansion, higher water sorption, higher polymerization shrinkage, and lower tensile strengths, cohesive as well as adhesive chip fractures occur three to four times more often with microfilled composite resins than with conventional composite resins. Microfilled composite resins are indicated for esthetic purposes. They are contraindicated for Class IV and stress-bearing restorations. They are indicated for limited use in Class I restorations where esthetics is of primary importance. The technique of use must include acid-etching and intermediate bonding. The microfilled composite resins enjoy a smooth finish and high luster. This offers advantages in areas where smoothness is paramount. They may replace conventional composite resins for resurfacing existing restorations and veneering stained or mottled anterior teeth. They are indicated for treatment of cervical erosion.

Chemical Phenomena↗
PubMed1982

The use of glazing materials for finishing dental composite resin surfaces.

The purpose of this study was to investigate the retention of glazes on polished composite surfaces. Sections of three differently resin-coated composites have been prepared in vitro and examined by scanning electron microscopy (SEM). All samples showed an interrupted interstice between glaze and composite. After ultrasonic cleaning of the composite surface, the empty porosities do not provide enough mechanical retention to retain the glaze. The difference in physical properties of both components may explain the releasing of the sealant. Surface conditioning with H3PO4 (37%) enhances the mechanical retention on coarse-grained composites. The same effect occurs using chloroform. The chemical also realized a partial chemical bond. however, it has been proved to be insufficient to prevent glaze releasing. Consequently, the use of glazing materials seems unsuitable for a permanent gloss on composite surfaces.

Chemical Phenomena↗
PubMed1982

Observation and comparison of polished composite surfaces with the aid of SEM and profilometer.

Fourteen different composites were polished in vitro with Sof-lex 3M discs. The results were examined clinically, with SEM, and profilometrically. According to the clinical study the different materials were divided into three groups. Group A consisted of five composites, that could be polished up to a fair gloss. Group B contained five composites, where only a semi-gloss could be obtained. Group C contained four products, whose surfaces remained dull after whatever polishing procedure. The SEM study affirmed these results. The products of group A showed smooth and homogeneous surfaces; hence their name: smooth-surface composites. The products of group B can be considered as classic composites. Group C contains among others the glass ionomer cements. The profilometrical study pointed out that the roughness degree of group A was three times smaller than that of group B and five times smaller than that of group C. The polishing procedure was further analysed. Polishing material, technique and time are the most important factors in the finishing of composite fillings.

Composite Resins↗
PubMed1982

Observation and comparison of polished composite surfaces with the aid of SEM and profilometer. II. Following tooth cleaning procedures.

After cleaning with an abrasive toothpaste, fourteen polished composites were examined in vitro SEM and profilometrically. It was shown that the smooth surface composites kept a remarkable smoothness. The classic composites coarsened profilometrically eight times under these testing conditions, and the glass-ionomers fourteen times. SEM pictures pointed out that the organic matrix was the weakest link for classic composites as well as for glass-ionomer cements. The glass-ionomers were the roughest group because of the larger grain size, numerous cracks and porosities. The porosities hampered the roughness measurements in all materials and contributed to a large extent to the roughness of the products.

Composite Resins↗
PubMed1982

A new in vivo replica technique for scanning electron microscope study of dental plaque morphology.

For the micro-morphological investigation of soft oral tissues and deposits on the teeth in vivo, the use of an accurate replica technique is essential if the object under study cannot be examined directly. The conventional replica techniques based on resin or elastomer positive dies, have some limitations due to the instability of the sample die in the scanning electron microscope (S.E.M) conditions and artifacts induced at higher magnifications. Therefore, a new replica technique has been developed using a low viscosity impression material that is subsequently copperplated and poured with synthetic plaster. This offers a stable metal positive die suitable for direct examination in the S.E.M. without prior gold evaporation. Higher magnifications (greater than 7500) are easily obtained without the danger of artifacts. Reproduction of details is of a high order, and the reproduction ability depends only on the accuracy of the first impression. This technique offers new possibilities of discerning fine changes in surface detail in longitudinal clinical investigations.

Adult↗
PubMed1982

Unreacted methacrylate groups on the surfaces of composite resins.

The unreacted methacrylate groups on the surface of conventional composites and microfilled composites were studied by means of multiple internal reflection infrared spectroscopy. The influences of polymerization time, temperature, and the effect of polishing were studied. We also attempted to relate the results of some mechanical tests to the degree of chemical unsaturation measured in the different resins. All surface treatment and manipulative variables caused a decrease in double bond content and interfacial bond strength.

Acrylates↗
PubMed1981

Characterization of composite resins by NMR and TEM.

This investigation demonstrated that the monomer composition of the investigated restorative resins varied from brand to brand. The NMR analysis showed that most filling materials contained the bis-GMA, iso-bis-GMA, and TEDMA monomers in varying concentrations. The high TEDMA monomer concentration in the smooth-surface composites and, in one case (Isopast and Isocap), the total absence of the bis-GMA system are clearly evident. We can, therefore, expect that the clinical properties of the microfilled, smooth-surface materials cannot be generalized inside the group, and that they will differ from those of the conventional composites. The use of submicron filling particles in the matrix phase is also present in some conventional materials.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1981

An universal and accurate replica technique for scanning electron microscope study in clinical dentistry.

One of the main concerns of dental research is the observation of the oral tissues and the materials applied to the dentition. The changes in composition and structure of the outer surfaces and the materials deposited on these surfaces are of special interest. In the literature, a variety of replica techniques for these purposes is described (Grundy in 1971 [12]; Saxton in 1973 [25]). The use of these techniques is limited because of artifacts in the samples, and a restricted resolution power resulting from useful magnifications in the order of 800x. An accurate and universal replica technique for the examination of specimens to be viewed under the SEM has been developed. The first impression is made by a light body silicone elastomer (President Coltene). The positive replica is made by electrodeposition of copper in an electro plating bath (Acru plat 5 electronic, Dr. Th. Wieland, D-7530 Pforzheim). The reliability and accuracy of this replica technique was verified by a scanning electron microscopic comparison of the replicas and the actual structures of etched enamel. To illustrate the applicability of the replica technique to structures with much lower hardness, also high resolution images of dental plaque were produced. The copper surface offers a perfect, original and proper electroconductive medium that withstands the bombardment of electrons and the relatively severe conditions in the scanning electron microscope. Reproducibility was accurate as judged by the duplication in position, size, and shape of the fine detail at magnifications of 7500x offering a resolution of 25 nm.

Bacteria↗