The fate of preserved autogenous bone graft

Certain clinical conditions exist in which a section of cranial bone is removed but not immediately replaced at the initial procedure. Preservation of this bone can provide a valuable autogenous donor source for a future reconstructive procedure. The purpose of our study was to compare the volume retention of fresh autogenous bone with that of preserved autogenous bone as inlay and onlay cranial grafts. Two bone grafts were harvested from the skull of 15 adult New Zealand White rabbits. The graft volumes were calculated, and the graft were preserved in a normal saline-antibiotic solution at -20 degrees C. Three months later, during the second procedure, a fresh graft was harvested and then placed in the preexisting occipital defect as an inlay graft. Also at this time, the preserved grafts were placed, one as an inlay graft in the fresh occipital defect and the other as an onlay graft in the frontal region. The animals were sacrificed 3 months later, and the percentage of graft volume retention was determined. The fresh inlay grafts had a mean volume retention of 85.1 percent, while the preserved inlay nad onlay grafts had 61.8 and 75.9 percent mean volume retention, respectively. It is concluded that while fresh cranial autograft remains the "gold standard" for craniofacial reconstruction, preserved autogenous cranial bone is a viable alternative for inlay and onlay grafting of the craniofacial region.     

A comparative study of osseointegration of titanium implants in autogenous and freeze-dried bone grafts

PURPOSE: This study was undertaken to compare the rate and degree of osseointegration of dental implants when placed into either autogenous corticocancellous chip or freeze-dried corticocancellous chip bone grafts. MATERIALS AND METHODS: The canine ilium was used as the model site. Thirty experimental and 15 control implants were placed in 15 dogs: autogenous versus freeze-dried corticocancellous chip bone grafts around the exposed implant surfaces. In addition to the placement of control implants, the apical portion of the grafted implants acted as their own control. The implants were harvested at 1, 2, and 3 months. The evaluation of the integration process was performed by means of light microscopy, microradiography, and histomorphometry. RESULTS: Using this model, the results indicate that at 1 month there was no statistical difference in the degree of osseointegration in the two bone grafts. At 2 months, there was a statistically greater degree of osseointegration noted in the autogenous corticocancellous chip sites than in the freeze-dried bone grafts. At 3 months, the degree of osseointegration in the two groups was 70% and 33%, respectively. At 3 months, there was virtually 100% integration with trabecular bone at the control implant sites. CONCLUSION: The results indicate that at 2 months postoperatively implants placed in an autogenous bone chip graft osseointegrate to a significantly greater degree than implants placed in a freeze-dried bone chip graft, and this difference remains at 3 months.     

Long-term evaluation of the use of coralline hydroxyapatite in orthognathic surgery

PURPOSE: This prospective study was designed to evaluate the long-term clinical and radiographic results of porous block hydroxyapatite (PBHA) used as a synthetic bone graft in orthognathic surgery and craniofacial augmentation. PATIENTS AND MATERIALS: A total of 245 consecutive patients were treated initially. Inclusion criteria for this study included a minimum clinical and radiographic follow-up of 5 years. In addition, all patients with known implant failures were included regardless of whether they met the study criteria. There were 111 patients that met the criteria for inclusion in this study. All patients had undergone orthognathic surgery with rigid fixation and had had inlay or onlay PBHA implants placed. Ninety-six percent of the implants were placed through an intraoral approach. Long-term postoperative radiographs were visually compared with immediate postoperative radiographs for implant position, stability, resorption, and other significant radiographic changes. The clinical examination evaluated for signs and symptoms of infection, wound dehiscence, implant exposure, implant displacement, changes in the overlying mucosa, and development of oronasal or oroantral fistulae. RESULTS: Four hundred seventy-one implants were placed: 403 in the maxilla, 44 in the mandible, and 24 in the periorbital region. There were 289 implants placed in direct communication with the maxillary sinus. The average follow-up time was 7.2 years (range, 5.0 to 10.3 years). Twenty-three implants (4.9%) were removed during the evaluation period. Lateral maxillary wall grafting had 95.7% success, with nine implants being lost in three patients. One chin implant was removed because of dissatisfaction with the aesthetics. Seven (14%) midpalatal implants used for maxillary expansion were lost, primarily because of exposure of the implant to the oral or nasal cavity at the time of surgery. When PBHA was used for alveolar cleft grafting, there was a 100% failure rate. CONCLUSION: The use of PBHA as a bone graft substitute in orthognathic surgery and for facial augmentation showed a high percentage of success and efficacy. However, adequate soft tissue coverage in the nasal floor and on the palate are paramount for success of midpalatal implants. PBHA should not be used for alveolar cleft grafting. Rigid fixation for inlay implants in the maxilla is important to provide stress shielding of the material and minimize micromovement during the initial healing phase.     

