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Direct pulp capping with a hydroxyapatite ceramic in rat molars induced the formation of reparative dentin in the exposure sites after 2 weeks. In addition, foci of acute and chronic pulpitis were detected. After 6-8 weeks of application of the material partial or total necrosis occurred. The use of hydroxyapatite as a possible pulp capping material is discussed.
Hydroxyapatite is a mineral substance which, day after day, is getting success, in the field of odontology, thanks to the versatility of its uses. After having been employed on the different methods that the dentist has at his disposal, in order to make up for the alveolar ridge atrophy, a case has been explained, that has been solved through the use of porous hydroxyapatite, referred to as "Interpore 200".
Bone attachment to two classes of hydroxyapatite (HA) coated polymers was evaluated mechanically and histologically. Particulate HA was molded into the surface of thermoplastic implants and cast into the surface of thermoset implants. Coated and uncoated implants of both types were implanted in the distal femurs of rabbits for four and twelve weeks. After sacrifice, the bone/implant interface was evaluated mechanically via a push-out test with a servohydraulic test system. Paired statistical analysis revealed significantly greater shear strengths for coated vs. uncoated implants for both polymer systems at both time periods. Mixed mode of failure occurred with particle removal from the polymer surface and from the bone. One animal at each time period was saved for histology. Histology at both time periods indicated direct bone apposition to the HA coating as compared to a fibrous encapsulation about the uncoated implants. This was confirmed with backscatter scanning electron microscopy and scanning acoustic microscopy. Hydroxyapatite coatings significantly improve the bond strength between polymers and bone by allowing direct bone apposition and some mechanical interlocking with the bone.
Salivary protein involvement in the formation of acquired enamel pellicle, so far, has been discussed in terms of hydroxyapatite (HA)-reactive salivary proteins only from the parotid gland. This study was undertaken to seek this type of protein in the human whole (mixed) saliva and to investigate its normal and pathological variations. Several kinds of hydroxyapatite, either biogenous or synthesized by solid phase reaction, were used as a powder (250 mesh). HA was incubated with concentrated whole saliva at 25 degrees for 30 min. After centrifugation and filtration salivary proteins were analysed on a Multiphor isoelectrofocusing gel electrophoresis. The control salivary proteins were separated into three major groups; acidic (A1-A8), neutral neutral (N1-N4), and basic (B1-B3) isoelectric point (pI). In the HA incubated sample, one of the major neutral bands (NI) preferentially disappeared at about pI 7.5. This NI band was missing or scarce in the parotid saliva and had an amino acid composition rich in glycine, lysine, serine, glutamic acid, aspartic acid, and histidine. This protein was considered to be one of the major HA-reactive proteins in human whole saliva.
Adsorption of human salivary protein on synthetic hydroxyapatite after fluoridation of the mineral phase was tested using an experimental system previously described. The salivary protein adsorption on fluoridated apatite was considerably decreased compared to the adsorption obtained with untreated hydroxyapatite. The calcium-precipitable human salivary glycoprotein still seemed to be selectively adsorbed. Liberation of fluoride under the effect of the salivary proteins was also observed. Fluoridation of enamel may decrease pellicle formation with competitive adsorption effect between salivary proteins and fluoride.
High-performance liquid chromatography using spherical aggregates of strontium-phosphate hydroxyapatite(SrHA) micro-crystals as adsorbent has been developed; preliminary performance tests were carried out by using several types of protein. It can be deduced that, in parallel with the case of usual calcium-phosphate hydroxyapatite(CaHA), with SrHA also, two types of effective surface, vector a (or vector b) and vector c surfaces, appear on the crystal: the same protein molecular generally shows slightly different chromatographic behaviors between the CaHA and the SrHA packed column. Combining the SrHA and the CaHA packed column would lead to an efficient fractionation of a particular molecule from an assembly of molecules with subtle structural differences from one another.
