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J Arends

Publications and source records attributed to J Arends.

At least 73 records · Page 4Linked to original sources
PubMed1994

Orientational micro-Raman spectroscopy on hydroxyapatite single crystals and human enamel crystallites.

Single crystals of synthetic hydroxyapatite have been examined by orientational micro-Raman spectroscopy. The observed Raman bands include the PO4(3-)/OH-internal and external modes over the spectral range from 180 to 3600 cm-1. The Raman-active symmetry tensors (A, E1, and E2) of crystal-class C6 have been assigned to these bands. Intensities of the Raman bands are invariant to the orientation of the a- or b-axis of a single crystal, but depend solely on the c-axis orientation. Changes in the spectral profile thus reflect changes in the c-axis orientation, which, with respect to the known excitation/observation coordinates, can be determined through the angular dependencies of Raman bands due to A and E2 symmetries. The useful bands are those of the PO4(3-)v4 vibrational mode, which contains relatively well-defined bands due to E2 (581 cm-1) and A (593 cm-1) symmetries. A preliminary Raman study on crystallites near the intact outer surface of human enamel has also been carried out. Strong orientational dependencies similar to those of hydroxyapatite single crystals have been observed among the bands in enamel spectra. This suggests that the crystallites in the region investigated are highly oriented. The results were consistent with an averaged orientation of the crystallite c-axis being perpendicular to the outer surface.

Crystallography↗
PubMed1993

Quantification of deposits formed in the oral cavity on various materials after a 1-year period.

Deposits are formed on natural teeth as well as on various polymeric and metallic materials. Deposit formation is complex and controlled by numerous poorly understood parameters. This article presents a new method for quantification of in vivo deposit formation on multiple materials. Seven different materials were positioned at six different sites in the buccal flanges of a removable prosthesis. Nine volunteers wore these prostheses for 1 year. The deposits were graded by three independent observers under a stereomicroscope at X20 magnification. Plots of average deposition value averaged for all participants and sites are given. Polymethyl methacrylate (PMMA) had the lowest deposition value in this trial. The standard error is approximately 15% of the mean value. The results show that after 1 year in vivo the roughness of the experimental materials increased by a factor of two to six times. The method presented is suitable to quantify deposit formation on multiple materials in vivo.

Aged↗
PubMed1993

Gammahydroxybutyrate and narcolepsy: a double-blind placebo-controlled study.

We treated 24 patients with narcolepsy for 4 weeks with gammahydroxybutyrate (GHB), 60 mg/kg/night, in a randomized double-blind placebo-controlled cross-over trial. Both clinical and polysomnographic criteria were used to assess the results. Compared to placebo, GHB reduced the daily number of hypnagogic hallucinations (from 0.87 to 0.28; p = 0.008), daytime sleep attacks (from 2.27 to 1.40; p = 0.001) and the severity of subjective daytime sleepiness (from 1.57 to 1.24 on a 0-4 scale; p = 0.028). The number of daily cataplexy attacks was reduced from 1.26 at baseline to 0.56 after 4 weeks of GHB intake. This reduction, however, was not statistically significantly different from the difference between baseline and placebo. GHB stabilized nocturnal rapid eye movement (REM) sleep, i.e. it reduced the percentage of wakefulness during REM sleep (p = 0.007) and the number of awakenings out of REM sleep (p = 0.016), and tended to increase slow wave sleep (p = 0.053). Adverse events were few and mild. We conclude that GHB is an effective and well-tolerated treatment for narcolepsy.

Adolescent↗
PubMed1993

No evidence for feedback inhibition of hepatic apolipoprotein B (apo B) production after extracorporeal low density lipoprotein precipitation as determined by [1-13C]leucine infusion in normal volunteers.

To determine the impact of an acute reduction of the circulating mass of apolipoprotein B (apo B) on apo B metabolism we studied six healthy male volunteers before (day 0), 1 day after (day 2), and 7 days after (day 8) an LDL apheresis treatment which reduced apo B mass by 59%. Appearance of newly synthesized apo B in plasma VLDL and LDL was studied using a primed-constant infusion of [1-13C]-leucine. VLDL apo B pool size and fractional VLDL apo B production rate calculated using a one-compartment model were similar on all 3 study days. Absolute VLDL apo B production was not statistically different throughout the study (19.7 +/- 12.3, 19.5 +/- 7.5, 29.1 +/- 17.7 mg kg-1 day-1). LDL apo B fractional production rate was increased on day 2 (0.38 +/- 0.17, 0.68 +/- 0.08, 0.37 +/- 0.06 pools day-1 on days 0, 2, and 8; P < 0.01). Absolute LDL apo B production, however, remained constant throughout the study (10.8 +/- 3.3, 11.0 +/- 1.9, 10.8 +/- 3.1 mg kg-1 day-1). We conclude that in healthy male volunteers acute reduction of the circulating apo B mass by LDL apheresis does not affect apo B metabolism significantly.

