Many patients turn to dental implants for oral rehabilitation, often because they have unsuccessfully worn a conventional removable denture, or they desire a more stable or fixed prosthesis. The implants may be restored with a fixed or removable prosthesis with an associated increase in chewing ability, function, esthetics, and phonetics.1
Pure titanium and its alloys were proposed as implant materials, and have been successfully used in reconstructive surgery and prosthetic treatment because of their biocompatibility and osseointegration.2,3 The biologic properties of titanium may be explained on the basis of tightly adherent oxide layer buildup of a combination of TiO, TiO2, Ti2O3, and Ti3O4, which immediately forms on the metal surface.4
It has been almost 30 years since the application of synthetic biomaterials that resembles, conducts, or induces bone formation. These materials are collectively called bioceramics. They include bioactive glass and glass ceramics. They are polycrystalline ceramic forms of calcium phosphate salts: hydroxyapatite and tricalcium phosphate. One drawback is their limited mechanical properties represented by brittleness, which results in low impact resistance and low tensile strength.5,6 As a solution to this problem, a thin coating of bioactive calcium phosphate ceramic on bioinert metallic endosseous implant has been introduced, thus, combining the strength of metal and the favorable properties of the bone-bonding capacity of bioceramic coatings that may help cementless fixation of dental prostheses.7
When materials are implanted in living bone, the interfacial occurrence differs depending on bone response to different surface properties. This involves topographic and morphologic properties, and surface chemistry of the implanted material. Many studies on hydroxyapatite-coated titanium implants have shown that a thin layer of hydroxyapatite displays many biologic advantages, such as the promotion of normal bone apposition on its surface, firm attachment at hydroxyapatite coating-bone interface, enhancement of bone ingrowth into pores of hydroxyapatite-coated metallic implants, and protection of surrounding bone against metal-ion release from the substrate8 (i.e., hydroxyapatite coating on metal implants demonstrated bone binding capability and osteoconductive property compared to uncoated ones).9,10
In 1985, Brånemark2 defined contact osteogenesis: “osseointegration” as “a direct connection between living bone and a load-carrying endosseous implant at the light microscopic level.” Two years later, Meffert et al11 redefined and subdivided osseointegration into: “Adaptive osseointegration,” which has osseous tissue approximating the surface of the implant without apparent soft tissue interface at the light microscopic level; and “Biointegration,” which is a direct biochemical attachment of living bone to the surface of an implant that is independent of any mechanical interlocking mechanism and is identifiable at the electron microscope level.11–13 The bone-titanium interface is well known as osseointegration, while the bone-hydroxyapatite coated implant interface is termed biointegration13 or “Bonding osteogenesis.”14
Many studies detected the presence of direct bone contact without any intervening fibrous tissue noted on the surface titanium implant.14–19 However, a constant finding was the presence of a 100–400 A° thick amorphous granular layer between the mineralized bone and implant surface.15 Analyses of this partly calcified layer revealed that it was in direct continuity with the implant surface and fuses with the oxide layer present on titanium implant surfaces.18,20 This layer was termed biologic apatite.21 The exact bond between this layer and the implant surface is not fully understood but thought to be a weak form of van der Waals bond, a direct-chemical bond or a mixture of both.18,22 On the other hand, evidence suggesting a chemical bonding between hydroxyapatite and living bone has been reported.23 Several authors23–25 histologically confirmed intimate contact between the hydroxyapatite surface and bone, even at the ultrastructural level, while a commercially pure titanium (cpTi) presented a zone consisting of a collagen-free cellular ground substance, at the interface with living bone.26 These findings led to the speculation that a strong and intimate bonding between hydroxyapatite and bone can be achieved at their interface.
Many coating techniques of hydroxyapatite to a metal surface were employed, such as plasma spraying,7,8 electrodeposition,27 electrophoresis,28 sputtering,29 hot isostatic pressing,30 and anodic oxidation with thermal treatment.31 These techniques had the disadvantages of induction of impurities as α and β-tricalcium phosphate, tetracalcium phosphate, and oxyhydroxyapatite due to thermal decomposition of hydroxyapatite during processing affecting the long-term clinical fixation of the implant because of their high rate of solubility, increased amount of hydroxyapatite crystals that weaken the bonding between coating and substrate, or few hydroxyapatite crystal precipitations that impair biocompatibility.31,32
Because the coating is in direct contact with the bone and body fluid, the coating characteristics are influential in the fixation mechanism and clinical performance of the implants. Therefore, it is crucial to control the coating characteristics by varying the processing conditions. The coating specification includes purity (phase composition), crystallinity, microstructure, porosity, surface morphology, surface texture, and coating thickness.33 Therefore, this study aimed at obtaining a thin and uniform hydroxyapatite coating on the cpTi substrate using the electroplating technique with hydrothermal treatment in a trial to optimize the hydroxyapatite coating criteria. In addition, in vivo evaluation of the resultant bone bonding potentiality caused by this precipitated hydroxyapatite film for achieving biointegration.
Materials and Methods
A cpTi implant system was selected in this study (TUT Dental implants, Egyptian Co. for Dental Implants [ECDI], Cairo, Egypt). The implants had the dimensions of 7-mm height and 3.4-mm diameter. Twenty implants were divided equally into 2 main groups (n = 10). One group was cpTi implants utilized as received (i.e., already sterilized), while the other one represented a metallic substructure to receive hydroxyapatite coating by electrochemical plating. The implants of both groups were intended to be inserted in the tibiae of 10 New Zealand male rabbits.
Two additional 7-mm sided and 3.4-mm thickness square-shaped samples of a commercially pure titanium ingot supplied by the same manufacturer were obtained by laser cutting (Cuto 20; Jeanwiritz, Germany). The obtained samples were employed for characterization and follow-up of the hydroxyapatite deposited coating before and after sterilization.
