The International Journal of Oral & Maxillofacial Implants, 02/2005

Purpose: To investigate whether ultrasound can stimulate osteoconduction in the mandible, an attempt was made to stimulate the osteoconductive process with low-intensity pulsed ultrasound in rats. Materials and Methods: In 64 rats, a 5.0-mm diameter circular mandibular defect was made in the ramus and, subsequently, covered on both sides with collagen membranes. Two groups were studied, an ultrasound treatment group and a placebo treatment group. At 2 and 4 weeks, the remaining defect area was measured using microradiographs, and the amount of osteoconduction was expressed as the percentage of defect closure. Results: At 2 and 4 weeks, there was no significant difference in the percentage of defect closure between the groups. Discussion: An explanation may be that ultrasound does not exert an effect in an area where wound healing is already expected to be at an optimal level. Conclusion: There was no evidence that low-intensity pulsed ultrasound stimulates osteoconduction in a bone defect in the rat mandible that is covered by a collagen membrane.

Purpose: The effect of hydroxyapatite (HA) crystallinity on protein adsorption and osteoblast precursor cell attachment to HA was investigated. Materials and Methods: Different weight ratios of 100% crystalline HA and 100% amorphous calcium phosphate powders were mixed and pressed into disks (0.5 g) of different crystallinities-either 0% (HA0), 30% (HA30), 50% (HA50), 70% (HA70), or 100% (HA100). Results: X-ray diffraction indicated differences in HA crystallinities. In addition, dissolution of the HA was dependent on its crystallinity, with an increase in phosphorus dissolution as the degree of crystallinity was decreased. No significant difference in albumin adsorption and initial osteoblast precursor cell attachment was observed in the range of HA0 to HA70 surfaces. However, a significantly lower albumin adsorption and initial osteoblast precursor cell attachment were observed on HA100. Discussion: It was suggested that changes in ionic interactions as a result of a change in crystallinity affect the amount of calcium ion ligands readily available to electrostatically bind to proteins. Conclusion: It was thus concluded from this study that HA crystallinity affects the amount of albumin adsorbed and initial osteoblast attachment.

Purpose: The objective of this study was to evaluate whether the local administration of growth hormone (GH) would influence the formation of peri-implant bone around titanium sheets placed in the tibiae of young rabbits. Materials and Methods: Thirty-two New Zealand rabbits were randomly placed in 1 of 2 groups: the experimental group, in which 4 IU (1.2 mg) of lyophilized powder (GH) was added to a surgically created defect at implant placement, or the control group, in which an implant sheet was placed without hormonal treatment. Animals were sacrificed at 1, 2, 3, and 6 weeks after surgery, and histologic sections were stained with Masson, Alcian blue, picrosirius, and hematoxylin-eosin and observed under light microscopy. The sections were analyzed morphometrically and densitometrically to calculate the amount of newly formed bone. Results: At week 2, GH-group sections showed enhanced growth of the trabeculae from the periosteal tissue, with thicker and more irregular trabeculae than those observed in control group specimens. A tendency toward greater bone area and lesser density was observed in the GH group, although the groups did not differ significantly. Nevertheless, bone-to-implant contact in weeks 2 and 6 was significantly greater in the GH group (P .05). Discussion: An increase in the cortical response from periosteal and endosteal reactions was observed with the high local administration of GH, in disagreement with most authors. In the first phases of bone repair, the osteons were more disorganized; they were more organized by the sixth week. Conclusion: Local administration of GH could stimulate the first phases of the bone remodeling process in this experimental model.

