Biomedical subjects

L C Chow

Publications and source records attributed to L C Chow.

At least 73 records · Page 4Linked to original sources

PubMed1991

Effects of an acidic calcium phosphate solution and the intraoral fluoride-releasing device on dental caries and fluoride uptake in rats.

This investigation comprised two studies evaluating the effects of an acidic calcium phosphate solution (CPS) on fluoride uptake in the enamel, glycolysis of dental plaque, the incidence of dental caries and urinary fluoride concentrations of rats wearing an intraoral fluoride-releasing device (IFRD). In the first study, CPS-fluoride treatment preceded the cariogenic challenge. In the second study, the cariogenic challenge preceded the treatments. In the first study, CPS treatments increased the ability of enamel to bind fluoride. However, the enamel-bound fluoride exerted a negligible effect on plaque glycolysis as measured by the pH decrease after sucrose challenge. In the second study CPS augmented the caries inhibition for both the sulcal-morsal and buccal-lingual surfaces. In both studies the IFRD significantly restricted the development of carious enamel on the sulcal-morsal surfaces and caused elevated concentrations of fluoride in the urine independent of CPS treatments.

Actinomyces viscosus↗

PubMed1991

Deposition of fluoride on tooth surfaces by a two-solution mouthrinse in vitro.

A constant-composition fluoride (F) titration method was used to measure the amount of leachable F deposited on tooth surfaces in vitro by a 1-min rinse with a 228-ppm F solution (12 mmol/l sodium fluoride). The mean F uptake was 0.23 +/- (SE) 0.07 microgram/cm2, corresponding to less than 0.2% of the F contained in the rinse. The present study describes a new F rinse system that consisted of two solutions. Solution A contained a soluble calcium salt and a buffer. Solution B contained sodium fluorosilicate, a complex fluoride salt. When solutions A and B were combined, the free F ions produced by hydrolysis of fluorosilicate caused precipitation of calcium fluoride during the 1-min application time. The F uptake produced by the two-solution rinse was 4.36 +/- 0.16 micrograms/cm2, which was approximately 19 times greater than that produced by the sodium F rinse with the same F content. Since the cariostatic effects from F rinses are believed to derive from their ability to deposit labile F in the oral cavity, the two-solution rinse may be more efficacious than the rinses currently in use.

Calcium Chloride↗

PubMed1991

Permselectivity of sound and carious human dental enamel as measured by membrane potential.

A microwell technique was used for determination of the permselectivities of sound and carious enamel in the same slice of tooth. The permselectivity determination was accomplished by drilling microwells in the enamel and filling them with a simulated plaque fluid containing lactate, carbonate, and inorganic ions at concentrations similar to those in resting plaque fluid, but with different concentrations of KCl. The electrical potentials developed across the enamel membrane were measured with microreference electrodes placed in the wells or in the solution outside the tooth. The results showed that the membrane potential was a function of the composition of the solutions separated by the enamel membrane and was independent of the composition of the solutions in the adjacent wells. The enamel was found to be cation-permselective, and sound enamel was more permselective than carious enamel. The flux rate of K+ was estimated from the change in the K+ concentration of the well solution as a function of time. The flux rate and the membrane potential data were used in the Nernst-Planck Flux Equation for calculation of the diffusion coefficient of K+ through enamel. The results indicate that the permselectivity of enamel can greatly influence the diffusion of ions through enamel membranes.

Carbonic Acid↗

PubMed1990

In vitro evaluation of the sealing ability of a calcium phosphate cement when used as a root canal sealer-filler.