Adult↗
PubMed1993

Inhibition of bovine dentin demineralization by a glutardialdehyde pretreatment: an in vitro caries study.

Intact bovine dentin specimens were demineralized in 25 mmol acetic acid buffers (pH 5), with and without a 5-min pretreatment with an acidic 2% glutardialdehyde (GDA) solution. The results demonstrate that GDA inhibits dentin demineralization and that the inhibition depends strongly on the initial calcium and phosphate concentration in the demineralization solution. The observed inhibition increases from about 5% without calcium and phosphate to 38% with a calcium and phosphate concentration initially of 6.4 mmol and 4.1 mmol, respectively. The inhibition can be explained either by a reduction of calcium and phosphate diffusion out of the lesion or by the retention of mineral inhibitors in the dentin.

Animals↗
PubMed1993

Fluoride and mineral content in hyper-remineralized coronal bovine dentine in vitro after an acid challenge.

In this paper the acid resistance of hyper-remineralized dentine was quantified by means of fluoride and mineral measurements. Hyper-remineralization was achieved by demineralization of dentine in an acidic gel system (pH 5) for 3 weeks, followed by remineralization in a solution containing 1.5 mM Ca, 0.9 mM phosphate and 10 ppm F at pH 7 and 37 degrees C for 8 days. The samples were subsequently again demineralized in the gel system mentioned for 1, 2 and 3 weeks. Analysis for fluoride was done by means of the microdrill biopsy technique and to obtain information on the fluoride distribution by secondary ion mass spectrometry (SIMS); mineral was assessed by microradiography. The results showed that in hyper-remineralized dentine the original fluoride content was approximately 30,000 ppm F. This value was still in the same order after the acid challenge of 3 weeks at pH 5. These values were substantially higher than the baseline values in sound or in demineralized dentine being about 900 ppm F. The main microradiographic result was that there was no significant mineral change in the hyper-remineralized dentine due to the acid challenges. There was, however, a tendency for mineral redistribution deeper into the dentine lesion leading to lamination phenomena. The SIMS experiments on some of the samples showed a fluoride distribution in agreement with the microdrill fluoride data. Furthermore a fluoride redistribution took place in deeper parts of the lesion due to the acid challenges. The combined fluoride concentration and microradiographical data indicate that fluoride-enriched and highly mineralized hyper-remineralized dentine is more acid resistant than sound or demineralized dentine.

Animals↗
PubMed1993

Long-term fluoride release of visible light-activated composites in vitro: a correlation with in situ demineralisation data.

Fluoridated composites are able to reduce or inhibit secondary caries around fillings. The aims of this study were firstly to investigate the amount of F released in vitro from composites with a F content between 0 and 26 vol% as a function of time over a 1-year period. A second aim was to correlate the in vitro data on F release with enamel demineralisation data in situ after a 1-month period. The results show that all fluoridated composites release sizable amounts of F in solution, the total amounts of F released from three composites were proportional to log t over at least 1 year. In one case proportionality of the total amount of F released with t was observed. Possible mechanisms of F release are considered. The results presented also show a linear relation between the log of in vitro F release data and the effects on enamel demineralisation in situ next to the composite. Extrapolation of the data reveals that a F release of about 200-300 micrograms/cm2 over a 1-month period from a fluoridated composite would completely inhibit secondary caries under plaque conditions.

Acrylic Resins↗
PubMed1993

Detection and quantification of calcium fluoride using micro-Raman spectroscopy.