Purpose: The carbon dioxide (CO²) laser has been shown to be suitable for the treatment of ailing implants. However, comparatively little is known about bone regeneration after laser treatment. Therefore, the purpose of this study was to determine the course of bone regeneration after peri-implant care with the CO² laser. Materials and Methods: In 6 beagle dogs, a total of 60 implants and bony defects were treated either conventionally by air-powder abrasive (group 1), by laser irradiation alone (group 2), or by a combination of the 2 (group 3). After therapy, polychrome sequence labeling was performed using 4 different markers. Four months later, after sacrifice, histologic sections were photographed and scanned. In each specimen, the 4 stained areas were detected with special software and indicated as a percentage of the standardized measurement frame. Lastly, the time-course of the bone regeneration was determined for each of the 3 therapy groups. Results: Fluorescence microscopy demonstrated maximum bone regeneration after 8 weeks in all 3 therapy groups. In this period, groups 2 and 3 showed significantly greater amounts of newly formed bone than group 1 (P .03 and P .05, respectively). However, there was no difference in bone regeneration between groups 2 and 3. Discussion: Using fluoresence microscopy, it was possible to analyze and interpret the bone regeneration processes during all 4 application phases of the 3 groups. Conclusions: These results support the hypothesis that CO² laser irradiation renders significantly more new bone formation, especially 5 to 8 weeks postoperatively, than conventional decontamination in the dog model. Further investigation will be required to determine the clinical efficacy.

Purpose: The purpose of this work was to study the bone tissue reaction after porous polyethylene (Polipore) implantation into surgical defects in the parietal bones of rats with streptozotocin-induced diabetes, treated with salmon calcitonin. Materials and Methods: Porous polyethylene implants were placed in bone defects created in 36 adult female rats. The rats were divided into 3 equal groups: diabetic treated with calcitonin (DCa), diabetic (D), and control (C). The animals of the DCa group received applications of salmon calcitonin on alternating days immediately after the surgery until sacrifice. The rats were sacrificed after 15, 30, 60, and 90 days, and the defects were examined histologically and statistically through histomorphometric analysis. Results: Histomorphometric analysis showed that there was no statistically significant difference in the mean quantity of inflammatory cells among all study groups after 15 and 90 days. At 30 days, a statistically significant difference was observed between the D and C groups and the D and DCa groups. At 60 days, there was no statistically significant difference between the D and DCa groups. Discussion: Porous polyethylene can be considered an option for implant material when there are investigations that prove its biocompatibility and stability in the host tissues. Salmon calcitonin positively aided the bone repair and attenuated the inflammatory response until 30 days after the surgery. Conclusion: Porous polyethylene was tolerated by the host tissues in all groups, and moderate chronic inflammatory reaction was observed up to the 90-day period. Salmon calcitonin attenuated the inflammatory response up until 30 days.

Purpose: The purpose of this study was to evaluate patient, implant, and treatment characteristics to identify possible prognostic factors for implant failure. Materials and Methods: Out of a database with different dental implant treatment protocols, a research database of 1 randomly selected implant per patient was created. The database consisted of 487 implants. Of these, 80 were withdrawn, 36 failed, and 371 remained successful during a 5-year follow-up period. Potential risk factors were evaluated by chi-square tests and post hoc analyses. Results: Significant or strongly significant differences were found regarding implant failures as a result of jawbone quality, jaw shape, implant length, treatment protocol, and combinations of jawbone-related characteristics. Responsible clinics and number of implants supporting the restoration were factors that could not be associated with implant failure. Discussion: Implant failures in this study were more often seen when negative patient-related factors were present. Approximately 65% of the patients with a combination of the 2 most negative bone-related factors (jawbone quality 4 and jaw shape D or E) experienced implant failure. However, only 3% of the patients had this combination. Implant length, the only implant-related factor evaluated, was also significantly correlated with the success rate, but implant length could also be regarded as a result of the jawbone volume available. Another negative patient-related factor was the treatment protocol; however, in most cases this was also indirectly or partly related to the status of the jawbone available for implant placement. Conclusion: Patient selection appears to be of importance for increasing implant success rates.

Purpose: The aim of this study was to evaluate implants placed according to several methods of sinus floor augmentation. Materials and Methods: Forty-eight patients (median age of 62 years, range 23 to 89) had been treated at least 3 years prior to examination with screw-type implants in the posterior maxilla. Depending on the vertical dimension of the residual bone, 1 of 3 surgical procedures had been performed: sinus lift by lateral antrostomy (SL) in 13 patients; osteotome technique (OT) in 18 patients; standard implantation in 17 patients (control). In each patient 1 implant was randomly chosen for analysis (48 implants with a mean observation time of 4.6 ± 1.4 years). Examination included probing pocket depth (PPD) measurement and radiographic examination. Radiographs were digitized to assess the marginal bone level. Differences between the groups were tested using analysis of variance, the Student t test and the Kruskal-Wallis test. Results: Mean PPD was 3.0 mm for the SL, 3.1 mm for OT, and 3.1 mm for control. The mean radiographic bone level was 1.53 mm for SL, 2.40 mm for OT, and 1.96 mm for control. No statistically significant differences were found between the groups for either of these parameters. Discussion and Conclusion: Clinical examinations as well as radiographically stable bone levels indicated similar biomechanical conditions for prosthetic restorations when applying the 3 surgical procedures tested.

