Uptake and biodistribution of 99mtechnetium methylene-[32P] diphosphonate during endosteal healing around titanium, stainless steel and hydroxyapatite implants in rat tibial bone

Early evaluation of intraosseous implant success and failure is critical, but, until now, there have been no reliable systems of measurement. The present study assessed whether the use of 99mtechnetium methylene-[32P]diphosphonate (99mTcMD32P), a marker for both bone formation and mineralization, can indicate if an implant is bone-bonding or non-bonding. Moreover, this study examined how bone-bonding (titanium and hydroxyapatite) and non-bonding (stainless steel) implants affected the normal healing of bone after marrow ablation, as measured by uptake of 99mTc and 32P. Titanium, hydroxyapatite and stainless steel implants were placed in the right tibiae of Sabra strain rats following ablation of the marrow, and 99mTcMD32P was injected 18 h before harvest. AT 3, 6, 14, 21 and 42 d (and in some experiments, on days 28 and 35) post-injury, the treated and contralateral tibiae were removed and cleaned of soft tissue. The uptake of 99mTc and 32P was measured in the whole bone, as well as in its organic and inorganic phases. Effects of the implants were assessed by comparing the treated to the untreated tibia in each rat. The distribution of 99mTc and 32P varied with each implant. After the insertion of titanium, increased 99mTc uptake was seen in whole bone and in the inorganic and organic phases at days 6-14. 32P uptake in whole bone and in the inorganic phase increased only at day 6, and 32P uptake was decreased in the organic phase at that time. In tibiae implanted with hydroxyapatite, 99mTc and 32P uptake was seen in the whole bone at days 6 and 14. While 99mTc uptake was increased in both the organic and inorganic phases, 32P uptake into the organic phase was decreased at both day 6 and day 14. In tibiae implanted with stainless steel, effects were observed only on day 6. The increased 99mTc uptake in whole bone reflected increases in both the organic and mineral phases. Increased 32P uptake was observed in whole bone as well, due to an increase in the 32P uptake in the mineral phase only; incorporation of 32P in the organic phase was comparable to that found in the contralateral limb. The results of this study indicate that implants alter bone healing, as indicated by the uptake of 99mTc and 32P in the different bone compartments. Moreover, decreased 32P uptake by the organic phase in the presence of bone-bonding implants suggests that cleavage of 99mTcMD32P into its technetium and methylene diphosphonate moieties was inhibited, perhaps as a function of the onset of calcification in the newly synthesized osteoid. The effect of the implants on bone healing was observed on days 6-14, when active bone formation and mineralization were occurring, supporting the hypothesis that these materials events associated with initial calcification. Uptake of 99mTc varies as a function of time, and uptake of 32P varies with time and distribution in the mineral or organic phase of bone, suggesting that these parameters may be useful as indicators of bone-bonding.

Can hydroxyapatite deposition in the eye cause a neutrophil-related inflammatory reaction?

Patients with chronic renal failure on intermittent dialysis sometimes develop an acute diffuse conjunctival and episcleral hyperaemia. In this study the hypothesis was tested whether the precipitation of hydroxyapatite crystals could result in an inflammatory reaction mediated by enzymes liberated from polymorphonuclear leucocytes (PMN). Ingestion of the crystals by PMN's can result in cell death and membranolysis and subsequent release of intracellular enzymes into the surrounding tissues. This 'suicide sac' hypothesis for the inflammatory reactions of the conjunctiva and episclera was rejected after histopathological examination of conjunctival biopsies failed to show complement activation or crystal ingestion by PMN's despite the presence of small subepithelial hydroxyapatite crystals.

DNA polymerase delta of Physarum polycephalum

DNA polymerase delta from the phylogenetically ancient slime mold Physarum polycephalum has been 380-fold enriched from amoebae. It was found to have the properties typical for this type of DNA polymerase from higher eukaryotes with regard to effectors, template-primer acceptance, co-purification with 3'-5'-exonuclease activity, as well as the effect of endogenous proliferating cell nuclear antigen (PCNA) from amoebae on the stimulation and processivity of DNA synthesis. An identified cDNA fragment shows 65.5% identical amino acides with DNA polymerase delta from Saccharomyces pombe. The molecular mass of the polymerase is 125 kDa while that of PCNA is 35 kDa. During size-exclusion chromatography, the highly purified polymerase eluted in the position of 125 kDa, suggesting that no other proteins were tightly complexed with the enzyme. The DNA polymerases from the (mononucleate) amoebae and from the (multinucleate) plasmodia of P. polycephalum have very similar properties in contrast to their differences in phenotype and their mode of nuclear division. The polymerase shows a higher degree of similarity than DNA polymerase alpha, and especially the beta-like DNA polymerase, with the corresponding polymerases of higher eukaryotes. According to antibody staining, DNA polymerase delta is readily fragmented by proteases, even in the presence of inhibitor cocktails. Including freshly prepared cell lysates, proteolytic fragments are reproducible, the most abundant being 50 kDa in size. The DNA polymerase is recognized by the antisera against two peptides which have been derived by PCR-screening of plasmodial cDNA. One of the proteolytic splitting sites is located within an eight amino-acid stretch between the two antigenic sequences.

Substitutions of aspartic acid for glycine-220 and of arginine for glycine-664 in the triple helix of the pro alpha 1(I) chain of type I procollagen produce lethal osteogenesis imperfecta and disrupt the ability of collagen fibrils to incorporate crystalline hydroxyapatite

We identified two infants with lethal (type II) osteogenesis imperfecta (OI) who were heterozygous for mutations in the COL1A1 gene that resulted in substitutions of aspartic acid for glycine at position 220 and arginine for glycine at position 664 in the product of one COL1A1 allele in each individual. In normal age- and site-matched bone, approximately 70% (by number) of the collagen fibrils were encrusted with plate-like crystallites of hydroxyapatite. In contrast, approximately 5% (by number) of the collagen fibrils in the probands' bone contained crystallites. In contrast with normal bone, the c-axes of hydroxyapatite crystallites were sometimes poorly aligned with the long axis of fibrils obtained from OI bone. Chemical analysis showed that the OI samples contained normal amounts of calcium. The probands' bone samples contained type I collagen, overmodified type I collagen and elevated levels of type III and V collagens. On the basis of biochemical and morphological data, the fibrils in the OI samples were co-polymers of normal and mutant collagen. The results are consistent with a model of fibril mineralization in which the presence of abnormal type I collagen prevents normal collagen in the same fibril from incorporating hydroxyapatite crystallites.

