Biomedical subjects

L C Chow

Publications and source records attributed to L C Chow.

At least 55 records · Page 3Linked to original sources

PubMed1995

Histopathological reaction of calcium phosphate cement in periodontal bone defect.

In this study, we evaluated the osteoconductivity of calcium phosphate cement (CPC) as compared to that of a current hydroxyapatite-based material (AP) by implanting the materials in surgically formed defects in the jaws of dogs. One month post-operation, slight inflammatory reactions were observed in tissue areas adjacent to either CPC mass or AP. Three months after operation, the CPC mass-filled defects were covered with periosteum and bone tissues. The CPC mass in the defects was partially replaced by newly formed bone. In bone defects filled with AP, most of the interparticle space was filled with connective tissues including bone tissues. Six months post-operation, the CPC mass-filled defects were covered with periosteum and new bone, and most of the CPC mass was replaced by bone. Interparticle spaces of AP were filled with connective tissues and bone tissues.

Alveolar Bone Loss↗

PubMed1994

Behavior of a calcium phosphate cement in simulated blood plasma in vitro.

OBJECTIVES: The purpose of this study was to gain a better understanding of the integration of calcium phosphate cement (CPC) implants in biological tissue. METHODS: An in vitro continuous flow system was employed to examine the protracted behavior of disc-shaped specimens of this bioactive material under sustained physiological-like solution conditions. Weight measurement, diameteral tensile strength measurement (DTS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and powder x-ray diffraction (XRD) were used to characterize the CPC samples as a function of immersion time. RESULTS: When CPC was immersed in simulated blood plasma in which the Ca (2.5 mmol/L) and inorganic phosphate (1.0 mmol/L) levels were kept constant, both the weight and DTS of the specimens steadily increased to about 1.5 times their original values over a period of 20 wk. SEM observations showed new precipitate formations in intimate contact with the original CPC surface. FTIR and XRD analyses revealed that the precipitate was a B-type carbonate hydroxyapatite (OHAp), the type of OHAp observed in bone and dentin. On the other hand, the interior of CPC discs did not show an increase in either bulk density or OHAp content. Thus, the increases in weight and DTS are attributable to the OHAp precipitation on the CPC surface. SIGNIFICANCE: The results suggest that under in vivo conditions, CPC implants would not dissolve in physiological fluids. OHAp coatings may form on the implants, which may enhance bonding of implants to bone by mechanically strengthening the interface between them.

Biocompatible Materials↗

PubMed1994

Physical and chemical properties of resin-reinforced calcium phosphate cements.

OBJECTIVES: The purpose of this study was to improve the handling and physical properties of a self-setting, water-based calcium phosphate cement by combining it with polymerizable resins and to study the setting reactions involved. METHODS: Dual-cured composite cements were prepared from a calcium phosphate cement powder and dental monomers that contain carboxylated hydrophilic resins or resin/water mixtures. The setting reaction of the calcium phosphate cement in the presence of the resins was evaluated by pH measurements, infrared spectroscopy, diametral tensile strength, x-ray diffraction analysis, and scanning electron microscopy. RESULTS: Carboxylated resins were chosen because they can form ionic bonds to the mineral filler, which was confirmed by appearance of an infrared absorbance peak at 1552 cm-1 within 24 h after mixing due to the formation of a carboxylate salt. Hydroxyapatite did not develop in composites prepared from resin and calcium phosphate cement. However, composites from calcium phosphate cement, resin and water showed approximately 40% hydroxyapatite. The resulting composite cements have moderately high DTS of 14-15 MPa and high pH. SIGNIFICANCE: Hydrophilic acidic resins allows mixing with water and/or allow rapid diffusion of water into the resinous cement so that the dissolution and reprecipitation processes required for the conversion of the calcium phosphate components to hydroxyapatite can occur. The characteristics of the resulting composite cements suggest that the materials may be useful in pulp capping and/or cavity lining.

Calcium Phosphates↗

PubMed1994

Effects on whole saliva of chewing gums containing calcium phosphates.

