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Biomedical subjects

A J Feilzer

Publications and source records attributed to A J Feilzer.

At least 19 recordsLinked to original sources
PubMed2001

Modeling of viscoelastic behavior of dental chemically activated resin composites during curing.

Shrinkage stresses generated in dental resin composites during curing are among the major problems in adhesive dentistry, because they interfere with the integrity of the restored tooth. The aim of this study was to find a mechanical model to describe the viscoelastic behavior of a two-paste resin composite during curing, to aid our understanding of the process of shrinkage stress development. In this study, stress-strain data on Clearfil F2 during curing were obtained by a dynamic test method and analyzed using three mechanical models (Maxwell, Kelvin, and the Standard Linear Solid model). With a modeling procedure, the model's stress response was compared with the experimental stress data, and the material parameters were calculated. On the basis of the modeling and evaluation results, a model for describing the viscoelastic behavior of the shrinking resin composite was selected. The validation results showed that the modeling procedure is free of error, and that it was capable of finding material parameters associated with a two-parametric model with a high degree of accuracy. The viscoelastic behavior of the shrinking resin composite, as excited by the conditions of the test method, cannot be described by a single mechanical model. In the early stage of curing, the most accurate prediction was achieved by the Maxwell model, while during the remainder of the curing process the Kelvin model can be used to describe the viscoelastic behavior of the two-paste resin composite.

Dental Cements↗
PubMed2000

The influence of surface roughness on porcelain strength.

OBJECTIVES: In order to adjust occlusion, the functional surfaces of porcelain restorations are often ground and mechanical machining is even an essential part of the CAD-CAM process for these restorations. The aim of this study was to investigate the influence of the finishing procedures on the biaxial flexure strength of four commercial porcelains. METHODS: Four commercial porcelains of which two are used for metal-ceramic restorations (Flexo Ceram Dentine and Vita VM K68) and two for veneers and inlays (Duceram LFC Dentine and Cerinate BODY) are used in this study. For each porcelain, sixty discs (Ø = 22 mm, h = +/- 2.0 mm) were produced using twelve different finishing procedures. Twenty discs were left untreated, twenty discs were milled, using a high-speed diamond disc, and twenty discs were machined in a high-speed grinding/polishing device. Half of the samples were glazed. In each of these six groups, half of the samples were stored for 16 h at 80 degrees C in a 4% acetic acid solution. The biaxial flexure strength was determined using the ball-on-ring method. In each group the roughness of the surface was determined and examined via SEM. RESULTS: With the exception of Flexo Ceram Dentine, a significant correlation was found between the roughness of the surface and the biaxial strength: the smoother the surface, the stronger the sample. The differences in biaxial strength may be attributed to the stress concentration of an applied load due to the roughness of the surface caused by mechanical finishing or chemical action. The fact that the strength of Flexo Ceram Dentine was not affected by the different surface treatments is probably due to the size of the leucite particles, which apparently induce more stress concentration than the surface flaws and the roughness of the surface. SIGNIFICANCE: It was concluded that surface roughness determines the strength of a porcelain material, except where the inner structure of the material causes greater stress concentration than that caused by the combination of surface roughness and surface flaws.

Ceramics↗
PubMed2000

The air-abrasion technique versus the conventional acid-etching technique: A quantification of surface enamel loss and a comparison of shear bond strength.

The purpose of this study was to quantify the surface enamel loss that results when an air-abrasive technique is used and to compare the shear bond strength of different prebonding and bonding methods. Enamel loss was determined for 2 enamel-conditioning methods: acid etching with 37% phosphoric acid; and sandblasting with 50 microm aluminum oxide particles under different conditions. A profilometer was used to determine the surface enamel loss. Forty-two bovine teeth were divided into 7 groups (N = 6). The statistical comparison of the different groups was carried out by analysis of variance. The results showed that under certain conditions the enamel loss associated with sandblasting is equal to or smaller than that resulting from acid etching. In addition, the effectiveness of different prebonding and bonding techniques used in the bonding of orthodontic brackets was evaluated by means of shear bond strength measurements. For bonding, 1 resin and 1 glass ionomer cement were evaluated; for prebonding, a sandblaster, 2 different polyacrylic acids and phosphoric acid were tested. Seventy bovine teeth were divided into 7 groups (N = 10) and then stored in water for 24 hours. An Instrom testing machine was used to determine bond strengths, and the 7 groups were compared by means of analysis of variance. The significance of post hoc tests was predetermined at P <.003. The results showed that the bond strength of the sandblasted groups was significantly lower than that of the etching groups. This indicates that sandblasting is not an alternative for the acid-etching technique currently used in orthodontic practice.

