Biomedical subjects

J G Wolke

Publications and source records attributed to J G Wolke.

At least 19 recordsLinked to original sources

PubMed2000

Effect of surface roughness and calcium phosphate coating on the implant/bone response.

The influence of surface roughness and calcium phosphate (Ca-P) coating on the bone response of titanium implants was investigated. Four types of titanium implants, i.e. as-machined, grit blasted, as-machined with Ca-P sputter coating, and grit blasted with Ca-P sputter coating, were prepared. The Ca-P sputter-coating, produced by using the RF magnetron sputter technique, was rapid heat-treated with infrared radiation at 600 degrees C. These implants were inserted into the left and right femoral condyles and the left and right tibial diaphyses of the rabbits. After implantation periods of 2 and 12 weeks, the bone-implant interface was evaluated histologically and histomorphometrically. Histological evaluation revealed no new bone formation around different implant materials after 2 weeks of implantation. After 12 weeks, bone healing was almost completed. For both tibial and femoral implants, Ca-P coated implants always showed a higher amount of bone contact than either of the non-coated implants. On the other hand, surface roughness improved only the response to implants inserted into the tibial diaphysis. On the basis of these findings, we concluded that 1) deposition of a sputtered Ca-P coating on an implant has a beneficial effect on the bone response to this implant during the healing phase, and 2) besides implant surface conditions the bone response is also determined by local implant site conditions.

Aluminum Oxide↗

PubMed2000

A mechanical evaluation of TiO2-gritblasted and Ca-P magnetron sputter coated implants placed into the trabecular bone of the goat: Part 1.

The influence of Ca-P magnetron sputter coated implants on the mechanical anchorage was evaluated in a goat model. Therefore, uncoated and coated screw designed commercially pure titanium TiO2-blasted implants were inserted into the trabecular bone of the femoral condyles of 12 goats. The thicknesses of the coatings were 0.1 micron (CaP-0.1), 1.0 micron (CaP-1) and 4.0 microns (CaP-4). In addition, uncoated TiO2-blasted implants (Ti) were used as control. Evaluation of the interface strength and appearance, using torque test and scanning electron microscopy, was done at implantation periods of 6 and 12 weeks. Although, especially at 6 weeks of implantation, the Ca-P coated implants showed higher failure torque values than the TiO2 blasted implants, the observed differences for type of implant and evaluation period were not significant (P > 0.1). SEM evaluation showed that all implants with failure values of more than 100 N conducted bone growth into their screw threads. In addition, we observed that the fracture plane for the CaP-4 implants was situated at the coating-implant interface or inside the coating. For the CaP-1 and CaP-0.1 the fracture line could not be determined definitely. For the Ti implants, the fracture torque testing resulted in failure at the bone-implant interface. Therefore, we conclude that all implants resulted in a good bonding strength with the surrounding bone. The sputtered Ca-P coatings seemed to improve the initial fixation of the TiO2 blasted implants.

Animals↗

PubMed2000

A histological evaluation of TiO2-gritblasted and Ca-P magnetron sputter coated implants placed into the trabecular bone of the goat: Part 2.

The aim of this study was to investigate the synergetic influence of surface topography and chemical composition of oral implant materials on bone response. For the experiment screw designed implants were used. The implants were grit-blasted with TiO2 particles. The implants were left uncoated (Ti) or provided with three different amorphous/crystalline Ca-P magnetron sputter coatings, resp. 0.1 micron (CaP-0.1), 1 micron (CaP-1) and 4 microns (CaP-4), in thickness. The implants were inserted in the medial femoral condyles of 12 goats. Each femur received 2 implants. After implantation periods of 6 and 12 weeks the implants were retrieved and prepared for histological and histomorphometrical evaluation (bone contact and bone mass). The light microscopy revealed that bone response to CaP-4 and CaP-1 implants was similar. For example, after 12 weeks, screw threads were almost completely covered with bone. In contrast to CaP-0.1 and Ti implants, where bone apposition was less pronounced. Histomorphometry demonstrated that the bone-to-implant contact for the CaP-1 and CaP-4 implants was significantly higher (P < 0.05) than for the CaP-0.1 and Ti implants. This difference existed already after 6 weeks and was even enhanced after 12 weeks. The bone mass measurements revealed that only at 12 weeks CaP-4 implants had significantly more bone contact inside the screw threads than non-coated Ti-implants (P < 0.05). Supported by our findings, we conclude that the additional application of a 1-4 microns thick Ca-P magnetron sputter coating can further improve the healing response to surface roughened oral implants placed into trabecular bone.