Dental properties of antiseptic throat lozenges formulated with sugars or Lycasin

Thirteen different formulations of throat lozenges were examined for their acidity, demineralizing action on hydroxylapatite, and fermentability by human dental plaque micro-organisms. Their flavouring acids gave them low pH values in the range 2.6-3.7, leading to the dissolution of calcium and phosphorus from hydroxylapatite. The combination of antiseptics and flavouring acids in the lozenges inhibited microbial growth and metabolism. In the absence of any antiseptics and flavouring acids, the growth and metabolic activity of cultures of plaque micro-organisms were significantly greater on sucrose+glucose lozenges than on a new Lycasin formulation.

Histological evaluation of a biodegradable Polyactive/hydroxyapatite membrane

Guided tissue regeneration (GTR) is a technique which is used for the treatment of bone defects associated with periodontal disease or enossal dental implants. In most experimental studies on GTR, non-degradable membranes are used. A drawback inherent to such devices is that at the end or in the course of the wound healing they have to be removed. Therefore, the aim of the present study was to investigate a new biodegradable membrane material for use in GTR, which also has excellent mechanical properties and is biocompatible. The material is a composite consisting of poly(ethyleneglycol terephthalate) and poly(butylene terephthalate) segmented copolymer (PEG/PBT), which for the experiments was used in pure form and also mixed with hydroxyapatite (HA) grains. Subcutaneous and subgingival implantation studies in goats were performed to determine the biocompatibility and biodegradability characteristics of several of these materials. Differences between materials were introduced in the production process, PEG/PBT ratio, material thickness and presence of HA. Implantation periods were 3, 6 and 12 wk. The histological results indicated that all investigated materials were biocompatible with the surrounding tissue. Degradation of the membranes was attended by a mild cellular reaction. The degradation process was mainly influenced by the PEG/PBT ratio. A higher PBT content resulted in a decreased degradation.

Electron and mechanical properties of bone during heating, evaluated by exoelectron emission and ultrasound

Exoelectron spectroscopy and ultrasound velocity (USV) measurements have been applied to analyse both the electron and mechanical behaviour of compact bone tissue and its main components--collagen and hydroxyapatite (HAP)--in the temperature range 20-80 degrees C. The special exoelectron method with additional IR illumination has been pioneered for the above objective. Thermally induced variations of the electron structure of bone tissue and HAP were manifested at 55 degrees C, but in collagen they were near 75 degrees C. The greatest decrease in USV was at 35-65 degrees C in collagen and at 55-70 degrees C in bone. No changes of USV in HAP were revealed. The coincidence of temperatures of the exoemission maxima and of the USV most expressed gradient in fresh bone and collagen proves the correlation between electron and mechanical behaviour during heating, connected with the partial denaturation of collagen.

Salivary amylase promotes adhesion of oral streptococci to hydroxyapatite

Recent studies have demonstrated that several species of oral streptococci, such as Streptococcus gordonii, bind soluble salivary alpha-amylase. The goal of the present study was to determine if amylase immobilized onto a surface such as hydroxyapatite can serve as an adhesion receptor for S. gordonii. Initially, human parotid saliva was fractionated on Bio-Gel P60, and fractions were screened for their ability to promote adhesion of S. gordonii to hydroxyapatite. Fractions containing alpha-amylase and proline-rich proteins promoted the adhesion of [3H]-labeled S. gordonii to hydroxyapatite. Similar findings were obtained with purified amylase and acidic proline-rich protein 1 (PRP1). Incubation of S. gordonii G9B in the presence of starch and maltotriose increased the binding of this strain to amylase-coated hydroxyapatite, while the adhesion of S. sanguis 10556 to amylase-coated hydroxyapatite was not affected by these saccharides. These results suggest that amylase may serve as a hydroxyapatite pellicle receptor for amylase-binding streptococci. Furthermore, starch and starch metabolites may enhance the adhesion of amylase-binding streptococci to amylase in dental pellicles to augment the formation of dental plaque.

Accumulation of technetium-99m methylene diphosphonate. Conditions affecting adsorption to hydroxyapatite

Experiments were carried out to explore the mechanism of technetium-99m methylene diphosphonate (99mTc-MDP) adsorption with various calcium compounds including hydroxyapatite powder. 99mTc-MDP adsorption to hydroxyapatite was markedly inhibited by the addition of either pyrophosphate or methylene diphosphonate (MDP). Moreover, adsorbed 99mTc-MDP was partly removed by rinsing with pyrophosphate solution. Adsorption was pH-dependent and was inhibited by univalent cations, adenosine triphosphate solution, and guanosine triphosphate. Adsorption was most apparent to hydroxyapatite and calcium pyrophosphate and was less marked for the other calcium compounds tested. It is suggested that 99mTc-MDP adsorption is affected by the hydroxyapatite crystalline structure and environmental factors such as pH and the presence of phosphates, calcium compounds, and various cations.

Vitamin K intake and osteocalcin levels in women with and without aortic atherosclerosis: a population-based study

Protein-bound gamma-carboxyglutamate (Gla) has been demonstrated in calcified atherosclerotic plaques. Vitamin K is required for the formation of Gla-residues. As the biological activity of Gla-proteins appears to be strictly dependent on the presence of the Gla-residues, vitamin K status may be an important factor in the development and progression of atherosclerotic calcifications. We studied the association of vitamin K status, as assessed by nutritional vitamin K intake and the measurements of two circulating immunoreactive osteocalcin (irOC) fractions, with aortic atherosclerosis in a population-based study of 113 postmenopausal women. Women with calcified lesions (n = 34) had a 42.9 micrograms lower mean age-adjusted dietary vitamin K intake/day (95% C.I. -6.6 to 92.5) than those without calcifications (n = 79). Atherosclerotic women had higher irOC levels with a low affinity for hydroxyapatite (irOCfree): age-adjusted difference of 0.32 ng/ml (95% C.I. 0.03 to 0.61). In addition, the high affinity irOC levels expressed as a percentage (hydroxyapatite binding capacity, HBC) were 5.12% (95% C.I. 1.32 to 8.92) lower in women with calcifications. Our study indicates that women with aortic atherosclerosis have an impaired vitamin K status as reflected by a lower nutritional vitamin K intake, an increased irOCfree level and a reduced HBC level. An impaired vitamin K status in subjects with atherosclerosis is compatible with the view that vitamin K or Gla-containing proteins are involved in the development of calcification of the vessel wall.

