David Kohavi

Mechanism of adsorption of human albumin to titanium in vitro

Our previous studies have shown that human albumin is one of the main salivary proteins that adsorb to titanium (Ti). The goal of the present study was to investigate the role of electrostatic interactions in the adsorption of human albumin to Ti-oxide (TiO2) in vitro. The binding profile of human albumin to Ti was analyzed according to an adsorption isotherm. Purified human serum albumin (HSA) was suspended with native, calcium-, magnesium-, or potassium-treated commercially pure Ti powders, at pH 3.0 and 7.0. The amount of unadsorbed protein in the supernatant fluid was measured. The maximum amount of adsorbed albumin was 0.13 mg/1.0 g Ti. The albumin-Ti association constant was 2.77 mL/mg. Pretreatment of Ti with calcium, or magnesium alone, or combined with increasing pH values (3.0-7.0) resulted in augmented adsorption of HSA to Ti. No increase in adsorption was observed following pretreatment of Ti with potassium. These results point to the involvement of electrostatic interactions in the adsorption of HSA to TiO2.

Adsorption of human salivary proteins to titanium powder. I. Adsorption of human salivary albumin

Titanium (Ti) is among the most widely used implant materials in dentistry today. The success of Ti implants is associated with their interactions with the surrounding tissues and biological fluids. In the present study, the adsorption of salivary proteins to Ti and the effect of calcium (Ca) on this process were investigated. Untreated and Ca-treated Ti powders were suspended in human clarified whole saliva. After incubation, the supernatant fluid was collected for protein analysis. The powders were then washed and resuspended in EDTA to desorb proteins from Ti surfaces. Sodium dodecylsulphate polyacrylamide gel electrophoresis and Bradford protein assay were conducted to determine the concentration and type of proteins that adsorbed onto Ti surfaces. The presence of Ca ions enhanced the adsorption of salivary proteins to Ti. A 66 kDa protein, identified by immunoblotting as albumin, was found as the main adsorbed salivary protein. Adsorption of albumin to Ti pretreated with Ca was significantly greater than to native Ti. The Ca-dependent adsorption process was reversed by EDTA. The data suggest that salivary albumin is one of the main constituents of a salivary biofilm formed on Ti dental implants and its adsorption to Ti surfaces is Ca-dependent. The presence of albumin on Ti dental implants may affect plaque accumulation on the implants and the biocompatibility of Ti implants.

Periodontal status following the alignment of palatally impacted canine teeth

Twenty-three patients who had completed treatment to resolve the unilateral palatal impaction of a maxillary canine by orthodontic means were examined 2.3 years (mean) after all appliances had been discarded. Scores were noted for the plaque index, gingival index, attached gingiva, pocket depth, and bone support on each of the affected teeth and also on the contralateral canine which had been unaffected and thus acted as a control. In addition, the teeth immediately adjacent to both canines were similarly scored. The results indicated no significant difference in the plaque index and the amount of attached gingiva, while the gingival index, pocket depth, and particularly the bone support all showed statistically valid differences. It is suggested that in these cases a postorthodontic assessment of the state of the supporting tissues be performed and periodontal treatment instituted in those requiring it.

Endosseous implant anchorage is critically dependent on mechanostructural determinants of peri-implant bone trabeculae

Low bone mass is highly prevalent among patients receiving endosseous implants. In turn, the implantation prognosis in low‐density skeletal sites is poor. However, little is known about the mechanostructural determinants of implant anchorage. Using metabolic manipulations that lead to low bone density and to its rescue, we show here that anchorage is critically dependent on the peri‐implant bone (PIB). Titanium implants were inserted horizontally into the proximal tibial metaphysis of adult rats 6 weeks after orchiectomy (ORX) or sham ORX. Systemic intermittent administration of human parathyroid hormone (1–34) [iahPTH(1–34)] or vehicle commenced immediately thereafter for 6 weeks. The bone‐implant apparatus was then subjected to image‐guided failure assessment, which assesses biomechanical properties and microstructural deformation concomitantly. Anchorage failure occurred mainly in PIB trabeculae, 0.5 to 1.0 mm away from the implant. Mechanically, the anchorage performed poorly in ORX‐induced low‐density bone, attributable mainly to decreased trabecular number. iahPTH(1–34) rescued the PIB density and implant mechanical function by augmenting trabecular thickness (Tb.Th). However, implant biomechanical properties in low‐density bone were relatively insensitive to implant surface treatment that affected only the osseointegration (%bone‐implant contact). These results support a model wherein anchorage failure involves buckling of the weakest trabecular struts followed by sequential failure of the stronger trabeculae. Treatment with iahPTH(1–34) induced thicker struts, which were able to delay and even prevent failure of individual elements, thus implicating trabecular thickness as a prime target for enhancing implant anchorage by systemic bone anabolic therapy.