Analysis of Variance↗

PubMed1999

Fatigue behavior of calcium phosphate coatings with different stability under dry and wet conditions.

To obtain stable plasma sprayed calcium phosphate coatings, coatings with a high crystallinity and low solubility were developed. However, stability of ceramic coatings is also influenced by their fatigue resistance. Recently, fatigue failure was proposed to explain coating detachment from implants under loaded conditions. Therefore, plasma-sprayed calcium phosphate coatings with different crystallinity were investigated in vitro for fatigue failure. An amorphous and a crystalline hydroxylapatite coating (AHA and CHA) and a highly crystalline fluorapatite coating (FA) were subjected to cyclic load tests, both in dry conditions and in simulated body fluid (SBF). The results in SBF revealed that the crystalline CHA and FA coating detached completely at the highest stressed middle section of the bar. The FA coating delaminated earlier than the CHA coating. The amorphous AHA coating showed only partial coating loss at the completion of the test. Tests in dry conditions did not reveal any change in the coatings tested. These results suggest a relation between crystallinity of apatite coatings and their failure due to fatigue: high crystallinity coatings demonstrate earlier and more complete fatigue failure than the amorphous apatite coatings. It can be concluded that coating stability is not determined solely by static dissolution, but by fatigue failure as well.

Biocompatible Materials↗

PubMed1999

In vitro dentine hardness following gamma-irradiation and freezing.

OBJECTIVES: To investigate the short term effects of gamma-irradiation and conventional freezing on the hardness of human dentine. METHODS: Twenty-one dentine disks were produced by transverse sectioning 21 sound extracted human permanent molar teeth. The 2.1 mm thick disks were wet polished using 4000 grit polishing paper. Three lines were drawn dividing each disk into six symmetrical areas. Seven disks were randomly assigned for freezing in water at -18 degrees C for 12 days; seven were exposed to a single dose of 25.2 kGy gamma radiation in water; seven were kept in water at 20 degrees C for 12 days (control). Before treatment, three Vicker's indentations at a load of 30 kg and a dwelling time of 20 s were made in one half of each disk, at equal distances from its edge and centre. Using light microscopy and image analysis software, the indentation diagonals were measured 4 h after preparation. Vicker's hardness values (VHN = kg/mm2) were calculated for each indentation. Following the treatment, VHNs were calculated again, for three symmetrical indentations in the second half of each disk. A statistical analysis was performed using the Wilcoxon rank sum test. RESULTS: The frozen group showed no changes following the treatment (VHN = 58 +/- 6 before vs. 57 +/- 6 after). The irradiation and control groups showed some hardening (VHN = 53 +/- 7 vs. 59 +/- 8; 57 +/- 3 vs. 63 +/- 6, respectively), however all values were within the normal variation. CONCLUSION: Both conventional freezing at -18 degrees C for 12 days in water, and a single gamma-irradiation dose of 25.2 kGy in water, appeared to have no short term effects on the hardness of human coronal dentine.

Dentin↗

PubMed1998

In vivo dissolution behavior of various RF magnetron sputtered Ca-P coatings.

Radiofrequency magnetron sputter deposition was used to deposit Ca-P sputter coatings on titanium discs, and these coatings were implanted subcutaneously into the backs of rabbits. Half of the as-sputtered coatings were subjected to additional heat treatment for 2 h at 500 degrees C. X-ray diffraction (XRD) demonstrated that annealing at 500 degrees C changed the amorphous sputtered coating into an amorphous-crystalline apatite structure. Scanning electron microscopic (SEM) examination of the sputtered coatings showed excellent coverage of the substrate surface. Annealing of the 4-microm-thick coatings resulted in the appearance of small cracks. SEM demonstrated that until 4 weeks of implantation, all heat-treated coatings were present and all amorphous coatings were completely or mostly dissolved. Fourier transform infrared spectroscopy showed the formation of carbonate apatite (CO3-AP) on these specimens. Furthermore, XRD analysis showed that these CO3-AP precipitated coatings disappeared after 8 weeks of implantation. On the other hand, SEM inspection of these specimens revealed that the 4-microm heat-treated coating was still partially maintained and that small Ca-P crystals were present on the titanium substrate. On the basis of these results, we conclude that apparently 0.1 microm heat-treated Ca-P sputter coating is of sufficient thicknesses to stimulate carbonate apatite deposition under in vivo conditions.

