Inhaltsverzeichnis:Oral & Craniofacial Tissue Engineering 2 (2012), Nr. 4 (15.12.2012)
Seiten: 261 - 337
Seite 261-262, Sprache: Englisch
Editorial: Ockham's Razor and CD34+
Jensen, Ole T.
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Purpose: This study investigated the role of the bone marrow-derived CD34+ cell in a milieu of osteoprogenitor cells, bone marrow plasma cell adhesion molecules, recombinant human bone morphogenetic protein (rhBMP), and a matrix of crushed cancellous allogeneic bone in the clinical regeneration of functionally useful bone in craniomandibular reconstructions. The history and current concepts of bone marrow hematopoietic stem cells and mesenchymal stem cells are reviewed as they relate to bone regeneration in large continuity defects of the mandible.
Materials and Methods: Patients with 6- to 8-cm continuity defects of the mandible with retained proximal and distal segments were randomized into two groups. Group A received an in situ tissue-engineered graft containing 54 ± 38 CD34+ cells/mL along with 54 ± 38 CD44+, CD90+, and CD105+ cells/mL together with rhBMP-2 in an absorbable collagen sponge (1 mg/cm of defect) and crushed cancellous allogeneic bone. Group B received the same graft, except the CD34+ cell concentration was 1,012 ± 752 cells/mL. The results were analyzed clinically, radiographic bone density was measured in Hounsfield units (HU), and specimens were analyzed histomorphometrically.
Results: Forty patients participated (22 men and 12 women; mean age, 57 years). Eight of 20 group A patients (40%) achieved the primary endpoint of mature bone regeneration, whereas all 20 group B patients (100%) achieved the primary endpoint. CD34+ cell counts above 200/mL were associated with achievement of the primary endpoint. Bone density was lower in group A (424 ± 115 HU) than in group B (731 ± 98 HU). Group A bone showed a mean trabecular bone area of 36% ± 10%, versus 67% ± 13% for group B.
Conclusions: The CD34+ cell functions as a central signaling cell to mesenchymal stem cells and osteoprogenitor cells in bone regeneration. The mechanism of bone marrow-supported grafts requires a complete milieu to regenerate large quantities of functionally useful bone. CD34+ cell counts in a concentration of at least 200/mL in composite grafts are directly correlated to clinically successful bone regeneration.
Schlagwörter: bone regeneration, hematopoietic stem cells, mesenchymal stem cells, recombinant human bone morphogenetic protein
In the face of extraordinary advances in the prevention, diagnosis, and treatment of human diseases, the inability of most tissues and organs to repair and regenerate after damage is a problem that needs to be solved. Stem cell research is being pursued in the hope of achieving major medical breakthroughs. Scientists are striving to create therapies that rebuild or replace damaged cells with tissues grown from stem cells that will offer hope to people suffering from various ailments. Regeneration of damaged periodontal tissue, bone, pulp, and dentin is a problem that dentists face today. Stem cells present in dental pulp, periodontal ligament, and alveolar bone marrow have the potential to repair and regenerate teeth and periodontal structures. These stem cells can be harvested from dental pulp, periodontal ligament, and/or alveolar bone marrow; expanded; embedded in an appropriate scaffold; and transplanted back into a defect to regenerate bone and tooth structures. These cells have the potential to regenerate dentin, periodontal ligament, and cementum and can also be used to restore bone defects. The kind of scaffold, the source of cells, the type of in vitro culturing, and the type of surgical procedure to be used all require careful consideration. The endeavor is clearly multidisciplinary in nature, and the practicing dental surgeon has a critical role in it. Playing this role in the most effective way requires awareness of the huge potential associated with the use of stem cells in a clinical setting, as well as a proper understanding of the related problems.
