Coating of titanium with hydroxyapatite leads to decreased bone formation: A study in rabbits.

OBJECTIVES: An experimental rabbit model was used to test the null hypothesis, that there is no difference in new bone formation around uncoated titanium discs compared with coated titanium discs when implanted into the muscles of rabbits. METHODS: A total of three titanium discs with different surface and coating (1, porous coating; 2, porous coating + Bonemaster (Biomet); and 3, porous coating + plasma-sprayed hydroxyapatite) were implanted in 12 female rabbits. Six animals were killed after six weeks and the remaining six were killed after 12 weeks. The implants with surrounding tissues were embedded in methyl methacrylate and grinded sections were stained with Masson-Goldners trichrome and examined by light microscopy of coded sections. RESULTS: Small amounts of bone were observed scattered along the surface of five of the 12 implants coated with porous titanium, and around one out of 12 porous coated surfaces with Bonemaster. No bone formation could be detected around porous coated implants with plasma-sprayed hydroxyapatite. CONCLUSION: Porous titanium coating is to some degree osteoinductive in muscles.

The effect of fluoride surface modification of ceramic TiO2 on the surface properties and biological response of osteoblastic cells in vitro.

This study investigates the effect of fluoride surface modification on the surface properties of polycrystalline ceramic TiO(2) and the biological response of murine osteoblast cells to fluoride-modified TiO(2) in vitro. Fluoride concentrations up to 9 at.% were detected and the fluoride was found to bind to the surface in a ligand exchange reaction between surface hydroxyl groups and the fluoride anions from the HF. No significant changes in the surface topography were detected. In vitro experiments were performed in order to evaluate the biological response of the MC3T3-E1 cells to the fluoride-modified ceramic TiO(2) surfaces. No difference in the lactate dehydrogenase (LDH) activity was seen in comparison to unmodified samples, apart from the highest fluoride concentration (∼9 at.%) which was found to be more toxic to the cells. Real-time PCR analysis showed no conclusive evidence for the fluoride-induced promotion of osteoblast differentiation as no significant increase in the collagen-1, osteocalcin, or BMP-2 mRNA levels was detected on the fluoride-modified ceramic TiO(2) surfaces apart from one group, which showed an elevated osteocalcin level and higher number of cells. Since the observed grain boundary corrosion is also anticipated to reduce the mechanical properties of ceramic TiO(2), this surface modification method may not be an ideal method for improving the osteogenic response of ceramic TiO(2) scaffolds.

Impact of trace elements on biocompatibility of titanium scaffolds.

A titanium oxide scaffold has recently been reported with high compressive strength (>2 MPa) which may allow its use in bone. However, would it be possible to enhance the scaffolds' performance by selecting a titanium oxide raw material without elemental contamination? Elements in implant surfaces have been reported to provoke implant failure. Thus, this study aims to compare different commercial titanium dioxide powders in order to choose the appropriate powder for scaffold making. The x-ray photoelectron spectroscopy (XPS) analysis identified the trace elements, mainly Al, Si, C, Ca and P. Cellular response was measured by cytotoxic effect, cell growth and cytokine secretion from murine preosteoblasts (MC3T3-E1) in vitro. The XPS data showed that traces of carbon-based molecules, silicon, nitrogen and aluminium in the powder were greatly reduced after cleaning in 1 M NaOH. As a result, reduction in cytotoxicity and inflammatory response was observed. Carbon contamination seemed to have a minor effect on the cellular response. Strong correlations were found between Al and Si contamination levels and the inflammatory response and cytotoxic effect. Thus, it is suggested that the concentration of these elements should be reduced in order to enhance the scaffolds' biocompatibility.

Implants and/or teeth: consensus statements and recommendations.

