Enhanced binding of low-affinity antibodies interacting simultaneously with targeted cell surface molecules and Fc receptor.

The possibility that different forms of class I molecules might be expressed on the cell surface of lymphocytes has been investigated periodically over the past several decades. A series of major histocompatibility complex (MHC) class I-specific monoclonal antibodies, including the commonly used antibodies 64-3-7 and 25-D1.16, bind B cells differentially, suggesting the existence of differentially expressed class I-associated cell surface determinants on B lymphocytes. However, the ability of antibodies to bind cells is determined by the sum of interactions between the antibodies and the molecules expressed on the cell surface. The interactions of class I-specific antibodies with B cells were dissected, revealing dual specificity of the antibodies for the targeted class I molecules, as well as to Fc receptors preferentially expressed by B cells. We demonstrate that antibodies simultaneously bind targeted class I molecules and Fc receptors expressed on the surface of B cells. Simultaneous binding to two cell surface structures significantly enhances the class I-specific binding pattern of certain antibodies by increasing their avidity, leading to apparent cell-specific differences in MHC expression patterns. We conclude that no differences in MHC structures need be postulated to account for the observed binding patterns.

Monomeric class I molecules mediate TCR/CD3 epsilon/CD8 interaction on the surface of T cells.

Both CD8 and the TCR bind to MHC class I molecules during physiologic T cell activation. It has been shown that for optimal T cell activation to occur, CD8 must be able to bind the same class I molecule that is bound by the TCR. However, no direct evidence for the class I-dependent association of CD8 and the TCR has been demonstrated. Using fluorescence resonance energy transfer, we show directly that a single class I molecule causes TCR/CD8 interaction by serving as a docking molecule for both CD8 and the TCR. Furthermore, we show that CD3epsilon is brought into close proximity with CD8 upon TCR/CD8 association. These interactions are not dependent on the phosphorylation events characteristic of T cell activation. Thus, MHC class I molecules, by binding to both CD8 and the TCR, mediate the reorganization of T cell membrane components to promote cellular activation.

Onplant-supported orthodontic anchorage.

The use of onplant-supported orthodontic anchorage is still in its early stages. The concepts presented in this article have tried to stress the importance of anchorage control in orthodontic cases, some problems associated with traditional means to augment orthodontic anchorage, the rationale for developing a skeletal anchorage unit based on endosseous implant technology, and the effectiveness of the onplant as an anchorage unit. Cephalometric superimpositions are most likely the best method to determine the effectiveness of the onplant's contribution to anchorage control and have been included here to that end. Further research into its effectiveness may broaden the use of onplants in future orthodontic cases.

Bone gap healing in the dog using recombinant human bone morphogenetic protein-2.

PURPOSE: This study investigated bone gap healing in a zygomatic arch defect using recombinant human bone morphogenetic protein-2 (rhBMP-2; Genetics Institute, Andover, MA) in an absorbable collagen sponge (ACS) carrier. METHODS: Zygomatic arch osteotomies were completed 15 mm apart and the arch was mobilized in 6 adult female mongrel dogs. The segment was then repositioned laterally 8 to 10 mm and secured with a titanium reconstruction plate. Bone gaps in either the right or left arches received rhBMP-2, with the contralateral side being left empty in 4 animals and the defects received buffer/ACS without rhBMP-2 in 2 animals as controls. Submentovertex radiographs were taken immediately postoperatively and every 4 weeks until killing at 12 weeks. RESULTS: Clinical evaluation indicated no significant differences in the degree of inflammation between the groups. However, the rhBMP-2 sites were found to be firm on palpation, in contrast to a soft tissue defect palpated in the control sites. Radiographic examination showed significant bone formation in all rhBMP-2 grafted sites as early as 4 weeks. The radiopacity of the bone continued to increase over the time of this study. Five of six control sites did not show bone formation through the course of this study. In addition to lack of bone formation, 5 of 6 control sites showed collapse of the repositioned arch. All arches in the rhBMP-2 sites remained in their lateral position and formed bone in the gaps. In 2 animals, bone formation moderately exceeded the confines of the gap, and in 2 animals excessive bone formation occurred. CONCLUSIONS: This study confirms that rhBMP-2 has the potential to be used to stimulate bone gap healing in the craniofacial complex.