In vivo evaluation of recombinant human osteogenic protein (rhOP-1) implants as a bone graft substitute for spinal fusions

STUDY DESIGN: Posterior spinal fusion segments were evaluated in adult mongrel dogs at 6, 12, and 26 weeks post-implantation. Four sites on each animal received implants consisting of recombinant human osteogenic protein-1 on a bone collagen carrier, bone collagen carrier alone, autogenous iliac crest bone, or no implant material. OBJECTIVE: To determine the efficacy of recombinant human osteogenic protein-1 as a bone graft substitute in achieving posterior spinal fusion and compare the results to those obtained using autogenous bone graft. SUMMARY OF BACKGROUND DATA: Posterior spinal fusion generally includes onlay grafting of autogenous or allogeneic bone after decortication of bony surfaces of the vertebral elements. The search for an acceptable bone graft substitute material has in recent years centered upon proteins capable of inducing bone in vivo. Recombinant human osteogenic protein-1 has demonstrated efficacy in healing large segmental osteoperiosteal defects in rabbits, dogs, and monkeys and appears ideally suited as a bone graft substitute for spinal fusions. METHODS: The quality of fusion and new bone formation was evaluated using plain films, computed tomography, and magnetic resonance imaging. RESULTS: Radiographic and histologic studies demonstrated that recombinant human osteogenic protein-1-treated fusion segments attained a stable fusion by 6 weeks post-implantation and were completely fused by 12 weeks. The autograft sites demonstrated fusion at 26 weeks post-implantation. CONCLUSIONS: The results indicated that recombinant human osteogenic protein-1 is an effective bone graft substitute for achieving stable posterior spinal fusions in a significantly more rapid fashion than can be achieved with autogenous bone graft.     

Sinus inlay bone augmentation: comparison of implant positioning after one- or two-staged procedures

PURPOSE: This study was undertaken to compare implant angulation and position after one- or two-stage sinus inlay bone augmentation. PATIENTS AND METHODS: Twenty patients were retrospectively selected; group 1 (n = 10) was operated on with a one-stage procedure, and group 2 (n = 10) with a two-stage operation. Casts processed for the final permanent or temporary bridgework were collected and photographed from an oblique anterior view paralleling the alveolar crest on the right and left sides, as well as from an occlusal view. The angle between impression pins inserted in the abutments relative to the true vertical was recorded. In the occlusal view, the midpoints of the abutments were related to an individual computerized superimposed parabola. RESULTS: The implants inserted during the one-stage procedure were generally placed more palatally (Wilcoxon rank sum test, P = .0101) and angled more palatally (P = .0009) compared with those placed with the two-stage operation. CONCLUSION: This study showed that the two methods of treating patients by sinus inlay bone augmentation differed significantly with regard to placement and angulation of the implants. A two-stage procedure seems to offer the surgeon more optimal conditions for positioning the implants.     

