Hydroxyapatite cement. I. Basic chemistry and histologic properties

Hydroxyapatite cement: an alternative for craniofacial skeletal contour refinements

Hydroxyapatite cement is a calcium phosphate preparation composed of tetracalcium phosphate and dicalcium phosphate anhydrous powders. When mixed with water it isothermically forms a paste which can easily be shaped intraoperatively. This mixture sets in approximately 15-20 min and converts into water insoluble, nonceramic, microporous hydroxyapatite in 4 h. This biomaterial was used to correct either congenital or traumatic craniofacial contour irregularities or deficiencies in 20 patients. On follow-up there was only one patient who required repeat surgery for further correction, there were no other complications. The good cosmetic results, the ease of operation, the pliability of the cement paste allowing precise moulding during application, the short operation time and the avoidance of a donor site makes hydroxyapatite cement an attractive material for treating craniofacial contour defects. Careful long term follow-up is necessary to establish its safety and reliability.

Bone substitutes

The search for the ideal bone substitute began hundreds of years ago, and continues today. While numerous choices have been proposed and tested, with varying degrees of success, there remain many challenges related to the use of bone substitutes in craniofacial reconstruction. This paper presents a review of the history of bone substitute research, a discussion of currently popular materials, and elucidation of the challenges to be faced as we approach the new millennium.

Ostrich eggshell as a bone substitute: a preliminary report of its biological behaviour in animals--a possibility in facial reconstructive surgery

The aim of this study was to assess the biological behaviour of an implant of ostrich eggshell in various animal models of facial bone reconstruction. The implant was first bioassayed in a rat muscle pouch (n=10), and then tested as an interpositional graft in rat (n=10) and rabbit (n=5) cranial defects. It was finally used as an onlay graft on rabbit mandibles (n=5). Animals were killed after two months in the bioassay, three months in the interpositional model, and six months in the onlay model. The specimens were studied by contact radiography and standard histological techniques. All animals showed normal wound-healing. In the bioassay, the implants produced only a minimal inflammatory reaction. In the interpositional model, the implants maintained a good contour, but there was no sign of graft-remodelling. In the onlay model, the grafts were stable and partly osteointegrated. The onlay graft model gave the most promising results. Because ostrich eggshell is inexpensive and has good mechanical properties, it deserves further study. Long-term studies will clarify its possible role in maxillofacial surgery.

State of the art in craniofacial surgery: nonsyndromic craniosynostosis

Craniosynostosis refers to the premature fusion of one of the six major sutures of the cranial vault. Functionally, craniosynostosis may be defined as the premature conversion of the dynamic region of growth and resorption between two adjacent bones of the cranium into a static region of bony union. Molecular analysis has blurred the traditional categories of nonsyndromic and syndromic synostosis to some extent, but, in general, the distinctions between the two groups still hold true. The complexity of the congenital anomalies may be limited with the former, whereas the latter usually requires reoperations and correction of the facial skeleton. This article briefly outlines the characteristic deformities produced from nonsyndromic craniosynostosis. Various approaches to surgical correction of the deformities are described. Finally, new biomaterials that are used in the correction of nonsyndromic craniosynostosis are reviewed.

Alloplastic implantation

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Define an alloplastic material and know the differences between an alloplast and other types of implants available for surgical use. 2. Determine the biologic response to alloplastic implantation and the material and host characteristics that contribute to long-term reconstruction success with their use. 3. Review the criteria for choosing a specific alloplastic material for a reconstruction site and the principles of surgical technique for its proper placement. 4. Evaluate the various alloplastic material types that are currently available for surgical use and be able to discuss several physical properties of each as they relate to handling and clinical implantation. 5. Discuss the complication of alloplastic infection, its pathogenesis, preoperative and intraoperative measures for its avoidance, and the postoperative management of its occurrence.

Calcium sulfate- and calcium phosphate-based bone substitutes. Mimicry of the mineral phase of bone

Calcium sulfate and calcium phosphate have provided the orthopedic surgeon a viable alternative to autogenous bone grafting as either an osteoconductive bone void filler or a bone graft extender. These materials mimic the mineral phase of bone and are resorbed at a rate similar to the rate of bone formation. Thus, they are able to provide some structural support and prevent ingrowth of fibrous tissue while facilitating creeping substitution by the host bone.

alpha-BSM: a biomimetic bone substitute and drug delivery vehicle

alpha-BSM is a biomimetic endothermically setting apatitic calcium phosphate bone substitute material. Its injectability and ability to harden at body temperature in the presence of physiologic saline, and other buffering agents, makes it an attractive clinical bone substitute and delivery vehicle for therapeutic agents in orthopaedic and dental applications. In osseous tissue, alpha-BSM alone remodels into bone and promotes bone healing. alpha-BSM treatment has been shown in several animal models to be effective in promoting healing of surgically created critical size defects and restoring bone biomechanical strength to values equal to or greater than values achieved with autograft controls. In vitro studies with alpha-BSM containing gentamicin show that antibiotics can be incorporated stably into alpha-BSM and that the release kinetics can be controlled with the appropriate formulation and preparative procedures. Growth factors and enzymes also are compatible with the alpha-BSM setting reaction. The incorporation of recombinant human bone morphogenetic protein-2 with alpha-BSM was shown to be effective in stimulating bone formation and accelerating restoration of the differentiated phenotype in an osteotomy model. Clinical trial investigators in Europe currently are using alpha-BSM implantations for treatment of fractures and other indications.

