The International Journal of Oral & Maxillofacial Implants, 02/1995

A study was performed in two large hound dogs to evaluate the bone induction potential of demineralized freeze-dried bone (DFDBA) placed into defects adjacent to implants that were placed into extraction sockets. Two implants were untreated controls, two implants received only Gore-Tex Augmentation Membrane (GTAM), two implants received GTAM and autologous bone, and six sites received GTAM and DFDBA. DFDBA was prepared from the long bones of a dog of the same breed as the experimental dogs. P2, P3, and P4 were extracted bilaterally, and buccal defects were created and measured. Twelve commercially pure titanium Brånemark implants were placed. At 12 weeks, clinical measurements were taken and the dogs were sacrificed. The untreated control defects had a mean clinical bone fill of 1.75 mm (37%). Sites treated with autologous bone had a mean of 5.0 mm (95%) of clinical bone fill within the original defects. Sites treated with DFDBA and barriers had 3.8 mm (75%) of bone fill, while sites treated with membranes alone had a mean of 4.2 mm (80%) of bone fill. Histologic evaluation revealed that DFDBA sites had retained nonviable bone chips in 45.4% of the bone matrix, and only 8.3% was lamellar bone. Autologous graft sites had 26.2% retained bone chips within the bone matrix, and 61% percent of the matrix consisted of lamellar bone. For GTAM-only sites, 70.2% of the matrix was lamellar bone and 29.8% was woven bone. Retained DFDBA bone chips were nonviable, occasionally surrounded by woven bone, and appeared to break up and then remineralize without the presence of osteoclastic or osteoblastic activity. Retained autologous bone chips were surrounded and incorporated by the host bone. The autologous bone grafts and DFDBA implants were considered to be osteoconductive. For the three treatment groups, within the defects there were sparse bone-implant contacts. The results indicate that GTAM barriers alone or with autologous bone grafts produced the best clinical and histologic results. DFDBA did not appear to induce bone formation in any of the evaluated specimens. Keywords: autologous grafts, demineralized freeze-dried bone, immediately placed implants, remineralization

A rat tibia model was developed to analyze bone formation leading to osseointegration with threaded titanium implants. Miniaturized titanium implants were placed in the anterior aspect of the upper tibia of rats weighing 350 g. Twenty-four rats were involved; 12 rats were sacrificed at 6 weeks, and another two rats were sacrificed weekly for 6 weeks following implantation. Four days prior to sacrifice, the animals were injected intraperitoneally with 3H-proline (10 µCi/g body weight). The rats were fixed by perfusion with 5% glutaraldehyde, and the tibia were decalcified and embedded in Epon. The implants were removed from the embedded bone by fracturing, and the specimens re-embedded. Sections were prepared for light and electron microscopy and radioautography. Morphologic observations indicated that implant placement resulted in bone necrosis and resorption. This was followed by bone growth from the old bone surfaces filling the threads with vascular channels and new lamellar bone. Osseointegration was complete at 6 weeks in all animals examined. Electron microscopy at various places along the bone-titanium interface showed an amorphous layer, a granular electron-dense layer, or a layer of uncalcified collagen fibrils. At each week after surgery, radioautography showed the position and thickness of new bone labeled with 3H-proline during the last 4 days. Radiolabeled new bone was deposited only on previously existing bone and extended toward the available space. Since there was no apparent relationship between the implant and the new bone, it was suggested that titanium is biocompatible, but not necessarily osteoinductive. Keywords: bone formation, osseointegration, titanium implants

Torque failure for endosseous implants has been used as a biomechanical measure of anchorage, though the significance of such data is not known. A practical understanding of the resistance to torque failure of implant-tissue interfaces at stage 2 surgery would help in assigning torque levels for implant abutment-screw fastening. The purpose of this study was to measure torque failure levels of commercially pure (CP) titanium, Ti-6Al-4V, hydroxyapatite-coated (HA-coated) screw-shaped implants placed into the maxillae and mandibles of baboons. Implants identical in size were placed into the edentulous posterior maxillae and mandibles of six female baboons (n =37 each group) using a standardized surgical protocol. Reverse-torque data were collected at postinsertion time intervals ranging from 3 to 4 months using a counterclockwise torque driver and the data were analyzed (repeated measures ANOVA) for torque differences related to time, biomaterial, and jaw. The HA-coated implants exhibited significantly greater torque-removal values compared to both metallic implants (HA: 186.0 Ncm [50.1]; Ti-6Al-4V: 78.6 Ncm [18.1]; CP Ti 74.0 Ncm [24.4]). Analysis of torque interactions with jaw showed no significant difference; however, the mandible was found to be greater than the maxilla in torque resistance for all groups tested. Understanding the risks in inferring animal data to human application, the clinical implications of these data suggest that the recommended torque level of 35 Ncm for abutment fastening may provide a margin of safety for most implants of similar design and material as used in this study. The range of data suggests that 1 in 20 metallic implants may fall below this torque-fastening level. Keywords: baboon jaws, commercially pure titanium, hydroxyapatite-coated implants, Ti-6Al-4V implants, torque failure