The Hydroxyapatite Coating Technique
The coating mechanism involved 2 steps: first, precipitation of CaHPO4·2H2O by electroplating; then hydrothermal phase transformation reaction to obtain hydroxyapatite (Ca5 (PO4)3·OH). Each implant was sandblasted for 1 minute using 30–120-μm alumina powder to maximize the surface area subjected to the coating procedure. Ten implants and 2 specimens were rinsed by acetone in an ultrasonic bath, followed by washing with distilled water to remove any surface debris. Then, they were individually coated with a thin silica and titania polymeric film (Tetra-iso-propyl orthosilicate and tetra-iso-propyl orthotitanate; Wako Pure Chemical, Osaka, Japan) to increase the surface reactivity of the metallic substructure.34 The sol-gel process was employed for coating with this polymeric film through dipping the implants and samples in a precursor solution of metal alkoxides (M-(OR)n + R alkyl radical) capable of forming alkoxide complexes. A polycondensation reaction took place to form a rigid gel according to the following mechanism: dilute sol → entrained dilute sol → aggregation → gelation → alcohol/water evaporation → film collapse and/or pores formation → deposited film.
Electrochemical plating was then accomplished using an electrolytic solution of Ca(NO3)2·4H2O and NH4H2PO4. The pH of the solution was kept at 3.6–4, while an electric current was adjusted and monitored during deposition for 6 hours using a potentiostat/galvanostat (DAR Model 273). The dipped-coated implants and specimens served as a cathode, a platinum basket served as an anode, and the calcium phosphate solution was the electrolyte. The coated implants were rinsed and dried. Finally, putting them in an autoclave (243AC, T304, 100990; Parr Instrument Co., IL) and boiling under a steam pressure of 10 atmospheres at 180°C for 3 hours in 1 mol/L sodium hydroxide was performed to apply hydrothermal treatment.
Surface Characterization
Surface characteristics included phase distinction, surface morphology, and texture of cpTi and hydroxyapatite coating specimens. In addition, the thickness of the hydroxyapatite coat was also measured.
The phase of the deposited coat had been characterized using x-ray diffraction. An x-ray diffractometer (Burker Axs D8 Advance, Karlsruhe, Germany) was employed for chemical analysis of the crystalline deposited coat. The patterns obtained as a function of intensity (count) versus 2θ were compared with the International Center for Diffraction Data card 9-432 for hydroxyapatite. The surface roughness of coated and uncoated specimens was measured using mechanical contact surface profilometry (HOMMEL Tester T2–2 profilometer; Hommelwerke GmbH, VS-Schwenningen, Germany). The arithmetic mean of the absolute departures of roughness profile from the mean line defined for a profile represents the surface roughness in μm. The thickness of the hydroxyapatite coating layer was also measured for the coated specimens by a thickness gauge positector (Positector 6000, Model F; BYK-Gardner GmbH, Geretsried, Germany) before and after γ-radiation sterilization. Representative samples of the implant were scanned using a scanning electron microscope (SEM) (Joel JSM5410; TSU, Japan) to examine the surface morphology and grain size.
Sterilization of the Coated Implants
Before the surgical procedure, it was mandatory to expose the hydroxyapatite-coated implants to an identical sterilization cycle like that of the as-received cpTi implants in order to eliminate microorganism influence. Hydroxyapatite-coated implants were exposed to the specified γ-radiation dose: 2.5 mega rad, in the range of 1.0023 KGy/hr at the time of sterilization (60 Co, Baha Baha Indian Cobalt-60,4000A, National Center for Radiation Research and Technology NCRRT, Cairo, Egypt). Similarly, sterilized hydroxyapatite-coated specimens were characterized as previously mentioned to deduce probable changes that might occur for the coating.
Surgical Procedures and Histological Examination
Ten adult New Zealand male rabbits weighing between 3.2 and 3.7 kg received 2 endosseous implants, 1 cpTi and the other 1 hydroxyapatite-coated inserted bilaterally in the tibiae shafts. Five animals received cpTi implants in the right tibial shafts and hydroxyapatite-coated in the left ones, while the other 5 animals received the remaining implants in an inverse design (i.e., the hydroxyapatite-coated implants were inserted in the right tibial shafts, while cpTi in the left tibial shafts). The animals were fasted 12 hours before surgery. Ketamine 50 mg/kg body weight (ketamine [as HCL] 50 mg/ml; EIPICO, Egypt) and xylazine were administered intramuscularly (xylazine 20 mg, M.H. Reg. No. 1373/99 Vet; ADWIA, Egypt.). In addition, 2% lidocaine was injected locally at the surgical sites (Mepecaine, Alexandria Co. for Pharmaceuticals, Egypt.). After sedation, the region of the tibiae of each animal was shaved and thereafter washed with iodine.
Surgical procedures were conducted in compliance with the ethical principles for animal research, as approved by institutional guidelines. An approximate 3-cm long incision was made to expose the tibiae shafts through blunt dissection. Bone was perforated using segmental drills at a low-speed with saline cooling, and the bone holes were carefully threaded. The implants were gently screwed into place, healing covers were placed (Fig. 1), and the fascia and skin were sutured. After the surgery, each animal received intramuscular PAN-Terramycin antibiotic at a dose of 1 cm3/10 kg (Oxytetracycline HCl; Pfizer, Egypt.) to protect against postoperative infection, and analgesic at 0.05 mgm/kg for 3 successive days. The animals were allowed full-weight bearing without any mobility restrictions immediately postoperatively.
;)
Fig. 1.:
Inserted cpTi implant in the tibia of the rabbit.
Animals were sacrificed after 8 weeks following implant insertion by giving an overdose of intravenous Nembutal (NYSE:LLY, Indianapolis, IN). The right and left tibiae were removed from each rabbit, and bone columns containing the implants were immediately immersed in 10% buffer formalin solution for fixation of the specimens for 48 hours. At sacrifice, there was no indication of inflammation, gross infection, or tissue reaction around the implants. At the time of exposure, all implants were in place, and no implants were lost during the course of the study.
Each specimen was dehydrated in graded alcohol series for 10 hours and embedded in methyl methacrylate without decalcification. After polymerization, sections were made through the longitudinal axis of the implants and through the surrounding nondecalcified bone. The embedded tissue was cut into 150-μm thick sections with a low-speed diamond wheel using tap water lubrication. The sections were sanded on an abrasive paper under tap water to obtain a uniform surface finish.
For histological study, specimens were gold sputtered and examined using an SEM (Philips, XL30, 5600 MD; Eidhoven, Holand) at 10× spot magnification. The gap dimension at the bone-implant interface around all threads throughout the length of the implant body was measured and compared with that of the control group at 2000× spot magnification.
Statistical Analysis
The determined surface roughness and measured gap distance dimensions along the bone-implant interface were collected, tabulated, and statistically analyzed using the Mann-Whitney test at P < 0.0001.