Reaction of calcium phosphate cements with different amounts of tetracalcium phosphate and dicalcium phosphate anhydrous

Calcium phosphate cements (CPCs) with different amounts of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) (TTCP/DCPA molar ratio from 0.25 to 2.00) were prepared to further understand the setting reaction and the factors that could influence the properties of CPCs. Quantitative X-ray diffraction patterns, Fourier transform IR spectra, and diametral tensile strength of the set mass were measured along with pH measurements of the CPC suspension. Calcium-deficient hydroxyapatite (d-HAP) with a calcium to phosphate molar ratio of approximately 1.5 was formed initially in the CPC setting consisting of an equimolar mixture of TTCP and DCPA. This gradually transformed into stoichiometric HA (s-HA) with increasing incubation time. The s-HA was formed in the initial stage when the CPC contained an excess amount of TTCP. In contrast, maturation to s-HAP was slow when the CPC contained excess amounts of DCPA. The highest mechanical strength of set CPC was associated with an equimolar mixture of TTCP and DCPA, and the mechanical strength decreased as the TTCP/DCPA molar ratio deviated from 1.00. We concluded, therefore, that the setting reaction and the nature of the resulting set mass are dependent on the molar ratios of TTCP and DCPA.

Use of hydroxyapatite bone cement to prevent cerebrospinal fluid leakage through the frontal sinus: technical report

OBJECTIVE

To test the efficacy of a simple technique of frontal sinus obliteration during low frontal craniotomy using hydroxyapatite cement instead of more traditional methods, such as pericranial flaps, free muscle or adipose grafts, lumbar drainage, or fibrin glue.

METHODS

Eight patients undergoing low frontal craniotomy for intradural surgery had the frontal sinus obliterated by careful removal of mucosa followed by filling of the sinus with hydroxyapatite bone cement. No other adjuncts for preventing cerebrospinal fluid leakage through the sinus were used.

RESULTS

At an average follow-up of 9 months, there were no cerebrospinal fluid leaks, infections, instances of resorption, or cosmetic deformities.

CONCLUSION

Hydroxyapatite bone cement seems to be a simple and effective method for frontal sinus obliteration and prevention of cerebrospinal fluid leakage.

Grafts amd implants in rhinoplasty and nasal reconstruction

The quest for nasal symmetry and balance with the face often mandates the need for implantable materials to sculpt and rebuild the nasal skeleton and the overlying tissues. A suitable implant must be biocompatible, strong, and elastic. Implant materials that may be used in the nose can be divided into four groups: autografts, homografts, xenografts, and alloplasts. Each type of implant is reviewed and discussed in the context of rhinoplasty and nasal reconstruction.

Efficacy of gentamycin-impregnated resorbable hydroxyapatite cement in treating osteomyelitis in a rat model

OBJECTIVE

To test the effectiveness of a self-setting hydroxyapatite cement (HAC) as a carrier of gentamycin for the treatment of chronic osteomyelitis in a rat model by using a void-fill placement technique.

DESIGN

Osteomyelitis of the tibia was created with Staphylococcus aureus (ATCC 49230) in sixty retired female breeder Sprague-Dawley rats by using the model by Korkusuz et al. (J Bone Joint Surg 1993;75B:111-114). At seven weeks after infection, all animals demonstrated clinical and radiographic signs of osteomyelitis and were debrided and divided into four treatment groups: A, debridement only; B, debridement and daily intraperitoneal gentamycin (0.2 milligram per kilogram per day); C, debridement and gentamycin-impregnated HAC in a void-fill model (1.0 milligram per kilogram of gentamycin); and D, debridement and gentamycin-impregnated polymethylmethacrylate (PMMA) beads (1.0 milligram per kilogram of gentamycin). Tibiae were harvested at zero weeks (control, n = 6), three weeks (n = 3 per group), five weeks (n = 4 per group), and seven weeks (n = 4 per group) and analyzed with quantitative bacteriologic analysis.

OUTCOME MEASUREMENT

Qualitative bacteriologic analysis was performed by using serial dilution plating of homogenized tissue samples on standard soy trypticase agar plates. Reexamination by phage typing was performed to exclude contamination.

RESULTS

The quantitative counts for Groups C (HAC) and D (PMMA) were significantly less (p < 0.003) than those for Group A (debridement alone) or Group B (intraperitoneal gentamycin) at all time points after time zero. There was no difference between Groups C and D at any time point.