Histopathologic study was done to reveal the difference of bony interface in the mandibular bone between titanium blade implants and titanium implants coated with the mixture of hydroxyapatite-alumina by the plasma-spray technique, using the improved undecalcified histologic technique and the image analyzing system. In 4 adult shepherd dogs, the implantation was performed in the molar region of the mandible 2 months after tooth extraction. The coated implants and the non-coated ones were inserted respectively in the mandibles. They were sacrificed on the 5th, 7th, 14th and 28th day postoperatively. In 5-day implant after insertion, granulation tissues or fibrous connective tissues were observed around both implants in bone tissues. In 7-day implant, osteoid tissues regenerated around the apex of both implants, but attached a little to them. In 14-day implant, osteoid tissues or woven bone regenerated around both implants and attached more to the coated implant (approximately 13.7%) than the non-coated one (approximately 6.0%). In 28-day implant, regenerative woven or lamellar bone attached much more to the coated implant (approximately 63.4%) than the non-coated one (approximately 8.8%). Bony interface increased remarkably in the coated implants, chronologically. The results showed that the plasma-sprayed hydroxyapatite-alumina coating was effective for the initial fixation of endosseous dental implants.
Porous hydroxyapatite (Interpore 500) formed by conversion of the Porites goniopora coral exoskeleton has pores averaging 600 micrometers and pore interconnections averaging 260 micrometers in diameter. In the proximal tibial metaphysis of eight dogs, a defect one cubic centimeter in size was created unilaterally and was fitted with a block of Interpore 500. Both proximal tibial metaphyses were retrieved at two, four, six, and twelve months. Stained undecalcified sections were examined by light microscopy and quantitated by histometric methods. The implant-side specimens contained compact bone along the external surface and trabecular bone interiorly. The interior of these specimens was composed of 51.9 +/- 1.3 per cent soft tissue, 13.0 +/- 1.2 per cent bone, and 35.1 +/- 1.2 per cent Interpore 500 (mean and standard error). The interior of the normal specimens was composed of 79.7 +/- 1.4 per cent soft tissue and 20.2 +/- 1.4 per cent bone. The allocation of implant pore space between bone and soft tissue was proportional to that of bone and soft tissue in the normal tibiae. The stereological distribution of regenerated bone in the porous hydroxyapatite was also the same as in the normal tibiae. The appositional process of incorporation of the implant was confirmed by the finding that 66.5 per cent of the surface of the Interpore 500 was covered with bone ingrowth at twelve months.
For the development of a new implantable biomaterial that possesses osteogenetic ability, bone matrix morphogenetic proteins were bound to hydroxyapatite (BMP-HAP). A crude protein extract including the bone morphogenetic protein (BMP) fraction was precipitated in the pores of hydroxyapatite (HAP) inside of a dialysis sac. In tissue culture, BMP-HAP or HAP was used as substratum for rat mesenchymal muscle cell explants. The BMP-HAP and HAP controls were also implanted in the muscle pouches of mice. New cartilage and/or new bone formation was observed on the exterior surface of BMP-HAP but not of HAP controls. Implantation of this HAP into bone marrow cavities of rabbit femoral and tibial condyle produced new bone formation. The deposits extended further inside BMP-HAP than HAP pores. The pore diameters of 90-200 microns produced earlier ingrowth than into larger pore sizes. BMP-HAP should be tested for clinical application as osteogenetic biomaterial for augmentation of bone regeneration.
