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Biomedical subjects

G Vanherle

Publications and source records attributed to G Vanherle.

At least 55 records · Page 3Linked to original sources
PubMed1996

[Resin-modified glass-ionomers in dentistry].

The resin-modified glass-ionomers contain the essential components of both a conventional glass-ionomer and a visible light-cured resin. They have several advantages like longer working time, shorter setting time, bonding to tooth structure, fluoride-release, better aesthetics than conventional glass-ionomers and ease in use. As disadvantages can be mentioned the polymerisation shrinkage, trapping of air-bubbles, difficulties in colour choice and contouring. A physical and mechanical characterisation was necessary to define the possibilities and limits of these materials. It can be stated that the strength and aesthetic appearance of resin-modified glass-ionomers are less than that of composites, but better than that of conventional glass-ionomers. Clinically, this is expressed in a rough and dull surface compared to a composite restoration. They are not indicated in stress bearing areas. Consequently, they are mainly indicated in cervical class V-restorations in the postcanine region, and probably restorations in pedodontics, geriatric dentistry and for patients with a high caries activity.

Compomers↗
PubMed1996

[Damage to composite restorations].

The expression of damage in dental composite restoratives varies widely, going from some local damage as in attrition facets, to generalized failure or collapes of a restoration. However, crack growth lies on the basis of both aforementioned phenomena. It is therefore of primary importance to gain insight in the way structurally differing materials respond to external stress. It is the aim of the present review to summarize some recent in vitro studies that deal with simulation of wear and fatigue phenomena in dental composite restorative materials.

Composite Resins↗
PubMed1996

[Characterization of resin-containing glass ionomers].

Recently, several new resin-modified glassionomers have been introduced on the dental market. At the moment a real confusion exists over the right terminology of the products and its limits in use. Therefore, an in vitro and in vivo study with simultaneously a comparison with conventional glassionomers and composite resins was really necessary. This study revealed that resin-modified glassionomers have physico-mechanical properties that are situated between those of conventional glassionomers and composite resins. The manufacturers have a different approach concerning the particle size distribution. The new materials give a rough surface. They are not indicated for posterior restorations, because their surface hardness is too low compared to that of enamel, and their fatigue resistance is insufficient. The elasticity decreases during setting and maturation. Consequently, they are mainly indicated in situations that require a moderate strength and esthetics, for patients with a high caries activity and when ease in use is requested.

Composite Resins↗
PubMed1996

[Micro-abrasions of enamel: an alternative to the elimination of superficial demineralization and decalcification].

Tooth discoloration's may cause serious damage to the aesthetic appearance of the patients. These discoloration's can be treated in several ways but up to lately tooth structure had to be removed in an irreversible manner in order to provide sufficient bulk for the new restorative material. Nowadays thanks to the work of T. Croll and others a method has been established in a scientific way whereby tooth discoloration's confined to the outermost layer of enamel can be removed, through the application of an compound called PREMA which will simultaneous erode and abrade the enamel surface. If carefully selected the discoloration can be removed with only a limited loss of tooth structure. The authors describe the historical background of the method. Furthermore patient's selection, specific instruments and materials are described in detail. The clinical procedure is explained step by step, followed by a complete report of the effects of the procedure on the different tooth structures. Finally the long term results are discussed and the possibility to enhance the result by combining this method with home bleaching.

Complex Mixtures↗
PubMed1996

The interaction of adhesive systems with human dentin.

PURPOSE: To investigate the interaction of six experimental and commercial bonding systems with dentin in vivo. MATERIALS AND METHODS: One-Step, Clearfil Liner Bond 2, OptiBond, Permagen with 10% phosphoric acid, Permagen with 35% phosphoric acid, and Prime & Bond were applied in standard Class I occlusal cavities in premolars scheduled for extraction for orthodontic reasons, combined either with a self-cured or with a light-cured resin composite. The teeth were carefully extracted 5 minutes after resin polymerization and fixed in 2.5% glutaraldehyde. After fixation, the specimens were dehydrated, sectioned, and processed for field-emission SEM. RESULTS: Although some systems produced gap-free intact interfaces in specific specimens, all of them showed detachment at the transition between the resin-dentin interdiffusion zone and the fluid resin placed over it. It was apparent that the presence of air-bubbles and/or thick layers of polymerized-filled fluid resin resulted in less frequent separation areas at the resin-dentin interface, providing support for the concept of the elastic cavity wall. It was also confirmed that some dentin adhesive systems do not form a thick layer over the dentin, otherwise the resin composite would not have penetrated the dentin tubules.

Adolescent↗
PubMed1996

[Dental care using silver amalgam].