Acid Etching, Dental↗
PubMed2000

Visco-elastic parameters of dental restorative materials during setting.

Contraction stresses generated in restoratives during setting are among the major problems in adhesive dentistry, since they often result in loss of adhesion from the cavity walls or in post-operative pain. The rate of stress development and the ultimate magnitude of the stress, which determine the seriousness of these problems, depend on the relatively unknown visco-elastic behavior of the restoratives during setting. The aim of this study was to determine the visco-elastic parameters during setting, to aid our understanding of the process of contraction stress development. A dynamic mechanical method was used in which the materials were subjected to periodic strain cycles in a universal testing machine during the first 60 min of setting. The visco-elastic parameters (viscosity eta and Young's modulus E) were calculated by analysis of the experimental stress-strain data with a simple mechanical model according to Maxwell. Two restorative materials from different classes were investigated: a two-paste resin composite and a conventional glass-ionomer cement. A comparison of the results showed significant differences in the development of viscosity and stiffness in the early stage of setting. The resultant relaxation time (eta/E) of the glass ionomer remained at a low level during the first 15 min, whereas that of the resin composite increased markedly. This is of clinical importance, since it implies that, during the early setting stage, glass ionomers are better capable of reducing the contraction stresses than resin composites, thus increasing the likelihood that the bond with the cavity walls will form and survive during setting.

Composite Resins↗
PubMed1998

Quantification of fracture healing with three-dimensional computed tomography.

Quantitative methods are necessary for an objective evaluation of fracture healing. Three-dimensional computed tomography (CT) for the measurement of callus volume and density could be such a method and was investigated in an animal model. In 23 goats a closed tibial fracture was created and stabilized with a cast. The animals were killed at 2, 4 and 6 weeks for radiographical, CT and biomechanical analysis. From the CT scans a three-dimensional reconstruction of the callus was made to measure its volume and mean density. At 2 weeks the callus volume had already reached its maximum. In contrast, callus density, torsional strength and torsional stiffness increased over time (P < 0.0001, analysis of variance, ANOVA). Multiple regression analysis showed that the callus volume was not related to the torsional properties. However, callus density was a significant explanatory variable for both torsional strength (R2 = 0.72, P < 0.0001) and torsional stiffness (R2 = 0.82, P < 0.0001). Therefore, callus density as measured by three-dimensional CT is a predictor of the extent of fracture consolidation. CT with three-dimensional reconstruction of the callus seems a valid technique for the quantification of fracture healing.

Analysis of Variance↗
PubMed1998

A radiographic and scanning electron microscopic study of approximal margins of Class II resin composite restorations placed in vivo.

INTRODUCTION: Clinical studies on the quality of Class II amalgam and resin composite restorations frequently report defective cervical margins. AIM: The aim of this study was to evaluate the quality of the approximal margins of Class II resin composite restorations placed in vivo using various application techniques and adhesive systems. MATERIALS AND METHODS: Class II restorations were placed in premolar teeth in vivo, using different adhesive systems and application techniques. After extraction of the teeth, the restorations were evaluated radiographically and by SEM. RESULTS: One-hundred and forty-four resin composite Class II restorations were evaluated. According to the radiographs, 4% of the restorations were overfilled and 33% were underfilled. SEM pictures revealed that 43% of the restorations were overfilled and 25% underfilled. Thirty-two per cent of the restored teeth showed a flash of bonding agent on the approximal surface. CONCLUSIONS: Class II resin composite restorations placed in vivo may be found frequently to show imperfect cervical margins. Overextended margins observed by SEM are difficult to detect on radiographs. When seen on a radiograph, a thick layer of bonding agent may be interpreted as an underfilled restoration.

Acid Etching, Dental↗
PubMed1998

Marginal integrity and postoperative sensitivity in Class 2 resin composite restorations in vivo.

