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Case: Although implanted tuberculosis (TB) is rare, a single lot of cellular bone matrix was found to be infected with TB, leading to devastating outcomes. We present 2 cases referred to our institution because of instrumentation failure caused by TB inoculation of cellular bone matrix., Conclusion: Irrespective of spinal region of implanted TB infection, excision of infected bone, extensive irrigation and debridement, and instrumented stabilization are of primary importance to ensure TB eradication and adequate stabilization., Competing Interests: Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSCC/C93)., (Copyright © 2023 by The Journal of Bone and Joint Surgery, Incorporated.)

Objective: Previous studies have shown that intrinsic behavior of subchondral bone marrow stem cells (BMSCs) is influenced by donors and locations. To understand the variability in cartilage repair outcomes following bone marrow stimulation, we tested the hypothesis that in vivo cartilage repair correlates with in vitro biological properties of BMSCs using a rabbit model., Methods: Full-thickness cartilage defects were created in the trochlea and condyle in one knee of skeletally mature New Zealand White rabbits ( n = 8) followed by microdrilling. Three-week repair tissues were analyzed by macroscopic International Cartilage Repair Society (ICRS) scores, O'Driscoll histological scores, and Safranin-O (Saf-O) and type-II collagen (Coll-II) % stain. BMSCs isolated from contralateral knees were assessed for cell yield, surface marker expression, CFU-f, %Saf-O, and %Coll-II in pellet culture followed by correlation analyses with the above cartilage repair responses., Results: In vivo cartilage repair scores showed strong, positive correlation with cell number, clonogenic, chondrogenic, and matrix production (Coll-II, GAG) potential of in vitro TGF-βIII stimulated BMSC cultures. Trochlear repair showed clear evidence of donor dependency and strong correlation was observed for interdonor variation in repair and the above in vitro properties of trochlear BMSCs. Correlation analyses indicated that donor- and location-dependent variability observed in cartilage repair can be attributed to variation in the properties of BMSCs in underlying subchondral bone., Conclusion: Variation in cell number, clonogenic, chondrogenic, and matrix production potential of BMSCs correlated with repair response observed in vivo and appear to be responsible for interanimal variability as well as location-dependent repair.

Traditional guided bone regeneration techniques include flap mobilization and placement of a bone graft, often with the use of space-maintaining devices and cell-occlusive membranes. This approach is associated with frequent complications that negatively affect the outcome of the augmentation and the peri-implant soft tissue esthetics. Although current tunneling techniques have focused on periodontal soft tissue applications, earlier publications described their use for horizontal augmentation of mandibular posterior edentulous ridges in full-denture patients. More recently, the use of recombinant human platelet-derived growth factor (rhPDGF-BB) was tested with different bone matrices to treat maxillary anterior edentulous spans. The present case series reports the use of a subperiosteal minimally invasive aesthetic ridge augmentation technique (SMART) to treat 60 single and multiple edentulous, dentate, and implant sites on 21 patients and five treatment categories with a follow-up period ranging from 4 to 30 months. The technique includes the use of a laparoscopic approach to deliver a growth factor/xenograft combination into a subperiosteal pouch. No flap elevation, cell-occlusive membranes, space-maintaining devices, or decortication procedures were used. The results from this case series demonstrated predictable and consistent bone regeneration. The average gain in ridge width for all treatment categories was 5.11 mm (SD 0.76 mm), which compares favorably with previously published reports. Morbidity and complication rates were consistently reduced as well. Human histology results show xenograft particles surrounded by newly formed bone. The role of the periosteum as a source of pluripotent cells in growth factor–mediated bone regeneration is discussed.