To evaluate chewing gums as a vehicle to increase salivary mineral saturation levels and enhance salivation, monocalcium phosphate monohydrate (MCPM) and an equimolar mixture of tetracalcium phosphate (TTCP) with dicalcium phosphate anhydrous (DCPA) were chosen as experimental chewing gum additives. Each of eight subjects chewed a commercial sugarless bubble gum (control) for 16 min or the same gum to which 5 wt% of MCPM or the TTCP-DCPM mixture had been added. The saliva samples collected every 2 min were analyzed for weight, pH, and total calcium (Ca) and phosphate (P) concentrations. Both experimental gums were found to increase significantly the Ca and P concentrations of saliva during the 16-minute period even more than with a previously evaluated gum that contained dicalcium phosphate dihydrate. The degree of saturation of tooth mineral was significantly increased by both experimental gums, with the greater increase being produced by the TTCP-DCPA gum. The MCPM gum produced a significantly greater saliva flow and a lower salivary pH than did the control and TTCP-DCPA gums. The results suggest that the experimental gums may be useful for promoting remineralization in general and for inducing salivation in xerostomic patients.

Adult↗

PubMed1993

Facial skeletal augmentation using hydroxyapatite cement.

This study investigates the use of a new calcium phosphate cement, which sets to solid, microporous hydroxyapatite, for facial bone augmentation. In six dogs, the supraorbital ridges were augmented bilaterally with this hydroxyapatite cement. On one side, the hydroxyapatite cement was placed directly onto the bone within a subperiosteal pocket. On the opposite side, the cement was contained within a collagen membrane tubule and then inserted into a subperiosteal pocket. The use of collagen tubules facilitated easy, precise placement of the cement. All implants maintained their original augmented height throughout the duration of the study. They were well tolerated without extrusion or migration, and there was no significant sustained inflammatory response. Histologic studies, performed at 3, 6, and 9 months revealed that when the cement was placed directly onto bone, progressive replacement of the implant by bone (osseointegration of the hydroxyapatite with the underlying bone) without a loss of volume was observed. In contrast, when the cement-collagen tubule combination was inserted, primarily a fibrous union was noted. Despite such fibrous union, the hydroxyapatite-collagen implant solidly bonded to the underlying bone, and no implant resorption was observed. Hydroxyapatite cement can be used successfully for the experimental augmentation of the craniofacial skeleton and may be applicable for such uses in humans.

Animals↗

PubMed1993

Polymeric calcium phosphate cements: analysis of reaction products and properties.

Chemical and mechanical properties of water-based polymeric calcium phosphate cements (PCPC) were investigated. These cements were derived from mixing several types of water-soluble polymers, e.g., gelatin, poly(vinyl alcohol) (PVA), and poly(alkenoic acids) such as poly(acrylic acid), with a calcium phosphate cement (CPC) mixture consisting of equimolar amounts of tetracalcium phosphate (TTCP) and anhydrous dicalcium phosphate (DCPA) as well as several other TTCP-containing mixtures. Cement formation was observed with all of the PCPCs. With the gelatin and PVA cements, significant amounts of hydroxyapatite (HA) formation were observed within 24 h. Their setting times and mechanical properties were similar to those of the purely inorganic CPC that is derived from the reaction of TTCP and DCPA in water. Although the mechanical properties of a gelatin-CPC cement were only slightly improved, its handling characteristics were superior to that of CPC. Significantly faster setting and stronger cements were obtained using polycarboxylic acid polymers with CPC. However, only small amounts of HA were observed in these types of polymeric cements even after 1 mon storage in distilled water at 37 degrees C. This research demonstrates the feasibility of preparing several new types of dental cements based on the interaction of water-soluble polymers with a self-setting calcium phosphate powder mixture.

Acrylic Resins↗

PubMed1993

Polymeric calcium phosphate cements: setting reaction modifiers.

In this study, the effects of several additives on the setting behavior and mechanical properties of polymeric calcium phosphate cements were investigated. The cements were derived from a polycarboxylic acid (PCA) and a calcium phosphate cement (CPC) powder that consisted of equimolar amounts of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA). Retardation of the setting reaction in the PCA-CPC cements was observed by adding tribasic sodium phosphate and fluorides such as stannous fluoride, zirconium(IV) fluoride and titanium(IV) fluoride. It was found that increasing the concentration of these additives decreased the mechanical strength of the cements. However, improvements in both setting and mechanical properties for the PCA-CPC cements were observed by the combined use of 8% (w/w) stannous fluoride and 10% (w/w) tartaric acid. The mechanical properties of the PCA-CPC cement also were improved by adding calcium acetate, calcium methacrylate, zirconium(IV) sulfate and phosphonoacetic acid.

Acetates↗

PubMed1992

Procedure for the study of acidic calcium phosphate precursor phases in enamel mineral formation.