The use of high-density polyethylene implants in facial deformities

OBJECTIVE: To determine the usefulness of porous high-density polyethylene implants (Medpor) in a variety of facial skeletal deformities and subcutaneous defects, excluding those associated with acute maxillofacial trauma. DESIGN: Case series. SETTING: Academic tertiary care referral center in Baltimore, Md. PATIENTS: Thirty-four patients (age range, 20-74 years) with facial deformities requiring skeletal defect reconstruction or augmentation (38 cases), treated between January 1, 1992, and January 1, 1997. Follow-up ranged from 6 months to 40 months. MAIN OUTCOME MEASURES: Age, type and origin of the deformity treated, type of treatment, and complications. RESULTS: Types of deformities and defects treated include 7 patients with orbital defects (secondary traumatic or oncologic deformities), 8 with temporal fossa defects, 8 with frontocranial defects, 4 with maxillary or malar defects, 7 with calvarial bone graft donor site defects, 2 with microtia, and 2 with chin deficiency. Forty implants were placed. Complications included implant exposure in 4 patients and inappropriate augmentation in 1 patient (chin implantation). CONCLUSIONS: High-density polyethylene implants offer an excellent alternative to autogenous and other alloplastic materials in reconstruction of many facial defects and deformities. Advantages include its versatility and relatively ideal pore size that allows for excellent soft tissue ingrowth and coverage. Disadvantages include its rigid nature and difficulty in contouring to the surface of complex skeletal structures.     

Interrelations of soft and hard tissues for osseointegrated implants

Success in using osseointegrated dental implants-optimal function, esthetics, and phonetics-requires selection of the treatment modality that is optimal for the patient, protection of tissue blood supply, and adherence to a plan based on a thorough analysis of all deviations from the normal anatomy. The options for correction of hard-tissue deficiencies are mechanical modification of the implants and reconstructive surgery. Mechanical approaches reduce the time needed for reconstruction but direct the occlusal forces in unnatural directions. Surgical reconstruction is preferable. Any bone graft must be precisely fitted to the recipient site to facilitate revascularization. Restoration of hard-tissue dimensions usually requires soft-tissue coverage and augmentation. There are two basic options: (1) flaps with or without inlay or onlay grafts and (2) controlled tissue expansion. An onlay graft can help restore soft-tissue height and width. Inlay grafts have greater vascularity than onlay grafts, and the color matching is better. Controlled tissue expansion creates "like" tissue without a secondary defect, and fewer tissue transfers are needed. However, the technique is difficult, and the patient must make multiple visits to the office. For implant placement to be successful, the patient's expectations must be understood, and the benefit-to-risk ratio should be extremely high.     

The effects of guided bone regeneration and grafting on implants placed into immediate extraction sockets. An experimental study in dogs

Guided bone regeneration (gbr) for the treatment of insufficient bone volume around implants can be performed using membranes with or without grafting materials (i.e., autogenous, allogenous, xenogenous, or alloplastic grafts). A possible way to evaluate the quality of implant osseointegration is the torque necessary to remove implants from their bony housing. The aim of this study was to compare the torques necessary to remove dental implants from implant beds reconstructed with different bone substitutes and GBR or GBR alone in 6 adult mongrel dogs. All mandibular premolars were extracted and 3 extraction sockets on each side were enlarged using a trephine bur. A 13 mm titanium screw-type dental implant (3.75 mm diameter) was placed in each enlarged extraction socket so that only the apical 3 to 4 mm were engaged in bone. The 3 defects were then randomly treated with either 1) canine demineralized freeze-dried bone allograft (DFDBA) plus GBR using an expanded polytetrafluoroethylene membrane (DFDBA+GTAM); 2) bioabsorbable hydroxyapatite and GBR (HA+GTAM); or 3) GBR (GTAM alone). After 6 months, the torque to remove the implants was measured in 4 animals and analyzed using ANOVA. There were no statistically significant differences between the 3 groups (GTAM alone: 46.37+/-16.41 Ncm; HA+GTAM: 46.00+/-16.59 Ncm; DFDBA+ GTAM: 52.15+/-29.24 Ncm). In addition, the influence of early removal of barriers on the torque values was evaluated with the t-test. Comparing exposed versus retained membranes by treatment modality, the only statistically significant difference was found in the DFDBA+GTAM group. When the torque values of all implants with exposed and retrieved membranes were compared to all those with retained membranes a significant difference could be detected. Histologic sections were prepared from the 2 dogs not included in the removal torque testing. In the histometric analysis the GTAM alone group showed a mean mineralized bone-to-implant-contact of 27.1%, the DFDBA+GTAM group of 34.6%, and the HA+GTAM of 39.3%. The mineralized bone-to-implant-contact of the HA+GTAM group was significantly higher than that of the GTAM alone group. In addition, the mineralized bone-to-implant-contact was divided into an apical and coronal part using the apical seventh thread as the dividing landmark. In the apical region, there was no significant difference between the groups regarding mineralized bone-to-implant-contact. In the coronal part the mineralized bone-to-implant-contact of the GTAM alone group was significantly lower compared to the other 2 groups. Within the limits of this investigation, it can be concluded that the type of grafting material will not influence torque removal values, but that early membrane exposure and removal will negatively influence the torque measurements. The combination of GBR with a bone substitute increased the mineralized bone-to-implant contact.     