Study Design: An in vivo animal experimental study., Objective: To investigate the hydroxyapatite (HA) coating in a modified fusion cage in improving the results of cervical intervertebral fusion and the role of combination of IGF-I and TGF-β1 treatment in a goat cervical spine interbody fusion model., Materials and Methods: Thirty-two goats were divided into 4 groups (n=8 for each) and underwent C3-4 discectomy and intervertebral fusion by the following methods: group 1, autologous tricortical iliac crest bone graft; group 2, cage only; group 3, cage coated with HA; group 4, cage coated with HA+IGF-I and TGF-β1. Radiography was performed preoperatively, postoperatively, and after 1, 2, 4, 8, and 12 weeks. At the same time points, disk space height, intervertebral angle, and lordosis angle were measured. At 12 weeks postoperatively, the goats were killed and fused segments were harvested. Biomechanical study was performed in flexion, extension, axial rotation, and lateral bending with a nondestructive stiffness method to determine the range of motion and stiffness. All cervical fusion specimens underwent histomorphologic studies., Results: All 3 cage-treated groups showed significantly higher values for disk space height, intervertebral angle, and lordosis angle compared with the autologous tricortical iliac group at 1, 2, 4, 8, and 12 weeks after surgery (P<0.05). The stiffness of hat-shaped cervical intervertebral fusion cage coated with HA+IGF-I and TGF-β1 in flexion, extension, and lateral bending was significantly greater than that of the other groups (P<0.05), and the stiffness of hat-shaped cervical intervertebral fusion cage coated with HA in extension, axial rotation, and lateral bending was significantly greater than that of fusion with the bone graft and cage-only groups (P<0.05). Histomorphologic evaluation showed better fusion in 3 cage groups than in the bone graft group. In group 4 of the cage coated with HA+IGF-I and TGF-β1, a slightly more advanced bone matrix formation was shown than in groups without coating., Conclusions: HA coating can improve the fusion effect of the cervical intervertebral cage, and IGF-I and TGF-β1 can enhance bone fusion.

Objective: A versatile neurosurgical approach, the retrosigmoid craniectomy (RS) has traditionally been associated with high rates of post-operative cerebrospinal fluid (CSF) leak, headaches, and aesthetic defects. We introduce a simple surgical strategy for bony cranial reconstruction designed to minimize peri-operative complications and improve cosmetic outcomes., Methods: In accordance with the Institutional Review Board, the senior author's (G.M.M.) records were queried between 2006 and 2014. We identified 50 consecutive patients who underwent demineralized bone matrix (DBM)-augmented cranioplasty after RS for MVD (DBM group) and 92 consecutive patients in whom standard cranial reconstruction was undertaken using autologous bone chips only after RS for MVD (non-DBM group). Demographic and clinical information regarding the laterality of each operation, intra-dural drilling for petrous hyperostosis, method of dural closure, length of hospitalization, presence of post-operative headaches, and procedure-related complications were collected and analyzed., Results: The DBM and non-DBM cohorts were well matched for age, laterality of procedure, surgical indications, primary versus revision surgery, intra-dural drilling of petrous hyperostosis, and dural closure techniques. Trigeminal neuralgia was the most common surgical indication (98.6%) in each cohort. Post-operatively, 15% of patients in non-DBM group experienced chronic headaches at the last follow-up compared to only 8% of the patients in the DBM group (p=0.21). The non-DBM patients also suffered more incisional pain in comparison to the DBM patients (7.6% vs. 0%, p=0.045)., Conclusion: DBM-augmented reconstruction of posterior fossa defects resulted in low rates of post-operative headaches, better cosmetic outcomes, and represents a simple and effective cranioplasty option for skull base surgeons., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Tendon-bone healing is crucial in success of anterior cruciate ligament (ACL) reconstruction surgery. Demineralized bone matrix (DBM) is a physiological component that has the inherent potential of bone regeneration. We hypothesized that the alternative bone substitute can affect the structural properties of tendon graft in tibial tunnel healing. Five 12-week-old New Zealand white rabbits in study group underwent unilateral ACL reconstructions plus the application of 0.5 cc DBM in the tibial tunnel. The assessment included radiological assessment and histologic and immunohistochemical analyses. Radiological examination revealed that DBM group had the least displacement of tendon in tibial tunnel (0.4 ± 0.12; P = 0.03). Histologic examination showed significantly better integration between tendon and bone in DBM group (77.62 ± 2.08; P = 0.001). On immunohistochemical analysis, the DBM group showed significantly higher expressions of bone morphogenetic protein-2 and vascular endothelial growth factor than control group (51.98 ± 3.02, 84.06 ± 1.86; P = 0.001, P < 0.001). DBM enhances the tendon-bone healing in ACL reconstruction. DBM has the potential use in ACL surgery., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The osteoinductive properties of demineralised bone matrix have been demonstrated in animal studies. However, its therapeutic efficacy has yet to be proven in humans. The clinical properties of AlloMatrix, an injectable calcium-based demineralised bone matrix allograft, were studied in a prospective randomised study of 50 patients with an isolated unstable distal radial fracture treated by reduction and Kirschner (K-) wire fixation. A total of 24 patients were randomised to the graft group (13 men and 11 women, mean age 42.3 years (20 to 62)) and 26 to the no graft group (8 men and 18 women, mean age 45.0 years (17 to 69)). At one, three, six and nine weeks, and six and 12 months post-operatively, patients underwent radiological evaluation, assessments for range of movement, grip and pinch strength, and also completed the Disabilities of Arm, Shoulder and Hand questionnaire. At one and six weeks and one year post-operatively, bone mineral density evaluations of both wrists were performed. No significant difference in wrist function and speed of recovery, rate of union, complications or bone mineral density was found between the two groups. The operating time was significantly higher in the graft group (p = 0.004). Radiologically, the reduction parameters remained similar in the two groups and all AlloMatrix extraosseous leakages disappeared after nine weeks. This prospective randomised controlled trial did not demonstrate a beneficial effect of AlloMatrix demineralised bone matrix in the treatment of this category of distal radial fractures treated by K-wire fixation.