Purpose: The purpose of this study was to compare the marginal bone loss (MBL), complications, and 12-year survival rates of commercially pure titanium (cpTi) and hydroxyapatite (HA)-coated implants placed in the maxilla. Materials and Methods: The study group consisted of 120 patients (77 women, 43 men) treated from 1988 to 1997. A total of 388 implants (156 cpTi and 232 HA-coated) were placed in the maxilla. There were 126 immediate (32.5%) and 262 (67.5%) nonimmediate implants. Patients were evaluated annually. Mean follow-up was 60 ± 32.3 months. MBL was measured on radiographs using the implant threads as the dimensional reference. MBL, complications, and 12-year survival and success rates were correlated with implant coating, time of implantation, implant dimensions, and position in arch. Results: Total mean MBL was 1.07 ± 2.16 mm. MBL was significantly lower with cpTi implants (0.55 ± 1.04 mm) compared to HA-coated implants (1.51 ± 2.71 mm) (P .001). No statistical difference in regard to MBL was found between immediate and nonimmediate implants (0.86 ± 1.8 mm vs 1.16 ± 2.3 mm). The total 12-year survival rate was 91.4%. HA-coated implants had a significantly higher 12-year survival rate than cpTi implants (93.2% vs 89%; P .03). Nonimmediate implants had a significantly higher failure rate (8.2%) than the immediate implants (1.3%) (P .009). No correlation was found between type of implant coating and late implant failure. Discussion: Immediate implants can serve as a predictable option, providing higher survival and success rates. HA-coated implants tended to fail less during the surgical phase, but had higher mean MBL compared to cpTi implants. Conclusions: HA-coated implants had greater MBL than cpTi implants but a higher 12-year survival rate. Immediate implants had a lower failure rate than the nonimmediate implants in this study population.

Purpose: The purpose of this prospective study was to evaluate the safety of zygomatic bone harvesting and to determine whether a particulated zygomatic bone graft can be used simultaneously with 1-stage dental implants to reconstruct resorbed edentulous alveolar ridges. Materials and Methods: Altogether, 82 dental implants were placed in 32 patients. Particulated bone grafts harvested from the zygomatic process were used in 72 of the implant sites. The volume of bone harvested, intraoperative complications, morbidity, and complications on follow-up visits were recorded. Implant survival was examined prospectively. Results: As a harvest site, the zygoma yielded enough bone to complete the reconstructions in each case. The average zygomatic bone graft volume was 0.90 mL (SD 0.30). Perforation of the maxillary sinus occurred at 11 zygomatic sites. None of these perforations led to postoperative problems. No paresthesias or other complications were noted during follow-up examinations. Mean duration of postoperative swelling was 4.5 days, and patients used pain medication for a mean duration of 4 days. After the mean follow-up period of 26.9 months postplacement, 80 of 82 implants were osseointegrated (survival rate 97.6%). Discusssion: Zygomatic bone is an alternative donor site for bone harvesting with low morbidity. The bone graft yielded is sufficient for use in 2 to 3 implant sites. Conclusions: The zygoma was a safe intraoral bone harvesting donor site in this patient population. Further, the use of simultaneous particulated zygomatic bone grafts and 1-stage implant placement appears to be an effective procedure.

