The International Journal of Oral & Maxillofacial Implants, 02/2006

Purpose: The purpose of this study was to investigate the effect of 3 different abutment types on the stress distribution in bone with inclined loads using finite element analysis. Materials and Methods: The 1-body, internal-hex, and external-hex implant systems were modeled to study the effect of abutment type on stress distribution in bone. The bone model used in this study comprised compact and spongious bone assumed to be homogeneous, isotropic, and linearly elastic. Results: In the case of the 1-piece implant, the load was transferred evenly not only in the implant system but also in bone. However, the maximum Von Mises stress generated in bone with the 1-piece implant was always higher than that generated with the internal-hex implant, regardless of load angle inclination. In the case of the internal-hex implant, the contact condition with friction between abutment and implant in the tapered joints and at abutment neck reduced the effect of bending caused by horizontal component of inclined load. The maximum Von Mises stress in bone was the highest for the external-hex implant. Discussion: It was found that the internal-hex implant system generated the lowest maximum Von Mises stresses for all loading conditions because of reduction of the bending effect by sliding in the tapered joints between the implant and abutment. Conclusions: It was concluded that abutment type has significant influence on the stress distribution in bone because of different load transfer mechanisms and the differences in size of the contact area between the abutment and implant. (Basic Science) Keywords: 1-piece implants, external-hex abutment connection, finite element analysis, internal-hex abutment connection, stress distribution

Purpose: The objective of this study was to test the hypothesis that fluoride-modified titanium surfaces would enhance osteoblast differentiation. Osteoblast growth on a moderately rough etched fluoride-modified titanium surface (alteration in cellular differentiation) was compared to osteoblast growth on the same surface grit-blasted with titanium dioxide. The potential role of nanometer-level alterations on cell shape and subsequent differentiation was then compared. materials and methods: Human embryonic palatal mesenchymal (HEPM) cultures were incubated on the respective surfaces for 1, 3, and 7 days, followed by analysis for cell proliferation, alkaline phosphatase (ALP) -specific activity, and mRNA steady-state expression for bone-related genes (ALP, type I collagen, osteocalcin, bone sialoprotein [BSP] II, Cbfa1, and osterix) by real-time polymerase chain reaction (PCR). Results: The different surfaces did not alter the mRNA expression for ALP, type I collagen, osterix, osteocalcin, or BSP II. However, Cbfa1 expression on the fluoride-modified titanium surface was significantly higher (P .001) at 1 week. The number of cells on this surface was 20% lower than the number of cells on the surface TiO2-blasted with 25-mm particles but not significantly different from the number of cells on the surface TiO2-blasted with 125-mm particles. Cells grown on all the titanium surfaces expressed similar levels of ALP activity. Conclusions: The results indicated that a fluoride-modified surface topography, in synergy with surface roughness, may have a greater influence on the level of expression of Cbfa1 (a key regulator for osteogenesis) than the unmodified titanium surfaces studied. (Basic Science) Keywords: Cbfa1, dental implants, osseointegration, osteoblasts

Purpose: Radiation therapy influence on bone healing around 3 types of endosseous dental implants in dogs was evaluated. materials and methods: Implants with 3 different surfaces (A = machined commercially pure titanium screws, B = commercially pure titanium plasma spray-coated cylinders, C = hydroxyapatite [HA] -ceramic coated cylinders) were first implanted unilaterally into the right posterior edentulous mandibles of 7 dogs as nonirradiated controls. After 12 weeks without functional loading and after sequential fluorochrome labeling these implants were retrieved by block dissection. In this same surgery, implants were placed on the contralateral side. Three weeks postimplantation the implant-containing hemimandibles were Cobalt 60 irradiated with the biologic equivalent of 5,000 cGy. Twelve weeks postimplantation and after labeling these irradiated implants were retrieved at sacrifice. On scanning electron, light, and fluorescence microscopic images of undecalcified longitudinal ground sections of the implants with surrounding tissues, percent bone-to-implant contact (% BIC), bone formation, and remodeling were histometrically and subjectively evaluated. Results: Woven bone formation started 1 week after implantation at the implant interfaces on both the nonirradiated and the irradiated sides. Average BICs (total/cortical/spongious bone bed) of 26%/49%/36% for surface A, 46%/48%/64% for surface B, and 81%/83%/78% for surface C were observed. In the irradiated hemimandibles average BICs (total/cortical/spongious bone bed) were reduced to 11%/9%/4% for surface A, 43%/46%/43% for surface B, and 63%/85%/76% for surface C, with increased resorption of peri-implant bone and retarded bone formation after irradiation. Discussion: Reductions of total % BIC in all irradiated implants, though not statistically significant, were significant (P = .05) on implant surfaces A and B in the spongious bone bed. Conclusion: Retarded bone formation on surfaces A and B in the spongious bone bed represented a more radiation-sensitive situation at the time of radiation onset compared to advanced bone formation and maturation at surface C. Keywords: bone-implant contact, histomorphometry, implant surfaces, radiation