A calcium phosphate cement (CPC) was examined for its ability to seal the root canal when used as a sealer-filler. Extracted human teeth were divided into three groups. Root canals were filled with either CPC paste containing dicalcium phosphate anhydrous (group 1), CPC containing dicalcium phosphate dihydrate (group 2), or gutta-percha points sealed with Grossman's cement (group 3). After filling, all specimens were kept in 100% humidity for 1 day, immersed in a CaPO4 solution or distilled water at 37 degrees C for 1 wk, and then immersed in 1% Poly-R dye solution at 37 degrees C for 1 wk, after which they were rinsed and sectioned longitudinally for microscopic examination. Specimens in groups 1 and 2, especially those aged in the CaPO4 solution showed considerably less dye penetration than those in group 3. The good sealing ability of the CPC against dye penetration in vitro suggests that it may provide an adequate seal of the canal without a separate sealer.

Calcium Phosphates↗

PubMed1990

Enhanced root fluoride uptake by monocalcium phosphate monohydrate gels.

Application of monocalcium phosphate monohydrate (MCPM) gel, which produces small amounts of dicalcium phosphate dihydrate in enamel, was previously shown to increase the enamel reactivity with fluoride (F). This study was conducted to determine whether the MCPM gel treatment is also effective in enhancing F uptake by root surfaces of human teeth. The results show that samples receiving daily treatments with MCPM gel for 10 min followed by immersion in a 1-ppm F solution for 5 days acquired a significantly greater amount of F compared to the controls which had the same exposure to the F solution. Because the F solution was undersaturated with respect to calcium fluoride (CaF2), the F incorporated into the root is apparently apatitic and not CaF2. This experimental treatment should be feasible in the clinical situation since only a short treatment time was required and delivery of the MCPM gel to specific sites was relatively easy.

Calcium Phosphates↗

PubMed1990

Assessment of loosely-bound and firmly-bound fluoride uptake by tooth enamel from topically applied fluoride treatments.

The amounts of loosely-bound fluoride (F) deposited on human enamel by two topical F treatments were measured with use of a constant-composition F washing method. Enamel biopsies conducted before treatment and after the washing were used for determination of the firmly-bound F uptake. The results showed that (1) the washing system did not remove F from untreated enamel surface, (2) a four-minute application of an acidulated phosphate fluoride (APF) gel deposited 27.2 (2.4) (mean, S.E.) micrograms of loosely-bound F per cm2 of enamel surface and 186 (111) ppm of firmly-bound F in the outer 10 microns of enamel, and (3) a four-minute application of a pH-2.1 dicalcium phosphate dihydrate (DCPD)-forming solution followed by APF produced 44.9 (3.1) micrograms/cm2 of loosely-bound F and 1280 (354) ppm of firmly-bound F in the outer 10 microns of enamel. The results showed that the DCPD pre-treatment effectively enhanced the enamel reactivity with F, so that the DCPD-APF treated enamel acquired greater amounts of both loosely-bound F and firmly-bound F than did samples treated with APF alone.

Acidulated Phosphate Fluoride↗

PubMed1990

Micro-analysis of plaque fluid from single-site fasted plaque.

Despite the site-specific nature of caries, nearly all data on the concentration of ions relevant to the level of saturation of plaque fluid with respect to calcium phosphate minerals or enamel are from studies that used pooled samples. A procedure is described for the collection and analysis of inorganic ions relevant to these saturation levels in plaque fluid samples collected from a single surface on a single tooth. Various methods for examining data obtained by this procedure are described, and a mathematical procedure employing potential plots is recommended.

Colorimetry↗

PubMed1990

Setting reactions and compressive strengths of calcium phosphate cements.

Setting reactions and compressive strengths of a self-hardening calcium phosphate cement (CPC) were investigated. The CPC consists of tetracalcium phosphate (TTCP) and anhydrous dicalcium phosphate (DCPA). The cement specimens were prepared by mixing 0.7 g of the powder (TTCP 72.9 wt% + DCPA 27.1 wt%) with 0.175 mL of the liquid (25 mmol/L H3PO4 and 1.32 mmol/L sodium fluoride). The specimens were removed from the molds at pre-determined time intervals after being mixed, and their compressive strengths were measured. Immediately afterward, the fractured specimens were rapidly frozen in ethanol (-80 degrees C), lyophilized, and examined by powder x-ray diffraction and scanning electron microscopy (SEM). The results showed that (1) hydroxyapatite was the only reaction product; (2) the reaction was nearly completed within four h, during which both the reaction product and compressive strength increased linearly with time, resulting in a strong correlation between the two; and (3) fully set CPC consisted primarily of small rod-like crystals and some platy crystals.