Considerable evidence suggests that an acidic calcium phosphate, such as octacalcium phosphate (OCP) or brushite, is involved as a precursor in enamel and other hard tissue formation. Additionally, there is in vitro evidence suggesting that fluoride accelerates and magnesium inhibits the hydrolysis of OCP to hydroxyapatite (OHAp). As the amount of OCP or brushite in enamel cannot be measured directly in the presence of an excess of hydroxyapatite, a procedure was developed that allows for their indirect in vivo quantification as pyrophosphate. This permits study of the effects of fluoride and magnesium ions on enamel mineral synthesis. Rat incisor calcium phosphate was labeled by intraperitoneal injection of NaH2(32)PO4. The rats were then subjected to various fluoride and magnesium treatments with subcutaneous implanted osmotic pumps. They were then killed at predetermined intervals; the nascent sections of the incisors were collected, cleaned, and pyrolyzed at 500 degrees C for 48 hours to convert acidic calcium phosphates to calcium pyrophosphate; the pyrophosphate was separated from orthophosphate by anion-exchange chromatography; and the resulting fractions were counted by liquid scintillation spectrometry. The activities of the pyro- and orthophosphate fractions were used to calculate the amount of acidic calcium phosphate present in the nascent mineral. The results demonstrated that the percentage of radioactive pyrophosphate in nascent incisors decreased with time, with increasing serum F- concentration, and with decreasing serum magnesium content. The technique described here should prove to be a powerful new tool for studying the effects of various agents on biological mineral formation.

Administration, Cutaneous↗

PubMed1992

Deposition of loosely bound and firmly bound fluorides on tooth enamel by an acidic gel containing fluorosilicate and monocalcium phosphate monohydrate.

The amounts of loosely bound fluoride (F) deposited on human enamel by 4-min and 2-hour treatments with either acidulated phosphate fluoride (APF) or a monocalcium phosphate monohydrate and sodium hexafluorosilicate (MCPM-SHFS)-containing gel were measured with the use of a constant-composition F washing method. Enamel biopsies conducted before treatment and after washing were used to determine the firmly bound F uptake. The results showed that the MCPM-SHFS treatments produced significantly more loosely bound F than did the APF treatments. The 4-min treatment with either APF or MCPM-SHFS did not produce significant firmly bound F deposition, but the 2-hour treatments did, with that produced by MCPM-SHFS being significantly greater. The MCPM-SHFS gel, which had the same F content as APF and which may be applied to the proximal tooth surfaces in vivo without the use of a tray, has the potential to be more efficacious than APF because it deposits greater amounts of both loosely bound and firmly bound F.

Acidulated Phosphate Fluoride↗

PubMed1992

Effect of a two-solution fluoride mouthrinse on remineralization of enamel lesions in vitro.

A previous study showed that a two-solution fluoride (F) rinse deposited significantly more loosely-bound F on the tooth surface than did a sodium fluoride (NaF) rinse with the same F concentration (12 mmol/L). In the present study, this experimental rinse was evaluated for its ability to cause remineralization of enamel lesions in an in vitro pH-cycling model. Caries-like lesions were formed in the enamel of extracted human molars by means of a pH 4 demineralizing solution. Fifty-one approximately 120-microns-thick sections containing lesions were randomly divided into (1) control, (2) NaF rinse, and (3) two-solution F rinse groups. With the cut surfaces protected, the control samples were immersed in a pH 7 remineralizing solution for 12 days, and twice daily the sections were also exposed to a pH 4 demineralizing solution for 30 min. Samples in the NaF group received an additional one-minute rinse with a NaF (12 mmol/L) solution twice daily. Samples in the two-solution rinse group received the rinse treatment with a 12 mmol/L F solution prepared by combination of a Na2SiF6 and phosphate-containing solution with a calcium solution just before use. The mineral contents of the lesions were assessed by quantitative microradiography. The results showed that (1) no significant de- or remineralization was detected in the controls; (2) a 46% decrease in mineral loss (delta Z) of the lesion was produced by the NaF rinses; and (3) a 94% decrease in delta Z and a 20-microns-thick, mineral-dense surface-coating were produced by the two-solution F rinse treatment.

Apatites↗

PubMed1992

In vivo fluoride concentrations measured for two hours after a NaF or a novel two-solution rinse.