Investigations on the caries-preventive effect of calcium fluoride have been seriously hampered by the lack of adequate detection techniques. In this paper, the micro-Raman technique is introduced as a suitable method for CaF2 quantification with a spot size typically 5 microns. Advantages of this measuring technique and associated problems are described for CaF2 determination in the presence of large amounts of hydroxyapatite. The data show that a comparative analysis of Raman intensities of calcium fluoride and phosphate ions of hydroxyapatite can be used for quantification of CaF2 concentrations. The intensity behaviour of the CaF2 and hydroxyapatite Raman lines is explained considering the absorption-scattering cross-sections of the two components. The ratio of the Raman intensity (322 cm-1) of CaF2 to the phosphate Raman intensity (432/447 cm-1) of hydroxyapatite was found to be related linearly to the ratio of the concentration of CaF2 to that of hydroxyapatite. At present, the lower limit of CaF2 quantification is approximately 3 wt%. The technique has already been applied on fluoridated bovine enamel, and Raman emissions due to CaF2 or CaF2-like material formed on/in enamel have been detected for the first time.

Animals↗
PubMed1993

Shrinkage prevention of in vitro demineralized human dentine in transversal microradiography.

The shrinkage of demineralized dentine is a serious problem in the assessment of mineral distributions and mineral changes by means of microradiography. In this article it is shown that a treatment with ethanediol of the thin slices used for transversal microradiography prevents shrinkage for about 1 h. Without this so-called diol treatment, the shrinkage effects in demineralized dentin are about 20% in lesion depth and about 30% in mineral loss (delta Z) after 120-second drying in air. The prevention of shrinkage by diol treatment of dentine lesions is not influenced by the presence of a surface layer.

Dentin↗
PubMed1993

Shrinkage of sound and demineralized human coronal dentine slabs.

In this article a method is presented for dentine shrinkage measurements. The relative shrinkage of sound dentine slabs is assessed using a Perthometer with respect to a steel reference. The relative shrinkage of lesions in dentine slabs can be estimated using combined Perthometer/microradiography measurements. The results show that the relative lesion shrinkage of lesions in thick slabs is quite different from the shrinkage of lesions in thin sections used for microradiography. The relative lesion shrinkage is, for periods up to 30 min, linear with the air drying period and increases strongly with the demineralization period. The previously published diol treatment is capable of reducing the relative lesion shrinkage in thick dentine slabs to negligible values.

Dentin↗
PubMed1993

Combined Raman and SEM study on CaF2 formed on/in enamel by APF treatments.

Raman spectra containing the distinct band at 322 cm-1 due to CaF2 or CaF2-like material formed in/on fluoridated bovine enamel were recorded using a micro-Raman spectrograph. Due to increasing levels of background fluorescence with increasing thickness of enamel, the Raman measurements were carried out on thin regions of wedged enamel sections. The distribution of the CaF2 or CaF2-like material was estimated using a simple model. The results indicate that 1/3 of the total CaF2 was concentrated within the narrow depth < 2 microns with high CaF2 concentrations (> 10 wt%), and that the majority of the CaF2 was distributed over the depths up to 26 microns (1 wt% CaF2). SEM observations on fractured fluoridated enamel confirmed that morphological changes were present in the depth range comparable to that of the high CaF2 concentration region expected from the Raman analysis. In deeper regions where lower concentration (< 10%) but a large amount of CaF2 was still expected, the SEM images failed to distinguish between the normal and fluoridated enamel. After KOH treatment, the Raman spectra did not show evidence of the CaF2 peak and the SEM micrographs also confirmed the removal of globules. The peak position of the Raman band of the CaF2 formed by the fluoridation was identical to that of pure CaF2. However, the linewidth was 23 cm-1 (FWHM) and a factor of 2 broader than that of pure CaF2 (12 cm-1). This implies that the lattice dynamics of the CaF2 formed by fluoridation is different from of pure CaF2, and that the material formed is 'CaF2-like' or 'disordered CaF2'.

Acidulated Phosphate Fluoride↗
PubMed1993

Raman spectra of human dental calculus.

Raman spectra of human dental calculus have been observed for the first time by use of micro-Raman spectroscopy. The spectral features of calculus were influenced easily by heating caused by laser irradiation. Therefore, the measurements were carried out at relatively low power (5 mW, 1-micron spot size). The spectra could be characterized as phosphate vibrational bands due to the v1, v2, v3, and v4 modes. The overall spectral features did not resemble those of pure minerals such as brushite, octacalcium phosphate, and hydroxyapatite. There were spectral differences among mixed calculus particles obtained from 18 adults, probably due to variations in local mineral composition and differences among patients. However, the averaged spectral features did not vary significantly with formation period from 1 to 6 months. Freshly removed and stored (5-11 months) calculus also gave comparable Raman spectra. Measurements on a fractured sample indicated that Raman spectra at saliva and dentin interfaces are nearly identical, and major mineral constituents may not vary significantly along the growth axis of calculus.