CONCLUSION

HAC is an effective adjuvant in treating chronic osteomyelitis in a rat model when using a void-fill placement technique.

Osteotransductive bone cements

Calcium phosphate bone cements (CPBCs) are osteotransductive, i.e. after implantation in bone they are transformed into new bone tissue. Furthermore, due to the fact that they are mouldable, their osteointegration is immediate. Their chemistry has been established previously. Some CPBCs contain amorphous calcium phosphate (ACP) and set by a sol-gel transition. The others are crystalline and can give as the reaction product dicalcium phosphate dihydrate (DCPD), calcium-deficient hydroxyapatite (CDHA), carbonated apatite (CA) or hydroxyapatite (HA). Mixed-type gypsum-DCPD cements are also described. In vivo rates of osteotransduction vary as follows: gypsum-DCPD > DCPD > CDHA approximately CA > HA. The osteotransduction of CDHA-type cements may be increased by adding dicalcium phosphate anhydrous (DCP) and/or CaCO3 to the cement powder. CPBCs can be used for healing of bone defects, bone augmentation and bone reconstruction. Incorporation of drugs like antibiotics and bone morphogenetic protein is envisaged. Load-bearing applications are allowed for CHDA-type, CA-type and HA-type CPBCs as they have a higher compressive strength than human trabecular bone (10 MPa).

Oral and periodontal tissue. Maintenance, augmentation, rejuvenation, and regeneration

This article discusses the controversies, usefulness, and limitations of oral and periodontal tissue maintenance, augmentation, rejuvenation, and regeneration in the dog and cat. It details many of the specialized materials and techniques used in these procedures in attempts to re-establish healthy conditions within the periodontium. Bone loss following tooth extraction is discussed with consideration as to which teeth should have alveolar ridge maintenance procedures and the important reasons as to why. Radiographs show the degree of improvement demonstrated in treatment of various cases involving bone loss from periodontal disease, treatment of bone injuries with oral fractures and their prevention.

Revision of failed pedicle screws using hydroxyapatite cement. A biomechanical analysis

STUDY DESIGN

The biomechanical influence of in situ setting hydroxyapatite cement was examined for use in pedicle screw revision surgery. Pull-out testing of control and pedicle screws augmented with hydroxyapatite cement was performed in human cadaver vertebrae.

OBJECTIVES

To determine the immediate effect of using hydroxyapatite cement to augment revision pedicle screws after failure of the primary pedicle screw fixation.

SUMMARY OF BACKGROUND DATA

The potential problems associated with using polymethylmethacrylate to augment revision pedicular instrumentation have prompted the search for other solutions. The introduction of resorbable hydroxyapatite pastes may have provided new biocompatible solutions for pedicle screw revision.

METHODS

Ten human cadaver vertebrae were instrumented with 6.0-mm pedicle screws in each pedicle. The screws were loaded to failure in axial tension (pull-out). The failed pedicles then were instrumented with 7.0-mm pedicle screws, either augmented with hydroxyapatite cement or nonaugmented, which also were loaded to failure. Finally, the nonaugmented 7.0-mm screw hole was reinstrumented with a hydroxyapatite cement-augmented, 7.0-mm pedicle screw and loaded to failure.

RESULTS

The pull-out strength of the 7.0-mm, hydroxyapatite cement-augmented screws was 325% (P = 2.9 x 10(-5)) of that of the 6.0-mm control screws, whereas the strength of the 7.0-mm nonaugmented screws was only 73% (P = 2.0 x 10(-2)) of that of the 6.0-mm control screws. The 7.0-mm screws augmented with hydroxyapatite cement also were able to salvage 7.0-mm pull-out sites to 384% (P = 6.9E-5) of the pull-out strength of the 7.0-mm nonaugmented screws.

CONCLUSIONS

Hydroxyapatite cement may be a mechanically viable alternative to polymethyl methacrylate for augmenting revision pedicular instrumentation and should be considered for future experimental, animal, and clinical testing.

Preliminary evaluation of hydroxyapatite cement as an augmentation device in the edentulous atrophic canine mandible

OBJECTIVE

The purpose of this study was to answer the following two questions: (1) Can hydroxyapatite cement in combination with demineralized freeze dried bone feasibly augment the dimension of an atrophic edentulous canine mandible? (2) What is the histologic fate of an augmentation graft composed of hydroxyapatite cement and demineralized freeze dried bone placed on the surface of an atrophic edentulous canine mandible?

STUDY DESIGN

Each of four mixed-breed canines (weighing 50 to 60 pounds) underwent bilateral mandibular dental extraction (canine to second molar) and radical alveolectomy. After 4 months of healing, a bilateral subperiosteal mandibular augmentation graft was put into place, with hydroxyapatite cement/demineralized freeze dried bone on the surface of one hemimandible and porous granular hydroxyapatite and demineralized freeze dried bone on the surface of the other hemimandible. The animals were killed after functioning on a soft diet for 9 months, and the grafted hemimandibles were harvested.

