Biomedical subjects

G Vanherle

Publications and source records attributed to G Vanherle.

17 recordsLinked to original sources

PubMed1992

Stress-induced cervical lesions.

The increasing occurrence of dental lesions at the cervical surfaces requires more knowledge of the causes of the process. Acidic and abrasive mechanisms have clearly been documented as causes but the stress theory by Lee and Eakle is still controversial. This report describes several incidences of possible stress-induced lesions according to the characteristics described by Lee and Eakle. The occurrences of subgingival lesions lend credence to the stress-induction theory by exclusion of other superimposing etiologic factors. With the current concepts, a perceptive approach to the treatment of cervical lesions can be executed.

Bite Force↗

PubMed1992

In vitro vibrational wear under small displacements of dental materials opposed to annealed chromium-steel counterbodies.

In vitro vibrational wear tests were performed on 17 composites and one amalgam with human enamel as a reference. The specimens were fixed on a computer-controlled X-Y translation table that generated an oscillatory movement under small displacements. The dental material specimens were in permanent contact with an annealed chromium-steel counterbody. The tests were performed in ambient air of normal humidity at room temperature under non-lubricated sliding conditions. The friction between the counterbody and each of the various materials was measured on-line. After completion of the tests, the wear volumes were determined by contactless profilometry, and the wear pattern was studied with SEM. The simple vibrational test used in this study allowed a fast classification of different dental materials in terms of the relative wear on either the specimen or the counterbody material. The ratio of the wear volume of the counterbody versus the wear volume of the dental material specimen was used to accurately classify the materials according to their in vitro wear behavior, especially when this ratio was related to the total wear volume of the dental material specimen and the counterbody. From an analysis of the wear behavior of the both contacting materials, it became obvious that neither the wear of the dental materials nor of the chromium-steel counterbody appears to correlate with either the inorganic filler hardness, the intrinsic surface roughness, the surface hardness or the Young's modulus of the dental materials.

Chromium Alloys↗

PubMed1992

A classification of dental composites according to their morphological and mechanical characteristics.

The on-going search for a biologically acceptable restorative material has brought a confusing variety of composites on the dental market. In the present study, commercially available composites are categorized as a function of their mean particle size, filler distribution, filler content, Young's modulus, surface roughness, compressive strength, surface hardness, and filler morphology. Out of this information, it can be concluded that the materials of choice for restoring posterior cavities at present are the Ultrafine Compact-Filled Composites because their intrinsic surface roughness, Young's modulus and, indirectly, their filler content, compressive strength, and surface hardness are comparable to the same properties of enamel and dentin. The Ultrafine Midway-Filled Composites seem to be very satisfactory materials for anterior use.

Composite Resins↗

PubMed1992

Marginal adaptation of four tooth-coloured inlay systems in vivo.

This study investigates the margin quality of four different tooth-coloured inlay systems using computer-aided quantitative margin analysis under scanning electron microscopy. Three types of restorations involved chairside procedures using a commercial CAD-CAM apparatus: one type of inlay restoration was milled from preformed glass ceramic blocks, the other two inlay types were milled from preformed porcelain blocks. The fourth system was based on an experimental indirect composite inlay system. Each inlay type was luted with its respective dual-curing luting composite, which was supplied with the system. After 6 months of clinical service, all four systems revealed a significant percentage of submargination indicating occlusal wear of the luting composite. The porcelain inlays and the composite inlays luted with their respective experimental luting composite showed the best marginal adaptation. Luted glass ceramic inlays, in particular, suffered from a significantly higher percentage of inlay margin fractures (9 per cent) and marginal openings (4 per cent) than the other systems. A possible explanation is that the glass ceramic subsurface structure at the inlay-lute interface was weakened by etching with ammonium bifluoride.

Acid Etching, Dental↗

PubMed1992

Marginal accuracy of CAD/CAM inlays made with the original and the updated software.

The software driving the Cerec CAD/CAM system has recently been updated. In this study, the marginal accuracy of computer-machined porcelain inlays was determined using the original and the updated software. Two types of MOD cavities in Frasaco resin teeth were prepared with either sharp or rounded box corners. The distance of the occlusal and proximal marginal interface was determined using a measuring microscope. The mean occlusal interfacial distance was 52 microns for both programs. Only the box corners showed a significantly larger space, of which the mean value was approximately 200 microns. The updated version improved the marginal accuracy at the box corners. Further reduction of the interfacial distance was accomplished by rounding the sharp box corners.