The concentrations of fluoride in various samples from the oral environment were measured at timed intervals after a novel rinse or a NaF rinse, both containing a total of 12 mmol/L (228 ppm) fluoride. The novel rinse consisted of two solutions mixed just before application: Part A contained calcium chloride and sodium acetate; part B contained a hydrolyzable source of fluoride (sodium hexafluorosilicate) and sodium phosphate. Samples were obtained as follows: Single-site plaque-fluid samples were obtained by centrifugation of first-molar plaque; pooled whole-plaque samples were collected from second molars; centrifuged, pooled whole-saliva was collected by vacuum. All samples were analyzed by micro-analytical methods. Results showed that, compared with NaF, the two-solution rinse produced significantly higher salivary fluoride concentrations, plaque-fluid fluoride concentrations, and acid-extractable fluoride in the whole plaque by factors of about 4, 2, and 6, respectively, at 120 min. The results of this study suggest that the new rinse may provide a greater cariostatic effect at the same fluoride dosage than does a NaF rinse.

Adult↗

PubMed1992

Histopathological reactions of calcium phosphate cement.

Calcium phosphate cement (CPC) consisting of Ca4 (PO4)2O and CaHPO4 (2H2O) was recently developed. This study evaluated in vivo aspects of CPC and CPC mixtures compared to those of commercial hydroxyapatite (HP) and several endodontic materials: Grossman's cement (GC), calcium hydroxide-iodine paste (CHP) and gutta-percha plate (GP). Biocompatibility of subcutaneous implants in Donryu rats was evaluated after one month. Results showed very slight inflammatory reactions from CPC, CPC mixtures and HP. The materials were surrounded by thin fibrous connective tissues with a small number of lymphocytes and plasma cells. Severe inflammatory reactions were provoked by GC. Granulation tissues induced by CHP resembled those of pseudoxanthomatous granuloma. The GP material was encapsulated by relatively thick fibrous connective tissues with little inflammatory reactions.

Animals↗

PubMed1992

Experimental hydroxyapatite cement cranioplasty.

Hydroxyapatite cement is a calcium phosphate-based material that when mixed with water forms a dense paste that sets within 15 minutes and isothermically converts in vivo to a microporous hydroxyapatite implant. This cement was used to reconstruct bilateral 2.5-cm-diameter full-thickness critical-sized parietal skull defects in six cats. One side was reconstructed with 100 percent hydroxyapatite cement, and the other with a mixture of 50 percent hydroxyapatite cement and 50 percent ground autogenous bone by weight. These animals were sacrificed at 6 and 12 months after implantation. Positive and negative controls also were prepared. The anatomic contour of the soft tissue overlying all hydroxyapatite cement implants was well maintained, there were no wound infections or structural failures, and the implants were well tolerated histologically. None of the negative (unreconstructed) control defects was completely filled with repair bone, and all positive (methyl methacrylate) controls demonstrated foreign-body giant-cell formation and fibrous encapsulation of the implants. Examination of decalcified and undecalcified sections revealed progressive but variable replacement of the cement by new bone and soft tissue without a change in the shape or volume of the hydroxyapatite cement-reconstructed areas. New bone comprised 77.3 and 64.7 percent of the tissue replacing the hydroxyapatite cement and hydroxyapatite cement-bone implants, respectively. Replacement of the hydroxyapatite cement implants by new bone is postulated to occur by a combination of osteoconduction and implant resorption. These results indicate that further experimental research leading to the possible application of hydroxyapatite cement for full-thickness calvarial defect reconstruction in humans is warranted.

Animals↗

PubMed1991

Hydroxyapatite cement. I. Basic chemistry and histologic properties.

Hydroxyapatite cement is a unique calcium phosphate preparation that can be shaped intraoperatively and sets in vivo to an implant composed of microporous hydroxyapatite. The histologic response to this cement was evaluated by implanting disks made of this material within the heads of nine cats. Three sets of 12 hydroxyapatite cement disks were produced containing 0%, 10%, and 20% macropores by volume, respectively. The disks were implanted subcutaneously, intramuscularly, above the periosteum of the skull, and directly onto the surface of the calvarium. Each macropore percentage was represented in each tissue plane, and animals were killed up to 9 months postoperatively. There were no toxic reactions, implants extruded, or wound infections. Histologic examination of the implant-soft-tissue interfaces revealed a transient inflammatory response without foreign body reaction. The disks were resorbed over time in direct proportion to their macropore content (surface areas) in all groups except for those disks placed directly onto the surface of the calvarium below the periosteum. In this group, numerous foci of bone formed at the skull-implant interface, with variable replacement of the deep surface of these implants by bone. Implant replacement by bone is postulated to occur through a combination of implant resorption coupled with osteoconduction. Based on these properties, hydroxyapatite cement may prove useful when applied to the reconstruction of non-stress-bearing skeletal tissue.

Animals↗

PubMed1991

Hydroxyapatite cement. II. Obliteration and reconstruction of the cat frontal sinus.