In August 23-25, 2007, the Scandinavian Society for Prosthetic Dentistry in collaboration with the Danish Society of Oral Implantology arranged a consensus conference on the topic 'Implants and/or teeth'. It was preceded by a workshop in which eight focused questions were raised and answered in eight review articles using a systematic approach. Twenty-eight academicians and clinicians discussed the eight review papers with the purpose to reach consensus on questions relevant for the topic. At the conference the consensus statements were presented as well as lectures based on the review articles. In this article the methods used at the consensus workshop are briefly described followed by the statements with comments.

Analysing the optimal value for titanium implant roughness in bone attachment using a tensile test.

This study aims at studying the effect of surface roughness on bone attachment of coin-shaped titanium implants. All implants in this study were blasted with TiO(2) particles of 180-220 microm, and then divided into three groups. One group had no further surface treatment whereas the other two groups were subsequently etched with hot hydrochloric acid (0.01M or 1M). The surface topography of the implant specimens was examined by SEM and by a confocal laser scanner for a numeric evaluation of S(a), S(t) and S(dr). The ranging implants in the three groups differed significantly in surface structure. The implants with modified surfaces were then placed into the tibias of 12 rabbits (n=16). After 8 weeks healing, the attachment of bone to implants were examined using a standardised tensile test analysis. The implants that were only blasted (positive control) showed significantly better functional attachment (p<0.001) than the acid etched. Implant surfaces etched with 1M HCl solution had the lowest retention in bone. There was a negative correlation between the increasing roughness and mechanical retention in bone of the implants in this study. The results support observations from earlier studies that suggested an optimal surface roughness for bone attachment, identified by in situ tensile tests and expressed as the arithmetic mean deviation (S(a)), to be in the range between 3.62 and 3.90 microm and that a further attachment depended on mechanical interlocking between bone and implant.

The influence of static and dynamic loading on marginal bone reactions around osseointegrated implants: an animal experimental study.

Although it is generally accepted that adverse forces can impair osseointegration, the mechanism of this complication is unknown. In this study, static and dynamic loads were applied on 10 mm long implants (Brånemark System, Nobel Biocare, Sweden) installed bicortically in rabbit tibiae to investigate the bone response. Each of 10 adult New Zealand black rabbits had one statically loaded implant (with a transverse force of 29.4 N applied on a distance of 1.5 mm from the top of the implant, resulting in a bending moment of 4.4 Ncm), one dynamically loaded implant (with a transverse force of 14.7 N applied on a distance of 50 mm from the top of the implant, resulting in a bending moment of 73.5 Ncm, 2.520 cycles in total, applied with a frequency of 1 Hz), and one unloaded control implant. The loading was performed during 14 days. A numerical model was used as a guideline for the applied dynamic load. Histomorphometrical quantifications of the bone to metal contact area and bone density lateral to the implant were performed on undecalcified and toluidine blue stained sections. The histological picture was similar for statically loaded and control implants. Dense cortical lamellar bone was present around the marginal and apical part of the latter implants with no signs of bone loss. Crater-shaped bone defects and Howship's lacunae were explicit signs of bone resorption in the marginal bone area around the dynamically loaded implants. Despite those bone defects, bone islands were present in contact with the implant surface in this marginal area. This resulted in no significantly lower bone-to-implant contact around the dynamically loaded implants in comparison with the statically loaded and the control implants. However, when comparing the amount of bone in the immediate surroundings of the marginal part of the implants, significantly (P < 0.007) less bone volume (density) was present around the dynamically loaded in comparison with the statically loaded and the control implants. This study shows that excessive dynamic loads cause crater-like bone defects lateral to osseointegrated implants.

Polydimethylsiloxane as a tooth surface-bound carrier of triclosan: a new concept in chemical plaque inhibition.