Collagen fibers as a temporary scaffold for replacement of ACL in goats

ACL substitutes made of braided or plied purified collagen fibers and cross-linked with hexamethylenediisocyanate were implanted into a total of 14 adult goats to achieve resorption within 8 to 10 months. Two types of collagen fiber prostheses differing in degree of collagen purification were tested. The implants were harvested 2 to 11 months postimplantation, tested for mechanical strength, and evaluated by morphological methods. In the first group (n = 5), the less purified and less cross-linked collagen fiber ACL implant induced fast connective tissue ingrowth. At 6 months postimplantation, 40 to 60% of the collagen implant was resorbed. No studies on breaking strength were done in this group. In the second group, highly purified and more crosslinked ACL implants were less infiltrated by cells and were resorbed only by 10 to 20%. Still, the breaking strength was decreased to 10% of the original implant strength. In the second group, the fixation of the ACL implant in the bone tunnel with a bone wedge was insufficient (n = 6); however, additional fixation with metal screws was successful (n = 3). We conclude that cross-linked collagen fibers alone cannot be used as a safe ACL substitute as they quickly lose mechanical strength despite limited biodegradation.     

Implant reconstruction of the jaws and craniofacial skeleton

Full oral rehabilitation with a high degree of success is now possible with osseointegrated implants. Osseointegration is a direct connection between living bone and the titanium implant at the level of the light microscope. Osseointegrated implants are currently used to replace single teeth, support fixed bridges and stabilize full dentures. These implants can also be placed extraorally for attachment of facial prosthesis. The surgical technique used to place implants intraorally into jaws or facial skeleton is performed in two stages using a local anesthetic and/or conscious sedation. During stage I surgery, holes are placed into the jaw using a series of gradually larger diameter burs until the desired diameter and depth of the bony preparation is achieved. The implant is then placed. The implant must remain undisturbed for 4 months for osseointegration to take place. Stage II surgery is then required to remove the mucosa over the implant and place the transmucosal abutment. After 1-2 weeks of healing, the restorative dentist can take an impression and fabricate the prosthesis. On occasion, it is necessary to augment the height and width of the atrophic jaw with autogenous or allogeneic bone grafts prior to implant placement. Bone grafts are sometimes placed on the floor of the nose or the floor of the maxillary sinus. Guided tissue regeneration is a technique used to generate bone within bony defects adjacent to implants. With long-term rates of success (5 years) of 99% for implants placed in the mandible and 95% for those placed in the maxilla, reconstruction of the jaws and cranial facial skeleton with osseointegrated implants has become the treatment of choice.     