The effect of phytate on the adsorption of purified human salivary mucins (HWSM) onto hydroxyapatite (HAP) was studied using three incubation conditions. a. Preadsorption of HWSM onto HAP for 24 h, followed by 4 h coadsorption with phytate, resulted in at most a 25% decrease in HWSM binding. b. Preincubation of HAP with phytate for 24 h, followed by 4 h coadsorption with HWSM, resulted in a 40% decrease in binding of HWSM to HAP. c. Simultaneous incubation of HWSM and phytate with HAP resulted in a 50% decrease in HWSM binding. In contrast, the adsorption of phytate to HAP was not affected, irrespective of the incubation set up used. The adsorption of phytate to hydroxyapatite was accompanied by an increase in the phosphate concentration of the solution. The molar ratio of phosphate solubilized/phytate bound to HAP was approximately 2 to 3. On the other hand, under conditions when all phytate added became bound to HAP (i.e. HAP in excess over phytate), no increase in Ca-ions was observed. However, when free phytate was present (phytate in excess over HAP) approximately one mole of Ca-ions was released per mole free phytate. For comparison, the effect of phytate on the adsorption of porcine gastric mucin (PGM) and ovine submandibular mucin (OSM) was studied. Under conditions when HWSM binding to HAP was decreased by 10%, binding of PGM and OSM decreased by 65% and 100%, respectively.
Blocks of porous hydroxyapatite (dimensions, 2 X 3 X 4 mm3; sintering temperature, 1,150 degrees C; macroporosity, 48%; pore diameter, 50-300 microns) were implanted into the intervening space between the tibial periosteum and the tibialis anterior muscle in 36 male Wistar rats at the age of 5 months. Specimens from the lower leg were obtained 1, 2, 3, 5, 8 and 12 weeks after implantation. The implants were found to adhere firmly to the tibialis anterior in the 5 and 12 week-specimens. No inflammatory reactions were seen around the implants and a layer of fibrous tissue was observed between the implanted apatite block and the muscle in all specimens. The fibrous tissue penetrated deeply into pores of the apatite block. The resistance to pulling of the interface (3 X 4 mm2) between porous hydroxyapatite and the tibialis anterior muscle was measured using a universal testing machine. The mean of the resistance to pulling was 24.7 +/- 5.1 gf/mm2 in 4 specimens of 12 weeks implantation.
Recent evidence suggests that bone phosphate exists almost entirely as hydroxyapatite (HA). The relative deficiency of calcium and presence of substantial HPO2-4 in bone phosphate indicates modification of the ideal HA structure, however. An inability to resolve closely spaced lines in fine grained materials, coupled with the limited periodicity of the thin mineral crystals of bone have prevented definitive characterization of the structure of bone mineral using standard X-ray diffraction (XRD) techniques. We have applied computer deconvolution XRD techniques to aid in the resolution of component overlapped profiles from bone, synthetic hydroxyapatite (HA) and mixtures of bone and synthetic HA resulting from implantation studies. In the course of this resolution process separate profiles were resolved from the (002) profile of bone derived HA. The ratio of integrated intensities of these profiles to the intensity of the profile of synthetic HA appears to provide an approximate measure of the ratio of bone to synthetic HA in a given sample. The finding of shoulders on the (002) peak of bone provides the basis for resolution into separate profiles. The asymmetry of these shoulders in mature bone cannot be attributed to crystallinity, particle size, or computer artifact. The same finding has been previously reported in hydrolyzed, deproteinated bone. Further work will be needed to resolve the question of whether the structural heterogeneity implied by profile geometry is the result of multiple HA phases, surface layer structure involving hydrolysis and calcium absences, or some other factor.
A porous hydroxyapatite tracheal prosthesis was implanted in rabbits after resection of a 15 mm circular segment of the cervical trachea. Postoperatively the animals were followed by radiography, bronchoscopy, and microscopy at the time of autopsy. The longest survival time was 22 weeks. All the rabbits died of infection at the prosthetic site or of progressive stenosis at the anastomoses. The prosthesis was incorporated by surrounding tissues, but no overgrowth of ciliated epithelium on the luminal surface of the prosthesis was observed. Although a hydroxyapatite tracheal prosthesis is tolerated in rabbits, covering of the luminal surface of the prosthesis with a non-porous layer to prevent infection and to permit mucosal overgrowth is necessary to achieve better long-term results.