Background: The present prospective, randomized, double-blind study evaluated the bone-forming process around implants inserted simultaneously with anorganic bovine bone (ABB) in sinus grafting., Methods: A total of 18 threaded mini-implants with Osseotite (O) and Nanotite (N) surfaces were placed in seven patients (nine sites). After 12 months, the implants were retrieved and processed for histological analysis. A total of 18 cutting and grinding sections were investigated with bright-field light microscopy, circularly polarized light microscopy (CPLM), confocal scanning laser microscope (CSLM), and scanning electron microscope (SEM) with energy dispersive spectrometer (EDS)., Results: The bone-to-implant contact rate in native crestal bone was 62.6 ± 0.4% for N implants and 54.3 ± 0.5% for the O implants (p = 0.001). The collagen fibre density, as assessed by CPLM, was 79.8 ± 6.0 nm for the N group and 74.6 ± 4.6 nm for the O group (p < 0.05). Line scan EDS starting from ABB to newly formed bone showed a decrease in calcium content and an increase of carbon while phosphorus content was constant., Conclusions: While the N surface improved the peri-implant endosseous healing properties in the native bone, when compared to the O surface, it did not improve the healing properties in the bone-graft area., (© 2013 Australian Dental Association.)

The aim of the present animal study was to investigate the early healing processes developing in the post-extraction sockets preserved with a new-marketed collagen matrix as, to our knowledge, such investigations have not been reported so far. In both quadrants of the mandible of a mongrel dog, the distal sockets of the second premolars served as experimental sites for ridge preservation. The experimental site 1 was protected with a resorbable membrane and then with the collagen matrix. The experimental site 2 was filled with a xenograft and then covered with the collagen matrix. The samples were harvested after one month of healing. In both experimental sites, the bundle bone lining the inner surface of the alveolus was replaced with trabecular bone containing areas of woven bone. A continuous layer of osteoblasts could be observed on the surface of woven bone areas. Osteoclasts encased within resorptive lacunae lined the outer portions of bone walls for the experimental site 1. The trabecular bone occupied only the apical third of the socket in experimental site 1, but it was obviously more abundant in the experimental site 2, occupying also the central compartment of the socket. Moreover, the trabeculae of the bone occupying the inner area of the alveolus were thicker for the experiment site 2 than for experiment site 1, suggesting an increased osseous deposition in the latter situation. Our preliminary results suggest that the association collagen matrix plus xenograft may be a valuable method for ridge preservation.