RESULTS

Both hydroxyapatite cement and granular hydroxyapatite grafts appeared to augment the edentulous atrophic canine mandible. On histologic exam, the hydroxyapatite cement grafts showed osteoconduction and subperiosteal and endosteal osteonal bone formation, whereas the granular hydroxyapatite grafts showed only osteoconduction. Neither graft material showed chronic or acute inflammation.

CONCLUSION

Hydroxyapatite cement can function feasibly as a mandibular augmentation device. The histologic fate of hydroxyapatite cement is different from that of granular hydroxyapatite. It has a fate comparable to autograft or allograft cortical bone grafts.

Reinforcement of thoracolumbar burst fractures with calcium phosphate cement. A biomechanical study

STUDY DESIGN

A biomechanical study on the stabilization of thoracolumbar burst fractures.

OBJECTIVE

To demonstrate that the addition of a calcium phosphate cement into the fractured vertebral body through a transpedicular approach is a feasible technique that improves the stiffness of a transpedicular screw construct.

SUMMARY OF BACKGROUND DATA

Short segment pedicle screw instrumentation is a commonly used method for reduction and stabilization of unstable burst fractures. Recent investigators, however, have reported a high rate of instrumentation failure and sagittal collapse when there is a loss of anterior column support. In this study, the ability of a new hydroxyapatite cement to augment anterior column support was investigated in a burst fracture model.

METHODS

A cadaveric L1 burst fracture model was stabilized using short segment pedicle screw instrumentation. Specially instrumented-pedicle screws recorded screw-bending moments. The L1 vertebral body was reinforced with the hydroxyapatite cement through a transpedicular approach. Mechanical testing of the instrumented and instrumented-reinforced constructs were performed in flexion, extension, side bending, and torsion. Construct stiffness and screw-bending moments were recorded.

RESULTS

Transpedicular vertebral body reconstruction with hydroxyapatite cement reduced pedicle screw-bending moments by 59% in flexion and 38% in extension. Mean initial stiffness in the flexion-extension plane was increased by 40% (P < 0.05). There were no statistically significant differences in these parameters with lateral bending or torsional movements.

CONCLUSIONS

This hydroxyapatite cement compound augments anterior column stability in a burst fracture model. This technique may improve outcomes in burst fracture patients without the need for a secondary anterior approach.

Hydroxyapatite cement implant for regeneration of periodontal osseous defects in humans

A newly developed calcium phosphate cement used to promote bone regeneration in craniofacial defects was examined to determine its potential for treatment of periodontal osseous defects. Sixteen patients with moderate to severe periodontal disease and 2 bilaterally similar vertical bony defects received initial therapy including scaling and root planing followed by treatment with either calcium phosphate cement, flap curettage (F/C) or debridement plus demineralized freeze-dried bone allograft (DFDBA). Standardized radiographs were exposed at baseline and 12 months postsurgery for computer assisted densitometric image analysis (CADIA). The extent of the bony defect was determined during initial and 12 month re-entry surgery. Within 6 months of implant placement, 11 of 16 patients treated with calcium phosphate cement exfoliated all or most of the implant through the gingival sulcus. At all 16 test sites, a narrow radiolucent gap formed by 1 month postsurgery at the initially tight visual interface between the radiopaque calcium phosphate cement and the walls of the bony defect. Mean probing depth reduction and clinical attachment gain at sites treated with calcium phosphate cement were 1.6 mm and 1.3 mm, respectively at 1 year. Minimal bony defect fill was accompanied by mean crestal resorption of 1.4 mm. Alveolar crestal resorption at sites with calcium phosphate cement was statistically significant (P=0.001). These findings contrasted with the more favorable outcomes for controls treated with DFDBA or F/C. DFDBA sites exhibited probing depth reduction of 3.1 mm, clinical attachment gain of 2.9 mm, and defect fill of 2.4 mm. Respective clinical changes at F/C sites were 2.4 mm, 1.4 mm, and 1.1 mm. CADIA revealed clinically significant trends between the three treatment modalities at various areas-of-interest. Based on the findings of this study, there is no rationale available to support the use of hydroxyapatite cement implant in its current formulation for the treatment of vertical intrabony periodontal defects.