Loaded hydroxylapatite-coated implants and uncoated titanium-threaded implants in distracted dog alveolar ridges.

AIMS: The aim of this study was to determine the response of alveolar bone after it was augmented vertically with distraction osteogenesis, implanted with hydroxylapatite (HA)-coated implants and noncoated titanium-threaded implants, and subsequently loaded for 1 year. METHODS: Eight dogs each had 4 implants placed horizontally into an edentulous mandibular quadrant. After integration, a distraction osteogenesis device was fabricated in the laboratory. An osteotomy was made to allow the crest of the alveolar ridge to be distracted vertically. After 10 mm of vertical distraction, the distraction devices were stabilized with light cured resin. After bone fill of the distraction gap was radiographically confirmed in all dogs at 10 weeks, 2 implants were placed into the ridges. Four dogs had threaded titanium implants placed, and 4 dogs had threaded HA-coated implants placed, with 1 implant in the distracted bone and 1 implant in adjacent nondistracted bone, for both groups. After 4 months for implant integration, bridges were fabricated and secured to the implants with screws. Crestal bone levels were evaluated by radiographs through 1 year of function. Animals were killed after 1 year of loading for histologic evaluation. RESULTS: The vertical ridge augmentation averaged 8.8 +/- 1.0 mm after 10 weeks of healing after distraction. Analysis of variance indicated a significantly greater change from baseline for HA-coated implants and for distracted bone sites. Histologic examination showed that bone had formed between the distracted segments creating an augmented ridge. The average thickness of the labial cortex in the distraction gap was significantly thinner than the lingual cortex in distracted bone or the lingual and labial nondistracted cortical bone. The presence of a dental implant did not significantly affect cortical bone thickness. Serial sections showed that implants remained integrated and functional without soft tissue inflammation. CONCLUSION: Dental implants placed into alveolar ridges augmented with the technique of distraction osteogenesis were functional for the length of this study.

Preserving alveolar ridge anatomy following tooth removal in conjunction with delayed implant placement.

1. Prior to placing implants, the health of the adjacent teeth and supporting tissues should be good. The presence of acute infection (exudate, granulation tissue, gingival hyperplasia), poor oral hygiene, or active chronic periodontal disease are associated with an increased incidence of infection or tissue breakdown. 2. Avoid excessive dissection of papilla. 3. Stabilize membranes with apical tacks and secure the coronal portion to the implant with the cover screw. 4. Relieve the periosteum to allow for a tension-free closure. 5. Avoid postoperative trauma on the surgical site.

Report of the Sinus Consensus Conference of 1996.

Retrospective data from sinus floor augmentation bone grafts were collected from 38 surgeons for 1007 sinus grafts that involved the placement of 2997 implants over a 10-year period, with the majority of the implants followed for 3 years or more postrestoration. There were 229 implant failures reported. Various root-form implants and grafting modalities were used. A consensus conference was organized to evaluate the data and reach a consensus on optimal treatment protocols. The complete database demonstrated a 90.0% success rate for implants placed in sinus grafts with at least 3 years of function. Differences in grafting materials, implant surfaces, and timing protocols were statistically analyzed. However, the database was so multivariate and multifactorial that it was difficult to draw definitive conclusions; these must await controlled prospective studies. The consensus conference therefore developed and voted on multiple consensus statements derived by committee review for bone graft materials, type of implants, timing for implant placement, failure analysis, radiographic analysis, indications/contraindications, prosthetics, and nomenclature. Several consensus statements were obtained, the most significant being that the sinus graft should now be considered a highly predictable and effective therapeutic modality.

The effect of different membranes on onlay bone graft success in the dog mandible.

OBJECTIVE: The aim of this study was to compare resorbable membranes, nonresorbable membranes, and no coverage with respect to onlay bone graft healing in a dog. EXPERIMENTAL DESIGN: Each of four dogs had six corticocancellous blocks of ramus bone placed bilaterally as onlay grafts to the inferior lateral aspect of the mandible. On each side, one graft was left uncovered, one was covered with a collagen membrane, and one was covered with an expanded polytetrafluoroethylene membrane. Volume determinations were made at the time of graft placement and when the animals were killed. RESULTS: There were no statistically significant differences in bone volume or histologic outcome among the three groups.