Objective: To compare the effect of different defect diameters on healing in the middle 1/3 tibia monolayer cortical bone defect mouse model so as to establish an animal model for bone tissue engineering study, mechanism study on bone defect repair, and gene therapy research., Methods: Ten 8-week-old C57BL/6J mice, weighing (20 +/- 2) g, were randomly divided into 2 groups, 5 mice in each group. The middle 1/3 tibiae monolayer cortical bone defect model of 0.8 mm (group A) or 1.0 mm (group B) in diameter was established with burr drill. At 7, 21, and 28 days after modeling, the molybdenum target X-ray radiography was used to observe the defect repair; at 28 days, Micro CT and three-dimensional imaging were used to evaluate bone defect repair, and tibia specimens were harvested for HE staining., Results: At 7 days after modeling, tibia fracture occurred in 5 mice in group B, no fracture in group A. X-ray films, Micro CT scan, and HE staining showed bony union in group A at 28 days. The quantitative analysis of trabecular bone by Micro CT showed that trabecular number, connectivity density, and bone volume in group A were significantly greater than those in group B (P < 0.05), mean of segmented region--mean 2 was significantly less than that in group B (P < 0.05), but no significant difference was found in trabecular separation and trabecular thickness between 2 groups (P > 0.05)., Conclusion: The middle 1/3 tibia monolayer cortical bone defect mouse model of 0.8 mm in diameter is the ideal animal model for study repair mechanism of tibia defect or bone tissue engineering.

Background: Bone graft substitutes are widely used in spinal surgery. Here, serious complications associated with the bone graft substitute GeneX are presented. GeneX contains tri-calcium phosphate and calcium sulphate., Methods: GeneX was used in three patients who had spinal decompression and fusion. Mice were also injected with GeneX, demineralised bone matrix (DBX) or saline subcutaneously. After 24 h the extent of tissue damage and inflammation in tissue sections was quantified. To understand the licensing process for bone graft substitutes, the U.S. Food and Drug Administration (FDA) and the U.K. Medicines and Healthcare products Regulatory Agency (MHRA) websites were accessed., Results: All patients developed sterile pus in soft tissues adjacent to the GeneX followed by skin breakdown in two and pharyngeal perforation in one. In mice, GeneX produced moderate or severe skin damage compared with no or mild skin damage after DBX (p<0.05) or saline (p<0.05) injection. GeneX caused more inflammation in mouse dermis (1704±193 leucocytes/mm2, mean ± SE) than DBX (537 ± 266, p<0.01) or saline (136 ± 19, p<0.01). The FDA and MHRA classify bone graft substitutes as medical devices. In contrast with drugs, medical devices do not need to undergo clinical safety tests before obtaining FDA 510(k) clearance for use in patients., Conclusion: GeneX may cause soft tissue inflammation and destruction and should not be placed next to thin walled structures, such as skin or pharynx, because it may erode through these tissues. Bone graft substitutes should undergo mandatory detailed safety testing prior to approval. This could be achieved by reclassifying them as drugs.

Objectives: To assess the relationship between smooth and roughened implant surfaces of straight and narrow configurations with respect to microdamage of the bone surface during placement of dental implants., Materials and Methods: Straight and tapered, rough and smooth surface Nobel Biocare implants were placed into sheep mandibles. Microdamage within the bone adjacent to the implant surface was quantitated using a semi-automated digitized histomorphometric method., Results: Independent of implant type, microdamage, microcracks, cross-hatch damage and diffuse damage were significantly higher close to the implants compared with far from the implants. Microcracks and cross-hatch damage were higher for the rough cylindrical implants than all the other implant types., Conclusions: Insertion of a rough cylindrical implant type results in an increased fraction of microdamaged bone matrix in comparison to rough tapered, smooth cylindrical and smooth tapered implants., (© 2010 John Wiley & Sons A/S.)