Effects of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement

The effect of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement (aw-FSCPC) was investigated in a preliminary evaluation of aw-FSCPC containing drugs. Flomoxef sodium was employed as the antibiotic and was incorporated into the powder-phase aw-FSCPC at up to 10%. The setting time, consistency, wet diametral tensile strength (DTS) value, and porosity were measured for aw-FSCPC containing various amounts of flomoxef sodium. X-ray diffraction (XRD) analysis was also conducted for the identification of products. To evaluate the drug-release profile, set aw-FSCPC was immersed in saline and the released flomoxef sodium was determined at regular intervals. The spread area of the cement paste as an index of consistency of the cement increased progressively with the addition of flomoxef sodium, and it doubled when the aw-FSCPC contained 8% flomoxef sodium. In contrast, the wet DTS value decreased with increase in flomoxef sodium content. Bulk density measurement and scanning electron microscopic observation revealed that the set mass was more porous with the amount of flomoxef sodium contained in the aw-FSCPC. The XRD analysis revealed that formation of hydroxyapatite (HAP) from aw-FSCPC was reduced even after 24 h, when the aw-FSCPC contained flomoxef sodium at > or = 6%. Therefore, the decrease of wet DTS value was thought to be partly the result of the increased porosity and inhibition of HAP formation in aw-FSCPC containing large amounts of flomoxef sodium. The flomoxef sodium release from aw-FSCPC showed the typical profile observed in a skeleton-type drug delivery system (DDS). The rate of drug release from aw-FSCPC can be controlled by changing the concentration of sodium alginate. Although flomoxef sodium addition has certain disadvantageous effects on the basic properties of aw-FSCPC, we conclude that aw-FSCPC is a good candidate for potential use as a DDS carrier that may be useful in surgical operations.

Tissue response to fast-setting calcium phosphate cement in bone

Fast-setting calcium phosphate cement (FSCPC) is a promising new bioactive cement with a significantly short setting time (approximately 5-6 min) compared to conventional calcium phosphate cement (c-CPC) (30-60 min) at physiologic temperatures. As a result of its ability to set quickly, it is applicable in surgical procedures where fast setting is required. In this study, FSCPC was implanted in rat tibiae to evaluate tissue response and biocompatibility. FSCPC was converted to hydroxyapatite (HAP) in bone faster than c-CPC in the first 6 h. By 24 h, significant amounts of both FSCPC and c-CPC had been converted to HAP. The conversion of FSCPC into HAP further proceeded gradually, reaching 100% within 8 weeks. Infrared spectroscopic analysis disclosed the deposition of B-type carbonate apatite, which is a biological apatite contained in human dentin or bone, on the surface of the FSCPC. Histologically, FSCPC showed a tissue response similar to that of c-CPC. A slight inflammatory reaction was observed in the soft tissue apposed to both cements in the early period, and new bone was formed along the surface of the FSCPC at the adjacent bone. However, no resorption of either cement by osteoclasts or macrophages was observed within 8 weeks. We conclude that FSCPC is superior to c-CPC in clinical applications in oral and maxillofacial, orthopedic, plastic, and reconstructive surgery, since it shows a faster setting time and higher mechanical strength in the early period that are required in these surgical procedures, as well as osteoconductivity and excellent biocompatibility similar to that of c-CPC.

Repair of craniofacial defects with hydroxyapatite cement

PURPOSE

The objective of this study was to evaluate the course of healing of craniofacial bone defects when filled with hydroxyapatite cement and to determine whether adding various percentages by weight of demineralized bone powder to the cement will result in enhanced bone formation.

MATERIALS AND METHODS

The model for the study was the canine calvarium. The implants were placed into cranial defects and harvested at 3 or 6 months for qualitative evaluation by light microscopy, microradiography, and quantitative histomorphometry.

RESULTS

The implantation of hydroxyapatite cement resulted in characteristic replacement of the material with new bone ingrowth. The addition of demineralized bone powder to the hydroxyapatite cement appeared to improve the handling characteristics of the cement; however, improvement in the replacement of the material by bone was not observed. The implantation of only allogeneic demineralized bone showed limited new bone formation within the defect site.

CONCLUSIONS

Hydroxyapatite cement formed an effective osseoconductive scaffold for bone replacement. The addition of demineralized bone powder to the cement to serve as a carrier of osseoinductive factors did not result in additional bone being formed.

Effects of hydroxypropyl methylcellulose and other gelling agents on the handling properties of calcium phosphate cement

The calcium phosphate cement (CPC) used in this study was formed by combining equimolar amounts of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). This powder, when mixed with water, sets to a hard cement in about 30 min. However, the water-based CPC paste is not highly cohesive and is vulnerable to washout until hardening occurs. The objectives of this study were to investigate the effects on handling properties, washout resistance, cement hardening behavior, and mechanical properties of adding several gelling agents to CPC paste. Aqueous solutions that contained a mass fraction of 2-4% of hydroxypropyl methylcellulose (HPMC), carboxyl methylcellulose (CMC), chitosan acetate, and chitosan lactate were used as cement liquids. Hardening time was measured by the Gilmore needle test; resistance to washout was evaluated by the disintegration of the cement specimen in water with agitation; and mechanical strength was evaluated by the measurement of diametral tensile strength and compressive strength. Handling properties were greatly improved by the addition of HPMC, CMC, chitosan acetate, and chitosan lactate. Hardening time was retarded by the additions of HPMC and CMC, and mechanical strength was weakened by the addition of either the chitosan lactate or the chitosan acetate.