Results
Surface Characterization
The x-ray diffraction of the hydroxyapatite coating before and after sterilization is presented in Fig. 2. From Fig. 2A, the calculated (d) values and relative intensities (I/Io) as compared to the reference cards of hydroxyapatite undoubtedly coincide with those of pure crystalline hydroxyapatite (Ca5(PO4)3·OH) according to International Center for Diffraction Data 9-432 for hydroxyapatite. Meanwhile, the x-ray diffraction pattern of the same sample after γ-radiation sterilization (Fig. 2B) showed some differences when compared to its predecessor. There were decreases in intensities and broadening of the peaks at 2θ = 25.7 and 2θ = 30.8, which strongly support the possibility of small crystal domains (i.e., grain size refinement and/or low crystal order). The hydroxyapatite phase revealed decreasing in the semiquantitative amount of the crystalline phase from 89.9% to 87.2% after sterilization. Yet, the main peaks of hydroxyapatite preserved its existence in the same 2θ values. However, no decomposition occurred since no new peaks appeared.
Fig. 2.:
The x-ray diffraction-pattern of hydroxyapatite coating before (A) and after (B) sterilization.Fig. 3. Surface roughness (Ra) of cpTi (A) and hydroxyapatite-coated implants before (B) and after (C) sterilization.
The traced surface roughness of the uncoated cpTi and coated samples before and after sterilization is presented in Fig. 3. The measured arithmetic means in μm are presented in Table 1. As shown in Table 1, the surface roughness of cpTi (1.3 ± 0.5 μm) is significantly less than that of hydroxyapatite-coated samples, either before or after sterilization (2.7 ± 0.2 and 2.5 ± 0.4 μm, respectively). Considering the coating thickness, the precipitated coat before sterilization had a 69–78-μm thickness compared to 60–69 μm after γ-radiation sterilization.
Table 1: Surface Roughness Measurements of cpTi and Hydroxyapatite-Coated Implants Before and After Sterilization (n = 3)
An SEM study of pure titanium (Fig. 4) showed surface irregularities that appeared as undulating regions. Little microporosity had an average size of 0.5–1 μm of round, elliptical, and oval shape. Some of these pores were connected by dark grooves with a width of 0.5–1.5 μm. An SE micrograph of hydroxyapatite-coated specimen before sterilization revealed the presence of thin needle-like crystals, 3–8 μm long, and a nanometer diameter arranged nearly parallel to the surface metal substrate. Variant-sized micropores of 0.5–4 μm were also clearly seen (Fig. 5). However, densely packed and finer plate-like crystals were elicited in an SE micrograph after sterilization. The micropores had been reduced in size with a less roughened surface (Fig. 6).
Fig. 4.:
SE micrograph of cpTi.Fig. 5. SE micrograph of hydroxyapatite coating before sterilization.Fig. 6. SE micrograph of hydroxyapatite coating after sterilization.
Histological Study
The evaluation of the relative quantity and quality of bone tissue surrounding cpTi and hydroxyapatite-coated implants in terms of maturation and uniformity of structural quality, as well as the bone density, revealed the presence of intimate contact between bone and these implants. Magnification (10×) exhibited that the cpTi group had a less amount of bone regeneration with less density of bone trabeculae (Fig. 7). Meanwhile, the hydroxyapatite-coated group revealed a recognizable amount of bone regeneration, especially at the base of the implant, and the trabeculae of bone were clearly more and had a higher density (Fig. 8). SEM examination at 2000× revealed wide gaps not filled with bone in the cpTi group and bone trabeculae that appeared as threads (Fig. 9). On the other hand, there was close intimate contact between the bone and implant surfaces in the case of the hydroxyapatite-coated group (Fig. 10). Also, uniform healing was observed in the form of irregular fine bony trabeculae and ridges along the implant, with a tendency to migrate to the space formed between the implant and bone surface. There were denser bone trabeculae indicating more bone formation in respect to the hydroxyapatite group.
Fig. 7.:
SE micrograph of a histological slide of the cpTi implant.Fig. 8. SE micrograph of a histological slide of the hydroxyapatite-coated implant.Fig. 9. SE micrograph of the cpTi implant showing gap distance measurements at implant-bone interface.Fig. 10. SE micrograph of the hydroxyapatite-coated implant showing gap distance measurements at implant-bone interface. An arrow indicates the area of intimate contact.
Regarding the gap distance, larger gaps ranged from 0.721 to 2.31 μm and less intimate contact with bone in the case of the cpTi implants (Fig. 9). Meanwhile, hydroxyapatite-coated implants showed that most of the gaps around the implants were filled with new bone formation. In addition, the newly formed bone at the interfaces was spread more diffusely along the implant surfaces. Some areas showed intimate contact with bone, with marked uniformity in the contact line opposing the bone surface (Fig. 10). The gap distance ranged from 0 to 1.32 μm, as presented in Table 2.
Table 2: The Gap Distance at Bone-Implant Interface (n = 30)
Discussion
Structural and functional bonding between living bone and the surface of a load-bearing implant is believed to be an important factor in implant success.2 The common feature at the interface of metallic and bioceramic implant materials is the presence of a biologically active bone-like apatite intermediate layer through which these materials bond to bone.3,35 A prerequisite to predict correctly the lifelong stability of an implant is the comprehensive understanding of its surface characteristics because the interfacial occurrence at bone-implant relay on the implanted material criteria.
