Biomedical subjects

J L Ong

Publications and source records attributed to J L Ong.

At least 37 records · Page 2Linked to original sources

PubMed2000

Hydroxyapatite and their use as coatings in dental implants: a review.

At present, no standard manufacturing guideline exists for depositing hydroxyapatite (HA) on implant surfaces. Although animal and in vitro studies have reported on the benefits of using HA-coated implants as well as the risks of dissolution, these short-term studies did not demonstrate that the dissolution of the HA coating leads to a loss of implants. In addition, many in vivo and clinical studies did not include the chemical and structural characterization of the coatings, and thus comparisons between studies are difficult. In the clinics, the recommendation is that HA-coated screw implants be used for the anterior maxilla and posterior mandible where the bone depth exceeds 10 mm and when the cortical layer is thinner and spongiosia is less dense. In the posterior maxilla or when the cortical layer is very thin with low density, the use of HA-coated cylindrical implants is recommended. However, there are concerns for using HA-coated implants. The clinician needs to take into consideration the enhanced bacterial susceptibility of HA coatings compared with titanium implants. In addition, the clinician needs to consider the possible failure of HA coatings as a result of coating-substrate interfacial fracture. Finally, besides the surgical skills, it is also important that the clinical investigators be well versed with the materials characterization needed for HA-coated implants, the problems associated with the current HA coatings, and the indications for use. In addition, the correlation between well characterized coatings and their effect on bone formation rate and long-term implant success, coating-implant interfacial strength, and alternative superior coating process need to be investigated further.

Animals↗

PubMed1999

BMP stimulation of bone response adjacent to titanium implants in vivo.

The objective of this study was to evaluate the effect of bone morphogenetic protein (BMP) on the bond strength of titanium (Ti) implants at the bone-implant interface. Thirty-six Brånemark screw implants (3.75 mm diameter by 15 mm long) were implanted for 3 and 12 weeks. At 3 weeks after implantation, the mean reverse torque value for implants stimulated with BMP delivered using an atelopeptide type-I collagen carrier (74.2 +/- 5.2 N cm) was observed to be statistically greater (P < 0.000016) than the mean reverse torque value for control Ti implants (32.8 +/- 1.1 N cm). Similarly, at 12 weeks after implantation, the mean reverse torque value for implants stimulated with BMP (89.2 +/- 2.7 N cm) was statistically greater (P < 0.0042) than the mean reverse torque value for control Ti implants (75.8 +/- 2.4 N cm). In addition, histomorphometric evaluations indicated more bone contact with the BMP stimulated implant surfaces compared to the controls after 3 weeks implantation. It was concluded from this study that the use of BMP-atelopeptide type-I collagen mixture is an effective means of obtaining greater bond strength at the bone implant interface within a shorter time period than Ti implants without BMP.

Animals↗

PubMed1999

Osteoblast progenitor cell responses to characterized titanium surfaces in the presence of bone morphogenetic protein-atelopeptide type I collagen in vitro.

The goal of this study was to investigate the effect of bone cell response to titanium (Ti) surfaces in the presence of bone morphogenetic protein (BMP)-atelopeptide type I collagen mixture. The atelopeptide type I collagen was used as a potential carrier for the BMP. Sterilized 600-grit Ti samples were used as substrates for the cell culture study. X-ray photoelectron spectroscopy indicated the presence of TiO2 on the Ti surface. The in vitro cell culture study was performed using an osteoblast progenitor cell line derived from mice (2T9). At confluency, the cells cultured on Ti surfaces were divided into three groups: unstimulated culture, culture stimulated by BMP-atelopeptide type I collagen (40 ng/mL), and culture stimulated by atelopeptide type I collagen (40 ng/mL). The unstimulated and atelopeptide type I collagen cultures were controls in this study. After 4 days of incubation, protein production, alkaline phosphatase (ALP) activity, and hexosaminidase activity were observed to be the highest for cells exposed to the BMP-atelopeptide type I collagen mixture. Statistical differences in cellular protein production and ALP activity were observed between the controls and the surfaces exposed to the BMP-atelopeptide type I collagen mixture. Similarly, a statistical difference in hexosaminidase activity was observed between unstimulated Ti surfaces and surfaces exposed to BMP-atelopeptide type I collagen mixture. However, no statistical differences in protein production, ALP activity, and hexosaminidase activity were observed between cells exposed to atelopeptide type I collagen solution and the unstimulated surfaces.