Bone response to functioning implants in dog mandibular alveolar ridges augmented with distraction osteogenesis.

The specific aim of this study was to determine the response of alveolar bone after it was augmented vertically using distraction osteogenesis and subsequently loaded with implant restorations. Four dogs each had four implants placed horizontally into an edentulous mandibular quadrant and, after integration, a distraction osteogenesis device was fabricated in the laboratory. An osteotomy was made to allow the crest of the alveolar ridge to be distracted vertically. After 10 mm of vertical distraction, the device was stabilized with light cured resin. Following bone fill confirmation of the distraction gap at 10 weeks, two implants were placed into the ridges, one in distracted bone and one in nondistracted bone. After 4 months for implant integration, freestanding prostheses were fabricated. Crestal bone levels were evaluated throughout the period of function. Animals were sacrificed after 1 year of loading, for histologic evaluation of the bone. The vertical ridge augmentation averaged 8.85 +/- 1.05 mm after 10 weeks of healing following distraction, without change over 1 year of implant loading. Histologic examination showed that bone had formed between the distracted segments, creating an augmented ridge. The average thickness of the labial cortex in the distraction gap was significantly thinner than the lingual cortex in distracted bone and the lingual and labial nondistracted cortical bone. The presence of the dental implant did not significantly affect cortical bone thickness. Serial sections showed that implants remained integrated and functional without soft tissue inflammation. Dental implants placed into alveolar ridges augmented with the technique of distraction osteogenesis maintained bone and were functional for the length of this study.

Bone maintenance 5 to 10 years after sinus grafting.

PURPOSE: This radiographic study determined the amount of bone around hydroxyapatite (HA)-coated dental implants that were placed into bone-grafted maxillary sinuses. PATIENTS AND METHODS: Postoperative complex motion tomograms using the Grossman technique were taken on 16 patients who had 27 maxillary sinus grafts performed using particulate autogenous iliac bone with and without demineralized bone, autogenous iliac corticocancellous block with and without demineralized bone, and autogenous jaw bone with demineralized bone. Bone levels were measured from the new floor of the grafted sinus to the apex of the implant and to the alveolar crest. The resulting bone level measures were compared with the type of graft used. All patients had been restored for 5 to 10 years after simultaneous graft and implant placement. RESULTS: For all patients summed together, the average amount of bone from the top of the graft to the apex of the implant was 3.3 +/- 3.1 mm, and the average amount of bone from the top of the graft to the alveolar crest was 17.6 +/- 3.1 mm. The average level of bone in the sinuses of patients grafted with autogenous iliac bone was greater than the average level of bone in those grafted with autogenous bone combined with demineralized bone. CONCLUSION: The results of this study indicate that autogenous bone grafts are maintained in the maxillary sinus, but the results with autogenous bone alone are better than when demineralized bone is added. However, this difference may not be clinically significant.

An experimental study of mandibular arch widening in the dog using distraction osteogenesis.

PURPOSE: This study evaluated the amount of skeletal and dental widening of the mandible in the dog produced by using a tooth-borne distraction device. MATERIALS AND METHODS: Four adult mongrel dogs had osteotomies performed in the parasymphysis region and had a tooth-borne distraction appliance placed to widen the mandible 10 mm. The interarch distance between the canines and between the fourth premolar teeth, as well as between the intrabony markers, was compared. RESULTS: The canine teeth moved 95% of the distraction device movement, whereas the bone widened 55% of the distraction device movement. Histological evaluation showed woven bone formation within the distraction gap. CONCLUSION: This study shows that a tooth-borne mandibular widening device will move the teeth significantly more than the bone.

Skeletal and dental movements after anterior maxillary advancement using implant-supported distraction osteogenesis in dogs.