Polydimethylsiloxane (silicone oil) has an extremely low surface tension: It spreads over solid surfaces and forms a tenacious film which is hydrophobic and water-repellent. It is known that this liquid binds to hydroxyapatite and to dental enamel and changes the properties of these solids. It has been suggested that silicone oil may be applied to teeth and serve as a reservoir of lipid-soluble antibacterial substances which presumably will be slowly released into saliva due to their low solubility in water. The present paper reviews recent papers where this hypothesis is tested in vitro and in vivo. It was first shown that test tubes treated with the combination silicone oil and the lipid-soluble agent triclosan acquired a layer which inhibited bacterial growth in a culture of Streptococcus sobrinus (OMZ 176) which was grown in sucrose. Both growth in the medium and polysaccharide adsorption to the glass wall were inhibited. Silicone oil alone inhibited polysaccharide adsorption to some degree, whereas the growth in the medium was not affected. In a similar clinical plaque-inhibition study, topical application of silicone oil/triclosan to the teeth of a test panel showed marked plaque inhibition, particularly giving an increased number of teeth with scores of 0 (no plaque). In a study where silicone oil and triclosan were incorporated into a toothpaste, improved gingival health was observed after a period of one month. It is concluded that the use of silicone oil/triclosan in the manner described above represents a new principle in preventive dentistry. The results obtained seem to warrant further experiments with this combination.

Clinical effects and possible mechanisms of action of stannous fluoride.

Stannous fluoride was frequently used as a vehicle for fluoride in preparations used in caries prophylaxis in the 1960s and 1970s. At present it is not much used, although extensive research during the last two decades has established that stannous fluoride possesses several interesting properties which demonstrate that it deserves to be used in the prophylaxis against both gingivitis and caries. In the following, a review of the clinical properties of stannous fluoride is presented, together with a discussion of its merits compared with other fluoride vehicles in current use.

Dental plaque inhibition by a combination of triclosan and polydimethylsiloxane (silicone oil).

It has previously been shown that a toothpaste which contains triclosan and polydimethylsiloxane (silicone oil) improved gingival health in a test panel with established gingivitis more markedly than usually observed when testing commercial triclosan-containing toothpastes. In the present study the mode of action of combinations of silicone oil and triclosan was investigated. An in vitro experiment showed that triclosan was retained in a thin layer of silicone oil on the inner surfaces of test tubes that had been treated with the combination of triclosan and silicone oil. This triclosan was slowly released and inhibited the growth of bacteria in the test tubes. Silicone oil alone and in combination with triclosan was able to inhibit polysaccharide adhesion to the test tubes in the presence of a strain of Streptococcus sobrinus and a sucrose-containing medium. Corresponding in vivo experiments showed similar results; teeth topically treated with silicone oil and triclosan showed a marked plaque reduction, and those treated with silicone oil alone showed a moderate reduction, as compared with a placebo. The silicone oil plus 0.3% triclosan combination inhibited plaque formation also on proximal surfaces. It appears likely that this combination provides a reservoir of triclosan in the thin layer of silicone oil which binds strongly to teeth because of its low surface tension. Triclosan is then slowly released into saliva because of its low solubility in this fluid.

Oral hygiene, periodontal conditions and carious lesions in patients treated with dental bridges. A 15-year clinical and radiographic follow-up study.

A longitudinal study, extending over a period of 15 years, was carried out in a group of 102 patients who received 108 bridges made by the senior students at the Dental Faculty, University of Oslo, in 1967/68. The study included 343 abutment teeth, and the remaining teeth in the same jaw which received the restoration, 525 in all, served as control. The oral hygiene, gingival condition, pocket depth, caries on crowned teeth, location of crown margins and changes of alveolar bone level were recorded during the study. During the first 10 years, the patients received oral hygiene prophylaxis every 6 months. The mean age of the patients at the beginning of the study was 48 years. Of the original group of 102 patients, 88 attended the clinical examination after 5 years, 71 after 10 years, and 55 after 15 years. The amount of plaque did not differ between the crowned teeth and the control teeth during the observation period, while GI score 2 and 3 was more frequent in crowned teeth than in the control teeth during this period. This was mainly observed when the crown margins were located sub-gingivally. A slight increase in mean pocket depth was recorded in the crowned teeth while the mean pocket depth for the control teeth remained at the same level during the 15 years. Caries lesions were recorded in 3.3% of the abutment tooth surfaces at the 5th year, in 10.0% at the 10th year and in 12.0% at the 15th year examination. No statistical differences in bone loss could be detected between the control teeth and the crowned teeth.