INTRODUCTION: Problems that may arise in resin composite Class 2 restorations include microleakage and postoperative sensitivity. However, limited in-vivo research is conducted to evaluate these processes. AIM: The aim of this study was to assess postoperative sensitivity, microleakage and the pooling of adhesives in relation to Class 2 box-type composite restorations placed in vivo using various adhesive systems and application techniques. MATERIALS AND METHODS: One hundred and forty-four Class 2 box restorations were placed in the mesial and distal surfaces of 72 premolar teeth in-vivo using one of three combinations of adhesive systems and three filling techniques. After 6 weeks of clinical service postoperative sensitivity was recorded. The teeth were then extracted, immersed in a dye solution and sectioned. Microleakage and pooling of the adhesive was recorded. Statistical analysis involved logistic regression and chi2 tests to identify differences between groups at p < 0.05. RESULTS: Of the 144 restorations, 65 showed minimal cervical leakage in enamel, 5 suffered leakage into dentin and 74 were free of microleakage. No statistically significant differences were found in cervical microleakage between the adhesive systems or between filling procedures. Occlusal microleakage in the enamel was present in 16 of the 160 restorations. Liner Bond 2 restorations leaked significantly more at the occlusal surface (p < 0.05). Pooling of the adhesive was significantly less when PhotoBond was used. No spontaneous postoperative sensitivity was reported. Twenty-eight restorations were sensitive to loading. Postoperative sensitivity was significantly less in patients with Liner Bond 2 restorations. CONCLUSIONS: The adhesive systems used in this study showed minimal leakage into dentin in vivo. Using Liner Bond 2, restorations exhibited more occlusal leakage but were significantly less sensitive to loading.

Adhesives↗
PubMed1998

Class I occlusal composite resin restorations: in vivo post-operative sensitivity, wall adaptation, and microleakage.

PURPOSE: To investigate the effect of restoration technique and adhesive system on the post-operative sensitivity and marginal adaptation of Class I occlusal composite resin restorations placed in vivo. MATERIALS AND METHODS: 48 Class I cavities were restored in vivo according to one of three protocols: (1) Scotchbond Multi-Purpose/P50 placed in increments; (2) Scotchbond Multi-Purpose/P50 placed in bulk, and (3) Clearfil Liner Bond 2/Clearfil Ray Posterior placed in bulk. Post-operative sensitivity and sensitivity on loading were recorded 5-7 weeks after placement of the restorations; the teeth were cautiously extracted, immersed in a dye solution and sectioned. SEM observations were made from epoxy resin replicas. Microleakage and gap formation was assessed. RESULTS: No differences among adhesive systems or restoration procedures were found for microleakage. Post-operative sensitivity was reported in 14% of all teeth but was absent in the Clearfil Liner Bond 2 group. Sensitivity on loading was experienced by patients in 56% of the restorations. Group 1: nine teeth; Group 2: 15 teeth; Group 3: three teeth. Differences were statistically significant for all three groups. The SEM analysis showed that restorations placed in two layers showed less gaps than restorations placed in bulk.

Acid Etching, Dental↗
PubMed1997

The effect of curing light variations on bulk curing and wall-to-wall quality of two types and various shades of resin composites.

OBJECTIVES: This study evaluated the influence of light intensity and irradiation time variations on the curing efficacy of two types and various shades of resin composites and the effect of reduced light intensity on the preservation of wall-to-wall continuity. MATERIALS AND METHODS: Three microfilled composites (in three different shades) and one hybrid composite were used in this study. Polymerization shrinkage, and the hardness and adaptation of adhesive restorations in dentin cavities were determined at light intensities of 175 and 700 mW/cm2 and irradiation times of 10 and 60 s. Data were compared using in a general linear model analysis. RESULTS: Shrinkage measurements were the indication of conversion and conversion rate. Reduced intensity slowed down the rate of polymerization but did not reduce the conversion as long as an irradiation time of 60 s was employed. High-energy irradiation caused increased separation of the composite from the tooth structure. On the basis of obtaining optimal conversion and adaption, it was demonstrated that the irradiation time to be more effective than irradiation energy. SIGNIFICANCE: Light-cured composites require an understanding of their structure, pigmentation and irradiation parameters to obtain optimal performance. High intensity light-curing does not necessarily lead to optimal quality.