Histologic analysis of clinically retrieved titanium microimplants placed in conjunction with maxillary sinus floor augmentation

In this study, a new approach involving placement and subsequent retrieval of titanium microimplants was employed for the histologic investigation of the implant-tissue interface in conjunction with maxillary sinus floor augmentation. Nine patients scheduled for sinus floor augmentation and simultaneous placement of Br?nemark implants were included in the study. After a sinus graft procedure and placement of implants, an additional microimplant was placed into the graft through the lateral wall of the sinus. At abutment connection, the microimplants were retrieved using a 3- or 5-mm-wide trephine drill. Six specimens were retrieved after 6 to 14 months from sites augmented with particulate radiated mineralized cancellous allograft. Another six implants were retrieved after 6 to 12 months from maxillary sinuses augmented with particulate autogenous bone grafts. The histologic analysis showed distinct differences between the two types of grafts. The sites with autogenous bones grafts displayed a normal morphology of bone and bone marrow, including formation of bone on the surfaces of the grafted particles and remodeling of newly formed as well as grafted bone. The bone was more mature after 11 to 14 months than at 6 months. The allografted sites had a mixed morphologic appearance of newly formed bone and nonviable allograft particles (about 75% of the total bone area) in loose connective tissue. Significantly more bone was found at the autografted than at the allografted implants. The use of autogenous bone for augmentation of the maxillary sinus floor resulted in a greater amount of viable bone surrounding the implant; however, simultaneous placement of implants apparently resulted in a low proportion of bone-implant contact after 6 to 14 months irrespective of graft type.     

Endosseous implant and autogenous bone graft reconstruction of mandibular discontinuity: a 12-year longitudinal study of 31 patients

Surgical, medical, and prosthodontic records of 61 consecutively treated patients with mandibular discontinuity were reviewed retrospectively. All 61 patients had undergone discontinuity reconstruction with autogenous bone grafts; 31 of 61 had also received endosseous dental implants and a dental osseoprosthesis. Of these 31 implant-reconstructed patients, 23 had free autogenous nonvascularized and 8 had vascularized bone grafts. The surgical-prosthetic protocol consisted primarily of secondary, free autogenous nonvascularized bone graft reconstruction and secondary root-form endosseous implant and fixed prosthesis dental reconstruction. Vascularized bone (8 patients) or soft tissue (4 patients) grafts were utilized selectively for severely compromised patients after extensive oncologic resection, avulsive trauma, or after previous radiation treatment. Endosseous implant survival (95.5% in 31 patients), autogenous bone graft success (98.4% in 61 patients), and dental osseoprosthesis success (100% in 31 patients) were favorable. A high incidence (9.1%) of nonfunctioning (sleeping) implants was recorded for this patient population. The need to remove the titanium mesh tray for various reasons (17.6%) and the need to reconstruct soft tissue in the irradiated patient (12%) were noteworthy.     

Survival of cylindrical implants in composite grafted maxillary sinuses

PURPOSE: This retrospective study investigated the survival of dental implants placed in the maxilla after composite grafting of the sinus and an average of 55 months of loading. PATIENTS AND METHODS: Maxillary sinuses of 88 patients were grafted with autogenous cancellous bone combined with dense hydroxyapatite particles. After an average healing period of 3.4 months, hydroxyapatite-coated titanium endosseous implants were placed. A total of 388 implants were placed in grafted sinus floors, and 82 were placed in onlay grafted nonsinus position in the canine region. The implants were loaded with overdentures and fixed bridges 4 months (mean) after implantation, with a follow-up for a mean of 55 months. RESULTS: The cumulative implant survival was calculated according to the Kaplan-Meier method. Implant survival from the time of loading was 89% in full reconstructed cases and 90% in partially edentulous cases. The overall cumulative implant survival rate, including the loss in the surgical stage, was 82%. CONCLUSION: Implant loss in composite grafted maxillae after 70 months of follow-up was similar to loss in nongrafted maxillae.     

