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Biomedical subjects

F Sundström

Publications and source records attributed to F Sundström.

At least 19 recordsLinked to original sources
PubMed1996

Influence of paste temperature at curing on conversion rate and bending strength of light-cured dental composites.

Pastes of three dental composites were tempered to 20 degrees C, 37 degrees C and 60 degrees C. Test specimens (22 x 2 x 2 mm) were cured by light and stored in deionized water. Three-point bending strength was measured after 1 h and after 24 h. Degree of conversion on the surface exposed to the curing light and the opposite surfaces at the bottom of the mould was analysed by Fourier transform infrared (FTIR) after 1 h. After 1 h, specimens produced using the pastes cured at 60 degrees C showed significantly higher bending strength than the specimens produced using pastes cured at 20 degrees C and 37 degrees C. However, after 24 h the composites pretempered at the lower temperatures had developed the same level of bending strength as the composites cured at 60 degrees C. An increase in the degree of conversion with increased paste temperature was found in all materials after 1 h.

Acrylic Resins↗
PubMed1996

Mineral loss in incipient caries lesions quantified with laser fluorescence and longitudinal microradiography. A methodologic study.

The laser fluorescence method (LAF) was validated with longitudinal microradiography (LMR) for assessment of mineral loss in incipient caries lesions in human enamel. Fluorescence radiance scans and LMR recordings were made of 36 enamel slabs with incipient lesions. Original sound values for fluorescence radiance and enamel amount (kg.m-2) at the lesion site were reconstructed by a computer algorithm. Changes in fluorescence radiance and amount of enamel in each measuring point were calculated. The reconstruction method was tested on 20 sound enamel surfaces. The differences between measured and reconstructed values were -0.13 +/- 0.17% with LAF and 0.002 +/- 0.005 kg.m-2 with LMR. The repeatability of the caries quantification was tested by measuring one lesion 20 times. The fluorescence loss in this lesion was 18.2 +/- 1.0%. The enamel loss was 0.09 +/- 0.02 kg.m-2. The correlation between measurements with the two methods was r = 0.73. The non-destructive laser fluorescence method was concluded to be a sensitive and valid method for quantification of mineral loss in enamel caries lesions.

Adolescent↗
PubMed1996

Flexure strength of resin-modified glass ionomer cements and their bond strength to dental composites.

The flexure strength of three resin-modified glass ionomer cements and one conventional glass ionomer cement and their bond strength to dental composites were studied by measuring the three-point bending and the shear strengths. The bond strengths between the dental composite and the resin-modified glass ionomer cements were dependent on the curing modes. Resin-modified glass ionomer cements bonded significantly more strongly to cured dental composites than dental composites bonded to cured resin-modified glass ionomer cements. However, the dental composites showed a significantly stronger bonding to the resin-modified glass ionomer cements than to the cured conventional glass ionomer cement, to which the dental composite did not adhere without acid etching. The flexure strengths of the resin-modified glass ionomer cements were significantly improved compared with the conventional one but were still significantly lower than that of the dental composites.

Acid Etching, Dental↗
PubMed1996

Factors influencing shear strength of incrementally cured composite resins.

Factors influencing the shear strength of incremental curing of three different composite resins were examined. The first increment was cured under different surface conditions, in air, or under a coverglass. A separate experiment studied the effect of curing in nitrogen atmosphere. There was no difference in the shear strength of the specimens if the first increment was created in air or under a coverglass. One material (Heliomolar RO) showed higher shear strength when cured in increments and one when bulk-cured (Herculite XR). Curing increments in a nitrogen atmosphere increased the shear strength for two of the three materials tested (P50 and Heliomolar). The results showed that the bond strength between the increments of composites was influenced by the surface properties of the composites themselves after they had been cured under the different conditions; it was also affected by the inherent chemical and physical properties of the materials utilized.

Acrylic Resins↗
PubMed1995

A new method for in vivo quantification of changes in initial enamel caries with laser fluorescence.