Purpose: The relationship between computerized tomography (CT) values of bone surrounding endosseous implants and the cutting torque values required for self-tapping during implant placement was examined for the purpose of predicting the initial stability (bone quality) during implant placement by presurgical CT scan examinations and determining whether it can be quantified. Materials and Methods: The study sample consisted of 13 subjects with 56 implants. Sites for implant placement were determined based on CT data using implant planning software. The average CT values of the bone surrounding the simulated implants were calculated by the software. Using a stereolithographic drill guide, implants were placed at the locations indicated by the protocol. The cutting torque values required for self-tapping were measured during implant placement. The resulting CT values and cutting torque values were analyzed statistically for correlation. Results: The correlation was considered significant at a level of .01 or less, and the correlation coefficient was 0.77. Discussion: There was a strong correlation between CT values and cutting torque values in the clinical cases evaluated. These results indicate that it may be possible to predict and quantify initial implant stability and bone quality from presurgical CT diagnosis and implant simulation. Conclusion: Presurgical CT examination may be an effective technique for predicting initial stability of the implant and bone quality.

Purpose: The long-term results of endosseous implants depend on the maintenance of bone support. The aim of this study was to evaluate radiologically bone resorption around dental implants placed in grafted sinuses after up to 4 years of function. Materials and Methods: Between 1997 and 2001, augmentation of the maxillary sinus floor with alloplastic (Biostite) or xenogenic (Bio-Oss) materials was performed in 34 patients. Results: Eighteen patients participated in the study. Twenty-six sinus augmentations were performed on these 18 patients, and they received 37 implants. The change in marginal bone level around the implants at the mesial side was 1 mm during the first year after the abutment connection, followed by an annual loss of 0.1 mm. The change in marginal bone level around the implants at the distal side was 1.1 mm during the first year after the abutment connection followed by an annual loss of 0.2 mm. Discussion: The implant survival rate observed in this study is in line with data previously reported for patients treated with implants in the posterior maxilla without bone atrophy. The results for implants placed into sinuses grafted with Bio-Oss were similar to the results for implants placed in sinuses grafted with Biostite. Conclusion: Although this study involved a limited number of procedures, it confirmed that alloplastic and xenogenic materials can be reliable for bone regeneration in subantral cavities. The angular defects present both at the distal and mesial sides of the implants were comparable to those observed at implants placed in native bone.

Purpose: Lateral cephalometric films were examined for their validity as a tool for the postoperative evaluation of palatal implant placement. Materials and Methods: Cephalometric and histometric data of 20 partially edentulous human cadaveric maxillae were compared. Lateral cephalograms of the specimens were made, and the palatal complex was pencil traced. In addition, low-dose dental computerized tomography (CT) scans were obtained from every specimen. Based on the CT data, palatal implants (Orthosystem; Institut Straumann, Waldenburg, Switzerland) were placed. Postimplantation, another lateral cephalometric film was recorded. The specimens were prepared for histologic examination. The preoperative tracings were superimposed on the postoperative cephalometric films. Results: Of 20 implants placed, 12 were 4 mm long and 8 were 6 mm long. The distance between the cranial end of the implants and the nasal floor on microscopy ranged from 0.3 to 9.3 mm. Perforation of the nasal floor was absent throughout on intraoperative probing, while 2 implants projected beyond the nasal floor on histologic analysis of the specimens. An analysis of the superimposed pre- and postoperative cephalograms showed 5 implants projecting beyond the nasal floor. Histologically, only 1 of these projecting implants had actually caused perforation of the palatal complex. A comparison between the histometric and the cephalometric data showed that cephalometry, on average, imaged the palatal complex 0.8 mm below the actual anatomic site. Discussion and Conclusions: Twenty percent of palatal implants projecting beyond the nasal floor were false-positive records on the postoperative lateral cephalograms. Despite CT scans, 10% of the implants placed caused fenestration of the nasal cavity by histologic evidence. If the palatal complex was perforated, intraoperative probing with a periodontal probe did not confirm the perforation. Bone perforations up to 1.3 mm did not necessarily result in frank perforation of the nasal mucosa. Two-dimensional images could not be related to actual penetrations into the nasal cavity.