Dental amalgam is the most widely used filling material in dentistry. In our country there are an estimated 40 million amalgam fillings in place. The mercury present in these fillings has caused health concerns over the last 160 years that amalgam has been used in decayed teeth. The fears have always proven to be unjustified and no harmful effects have ever been demonstrated in dental patients. Mercury can be found in several forms. In dentistry, only the metallic form is used, while inorganic and organic compounds are also present in the environment. The metallic form is absorbed in the human body mostly through the lungs. Once mercury reaches toxic levels inside the body, it will interfere with cell metabolism. Most important among the target organs are the brain, the liver and the kidneys. Elimination occur through urine and feces. Mercury is universally found in blood and urine. The concentration depends on absorption by air, water, nutrition, medication (including dental fillings) and occupational hazards. There are four kinds of objectives to dental amalgam: oral galvanism, toxicity, allergenicity and ecological grievances. Disorders from oral galvanism are difficult and delicate to evaluate as the actual currents are very small. Furthermore, no significant difference can be found in current intensity between patients with and without complaints. Finally patients with complaints often present other oral disorders, the treatment of which most often eliminates all complaints that could be attributed to oral galvanism. Toxicity is dose dependent. Industrial safety rules indicate that the amount of mercury absorbed from dental amalgam fillings is far below the safety level. HgB and HgU levels in patients with amalgam fillings are situated well below the acceptable levels. Allergic disorders are observed in patients with amalgam fillings but far less than expected in view of the wide spread use of dental amalgam. The problem of mercury spilling from dental amalgam fillings into the environment will be resolved by strict legislation in the near future. In this context, it can be stated that the use of dental amalgam is safe and justified. Furthermore, it is also advisable as no other material can meet the actual dental needs as efficiently as can dental amalgam.

Corrosion↗
PubMed1996

Three-year clinical effectiveness of four total-etch dentinal adhesive systems in cervical lesions.

A 3-year follow-up clinical trial of two experimental Bayer total-etch adhesive systems and two commercial total-etch systems. Clearfil Liner Bond System and Scotchbond Multi-Purpose, was conducted to evaluate their clinical effectiveness in Class V cervical lesions. Four hundred twenty abrasion-erosion lesions were restored randomly using the four adhesive systems. There were two experimental cavity designs, in which the adjacent enamel margins either were or were not beveled and acid etched. Clearfil Liner Bond System and Scotchbond Multi-Purpose demonstrated high retention rates in both types of cavity design at 3 years. The two experimental Bayer systems scored much lower retention rates in both cavity designs at 3 years. None of the systems guaranteed margins free of microleakage for a long time. At 3 years, superficial, localized marginal discolorations were observed, the least for Clearfil Liner Bond System, followed by Scotchbond Multi-Purpose and the two experimental systems. Small marginal defects were recorded at the cervical dentin and the incisal enamel margin. Retention of Clearfil Liner Bond and Scotchbond Multi-Purpose appears to be clearly improved over earlier systems, but marginal sealing remains problematic. The two Bayer systems were found to be clinically unreliable.

Acid Etching, Dental↗
PubMed1996

[Characterization of glass ionomer cements containing resin].

Recently, several new resin-modified glassionomers have been introduced on the dental market. At the moment a real confusion exists over the right terminology of the products and its limits in use. Therefore, an in vitro and in vivo study with simultaneously a comparison with conventional glassionomers and composite resins was really necessary. This study revealed that resin-modified glassionomers have physico-mechanical properties that are situated between those of conventional glassionomers and composite resins. The manufacturers have a different approach concerning the particle size distribution. The new materials give a rough surface. They are not indicated for posterior restorations, because their surface hardness is too low compared to that of enamel, and their fatigue resistance is insufficient. The elasticity decreases during setting and maturation. Consequently, they are mainly indicated in situations that require a moderate strength and esthetics, for patients with a high caries activity and when ease in use is requested.

Chemical Phenomena↗
PubMed1996

[Micro-abrasion of the enamel: an alternative to the removal of demineralization and superficial decalcification].

Tooth discoloration's may cause serious damage to the aesthetic appearance of the patients. These discoloration's can be treated in several ways but up to lately tooth structure had to be removed in an irreversible manner in order to provide sufficient bulk for the new restorative material. Nowadays thanks to the work of T. Croll and others a method has been established in a scientific way whereby tooth discoloration's confined to the outermost layer of enamel can be removed, through the application of an compound called PREMA which will simultaneous erode and abrade the enamel surface. If carefully selected the discoloration can be removed with only a limited loss of tooth structure. The authors describe the historical background of the method. Furthermore patient's selection, specific instruments and materials are described in detail. The clinical procedure is explained step by step, followed by a complete report of the effects of the procedure on the different tooth structures. Finally the long term results are discussed and the possibility to enhance the result by combining this method with home bleaching.