Alkaline Phosphatase↗

PubMed1999

Protein adsorption and osteoblast responses to heat-treated titanium surfaces.

The clinical success of dental implants is governed in part by surface properties of implants and their interactions with the surrounding tissues. The objective of this study was to investigate the effect of heat-treated titanium (Ti) surfaces on protein adsorption and osteoblast responses in vitro. The passivated Ti samples used in this study were either nonheat-treated or heat-treated at 750 degrees C for 90 minutes. Using x-ray diffraction analyses, no oxide peaks were observed on the nonheat-treated surfaces, suggesting an amorphous oxide. Crystalline rutile TiO2 peaks were observed on the heat-treated Ti surfaces. The contact angles of water on heat-treated Ti surfaces (32.0 +/- 2.5 degrees) were statistically lower compared with the nonheat-treated Ti surfaces (47.7 +/- 2.3 degrees). In addition, the mean albumin concentration on the nonheat-treated Ti surfaces (3.57 +/- 0.33 micrograms/mL) was observed to be significantly different from the mean albumin concentration on heat-treated Ti surfaces (2.25 +/- 0.26 micrograms/mL). In the presence of an osteoblast precursor cell line, significantly different hexosaminidase activity, protein production, and alkaline phosphatase activity were observed for cells grown on heat-treated Ti surfaces compared with nonheat-treated Ti surfaces.

Adsorption↗

PubMed1998

Osteoblast precursor cell activity on HA surfaces of different treatments.

The clinical success of dental implants is governed by implant surfaces and bone cell responses that promote rapid osseointegration and long-term stability. The specific objective of this study was to investigate osteoblast precursor cell responses to hydroxyapatite (HA) surfaces of different treatments. Since the nature of bone cell responses in vitro is influenced by the properties of HA ceramics, this study was divided into two components: a chemical and crystallographic characterization of the HA ceramics and an in vitro cell culture study. The sintered HA samples were observed to have the highest crystallite size as compared to the as-received HA and calcined HA samples. No differences in the surface roughness and chemical composition were observed among the sintered, calcined, and as-received HA surfaces. In concurrence with the X-ray diffraction, high resolution XPS resolution of Ca 2p also indicated a higher crystallinity on sintered HA samples as compared to the calcined and as-received HA samples. As indicated by increased alkaline phosphatase-specific activity, increased cell-surface and matrix-associated protein, and 1.25 (OH2) vitamin D3-stimulated osteocalcin production, a more differentiated osteoblast-like phenotype was observed on the sintered HA surfaces compared to the as-received HA and calcined HA surfaces. An increased osteoblast-like cell activity on the sintered HA surfaces suggested that the crystallite size of HA surfaces may play an important role in governing cellular response.

Alkaline Phosphatase↗

PubMed1998

Auger electron spectroscopy and its use for the characterization of titanium and hydroxyapatite surfaces.

This review paper provides the basic background and underlying theory behind Auger electron spectroscopy (AES). Among the many surface analytical tools, AES has been shown to be very effective for surface composition analysis. These analyses are critically needed to better understand the interactions between the host and implant. The use of AES for titanium (Ti) and hydroxyapatite (HA) biomaterials characterization is demonstrated in this paper. The relative peak heights of TiL(2,3)M(2,3)V can be used as 'fingerprints' for TiO2 surfaces which have undergone different degrees of reduction. Similarly, for HA coatings, a shift in the phosphorus Auger peaks to a higher kinetic energy indicates the presence of a phosphate group, with strong P-O bonds. Depth compositional profiling and thin-film analysis can be performed using AES. In our studies, oxide thicknesses on Ti surfaces range from 36.8 +/- 7.4 A to 436 +/- 49 A depending on the surface treatment. Depth profiling can also be used to determine the subsurface composition of biomaterials. For HA coatings, a phosphorus concentration at the oxide/metal interface has been observed to be higher than at the outermost oxide surface. The HA coatings have also been observed to coexist within the titanium oxide, suggesting the occurrence of chemical bonding between the coatings and the metallic substrates. However, like other analytical tools, AES has its limitations. The electron beam damage can severely limit useful analysis of organic and biological materials and occasionally ceramic materials. Carbide buildup during long beam exposure times has been shown to affect the relative peak-to-peak intensities of the oxygen and metal Auger signals. The determination of film thickness requires a standard of known thickness and depth profiling of overlapping peaks can be very problematic. Even with these limitation, AES can be a powerful analytical tool for the characterization of biomaterial surfaces.