PURPOSE: This study evaluated skeletal and dental relapse in the dog after anterior maxillary advancement using an implant-anchored distraction osteogenesis device. MATERIALS AND METHODS: After the placement of implants into the palate, four dogs had a skeletally anchored distraction device fabricated and an anterior maxillary osteotomy performed. The distraction device was activated 0.5 mm two times each day to advance the anterior segment 10 mm in 10 days. The dental and skeletal changes were measured and compared for 26 weeks after distraction was completed. RESULTS: Tooth and radiographic measurements indicated that on the 10th day of distraction the average tooth advancement was 6.83 mm +/- 1.75 mm SD, and the average skeletal advancement, based on radiographs, was 8.67 mm +/- 1.25 mm SD. After 10 weeks, the average tooth advancement was 4.0 +/- 1.73 mm, and the average skeletal advancement was 8.67 +/- 3.59 mm. After 26 weeks, the average tooth advancement was 3.65 +/- 1.69 mm, and the average skeletal advancement was 8.0 +/- 1.98 mm. Bone healing occurred in all animals. The skeletal advancement 26 weeks after distraction was 85% of the initial advancement. The teeth adjacent to the distraction site initially moved 68% of the advancement, but the distance between the teeth subsequently decreased, with a resultant 36% advancement compared with the initial advancement. CONCLUSION: This study showed that skeletal fixation will result in bone movement greater than dental movement, indicating the need for skeletal anchorage to advance the maxilla.

Sinus augmentation for dental implants: the use of autogenous bone.

Autogenous bone has been the material of choice at our institution since 1983. The criteria for a successful graft in the sinus have been fulfilled based on functional stability in patients followed-up over 10 years in selected cases. Of 173 implants placed into autogenous bone grafted sinuses, 20 have been lost in four patients. Long-term follow-up is recommended for all graft materials used to support posterior maxillary restorations.

Radiocephalometric evaluation of a family with mandibulofacial dysostosis.

Persons from four generations of a family with mandibulofacial dysostosis (MFD), known as Treacher Collins (TC) Syndrome, were examined for the presence of clinical signs traditionally associated with this syndrome. In this family, 14 adults, who had been judged trait bearers by an earlier family study were included in this study. Maxillary and mandibular study models were taken of affected and unaffected family members. Panoramic cephalograms and lateral radiographs were taken. The lateral cephalograms were traced and digitized on a computer system and compared. The 117 cephalometric values of the trait bearers were compared with known standard values and nontrait bearing family members. In the trait bearing group, 81 of the 117 values and, in the nontrait bearing group, 72 of the 117 values were significantly different (p < 0.05) when comparing mean values to the accepted normal range. The interfamily comparison between trait-bearing and nontrait members revealed nine values to be significantly different. This indicates that cephalometric analysis of these patients, some of whom have minimal clinical expression of the gene, may have potential value for screening and further characterization of this condition. The results also suggest that intrafamily comparisons may be of greater value for diagnostic confirmation of TC than comparison with literature norms.

Hydroxyapatite-coated cylindrical implants in the posterior mandible: 10-year observations.

A total of 443 hydroxyapatite-coated cylindrical implants were placed into the posterior mandibles of consenting patients from July 1985 through December 1991. Implants were placed into ridges that had sufficient bone volume. Implants were also placed in ridges with thin bone, grafted bone, or immediate extraction sites, which occasionally resulted in increased morbidity. All were followed yearly with clinical and radiographic examinations. Life table analyses were performed using SAS software. Ten-year cumulative survival and nonmorbid (based on bone loss criteria) rates were determined for the four posterior tooth locations and for all posterior locations combined. Cumulative survival for implants was 0.858 +/- 0.056 in the first premolar region, 0.833 +/- 0.041 for the second premolar region, 0.785 +/- 0.041 for the first molar region, and 0.718 +/- 0.064 for the second molar region. When all posterior mandibular locations were taken together, the cumulative survival was 0.793 +/- 0.025. Cumulative nonmorbid rates were 0.816 +/- 0.056 for the first premolar, 0.729 +/- 0.049 for the second premolar, 0.600 +/- 0.046 for the first molar, and 0.507 +/- 0.066 for the second molar. The cumulative nonmorbid rate was 0.646 +/- 0.028 for all sites combined. Comparisons between sites indicated that the second molar site had statistically more morbidity than did the other three sites. Most of the problems were identified with 8-mm-long implants, especially in the second molar location. Clinical parameters, including the presence of keratinized gingiva and a hygienic restoration, were associated with survival. Both mechanical and inflammatory compromise were found to be reasons for implant failure.