Analysis of Variance↗
PubMed1997

Sealing ability of eight resin bonding systems in a Class II restoration after mechanical fatiguing.

OBJECTIVE: The purpose of this in vitro study was to evaluate eight different adhesive systems to determine whether functional loading affects the marginal integrity of Class II restorations. METHODS: In 80 extracted upper human premolars, Class II cavities were prepared and restored with eight different commercially available adhesive resin restorative systems. The occlusal margins were located in enamel and the gingival margins in dentin. During immersion in a dye solution, half of the restored teeth were exposed to a load-cycling procedure, after which all the specimens were sectioned, and the extent of dye penetration was visually examined using a stereo microscope. The results were analyzed statistically using the Mann-Whitney U-test and Wilcoxons Rank test. RESULTS: Exposure of the restorations to load cycling significantly reduced the marginal integrity cervically. Perfect sealing was found practically at all occlusal margins. Significant differences (p < 0.05) were found in the cervical sealing quality of the various adhesive systems. SIGNIFICANCE: The results of this study show that functional loading damages the cervical marginal seal of adhesive Class II restorations. For many adhesive systems, the setting shrinkage stress alone was not able to damage the marginal integrity cervically. Therefore, mechanical fatiguing distinguishes the sealing quality of adhesive systems in a more expressive way. There is a substantial difference in sealing quality between the various resin restorative systems tested.

Bite Force↗
PubMed1997

Polymerization contraction stress in thin resin composite layers as a function of layer thickness.

OBJECTIVES: In the present study, the effect of layer thickness on the curing stress in thin resin composite layers was investigated. Since the value of the contraction stress is dependent on the compliance of the measuring equipment (especially for thin films), a method to determine the compliance of the test apparatus was tested. METHODS: A chemically initiated resin composite (Clearfil F2, Kuraray) was inserted between two sandblasted and silane-coated stainless steel discs in a tensilometer. The curing contraction of the cylindrical samples was continuously counteracted by feedback displacement of the tensilometer crosshead, and the curing stress development was registered. After 20 min, the samples were loaded in tension until fracture. The curing stress was determined for layer thicknesses of 50, 100, 200, 300, 400, 500, 600, 700 microns, 1.4 mm and 2.7 mm. The compliance of the apparatus was calculated with the aid of a non-linear regression analysis, using an equation derived from Hooke's Law as the model. RESULTS: None of the samples fractured due to contraction stress prior to tensile loading. The contraction stress after 20 min decreased from 23.3 +/- 5.3 MPa for the 50 microns layer to 5.5 +/- 0.6 MPa for the 2.7 mm layer. The compliance on the apparatus was 0.029 mm/MPa. SIGNIFICANCE: A measuring method was developed which was found to be suitable for the determination of axial polymerization contraction stress in this films of chemically initiated resin composites. The method makes it possible to estimate the stress levels that occur in resin composite films in the clinical situation.

Analysis of Variance↗
PubMed1997

Influence of compliance of the substrate materials on polymerization contraction stress in thin resin composite layers.

The present study determined in a laboratory set-up the influence of compliance of the substrate material on polymerisation contraction stress for various thicknesses of bonded dental resin composite films. When the compliance of the tensilometer set-up was increased from 0.029 micron MPa-1 to 0.150 micron MPa-1, the contraction stress in films with a thickness of 100 microns and a diameter of 5.35 mm decreased from 22 to 7 MPa. For the 700 microns samples the stress decreased from 12 to 11 MPa. It was concluded that if compliance from the substrate materials is possible, a thinner resin composite film may effect a more reliable bond.

Chemical Phenomena↗
PubMed1997

Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives.

OBJECTIVES: This paper is intended to contribute to the recognition and understanding of problems related to polymerization shrinkage. DATA SOURCES: Scientific publications of relevance with regard to this subject were critically reviewed. STUDY SELECTION: The dimensional changes which develop during the curing of resin composites and glass polyalkenoate cements are studied, with special reference to methods of determining shrinkage, shrinkage stress and stress relief. CONCLUSIONS: As no method for handling the adhesive restorative materials has yet been described which guarantees a leakproof restoration, the practitioner has to accept the problem of polymerization shrinkage and destructive shrinkage stress. Only a proper understanding of the mechanisms that cause these problems and the techniques that may reduce their effects will enable the practitioner to derive maximum benefit from the application of resin composites and glass polyalkenoate cements in restorative dentistry.