Complex Mixtures↗
PubMed1995

Field emission SEM comparison of four postfixation drying techniques for human dentin.

Critical-point drying (CPD) is generally considered essential for the preparation of biologic specimens for electron microscopy. Several attempts have been made to introduce alternative techniques. More recently, this problem has arisen in dentistry, because of the new developments in dentin bonding. The present study focuses on three alternative techniques to CPD: hexamethyldisilazane (HMDS) drying, Peldri II drying, and air drying. Twenty-four dentin disks were obtained from noncarious extracted human molars by microtome sectioning parallel to the occlusal surface. The dentin surfaces were etched with polymer-thickened, silica-free, 10% phosphoric acid semigel, fixed, dehydrated, and dried with one of the four techniques. The specimens were observed in two perpendicular planes, showing dentinal tubules in longitudinal view and cross-section, using a field emission scanning electron microscope. The intertubular demineralized dentin zone was composed of three different successive layers, which did not substantially differ between CPD and Peldri II drying, but were more evident in HMDS-dried specimens: first, an upper layer of denatured collagen and residual smear layer particles, with sectioned collagen fibrils and few open intertubular pores; second, an intermediate layer of closely packed cross-sectioned collagen fibers; and third, a deeper layer with unfilled spaces, scattered hydroxyapatite crystals, and few collagen fibers. HMDS drying seemed to preserve better the collagen network and the microporosity of the demineralized dentin surface. Moreover, HMDS drying is easy to perform. The air-drying method caused some artefacts, such as surface collapsing and thickening of the denatured collagen layer.

Air↗
PubMed1995

In vitro fatigue behavior of restorative composites and glass ionomers.

OBJECTIVES: This in vitro study was conducted to investigate the fatigue behavior of several dental restoratives, including composites, glass ionomers and a resin-reinforced glass ionomer. METHODS: Fatigue was imposed under a reverse stress-controlled regimen, following a staircase approach. Samples were stored and tested under both dry and wet conditions. The following parameters were measured and analyzed: Young's modulus, restrained fracture strength, and flexural fatigue limit. RESULTS: As a general trend, all products showed a decrease in Young's modulus following water sorption. For all products except the resin-reinforced glass ionomer, the same trend was seen in the restrained fracture strength. This is, however, no longer valid for the flexural fatigue limit: the trend is steady-state for the glass ionomers, status quo for the resin-reinforced glass ionomer, and all composites tested show a decrease. SIGNIFICANCE: The diversity in structure of both composites and glass ionomers does not allow findings for one product to be extrapolated to other similar products.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1995

Clinical and semiquantitative marginal analysis of four tooth-coloured inlay systems at 3 years.

OBJECTIVES: The marginal quality of four tooth-coloured inlay systems was clinically investigated and subjected to computer-aided semiquantitative marginal analysis under scanning electron microscopy (SEM) after 3 years of clinical service. METHODS: Three of the restoration types were made using the Cerec CAD-CAM apparatus: one was milled from preformed glass ceramic blocks, and the two other inlay types were milled from preformed porcelain blocks. The fourth system was based on an experimental indirect resin composite inlay system. Each inlay type was luted with a different luting resin composite. The clinical evaluation was performed with a mirror and explorer by two clinicians separately, and the marginal analysis was conducted microscopically on replicas (SEM x 200). RESULTS: After 3 years in situ, all the restorations were clinically acceptable. No recurrent caries was observed. Marginal analysis under SEM detected a high percentage of submargination for all four systems, which suggests that their respective resin composite luting agents were all subject to wear. The percentage of marginal fractures on the enamel side as well as on the inlay side did not increase dramatically compared to the 6-month results. CONCLUSION: The first recall after 6 months of clinical service indicated how tooth-coloured inlays behave at their margins. The 3-year results confirmed the early findings, indicating that wear of resin composite lutes is important and present in all systems. The two ceramic materials showed a similar behaviour at the margins. The resin composite inlay performed better at the inlay site than at the enamel site.

Adult↗
PubMed1994

In vitro flexural fatigue limits of dental composites.

The flexural fatigue test equipment developed was used to study the fatigue behavior of dental restorative composites, using a "staircase" approach. Three commercial composites were tested after dry and wet storage conditions. The findings indicate that the method is accurate and reliable, and that changes due to water sorption are clearly reflected: The flexural fatigue limit decreases after water sorption. From the present results it seems that under environmentally controlled conditions, the fatigue behavior is characterized by a well-defined fatigue stress level above which the composites tested fail rapidly, and below which they survive.

Dental Materials↗
PubMed1994

Clinical relevance of laboratory fatigue studies.