Short-term healing following the use of calcium sulfate as a grafting material for sinus augmentation: a clinical report

Because of the frequent lack of bone in the posterior maxilla, sinus augmentation has become a commonly practiced treatment modality. Many different materials have been used for augmenting the sinus, and the ideal graft is yet to be found. The present article reports the results of sinuses grafted with calcium sulfate in 2 patients. Bone biopsies were harvested 9 months after the augmentation procedure. In the first patient, 3 titanium threaded-cylinder implants were placed in the grafted area after 9 months, while in the second, 1 acid-etched, screw-shaped titanium implant was placed simultaneously with the graft. Light microscopic evaluation revealed new bone formation with ongoing remodeling and progressive lamellar maturation in the specimens. No remnants of the alloplastic material were detectable in any section, either within the bone or in the medullary tissue. When reevaluated at the uncovering procedure, the implants were radiographically and clinically judged to be osseointegrated. These observations suggest that, when used in the appropriate form and with the proper technique, calcium sulfate is a promising graft material for sinus augmentation, producing adequate quantity and quality of new bone for implant placement.     

Evaluation of bovine-derived bone protein with a natural coral carrier as a bone-graft substitute in a canine segmental defect model

The efficacy of a bone-graft substitute (bovine-derived bone protein in a carrier of natural coral) in the healing of a segmental defect of a weight-bearing long bone was evaluated. Twenty dogs, divided into two groups, underwent bilateral radial osteotomies with creation of a 2.5 cm defect. On one side of each dog, the defect was filled with autogenous cancellous bone graft. Contralateral defects received, in a blinded randomized fashion, cylindrical implants consisting of natural coral (calcium carbonate) or calcium carbonate enhanced with a standard dose of bovine-derived bone protein (3.0 mg/implant; 0.68 mg bone protein/cm3). The limbs were stabilized with external fixators, and all animals underwent monthly radiographs. They were killed at 12 (group 1) or 24 (group 2) weeks, and regenerated bone was studied by biomechanical testing and histology. Radiographic union developed in all 20 radii with autogenous cancellous bone grafts and in all 10 of the radii with the composite implants. None of the radii with implants of calcium carbonate alone showed radiographic evidence of union. This represented a statistically significant difference between implant types. In addition, calcium carbonate implants both with and without bone protein demonstrated radiographic evidence of near total resorption of the radiodense carrier by 12 weeks. This resorption facilitated radiographic evaluation of healing. Mean values for biomechanical parameters of radii with the composite implants exceeded those for the contralateral controls at 12 and 24 weeks; the difference was statistically significant at 12 weeks. Histology revealed scant residual calcium carbonate carrier at either time in the defects with calcium carbonate implants; however, a moderate amount was present in defects with the composite implants. In these specimens, the residual carrier was completely surrounded by newly formed bone that may have insulated the calcium carbonate from further degradation. The present study used a carrier of granular calcium carbonate reconstituted with bovine type-I collagen to deliver an osteoinductive protein to the defect site. This carrier is of nonhuman origin (eliminating the risk of disease transmission or antigenicity) and resorbs rapidly. In this model, bovine-derived bone protein in a natural coral carrier performed consistently better than the gold standard autogenous cancellous bone graft in terms of the amount of bone formation and strength of the healed defect. This may have implications for removal of hardware or resumption of weight-bearing in certain clinical situations. These data also indicate that coralline calcium carbonate alone represents a poor option as a bone-graft substitute in this critical-sized segmental defect model.     

Mandibular onlay grafting using prefabricated bone grafts with primary implant placement: an experimental study in minipigs

The aim of this experimental study was to evaluate the use of prefabricated autogenous bone grafts as onlay grafts to the mandible. Excess bone of 10 x 12 x 40 mm was produced inside blocks of pyrolyzed bovine bone under a polylactic membrane coverage on the outside of the mandible in 15 adult G?ttingen minipigs. After 5 months, this bone was harvested and transferred to the premolar region of the mandibular body in 10 animals. Onlay grafts of mandibular bone were used as controls for the transplanted prefabricated grafts. All grafts were fixed by primary placement of one titanium implant each. Five animals served as ungrafted controls. Evaluation was performed after 3 months and 5 months, respectively. Two animals were lost to evaluation, and one scaffold became infected. Eleven of the remaining 12 scaffolds showed sufficient bone ingrowth for grafting. Three months after transplantation, bone volume of the prefabricated grafts was almost completely preserved, with only minimal resorption in the superficial pores of the scaffolds, while the control grafts exhibited partial resorption. The titanium implants, which had been placed at the time of only grafting, exhibited direct bone-implant contact. Five months after grafting, all titanium implants showed complete osseointegration, with direct bone-implant contact. The grafted bone exhibited a significant increase in bone density by appositional bone formation. The control grafts were nearly completely resorbed at that time.     

