Biomedical subjects
Publications and source records attributed to P Lambrechts.
A case of an incidentally found retroperitoneal schwannoma is reported. A schwannoma is a rare, benign tumor affecting the soft tissues and the viscera. In the presented case, the US and CT images suggested the nature of this benign tumor. Angiography confirmed the mass effect on the portal vein and subsequently the potential risk of portal thrombosis. The diagnosis was confirmed at surgery.
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.
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.
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.
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.
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.
The clinical effectiveness of two dentin adhesives, Clearfil New Bond and Scotchbond 2, was evaluated in two different cavity designs. Group A was without enamel bevel or acid etch and with a butt-joint cavity; and group B had enamel bevel, acid etch, and feather-edged cavities. The retentive rate and marginal adaptation were monitored for 2 years. In the Clearfil system, 21% of group A restorations failed after 2 years, whereas virtually all the group B restorations (99%) were retained. In addition, after 2 years, the total of debonded group A restorations in the Scotchbond 2 system expanded to 13%, whereas no restorations from group B were lost. There was clearly marginal deterioration in time irrespective of the bonding system. Nevertheless, the marginal adaptation of cervical lesions restored with Clearfil New Bond adhesive in combination with Clearfil Ray composite resin revealed fewer defects compared with the Scotchbond 2 adhesive with Silux Plus composite resin restorations. SEM evaluation disclosed composite resin remnants on the dentin surface in cavities with lost fillings, which indicates partial cohesive failure of the adhesive joint.
Two commercially available dentine-adhesive systems, Tenure and Tripton, were tested in two different cavity designs by placing 132 Class V composite restorations in cervical lesions of 35 patients. In Group A, the cervical restorations were placed totally in dentine without any intentional enamel involvement. In Group B, they were placed in dentine with adjacent enamel margins bevelled and acid etched. The retention rate, the evidence of clinical microleakage, and the marginal integrity were monitored over a 2-year period. The results of this clinical investigation indicate a high failure rate when only dentinal bonding was involved. A loss rate of 30% for Tenure and 55% for Tripton was noted in Group A after 2 years of clinical service. However, both adhesive systems used in combination with micromechanical retention on the enamel border (Group B) performed extremely well with only one restoration each having debonded over the 2-year period. Identically, marginal integrity and evidence of clinical microleakage more severely deteriorated with time for the Group A restorations in comparison with their Group B counterparts. In summary, the overall results were more positive for Tenure than for Tripton. It is concluded that micromechanical retention by acid etching of the enamel margin is still indispensable for the clinical success of cervical Class V composite restorations, primarily for retention and clinical microleakage and also, but to a lesser degree, for marginal adaptation.
Human enamel and dentin should be used as the physiologic standards with which to compare composite resins, especially in the posterior region. The intrinsic surface roughness of composite resins must be equal to or lower than the surface roughness of human enamel on enamel-to-enamel occlusal contact areas (Ra = 0.64 microns). Roughness determines the biologic strength of composite resins. The nanoindentation hardness value of the filler particles (2.91 to 8.84 GPa) must not be higher than that of the hydroxyapatite crystals of human enamel (3.39 GPa). Composite resins intended for posterior use should have a Young's modulus at least equal to, and preferably higher than, that of dentin (18.500 MPa). The compressive strength of enamel (384 MPa) and dentin (297 MPa) and the fracture strength of a natural tooth (molar = 305 MPa; premolar = 248 MPa) offer excellent mechanical standards to select the optimal strength for posterior composite resins. The in vivo occlusal contact area wear rate of composite resins must be comparable to the attritional enamel wear rate (about 39 microns/y) in molars. Differential wear between enamel and composite resin on the same tooth is a new criterion for visualizing and quantifying the wear resistance of composite resins in a biologic way. Posterior resins must have a radiographic opacity that is slightly in excess of that of human enamel (198% Al). Based on these standard criteria, it can be concluded that in the 21st century the ultrafine compact-filled composite resins may be the materials of choice for restoring posterior cavities.
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.
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.
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.
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.
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.
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.
An asymptomatic case of intrahepatic shunt between a portal and hepatic vein is presented. Ultrasound examination combined with Doppler sonography showed a communication between a dilated portal vein and a hepatic vein. Computed tomography and angiography confirmed the findings. Porto-hepatic venous shunting is very rare and has previously been reported in association with cirrhosis. The vascular malformation we present is believed to be a congenital anomaly, as no signs of cirrhosis or trauma were found.
Root resorption can be divided into two main categories: internal root resorption and external root resorption. Internal root resorption is a pathology that can lead to tooth destruction in the short term and must consequently be stopped as soon as possible by applying adequate canal treatment. Until now, despite many research studies, very little is known about its causes and the way this kind of resorption appears. There are many different forms of external root resorption and it has a very diverse etiology. An external root resorption can thus appear in case of orthodontic treatment or due to the pressure brought by cysts, tumours or impacted teeth. A trauma or an infection may also lead to the development of an external root resorption. Because they are so diverse, each of these forms of external root resorption requires a specific treatment. It should also be noted that internal root resorptions, and some forms of external resorption too, often respond favourably to a calcium hydroxide treatment.
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.