Gentamicin-loaded hydraulic calcium phosphate bone cement as antibiotic delivery system

A hydraulic calcium phosphate cement made of beta-tricalcium phosphate [beta-Ca3(PO4)2], monocalcium phosphate monohydrate [Ca(H2PO4)2-H2O], and water was used as a delivery system for the antibiotic gentamicin sulfate (GS). GS, added as powder or as aqueous solution, was very beneficial to the physicochemical properties of the cement. The setting time increased from 2 to 4.5 min with 3% (w/w) GS and then slowly decreased to 3.75 min with 16% (w/w) GS. The tensile strength increased from 0.4 to 1.6 MPa with 16% (w/w) GS. These effects were attributed to the presence of sulfate ions in GS. The release of GS from the cement was measured in a pH 7.4 phosphate-buffered saline solution at 37 degrees C by USP paddle method. Factors such as cement porosity, GS content and presence of sulfate ions or polymeric additives were investigated. The amount of GS released was roughly proportional to the square root of time up to approximately 50% release. Afterwards, the release rate markedly slowed down to zero. In all but two cement formulations, the total dose of GS was released within 7 days, indicating that no irreversible binding occurred between the cement paste and the antibiotic. When small amounts of hydroxypropylcellulose or poly(acrylic acid) were added to the cement, the maximum fraction released was a few percent lower than the total GS dose, suggesting some binding between the polymer and GS. The GS release rate was strongly influenced by the presence of sulfate ions in the cement paste and by the cement porosity. The higher the sulfate ion content of the cement paste, the lowe the GS release rate. This influence was attributed to the finer cement micro-structure induced by the presence of sulfate ions. Furthermore, when the initial cement porosity was increased from 38 to 69%, the release rate almost tripled (0.16 to 0.45 h-1/2). Finally, the biological activity of GS in the cement was maintained, as measured by assaying the release medium.

The investigation of biocompatibility and apical microleakage of tricalcium phosphate based root canal sealers

The biocompatibility and apical microleakage of tricalcium phosphate based Sankin Apatite (SA) Type I, II, and III root canal sealers were investigated. Teflon tubes containing freshly mixed test materials were implanted in the subcutaneous tissue of mice. The observation periods were 24 h, 7, and 30 days, after which the areas of tissue reaction to the implanted materials were histopathologically analyzed. A dye-recovery, spectrophotometric method was used to evaluate apical microleakage. Results showed that the severity of tissue reaction among the tested materials decreased with time and at the end of the observation period both SA Type II and Type III were found more biocompatible than either Type I or Grossman's cement (GC). On the other hand, a fibrous tissue capsule was seen around the implants. There was no significant difference in spectrophotometrically measured leakage among teeth obturated with the test materials.

Obliteration of the eustachian tube using hydroxyapatite cement: a permanent technique

Permanent obliteration of the eustachian tube via the middle ear traditionally has met with limited success. Combinations of muscle, fascia, adipose tissue, bone fragments, and inert material such as Proplast have been used to seal the middle ear from the nasopharynx by inciting a fibrous reaction within the lumen of the eustachian tube. Long-term follow-up has demonstrated repneumatization of the middle ear cleft in the majority of cases, indicating failure of the obliteration technique. This report describes a technique for successful long-term obliteration using hydroxyapatite cement. This new biomaterial possesses osseointegrative and osseoconductive properties that result in permanent obliteration by producing new bone formation within the lumen of the eustachian tube. This technique eliminates the complication of cerebrospinal fluid rhinorrhea in lateral skull base procedures that expose the eustachian tube to cerebrospinal fluid.

Non-decay type fast-setting calcium phosphate cement: setting behaviour in calf serum and its tissue response

Non-decay type fast-setting calcium phosphate cement (nd-FSCPC) was evaluated in terms of its setting behaviour in calf serum and its tissue response to investigate the feasibility of its clinical use in surgical applications. Non-decay type cements were prepared by adding various amounts of sodium alginate to the liquid phase of base cements, fast-setting calcium phosphate cement (FSCPC) and conventional calcium phosphate cement (c-CPC). Cement pastes were immersed in serum at 37 degrees C immediately after mixing, and decay behaviour, setting time and mechanical strength were measured to evaluate the possibility of their use in surgical applications. Also, nd-FSCPC was implanted into rat subcutaneous tissue for the initial evaluation of biocompatibility of this potential bioactive cement. nd-FSCPC set in approximately 6-7 min in serum, even when the cement paste was immersed in the serum immediately after mixing, whereas c-CPC and FSCPC decayed completely upon immersion. nd-FSCPC transforms to hydroxyapatite (HA) within 24 h and shows a diametral tensile strength of approximately 4-5 MPa. As a result of transformation to HA, nd-FSCPC showed excellent tissue response when implanted subcutaneously in rats. We conclude that nd-FSCPC has good potential value for use in orthopaedics, plastic and reconstructive surgery, and oral and maxillofacial surgery, where the cement is exposed to blood.