Schlagwörter: dental pulp stem cells, dentistry, human cementum-derived cells, periodontal ligament stem cells, stem cells from human exfoliated deciduous teeth, stem cells from root apical papilla
Purpose: Atrophic ridges usually have both hard and soft tissue shortages, and bone augmentation can make soft tissue closure difficult. The aim of this case series is to present a new method utilizing transfer of free fat tissue grafts (FFG) from the buccal fat bad (BFP) during bone augmentation to enhance immediate primary soft tissue closure and improve long-term soft tissue thickness and quality at the recipient site.
Materials and Methods: Patients with moderate to severe ridge atrophy in different regions of the jaws were treated over a 4-year period with bone augmentation and FFG. The BFP was the donor site for the FFG. Patients were examined clinically and radiographically (periapical) every 2 weeks. At 4 months, computed tomography was performed to evaluate the bone gain. Reentry was performed after 4 to 5 months to evaluate the soft tissue, obtain specimens for histologic examination, and insert implants.
Results: Twenty patients (18 women, 2 men; mean age 43 years) were followed for 4 to 42 months and received 92 implants in the augmented sites. The healing process was uneventful, with minimal morbidity. Bone volume increased by 4 to 8 mm horizontally and 3 to 6 mm vertically. Thick soft tissue was obtained at the recipient sites and around the dental implants, and histologic specimens showed that the FFG was replaced by fibrous tissue.
Conclusions: Harvesting of the FFG from the BFP is a simple procedure with minor complications, and manipulation and handling of the graft are easy. The FFG enhances primary soft tissue closure of augmented bone, prevents dehiscences, improves long-term soft tissue thickness, and mimics the attached gingiva in its fibrous healing.
Schlagwörter: autologous fat transfer, bone augmentation, buccal fat pad, fibrous healing, soft tissue grafts, soft tissue management
Purpose: Primary stability of dental implants, particularly when they are placed into immediate function in the maxilla, has been thought to be required. An alternative to primary stability is secondary stabilization, which can be obtained by a four-implant distribution pattern using 30-degree angulations for all four implants in the so-called "M-4" treatment scheme in combination with cross-arch stabilization from a prosthesis. If successful, the use of these two measures brings into question whether or not primary stability is required for immediate function in the maxilla.
Materials and Methods: Patients were treated with the M-4 implant scheme with immediate function, despite the instability of at least one of the four implants. Instability was defined as less than 15 Ncm of insertion torque and palpable mobility, and an average anteroposterior spread of 15 mm between each implant was sought. The patients were followed for 1 year.
Results: Ten patients were treated with a total of 40 implants. Composite insertion torque of the four implants was less than 100 Ncm in half of the patients; the average anteroposterior spread was 15.6 mm. After 1 year, no implants had been lost, and bone levels around all implants were at or near operative levels. There were no failures of provisional or definitive prostheses.
Conclusions: M-4 distribution of implants with an average of 15 mm of anteroposterior spread and cross-arch stabilization did not require that all four implants had high insertion torque; in fact, all mobile implants stabilized and osseointegrated under these conditions.
Schlagwörter: All-on-Four, anteroposterior spread, composite insertion torque, cross-arch stabilization, immediate function maxilla, insertion torque, M-4, primary stability, secondary stabilization
Purpose: It is hypothesized that local application of statins positively affects bone formation. The aim of this study was to evaluate the potential effect of topical slow-release simvastatin as a bone substitute on the healing of bone defects in rat tibia.
Materials and Methods: Granules of slow-releasing hydroxypropyl methylcellulose, with or without simvastatin, were inserted into critical-size defects in the tibiae of 16 rats (8 in the study group, 8 in the control group). Bone static and dynamic histomorphometric variables were examined at 2, 4, 6, and 8 weeks postsurgery.
Results: All indices examined in the study group indicated improved healing relative to the control group, although statistical significance was not demonstrated for all variables. In the static histomorphometric analysis, osteoid thickness and volume were significantly higher in the study group, but the fraction of trabecular surface covered with active osteoblasts, the fraction of trabecular surface covered with osteoid, and total calcified bone volume were not significantly higher in the experimental group. In the dynamic histomorphometric analysis, the mineral apposition rate, determined by time-repeated calcein labeling, was significantly higher in the study group than in the control group. Experimental time and dosage effects were observed for most bone values in the study group.