Biocompatible Materials↗

PubMed1998

Protein adsorption and osteoblast responses to different calcium phosphate surfaces.

The purpose of this study was to investigate the effect of sintering different calcium phosphate (CaP) surfaces on protein adsorption and osteoblast cell response. As-received and sintered hydroxyapatite (HA) and brushite were used in this study. X-ray diffraction revealed a poorly crystallized HA structure for the unsintered HA and a highly crystallized HA for the sintered HA surfaces. A brushite-type structure was indicated on the unsintered brushite surfaces, whereas sintered brushite surfaces contained mixtures of different CaP phases. Using 1 mg/mL albumin solution, protein was suggested to selectively adsorb on the CaP surfaces. A statistically higher albumin adsorption was observed on unsintered HA (9.5 micrograms/mL) and unsintered brushite (50.1 micrograms/mL) surfaces compared to sintered HA (3.2 micrograms/mL) and sintered brushite (3.4 micrograms/mL) surfaces. In the in vitro study using osteoblast cells, no statistical responses were observed between cells cultured on sintered HA and sintered brushite after 8 days of incubation. However, statistical differences in osteocalcin and protein production were observed between the unsintered HA and unsintered brushite. In addition, statistical differences in protein production, alkaline phosphatase activity, and osteocalcin production were observed between sintered CaP and unsintered CaP surfaces. From the protein adsorption and cell responses observed in this study, it was concluded that CaP surfaces need to be fully characterized prior to implantation.

Adsorption↗

PubMed1997

Properties of calcium phosphate coatings before and after exposure to simulated biological fluid.

The surface qualities of calcium phosphate (CaP) implants are important factors determining the nature and degree of cellular behaviour, especially cellular attachment, proliferation and differentiation. Thus, in this study, the chemical composition and crystallographic properties of radiofrequency sputter-deposited CaP coatings prior to and after in vitro immersion in a physiological solution were characterized. Significant differences in crystallite size were observed with different heat treatments, with coatings heat treated at 850 degrees C (CA8) having larger crystallites compared to coatings heat treated at 700 degrees C (CA7). However, no statistical difference in the Ca/P ratio, carbon concentration and surface energy were observed with different heat treatments. After immersion in a physiological solution, the crystallite size was significantly increased. The crystallite size for the CA8 and CA7 coatings remained statistically different after 1-week immersion in solution. An increase in carbon concentration was also observed for both samples after 1-week immersion in solution. However, no significant differences in the Ca/P ratio and surface energy were indicated between the two coatings after 1-week immersion in solution. In addition, no statistical difference in surface energy was observed for both samples initially and after 1 week.

Calcium Phosphates↗

PubMed1997

Surface roughness of titanium on bone morphogenetic protein-2 treated osteoblast cells in vitro.

Surface topography plays a critical role in the interaction of dental implants with adjacent tissues. No statistical differences in oxide composition and surface contamination were observed between 600 grit and polished titanium surfaces. The expression of osteoblast phenotype was enhanced when osteoblast progenitor cells (2T9) were stimulated with bone morphogenetic protein-2 on polished and 600 grit titanium surfaces. Bone morphogenetic protein-2 stimulated phenotypic expression on 600 grit titanium surfaces was marked by prolonged alkaline phosphatase specific activity and more rapid osteocalcin production as compared with the polished titanium surfaces. Because the surface area of the 600 grit titanium surface was shown to be 8 percent greater than that of the polished titanium surface, it is possible that increased surface area played a role in the enhanced expression of the osteoblast phenotype.

Alkaline Phosphatase↗

PubMed1996

Directly placed esthetic restorative materials--the continuum.

Because new restorative materials have had little clinical testing, it is difficult to make specific material recommendations for the esthetic restoration of carious teeth. Although fluoride-releasing materials have long been used successfully to restore carious teeth, little clinical documentation has been presented to support their use to inhibit recurrent caries, and their use as an effective restorative material may be questioned. Glass ionomers, compomers, and resin-modified glass ionomers are esthetic fluoride-releasing materials designed to restore teeth by bonding to tooth structure. This article describes the continuum of directly placed esthetic dental restorative materials, the efficacy of amalgam replacement restorative materials, and the role that fluoride-releasing materials may play in the inhibition of recurrent caries in vitro and in vivo.