Adult↗
PubMed1993

Analytical bias by contamination from hemolysis in determination of serum lactate dehydrogenase isoenzyme 1 in patients with testis germ cell tumors.

We investigated the impact of correction for contamination from hemolysis on serum lactate dehydrogenase isoenzyme 1 (S-LD-1) determinations. A study of hemolysates from 7 control patients showed a mean correction factor for the contamination of 0.1 U/L S-LD-1 for each 1 mg/L serum hemoglobin (S-Hb). S-LD-1 in a series of blood samples from 44 patients (EJC 1992;28:410-5) would decrease median 24 U/L (range 8-70 U/L) if the measurements were corrected with this factor. So we advice to correct S-LD-1 determinations for the contamination with a common correction based on the S-Hb concentrations in the samples.

Chemistry Techniques, Analytical↗
PubMed1993

Prenatal screening for neural tube defects, quality specification of maternal serum alphafetoprotein analysis.

The bimodal approach for quality specification in prenatal screening for neural tube defects has been used. The method for assessing specifications has been the expenses for the society. It has been shown that the cut-off values and analytical bias are of importance. It is recommended to use a reference serum for local calibration to keep the level within defined limits when changing to a new batch of reagents.

Female↗
PubMed1992

[Elimination of human chorionic gonadotropin in serum and urine after uncomplicated induced abortion during the first trimester].

Serum chorion gonadotropin was measured weekly in 12 women from the time of legal first trimester abortion until values were below 10 IU/L. The elimination followed a 2-component curve. The half-life in the first few days was 1.1 day, hereafter 4.2 days. Serum-HCG decreased to less than 10 IU/L within 22 to 40 days. The elimination of serum-HCG was found to decrease so uniformly, that values which do not decrease must be considered abnormal. A sensitive bedside urine-HCG test was found to be positive from 13 to 31 days after the abortion.

Abortion, Induced↗
PubMed1992

CA-125 as a maternal serum marker for Down's syndrome in the first and second trimesters.

CA-125, alpha-fetoprotein (AFP), and human chorionic gonadotropin (HCG) were determined in maternal serum in the first trimester from 14 women with a Down's syndrome fetus and 61 women with a healthy fetus. In the second trimester, 15 and 60 serum samples were determined from women with a Down's syndrome and a healthy fetus respectively. In both trimesters, maternal serum CA-125 was found to be elevated in Down's syndrome pregnancies compared with controls. Using discrimination functions, our preliminary results indicate that CA-125 is a better marker than AFP and HCG respectively for a Down's syndrome fetus in the first trimester and improves the detection rate in the second trimester.

Antigens, Tumor-Associated, Carbohydrate↗
PubMed1992

Cariostatic effect and fluoride release from a visible light-curing adhesive for bonding of orthodontic brackets.

This study was designed to investigate the cariostatic potential in vivo of a visible light-curing adhesive for the bonding of orthodontic brackets. The fluoride release of the adhesive in water and saliva was also measured. Ten orthodontic patients with premolars to be extracted participated. One bracket with Heliosit-Orthodontic (no fluoride) was positioned on the buccal surface of one premolar (control), and another bracket with Orthodontic cement VP 862 (containing fluoride) was positioned on the experimental contralateral premolar. The adhesives were cured with a Heliolux II lamp, and the teeth were extracted after 4 weeks. The patients used a fluoride toothpaste during the experiment. The mineral content of the enamel adjacent to the brackets was determined by quantitative microradiography. The fluoride release from disk-shaped plates of the fluoride adhesive was measured in water for a 6-month period and in human saliva for 24 hours. The fluoride adhesive reduced lesion depths by about 48% than the nonfluoride adhesive (P less than 0.05, t test). The largest release of fluoride from the plates in water was observable within the first week. However, a significant amount of fluoride was still released after 6 months. The fluoride release in saliva was significantly lower in human saliva at pH 7 than in water (P less than 0.01, t test). When salivary pH was lowered to 4, to mimic a cariogenic challenge, the amount of fluoride released increased up to the value measured in water. It was concluded that the regular use of fluoride toothpastes is insufficient to inhibit lesion development around orthodontic brackets.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesives↗