Our purpose was to evaluate the osteoconduction potential of mixed bovine bone (MBB) xenografts as an alternative for bone grafting of critical-size defects in the calvaria of rats. After surgery, in the time intervals of 1, 3, 6, and 9 months, rats were killed and their skulls collected, radiographed and histologically prepared for analysis. The data obtained from histological analysis reported that the particles of MBB did not promote an intense immunological response, evidencing its biocompatibility in rats. Our results clearly showed the interesting evidence that MBB was not completely reabsorbed at 9 months while a small amount of newly formed bone was deposited by osteoprogenitor cells bordering the defect. However, this discrete bone-forming stimulation was unable to regenerate the bone defect. Overall, our results suggest that the properties of MBB are not suitable for stimulating intense bone regeneration in critical bone defects in rats.

We used demineralised bone matrix (DBM) to augment re-attachment of tendon to a metal prosthesis in an in vivo ovine model of reconstruction of the extensor mechanism at the knee. We hypothesised that augmentation of the tendon-implant interface with DBM would enhance the functional and histological outcomes as compared with previously reported control reconstructions without DBM. Function was assessed at six and 12 weeks postoperatively, and histological examination was undertaken at 12 weeks. A significant increase of 23.5% was observed in functional weight-bearing at six weeks in the DBM-augmented group compared with non-augmented controls (p = 0.004). By 12 weeks augmentation with DBM resulted in regeneration of a more direct-type enthesis, with regions of fibrocartilage, mineralised fibrocartilage and bone. In the controls the interface was predominantly indirect, with the tendon attached to the bone graft-hydroxyapatite base plate by perforating collagen fibres.

Objective/hypothesis: Evaluate the treatment of labyrinthine fistula in a large series of middle ear cholesteatomas., Study Design: Case series in a tertiary referral center., Methods: Between January 2001 and December 2007, 361 ears affected by mastoid and middle ear cholesteatoma were operated at our institution. The incidence of labyrinthine fistula, preoperative and postoperative hearing function, preoperative symptoms, type of surgery, and intraoperative findings were all analyzed., Results: The incidence of labyrinthine fistula was 12.7 percent. During surgery the matrix over the fistula was removed in all but one case. A labyrinthine fistula occurred in larger cholesteatomas as demonstrated by the higher number of cases with more than two sites involved (P < 0.001), facial nerve exposed (P < 0.001), and stapes superstructure eroded (P = 0.010). Postoperative change of bone conduction threshold and postoperative dead ears were not significantly different between fistula and nonfistula cases., Conclusions: The preservation of the bone conduction threshold is a common finding in small fistulas and can be obtained also in "large" fistulas when appropriate surgical technique is used. In fistulas involving the promontory the matrix should be left in situ when the endosteum is involved.

Heterotopic ossification occurring after the use of commercially available bone morphogenetic proteins has not been widely reported. We describe four cases of heterotopic ossification in patients treated with either recombinant bone morphogenetic protein 2 or recombinant bone morphogenetic protein 7. We found that while some patients were asymptomatic, heterotopic ossification which had occurred around a joint often required operative excision with good results.

The aim of this study was to evaluate histological and radiological osseointegration characteristics of implanted di-/tri-calciumphosphate in patients bone substitute material in opening-wedge osteotomies patients. Up to now the hypothesis of bioresorption and replacement with vital bone bases on numerous animal studies showing complete remodelling within 12-26 weeks. Histological patient studies hardly exist. In this study 13 patient biopsies were collected 16 months after tibial osteotomy. Unlike animal studies the results showed mainly incorporated avital cement residues (38%) as well as new bone formation (61%). Radiological scoring confirmed increasing signs of osseointegration and an incomplete resorption. In conclusion degradation and replacement of di-/tri-calciumphosphate seems to be less accelerated in patients than prior animal studies indicated. Nevertheless, it shows excellent biocompatibility, good osteoconductive characteristics and may represents a useful alternative to autogenous graft.