Interaction of human gallbladder mucin with calcium hydroxyapatite: binding studies and the effect on hydroxyapatite formation

Calcium hydroxyapatite (HAP) crystals formed in vitro in the presence of polymeric human gallbladder mucin (1.0 mg/mL) were smaller (0.75 +/- 0.39 microns) than control crystals (7.86 +/- 2.76 microns), but the mucin did not affect the kinetics of crystal formation or alter the amount of mineral phase present at equilibrium. In contrast, glycopeptide subunits produced by proteolysis of the native mucin had no effect on HAP crystal size. Both native mucin and glycopeptides bound to mature HAP crystals, but the glycopeptides were much more readily displaced by phosphate ions. Therefore, in experiments where HAP was being formed, the phosphate ions inhibited the interaction of glycopeptides with the nascent HAP. These results indicate that gallbladder mucin may modulate HAP formation in vivo, and that this ability may be altered during pathological states, such as neutrophil infiltration or bacterial colonization, that may cause the release of proteinases capable of digesting mucin.

Hydroxyl groups in bone mineral

The question of whether the apatite crystals of bone contain hydroxyl groups was explored using magic angle spinning, proton nuclear magnetic resonance spectroscopy, and resolution enhanced Fourier transform infrared spectroscopy. The powdered bone samples were heated at 300 degrees C in air, in CO2 at 4 bar atmosphere, and at 300 degrees C in air and subsequently at 300 degrees C in CO2, to eliminate the effects of water tightly bound to the crystals and to prevent the degradation of carbonate groups and the elimination of potentially present OH groups. Results confirm earlier findings that bone apatite crystals do not contain detectable amounts of hydroxyl ions.

Osteopontin and related phosphorylated sialoproteins: effects on mineralization

Osteopontin is one of a family of phosphorylated sialoproteins found in the extracellular matrices of mineralized connective tissues. Solution studies from a variety of laboratories have shown that while some of these proteins (e.g., osteopontin, dentin sialoprotein) inhibit calcium phosphate production, others, such as bone sialoprotein, can act as a nucleator of calcium phosphate formation. The differences in the behaviors of these proteins can be related to their interactions with mineral crystal nuclei and crystal growth sites. The specificity of these interactions, in turn, can be related to differences in the primary structures of the sialoproteins and to the extent to which they are phosphorylated. In vitro systems for the study of osteopontins and osteopontin-related protein effects on mineral deposition are described, along with mechanisms explaining the contrasting abilities of the polyglutamate-containing bone sialoprotein to act as a nucleator, while the polyaspartate-containing osteopontin and dentin sialoproteins inhibit calcium phosphate formation and growth.

The effect of cadmium on the formation and properties of hydroxyapatite in vitro and its relation to cadmium toxicity in the skeletal system

In order to understand the biological action of cadmium (Cd) in inducing bone pathologies, the effect of Cd on the formation, structure, and properties of hydroxyapatite (HA) in vitro was investigated using three biologically relevant test systems: (1) direct precipitation of HA with no precursor phase; (2) transformation of amorphous calcium phosphate (ACP) to crystalline HA; and (3) growth of HA seed crystals. Cd-containing HA was prepared by transforming ACP to HA in the presence of Cd at a pH of 10; Cd/Ca ratios of 0.05, 0.10, and 0.20 were obtained. Infrared and x-ray diffraction analyses were performed on the Cd-HA samples, and measurements were made of Cd adsorption on HA and of the dissolution characteristics of Cd-containing HA. Cd incorporation in HA introduced little strain in the lattice but resulted in a decreasing C-axis spacing and a corresponding crystal size decrease in the C-axis direction. Cd incorporation had a nominal effect on HA dissolution. Cd had an inhibitory effect on HA formation kinetics in all three test systems. Infrared spectroscopy of Cd-HA showed a complex series of small changes in the spectra as a function of Cd concentration resulting from some distortion in the crystal perfection and symmetry. The interference of Cd with mineralization can be partially explained by its inhibitory effect on HA nucleation and growth in addition to any cellular involvement. Furthermore, Cd probably has little effect on bone mineral dissolution. Our results explain the Cd incorporation reported in bone.

Molecular mechanisms of dental enamel formation

Tooth enamel is a unique mineralized tissue in that it is acellular, is more highly mineralized, and is comprised of individual crystallites that are larger and more oriented than other mineralized tissues. Dental enamel forms by matrix-mediated biomineralization. Enamel crystallites precipitate from a supersaturated solution within a well-delineated biological compartment. Mature enamel crystallites are comprised of non-stoichiometric carbonated calcium hydroxyapatite. The earliest crystallites appear suddenly at the dentino-enamel junction (DEJ) as rapidly growing thin ribbons. The shape and growth patterns of these crystallites can be interpreted as evidence for a precursor phase of octacalcium phosphate (OCP). An OCP crystal displays on its (100) face a surface that may act as a template for hydroxyapatite (OHAp) precipitation. Octacalcium phosphate is less stable than hydroxyapatite and can hydrolyze to OHAp. During this process, one unit cell of octacalcium phosphate is converted into two unit cells of hydroxyapatite. During the precipitation of the mineral phase, the degree of saturation of the enamel fluid is regulated. Proteins in the enamel matrix may buffer calcium and hydrogen ion concentrations as a strategy to preclude the precipitation of competing calcium phosphate solid phases. Tuftelin is an acidic enamel protein that concentrates at the DEJ and may participate in the nucleation of enamel crystals. Other enamel proteins may regulate crystal habit by binding to specific faces of the mineral and inhibiting growth. Structural analyses of recombinant amelogenin are consistent with a functional role in establishing and maintaining the spacing between enamel crystallites.

Comparison of the early production of extracellular matrix on dense hydroxyapatite and hydroxyapatite-coated titanium in cell and organ culture

In order to investigate the earliest changes at the bone-hydroxyapatite (HA) interface, two materials, dense HA and HA-coated titanium alloy, were investigated for their ability to stimulate production of extracellular matrix both in cell and organ culture. Osteoblast-like cells were obtained from rabbit calvariae after preliminary culture for 3 d and seeded out onto the materials. When these cells were grown in culture on the dense HA no matrix production was seen with the scanning electron microscope after 4 d, but there did appear to be matrix produced on the rougher surface of the HA coating. In contrast, extracellular matrix production was greatly increased in organ culture where the material was placed on a section of bone, particularly on the HA coating, where it formed an organized layer of collagen within 4 d. These results showed that extracellular matrix production by both osteoblastic cells and in calvarial culture was greater on the HA coatings than dense HA. In addition, organ culture allows the investigation of the earliest changes in the bone-HA interface without having to undertake in vivo implantation studies of such short duration.