Calcium Phosphates↗

PubMed1990

Fluoride analysis in nanoliter- and microliter-size fluid samples.

A variety of techniques is described for measuring fluoride in volumes of from 0.005 to 5 microL, including: (1) micropipette procedures for transference and dilution of samples, (2) construction of miniature and micro fluoride-selective electrodes, and (3) methods for adapting standard electrodes for micro- and semi-micro volumes. These described techniques have a number of advantages, including speed of analysis, high accuracy, and adaptability to many types of fluid samples. Recent studies involving use of these procedures include the analysis of fluoride in: (1) plaque fluid samples from single sites before and after topical fluoride administration, (2) tooth mineral samples recovered by acid-etch or microdrill biopsy of enamel, and (3) fluid recovered from the interior of the tooth during simulation of the caries process.

Dental Enamel↗

PubMed1990

Tooth-bound fluoride and dental caries.

The cariostatic effects of tooth-bound fluoride reported in the recent literature are reviewed. Several treatment procedures which can increase the tooth-bound fluoride content are described. Based on this information, it is suggested that effectiveness of currently used topical fluoride treatments may be significantly increased by (1) including in the regimen a dicalcium-phosphate-dihydrate-forming treatment so that a portion of the labile fluoride is re-incorporated as tooth-bound fluoride, and (2) employing application methods which ensure the effective delivery of treatment agents to the fissures, and to approximal and cervical surfaces, where most caries occurs.

Animals↗

PubMed1989

A quasi-constant composition method for studying the formation of artificial caries-like lesions.

Caries-like lesions were formed in human tooth enamel in a quasi-constant composition titration system without the use of surface dissolution inhibitors or weak acids. The titration system maintained the composition of the demineralizing solution constant to within 6% on the average. Thus, the rate of lesion formation may be quantitatively assessed from the rate of titration. The system has sufficient sensitivity for measuring the rate of lesion formation in a small area, e.g., 15 mm2, of a single human enamel specimen.

Chemical Phenomena↗

PubMed1989

Early improvement in left ventricular diastolic function after relief of chronic right ventricular pressure overload.

Chronic right ventricular pressure overload is associated with left ventricular diastolic dysfunction. Whether or not an abrupt reduction in pulmonary artery pressure in patients with chronic pulmonary hypertension results in early improvement of left ventricular diastolic function is unknown. To assess this, the Doppler indexes of left ventricular diastolic function and echocardiographic measures of left ventricular volume were analyzed in 22 patients (age, 41 +/- 14 years, mean +/- SD) before and within 1 week after pulmonary thromboendarterectomy for chronic thromboembolic pulmonary hypertension. Mean duration of cardiopulmonary symptoms was 37 months (range, 4 months to 9 years). After operation, mean pulmonary artery pressure and pulmonary vascular resistance decreased (50 +/- 13 to 29 +/- 9 mm Hg and 904 +/- 654 to 283 +/- 243 dynes.sec/cm5, respectively, both p less than 0.001), pulmonary artery wedge pressure was unchanged (11 +/- 5 to 12 +/- 5 mm Hg), and cardiac index increased (2.0 +/- 0.5 to 2.8 +/- 0.7 l/min/m2 p less than 0.001). Left ventricular end-diastolic volume and stroke volume increased significantly (58.5 +/- 18.0 to 76.6 +/- 25.0 ml and 30.3 +/- 12.3 to 41.8 +/- 12.5 ml, respectively, both p less than 0.001) after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Comparison of fluoride uptake produced by tray and flossing methods in vitro.