Experiments with a toothpaste containing polydimethylsiloxan/triclosan.

Polydimethylsiloxan (silicone oil) adsorbs to solid surfaces and to teeth because of its low surface tension, forming a thin, resistant layer. Triclosan is a lipid-soluble, antibacterial substance which is added to toothpastes and mouthwashes to inhibit plaque. Triclosan can be dissolved in silicone oil, conferring an antibacterial property on the layer of silicone oil which forms on solid surfaces. The aim of the present study was to determine whether a toothpaste containing triclosan/silicone oil has any effect on established gingivitis in a test panel of 33 teenagers. This toothpaste and a placebo paste were randomly distributed to the panel, and the number of gingival bleeding points was recorded. No instruction in oral hygiene was given. The panel was then examined 4 wk later and the number of bleeding points again recorded. It was found that the reduction in bleeding points was significantly higher in the group which had used the triclosan/silicone oil paste than in the placebo group. Deposition of a lipid-soluble, antibacterial agent in a layer of silicone oil which adsorbs to the tooth surfaces because of its physical properties represents a new and promising principle in preventive dentistry.

Induction of calcium phosphate precipitation by titanium dioxide.

Titanium powder and various titanium dioxides were tested for their capacity to reduce the induction time for calcium phosphate precipitation from supersaturated solutions. Only after a pretreatment aimed at increasing its oxide surface layer was titanium powder found to accelerate the precipitation from solutions containing 2 mmol/L CaCl2, 2 mmol/L KH2PO4, 50 mmol/L Hepes, pH 7.2, and to induce precipitation from metastable solutions containing 1.2 mmol/L CaCl2, 1.2 mmol/L KH2PO4, 50 mmol/L Hepes, pH 7.2, at 37 degrees C. Even stronger effects were found when suspensions of the titanium dioxides anatase or rutile (10-50 micrograms/mL) were added to these solutions. TiO2 appeared to serve as a reactive substrate for secondary nucleation at a wide range of calcium-to-phosphate ratios and concentrations, even in the presence of 40 mg/mL bovine serum albumin, which completely inhibited precipitation in control incubations. These results suggest that the oxide surface layer of titanium implants may induce calcium phosphate precipitation in the metal-to-bone interface, which may play a role in the integration of such implants in bone.

A study on the mechanism of protein adsorption to TiO2.

The hypothesis that calcium ions adsorb to TiO2 and further to macromolecules with high affinity for Ca2+ was tested. The reaction of human serum proteins with TiO2 was examined and compared with the reaction with hydroxyapatite. The oxide covered titanium surfaces reacted with calcium when exposed to CaCl2 and calcium was identified to a depth of 17 nm into the oxide layer. Surface adsorbed serum proteins were dissolved by EDTA and analysis by the SDS-PAGE technique revealed that the surfaces of TiO2 and hydroxyapatite appeared to take up the same proteins selectively from human serum. Albumin, prealbumin and IgG were identified by immunoelectrophoresis. It is suggested that calcium binding may be one mechanism by which proteins adsorb to TiO2. It is well established that this is the case with hydroxyapatite.

[Frialit ceramic implants--a four-year follow-up study]. / Erfaringer med Frialit enkelttannsimplantat.

Sixty-two ceramic implants (Frialit) were installed in 53 patients with agenesia or loss of single teeth due to traumata or infection. Sixty-three per cent of the implants were operated in immediately after tooth extraction, whereas the rest were installed in a healed bony alveolar ridge. Eighty-five per cent of the implants were replacements for maxillary incisors. The average observation period was 4 years. During this period 10 implants were removed due to lack of osseointegration. Seven of these implants were lost in the healing period, the remaining 3 were removed after installation of the suprastructure. Eighty-four percent of the implants were successful after 4 years. Trauma in the maxillary region have caused fracture of the implants in 5 patients. Such incidents create therapeutic problems difficult to solve satisfactorily.