Purpose: The purpose of this study was to analyze healthy bone formation by means of histology and immunohistochemistry after grafting with a mixture of autologous ground calvarial bone, inorganic xenograft, platelet-rich plasma (PRP), and recombinant human tissue factor (rhTF). Materials and Methods: Maxillary sinus floor augmentation was performed on 3 patients by grafting with 5 to 10 mL of a paste consisting of autologous powder from calvarial bone (diameter 1 mm), 50% v/v anorganic bovine bone mineral xenograft (PepGen P-15, a new tissue-engineered bone replacement graft material), PRP (1.8 × 10⁶ platelets/mm³ plasma), and about 1 µg rhTF. Six and 10 months after grafting, bone cores were extracted for implant fixation and analyzed. Results: Histology demonstrated a high degree of inorganic xenograft integration and natural bone regeneration. Both the xenograft and newly synthesized bone were colonized with osteocytes and surrounded by osteoblasts. Six-month-old bone cores demonstrated a ratio of synthesized bone to xenograft particles ratio of 0.5, whereas 10-month-old cores demonstrated a ratio of 2. A low degree of inflammation could also be observed using S100A8 immunohistochemistry. Discussion: Autologous grafting in edentulous patients is a complex procedure; the successful substitution of synthetic analogs for ground bone is a major challenge. Conclusion: In this investigation, it was shown that inorganic xenograft in the harvested bone paste could be safe for patients and had high bone regeneration capacity over time. The sinus graft showed intense bone formation 6 months after grafting and a further increase in bone growth 10 months after grafting.

The clinical case presented is that of an edentulous female patient, a heavy smoker, who received implant-supported complete restorations in the maxilla and mandible using the immediate loading concept according to the Ankylos implant system. The patient received 12 commercially pure titanium (grade 2) Ankylos implants, 6 in the maxilla and 6 in the mandible. The implants were loaded immediately after surgery with temporary acrylic resin prostheses fabricated chairside using a prefabricated customized splint. The definitive ceramometal restorations were seated 4 months after surgery. Clinical and radiologic evaluation at 7 months after implant placement indicated functional bone anchorage of all implants, despite the patient being a smoker and having poor bone quality. The patient died 7 months after implant placement because of lung cancer; however, there was no known disease at the time of implant placement. After her death, the implants with the surrounding tissues were removed en bloc and examined histologically and histomorphometrically using undecalcified cut and ground sections. All implants were osseointegrated to some extent and surrounded by lamellar bone. However, around the upper, nonthreaded parts of the implants, much of the bone had been resorbed. In this region, fibrous connective tissue was in close contact with the titanium surface. Epithelial proliferation with pocket formation could not be observed in any of the implants. The histomorphometric evaluation of bone-implant contact in threads demonstrated a mean of approximately 51% of the available surface and a mean bone volume of approximately 52%, with a tendency toward greater contact and volume around the implants in the maxilla. If the nonthreaded cylindric portions of the implants were included, mean bone-implant contact was 46% and mean bone volume was 47%.

Invasion of the maxillary sinus is a relatively frequent complication in dental implant treatment of patients with inadequate bone height in the posterior maxilla. This event usually occurs during surgery and sometimes produces sinusitis. There is a paucity of reports in the literature of implants migrating into the sinus cavity after a period of function. In the 2 clinical cases presented, an intraosseous apical movement of the implants was produced several years after placement of the implants. Hypotheses and possible mechanisms by which an implant may migrate into the maxillary sinus are described.

This report describes treatment of a patient using vertical alveolar ridge augmentation performed prior to transposition of the inferior alveolar nerve (IAN). A preoperative computerized tomographic (CT) scan revealed 2 to 3 mm of bone above the canal in the left mandibular molar region. An autogenous bone graft harvested from the chin area was utilized along with a titanium mesh for vertical alveolar ridge augmentation in this area. CT scan after bone grafting revealed 5 mm of vertical ridge augmentation. Bone height above the IAN was 7 to 8 mm after bone grafting procedure. For IAN transposition, an osteotomy was performed to obtain a lateral access window located 4 mm below the crestal bone along the lateral side of the mandible. Two cylindric hydroxyapatite-coated implants were placed. Autogenous bone from the lateral access window that had been removed en bloc was particulated and placed around the implants. Because vertical alveolar ridge augmentation had been performed, the coronal portion of the implant was not exposed after transposition of the IAN. It is suggested that vertical ridge augmentation may be considered prior to transposition of the IAN in situations where minimal bone height exists above the IAN canal. However, long-term clinical investigations are recommended.