Surface Characterization
The excellent biocompatibility and corrosion resistance of titanium and its alloys are attributed to the oxide layer present on the surfaces that have a thickness of 2–5 nm.36 Because of the extremely slow growth of this layer during the course of implantation, amorphous hydrated titanium oxide rich in TiOH groups would form. The calcium and phosphorus are incorporated in the few nanometer-thick hydrated oxide layers.37 TiOH groups would be involved in the events leading to bone-implant osseointegration.38 Sufficient TiOH groups can be created either by a long period of implantation and/or through surface treatment.39
When bioceramics were implanted in the bone tissue, ionic species leach out from the materials into the surrounding medium, leaving SiOH groups on their surfaces. An ionic exchange between bioceramics and the host tissue would continue. The number of SiOH groups increases to such a level that they can induce apatite formation by taking calcium and phosphorus from body fluid. Once apatite nuclei form, they grow spontaneously.40 Ishizawa and Ogino,32 Shoeib,34 and Li et al37 suggested that the porous microstructure of TiO2 and SiO2 matrices that precipitate on the implant surface might be suitable as nucleation sites for the precipitation of calcium and phosphorous-forming calcium phosphate crystals, the precursor compound of hydroxyapatite. Thus, in this study, dipping of cpTi implants in silica and titania gel was performed to provide a sufficient number of SiOH and TiOH groups on their surfaces to be hydrolyzed for stimulation of hydroxyapatite nucleation before the electrochemical deposition of hydroxyapatite coating.41 In brief, the ability of an oxide layer to induce apatite formation is associated with an abundant OH group and negatively charged surfaces in a physiologic solution that are considered to be candidates for bone bonding potentiality.42,43
It has been found that the greatest bone regeneration occurred around hydroxyapatite that had a minimum of 85% crystalline hydroxyapatite.44 Fortunately, the precipitated semiquantitative amounts of the hydroxyapatite crystalline phase were 89.9% and 87.2% before and after sterilization, respectively. The hydrothermal treatment following electroplating performed under high pressure during autoclaving would be an aid to form pure and high crystalline hydroxyapatite (Fig. 2). The phase purity and crystallinity have a dominant influence on the degree of hydroxyapatite solubility and, therefore, the promotion of the long-term fixation of the implant. However, the consequent γ-radiation sterilization resulted in smaller packed plate-like crystals with narrower-sized pores that may provide a nanoscaled porous matrix suitable for nucleation of hydroxyapatite (Fig. 6).7,33 The liberation of the accumulated stress due to post-heat treatment might have aided in the resultant grain refinement, but not to the extent of decomposition of the hydroxyapatite phase, as reflected by the x-ray diffraction pattern, where no new peaks of impurities appeared, indicating that the hydroxylation of the coating was preserved. Also, the broadening of peaks shown by the diffraction profile at 2θ = 25.7 and 2θ = 31.8 accompanied with less intensities of these peaks might be an indication for the presence of an amorphous metaphase of higher internal energy.45 As well, increased internal energy might be due to greater boundary volume and more point defect of finer crystals. These slight changes after sterilization might lead to a higher dissolution rate essential for stimulation of bone formation.33
In agreement with the results of this study, it was proven that the hydroxyapatite coating on metal implants with a thin layer of about 50 μm resulted in rapid bone formation and significant interfacial attachment because of its osteoconductive property compared with uncoated ones.9,10 The surface texture would modify the osteogenic response; therefore, it is a very significant parameter in implant long-term fixation. Surface roughness measurement reflected the irregular morphology of the traced surface.33 It was demonstrated that the precipitation of apatite occurs in the depression and pores of the surface exposed to body fluid.45 Svehla et al46 in 2000 reported that the smooth Ti surface exhibited limited bony ingrowth but an improved response to rough surfaces within specific roughness range. Martin et al36 in 1995 strongly suggested a direct correlation between surface roughness and many aspects of cellular activity. Nevertheless, the proliferation rate was negatively impacted by increased surface roughness; alkaline phosphatase specific activity and possibly calcification were enhanced by that rough surface. In addition, protein synthesis, matrix production, and ribonucleic acid synthesis were surface sensitive. They were promoted in cell cultures on rough surfaces in contrast to the inhibition that occurs on a smooth surface. Osteoblast-like cells attachment was enhanced by rough substrate, while fibroblasts tend to accumulate on smooth surface. The results of this study support their postulation (Fig. 3; Table 1). In several in vivo studies, rough surfaces were found to produce greater bone growth and better bone fixation than smooth surfaces.46–48 This is confirmed by the shorter bone healing period of hydroxyapatite implants rather than that following Ti implants.11,19,49 Paradoxically, a rough surface might promote macrophage attraction rather than wound healing. It is possible in this case that the increased ion release might be responsible for the decreased bone fixation.50
Histological Study
New Zealand rabbits were selected for use as experimental animals in this study because they are comparatively easy to handle and maintain; healthy animals of this species are available from local laboratories. In addition, this species is also known to maintain uniformity in its genetic characteristics, and, therefore, there is very little difference in anatomical, histological, and physiologic characteristics among animals.51,52 Animal sacrifice was carried out 8 weeks after implant insertion because the bone healing response in such animals starts during the first week, peaks around 3–4 weeks, and arrives at a relative steady state with only minor bone remodeling 6–8 weeks after implant insertion. In fact, follow-up for more than 1 year later revealed that the general histological picture of bone and vascular architecture remained largely unchanged.4,49
Gotfredsen et al53 proposed the use of SEM images obtained with backscattered electrons in this study. This methodology allows for the use of thick sections and acquisition of high-contrast images because backscattered electron contrast is highly dependant on the atomic number of chemical specimens. Consequently, bone and hydroxyapatite appear darker than titanium.28
Bone healing around implants follows the same phases of normal bone healing, inflammatory, proliferative, and maturation phases. The interface zone that develops between the implant and healing bone depends on many variables, such as implant material, surgical technique, initial micromobility, and the type and status of bone in the recipient site.22 The bone-implant interface is a dynamic structure with multiple microscopic characteristics present in different portions of the implant surface. In some areas, a direct bonding to mineralized bone is present, while in other areas, a thin layer of unmineralized matrix is interposed between these 2 structures. The results obtained in this study are in agreement with the interface morphology already described around titanium and ceramic implants (Figs. 7 and 8).15 Bone-implant contact is also consistent with the results of other studies (Figs. 9 and 10; Table 2),53,54 although Weinlaeder et al17 reported a significantly greater amount of bone associated with hydroxyapatite-coated endosseous implants (71.35%) versus cpTi ones (45.66%) after 12 weeks of implantation in dogs. Others55,56 have demonstrated that at 1 year, the bone interface between hydroxyapatite and titanium implants is very similar.