In vivo bone strain patterns in the zygomatic arch of macaques and the significance of these patterns for functional interpretations of craniofacial form

It has been proposed that the mammalian facial skeleton is optimized for countering or dissipating masticatory stress. As optimized load-bearing structures by definition exhibit maximum strength with a minimum amount of material, this hypothesis predicts that during chewing and biting there should be relatively high and near uniform amounts of strain throughout the facial skeleton. If levels of strain in certain areas of the facial skeleton are relatively low during these behaviors, this indicates that the amount of bone mass in these areas could be significantly reduced without resulting in the danger of structural failure due to repeated masticatory loads. Furthermore, and by definition, this indicates that these areas are not optimized for countering masticatory stress, and instead their overall morphology and concentration of bone mass has most likely been selected or influenced mainly by factors unrelated to the dissipation or countering of chewing and biting forces. An analysis of in vivo bone strain along the lateral aspect of the zygomatic arch of macaques indicates the clear absence of a high and near uniform strain environment throughout its extent. Instead, there is a steep strain gradient along the zygomatic arch, with the highest strains along its anterior portion, intermediate strains along its middle portion, and the lowest strains along its posterior portion. These data, in combination with earlier published data (Hylander et al., 1991), indicate that levels of functional strains during chewing and biting are highly variable from one region of the face to the next, and therefore it is unlikely that all facial bones are especially designed so as to minimize bone tissue and maximize strength for countering masticatory loads. Thus, the functional significance of the morphology of certain facial bones need not necessarily bear any important or special relationship to routine and habitual cyclical mechanical loads associated with chewing or biting. Furthermore, the presence of these steep strain gradients within the facial skeleton suggests that the amount of bone mass in the low-strain areas may be largely determined by factors unrelated to processes frequently referred to as "functional adaptation," or conversely, that the "optimal strain environment" of bone varies enormously throughout the facial skeleton (cf., Rubin et al., 1994). Based solely on anatomical considerations, it is likely that the zygomatic arch is bent in both the parasagittal and transverse planes and twisted about its long axis. Due to constraints on rosette position, the strain data are incapable of determining if one or more of these loading conditions predominate. Instead, the strain data simply provide limited support for the possible presence of all of these loading regimes. Finally, as the masseter muscle is concentrated along the anterior portion of the zygomatic arch and as the arch has fixed ends, the largest shearing forces and the largest bending and twisting moments are located along its anterior portion. This in turn explains why the largest strains are found along the anterior portion of the zygomatic arch.     

Endoscopic application in aesthetic and reconstructive facial bone surgery

Twenty-three cases of endoscopically assisted facial bone surgery were performed over the past 3 years. Our series is consistent with 16 cases of aesthetic contouring surgery and 12 treatments of facial bone fracture, including three cases for recontouring of frontal bone, three cases for recontouring of zygoma, endoscopically assisted correction of three zygomatic and blowout fractures, four cases for rhinoplasty and septoplasty for deviated nose, and three cases for mandible contouring surgery. To accomplish this technique, a rigid 4-mm, 30-degree down-angled endoscope was used. The frontal bone or zygomatic arch was approached endoscopically through two or three small incisions on the frontal or temporoparietal scalp. All endoscopic instruments were then manipulated through these incisions. The approach for endoscopically assisted rhinoplasty is the same as with standard rhinoplasty procedures. The approach for zygoma complex and maxillary sinus needs an intraoral incision. Recontouring of zygoma, mandible, and nasal dorsum by an air-driven burr and rasp was performed with endoscopic visual assistance. A plate and screw fixation for zygomatic arch fracture requires an additional small skin incision over the plate for the trocar method. The duration of follow-up ranged from 6 months to 30 months. The postoperative course was satisfactory with a few complications. The extra time needed for the endoscopic procedures was less than 1 hour. Endoscopically assisted facial bone surgery can be performed with adequate visualization and direct manipulation of all facial bones. Complications usually associated with extensive incisions in the bicoronal approach may be avoided. Poor visualization in the conventional approach for operation of orbit, nose, maxillae, and mandible may be avoided by use of the endoscope. This technique may prove to be ideal for aesthetic surgery for facial skeleton with smaller scar and less morbidity.     