Animals↗

PubMed1998

Histomorphometrical and mechanical evaluation of titanium plasma-spray-coated implants placed in the cortical bone of goats.

The aim of this study was to investigate the biological and mechanical response of bone to titanium plasma-sprayed implants of different roughnesses. Three types of titanium plasma-spray coating were applied to beam-shaped implants: Ti2, Ti3, and Ti4, with a Ra of 16.5, 21.4, and 37.9 microm, respectively. An Al2O3 grit-blasted implant (Ti-un) with a Ra of 4.7 microm was used as a control. In total, 72 implants were inserted in the tibial cortical bone of nine adult female goats. These implants were evaluated histologically and mechanically 3 months after implantation. At the end of the experiment, of the 72 inserted implants, two implants (one Ti2 and one Ti4) were lost. Histological evaluation of the other retrieved implants revealed a uniform bone reaction for all implants. The unloaded plasma-spray coatings showed no signs of delamination at the implant-coating interface. Occasionally, particles of the Ti4 coating broke free and were found near the implant. Histomorphometry revealed no difference in bone contact for the different implants (P > 0.05). Furthermore, the push-out test showed no significant difference (P > 0.05). Linear regression showed no interaction between the push-out values and the roughness values (r = 0.5). On the basis of these results, it may be concluded that the used surface roughnesses did not lead to differences in bone response or mechanical attachment strength in goat cortical bone.

Animals↗

PubMed1998

Subperiosteal implantation of various RF magnetron sputtered Ca-P coatings in goats.

The aim of this study was to obtain more information about the initial biological events around RF magnetron sputtered calcium phosphate (Ca-P) coatings. Therefore, uncoated and coated disks were inserted subperiosteal into the tibia of a goat. The coatings were deposited on commercially pure titanium. The thickness of the coating was 0.1 or 2.0 microm. All the as-sputtered coatings were subjected to an additional heat treatment for 2 h at 500 degrees C. After 1 and 3 weeks of implantation the experimental disks were retrieved and prepared for histological and physicochemical analysis. The histological results demonstrated that the periosteum covered the specimens after both implantation periods. In between the periosteum and implant an acellular layer and a collagen matrix was observed. Energy dispersive spectrometry revealed that the acellular layer consisted of C, Ca, and P ions for the 0.1 microm thick Ca-P coatings. The 2 microm thick Ca-P coatings also showed the presence of sulfate ions in this layer. Only organic material was found on the titanium disks. Further, SEM showed that even after 3-week implantation, a substantial thickness of both coatings was still maintained. Thin film X-ray diffraction demonstrated that after both implantation periods, the CaP-0.1 coating was still present. FTIR of the retrieved specimens demonstrated on the coated disks the formation of additional carbonate apatite (CO3-AP) associated with an organic phase (NH2 groups). On basis of these findings we conclude that our experimental approach is very suitable for the investigation of the healing process around Ca-P coatings. Further, we again demonstrated that the initial interfacial response to Ca-P materials differs from titanium.

Animals↗

PubMed1998

The effect of titanium plasma-sprayed implants on trabecular bone healing in the goat.