Demineralised bone matrix (DBM) acts as an osteoconductive, and possibly as an osteoinductive, material. It is widely used in orthopaedic, neurosurgical, plastic and dental areas. More than 500,000 bone grafting procedures with DBM are performed annually in the US. It does not offer structural support, but it is well suited for filling bone defects and cavities. The osteoinductive nature of DBM is presumably attributed to the presence of matrix-associated bone morphogenetic proteins (BMPs) and growth factors, which are made available to the host environment by the demineralisation process. Clinical results have not been uniformly favourable; however, a variable clinical response is attributed partly to nonuniform processing methods found among numerous bone banks and commercial suppliers. DBMs remain reasonably safe and effective products. The ultimate safe bone-graft substitute, one that is osteoconductive, osteoinductive, osteogenic and mechanically strong, remains elusive.

Objective: To study the integration of mice [corrected] marrow stromal stem cells (MSCs) after transplantation into acellular extracellular matrix (AECM)., Methods: We got 16 femurs from 8 Kunming mice [corrected], the femurs were treated by Triton X-100 to get AECM, MSCs were collected from femoral marrow of 20 Kunming rats about a mouth old by PBS 4 ml, centrifuged and primary cultured in bottles, then the mice [corrected] MSCs were transplanted into AECM at a concentration of 5 x 10(6)/ml and cultured for 7 days. The integration of the donor cells was observed using one phase contrast microscope, a light microscope and a scanning electron microscope (SEM)., Results: In AECM bone lacunas there were MSCs nuclei stained blue. The nuclei were unevenly distributed in AECM with more in the peripheral AECM than in the central AECM and with more in the layer near culture medium than in the layer far away from culture medium. AECM possessed a good spatial scaffold structure, the marrow stromal stem cells were well integrated into AECM., Conclusion: AECM can be used as a good scaffold material for tissue engineered bone construction.

Object: The authors studied the effect of a resorbable graft containment device in a rabbit posterolateral lumbar spinal fusion model., Methods: Twenty rabbits were divided into four groups: autologous bone graft (ABG), ABG with the MacroPore containment device (ABG + MP), demineralized bone matrix (DBM), and DBM with the containment device (DBM + MP). Fusion mass was assessed at 6 weeks with high-resolution radiography and volumetric computerized tomography. The graft containment device was associated with alteration of the fusion mass structure and significant enhancement of fusion mass volume (ABG versus ABG + MP, p = 0.027; DBM versus DBM + MP, p = 0.043)., Conclusions: A bioabsorbable protective graft containment device successfully enhanced posterolateral spinal fusion mass volume.

Until now, modern miniature cryoprobes have been used successfully for the local destruction of soft-tissue tumors without damaging adjacent healthy tissue. In this study, the methodology of cryoablation was applied to bone, and the freezing effect as well as the cooling capacity of the probe were examined. Freezing was performed by cooling one or two probes, with a diameter of 3.2 mm, to -180 degrees C with liquid nitrogen. The cooling capacity of the probes was determined under optic and thermic control in a homogenous reference gel (gelatin), followed by an in vitro measurement on human bone. The simultaneous use of 2 probes resulted in a synergistic effect which produced an almost spherical expansion of frozen area in the homogenous gelatin. In vitro freezing of human tibiae produced equivalent freezing temperatures, with one or two probes, in comparison to the homogenous gelatin. An adequate tissue cooling of bone matrix can be achieved through the use of one or more miniature cryoprobes so that after in vivo testing, the use of this probe could possibly become an alternative or supplement to the surgical resection of pathologic bone processes.