Frontal sinus obliteration and reconstruction can be performed with autogenous grafts or synthetic implants, each of which has significant limitations. Hydroxyapatite cement, which can be shaped intraoperatively and sets to a microporous hydroxyapatite implant, was applied to this problem. Nine cats had the anterior table of their frontal sinus unilaterally removed and the sinus cavity stripped of its mucosa. Hydroxyapatite cement was used to obliterate the cavity and reconstruct the overlying anterior table defect. The unoperated side served as the control, and the animals were sacrificed up to 18 months postoperatively. There were no adverse reactions, infections, mucoceles, or implant extrusions. The normal anatomic contour of the forehead region overlying the hydroxyapatite cement implants was maintained in all animals. Histologic examination of undecalcified whole sinus sections revealed progressive replacement of the implants with woven bone without a loss of volume. Replacement of the hydroxyapatite cement by woven bone is postulated to occur through a combination of implant resorption coupled with osteoconduction. The use of hydroxyapatite cement proved successful for the reconstruction and obliteration of cat frontal sinuses, and may be appropriate for the same application in humans.

Animals↗

PubMed1991

The periapical tissue reactions to a calcium phosphate cement in the teeth of monkeys.

A calcium phosphate cement, Grossman sealer, and Sargenti N2 were compared under conditions where root canals of monkey incisors were deliberately overfilled and the apical tissue responses were evaluated histologically. The periapical tissues exposed to Sargenti N2 revealed severe irritation at all times through the 6-month experimental period. The reactions to Grossman sealer were milder but persisted throughout the observation period. The calcium-phosphate-cement treated animals showed mild tissue irritation after 1 month, but thereafter the adverse tissue reactions were minimal. New bone formation adjacent to the cement was also observed. These results point to the possibility that calcium phosphate cement might be used in simplified endodontic procedures. The compatibility of calcium phosphate cement with the periapical tissue suggests that the cement may have other applications in dentistry and medicine.

Animals↗

PubMed1991

Reversibility of cardiac abnormalities in human immunodeficiency virus (HIV)-infected individuals: a serial echocardiographic study.

Seventy adults who tested positive for human immunodeficiency virus (HIV) were prospectively studied with serial echocardiography to better define the prevalence and progression of cardiac disease in such patients. Fifty outpatients (Group A), including 44 with acquired immunodeficiency syndrome (AIDS) and 6 with AIDS-related complex, and 20 additional patients (Group B) with asymptomatic HIV infection had baseline echocardiographic studies at a time when no patient had symptomatic heart disease. Follow-up studies were performed at 9 +/- 3 months in 52 patients (74%) and again at 15 +/- 3 months after baseline studies in 29 patients (41%). During the study, 22 patients (44%) in Group A and 1 patient (5%) in Group B died. Cardiac abnormalities were noted in 26 patients (52%) in Group A and 8 patients (40%) in Group B (p = NS) on initial or follow-up study. An abnormal left ventricular ejection fraction (less than 45%) or fractional shortening (less than 28%) was seen in seven patients in Group A; of these, three had normal left ventricular function on a later echocardiogram. One patient in Group B had persistent left ventricular dysfunction. All patients in Group A with left ventricular dysfunction on two serial studies died within 1 year after the initial echocardiogram. Ejection fraction did not change between baseline and two follow-up studies in either group (A: 52 +/- 9 vs. 56 +/- 9 vs. 55 +/- 5%, p = NS; B: 58 +/- 6 vs. 58 +/- 5 vs. 59 +/- 6%, p = NS). Right-sided cardiac enlargement resolved in 18 patients (44%), including 5 of 10 in Group A and 3 of 8 in Group B.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Effects of pH and calcium on hydrolysis of Na2SiF6 and Na2SnF6. A quasi-constant composition titration study.

In the present work, hydrolysis reactions of sodium hexafluorosilicate (Na2SiF6) and sodium hexafluorostannate (Na2SnF6) were studied at various combinations of pH and calcium ion (Ca2+) concentrations using a quasi-constant composition titration method. Under high concentrations of hydrogen ion (H+) and Ca2+, the promoting effect of Ca2+ on the hydrolysis of Na2SiF6 was stronger than the inhibition effect of H+. However, the inhibition effect of H+ on the hydrolysis of Na2SnF6 was stronger than the promoting effect of Ca2+. Na2SiF6 and Na2SnF6 were found to have hydrolysis properties that may make them suitable for use with an acidic calcium phosphate solution in a topical fluoride treatment which forms dicalcium phosphate dihydrate as an intermediate.

Calcium↗