The adhesion of oral bacteria to modified titanium surfaces: role of plasma proteins and electrostatic forces

OBJECTIVES Modifications of titanium (Ti) implant surfaces have a significant effect on early biofilm formation and the outcome of implant procedures. The aim of this study was to examine the role of plasma proteins and electrostatic forces in the adhesion mechanism of oral bacteria to modified Ti surfaces. MATERIALS AND METHODS Ti discs with three different types of surface modifications, machined, acid-etched, and acid-etched and blasted, were examined for adhesion of oral bacteria: Streptococcus mutans, Porphyromonas gingivalis, and Fusobacterium nucleatum. Following pretreatment of the Ti with ion rich solutions or coating by human serum albumin or fibronectin, bacterial adhesion was examined by scanning electron microscopy and assessed quantitatively by DNA analysis. Ti coating by proteins as well as bacterial adhesion and their interrelationships were further investigated through confocal scanning laser microscopy. RESULTS Acid-etched and blasted Ti surfaces exhibited significantly higher amounts of bacteria adhesion than the other two surfaces. Calcium was found to serve as a bridging agent in the adhesion process of S. mutans and F. nucleatum to Ti surfaces. Although albumin coating of the Ti reduced the adhesion of S. mutans to all surfaces, it had no influence on the adhesion of P. gingivalis or F. nucleatum. Coating the Ti with fibronectin enhanced P. gingivalis and F. nucleatum adhesion. CONCLUSIONS Bacterial adhesion to Ti surfaces is roughness-dependent, and the adhesion mechanism is influenced by ions and proteins of the initial coating derived from the blood.

Adsorption of salivary proteins onto prosthetic titanium components

In vivo adsorption of salivary proteins onto prosthetic titanium components was analyzed after exposure of titanium abutments to the oral environment for a period of 2 to 6 weeks. Gel electrophoresis and Western immunoblotting were used to separate and identify the proteins, which were mainly alpha-amylase and serum albumin. Selective adsorption of proteins enables attachment of specific oral bacteria and thus may alter the composition of the dental plaque formed on titanium surfaces.

Periodontal status following the alignment of buccally ectopic maxillary canine teeth

Twenty-nine patients who had completed orthodontic treatment to resolve buccal displacement of maxillary canine teeth were examined 2.9 years (mean) after all appliances had been discarded. Thirteen of these patients had unilateral displacement, and sixteen were bilaterally affected. In the unilateral cases only the width of attached gingiva was significantly less than in the controls. In the bilateral cases the same observation was made, but here the gingival index and pocket depth also showed statistically significant increases, although the expression of these values was found to have doubtful clinical significance. Posttreatment periodontal assessment is recommended for these cases.

Trabecular Bone Gradient in Rat Long Bone Metaphyses: Mathematical Modeling and Application to Morphometric Measurements and Correction of Implant Positioning†

The distribution of trabecular structures in mammalian long bone metaphyses has been insufficiently explored. We show in rats that the trabecular bone structural parameters display a decreasing gradient, toward the diaphysis, that can be defined mathematically. This gradient is applicable for optimizing the reference volume in metabolic studies and for retrospective correction of implant positioning.

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.

Effect of titanium implants on primary mineralization following 6 and 14 days of rat tibial healing

The effect of pure commercial titanium implants on the process of primary mineralization was studied. This was examined by insertion of titanium implants into rat tibial bone after ablation. The effects of the titanium were studied through the behaviour of extracellular matrix vesicles (MV). Methods of morphometric analysis at the TEM level were applied. The insertion of titanium implants was followed by an increase in the number of MV as well as vesicular diameter and by a decrease in vesicular distance from the calcified front when compared to normal healing. These results suggest that the process of MV maturation around titanium implants was delayed when compared to normal primary bone formation during bone healing. The delay in mineralization was compensated by an increase in vesicle production, resulting in an enhancement of primary mineralization by the titanium.