The reinforcement of cancellous bone screws with calcium phosphate cement

The ability of calcium phosphate cement (CPC) to reinforce cancellous screws placed in previously stripped holes was studied in vitro. The distal end of canine femurs were harvested. A total of 15 screws were placed in six femurs. The pullout strength (failure force), failure displacement, stiffness, and energy absorbed were determined for the screws in the intact cancellous bone. Next, these stripped screw holes were packed with CPC. The pullout test was repeated, and the results were compared using a paired, Student's t test. We found that the CPC was able to reinforce the previously stripped holes and significantly increase the pullout strength (1,159 +/- 278 N versus 678 +/- 297 N) and the stiffness (1,990 +/- 569 N/mm versus 1,519 +/- 609 N/mm) of the constructs, as well as the energy absorbed by the constructs until failure (467 +/- 180 N.mm versus 278 +/- 140 N.mm). There was no difference in the failure displacement (0.94 +/- 0.23 versus 0.85 +/- 0.51 mm). This study documents the ability of CPC to acutely reinforce cancellous bone screws in a region with no or poor-quality cancellous bone.

Estimation of ideal mechanical strength and critical porosity of calcium phosphate cement

The ideal mechanical strength and critical porosity of calcium phosphate cement (CPC) were estimated to help determine ways to improve its properties. CPC at various porosities was made by packing CPC paste, at various powder-to-liquid (P/L) ratios (2.0-6.0), into a mold under various pressures (0-173 MPa). The mechanical strength of CPC, in terms of diametral tensile strength (DTS), increased with decreases in porosity. Intercrystalline fracture was observed in specimens made without the application of pressure, while fracture within the crystals increased with the packing pressure. These observations support the application of the relationship between DTS and porosity in fractographic equations. The ideal wet DTS and critical porosity of CPC were estimated to be 102 MPa and 63%, respectively. The minimum porosity of the currently used CPC was approximately 26-28%, even when it was packed under 173 MPa, and the maximum DTS value was thus approximately 13-14 MPa. Because reducing the porosity of currently used CPC would be difficult, we conclude that in CPC-related research, we should focus on ways in which to accelerate bone-replacing behavior, in addition to improving the mechanical strength of CPC.

Light and transmission electron microscopic studies following frontal sinus obliteration with ionomer cement in cats

Osteoplastic frontal sinus surgery in combination with sinus obliteration can be performed for various indications, including chronic sinusitis, frontal sinus trauma and removal of osteomas. In an experimental study using cats, the mucous lining of the frontal sinus was removed, the nasofrontal duct sealed with semifluid ionomer cement and the cavity filled with Ionogran, a solid and porous bone substitute based on ionomer cement. Histological investigations up to 1 year after surgery showed increasing sinus obliteration by regenerating bone, starting from the sinus wall, and formation of connective tissue between the cement grains. There was no evidence for mucosal regeneration. Electron microscopic examination of the interface between the cement and connective tissue revealed mesenchymal cells, collagen fibers and areas of mineralization in close contact with the implant material. Newly formed connective tissue matrix in intimate contact with the cement was a good indication for biocompatibility of the material and is a possible explanation for the implant's solid adhesion to bone. The present findings indicate that Ionogran is a suitable alloplastic material for experimental frontal sinus obliteration in cats.

In vivo setting behaviour of fast-setting calcium phosphate cement

The in vivo setting behaviour of fast-setting calcium phosphate cement (FSCPC) between femoral muscles of the rat was investigated to evaluate the possible value of FSCPC for medical and dental application. Conventional CPC (c-CPC) and FSCPC were implanted between femoral muscles, and various aspects of the setting behaviour such as setting time, mechanical strength and conversion ratio of cement into hydroxyapatite (HAP: Ca10(PO4)6(OH)2) were measured by the Vicat needle method, diametral tensile strength (DTS) measurement, and quantitative powder X-ray diffraction (XRD) analysis, respectively. The setting time of FSCPC in vivo was 5-7 min, in contrast to 48 min for c-CPC. As a result of its fast setting, set specimens of FSCPC showed higher mechanical strength from the initial stage than c-CPC. Higher DTS values were observed in FSCPC than c-CPC implanted after 24 h. Powder XRD analysis revealed faster conversion of FSCPC than c-CPC into HAP, which was responsible both for the faster setting and higher mechanical strength from the initial stage. We concluded, therefore, that FSCPC may be used for a wide range of clinical applications, i.e. fields where fast setting is required such as orthopaedic, plastic and reconstructive, and oral and maxillofacial surgery.