A new method for the in vivo assessment of changes in initial enamel caries lesions was developed and tested. A CCD camera equipped with a high-pass filter (lambda > 520 nm) collects the fluorescence image of carious teeth, illuminated intraorally with diffuse laser light (lambda = 488 nm). Incipient lesions show a loss in fluorescence to be expressed as a percentage of fluorescence radiance of sound tissue. A PC program (Inspektor, model QLF 1.0) is used for display, storage, and subsequent analysis of images. To enable the calculation of fluorescence loss, the fluorescence of sound tissue at the lesion site is reconstructed from the radiances of sound tissue bordering the lesion. This method was tested on 19 visually sound buccal surfaces in vivo. The differences between actual and reconstructed radiance was -1.6 +/- (SD) 1.1%, over areas varying between 8 and 14 mm2. The repeatability of the caries quantification was tested by measuring one arrested initial caries lesion 25 times in vivo. The lesion area was 0.56 +/- 0.20 mm2, and the loss of fluorescence was 17.6 +/- 0.7%, corresponding to a lesion depth of 17 +/- 2 microns. The new quantitative method was applied for the testing of an in vivo caries model using plaque-accumulating brackets on premolars scheduled for extraction. Videoimages were recorded in vivo before bracketing and 0, 2, 3, and 5 weeks after debracketing. Clear changes between the different time points were recorded for both lesion size and mineral content.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Strength and setting behavior of resin-modified glass ionomer cements.

Diametral tensile strength (DTS), fracture strength, and Vickers microhardness were tested in three resin-modified glass ionomer cements (GICs), one chemically set GIC, and one dental composite. For the DTS studies test discs were immersed in deionized water at 37 degrees C for 10 min, 1 day, and 28 days, respectively. Cured discs were also implanted in back muscles of rats for 28 days before testing. The effects of light irradiation time and delayed curing on the DTS of the cements were also studied. Significantly higher strength was observed in the resin-modified GICs in comparison with the chemically set GIC at all observation period. K71 showed the highest strength among the GICs. No strength reductions were detected after 28 days for the specimens in vivo. An illumination time of 20 sec was enough to obtain final strength in the PFA and K71 specimens, and 40 sec was needed in the VI specimens. The strength of the resin-modified GICs when light-cured was significantly higher than when the same cements were allowed to set without irradiation. The microhardness of the light-cured GICs was similar to that of the dental composite. Considering the improved fracture strength and surface hardness, it was concluded that the resin-modified GICs present an interesting material for further development.

Acrylic Resins↗
PubMed1995

Electrical impedance for estimation of irritation in oral mucosa and skin.

Our aim is to establish an objective, easy-to-use technique to evaluate tissue irritation in vivo using non-invasive electrical impedance measurements. Such a technique would facilitate testing the biocompatibility of various materials, and also in quantifying skin diseases and other processes involving structural changes. It has been found that irritation of the oral mucosa not clinically or histologically discernible could be detected with a simple device based on electrical impedance techniques. Originally, the key problem was to focus the probing electrical field in order to minimize artefacts emanating from tissue layers of no interest. The device was then refined and applied to skin testing. It was found that irritation effects far below the limit of the commonly used visual readings could be detected. In this case, it is desirable to exclude from the measurement tissue layers with no diagnostic information, or at least reduce their influence. In this paper, the essential steps of the development of a multi-frequency depth selective device are reviewed.

Artifacts↗
PubMed1994

Strategies for improving the assessment of dental fluorosis: focus on optical techniques.

In its milder forms, enamel fluorosis is characterized clinically by diffuse opacities. The appearance is due to optical properties of a subsurface or surface porous layer with lower mineral content. These areas usually have texture and color similar to those of initial caries lesions but generally another shape and location. Therefore, several optical methods, previously used to diagnose initial caries lesions, were applied to fluoride-induced opacities on extracted premolars and on incisors of four subjects in vivo. These methods included light-scattering measurements, white light illumination, violet light illumination, ultraviolet illumination, and laser fluorescence. Video images were captured with a charge-coupled-device (CCD) camera, digitized, and computer-processed. It is concluded that the light-scattering monitor can be used for the determination of the local porosity of fluorotic enamel and that the laser fluorescence method might be developed into a method applicable for the assessment of the severity of enamel fluorosis.

Fluorescence↗
PubMed1992

Comparison of laser fluorescence and longitudinal microradiography for quantitative assessment of in vitro enamel caries.

