W. Kalk

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.

Eleven-year study of hydroxyapatite implants

An 11-year clinical research study was conducted with both unloaded bulk hydroxyapatite implants and loaded hydroxyapatite-coated titanium implants. A total of 102 submerged bulk hydroxyapatite implants were placed after extraction of teeth to maintain the volume of the residual alveolar ridge by their physical presence. All 21 implants under fixed partial dentures and 51 of 81 implants under lower complete dentures remained submucosal. A total of 71 hydroxyapatite-coated titanium implants were connected with permucosal superstructures by use of a two-stage method. Modifications in design and in implantation technique were required. This long-term research indicates that cylindrical hydroxyapatite implants are reliable devices as natural tooth root substitutes that bond directly to bone instead of simply being osseointegrated.

Biodegradation of four calcium phosphate ceramics;in vivo rates and tissue interactions

To prevent exposure of artificial tooth root implants, a resorbable root implant may be developed, that in time will resorb in a vertical direction at the same rate as the alveolar ridge does after the loss of the natural teeth. Implants of four calcium phosphates: rhenanite, β-tricalcium phosphate, hydroxylapatite and magnesium-whitlockite were measured duringin vivo resorption and their interactions with the surrounding tissues at experimental periods of 6 weeks and 3 months were investigated. It was shown that a sequence of progressive resorptionin vitro does not correlate with the resorption rates found in thisin vivo experiment.In vivo hydroxylapatite was found to be less resorbable than magnesium-whitlockite and rhenanite less resorbable than β-tricalcium phosphate. Tissue interactions showed that resorption of the calcium phosphates was positively related to the number of osteoclast-like cells and did not completely correlate with the resorption measurements insofar that most rhenanite implants showed a more reactive peri-implant with the largest number of osteoclast-like cells, strongly affecting the implant surface. In contrast, two rhenanite implants showed intimate contact with bone after initial resorption. Because of this divergent reaction with rhenanite, furtherin vivo investigation on this material is proposed.

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.

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.

A histological and histomorphometrical evaluation of screw type calciumphosphate (Ca-P) coated implants: an in vivo experiment in maxillary cancellous bone of goats

The bone response to different calcium phosphate (Ca-P) coated implants was evaluated in a goat animal model. Two types of plasma spray coatings were applied to a commercially pure titanium (cpTi) tapered, conical screw-design implant (BioComp®); hydroxyapatite (HA-PS) and a dual coating, consisting of FA and HA (FA/HA-PS). In addition an amorphous RF magnetron sputter coating (Ca-P-a) and uncoated implants were investigated. Forty-eight implants were inserted in the maxilla of 12 adult female goats. After implantation periods of 3 and 6 months, the bone implant interface was evaluated histologically and histomorphometrically. After both implantation periods all plasma spray coated implants were maintained. On the other hand three Ca-P-a and two cpTi implants were lost. Histological examination revealed a better bone response to both plasma spray coated implants. Histomorphometrical evaluation confirmed this finding. At 3 and 6 months significantly higher percentages of bone contact (p<0.001, ANOVA) were measured for both plasma spray coated implants than for the cpTi and Ca-P-a implants, while no significant difference (p<0.05) existed between both implantation periods. Degradation of both plasma spray coatings was observed. Supported by the results, it is concluded that, although Ca-P coatings can improve the performance of dental implants, the presence of a Ca-P coating is not the only important factor for bone healing around implants placed in low density trabecular bone.

In vivo reactions to particulate rhenanite and particulate hydroxylapatite after implantation in tooth sockets

To gain more information on the in vivo behaviour of rhenanite (CaNaPO4), particles of this material and of hydroxylapatite were mixed with gelatin or saline and inserted in tooth sockets of beagle dogs for periods of 3 and 6 months. Rhenanite appeared to transform into an apatite containing carbonate, sodium and magnesium. Resorption of both calcium phosphate particles was not observed histologically and was not shown histomorphometrically. Calcium phosphates were not found in lymph node tissue. The presence of particles in the sockets gave rise to new bone formation. Histomorphometry demonstrated that statistically significant more bone deposition occurred on rhenanite particles than on hydroxylapatite particles. Also gelatin, meant as a spacer, contributed to new bone formation.

Assessment of bone surrounding implants in goats: ex vivo measurements by dual X-ray absorptiometry

The aim of the present study is to determine the possibility of measuring the bone mineral density (BMD) around implants by dual energy X-ray absorptiometry (DEXA). Therefore, the trabecular BMD was measured close to 127-600 microns and at a distance from various uncoated and Ca-P-coated implants inserted into the femoral condyle of goals. The implants were left in situ for 12 weeks. In addition, the bone-implant interface was evaluated histologically. For comparative reasons the BMD of non-implanted lateral and medial femoral condyles was also measured. The reproducibility of the measurements, expressed as a coefficient of variation, was found to be 0.44%. Moreover, the regions closest to the implants exhibited a higher BMD than all other regions, and the regions located in the medial condyle showed a higher BMD than the lateral condylar regions. Although the histological sections of the implants in the medial condyle demonstrated more bone contact with the coated than with the uncoated implants, a higher density was measured around the uncoated implants. The results regarding the non-implanted condyles indicated a higher density in the medial than in the lateral condyle. In view of these results, we conclude that BMD around dental implants depends on the location of the implant and that DEXA appears to be an excellent tool for analysing bone-implant reactions.

Fluorapatite and Hydroxyapatite Heat-Treated Coatings for Dental Implants

Sintered fluorapatite and hydroxyapatite ceramic implants have been shown to be non-degradable in animal and human research. It was found however that plasma-sprayed coatings of hydroxyapatite ceramic degraded in vivo, possibly because the ceramic lost almost 50% of its crystallinity during the plasma-spraying procedure. A heat treatment at 600° C proved to be the method op choice to reconstitute the crystallinity of the hydroxyapatite coating and to promote the transformation of α -tricalcium phosphate into the more stable β -tricalcium phosphate. Fluorapatite coatings did not loose their crystallinity during plasma-spraying and had the added advantage of stability due to the fluoride ion. The solubility in vitro of the fluorapatite and hydroxyapatite heat-treated coatings were compared to the sintered hydroxyapatite ceramic and the untreated hydroxyapatite coatings. Heat treatment reduced the dissolution rate of the hydroxyapatite coating which originally was 92%, to only 9%, while 13% of the fluorapatite coating was found to dissolve.

Composites of hydroxyapatite and bisphosphonate: properties and alveolar bone response

A composite was made by adsorption of the bisphosphonate [(3-dimethylamino-1-hydroxypropylidene)-1,1-bisphosphonate; dimethyl-APD] into an hydroxyapatite (HA) tube. Adsorbed dimethyl-APD did not change the bulk properties of the HA tube but the surface properties were altered. The amount of 0.1 mmol/L dimethyl-APD adsorbed into the HA tube was 0.78 ( ± 0.20) μg after 4 weeks. The composite tube of HA and dimethyl-APD placed after extraction of teeth in the premolar regions of dogs were biocompatible, stable and bonded strongly and intimately to the alveolar bone. Although there was no bone resorption around the composite tubes, no conclusion can be drawn yet from this study as far as local inhibition of alveolar bone resorption is concerned.