The bone response to different titanium plasma-sprayed implants was evaluated in a goat model. Therefore, beam-shaped implants were installed into the trabecular femoral condyles of 10 goats. These implants were provided with three different titanium plasma-sprayed coatings (Ti2, Ti3 and Ti4) with a Ra of 16.5, 21.4 and 37.9 microm, respectively. An Al2O3 grit-blasted implant (Ti-un) with a Ra of 4.7 microm was used as control. After an implantation period of 3 months, the implants were evaluated histologically and histomorphometrically. Only one implant (Ti3) was not recovered after the evaluation period. Light microscopy showed a limited amount of bone for the various implants. Most of the implants showed a different degree of fibrous tissue alternating with direct bone contact. Complete fibrous encapsulation of the implants was observed in some of the sections. No signs of delamination of the plasma-sprayed coating was visible. No significant difference in bone contact were measured between the different types of implants (P > 0.05). Histomorphometrical analysis revealed significantly higher bone mass close to the implant (0-500 microm) for the Ti3, Ti4 and Ti-un implants placed in the medial femoral condyle and the Ti4 implants placed in the lateral condyle. At distance (500-1500 microm), no difference in bone mass measurements between the different implants was observed (P > 0.05).

Aluminum Oxide↗

PubMed1998

Bone healing capacity of titanium plasma-sprayed and hydroxylapatite-coated oral implants.

The influence of surface quality, in particular surface topography and implant material, was evaluated by inserting titanium- and hydroxylapatite plasma-sprayed coated implants into the maxilla of 10 goats. Three types of plasma-spray coatings were applied to tapered, screw shaped implants; titanium plasma-spray coating (TPS), titanium plasma-spray coating with additional acid passivation (TPSA) and a bilayered coating (TPS/HA) consisting of titanium plasma-spray coating (TPS) and a hydroxylapatite part (HA). In addition, as-machined implants (TiM) were used as control. A total of 40 implants were inserted according a balanced split plot design. At the end of a 3-month healing period, it appeared that 5 implants (2 TPS, 1 TPSA, 1 TPS/HA and 1 TiM) were lost. Histological examination revealed a stronger bone response to TPS/HA coated implants. Even the TPS/HA coated implants induced bone formation on the part of the implant inserted into the sinus. No signs of delamination of the TPS coatings were visible. The HA part of the dual coating showed signs of degradation. Histomorphometrical analysis confirmed these findings. A significant difference in bone contact (P < 0.05) was measured between the TPS/HA coated implants and the other types of implants. Linear regression (r = 0.27) showed no correlation between the inscrew values at the base line and the bone contact measurements 3 months after healing. On the basis of these results, we can conclude that the chemical composition of the HA coating has a positive influence on the bone reaction. The influence of roughness is less evident.

Alveolar Process↗

PubMed1998

Calcium phosphate coatings for medical implants.

In surgical disciplines where bone has to be repaired, augmented or improved, bone substitutes are essential. Although bone banks, such as Eurotransplant, are founded to supply such substitutes, natural bone is not always adequate. For example, frequently these so-called bone grafts resorb after implantation (1). Further, they cannot be used for joint and tooth replacement, and recently worries have been raised about the transfer of infectious diseases. Therefore, interest has dramatically increased in the use of synthetic materials for replacement of lost or damaged bone tissue. The generic name of these tissue alternatives is biomaterials. A special class of these biomaterials is composed of metallic devices with coatings to improve bone bonding. These specialized coatings used to improve the metallic implant are the topic of this paper.

Adhesiveness↗

PubMed1997

The effect of Ca-P plasma-sprayed coatings on the initial bone healing of oral implants: an experimental study in the goat.

The response of bone of low density to uncoated, fluorapatite (FA), hydroxyapatite (HA), and hydroxyapatite heat treated (HAHT) plasma-sprayed coated implants was investigated 3 and 6 months after installation. Forty-eight threaded implants of commercially pure titanium were inserted into the maxilla of twelve goats according to a split-plot design. One goat died shortly after installation of the implants, five goats were sacrificed 3 months after installation, and the other six goats 6 months after installation. Histological evaluation revealed no difference in bone reaction between the 3- and 6-month implantation periods. In addition, probably due to the wide inter- and intra-animal variability, no significant difference between the 3- and the 6-month periods could be observed in the histomorphometrical measurements performed. Further, no significant differences were found in bone reaction among the various implant materials. Finally, qualitatively it appeared that all coatings showed reduction in coating thickness and that such reductions were most pronounced for the HA coatings.

Animals↗

PubMed1997

A histological and histomorphometrical evaluation of the application of screw-designed calciumphosphate (Ca-P)-coated implants in the cancellous maxillary bone of the goat.