Non-decay type fast-setting calcium phosphate cement: composite with sodium alginate

Non-decay type fast-setting calcium phosphate cement (nd-FSCPC) was prepared by introducing sodium alginate (0-2.0 wt%) into the liquid phase of FSCPC. nd-FSCPC was stable even when the cement paste was immersed in distilled water immediately after mixing, whereas conventional FSCPC (c-FSCPC) decayed completely within 1 min upon immersion. The setting time of the cement, approximately 5 min, was not dependent on the presence of sodium alginate. In contrast, the introduction of sodium alginate into conventional CPC, i.e. CPC without neutral phosphate in the liquid phase, resulted in no setting when the amount of sodium alginate introduced was more than 1 wt%. Powder X-ray diffraction analysis revealed no significant difference for the conversion of cement to apatite for any concentrations of sodium alginate studied (0-2.0 wt%). The mechanical strength of the cement increased rapidly with the addition of sodium alginate up to 0.8 wt% when the cement paste was immersed and kept in distilled water at 37 degrees C, whereas further addition of sodium alginate decreased the mechanical strength. The results obtained in this investigation, taken together with sodium alginate's known excellent biocompatibility and absorption behaviour, indicate that the use of sodium alginate composite FSCPC as nd-FSCPC should be of value in orthodontics and oral and maxillofacial surgery where the cement is exposed to blood.

Reconstruction of suboccipital craniectomy defects with hydroxyapatite cement: a preliminary report

Hydroxyapatite cement, a new biomaterial presently under clinical investigation, has been demonstrated to have potentially wide application in cranial reconstruction. We describe our experience with this biologic bone cement in the reconstruction of suboccipital craniectomy defects in seven patients after vestibular schwannoma removal. With up to 2-year follow-up, cranial bone integrity has been reestablished in five patients. Dissolution of cement has occurred in dependent areas and appears to be technique related. Cranial bone contour appears dependent on the amount of cement used. The frequency of debilitating postoperative headache was reduced in these patients when compared to patients who had no reconstruction of the craniectomy defect. Reconstruction of the bony defect after suboccipital craniectomy with hydroxyapatite cement is not only useful to restore cranial contour, but also appears to reduce some of the functional deficits attributed to this surgical approach.

Behavior of a calcium phosphate cement in simulated blood plasma in vitro

OBJECTIVES

The purpose of this study was to gain a better understanding of the integration of calcium phosphate cement (CPC) implants in biological tissue.

METHODS

An in vitro continuous flow system was employed to examine the protracted behavior of disc-shaped specimens of this bioactive material under sustained physiological-like solution conditions. Weight measurement, diameteral tensile strength measurement (DTS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and powder x-ray diffraction (XRD) were used to characterize the CPC samples as a function of immersion time.

RESULTS

When CPC was immersed in simulated blood plasma in which the Ca (2.5 mmol/L) and inorganic phosphate (1.0 mmol/L) levels were kept constant, both the weight and DTS of the specimens steadily increased to about 1.5 times their original values over a period of 20 wk. SEM observations showed new precipitate formations in intimate contact with the original CPC surface. FTIR and XRD analyses revealed that the precipitate was a B-type carbonate hydroxyapatite (OHAp), the type of OHAp observed in bone and dentin. On the other hand, the interior of CPC discs did not show an increase in either bulk density or OHAp content. Thus, the increases in weight and DTS are attributable to the OHAp precipitation on the CPC surface.

SIGNIFICANCE

The results suggest that under in vivo conditions, CPC implants would not dissolve in physiological fluids. OHAp coatings may form on the implants, which may enhance bonding of implants to bone by mechanically strengthening the interface between them.

Polymeric calcium phosphate cements: analysis of reaction products and properties

Chemical and mechanical properties of water-based polymeric calcium phosphate cements (PCPC) were investigated. These cements were derived from mixing several types of water-soluble polymers, e.g., gelatin, poly(vinyl alcohol) (PVA), and poly(alkenoic acids) such as poly(acrylic acid), with a calcium phosphate cement (CPC) mixture consisting of equimolar amounts of tetracalcium phosphate (TTCP) and anhydrous dicalcium phosphate (DCPA) as well as several other TTCP-containing mixtures. Cement formation was observed with all of the PCPCs. With the gelatin and PVA cements, significant amounts of hydroxyapatite (HA) formation were observed within 24 h. Their setting times and mechanical properties were similar to those of the purely inorganic CPC that is derived from the reaction of TTCP and DCPA in water. Although the mechanical properties of a gelatin-CPC cement were only slightly improved, its handling characteristics were superior to that of CPC. Significantly faster setting and stronger cements were obtained using polycarboxylic acid polymers with CPC. However, only small amounts of HA were observed in these types of polymeric cements even after 1 mon storage in distilled water at 37 degrees C. This research demonstrates the feasibility of preparing several new types of dental cements based on the interaction of water-soluble polymers with a self-setting calcium phosphate powder mixture.