The purposes of this study were to compare: (i) the fluoride (F) uptake by enamel in approximal areas of teeth when the F agent was applied in vitro via a tray or a flossing technique; and (ii) the effectiveness of two treatments--acidulated phosphate fluoride (APF) alone and CaHPO4.2H2O (DCPD)-forming pre-treatment followed by APF. Groups of three teeth (one premolar and two molars) were mounted in impression compounds simulating their oral configuration. In the tray group, teeth received one four-minute treatment by means of custom-formed trays. In the flossing group, the approximal areas of teeth were flossed for 40 sec twice daily for three days with an absorbent floss wetted with the treatment solution. All teeth were incubated in a saliva-like solution except during treatment. At the end of the three-day period, teeth were unmounted and washed in 1 mol/L KOH for 24 hours. The F uptake was calculated from biopsy data obtained before and after the treatment. The results showed that (i) DCPD-APF produced significantly greater F uptake than APF alone in both the tray and flossing methods, and (ii) the flossing technique produced significantly greater F uptake in the approximal areas than the tray method for either treatment.

Dental Devices, Home Care↗

PubMed1989

Formation of hydroxyapatite in hydrogels from tetracalcium phosphate/dicalcium phosphate mixtures.

Apatitic calcium phosphate cements, formed by the ambient reaction of tetracalcium phosphate (TTCP) with dicalcium phosphates (DCP), have been recently reported. H2O or dilute aq. H3PO4 (0.2%) is used as the liquid vehicle for this reaction. The aim of this study was to ascertain if hydroxyapatite (HAp) can form in self-cured hydrogel composites containing TTCP/DCP mixes. The setting times (ST) and diametral tensile strengths (DTS) of these hydrogel composites were also determined. The hydrogels were of two types: (1) vinyl thermosets derived from the copolymerization of HEMA (2-hydroxyethyl methacrylate) and cross-linking monomers, and (2) polyelectrolyte-based hydrogels formed from aq. poly(alkenoic acids), e.g., poly(acrylic acid). Cylindrical specimens 6 mm D x 3 mm H were prepared and stored in H2O for up to 30 days. The HEMA composites were hardened in 7-15 min by free radical initiation (benzoyl peroxide/tertiary aromatic amine). The polyelectrolyte cements were hardened in 6-8 min. After various periods of storage in H2O at 37 degrees C, some of the specimens were examined by X-ray spectroscopy for HAp. HAp formation was not observed in the HEMA composites even after 30 days of H2O storage but was detected in the polyacid cements. The 24-h DTS values of the HEMA composites (14-26 MPa) were higher than those of the polyacid cements (7-12 MPa). Both the H2O content and pH may thus be factors controlling the rate and extent of HAp formation in hydrogel composites containing TTCP/DCP mixtures.

Calcium Phosphates↗

PubMed1989

[An in vitro study of dentin hypersensitivity using calcium phosphate cement].

Calcium phosphate remineralizing slurry (CPRS), consisting of an equimolar mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD), has previously been shown to form hydroxyapatite (HAp) spontaneously at physiological pH. Since considerable amounts of HAp may be formed in situ by CPRS, it may be effective for desensitizing hypersensitive dentin by obturating exposed dentinal tubule openings. In the present study, the effects of topically applied CPRS to etched dentin surfaces were investigated. The samples were randomly divided into 3 groups: (1) the control specimens were soaked in a saliva-like (SL) solution (2) the specimens received either 10-minute or 1-hour treatment with CPRS and (3) the specimens were treated with viscous CPRS, containing carboxymethyl cellulose (CMC) gel, for 8 hours. The SEM observations revealed that the control specimens were covered with a thin layer of plate-like crystals indicative of octacalcium phosphate (OCP). No significant penetration of the crystals into the dentinal tubules was detected. In CPRS group, the 10-minute treatment produced a 10 to 15 microns thick dense layer of precipitation consisting of needle-, rod-, and plate-like crystals. The 1-hour treatment produced a similar precipitation except that the crystals were mostly needle-like. A cross section view of the samples indicated remarkable penetration of the crystals into the tubules, thus providing significant obturation of tubule openings. Samples in the CMC-gel group were covered with an even more impervious layer of precipitation consisting of crystals of a variety of morphologies.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium Phosphates↗

PubMed1988

Endomyocardial biopsy in patients with unexplained congestive heart failure.