The tendency of hydroxyapatite to incorporate carbonate ions from air during synthesis and/or the coating process renders the hydroxyapatite-coating more soluble, which seemed to be positive for the osseointegration process.28 The partial dissolution of hydroxyapatite makes the surrounding fluid rich in calcium and phosphate ions, and these released ions can trigger cellular differentiation and consequent bone formation.57,58 Calcium of hydroxyapatite-coated implants may facilitate the attachment of osteoblast cells to the implant surface via activation of integrin structures, and thereby bind to the arginine glycine aspartic acid domain of adhesive proteins (fibronectin, vitronectin, and osteopontin),59 and/or may form an electrostatic bond with polyanionic Ca++ binding proteins such as proteoglycan, osteocalcin, osteopontin, and osteonectin in bone matrix.60 This may explain the current histological findings of the closer contact of the newly formed bone observed along the hydroxyapatite-coated implant surface in comparison to the Ti implant surface, and perhaps illustrate the reason that hydroxyapatite- coated implants tend to exhibit biointegration rather than osseointegration of the uncoated implants.57,58
Conclusions
The technique of hydroxyapatite coating used in this study allowed the precipitation of thin and uniform pure hydroxyapatite crystals, as proved by x-ray diffraction, provided porous TiO2 and SiO2 matrices that are suitable for the nucleation sites of hydroxyapatite crystals, and prevented abrupt phase changes at the hydroxyapatite-coating substrate interface. The histological findings of this study led to the conclusion that the hydroxyapatite-coated implants had better performance regarding the bone-implant contact area than the uncoated ones. The characterization of the precipitated hydroxyapatite film is promising for the clinically successful long life fixation of implants. Further clinical investigations are recommended. Moreover, adhesiveness at bone-implant interface should be evaluated as a measure for proper osseous fixation.
Disclosure
The authors claim to have no financial interest in any company or any of the products mentioned in this article.
Acknowledgments
The authors thank Professor Dr. Amina Adds, Professor of Oral Biology, Ain Shams University, and dean of the Faculty of Dentistry, MUST University, Egypt, for her valuable guidance, assistance, and contribution to this work.
References
1. McCracken M, Lemon JE, Zinn K. Analysis of Ti-6Al-4V implants placed with fibroblast growth Factor 1 in rat tibia.
Int J Oral Maxillofac Implants. 2001;16:495-502.
2. Brånemark PI. Introduction to osseointegration. In: Brånemark PI, Zarb GA, Albrektsson T, eds.
Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. Chicago, IL: Quintessence; 1985:11-76.
3. van Noort R. Titanium: The implant materials of today.
J Mater Sci Mater Med. 1987;22:3801-3811.
4. Albrektsson T. Direct bone anchorage of dental implants.
J Prosthet Dent. 1983;50:255-261.
5. Jarcho M. Retrospective analysis of hydroxyapatite development for oral implant application.
Dent Clin North Am. 1992;36:19-26.
6. Inadome T, Hayashi K, Nakashima Y, et al. Comparison of bone-implant interface shear strength of hydroxyapatite-coated and alumina-coated metal implants.
J Biomed Mater Res. 1995;29:19-24.
7. Klein CPAT, Wolke JGC, de Bliek-Hogervorst JMA, et al. Features of calcium phosphate plasma-sprayed coating: An in vitro study.
J Biomed Mater Res. 1994;28:961-967.
8. Wang BC, Chang E, Lee TM, et al. Changes in phases and crystallinity of plasma-sprayed hydroxyapatite coating under heat treatment: A quantitative study.
J Biomed Mater Res. 1995;29:1483-1492.
9. Hayashi K, Uenoyama K, Matsuguch N, et al. Quantitative analysis of in vivo tissue responses to titanium oxide and hydroxyapatite-coated titanium alloy.
J Biomed Mater Res. 1991;25:515-523.
10. Jansen JA, van der Waerden JPCM, Wolke JGC. Histologic investigation of the biologic behavior of different hydroxyapatite plasma-sprayed coating in rabbit.
J Biomed Mater Res. 1993;27:603-610.
11. Meffert RM, Block MS, Kent JN. What is osseointegration?
Int J Periodontics Restorative Dent. 1987;4:9-21.
12. Block MS, Kent JN, Kay JF. Evaluation of hydroxyapatite coated titanium dental implants in dogs.
J Oral Maxillofac Surg. 1987;45:601-607.
13. Hobos Ichida E, Garcia L, eds. Biological consideration for osseointegration. In:
Osseointegration and Occlusal Rehabilitation. Tokyo, Japan: Quintessence; 1991:33-54.
14. Block MS, Kent JN, eds. The integral implants system and the science of hydroxylapatite-coated implant. In:
Endosseous Implants for Maxillofacial Reconstruction. Philadelphia, PA: Saunders; 1995:223-250.
15. Sennerby L, Ericson LE, Thomsen P, et al. Structure of the bone-titanium interface in retrieved clinical oral implants.
Clin Oral Implants Res. 1991;2:103-111.
16. Deporter DA, Watson PA, Pilliar RM, et al. A histological evaluation of a functional endosseous, porous-surfaced, titanium alloy dental implant system in the dog.
J Dent Res. 1988;67:1190-1195.
17. Weinlaeder M, Kenney EB, Lekovic V, et al. Histomorphome-try of bone apposition around three types of endosseous dental implants.
Int J Oral Maxillofac Implants. 1992;7:491-496.
18. Albrektsson T, Sennerby L. Direct bone anchorage of oral implants: Clinical and experimental considerations of the concept of osseointegration.
Int J Prosthodont. 1990;3:30-41.
19. Hansson HA, Albrektsson T, Brånemark PI. Structural aspects of the interface between tissue and titanium implants.
J Prosthet Dent. 1983;50:108-113.
20. Albrektsson T. Bone tissue response. In: Brånemark PI, Zarb GA, Albrektsson T, eds.
Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. Chicago, IL: Quintessence; 1990:129-143.
21. Jarcho M, Kay JF, Gumaer KI, et al. Tissue, cellular and subcellular events at a bone-ceramic hydroxyapatite interface.
J Bioeng. 1977;1:79-85.
22. Zoldos J, Kent J. Healing of endosseous implants. In: Block MS, Kent JN, eds.
Endosseous Implants for Maxillofacial Reconstruction. Philadelphia, PA: Saunders; 1995:40-69.
23. Jarcho M. Calcium phosphate ceramics as hard tissue prosthetics.
Clin Orthop Relat Res. 1981;157:259-277.
24. de Groot K, Geesink R, Kelin CP, et al. Plasma sprayed coatings of hydroxylapatite.
J Biomed Mater Res. 1987;21:1375-1381.
25. Piattelli A, Trisi P, Emanuelli M. Bone reactions to hydroxyapatite-coated dental implants in human: Histologic study using SEM, light microscopy and laser scanning microscopy.
Int J Oral Maxillofac Implants. 1993;8:69-74.