To qualify the contribution of the periodontal-ligament receptors to trigeminal inhibitory reflex responses, 20 subjects with maxillary implant-supported fixed prostheses opposing mandibular teeth or implants were compared to 10 subjects with removable dentures in the maxilla opposing implant-supported prostheses and 10 subjects with natural teeth in both jaws. Standardized mechanical taps were delivered to an implant, a denture tooth, or a natural tooth in the central incisor region of the maxilla. Bilateral surface electromyographic recordings of the masseter muscles were obtained while subjects maintained a constant myoelectric activity by clenching. Stimulation of an implant in partially edentulous subjects elicited a reflex response in 7 of 10 subjects. Likewise, stimulation of a tooth of a maxillary removable denture resulted in a clear reflex response in 5 of 10 totally edentulous subjects. On the other hand, a reflex response did only occur in 1 of 10 totally edentulous subjects with implant-supported prostheses in both jaws. It was concluded that the presence of some natural teeth in either the maxilla or mandible allowed the occurrence of a reflex response. In totally edentulous subjects, mucosal or periosteal mechanoreceptors, triggered by stimulation of the denture bearing area or by transmission of vibrations through the jaw bone, could be responsible for the remaining reflex responses. Keywords: masseteric reflex, oral implants, osseointegration, silent period

Five patients treated with radiotherapy and surgery for oral malignant tumors had a total of 20 Brånemark implants placed in irradiated bone of the mandible. The radiotherapy dose varied between 25 and 64 Gy (mean 40.3 Gy) with a biologically effective dose varying between 33.4 and 106.9. One implant did not osseointegrate, but 19 remain stable after 3 to 6 years of observation. The oral surgery procedures were carried out without adjunct hyperbaric oxygen therapy, and the successful results support the view that such adjunctive measures are not always necessary in the oral rehabilitation after radiotherapy. Keywords: implants, oral malignancies, radiotherapy

Two essentially different implant-prosthetic concepts are known for the treatment of edentulous maxillae. One concept propagates a "concentrated" arrangement of four to six implants in the premolar and anterior regions with a fixed cantilever superstructure. An alternative is a "spread-out" implant arrangement of six implants placed in the tuberosity, premolar, and anterior regions. The prosthetic rehabilitation consists of a fixed horseshoe-shaped bar and a removable prosthesis. A cantilever situation is avoided. The biomechanical aspects of these implant-prosthetic concepts were studied with clinical strain-gauge measurements and theoretical three-dimensional analysis using the finite element method. Results revealed that the distribution of bone stresses is more favorable with a spread-out implant arrangement than with a concentrated implant arrangement and cantilever restoration. The resistance to bending of a superstructure has an influence on bone stress concentration that should not be ignored. Stresses are controlled not only by the number or distribution of implants, but also by the material and design of the superstructure. Keywords: edentulous maxilla, finite element analysis, strain gauge measurement

Nineteen prosthodontic clinics participated in a prospective study of fixed prostheses supported by osseointegrated implants (FPOIs) with laser-welded titanium frameworks. Ninety-three patients with 100 FPOIs were included and followed for 2 years. The results from this group were compared to another group that was examined retrospectively. In the retrospective group (control group), 91 patients received 96 FPOIs with cast frameworks, and these patients were treated shortly before the patients in the titanium-framework group (test group). The two groups were treated at the same centers. The results for both groups were good, with only 1.2% of loaded implants lost during the follow-up period (1.6% in the titanium-framework group; 0.7% in the control group). One framework in each group fractured. However, in complete maxillary cases, there were significantly more subjects in the titanium-framework group who were affected by implant losses compared to the control group. There was also a tendency towards more fractures of artificial teeth and acrylic resin in the titanium-framework group, compared to the control group. A possible explanation might be that dental technicians at the different centers were not used to the design of the titanium frameworks when the study began. Thus, the results from the first 2 years are promising, but further studies are needed to establish the long-term serviceability of laser-welded titanium frameworks. Keywords: dental implants, multicenter study, titanium frameworks