STUDY OBJECTIVE: To determine the incidence of myocarditis proved by biopsy findings in patients presenting with unexplained congestive heart failure. DESIGN: Retrospective review. SETTING: General medical services of a Veterans Administration and university hospital. PATIENTS: Ninety consecutive patients presenting with unexplained congestive heart failure who had endomyocardial biopsy as a part of their diagnostic evaluation. MEASUREMENTS AND MAIN RESULTS: Classification of biopsy findings according to a recently proposed scheme for histologic diagnosis of myocarditis (Dallas criteria) showed myocarditis in only 4 of 90 (4.4%) patients (95% CI, 0.2 to 8.6), although two thirds of the patients had symptoms of congestive heart failure for less than 3 months. CONCLUSIONS: The incidence of myocarditis proved by endomyocardial biopsy findings is low in patients presenting with unexplained congestive heart failure and raises questions concerning the need for this procedure in this patient group.

Adolescent↗

PubMed1988

Doppler assessment of changes in right-sided cardiac hemodynamics after pulmonary thromboendarterectomy.

It is not known whether Doppler echocardiography can accurately follow changes in right-sided cardiac hemodynamics after a therapeutic intervention in patients with pulmonary artery (PA) hypertension. Therefore, Doppler measurements of the maximal velocity of the tricuspid regurgitant jet and the acceleration time of the PA velocity profile were obtained in 28 patients before and after pulmonary thromboendarterectomy for chronic thromboembolic PA hypertension. Doppler values were compared with hemodynamic variables obtained at cardiac catheterization. Postoperatively, decreases in mean PA pressure (50 +/- 14 to 28 +/- 8 mm Hg), transtricuspid systolic pressure difference (69 +/- 21 to 36 +/- 14 mm Hg) and Doppler measurement of the maximal velocity of the tricuspid regurgitant jet (4.1 +/- 0.7 to 2.7 +/- 0.5 m/s) were noted, while acceleration time increased (57 +/- 16 to 94 +/- 18 ms, all p less than 0.001) compared with preoperative values. For the population as a whole, the calculated systolic transtricuspid pressure difference determined from the maximal velocity of tricuspid regurgitation correlated well with the catheterization systolic transtricuspid pressure difference (r = 0.93, p less than 0.001) and the acceleration time correlated with mean PA pressure (r = -0.81, p less than 0.001). More importantly, the change in the maximal velocity of tricuspid regurgitation for postoperative patients was found to correlate with the change in catheterization systolic transtricuspid pressure difference (r = 0.82, p less than 0.001), while the change in acceleration time correlated weakly with the change in mean PA pressure (r = -0.41, p = 0.053).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Extracellular potassium concentrations in human dental plaque fluid recovered from single sites.

Previous studies using potassium ion-selective microelectrodes have demonstrated that potassium concentrations in dental plaque fluid obtained by centrifugation are identical to whole plaque values determined immediately after collection. Such procedures were now used to examine the variations in potassium concentrations between single-site samples of overnight-fasted resting plaque fluid. The potassium concentrations (67.3 +/- 10.8 mmol/l, N = 50) were similar to those found before in whole plaque within 1 min of removal from the mouth and did not appear to be site-dependent. Possible mechanisms for the maintenance of potassium in plaque fluid at higher than salivary levels are described.

Dental Plaque↗