Various studies already have shown that the occurrence of oral implant failure is higher in the maxilla than in the mandible. To learn whether Ca-P coatings can improve the success rate of oral implants in the maxilla, three different plasma-sprayed, Ca-P-coated, self-tapping Brånemark implants were inserted in the trabecular bone of the maxilla. Before the insertion of the implants, the two first upper premolars of 16 goats were bilaterally extracted. Four months later, each animal received four types of implants: three different Ca-P-coated types and one uncoated. After an endosseous period of 6 months, the implants were provided with permucosal abutments. Four months later the animals were killed. At the end of the experiment, it appeared that 10 of the 16 installed noncoated implants had failed while of the 48 Ca-P-coated implants, only 6 had failed. All successful implants were retrieved and prepared for histomorphometrical evaluation of the bone and gingiva response. The Ca-P-coated implants showed a significantly greater percentage of bone in contact with the implant surface compared with the uncoated implants. The length of the epithelium was not significantly different for the coated compared to the uncoated implants, but the connective tissue was significantly thicker for the noncoated implants than for the Ca-P-coated implants. Also, measurements revealed that all coatings showed reduction in thickness. On the basis of these findings, we concluded that the application of Ca-P coatings (1) improves the bone-implant reaction, although all coatings reduced in thickness, and (2) is of benefit during the healing period in less mineralized trabecular bone.

Animals↗

PubMed1997

Influence of rapid heating with infrared radiation on RF magnetron-sputtered calcium phosphate coatings.

This study evaluated the effect of rapid heating with infrared radiation on the physico-chemical and morphological properties of radio frequent (RF) magnetron-sputtered calcium phosphate (Ca-P) coatings. About 2.5 microm thick Ca-P coatings were deposited on titanium disks and cylinders. These specimens were left untreated or were heat treated by infrared radiation at 300, 400, 500, 600, and 700 degrees C for 4, 7, 11, 17, and 24 s. Subsequently, the specimens were immersed in simulated body fluid (SBF) for 1 day, 1 week, and 5 weeks. X-ray diffraction measurements showed that heating at 500 degrees C or higher resulted in an increase of coating crystallinity. In addition, FT-IR measurements revealed the appearance of OH peaks in the spectra of samples treated at 500-700 degrees C. Electron probe microanalysis showed that after 5 weeks of immersion about 40-50% of the coatings heat treated at 500 and 600 degrees C was maintained. The coatings heat treated at 700 degrees C showed no dissolution at all. On the other hand, as-coated and 300 degrees C treated films were dissolved within 1 day. Scanning electron microscopy of the samples showed that directly after heat treatment no apparent cracks were present in the coatings. On the basis of these findings, we conclude that rapid heating with infrared radiation around 600 degrees C is the best heat treatment for RF magnetron-sputtered coatings.

Biocompatible Materials↗

PubMed1997

Stability of radiofrequency magnetron sputtered calcium phosphate coatings under cyclically loaded conditions.

The stability of radiofrequency (RF) magnetron sputtered calcium phosphate was studied under cyclically loaded conditions. The coatings were deposited on titanium bars and tested in either dry or wet conditions X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and Fourier transform infrared (FTIR) spectroscopy were used to characterize the as-sputtered and tested coatings. XRD demonstrated that the amorphous structure after annealing at 650 C changed into a crystalline apatite structure. The residual stresses were determined by the XRD cos 2 i/i method. These residual film stresses were influenced by the coating conditions and the crystalline sputtered coating showed the presence of compressive stresses. SEM demonstrated that, after cyclic loading conditions in air, the crystalline sputter-coated Ti-6A1-4V bars showed a partial coating loss. Furthermore, in wet conditions (simulated body fluid) only the heat-treated sputter-coated bars appeared to be stable. On the other hand, the amorphous coating only showed signs of delamination in the more highly stressed regions, while in the less stressed regions a Ca-P precipitate was formed. On the basis of these results we conclude that calcium phosphate coatings subjected to cyclic loading conditions show an important difference in fatigue behaviour when tested in either dry or wet conditions.

Absorptiometry, Photon↗

PubMed1997

Formation and characteristics of the apatite layer on plasma-sprayed hydroxyapatite coatings in simulated body fluid.