From a clinical point of view, fatigue in dental restorative resins is discussed by the way that fatigue expresses itself in different forms in these materials. In vitro testing of the fatigue sensitivity of dental composites is far from conclusive: there is a need for standardized testing methodology. Some findings obtained with a recently developed fatigue machine, and interpreted as a function of masticatory stresses, indicate that the generalized form of fatigue will probably be limited to microfilled based composites.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1994

Morphological characterization of the interface between resin and sclerotic dentine.

Since dentine exposed to the oral environment undergoes important compositional and morphological transformations, bonding to it differs significantly from bonding to unaffected normal dentine. In this investigation, the interface between resin and sclerotic dentine, the dentine type clinically exhibited by cervical abrasive or erosive lesions, was morphologically characterized by scanning electron microscopy after an argon-ion-beam etching procedure. The microstructure of the resin-sclerotic dentine interface was compared with that produced to normal unaffected dentine in an attempt to find reasons for the reported less reliable bonding of adhesive resins to sclerotic dentine. A resin-dentine interdiffusion zone or hybrid layer with only a limited width was formed at the hypermineralized intertubular dentine. No or only short resin tags were developed in most dentinal tubules, since their orifices were obliterated due to increased peritubular dentine apposition, intratubular deposition of irregular minerals and formation of so-called sclerotic casts. Consequently, it is reasonable to predict that dentine adhesives with an adhesion strategy, which mainly involves micromechanical interlocking by the formations of a resin-dentine interdiffusion zone combined with resin-tag development into the dentinal tubules, will be less effective when applied to sclerotic dentine than to unaffected normal dentine. An adapted adhesive treatment may be necessary to make sclerotic dentine more receptive to bonding. Further research should be directed to develop adhesive systems that bond equally well to various kinds of dentine.

Acid Etching, Dental↗
PubMed1994

Dual cure luting composites--Part II: Clinically related properties.

Thirteen dual cure luting composites were compared in function of film thickness, consistency, and working time by using the American National Standard/American Dental Association (ANS/ADA) specifications for zinc phosphate cement and direct filling resins. The effect of temperature and setting reaction on the film thickness was also evaluated for some representative products. All three clinically related properties varied widely among the products investigated. A strong linear correlation was found between film thickness and consistency. This relation is supported by the temperature dependence of film thickness of dual cure luting composites. Cooling of the material increased the consistency, resulting in a larger film thickness, while heating reduced the film thickness because of the lower consistency. However, one product with a rather short working time at room temperature occasionally exhibited a dramatically enlarged film thickness after heating, probably caused by accelerated chemical polymerization. No correlation emerged between film thickness and maximum filler size or between consistency and filler weight content. Maximum filler size and filler weight content had been measured previously in Part I of this study. Scanning electron microscope (SEM) analysis of the cured film thickness samples revealed that the largest filler particles had been crushed under the heavy load pressure during film thickness measurement. The lack of correlation between consistency and filler weight content can be explained by the multifactorial determination of the consistency. It is concluded that the great diversity in the currently available luting composites makes clear specifications with regard to the optimum composition of luting composites urgently needed. Furthermore, more adequate methods for testing the film thickness of luting composites are also required.

American Dental Association↗
PubMed1994

Clinical status of ten dentin adhesive systems.

Laboratory testing of dentin adhesive systems still requires corroboration by long-term clinical trials for their ultimate clinical effectiveness to be validated. The objective of this clinical investigation was to evaluate, retrospectively, the clinical effectiveness of earlier-investigated dentin adhesive systems (Scotchbond, Gluma, Clearfil New Bond, Scotchbond 2, Tenure, and Tripton), and to compare their clinical results with those obtained with four modern total-etch adhesive systems (Bayer exp. 1 and 2, Clearfil Liner Bond System, and Scotchbond Multi-Purpose). In total, 1177 Class V cervical lesions in the teeth of 346 patients were restored following two cavity designs: In Group A, enamel was neither beveled nor intentionally etched, as per ADA guidelines; in Group B, adjacent enamel was beveled and conditioned. Clinical retention rates definitely indicated the improved clinical efficacy of the newest dentin adhesives over the earlier systems. With regard to adhesion strategy, adhesive systems that removed the smear layer and concurrently demineralized the dentin surface layer performed clinically better than systems that modified the disorderly layer of smear debris without complete removal. Hybridization by resin interdiffusion into the exposed dentinal collagen layer, combined with attachment of resin tags into the opened dentin tubules, appeared to be essential for reliable dentin bonding but might be insufficient by itself. The additional formation of an elastic bonding area as a polymerization shrinkage absorber and the use of a microfine restorative composite apparently guaranteed an efficient clinical result. The perfect one-year retention recorded for Clearfil Liner Bond System and Scotchbond Multi-Purpose must be confirmed at later recalls.

Clinical Trials as Topic↗