Bicuspid↗

PubMed1992

Morphological aspects of the resin-dentin interdiffusion zone with different dentin adhesive systems.

Cross-sections of resin-dentin interfaces were etched with an argon-ion beam to make their substructure detectable by scanning electron microscopy. The dentin adhesive systems were categorized morphologically into three groups, and an attempt was made to clarify their adhesive mechanism. The first group of products removed the smear layer. The argon-ion bombardment clearly disclosed a hybrid or resin-impregnated dentin layer. It is hypothesized that conditioning with acidic or chelating agents demineralized the dentin surface-layer to a certain depth, leaving behind a collagen-rich mesh-work. Hydrophilic monomers are then believed to alter this collagen-fiber arrangement in a way that facilitates penetration of the adhesive resin, resulting in a mechanical, intermingled link between collagen and the adhesive resin. The second group preserved the smear layer. In this case, the dentinal tubules were obliterated with globular particles at their orifices and remained patent underneath these smear plugs. This type of adhesive system aims at the incorporation of the smear layer into the hydrophilic monomers, which have an affinity for the organic and/or inorganic components of the underlying dentin. Finally, a third, small group only partly dissolved the smear layer, creating a thin resin-impregnated dentin layer and a resin-impregnated smear plug. This study clearly showed that the application of recent adhesive systems induced structural changes in the dentin surface morphology, creating a retentive interface, called the inter-diffusion zone, between the deep, untouched dentin layers and the composite filling material. This resin-dentin interdiffusion zone offers bonding sites for copolymerization with the resin composite and, concurrently, might have protective potential for the pulp tissues.

Acid Etching, Dental↗

PubMed1992

Factors affecting adhesion to mineralized tissues.

The objective of this paper is to review the literature concerning factors affecting adhesion to mineralized tissues. Factors related to the physicochemical structure of the adherents and to the inherent properties of composite restorative materials, along with the postulated bonding mechanisms of current adhesive systems, are discussed.

Acid Etching, Dental↗

PubMed1992

Dentin- and enamel-bonding agents.

The introduction of bonding agents in restorative dentistry has made it possible to adhere restorative materials to tooth structure. Since bonded restorations were introduced by Buonocore in 1955, extensive research has been conducted to develop systems that bond equally effectively to enamel and dentin. Researchers have identified a micromechanical retention mechanism for the attachment of hydrophobic resin restorative materials to both enamel and dentin that works if appropriate conditioning or priming steps are applied. At the dentin site, the modes of action of current adhesive systems converge to create a resin-dentin interdiffusion zone between the deep dentin structures and the filling material. To incorporate or remove the smear layer in this interdiffusion zone, different adhesion strategies are followed to obtain a resin-dentin bond. In the clinical situation, these modern dentin-bonding systems are more technique sensitive; the thickness of the interface, its elastic capacity, the polymerization efficiency and initiation of the bonding agent, and, finally, the application technique used for the restorative material play an important role in the final result.

Acid Etching, Dental↗

PubMed1991

An evaluation of different adhesive restorations in cervical lesions.

The restoration of 457 cervical lesions was completed with three different bonding agents. All restorations were divided into two categories. In group A the incisal enamel was neither bevelled nor etched. The lesion was cleaned, followed by the application of the bonding agent and the composite resin. The restorations were finished with a butt joint. In group B, after cleaning procedures, the incisal enamel of all lesions was bevelled and etched, followed by the application of the bonding agent and the composite resin. The restorations were finished to a feather edge. The results from this clinical investigation indicated a high failure rate when only dentinal bonding was involved. The group A restorations suffered from a high rate of loss after 6 months. Moreover, the rate of loss increased over subsequent months. The dentin bonding agents used in combination with micromechanical retention on the enamel border in the group B restorations, however, provided an acceptable clinical result. Not only was the percentage of lost restorations quite low after 6 months, but these bonding systems also offered a more reliable marginal adaptation compared with the enamel bond system. One may conclude that the use of a dentin bonding agent in combination with mechanical retention offers a better chance of clinical success in terms of marginal adaptation, retention, and esthetics.

Acid Etching, Dental↗

PubMed1991

Radiopacity of composites compared with human enamel and dentine.