Monoclonal antibodies against a high-molecular-weight agglutinin block adherence to experimental pellicles on hydroxyapatite and aggregation of Streptococcus mutans

High-molecular-weight (HMW) glycoproteins, agglutinins, in parotid saliva induce the aggregation of S. mutans and mediate binding of the bacteria to saliva-coated hydroxyapatite (SHA). Two types of monoclonal antibodies (mAb) directed against, respectively, protein and carbohydrate epitopes on the agglutinin have been reported to inhibit the aggregation of S. mutans. In this study, the mAbs were tested for their ability to block aggregation and adherence to SHA of S. mutans serotype c mediated by parotid, submaxillary, and whole saliva from three subjects. Both types of antibody inhibited the adherence and aggregation in a dose-dependent manner. However, individual variations were noted for the effects of the antibodies. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and subsequent immunoblotting with the antibodies revealed a > 300 kDa agglutinin component in all types of saliva and in the proteins desorbed from SHA. The degree of staining of this component in immunoblots of the salivas and the desorbates seemed to be paralleled by the rates of aggregation and adherence, respectively. Thus, our results indicate that the adherence to SHA as well as the aggregation of S. mutans serotype c is primarily mediated by structurally related, HMW glycoproteins in parotid, submaxillary, and whole saliva.

The influence of fluoride on the adsorption of proteoglycans and glycosaminoglycans to hydroxyapatite

Proteoglycans and their spatial arms, the glycosaminoglycans, are known to interact with hydroxyapatite, and are considered to have a role in the regulation of mineralization. This study investigates the interactive mechanisms, with particular attention directed at the influence of fluoride on the adsorption process. Proteoglycans and glycosaminoglycans were adsorbed to hydroxyapatite in the presence of fluoride (1-20 ppm range). The adsorbates included a chondroitin 4-sulfate-rich proteoglycan extracted from rat incisor dentine, hyaluronan, chondroitin 4-sulfate, and dermatan sulfate. The order of glycosaminoglycan in decreasing affinity for hydroxyapatite was chondroitin 4-sulfate, dermatan sulfate, and hyaluronan, and the individual glycosaminoglycans showed different responses to the presence of fluoride. Graded increases in fluoride (1-4 ppm) led to 5-40% reduction of glycosaminoglycan adsorption to hydroxyapatite. The proteoglycan showed less affinity for hydroxyapatite, and demonstrated a reduction in adsorption of up to 22% with 20 ppm fluoride. The inhibitory effect of fluoride indicated an electrostatic mechanism, presumably via the calcium sites in the hydroxyapatite lattice.

Human polymorphonuclear leukocyte phagocytosis of crystalline cholesterol, bilirubin, and calcium hydroxyapatite in vitro

We tested the hypothesis that human polymorphonuclear leukocytes (PMNs) phagocytize crystalline cholesterol, bilirubin, or calcium hydroxyapatite in vitro and in the process release oxygen metabolites and enzymes involved in the inflammatory process. Chemiluminescence (CL), elicited by the respiratory burst (release and activation of oxygen metabolites and enzymes) of PMNs during phagocytosis of a target particle, was used to quantitate PMN phagocytosis of each crystal. Significant CL (P < 0.05) was observed with cholesterol concentrations of 1.3-5.3 mg/ml and the dose-response was linear (r > or = 0.95). With bilirubin, significant CL was observed with concentrations of 0.07-0.33 mg/ml. The response to calcium hydroxyapatite was variable. Human PMNs phagocytize cholesterol, bilirubin, and to a lesser extent, calcium hydroxyapatite. PMN chemiluminescence was associated with phagocytosis, indicating that inflammatory substances are being released in the process. These results support the concept that crystals that occur in the gallbladder may initiate gallbladder inflammation.

Development of a titanium alloy suitable for an optimized coating with hydroxyapatite

By means of the metallurgical method of alloying, the thermal expansion coefficient of commercially pure titanium was adapted to that of hydroxyapatite (HA) in order to produce a tailored composite material with a maximum adhesion strength of HA to the metallic material. The alloying element chosen was manganese, which is an important trace element in the human organism. With the alloy TiMn6 a good compromise concerning the expansion coefficient, the mechanical properties and the biocompatible behaviour was found. With this alloy coatings with an extremely high adhesion strength could be produced, especially when the sol-gel process was used for HA precipitation. In addition, these layers fulfil the requirements of favourable thin coatings according to theoretical considerations.

Adherence of microorganisms to rat salivary pellicles

Numerous studies, using models to mimic the formation of the acquired pellicle, have concentrated on human saliva-coated hydroxyapatite; in contrast, although the rat is frequently used as an animal model, the information concerning the formation of pellicles from rat saliva is sparse. We compared the ability of Streptococcus and Actinomyces species to adhere to hydroxyapatite coated by rat saliva (rsHA) and human saliva (sHA). We also explored the influence of glucan synthesized in situ on the adherence of organisms. We show that each strain of organism has a distinct binding pattern, which was essentially the same with surfaces coated with either rat or human saliva. Dissolved rsHA beads revealed a major protein band (35-49 kD), identified as glutamine/glutamic-acid-rich protein; acidic proline-rich protein (31-45 kD and alpha-amylase (66 kD) were also identified. Overall, these in vitro data strongly suggest that the principles of bacterial adhesion to rsHA are similar to those observed with sHA.

Evaluation of the in vitro cariogenic potential of Streptococcus mutans strains isolated from 12-year-old children with differing caries experience

The limited usefulness of caries activity tests based solely on counts of mutans streptococci has been recognised increasingly. Such tests do not account for potential differences in cariogenicity of Streptococcus mutans strains harboured by individual patients. Hence, this study describes the evaluation of a simple and inexpensive method involving the dissolution of powdered hydroxyapatite as a means of determining the cariogenic potential of 64 freshly isolated strains of S. mutans from 24 children. Whilst it is apparent that differences between strains isolated from individuals could be demonstrated using this test, the variability observed was such that it was not possible to relate in vitro cariogenicity to actual clinical caries experience.