Background: Relative few reports exist concerning healing of laser created osteotomies over an extended period of time. The purpose of this study was to evaluate long-term healing, from 21 to 63 days, of osteotomy defects in the rat tibia created with the Nd:YAG and CO2 in the presence of a surface cooling spray of air/water., Methods: The experimental model consisted of 15 large Sprague-Dawley rats. Six treatment modalities were randomly distributed among 6 tibial recipient sites: 1) a negative control (no treatment); 2) a positive control (bur osteotomy); 3) CO2 laser at 5 W (860 J/cm2); 4) CO2 laser at 6 W (1,032 J/cm2); 5) Nd:YAG laser at 5 W (714 J/cm2); and 6) Nd:YAG laser at 7 W (1,000 J/cm2). All laser irradiation was delivered in the presence of a surface coolant consisting of air (15 psi) and sterile water. Five animals were sacrificed at each of 3 time intervals: 21, 35, and 63 days post-treatment. Multiple histologic sections from each treatment site were examined by light microscopy using hematoxylin and eosin Goldner's trichrome stains, and polarized light and evaluated for presence of a char layer, heat induced cracking, heat related alterations in cells or tissue matrix, and osseous regeneration., Results: Healing was severely delayed in all laser treated sites compared to positive control sites. Of the laser treated sites, those irradiated by CO2 laser at 5 W (780 J/cm2) exhibited the greater amount of bone regeneration. At best, however, only a small percentage of sections from any of the laser treated specimens showed evidence of bone regeneration within the ablation defect regardless of the post-treatment time interval., Conclusions: Under the conditions of this study, the osseous healing response was severely delayed by CO2 and Nd:YAG laser irradiation of bone, even in the presence of a surface cooling spray of air/water.

Activated adult human alveolar bone cells were isolated from 2-wk-old osteogenic tissue recuperated from dental implant surgeries following a two-step procedure. Osteogenic tissues were cultured as explant for 2 months. Cells began to migrate in the first 3 d and were confluent in 3-4 wk. However, adjacent to the explants, multicellular cell layers began to form in 10 d, and matrix mineralization was observed by 4 wk in these areas. These formations enlarged and by the end of the culture period, large diffuse matrix mineralization areas were observed. Light and electron microscopic observations confirmed the presence of a collagen matrix undergoing a mineralization process but showing important differences with the mineralized matrix tissue formed with a rat embryo calvaria bone cell system. This new model, using activated human alveolar bone cells, may provide a tool to investigate alveolar bone development and physiology and to set up new therapeutic approaches.

A model of bifocal distraction osteogenesis in the canine model was used to assess and quantitate the mineral content of the newly forming bone within the canine mandible. A 2-cm defect was created in the body of the mandible, and after a posterior osteotomy, the transport disk was advanced at 0.25 mm per 8 hours for 21 days and then held in rigid fixation for an additional week. As a control for this study, three additional dogs underwent the same procedure with the exception that the transport disk was not advanced. Electron dispersive spectroscopy analysis was performed on the newly formed regenerate bone and compared with areas of existing cortical bone of both the transport disk and the mandible. In the control model, special note was made of the pericortical callus at the osteotomy site as well as of the regenerative bone that filled the 2-cm defect in the body of the mandible. Calcium/phosphorous ratios were used to assess the composition of the mineralized regions of the mandible. The regenerate bone that filled the defect and the mineralized callus surrounding the site of osteoclasis in the control mandible were significantly different in composition when compared with the regenerate bone that formed during distraction osteogenesis. This suggests that distraction osteogenesis may effect an initial matrix production that is more similar in composition to the mature cortical bone from which it was derived than does periosteal regeneration and filling of an osseous defect.

HCl-demineralized mid-diaphyseal allogeneic segments of tibia were implanted in the lumbar muscles of rats fed either a magnesium-deficient or a magnesium-supplemented diet for one week prior to implantation and for three weeks thereafter. Histological studies, histochemical mucopolysaccharide determinations, tests for protease content of undemineralized bone tissue, and microradiography showed that in the normal hosts mostly trabecular bone grew into the heterotopic site, whereas in the deficient rats a large fibrous covering formed about the implant and in many instances cartilage was present in multiple locations under the fibrous coat. In some instances cartilage wedges, not preceded by multinucleated giant cells (matrixclasts), invaded the implant. This fibrocartilaginous response to an exogenous inductor resembled the modified growth pattern of bone recently reported in magnesium-deficient rats.