26. Albrektsson T, Jacobsson M. Bone-metal interface in osseointegration.
J Prosthet Dent. 1987;57:597-607.
27. Shirkhanzadeh M. Bioactive calcium phosphate coating prepared by electrodeposition.
J Mare Sci Lett. 1991;10:1415-1417.
28. Costa Cde A, Sena LA, Pinto M, et al. In vivo characterization of titanium implants coated with synthetic hydroxyapatite by electrophoresis.
Braz Dent J. 2005;16:75-81.
29. Ong JL, Lucas LC, Lacefield WR, et al. Structure, solubility and bond strength of thin calcium phosphate coating produced by ion beam sputter deposition.
Biomaterials. 1992;13:249-254.
30. Herø H, Wie H, Jørgensen RB, et al. Hydroxyapatite coating on Ti produced by hor isostatic pressing.
J Biomed Mater Res. 1994;28:343-348.
31. Ishizawa H, Ogino M. Formation and characterization of anodic titanium oxide films containing Ca and P.
J Biomed Mater Res. 1995;29:65-72.
32. Ishizawa H, Ogino M. Characterization of hydroxyapatite layers formed on anodic titanium oxide films containing Ca and P by hydrothermal treatment.
J Biomed Mater Res. 1995;29:1071-1079.
33. Sun L, Berndt CC, Khor KA, et al. Surface characters and dissolution behavior of plasma sprayed hydroxyapatite coating.
J Biomed Mater Res. 2002;62: 228-236.
34. Shoeib MA. Coating of composite materials with hydroxyapatite.
Galvanotechnik J. 2004;8:1866-1867.
35. Kitsugi T, Yamomuro T, Nakamura T, et al. Bone bonding behavior of three kinds of apatite containing glass ceramics.
J Biomed Mater Res. 1986;20:1295-1307.
36. Martin JY, Schwartz Z, Hummert TW, et al. Effect of titanium surface roughness on proliferation, differentiation and protein synthesis of human osteoblast-like cells (MG63).
J Biomed Mater Res. 1995;29:389-401.
37. Li P, Ohtsuki C, Kokubo T, et al. The role of hydrate silica, titania and alumina in inducing apatite in implants.
J Biomed Mater Res.1994;28:7-15.
38. Tengvall P, Lundstrom I. Physico-chemical consideration of titanium as biomaterials.
Clin Mater. 1992;9:115-134.
39. Li P, deGroot K. Calcium phosphate formation within sol-gel prepared titania in vitro and in vivo.
J Biomed Mater Res. 1993;27:1495-1500.
40. Li P, Ohtsuki C, Kokubo T, et al. Effect of ions in aqueous media on apatite formation on silica gel.
J Appl Biomater. 1993;4:221-229.
41. Nakahira A, Tamai M, Aritani H, et al. Biocompatibility of dense hydroxyapatite prepared using SPS process.
J Biomed Mater Res. 2002;62:550-557.
42. Paks GA. The isoelectric points of solid oxides, solid hydroxides and aqueous hydroxy complex systems.
Chem Rev. 1965;65:177-198.
43. Ji H, Marquis PM. The effect of heat treatment on the microstructure of plasma-sprayed hydroxyapatite coating.
Biomaterials. 1993;14:64-68.
44. Nrey EB, Le Geros RZ, Lynch KL, et al. Tissue response to biphasic calcium phosphate ceramic with different ratios of HA/βTCP in periodontal osseous defects.
J Periodontol. 1992;63:729-735.
45. Weng J Liu Q, Wolke JGC, et al. The role of amorphous phase in nucleating bone-like apatite on plasma-sprayed hydroxyapatite coating in simulated body fluid.
Mater Sci Lett. 1997;16:335-337.
46. Svehla M, Morberg P, Zicat B, et al. Morphometric and mechanical evaluation of titanium implant integration: Comparison of five surface structures.
J Biomed Mater Res. 2000;51:15-22.
47. Bowers KT, Keller JC, Randolph BA, et al. Optimization of surfaces morphology for enhanced osteoblast responses in vitro.
Int J Oral Maxillofac Implants. 1992;7:307-310.
48. Brunette DM. The effects of implant surface topography on the behavior of cells.
Int J Maxillofac Implants. 1988;3:231-246.
49. Wigianto R, Ichikawa T, Kawamoto N, et al. Three dimensional bone structure around hydroxyl apatite and titanium implants in rabbits.
Clin Oral Implatnts Res. 1999;10:219-225.
50. Osborn JF, Willich P, Meenen N. The release of titanium into human bone from a titanium implant coated with plasma-sprayed titanium. In: Heimke G, Soltesz V, Lee JC, eds.
Clinical Implant Materials: Advances in Biomaterials. Amsterdam: Elsevier; 1990:1:75-80.
51. Lugero GG, Caparbo VF, Guzzo ML, et al. Histomorphometric evaluation of titanium implants in osteo-porotic rabbits.
Implant Dent. 2000;9:303-307.
52. Narkhede PR. A histologic evaluation of the effect of electrical stimulation on osteogenic changes following placement of blade-vent implants in the mandible of rabbits.
J Oral Implantol. 1998;24:185-195.
53. Gotfredsen K, Wennerberg A, Johansson C, et al. Anchorage of TiO
2- blasted, HA-coated and machined implants: an experimental study with rabbits.
J Biomed Res. 1995;29:1223-1231.
54. Vidigal GM Jr, Aragones LC, Campos A Jr, et al. Histomorphometric analyses of hydroxyapatite coated and uncoated titanium dental implants in rabbit cortical bone.
Implant Dent. 1999;8:295-302.
55. Gottlander M, Albrektsson T. Histomorphometric studies of hydroxyapatite-coated and uncoated cp titanium implants in bone.
Int J Oral Maxillofac Implants. 1991;6:399-404.
56. Gottlander M, Albrektsson T, Carlsson LV. A histomorphometric studies of unthreaded hydroxyapatite-coated and titanium coated implants in rabbit bone.
Int J Oral Maxillofac Implants. 1992;7:485-490.
57. Ducheyne P, Liu Q. Bioactive ceramics: The effect of surface reactivity on bone formation and bone cell function.
Biomaterials. 1999;20:2287-2303.
58. Monteiro MM, Rocha NCC, Rossi AM, et al. Dissolution properties of calcium phosphate granules with different compositions in simulated body fluid.