The effect of milk and kappa casein on streptococcal glucosyltransferase

Many dietary components such as carbohydrates, lipids and proteins may be incorporated into the salivary pellicle and thus may affect glucosyltransferase (GTF) activity on pellicle surfaces. The effect of milk on streptococcal GTF activity was determined. Milk, when coated onto buffer-coated hydroxyapatite or saliva-coated hydroxyapatite (sHA), reduced the subsequent adsorption of GTF onto the surfaces. Milk also reduced the expression of enzymatic activity of GTF adsorbed onto sHA. kappa-Casein, when present on the surface of sHA, reduced the adsorption of GTF activity onto sHA, resulting in reduced glucan formation. alpha-Casein had no effect on the adsorption of GTF onto sHA or on subsequent glucan formation. Both milk and kappa-casein reduced activity of the enzyme in solution. The presence of milk and kappa-casein fractions on the surface of sHA and in solution with GTF can clearly modulate glucan formation in vitro.

Formation of phosphate-containing calcium fluoride at the expense of enamel, hydroxyapatite and fluorapatite

During the caries process complex reactions involving calcium, phosphate, hydrogen and fluoride ions as main species take place. In this study the precipitation and dissolution reactions occurring in suspensions of enamel, hydroxyapatite (HAP) and fluorapatite (FAP) on addition of fluoride were investigated under well-defined conditions. pH and pF were monitored; calcium and phosphate concentrations were measured at selected times; the solid phases were examined by infra-red, X-ray diffraction and transmission electron microscopy. Precipitation of phosphate-containing calcium fluoride crystals, CaF2(P), can cause severe reduction in the calcium ion concentration and release of hydrogen ions from the precipitated phosphate. These reactions result in considerable dissolution of enamel, HAP and even of FAP. More of the added mineral dissolves with 50 mmol/l fluoride than with 10 mmol/l fluoride, mainly due to the greater reduction in calcium ion concentration. This work shows that phosphate-containing calcium fluoride is most likely an important compound to be considered in the caries process.

The effect of milk and casein proteins on the adherence of Streptococcus mutans to saliva-coated hydroxyapatite

Experiments sought to determine the nature of the binding of milk proteins to hydroxyapatite (HA) and to saliva-coated hydroxyapatite (sHA), and to determine the effect of milk and casein on the adherence of Streptococcus mutans GS-5 to sHA. The binding of radiolabelled alpha-casein to HA was reduced when incubated simultaneously with parotid saliva, and enhanced in the presence of milk. The binding of beta- and kappa-casein to HA was unaffected by the presence of parotid saliva and enhanced by the presence of milk. The in vitro bacterial adherence of Strep. mutans GS-5 to sHA beads was reduced when beads were coated with milk instead of buffer, or when bacteria were added to sHA in the presence of milk instead of buffer. Casein proteins (alpha, beta, kappa) added to sHA simultaneously with bacteria inhibited the adherence of Strep. mutans GS-5 to sHA. kappa-Casein, when bound to sHA, inhibited streptococcal adherence to sHA; alpha- and beta-casein, when bound to sHA, had no effect on streptococcal adherence. Fractionation of kappa-casein by anion-exchange chromatography revealed the anti-adherence activity of kappa-casein was mediated primarily by a 40,000 mol. wt. glycoprotein-containing fraction. These data show that milk, particularly kappa-casein fractions, can modulate the adherence of Strep. mutans GS-5 to SHA surfaces in vitro.

Crystal-membrane interaction in kidney stone disease

Urolithiasis is a multifaceted process that initiates with the formation of microcrystals in the urine and terminates with the formation of mature renal calculi. The attachment of crystals by the urothelium is a major event in the successful formation of the mature stone. The papillary tip is the primary site for crystal attachment and stone maturation, and the attachment process appears to be mediated by specific molecular interactions between molecular structures on the surfaces of stone crystals and molecular arrays on the surfaces of cell membranes. Animal models have demonstrated the interaction between cells and crystals, and they have suggested a correlation between cellular damage and crystal interaction, especially when crystals bind to and then break free from the tubular epithelium. Cell culture studies on inner medullary late collecting duct (IMCD) cells have demonstrated that calcium oxalate monohydrate, hydroxyapatite, and uric acid crystals bind to IMCD cells in primary culture. The attachment of these crystals to IMCD cells was crystal structure dependent, saturable, and competitively inhibitable if more than one crystal type was present at the same time. The crystals preferentially attach to cells that have lost partial or complete intercellular junctional integrity. These crystal-attaching cells appear to have altered membrane composition and/or structure. Recent studies on red blood cells and IMCD cells that have been enriched with cholesterol and selected phospholipids suggest that crystal-membrane phospholipid interactions play a major role in crystal attachment.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of crystal formation by bone phosphoproteins: role of glutamic acid-rich sequences in the nucleation of hydroxyapatite by bone sialoprotein

Bone sialoprotein (BSP) is a bone-specific glycoprotein containing phosphoserine and sulphotyrosine residues and regions of contiguous glutamic acid residues. Recent studies in this laboratory have shown that BSP is capable of nucleating the bone mineral hydroxyapatite in a steady-state agarose gel system. We show here that chemical modification of carboxylate groups abolishes the nucleation activity of BSP, but enzymic dephosphorylation has no effect. Formation of hydroxyapatite is also induced by poly(L-glutamic acid) and poly(D-glutamic acid), but not by poly(L-aspartic acid) or poly(L-lysine). Calreticulin, a muscle protein with short sequences of contiguous glutamic acid residues, also lacks nucleation activity. These findings suggest that the nucleation of hydroxyapatite by BSP involves one or both of the glutamic acid-rich sequences. Based on these findings and others, we propose that polycarboxylate sequences represent a general site for growth-modulating interactions between proteins and biological crystals.