Plasma-sprayed hydroxyapatite (HA) coatings were incubated in simulated body fluids (SBFs) for different periods of time to investigate the nucleation and growth of apatite on their surface. The layer that formed was recognized as having similarities to bone apatite because it is poorly crystallized, non-stoichiometric or calcium deficient, and contains carbonate and magnesium. Scanning electron microscopy (SEM) and infrared spectroscopy (IR) were employed to investigate the morphological changes of the coating surface and the structure of the grown layer respectively. In the first few hours, calcium and phosphate ions dissolved from the coatings so as to increase their local supersaturation to a higher degree, thereafter followed by the nucleation and growth of apatite. The nucleation occurred firstly on the recessed regions, inside pores and cracks where the higher supersaturation was readily maintained. Only after 24 h incubation was a complete layer formed on the surface of the coating. There is no obvious interface between the grown layer and the underlying coating. Heat treatment in the air made the apatite transform into biphasic calcium phosphate of HA and tricalcium phosphate, with a blue colour because of trace manganese ions. The heat-treated HA coating showed no dissolution by SEM observation. This resulted in no precipitation on the surface. When SBF was used with two-fold higher ion concentrations, the apatite layer formed slowly in 72 h without dissolution of the coating surface. This may mean that the microenvironment with a sufficiently high degree of supersaturation of calcium and phosphate ions is crucial for apatite to nucleate and grow in SBF, while the HA crystalline structure is not critical in the nucleation process, as expected.

Apatites↗

PubMed1997

Fast precipitation of calcium phosphate layers on titanium induced by simple chemical treatments.

A simple two-step chemical treatment, i.e. etching with HCl and H2SO4 followed by immersion in boiling dilute NaOH solution, has been developed by our group to prepare bioactive microporous titanium surfaces allowing fast deposition of a calcium phosphate layer (CPL) from an in vitro supersaturated calcification solution (SCS). In this work, a precalcification (Pre-Ca) procedure was applied by soaking the two-step treated titanium in Na2HPO4 and then saturated Ca(OH)2 solution before immersion in SCS to accelerate further the CPL precipitation. The treated titanium surfaces with Pre-Ca were characterized after 1, 2, 4, 8 and 16 h of immersion in SCS by means of scanning electron microscopy together with energy dispersive X-ray analysis, X-ray diffraction and infrared absorption analysis. It was observed that the CPL precipitation rate with Pre-Ca averaged 1 microm h-1, twice as fast as without Pre-Ca. No precipitation was observed on untreated titanium with Pre-Ca up to day 14 of immersion in the SCS.

Calcium Hydroxide↗

PubMed1996

Evaluation of plasma-spray and magnetron-sputter Ca-P-coated implants: an in vivo experiment using rabbits.

The bone response to different plasma-spray and magnetron-sputter calcium phosphate (Ca-P)-coated implants was evaluated in a rabbit animal model. Four types of Ca-P coatings have been investigated: a plasma-spray Ca-P coating (HA-PS), a heat-treated plasma-spray Ca-P coating (HA-PS/ht), an amorphous magnetron-sputter coating (Ca-P-a), and a crystalline magnetron-sputter coating (CA-P-c). Seventy-two specially designed cylindrical implants were inserted in the lateral and medial femoral condyles of 18 New Zealand White rabbits. The four differently coated implants were positioned in one animal according to a split-plot design. After implantation periods of 3, 6, and 9 weeks, the bone-implant interface was evaluated histologically. Besides descriptive light microscopical evaluation, quantitative histomorphometrical measurements were done to determine bone contact and the amount of bone surrounding the implant-bone interface. Light microscopical examination revealed that all types of coatings followed the same process of bone healing. Measurements of bone contact at 6 and 9 weeks did not reveal significant differences between the various coatings. For the amount of bone, in a circular region at a certain distance from the implant, the Ca-P-c-coated implants showed a significantly greater amount of bone after 6 weeks of implantation than did the other three Ca-P coatings. At 9 weeks this difference could no longer be measured. On the basis of these findings we concluded that magnetron-sputtered Ca-P coatings show the same process of bone healing as the plasma-sprayed Ca-P coatings when inserted into the trabecular femoral bone of rabbits.

Animals↗