A 99.5 per cent pure aluminium step-wedge served as reference for evaluating the radiopacity of 55 anterior and posterior composites. The radiopacity of all materials evaluated was compared with the radiopacity of human enamel and human dentine of equivalent sample thickness. Seventeen composites exhibited a radiopacity significantly greater than that of enamel. Some composites intended for posterior use lack the radiopacity required for posterior composite restorations.

Analysis of Variance↗

PubMed1991

Trends in the selection of dental filling materials.

In 1983 and 1988 a questionnaire was sent to a random sample of Belgian dentists to compare the selection of filling materials such as amalgam and gold with the tooth-coloured filling materials, composites and glass polyalkenoate (ionomer) cements, for the restoration of Class II lesions in premolar and permanent molar teeth. Despite the increasing demand for aesthetics to be considered, the use of composite resins in the posterior region only increased moderately over the assessment period, while amalgam maintained its leading position as the restorative material of choice in premolar and molar teeth. Only in situations where aesthetics played a primary role did composite resins gain over silver-based fillings. There was no change in the use of gold as an indirect restorative material. Finally, the selection rate of glass ionomers increased slightly.

Acid Etching, Dental↗

PubMed1991

The surface roughness of enamel-to-enamel contact areas compared with the intrinsic roughness of dental resin composites.

The purpose of this study was to determine the surface roughness of enamel-to-enamel contact areas in order to provide a standard for comparison with surface characteristics of commercially available composite restorative materials. In addition, the inherent surface roughness of resin composites was evaluated profilometrically after a toothbrush abrasion procedure. A one-sided t-test analysis was performed to outline significant differences between the surface roughness value of enamel facets and that of the respective composite samples. A surface roughness of 0.64 +/- 0.25 micron (mean +/- S.D.) was found for the enamel-to-enamel contact areas.

Bicuspid↗

PubMed1990

Aesthetic limits of light-cured composite resins in anterior teeth.

The aesthetic limits of light-cured composite resins in anterior teeth are determined mainly by the size and nature of the lesion and the respective preparation. Also the shortcomings of the restorative material itself are of primary importance. The oral environment and the ageing effects ultimately limit the aesthetic expectations.

Chemical Phenomena↗

PubMed1990

[Dental adhesion: foundations and clinical results].

Adhesion is one of the most frequently used words nowadays in dentistry. Although our knowledge on adhesion continues to improve daily, the situation is, however, far from understood. There is still confusion over what adhesion really is, what it means, and how it should be evaluated. The first part of this article deals with the general principles of adhesion and the specific within the dental profession over the clinical efficiency of available adhesive dentinal restorative systems. The second part of this paper presents the 2-year in-vivo results of four commercially available dentinal adhesive systems. From this trial, it seems that the more recent approach in obtaining adhesion to dentine is the most promising in terms of retentive capacities.

Adhesiveness↗

PubMed1989

Mechanical properties and filler fraction of dental composites.

Several mechanical properties of experimental composites and an unfilled resin were studied. The dynamic Young's modulus was measured with a non-destructive dynamic method. The Young's modulus and also the transverse strength were determined statically by means of three-point bending. The hardness was studied by means of Wallace indentation depth measurements, and in vitro wear resistance was assessed under stress-bearing conditions. An exponential regression of the results measured for each property as a function of the volumetric filler fraction was appraised. An excellent correlation was found with each property. This exponential mixture rule is proposed for the study of the mechanical properties of isotropic dental composites.

Composite Resins↗

PubMed1989

Quantitative in vivo wear of human enamel.

In this study, the attrition wear, also called occlusal-contact-area wear, of human enamel was measured quantitatively with a computerized three-dimensional measuring technique over a period of four years. Tooth replicas from a clinical trial were used. A running-in wear period after restorative treatment, followed by steady-state wear, was suggested. The average steady-wear rate on occlusal contact areas was about 29 microns per year for molars and about 15 microns per year for premolars.

Adolescent↗

PubMed1989

[Experience with composite filling materials for posterior teeth].

Currently the discussion about the use of composite materials for posterior teeth is controversial. Although practiced by many dentists, the method has not been universally accepted. The function of this filling material is impaired by its insufficient wear resistance and polymerisation shrinkage, and improvements of clinical application are the only means to prevent marginal gap formation and early secondary caries. In view of these shortcomings all dentists should use composite materials for posterior teeth only in carefully selected indications.

Composite Resins↗