The present work is concerned with a sensitive and fast micromethod for separation of single- and double-stranded molecules of nucleic acid by hydroxyapatite (HAP) thin-layer chromatography. The thin layers were obtained by precipitation of ground HAP particules into the surface of the plates in water. Chromatography in sodium phosphate buffer makes it possible to separate from 1 to 50 micrograms of nucleic acids for 30--50 sec. Thereby double-stranded molecules remain at the starting line, whereas single-stranded DNA or RNA follow up the solvent. For quantitative assay of nucleic acids by HAP thin-layer chromatography, the plates were scanned in UV light, radioactivity was measured without extracting substances from HAP and DNA and RNA were eluted with the help of phosphate buffer. A simple and accurate determination method has been suggested consisting in dissolving HAP in perchloric acid followed by hydrolysis of nucleic acids and spectrophotometry of solutions. The retrieval of the material after chromatography in 99 +/- 2%, the mean determinations error is 2--3%. The conditions are described for extraction, after thin-layer chromatography, of desalted and concentrated DNA, ready for use in later experiments. The paper describes a method: for determination of the degree of DNA nativity; quantitative determination of DNA in solutions, containing admixtures; separation of synthesized RNA from its precursors and from the DNA template; assay of DNA thermostability; investigation of the kinetics of DNA reassociation and DNA-DNA hybridization. Some results obtained from hydroxyapatite thin-layer chromatography are discussed.
Experimental histologic and biomechanical studies were performed in 52 dogs by use of a bone substitute composed of hydroxyapatite converted from sea coral calcite. The results demonstrate some potentially useful practical applications. The material was totally incorporated in bone. Although initially too weak to tolerate physiologic stresses, once incorporated it becomes almost as strong as the native bone. Clinical experience with internal fixation of fractures with hydroxyapatite in 18 patients is encouraging.
Adsorption isotherms of alizarin red S on hydroxyapatite were supplemented with additional data to provide a simple model of adsorption. The model treats the adsorbing surface as a mosaic of unit cell a-c faces which have an area of 65 A2 each. The adsorbate of the model has molecular dimensions consistent with a 1:1 relationship between adsorbate and adsorption site. By comparing slurries of hydroxyapatite which differed by a factor of 4 in surface area of the solid, it was found that the isotherm based on edge-on adsorption was best simulated by the model. A method for compensating for differing degrees of surface coverage is described.
Blocks of porous ceramic hydroxyapatite (dimensions, 2.5 X 1.25 X 0.5 cm; sintering temperature, 1300 degrees; macroporosity, 56%; average pore size 0.18 mm2) were implanted into surgically created defects in dog femora. The implants were retrieved up to 3.5 years after implantation. The implants were 3.5 years after implantation. The implants were firmly attached to the bone. Histologic evaluation suggests that optimal contact between bone and implant should be provided to accelerate bone ingrowth. Bone growth in the pores reached a maximum level after 35 weeks, at which time about one-third of the pore space was filled with bone. When measuring the relative surface areas of bone and ceramic on histologic slides, no change in ceramic mass could be detected, indicating that hydroxyapatite ceramics are not affected by biodegradation processes. The implants effectively provided a scaffold for bone growth bridging a larger bone defect.
The authors estimated the porous hydroxyapatite alloplasts in the treatment of periodontitis in a clinical and radiological way. The material has been used in 30 patients who had bone pockets deeper than 6 mm. Together, 46 bone pockets were filled. We obtained reduction of the depths of the pockets of 3.02 mm, decrease of the degree of the teeth mobility and the improvement of Engelberger, Marthaler and Raitetschak's radiological indicator by 13%. The results were compared with other works describing the usage of this material in stomatology. Basing on the literature the authors also presented the histological changes in periodontium tissues after the usage of tricalcium phosphate and compact and porous alloplastic hydroxyapatite ceramics.