A new quantitative, non-destructive method using laser-induced fluorescence (LAF) was compared with longitudinal microradiography (LMR) for assessment of mineral changes in enamel slices using an in vitro caries model. Ten enamel slices, cut longitudinally from sound natural smooth surfaces of human teeth, were exposed to de- and remineralization in a pH-cycling model. The enamel slices were subjected to LAF and LMR measurements before and at 2, 4, 7, and 9 days of demineralization. For LAF, the average fluorescence radiance decreased during the demineralization period with 11% by day 2 and 49% by day 9. For LMR, the corresponding average loss of mineral content changed with 0.01 and 0.10 kg.m-2 over the same time period. The mineral losses in each individual enamel slice measured with the two techniques were strongly correlated, r = 0.97. The Spearman rank correlation coefficient for all LAF and LMR demineralization results was 0.86. The precision (coefficient of variation) for LAF was 3.1%, corresponding to 0.005 kg.m-2, and the repeatability error for LMR was 0.02 kg.m-2, indicating a lower discrimination threshold for LAF compared to LMR. It was concluded that the new, sensitive, non-destructive LAF method provides possibilities for further improvement in the quantification of initial caries lesions in natural smooth enamel surfaces for use in in vitro studies. Furthermore, it offers potential in in situ caries studies as well as a tool in the diagnosis of early enamel caries in vivo.

Contrast Media↗
PubMed1991

Fluorescence in dissolved fractions of human enamel.

Fluorescence induced by laser light is useful in early detection of enamel caries. The present work studied the fluorescence emission pattern in dissolved human enamel and in different molecular weight fractions obtained after gel chromatography or dialysis followed by ultrafiltration. For comparison, solutions of synthetic hydroxyapatite and bovine enamel were used. When the entire emission and excitation spectra of the corresponding excitation and emission wavelengths in the solutions of human enamel and bovine enamel were compared, no distinct differences were found between the solutions. With excitation at 375 nm, emission peaks were found at 460 and 560 nm, indicating the presence in human enamel solution of two different chromophores, unevenly distributed over the molecular weight fractions. The 460-nm and the lower 560-nm fluorescence peaks seem to be derived from both organic and inorganic components. The inorganic substances contributing to both the 460-nm and 560-nm peaks were incorporated in complexes. The 560-nm emission peak elucidates part of the basis of the laser fluorescence method.

Adolescent↗
PubMed1991

Initial caries diagnosis in rat molars, using laser fluorescence.

Scoring of enamel caries in rat molars in ordinary light and in laser fluorescence was compared. Fifty rats were infected with Streptococcus mutans; 5 served as control rats, and the other 45 were fed a cariogenic diet for 15-20 days. With Keyes's system, the total enamel caries score for 35 of the test rats was 29.1 lesions per rat (l/r) in ordinary light and 39.6 l/r in laser fluorescence. The corresponding scores for fissure caries were 15.9 l/r and 21.6 l/r, respectively. Fissure caries scores of thin, longitudinal, central sections from the molars of the 10 remaining test rats were 18.0 l/r in ordinary light, 21.4 l/r in laser fluorescence, and 17.1 l/r in microradiographic analysis. In conclusion, the use of laser fluorescence improves scoring of early enamel carious lesions in rat molars, offering potential reductions in test time and/or sucrose load in animal caries research.

Animals↗
PubMed1990

In vitro fluoride uptake by enamel and dentin. A comparative study of two varnishes.

The uptake of fluoride in enamel and dentin after application of an experimental fluoride varnish has been studied and compared with the uptake from a commercially available varnish (Duraphat). Each varnish was applied to 10 extracted human cuspid teeth. Successive etchings with perchloric acid were carried out separately in enamel and root dentin to obtain samples at three different depths. The concentrations of fluoride and calcium in the samples were determined, and the fluoride uptake was calculated. The experimental varnish gave a significantly greater fluoride uptake at all three sample depths in both enamel and dentin.

Cuspid↗
PubMed1989

Evaluation of a model for short-term clinical testing of cariogenicity.

Conventional mirror and probe examination and laser fluorescence were used to score caries-like alterations on the buccal surfaces of posterior teeth in 60 panelists, allotted to one of three groups. All subjects refrained from oral hygiene for five days. In one group each subject consumed 12 sucrose candies daily between meals and in the second group each subject similarly consumed 12 palatinose (isomaltulose) candies. The third group served as a control. At the end of the experimental period the tooth surfaces reexamined. Conventional and laser fluorescence scoring techniques showed an increase in the number of caries-like alterations for all groups, but there were no significant differences between the groups. For all groups, the laser method gave significantly greater scores throughout. The findings imply that certain aspects of the early development of enamel caries in subjects regularly using fluorides must be considered in the design of a short-term cariogenicity test. It is concluded that sensitive quantitative methods for the registration of caries are necessary in such tests.