J Biomed Mater Res. 2003;1:299-305.
59. Sul YT, Johansson C, Albrektsson T. Oxidized titanium screws coated with calcium ions and their performance in rabbit bone.
Int J Oral Maxillafac Implants. 2002;17:625-634.
60. Martin RI, Brown PW. Aqueous formation of hydroxyapatite.
J Biomed Mater Res. 1997;35:299-308.
Abstract Translations
GERMAN / DEUTSCH
AUTOR(EN): Nadia A. Badr, BDS, MS, PhD, Amany A. El Hadary, BDS, MS, PhD. Schriftvekehr: Amany A. El Hadary, BDS, MS, PhD, Postfach 621 El-ORMAN 12612 GIZA, Ágypten.Fax: +202 3817591, Telefon: +20 10 5156555/+20 12 3416636, eMail:[email protected]
Charakterisierung von mit Hydroxylapatit elektroplattierten cp-Titan-Implanaten sowie deren Möglichkeiten zur Knochengewebsintegration: eine Studie am lebenden Objekt
ABSTRACT: Zielsetzung: Diese Studie war darauf ausgelegt, die Verwendung einer Beschichtung mit Hydroxylapatit (HA) auf der Oberfläche von cp-Titan-Implantaten unter Anwendung einer Elektroplattierungstechnik zu beschleunigen. Nach einer Charakterisierung der HA-Beschichtung wurde eine Beurteilung der Knochen-Implantat-Schnittstelle und der Knochengewebsintegration von sowohl cp-Titan-Implantaten als auch HA-beschichteten Implantaten durchgeführt. Materialien und Methoden: Zwanzig Implantate wurden zu gleichen Teilen auf zwei Hauptgruppen verteilt (n = 10). 10 (cp-Titan) Implantate wurden wie geliefert verwendet, während die anderen mit einer HA-Beschichtung versehen und sterilisiert wurden. Die Implantate beider Gruppen wurden in die Schienbeine von Neuseeland-Hasen eingepflanzt. Die Reinheit sowie die Kristallisierung der HA-Beschichtung wurden mittels EDX bestimmt. Die Körnungsmorphologie wurde mit Hilfe des Rasterelektronenmikroskops untersucht. Die Oberflächentextur wurde vor sowie nach dem Sterilisierungsprozess über ein Oberflächenmessgerät ermittelt. Die histologische Untersuchung mit dem Rasterelektronenmikroskop wurde zur Qualifizierung des regenerierten Knochengewebes sowie zur Messung der Spaltengröße an der Knochen-Implantat-Schnittstelle eingesetzt. Ergebnisse: Reines Kristallin bei der HA-Beschleunigung mit einer Dicke von 69-78 μm und einer rauen Oberfläche (2,7 ± 0,2 μm) im Vergleich zu den geglätteten cp-Titan-Implantaten (1,3 ± 0,5 μm). Die Sterilisierung unter Anwendung von y-Strahlung ergab eine feinere Körnung und eine nur unwesentlich glattere Oberfläche. Die histologische Untersuchung der cp-Titan-Implantate wies ein geringeres Ausmaß an Knochengewebsintegration mit wenigen und weniger dichten Knochentrabekeln aus. Außerdem war die Spaltengröße deutlich höher (1,29 ± 0,51 μm). Dagegen wiesen die mit HA beschichteten Implantate ein bemerkenswertes Maß an Knochengewebsintegration mit mehr und dichteren Knochentrabekeln auf und der Spaltenabstand bewegte sich in einem Messrahmen von 0-1,32 μm. Schlussfolgerung: Die angewendete Technik führte zur Ausbildung einer dünnen und gleichmäßig kristallinen Beschichtung mit Hydroxylapatit. Die Charakterisierung des beschleunigten Films stellt sich für den langfristigen Behandlungserfolg bei Knochenfixierungen in der klinischen Anwendung als viel versprechend dar.
SCHLÜSSELWÖRTER: Beschichtung mit Hydroxylapatit, Charakterisierung der Oberfläche, Biointegration
SPANISH / ESPAÑOL
AUTOR(ES): Nadia A. Badr, BDS, MS, PhD, Amany A. El Hadary, BDS, MS, PhD. Correspondencia a: Amany A. El Hadary, BDS, MS, PhD, B.O. Box 621 El-ORMAN 12612 GIZA, EGYPT. Fax:+202 3817591, Teléfono +20 10 5156555/+20 12 3416636, Correo electrónico:[email protected]
Caracterización de hidroxiapatita electrogalvanizada a un implante de cp-titanio y su potencialidad de integración al hueso: Estudio In Vivo
ABSTRACTO: Propósito: Este estudio fue diseñado para precipitar un recubrimiento de hidroxiapatita (HA) sobre la superficie de implante (cpTi) usando una técnica de electrogalvanizado. Luego de la caracterización del revestimiento de HA, se evaluó la relación hueso-implante y la integración ósea de los implantes (cpTi) y revestido con HA. Materiales y Métodos: Se dividieron veinte implantes en dos grupos principales (n = 10). Diez implantes (cpTi) se utilizaron como fueron recibidos mientras que los otros fueron revestidos con HA y esterilizados. Se colocaron los implantes de ambos grupos en la tibia de conejos de Nueva Zelanda. Se caracterizó la pureza y cristalinidad de la HA usando EDX. Se examinó la morfología de los granos con SEM. Un perfilómetro evaluó la textura de la superficie antes y después de la esterilización. Se usó análisis histológico a través del SEM para calificar la oseointegración del hueso regenerado y para medir la distancia de contacto entre el hueso e implante. Resultados: El precipitado del espesor de la HA cristalina pura (69 a 78 μm) y superficie áspera (2,7 ± 0,2 μm) comparado con la lisa (cpTi) (1,3 ± 0,5 μm). La esterilización con rayos gamma resultó en granos más finos y una superficie insignificadamente más lisa. El análisis histológico del implante (cpTi) exhibió menos cantidad de regeneración de hueso con menos y menos densa trabéculas óseas y la distancia del espacio fue significativamente alta (1,29 ± 0,51 μm). De mientras, los implantes recubiertos con HA demostraron una cantidad reconocible de regeneración del hueso con más y más densa trabéculas óseas y una distancia del espacio que varió entre (0-1,32 μm). Conclusión: La técnica empleada proporcionó un revestimiento de HA pura y cristalina delgada y uniforme. La caracterización de la película precipitada es prometedora para una adhesión clínica exitosa de largo plazo del hueso.