Composite Resins↗

PubMed1996

Effect of surface topography of titanium on surface chemistry and cellular response.

Surface topography plays a critical role in the interaction of dental implants with adjacent tissues. It has been hypothesized that an increase in surface roughness will result in an increase in calcium and phosphorus deposition after immersion in a simulated physiological solution and will increase protein production and calcium uptake by osteoblast-like cells. With the use of a profilometer, titanium samples ground with 600 grit silicon carbide paper were observed to have an average roughness (Ra) value of 0.28 +/- 0.03 micron, whereas titanium samples polished with 0.3 micron Al2O3 exhibited a Ra value of 0.11 +/- 0.01 micron. X-ray photoelectron spectroscopy analyses indicated the presence of calcium, phosphorus, sodium, and chlorine on both surface conditions after immersion in a protein-free physiologic solution. No significant difference in calcium and phosphorus concentrations were observed between the 600 grit or Al2O3 polished titanium samples after immersion in solution. The Ca/P ratio for both 600 grit and Al2O3 polished titanium was in the range of 0.8 to 1.1 after 12 days in solution. The percent protein retained by the rat bone marrow cell layer on both the Al2O3 polished and 600 grit titanium surfaces increased dramatically during the initial 3 days of the study. The 45Ca assays revealed no significant difference in cellular calcification on Al2O3 polished and 600 grit titanium surfaces. For both the Al2O3 polished and 600 grit surfaces, a sharp increase in 45Ca incorporation was observed after 9 days incubation.

Aluminum Oxide↗

PubMed1995

Cellular response to well-characterized calcium phosphate coatings and titanium surfaces in vitro.

The cellular response to well-characterized Ca-P and Ti surfaces was analyzed. This study indicated that the ion-beam sputtering process could produce a hydroxyapatite-type coating. However, structural alterations such as the incorporation of CO3 and the loss of the OH groups were observed. The Ti surfaces were shown to be predominantly amorphous TiO2. The in vitro cell culture study showed no significant differences in cell number for the Ti and Ca-P surfaces throughout the 12-day study. Furthermore, the initial percentage of protein within the cell layers was significantly lower for cells on Ca-P surfaces compared with the cell layer on Ti surfaces. However, after 3 h incubation, no significant difference in the percentage of protein was observed for the Ti and Ca-P surfaces.

Animals↗

PubMed1995

Determination of doubly labeled water by gas-phase Fourier transform infrared spectroscopy.

Both 2H (deuterium) and 18O (oxygen 18) in isotopically enriched water have been detected by gas-phase Fourier transform infrared (FTIR) spectroscopy at 2,720 and 3,661.8 cm-1, respectively. A linear relationship between varying concentrations of each of these isotopes and their absorbance at the above frequencies indicates that gas-phase FTIR may provide a rapid and potentially less expensive approach to measure doubly labeled water in biological fluids for the estimation of energy expenditure and total body water.

Body Water↗

PubMed1994

Dissolution/reprecipitation and protein adsorption studies of calcium phosphate coatings by FT-IR/ATR techniques.

The surfaces of bioactive Ca-P ceramics immediately change when exposed to proteinaceous solutions. The dissolution behavior and protein interactions of these bioactive materials at the bone/implant interface need to be investigated to understand their material-cellular interactions fully. In this study, FT-IR/ATR techniques were used to study the in situ phosphate release kinetics of Ca-P coatings. The net loss of phosphate molecules from coatings was slower in saline solutions compared with alpha-MEM solutions. Coatings exposed to alpha-MEM solutions containing fibronectin released phosphate molecules slower than coatings exposed to alpha-MEM solutions containing albumin. Conformational changes in fibronectin and albumin adsorbed onto Ca-P and uncoated germanium surfaces were also investigated using FT-IR/ATR spectroscopy. Analysis of changes in the amide I bands indicated that there was a greater loss of beta-sheet structure in adsorbed fibronectin on Ca-P coatings when compared with bare germanium surfaces. Although albumin did change its structure upon adsorption on both Ca-P and germanium, unlike fibronectin, adsorbed albumin structure was similar on Ca-P coatings and germanium. Furthermore, with time the conformation of adsorbed fibronectin and albumin appeared to be very stable on Ca-P coatings, whereas albumin adsorbed to germanium exhibited an increase in ratio of alpha-helix to beta-turn.

Adsorption↗

PubMed1994

Post-deposition heat treatments for ion beam sputter deposited calcium phosphate coatings.