Adolescent↗
PubMed1988

Intradental nerve activity and jaw-opening reflex in response to mechanical deformation of cat teeth.

Mechanical stress was applied to canine teeth in anaesthetized cats to excite intradental A-fibres and to produce digastric muscle EMG responses. Activity in the intradental sensory units was recorded by two electrodes, one inserted in a dentinal cavity, the other in contact with the gingival sulcus. A pneumatically driven piston was used to cause a mechanical stress (10-150 N) on the stabilized tooth crown for 30 s, with instantaneous onset and release. Application of a load of 30 N produced a momentary burst of impulses in 2 of 12 teeth; 8 out of 10 teeth responded when 150 N was used. Digastric EMG responses were obtained at and above 60 N. Removal of the coronal pulp or cooling of the tooth crown with ethyl chloride abolished this reflex, whereas percussion of the tooth still produced a digastric response. Our results suggest that load-induced deformation of teeth activates intradental sensory mechanisms and a reflex withdrawal reaction unrelated to periodontal stimulation.

Animals↗
PubMed1985

Laser-induced fluorescence from sound and carious tooth substance: spectroscopic studies.

Fluorescence spectra of dentine and enamel illuminated with laser light of wavelengths of 337, 488, 515 and 633 nm respectively were recorded. The fluorescence obtained by illumination with UV laser light at 337 nm had a peak at about 400 nm in dentine as well as enamel. Compared to intact enamel the fluorescence from enamel with initial carious lesions was of lower intensity and had a slight red shift. No fluorescence within the visible range was obtained by illumination with a low power He-Ne laser at 633 nm. Illumination at 488 nm produced fluorescence with a peak at about 540 nm in dentine as well as enamel. The difference in the intensity of fluorescence between sound and carious enamel was generally greater at this wavelength than at any of the others tried, and the red shift from the carious enamel was also more pronounced. Illumination at 515 nm produced fluorescence of similar wavelengths but with much less difference between intact and carious enamel. It was concluded that illumination at 488 nm was the most suitable wavelength of those investigated for the detection of initial carious lesions by the fluorescence technique.

Dental Caries↗
PubMed1984

Temperature rise during root canal preparation--a possible cause of damage to tooth and periodontal tissue.

Temperature rise on the surface of extracted human premolar roots was recorded during root canal preparation using a thermo-couple. It was found that time, pressure exerted on the reamer, type of reamer and rotational speed influenced the temperature rise. Starting from about 30 degrees C temperatures up to 87 degrees C were recorded, generally in less than 50 seconds' working time, using routine instrument and technique. Possible effects of this temperature rise on tooth substance, periodontal membrane and supporting bone are discussed.

Dental Instruments↗
PubMed1984

A follow-up study of screwpost-retained amalgam crowns.

A follow-up study of amalgam crowns retained with brass screwposts (Dentatus) has been performed. The teeth had been restored by undergraduates at the Department of Cariology, School of Dentistry, Stockholm, during the years 1970-1976. Radiographs of the teeth made at the time of insertion of posts were available in all cases. The material comprised 56 teeth with altogether 69 screwposts. Average observation time was 7.8 years. Anamnestic data were collected and clinical and radiographic investigations of the restored teeth and surrounding tissues were carried out. Of the 56 teeth, 8 teeth containing altogether 11 screwposts had been lost by extraction. Annotations from the treating dentists were available in all cases and showed that five of the extractions had been necessary because of extensive caries, one because of parodontitis and two because of root fractures. No corrosion of screwposts had been observed in the fractured teeth. The anamnestic investigation revealed sporadic tenderness and metallic taste in only a few cases. The most frequent clinical findings were discoloration and pitting of amalgam surfaces and discoloration of tooth substance and gingiva. The discolorations of the gingiva were related to restorations extending below the gingival margin. No clinical or radiographic signs of corrosion of screwposts were found in the investigated teeth.

Crowns↗