Excessive heat generation at the implant-bone interface may cause irreversible bone damage and loss of osseointegration. The effect of heat generation in vitro at the implant surface caused by abutment reduction with medium- and extra-fine-grain diamond and tungsten burs in a high-speed dental turbine was examined. Titanium-alloy abutments connected to a titanium-alloy cylindrical implant embedded in an acrylic-resin mandible in a 37°C water bath were reduced horizontally and vertically. Temperature changes were recorded via embedded thermocouples at the cervix and apex of the implant surface. Analysis of variance for repeated measures was used to compare seven treatment groups. Thirty seconds of continuous cutting with standard turbine coolant caused a mean temperature increase of 1°C with a maximum of 2°C. Similar tungsten cutting caused a mean increase of 2°C with a maximum of 4.7°C, significantly higher than diamond reduction. Additional air-water spray for continuous tungsten cutting had no significant effect, while intermittent cutting for 15-second increments reduced the temperature increase by 75%. Thus, abutment reduction with medium-grit diamonds using intermittent pressure and normal turbine coolant is unlikely to cause an interface-temperature increase sufficient to cause irreversible bone damage and compromise osseointegration. Keywords: cutting instrument, heat generation, implant abutment preparation, irrigation

To evaluate the effects of a stress-absorbing superstructure on the interface of an integrated implant, the bone/hydroxyapatite-coated (HA-coated) implant interface was histologically and histomorphometrically analyzed using monkeys. A total of 12 HA-coated implants were placed in the edentulous mandible of three monkeys. Polyurethane elastomer was selected as the stress-absorbing material. A superstructure incorporating a stress-absorbing system was placed on six implants (stress-absorbed group) and a superstructure without such a system was set on the other six implants (non-stress-absorbed group). After 12 months, undecalcified ground sections were prepared and the bone/implant interface was analyzed. Clinically, all implants in both groups were immobile and mild inflammation around the peri-implant gingiva was seen. Histologically, direct bone contact was observed around all of the implants in both groups. However, histomorphometrically, the amount of bone around implants was greater in the stress-absorbed group. Bone was more highly apposed to the implant at the apical portion than at the axial portion. These different findings could be the result of stress-breaking against functional loading to the bony interface of these HA-coated implants. Keywords: hydroxyapatite-coated implant, stress-absorbing system, superstructure

The present study aimed to evaluate reliability of the Periotest instrument in baseline mobility measurement of craniofacial implants in a human wet bone specimen. Sixteen 4.0-mm craniofacial Brånemark implants were placed in the most common sites for craniofacial implant placement. A 5.5-mm abutment was attached to each implant except one in the mastoid bone, which was connected with a bone-anchored hearing aid (BAHA) abutment. Baseline Periotest values (PTVs) were recorded on each abutment at different vertical measurement points by three different clinicians using three Periotest devices. Baseline PTVs for each abutment ranged between -1.23 and -5.90. Interoperator and interinstrumental variability did not influence PTVs; however, the vertical measurement point on the abutment proved to have a strong effect on PTV recordings. Keywords: craniofacial implant, implant, implant mobility, osseointegration, Periotest

This study presents data related to 136 patients who were treated with 300 implants in the edentulous mandible anterior to the mental foramina. Two implant systems were used: the titanium plasma-sprayed screw implant (TPS) and the intramobile cylinder implant (IMZ) in three different modifications. The longest observation time was 11 years, with a mean of 5.7 years. Patients were recalled for regular clinical examinations once every 6 months. After prosthesis placement, only a few implant losses were recorded, although critical states could be found according to periodontal standards. This led to the definition of success criteria according to clinically tolerable bone loss or pocket-probing depths. The 5-year survival rate considering the implant loss was greater than 90% for all implant systems and was lowest for the new type IMZ 3.3. Selecting a vertical bone loss of 4 mm or more as failure criterion reduced the survival rates, which then ranged from 83% to 97% (according to the implant system) for the 5-year interval. The mean annual bone-level change was identified individually for each implant using a linear-regression model. Keywords: edentulous mandible, IMZ implants, long-term follow-up, mean annual bone-level change, overdenture, success criteria, success rates, TPS implants