Composite Resins↗
PubMed1995

The influence of water sorption on the development of setting shrinkage stress in traditional and resin-modified glass ionomer cements.

OBJECTIVES: The aim of this study was to determine the setting stress development for some traditional and resin-modified glass ionomer cements and to assess the effect of early water exposure to this stress. METHODS: The development of the setting stress of the glass ionomer cements was determined in a tensilometer set-up as described earlier by Feilzer et al. (1987). RESULTS: The results of this study show the influence of water sorption on the development of setting shrinkage stress in bonded glass ionomer cements. When curing took place under isolated conditions (no hydration or dehydration), all the traditional glass ionomer cements investigated fractured spontaneously, either adhesively and/or cohesively, due to the developing stress. Early exposure to water led to stress relief and prevented spontaneous fracturing. For the light-cured products, no spontaneous failures were observed under isolated conditions. Stress relief due to water sorption reversed the contraction stress into an expansion stress. SIGNIFICANCE: Exposure of traditional glass ionomer cements to water at an appropriate time by the use of permeable matrix systems is advised. Whether the conversion of contraction stresses into expansion stresses as observed for the resin-modified products, is beneficial for a restoration requires further study.

Absorption↗
PubMed1995

Influence of light intensity on polymerization shrinkage and integrity of restoration-cavity interface.

The results of this study showed that the use of high intensity curing light units negatively affected the integrity of the restoration-cavity interface in class V restorations This is explained by the high reaction rates of light curing resin composites. The interfacial integrity was better preserved with low light intensity as it extends the visco-elastic stage of the setting materials, thereby moderating the setting stress development. The ultimate polymerization shrinkages for both conditions were equal, which suggested equal degrees of conversion and thus equal material properties. The results may alleviate the trend in using higher intensity light curing units and in particular the development of units with laser beams in an attempt to further increase conversion rates.

Composite Resins↗
PubMed1995

Tensile strength of thin resin composite layers as a function of layer thickness.

As a rule, cast restorations do not allow for free curing contraction of the resin composite luting cement. In a rigid situation, the resulting contraction stress is inversely proportional to the resin layer thickness. Adhesive technology has demonstrated, however, that thin joints may be considerably stronger than thicker ones. To investigate the effects of layer thickness and contraction stress on the tensile strength of resin composite joints, we cured cylindrical samples of a chemically initiated resin composite (Clearfil F2) in restrained conditions and subsequently loaded them in tension. The samples had a diameter of 5.35 mm and thicknesses of 50, 100, 200, 300, 400, 500, 600, and 700 microns, 1.4 mm, or 2.7 mm. None of the samples fractured due to contraction stress prior to tensile loading. Tensile strength decreased gradually from 62 +/- 2 MPa for the 50-microns layer to 31 +/- 4 MPa for the 2.7-mm layer. The failures were exclusively cohesive in resin for layers between 50 and 400 microns thick. Between 500 and 700 microns, the failures were cohesive or mixed adhesive/cohesive, while the 1.4- and 2.7-mm layers always failed in a mixed adhesive/cohesive mode. For the resin composite tested, the contraction stress did not endanger the cohesive strength. It was concluded that if adhesion to tooth structure were improved, thinner adhesive joints might enhance the clinical success of luted restorations.

Composite Resins↗
PubMed1993

Setting stresses in composites for two different curing modes.

As a continuation of a study into the development of the polymerization shrinkage stress of chemically initiated composites (CC), the development of the polymerization shrinkage stress of light-initiated composites (LC) in relation to the configuration-factor was determined. During setting, the LC composites generated a higher polymerization shrinkage stress, developed higher cohesive strength to resist this stress and showed less flow than their CC analogues. Trying to find a comprehensive explanation for the differences in behavior of stress development in LC and CC composites, the effect of mixing-in of porosity was also investigated on LC composites. Mixing-in of porosity slowed down and decreased the shrinkage stress development. This was attributed to either oxygen inhibition due to admixed air or to an increase of free surface from the presence of pores within the bulk of the composite.

Composite Resins↗