Calcium phosphate coatings produced using the ion beam sputter deposition process are amorphous. To produce crystalline coatings, a series of different post-deposition heat treatments were conducted. Heat treatments conducted at temperatures less than 500 degrees C did not produce crystalline phases in the coatings. A 500 degrees C post-deposition heat treatment provided the energy required to produce a hydroxyapatite (HA)-type coating as determined using X-ray diffraction and Fourier transform IR spectroscopy (FTIR). Although post-deposition heat treatments can reduce the adhesion of a coating to its substrate, the 500 degrees C heat treatment did not decrease the coating bond strength. Heat treatments conducted at 600 degrees C were found to produce crystalline HA-type coatings but these heat treatments significantly reduced the coating bond strength. Cracks were observed on the surface of the 600 degrees C heat treated coatings. FTIR analysis revealed a new absorption band at 820 cm-1 for the 600 degrees C heat treated coatings, suggesting the formation of a new phase.

Calcium Phosphates↗

PubMed1992

Structure, solubility and bond strength of thin calcium phosphate coatings produced by ion beam sputter deposition.

Ion beam sputter deposition was used to produce thin calcium phosphate coatings on titanium substrates. Structure, solubility and bond strength of the as-sputtered and heat treated coatings were evaluated. X-ray diffraction (XRD) analysis of the heat treated coatings revealed a hydroxyapatite-type structure. The heat treated coatings were found to have significantly lower solubility as compared to the amorphous as-sputtered coatings. Although the crystalline coatings exhibited the lowest solubility, in general, the bond strengths were lower for the heat treated coatings.

Bone and Bones↗

PubMedDate not supplied

Effect of transforming growth factor-beta on osteoblast cells cultured on 3 different hydroxyapatite surfaces.

In this study, the specific objective was to investigate the combined effect of different treatments of transforming growth factor-beta (TGF-beta) and hydroxyapatite (HA) on osteoblast response in vitro. Since the nature of bone cell responses in vitro is influenced by the properties of HA ceramics, this study was divided into 2 components: a chemical and crystallographic characterization of the HA ceramics, and an in vitro cell culture study. Sintered HA samples were observed to have the highest crystallite size, compared to as-received HA and calcined HA samples. No differences in surface roughness and chemical composition were observed between the sintered, calcined, and as-received HA surfaces. In concurrence with the x-ray diffraction, high-resolution x-ray photoelectron spectroscopy of Ca 2p also indicated a higher crystallinity on sintered HA samples compared to calcined and as-received HA samples. Protein production by osteoblast cells was not statistically different on the 3 HA surfaces in the absence of TGF-beta. However, there was a dose-dependent increase in TGF-beta-stimulated protein production on the 3 different HA surfaces. As indicated by increased alkaline phosphatase-specific activity, as well as 1,25 (OH2) vitamin D3-stimulated osteocalcin production, a more differentiated osteoblastlike phenotype was observed on the sintered HA surfaces compared to the as-received HA and calcined HA surfaces. An increased osteoblast-like cell activity on sintered HA surfaces in the presence of different TGF-beta dosage suggested that sintering of HA surfaces may play an important role in governing cellular response.

Alkaline Phosphatase↗

PubMedDate not supplied

Surface characterization of radio-frequency glow discharged and autoclaved titanium surfaces.

To characterize titanium surfaces treated with radio-frequency glow discharge (RFGD) after media exposure, surface chemical analyses were performed using x-ray photoelectron spectroscopy. Auger electron spectroscopy, and Fourier transform infrared-reflection absorption spectroscopy (FTIR-RAS). The RFGD treatments resulted in a cleaner surface as compared to as-sputtered or as-autoclaved titanium specimens. The oxide thickness of RFGD-treated titanium specimens was not statistically different from the as-autoclaved and as-sputter cleaned titanium specimens. Exposure to a phosphate-buffered saline solution revealed a greater deposition of calcium and phosphorous on the RFGD-treated surfaces. Auger electron spectroscopy depth profiles showed that calcium and phosphorous ions diffused into the titanium oxide layer. The calcium and phosphorous deposits were identified as amorphous calcium phosphate compounds using FTIR-RAS. These results suggest that RFGD treatments of titanium enhance calcium and/or phosphate affinity because of an increase in elemental interactions at the surface, thereby resulting in the formation of amorphous calcium phosphate compounds.

Buffers↗