Rehabilitation of patients with severely resorbed maxillae by means of implants with or without bone grafts. A 1-year follow-up study

Forty-three patients with severely resorbed maxillae who had been referred for implant treatment were assigned to one of three treatment groups: bone grafting and implant placement (graft group); modified implant placement but no bone grafting (trial group); or optimized complete dentures (no-implant group). Sixteen, 20, and 7 patients, respectively, were assigned to the three groups. At the 1-year follow-up, 10% of the implants had been lost. Only a few of the failures (3/22) occurred after prosthesis placement. The cumulative success rates were 83% in the graft group and 96% in the trial group. A substantial reduction of the grafted bone, especially of the onlay grafts, occurred in many patients. During the period from prosthesis connection to the 1-year follow-up, marginal peri-implant bone loss was on average 0.5 mm. Despite the often demanding procedures involved, all but one patient in each implant group said that they would undergo the treatment again. Most patients were very satisfied with the treatment outcome and their improved masticatory ability. Those who had renounced implant treatment appeared modestly adapted to their optimized dentures, but reported retention problems and less satisfaction with mastication.     

Radiographic modalities for diagnosis and treatment planning in implant dentistry

Early in the development of implant technology it became apparent that conventional dental imaging techniques were limited for evaluating patients for implant surgery. During the treatment planning phase, the recipient bed is routinely assessed by visual examination and palpation, as well as by periapical and panoramic radiology. These two imaging modalities provide a two-dimensional image of mesial-distal and occlusal-apical dimensions of the edentulous regions where implants might be placed. When adequate occlusal-apical bone height is available for endosteal implants, the buccal-lingual width and angulation of the available bone are the most important criteria for implant selection and success. However, neither buccal-lingual width nor angulation can be visualized on most traditional radiographs. Although clinical examination and traditional radiographs may be adequate for patients with wide residual ridges that exhibit sufficient bone crestal to the mandibular nerve and maxillary sinus, these methods do not allow for precise measurement of the buccolingual dimension of the bone or assessment of the location of unanticipated undercuts. For these concerns, it is necessary to view the recipient site in a plane perpendicular to a curved plane through the arch of the maxilla or mandible in the region of the proposed implants. Implant dentists soon recognized that, for optimum placement of implants, cross-sectional views of the maxilla and mandible were the ideal means of providing necessary pre-operative information. Today, the two most often employed and most applicable radiographic studies for implant treatment planning are the panoramic radiograph and tomography. Although distortion can be a major problem with panoramic radiographs, when performed properly they can provide valuable information, and are both readily accessible and cost efficient. To help localize potential implant sites and assist in obtaining accurate measurements, it is recommended that surgical stents be used with panoramic radiographs. In simple cases, where a limited number of implants are to be placed, panoramic radiography and/or tomography may be used to obtain a view of the arch of the jaw in the area of interest. For complex, cases, where multiple implants are required, the CT scan imaging procedure is recommended. Because of its ability to reconstruct a fully three dimensional model of the maxilla and mandible, CT provides a highly sophisticated format for precisely defining the jaw structure and locating critical anatomic structures. The use of CT scans in conjunction with software that renders immediate "treatment plans" using the most real and accurate information provides the most effective radiographic modality currently available for the evaluation of patients for oral implants. To follow patients after implant surgery, DSR can be helpful by addressing the limitations of other radiographic modalities in detecting postoperative changes. By eliminating unchanged information, DSR allows the clinician's eye to focus on actual changes that have occurred between the recordings of two images.