Salivary receptors for recombinant fimbrillin of Porphyromonas gingivalis

Fimbriae are considered important in the adherence and colonization of Porphyromonas gingivalis in the oral cavity. It has been demonstrated that purified fimbriae bind to whole human saliva adsorbed to hydroxyapatite (HAP) beads, and the binding appears to be mediated by specific protein-protein interactions. Recently, we expressed the recombinant fimbrillin protein (r-Fim) of P. gingivalis corresponding to amino acid residues 10 to 337 of the native fimbrillin (A. Sharma, H.T. Sojar, J.-Y. Lee, and R.J. Genco, Infect. Immun. 61:3570-3573, 1993). We examined the ability of individual salivary components to promote the direct attachment of r-Fim to HAP beads. Purified r-Fim was radiolabeled with 125I and incubated with HAP beads which were coated with saliva or purified individual salivary components. Whole, parotid, and submandibular-sublingual salivas increased the binding of 125I-r-Fim to HAP beads. Submandibular-sublingual saliva was most effective in increasing the binding of 125I-r-Fim to HAP beads (1.8 times greater than that to uncoated HAP beads). The binding of 125I-r-Fim to HAP beads coated with acidic proline-rich protein 1 (PRP1) or statherin was four and two times greater, respectively, than that to uncoated HAP beads. PRP1 and statherin molecules were also found to bind 125I-r-Fim in an overlay assay. The binding of intact P. gingivalis cells to HAP beads coated with PRP1 or statherin was also enhanced, by 5.4 and 4.3 times, respectively, over that to uncoated HAP beads. The interactions of PRP1 and statherin with 125I-r-Fim were not inhibited by the addition of carbohydrates or amino acids. PRP1 and statherin in solution did not show inhibitory activity on 125I-r-Fim binding to HAP beads coated with PRP1 or statherin. These results suggest that P. gingivalis fimbriae bind strongly through protein-protein interactions to acidic proline-rich protein and statherin molecules which coat surfaces.

Interactions of fluoride and non-fluoride agents with the caries process

Fundamental to the caries process and its inhibition is an understanding of the composition and structural relationships of dental mineral. These have received greater study in recent years, leading to a better understanding of the processes involved. Fluoride has been the most successful of the anti-caries agents to date, and many studies have concentrated on this ion. The anti-caries action of fluoride has been only partially explained by the early finding that fluoride-treated mineral was less soluble, and this criterion is now less widely accepted. The dissolutive process of caries is inhibited by fluoride, monofluorophosphate, trimetaphosphate, and zinc. However, only the first three of these show anti-caries activity. The presence of fluoride during in vivo and in vitro caries is conducive to the formation of an apparently intact surface zone. Current evidence is that this zone reforms during the caries process, thus acquiring fluoride and having larger crystallites compared with sound enamel. Trimetaphosphate also favors the formation of a surface zone. There is a clear beneficial involvement of fluoride, even at low levels, in the process of lesion remineralization. It is highly probable that this process results from re-growth of residual enamel crystallites rather than de novo precipitation of calcium phosphates. Levels of fluoride found in saliva can interact with dental mineral. Although zinc has been shown to adsorb upon apatite mineral and to restrict subsequent crystal growth, it does not appear to affect the action of fluoride, including remineralization, adversely. This may be due to the fact that the uptake of zinc is reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystals in equine articular cartilage

Crystal deposits have been observed in equine articular cartilage and identified by scanning electron microscopy and X-ray diffraction as octacalcium phosphate and calcium pyrophosphate dihydrate. Of 89 equine fetlock joints examined 10 contained evidence of calcification visible by eye. It is suggested that the deposition of crystals may be a mediator of arthritis in horses and may also cause damage directly.

Anticancer effects of adriamycin-loaded hydroxyapatite implants determined in a Swarm rat chondrosarcoma model

We investigated the antitumor effects of adriamycin (ADR)-loaded hydroxyapatite (HAP) beads in a Swarm rat chondrosarcoma model. When one ADR-loaded HAP bead (ADR: 0.8 mg/bead) was implanted into the central portion of a rat bearing tumor, the ADR-loaded HAP beads showed good therapeutic effects, increasing the life span (ILS) by 90%. Significantly, leukopenia and diarrhea were not observed. These results suggest that HAP delivery offers an interesting and a potentially effective method.

Dual-energy X-ray absorptiometry for measuring total bone mineral content in the rat: study of accuracy and precision

Sequential studies of osteopenic bone disease in small animals require the availability of non-invasive, accurate and precise methods to assess bone mineral content (BMC) and bone mineral density (BMD). Dual-energy X-ray absorptiometry (DXA), which is currently used in humans for this purpose, can also be applied to small animals by means of adapted software. Precision and accuracy of DXA was evaluated in 10 rats weighing 50-265 g. The rats were anesthetized with a mixture of ketamine-xylazine administrated intraperitoneally. Each rat was scanned six times consecutively in the antero-posterior incidence after repositioning using the rat whole-body software for determination of whole-body BMC and BMD (Hologic QDR 1000, software version 5.52). Scan duration was 10-20 min depending on rat size. After the last measurement, rats were sacrificed and soft tissues were removed by dermestid beetles. Skeletons were then scanned in vitro (ultra high resolution software, version 4.47). Bones were subsequently ashed and dissolved in hydrochloric acid and total body calcium directly assayed by atomic absorption spectrophotometry (TBCa[chem]). Total body calcium was also calculated from the DXA whole-body in vivo measurement (TBCa[DXA]) and from the ultra high resolution measurement (TBCa[UH]) under the assumption that calcium accounts for 40.5% of the BMC expressed as hydroxyapatite. Precision error for whole-body BMC and BMD (mean +/- S.D.) was 1.3% and 1.5%, respectively. Simple regression analysis between TBCa[DXA] or TBCa[UH] and TBCa[chem] revealed tight correlations (n = 0.991 and 0.996, respectively), with slopes and intercepts which were significantly different from 1 and 0, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

An in vitro investigation of the cariogenic potential of oral streptococci

Whilst the importance of the mutans streptococci in the aetiology of dental caries is clear, a number of studies have described caries development in their absence. This investigation aimed to assess the cariogenic potential of Streptococcus gordonii, Strep. sanguis, Strep. vestibularis and Enterococcus faecalis in comparison with Strep. mutans and Strep. sobrinus, using a recently described in vitro model. In the presence of a 146 mM sucrose solution and powdered hydroxyapatite, each species was incubated for 5 h, after which acid anion production, calcium release and change in pH were measured. It was possible to assign each species to one of three groups, with E. faecalis, Strep. gordonii, Strep. sanguis exhibiting low, Strep. vestibularis intermediate, and Strep. mutans and Strep. sobrinus high in vitro cariogenic potential. This assay could be used as a screening test to assess the potential cariogenicity of a range of bacterial species.