PALABRAS CLAVES: revestimiento de hidroxiapatita, caracterización de la superficie, biointegración
PORTUGUESE / PORTUGUÊS
AUTOR(ES): Nadia A. Badr, Cirurgiã-Dentista, Mestre em Ciência, PhD, Amany A. El Hadary, Cirurgião-Dentista, Mestre em Ciência, PhD. Correspondência para: Amany A. El Hadary, BDS, MS, PhD, B.O. Box 621 El-ORMAN 12612 GIZA, EGYPT. Fax:+202 3817591, Telefone +20 10 5156555/+20 12 3416636, E-mail:[email protected]
Caracterização de Implante de Titânio-cp Galvanizado por Hidroxiapatita e sua Potencialidade de Integração do Osso; Estudo in Vitro
RESUMO: Objetivo: Este estudo foi projetado para precipitar a camada de hidroxiapatita (HA) na superfície de implantes (cpTi) usando a técnica de eletrogalvanização. Após a caracterização da camada de HA, a interface osso-implante e a integração do osso de ambos os implantes (cpTi) e cobertos por HA foram avaliadas. Materiais e Métodos: Vinte implantes foram divididos igualmente em dois grupos principais (n = 10). Dez (cpTi) implantes utilizados como recebidos, enquanto os outros foram cobertos por HA e então esterilizados. Os implantes de ambos os grupos foram inseridos nas tíbias de coelhos da Nova Zelândia. A pureza e critalinidade da camada de HA foram caracterizadas usando EDX. SEM examinou a morfologia dos grãos. O perfilômetro avaliou a textura da superfície antes e depois da esterilização. Exame histológico por SEM para qualificar a osseointegração do osso regenerado e para medir a distância do gap na interface osso-implante. Resultados: Precipitado de HA puro cristalino com espessura de (69-78 μm) e superfície rugosa de (2.7 ± 0.2 μm) em comparação com a suave (cpTi) (1.3 ± 0.5 μm). A esterilização de radiação-γ resultou em grãos mais finos e superfície insignificante mais suave. Exame histológico de implante (cpTi) exibiu menor quantidade de regeneração do osso com poucas e menos densas trabéculas e a distância do gap foi significantemente alta (1.29 ± 0.51 μm). Enquanto isso, o implante coberto por HA mostrou quantidade reconhecível de regeneração do osso com mais e mais densas trabéculas de osso e a distância do gap começava em (0-1.32 μm). Conclusão: A técnica empregada forneceu camada de HA pura cristalina fina e uniforme. A caracterização do filme precipitado é promissora para fixação óssea clínica bem-sucedida de longo prazo.
PALAVRAS-CHAVE: camada de hidroxiapatita, caracterização da superfície, biointegração
АВТОРЫ: Nadia A. Badr, бакалавр стоматологичeской xирургии, магистр eстeствeнныx наук, доктор философии, Amany A. El Hadary, бакалавр стоматологичeской xирургии, магистр eстeствeнныx наук, доктор философии. Почтовый адрeс: Amany A. El Hadary, BDS, MS, PhD, B.O. Box 621 El-ORMAN 12612 GIZA, EGYPT. Факс:+202 3817591, тeлeфон: +20 10 5156555/+20 12 3416636, Адрeс элeктронной почты:[email protected]
Xарактeристика им плантата из ком мeрчeски чистого титана с элeктрол итичeским гидрокс иапатитовым покры тиeм и eго потeнц иальная оссeоинтe грация: исслeдова ниe in vivo
РEЗЮМE. Цeль: данноe исслeдованиe прeдназначeно для изучeния осаждeния гидроксиапатитового (hydroxyapatite, НА) покрытия на повeрxность имплантата из коммeрчeски чистого титана (commercially pure Titanium, cpTi) с использованиeм элeктролитичeского мeтода. Послe описания гидроксиапатитового покрытия была произвeдeна оцeнка взаимодeйствия с костью и оссeоинтeграции как имплантатов cpTi, так и имплантатов с гидроксиапатитовым покрытиeм. Матeриалы и мeтоды: двадцать имплантатов были раздeлeны поровну на двe основныe группы (n=10). Дeсять имплантатов cpTi использовались бeз обработки, тогда как остальныe были покрыты слоeм гидроксиапатита и затeм стeрилизованы. Имплантаты обeиx групп были установлeны в большeбeрцовую кость новозeландским кроликам. Хистота и кристалличность гидроксиапатитового покрытия опрeдeлялись с помощью исслeдования рeнтгeновского спeктра рассeивания энeргии. Морфология волокон исслeдовалась с помощью сканирующeго элeктронного микроскопа. Структура повeрxности до и послe стeрилизации оцeнивалась с помощью профиломeтра. Гистологичeскоe исслeдованиe с помощью сканирующeго элeктронного микроскопа проводилось для оцeнки оссeоинтeграции восстановлeнной кости и для измeрeния размeра промeжутка в области контакта кости и имплантата. Рeзультаты: чистый кристалличeский гидроксиапатитовый осадок толщиной 69-78 мкм и шeроxоватая повeрxность (2,7±0,2 мкм) сравниваeтся с гладкой при использовании титана cpTi (1,3±0,5 мкм). Стeрилизация с помощью гамма-излучeния обусловила болee тонкиe волокна и нeзначитeльно болee гладкую повeрxность. Гистологичeскоe исслeдованиe имплантата cpTi показало мeньшую стeпeнь рeгeнeрации при нeзначитeльном количeствe и мeньшeй плотности трабeкул кости, при этом размeр промeжутка был достаточно вeлик (1,29±0,51 мкм). В то жe врeмя имплантат с гидроксиапатитовым покрытиeм показал распознаваeмую стeпeнь рeгeнeрации кости при большeм количeствe и большeй плотности трабeкул кости, при этом размeр промeжутка составлял 0-1,32 мкм. Вывод: примeнeнный мeтод обeспeчил получeниe тонкого слоя и однородной кристалличности покрытия. Свойства осаждeнной плeнки открывают пeрспeктиву ee успeшного использования в клиничeской практикe для длитeльной фиксации кости.
КЛЮХEВЫE СЛОВА: гидроксиапатитовоe покрытиe, xарактeристика повeрxности, биоинтeграция