Chemical analysis and scanning electron microscopy of acquired pellicle formed in vivo on stannous fluoride treated enamel.

Stannous fluoride (SnF2) has been shown to be an effective caries preventive agent. After topical treatment of enamel surfaces, two reaction products have been demonstrated to precipitate on the surfaces, a larger type of globules, probably a calcium fluoride like product, and a smaller type of globules, probably a tin phosphate. The aim of the present study was to examine the amino acid composition and the formation of the acquired pellicle on SnF2-treated enamel in vivo. The chemical composition was examined by amino acid analysis of pellicle material collected in vivo from SnF2-treated enamel surfaces. Pellicle formation was examined by scanning electron microscopy on SnF2-treated enamel fragments carried in the mouth for 2 h. The results showed that pellicle material was formed in abundant amounts and covered the globular surfaces following the SnF2 treatment. The chemical analyses showed amino acid profiles with high content of acidic and neutral amino acids. The profiles were different from known amino acid profiles obtained from analyses of pellicle material collected from untreated enamel surfaces.

Treatment of dentin with stannous fluoride--SEM and electron microprobe study.

The effect of SnF2-treatment of dentin surfaces was investigated by means of scanning electron microscopy (SEM) and electron microprobe analysis. Human dentin was treated with aqueous SnF2 solutions of concentrations varying from 1 to 10%. The treatment periods lasted for 1, 5, 10, or 60 min. Both tin and fluoride were identified on the surfaces. The concentration varied depending on the extensiveness of the treatment. Immersion in 1 M KOH for 15 h removed both tin and fluoride from the surfaces. This reaction was not observed after immersion in H2O for the same time period. Examination of the SnF2-treated dentin surfaces showed a dense layer of globular particles and in addition some larger particles. The dentinal tubules were totally covered even after the treatment with the lowest concentration of SnF2. Deposition of tin- and fluoride-containing globules on dentin surfaces may be of clinical interest. This layer may have importance both for the caries resistance of dentin and for hypersensitivity reactions.

Scanning electron microscope and electron microprobe study of reactions of stannous fluoride and stannous chloride with dental enamel.

Stannous fluoride but not stannous chloride has shown a caries inhibiting effect in animal studies. The effect of aqueous solutions of stannous fluoride and stannous chloride on dental enamel surfaces was investigated by scanning electron microscope and analytical electron microprobe. Some large globules and a continuous layer of small globules were observed after stannous fluoride treatment. The large globules were soluble in both water and alkali, whereas the small ones were only soluble in alkali. Both fluoride and tin were found to be present on the enamel surfaces by the electron microprobe after stannous fluoride treatment. The fluoride could not be detected after immersion in distilled water whereas alkali treatment removed the tin. The large fluoride-containing globules may consist of calcium fluoride as this substance is known to be slightly soluble in water and soluble in alkali. Stannous chloride treatment gave a layer of small tin-containing globules with properties similar to the layer formed on enamel treated with stannous fluoride. It is therefore suggested that the tin-containing layer is not associated with caries protection whereas calcium fluoride-like deposition on the enamel probably is a factor in the caries inhibition caused by stannous fluoride.

Plasma fluoride levels in man following intake of SnF2 in solution or toothpaste.

The degree and rate of fluoride absorption in five volunteers were studied after ingestion of SnF2 and NaF solutions or SnF2 toothpaste. The fluoride concentration in plasma was followed for eight hours. The relative bio-availability of fluoride was calculated and was similar for both the NaF and SnF2 solutions, although the latter solution showed a somewhat faster absorption rate. The bio-availability of fluoride from the SnF2 dentifrice was 85%.