Professional topical fluoride applications--clinical efficacy and mechanism of action

All currently used topical fluoride agents deposit soluble fluoride as calcium fluoride on enamel or in lesions. Calcium fluoride serves as a source of fluoride for the formation of fluorapatite. The latter phase is formed when pH drops in plaque, not during topical application. The potential for calcium fluoride formation should probably be increased in topical fluoride agents. In countries with low caries prevalence, the clinical recommendations for topical fluoride need to be reconsidered. Toothpaste is the basic fluoride regimen recommended for everybody. The need for additional fluoride supplementation depends on caries activity. There is no distinct difference in the caries-preventive effects of concentrated fluoride solutions, gels, or varnishes. Thus, the choice of method depends on costs, convenience, patient acceptance, and safety. The use of fluoride varnishes has proven to be a feasible and safe method of fluoride application. With fluoride varnishes, the amounts of fluoride exposure can be better controlled, and less chair-time is required compared with conventional solutions and gels. No dose-response effect to concentrated fluoride agents is apparent, and the benefit of frequent application is not clearly established. In individuals with the most severe cariogenic challenge, combinations of fluoride and antimicrobials may give better clinical effects than fluoride alone.

Calculus formation and inhibition

The formation, development, and dissolution of hard deposits such as calculus are complex processes that involve numerous calcium phosphate phases as well as the interaction of these ions with organic molecules. Although formation is determined by thermodynamic driving forces, kinetic factors are also important determinants for the precipitation of specific calcium phosphate phases. The overall process, therefore, may involve the formation of metastable intermediates which may subsequently transform into the more stable hard deposits observed in vivo. A knowledge of the kinetics of growth of both individual calcium phosphate phases and their mixtures is important for elucidating the mechanism of calculus formation. Although salivary proteins are effective inhibitors of the mineralization reactions that take place in dental plaque, once adsorbed, their conformation may change to present surfaces that catalyze the nucleation of mineral phases. The variable pH conditions in plaque, expressed in terms of free ionic concentrations, will markedly alter the supersaturations with respect to typical calcium phosphate precursor phases such as dicalcium phosphate dihydrate (DCPD) and octacalcium phosphate (OCP). Physical-chemical studies have shown that the mineralization of all the calcium phosphate phases is controlled by reactions at the surface rather than by diffusion of lattice ions through the contacting liquid phase. This makes the rates of reaction very sensitive to ions and molecules in the solution that may absorb at the active growth sites and, while not significantly incorporating into the precipitated crystal phases, markedly influences the rates of mineralization and demineralization.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural arrangements at the interface between plasma sprayed calcium phosphates and bone

Plasma sprayed coatings of tetracalcium phosphate, magnesium whitlockite and three types of hydroxyapatite, varying in degree of crystallinity, were evaluated with light microscopy, scanning electron microscopy and backscatter electron microscopy (BSE) after implantation periods of 1, 2 and 4 wk in rat femora. BSE revealed that both tetracalcium phosphate and semi-crystalline hydroxyapatite underwent distinct bulk degradation and loss of relatively large particles. Amorphous hydroxyapatite showed a gradual surface degradation, indicated by a transition zone varying in grey level between that of the coating and bone tissue, while degradation was negligible with the highly crystalline material and magnesium whitlockite. Degradation appeared to be related to bone apposition, since more bone seemed to be present on amorphous hydroxyapatite and tetracalcium phosphate, as compared to highly crystalline hydroxyapatite and magnesium whitlockite coatings. At the interface between bone and magnesium whitlockite, a seam of unmineralized bone-like tissue was frequently seen with light microscopy, while few areas with bone contact were present. X-ray microanalysis revealed that both the magnesium whitlockite coating and the unmineralized bone-like tissue contained substantial amounts of aluminium which, in addition to possible influences of magnesium, may have caused the impaired mineralization. The results of this preliminary study indicate that, with regard to early bone formation, amorphous hydroxyapatite coatings seem to be beneficial over highly crystalline coatings. However, further experiments should be performed to give conclusive data on (i) the statistical significance of the differences in bone apposition rate, and (ii) the long-term behaviour of both amorphous and highly crystalline coatings in bone and their relation to implant performance.

Isolation and characterization of a mouse amelogenin expressed in Escherichia coli

A mouse cDNA encoding a 180 amino acid amelogenin was subcloned into the pET expression plasmid (Novagen, Madison, WI) for production in Escherichia coli. A simple growth and purification protocol yields 20-50 mg of 95-99% pure recombinant amelogenin from a 4.5-liter culture. This is the first heterologous expression of an enamel protein. The expressed protein was characterized by partial Edman sequencing, amino acid composition analysis, SDS-PAGE, Western blotting, laser desorption mass spectrometry, and hydroxyapatite binding. The recombinant amelogenin is 179 amino acids in length, has a molecular weight of 20,162 daltons, and hydroxyapatite binding properties similar to the porcine 173 residue amelogenin. Solubility analyses showed that the bacterially expressed protein is only sparingly soluble in the pH range of 6.4-8.0 or in solutions 20% saturated with ammonium sulfate. The purified protein was used to generate rabbit polyclonal anti-amelogenin antibodies which show specific reaction to amelogenins in both Western blot analyses of enamel extracts and in immunostaining of developing mouse molars.

Inhibition of calcium phosphate precipitation by bile salts: a test of the Ca(2+)-buffering hypothesis

The ability of bile salts to inhibit the precipitation of either calcium hydroxyapatite or its precursor, amorphous calcium phosphate, by reducing Ca2+ activity or poisoning nascent crystals was determined. When apatite precipitated rapidly (1-4 h), glycocholate and taurine-conjugated bile salts (up to 100 mM) had little effect on apatite formation, but prevented amorphous calcium phosphate precipitation by lowering Ca2+ activity. In contrast, glycodeoxycholate and glycochenodeoxycholate (2-3 mM) inhibited apatite formation for at least 24 h by poisoning embryonic apatite. When apatite precipitated slowly (> 24 h), all the dihydroxy bile salts prevented apatite formation for at least 4 days. At constant initial supersaturation, the phosphate concentration determined the degree of inhibition caused by the six bile salts mixed together in physiologic proportion. At low phosphate concentrations (1.2 mM) total inhibition was achieved by poisoning embryos (approximately -5 mM total bile salt), but with 4.0 mM phosphate only approximately 60% inhibition was attained (150 mM bile salt) by a combination of poisoning and Ca(2+)-buffering. Thus, at low supersaturation all dihydroxy bile salts can prevent apatite formation by reducing free Ca2+ (taurine and glycine conjugates) or poisoning embryos (glycine conjugates). With mixtures of bile salts at higher supersaturation, inhibition of apatite depends on a combination of poisoning and reduction of free Ca2+, mainly caused by glycodeoxycholate and glycochenodeoxycholate.