Conclusion: The findings indicate that topical application of simvastatin for the treatment of bone defects enhances the process of healing. Dosage and the methodology of administration require further calibration.
Schlagwörter: animal study, bone healing, bone substitutes, simvastatin, statins
While the AIDS epidemic of the 1980s taught the medical and dental professions much about immune cells and the immune system's cellular relationships, the bisphosphonate-induced osteonecrosis epidemic of the past decade has taught these same professions much about bone turnover, bone cell cross talk, the response and functional relationship of bone cells to loading, and drug effects on cellular dynamic relationships. The present article explores the literature as well as both evidence- and experience-based data to discuss known bone pathologies and physiologic mechanisms as well as uncover new findings: (1) bone remodeling is the mechanism by which bone adapts to loading stresses, termed either bone modeling or Wolff's law, and it is also the mechanism for bone renewal; (2) osteoclastic bone resorption triggers bone renewal at a rate of about 0.7%/day by its release of growth factors; (3) bisphosphonates prevent the renewal of old and injured bone, thus making it brittle and more likely to fracture over time; (4) bisphosphonates have a half-life in bone of 11 years because of their irreversible binding to bone via their central carbon atom; (5) when administered intravenously, bisphosphonate loads bone and accumulates in bone 142.8 times faster than when administered orally; (6) osteoclastic resorption of bisphosphonate-loaded bone results in osteoclast death in which the cell bursts, releasing the bisphosphonate molecules to reenter the local bone or bone marrow in a re-dosing effect; (7) endosteal osteoblasts are dependent on the osteoclastic resorption/growth factor release/new bone formation mechanism of bone renewal, whereas periosteal osteoblasts are not; and (8) it is likely that endosteal osteoblasts and periosteal osteoblasts have different cell membrane receptors and arise from separate embryologic niches.
Schlagwörter: bisphosphonates, bisphosphonate-induced osteonecrosis of the jaw, bone modeling, bone remodeling, bone resorption, osteoblasts, osteoclasts, osteoporosis
Reconstruction of complex maxillofacial defects where the use of bone morphogenetic protein-2 composite grafts may be preferred can be done using perforated titanium shells or forms that confine the graft material and simultaneously establish the desired shape of the augmentation without resorting to autogenous block bone grafting. Reported here is a method for creation of rapid-prototype titanium bone forms, which was developed from a software program, to reproduce bone morphology precisely. The technique and treatment planning objectives are elucidated, especially with regard to complex vertical augmentations.
Schlagwörter: bone forms, bone morphogenetic protein-2, rapid-prototype titanium, titanium shells, treatment planning, vertical augmentation
Purpose: This study used finite element analysis and a clinical case example to test the hypothesis that a wing-thread placed 4 mm below the top of an implant would decrease crestal bone loss in function.
Materials and Methods: Finite element analysis was used to compare standard and wing-thread implants subjected to axial and off-axis forces based on the hypothesis that decreasing bone strain at the alveolar crestal margin improves peri-implant bone stability. A clinical case example of the wing-thread implant was followed for 30 months.
Results: Stress concentration was diminished at the crest when a wing-thread was used compared to a standard implant body. Ninety-degree lateral forces were diminished by a factor of 10 in the wing-thread implant. A patient followed for 30 months showed stable bone levels around the wing-thread implants.
Conclusion: The wing-thread hypothesis appears to have some support for increasing bone stability based on finite element analysis and early clinical results.
Schlagwörter: biomechanics, bone loss, bone strain, mechanostat, peri-implantitis, wing-thread
Seite 335, Sprache: Englisch
From Junk to Treasure: September 2012
Glick, Paul L.
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Seite 336-337, Sprache: Englisch
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