Inactivation of the Porphyromonas gingivalis fimA gene blocks periodontal damage in gnotobiotic rats

Fimbrial production by Porphyromonas gingivalis was inactivated by insertion-duplication mutagenesis, using the cloned gene for the P. gingivalis major fimbrial subunit protein, fimA. by several criteria, this insertion mutation rendered P. gingivalis unable to produce fimbrilin or an intact fimbrial structure. A nonfimbriated mutant, DPG3, hemagglutinated sheep erythrocytes normally and was unimpaired in the ability to coaggregate with Streptococcus gordonii G9B. The cell surface hydrophobicity of DPG3 was also unaffected by the loss of fimbriae. However, DPG3 was significantly less able to bind to saliva-coated hydroxyapatite than wild-type P. gingivalis 381. This suggested that P. gingivalis fimbriae are important for adherence of the organism to saliva-coated oral surfaces. Further, DPG3 was significantly less able to cause periodontal bone loss in a gnotobiotic rat model of periodontal disease. These observations are consistent with other data suggesting that P. gingivalis fimbriae play an important role in the pathogenesis of human periodontal disease.

Long-term in vivo study of plasma-sprayed coatings on titanium alloys of tetracalcium phosphate, hydroxyapatite and alpha-tricalcium phosphate

In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium plugs of standard size were implanted in dog femora. The bone bonding and bone formation of hydroxyapatite, alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate plasma-sprayed coatings were evaluated by mechanical push-out tests and histological observations after 3, 5, 15 and 28 months of implantation. During this time all coating types degraded. alpha-TCP showed the most significant degradation after 3 months of implantation. Hydroxyapatite and tetracalcium phosphate showed significant signs of degradation after about 5 months of implantation. All coatings showed a small increase in bone bonding after 5 months of implantation. In general, all types of implants showed similar bone response, some bone contact and several remodelling lacunae along the surfaces after long-term implantation.

Experiments on the initiation of calcium fluoride formation with reference to the solubility of dental enamel and brushite

As calcium fluoride formation following topical application of fluoride may be responsible for at least some of the caries-reducing effect of fluoride, the concentration of fluoride necessary to induce its formation were examined. The aim was to determine the degree of supersaturation with respect to calcium fluoride necessary for inducing its spontaneous precipitation, with close reference to its possible formation and retention on dental hard tissue when topical fluoride solutions are used clinically. Powdered enamel or brushite were suspended for 4 h in aqueous solutions buffered at pH 7.2 and 5.0. After the equilibration, ion concentrations were determined and degrees of saturation with respect to apatite and brushite were calculated. In aqueous solutions at pH 7.2 and 5.0 with similar concentrations as those found in the equilibrated suspensions the fluoride concentration was adjusted to from 5 to 500 parts/10(6). After 2 h of gentle agitation the supernatant was analysed, the precipitate (if any) isolated and examined by X-ray diffraction. Initiation of spontaneous calcium fluoride formation required a calcium fluoride ion-activity product of 10(-7.6) or more, 300 parts/10(6) fluoride were necessary to initiate calcium fluoride formation in neutral solution saturated with enamel, and the increased solubility of enamel apatite at low pH allowed calcium fluoride formation from solutions with as low as 100 parts/10(6) fluoride. When phosphate was present in the solution a competing apatite formation could mask the calcium fluoride formation. In neutral solutions saturated with respect to brushite, spontaneous fluorapatite formation was initiated by 100 pats/10(6) fluoride. With 200 parts/10(6) fluoride a further competing formation of calcium fluoride occurred.

Proteus mirabilis biofilms and the encrustation of urethral catheters

Bacterial biofilms were observed on 69 of 75 catheters taken from patients undergoing long-term bladder management. Ten catheters were colonized by pure cultures of Proteus mirabilis. In each of these cases the bacteria formed layers on the catheter surface, underlying encrustations of struvite and hydroxyapatite which partially or completely occluded the catheter lumen. Encrustation was also apparent on catheters colonized by P. mirabilis plus other species, but was rarely seen on catheters colonized by non-urease-producing species. These observations support the hypothesis that catheter encrustation is brought about by the activity of urease-producing biofilms and confirms that the main target in the control of catheter encrustation should be P. mirabilis.

Effects of low fluoride concentrations on formation of caries-like lesions in human enamel in a sequential-transfer bacterial system

Human enamel surfaces were exposed to sequential batch cultures of Streptococcus mutans NCTC 10832 in a sucrose-rich medium containing 0-5 mg/l added fluoride (F). In 10-day experiments, subsurface lesion formation was partly inhibited by 1 mg/l F and completely by 2 and 5 mg/l F, but small lesions formed in 2 mg/l F in 21-day experiments. Analysis of the spent media, together with analogous, bacteria-free experiments, suggested that lesion inhibition involved two main effects. First, inhibition of bacterial acid production reduced the pH fall, resulting in reduced undersaturation with respect to hydroxyapatite and consequently reduced rate of demineralization. Secondly, interaction of F with enamel mineral resulted in a small increase in reprecipitation during periods of supersaturation and a much larger reduction in demineralization during periods of undersaturation. It is concluded that, at low F concentrations, inhibition of bacterial acid production is a major factor in lesion inhibition, which may contribute significantly to caries prevention in vivo where plaque fluid F levels are raised by frequent topical applications.

The influence of histatin-5 fragments on the mineralization of hydroxyapatite

The adsorption of histatin 5 on hydroxyapatite (HAP) was determined and compared to that of several fragments of histatin 5, such as residues 1-16 (N16), 7-16 (M10), 9-24 (C16), 11-24 (C14), 13-24 (C12), 15-24 (C10). The influence of the adsorbed peptides on the seeded crystal growth of HAP was investigated with the constant composition method. The adsorption affinity of the peptides as well as their ability to inhibit mineralization was influenced by the length of the peptide chain. Histatin 5 showed the highest affinity, as determined by a Langmuir model, whereas the smaller C10 and C12 displayed the lowest equilibrium uptake. The smaller C10 and C12 peptides were, on the other hand, more effective as crystal growth inhibitors, indicating a more efficient coverage of surface active sites. Electrophoretic mobility data indicated an increase in the positive charge at the HAP surface in the presence of these peptides, which were efficient HAP crystallite dispersants.