Purpose: To find the optimal scaffold for tissue-engineered bone, one approach is to test existing biomaterials on their suitability as scaffolds. In this study, the suitability of different alloplastic and xenogenic biomaterials as scaffolds for ex vivo osteoblast cultivation was investigated. materials and methods: Normal human osteoblast cells were cultured on the surface of bovine collagenous materials, bovine hydroxyapatite, porcine gelatin, synthetic polymer, and collagen-containing bovine hydroxyapatite, and the investigation of proliferation was performed after 24, 72, and 120 hours. Measurement of the differentiation marker alkaline phosphatase and osteocalcin was made after 20 days of incubation. Results: The obtained data showed significantly higher proliferation and differentiation rates in cells cultivated on collagen-rich biomaterials in comparison to noncollagenous or collagen-poor biomaterials (P .05). Discussion: In tissue engineering the scaffold should be biocompatible and serve as a proper matrix for the cells to produce the new structural environment of extracellular matrix ex vivo. Collagen supports initial cell attachment and cell proliferation, allowing immature osteogenic cells to differentiate into mature osteoblasts, but collagen may not be the only dominating factor for cell-matrix interaction during ex vivo bone formation. Conclusion: These data suggest that a 3-dimensional collagen matrix can provide a more favorable environment for the attachment, proliferation, and differentiation of in vitro osteoblastlike cells, at least until the initial stage of differentiation, than noncollagenous biomaterials. (Basic Science) Keywords: collagen, osteoblasts, tissue engineering

Purpose: Osteoblast attachment on titanium surfaces is necessary to achieve new bone formation and osseointegration. The purpose of this study was to examine osteoblast attachment on irradiated titanium disks. materials and methods: Machined, hydroxyapatite (HA)-coated, sandblasted, and titanium plasma-sprayed (TPS) surfaces were irradiated with either a carbon dioxide (CO2) or an Er,Cr:YSGG laser. A control group of nonirradiated disks was also examined. Osteoblast cultures were cultivated on the titanium disks and examined with scanning electron microscopy. Results: The findings demonstrated that osteoblasts could be grown on all of the surfaces. Pseudopodia and a spread of cells that demonstrated maturation were observed on the lased irradiated titanium disks. Conclusions: The data show that laser irradiation of titanium surfaces may promote osteoblast attachment and further bone formation. (Basic Science) Keywords: laser irradiation, osteoblast attachment

Purpose: Few studies have directly compared the quality of bone generated by distraction osteogenesis with that generated by autogenous onlay grafting. The purpose of this study was to compare rates of bone turnover at 5 months in bone produced by distraction osteogenesis and onlay grafting. materials and methods: Alveolar defects created in jaws of American foxhounds were augmented with distraction osteogenesis or onlay grafting and allowed to heal for 5 months. The animals were then sacrificed and the jaws were resected and prepared for decalcified and undecalcified histologic examination. Results: Both procedures produced bone containing a mixture of haversian systems and trabecular bone. A significantly greater ratio of osteoblast-covered bone surface to total trabecular bone surface (mean ± SEM) was noted in distraction bone (0.124 ± 0.049) compared to onlay bone (0.081 ± 0.048) or control host bone (0.085 ± 0.042 mm) (P .05). In addition, significantly (P .05) greater numbers of osteoclasts per mm of bone surface were noted in distraction bone (0.939 ± 0.07) compared to onlay bone (0.605 ± 0.06) or control host bone (0.725 ± 0.08). No differences in rates of mineralization were noted between the groups. Discussion: While bone from both experimental groups appeared adequate for implant placement, distraction bone appeared to be remodeling at a higher rate than either onlay or control bone. Conclusion: Given that the state of healing of the bone in each of these comparative groups was examined at a static point in time, it is premature to draw conclusions about the efficacy of one procedure over the other. (Basic Science)

Purpose: The aim of this 3-year randomized controlled trial (RCT) was to compare biologic and technical treatment outcomes and patient satisfaction after early (= 14 days postimplantation) loaded implants with those of implants loaded after a healing period of 3 to 4 months in the edentulous maxilla. materials and methods: Twenty-four patients with completely edentulous maxillae were randomized into a test group (n = 16) and a control group (n = 8). All patients received 5 or 6 solid screw-type titanium implants with sandblasted, large-grit, acid-etched (SLA) surfaces. In total, 142 implants were placed and 139 implants were loaded with full-arch prostheses. Clinical assessments were obtained at loading and after 3, 6, 12, 24, and 36 months. Radiographs of implants and existing teeth were taken at loading; after 6, 12, 24, and 36 months; and at 12, 24, and 36 months, respectively. Results: The cumulative implant success rate 3 years after loading was 100%. At the 3-year examination the mean (P = .005), distal (P = .005), and mesial (P > .05) crestal bone levels were better in the test group. No significant differences between the test and control groups were noted for any other outcome measure. The most common adverse event in both groups was tooth-crown fracture. Discussion: A review of the literature, both printed and electronic, revealed no study fulfilling the criteria of an RCT dealing with the early loading of maxillary full-arch prostheses. This study fulfills those criteria. Conclusion: In this study population it has been concluded that the early (approximately 2 weeks) loading protocol is a viable alternative to the standard (3 to 4 months) protocol in the rehabilitation of a completely edentulous maxilla with a complete implant-supported fixed prosthesis. (Controlled Clinical Cohort Study)

Purpose: The authors' objective was to measure crestal bone level change in subjects with immediately loaded implants and to identify risk factors associated with changes in bone level. materials and methods: A retrospective cohort study design was used. The sample comprised subjects who had had endosseous implants placed and immediately loaded between July 2001 and July 2003. Demographic, health status-related, anatomic, implant-specific, prosthetic, and surgical variables were examined. The primary outcome variable was change in crestal bone level over time. Appropriate uni-, bi-, and multivariate statistics were computed. Results: The sample comprised 174 subjects who received 347 immediately loaded implants. The mean duration of radiographic follow-up was 6.9 ¡À 4.0 months, respectively. Mean changes in radiographic bone level were -0.5 mm and -0.6 mm on the mesial and distal surfaces, respectively, after a mean of 6.9 months of radiographic follow-up. Using least squares methods, it was estimated that radiographic bone levels would be -1.0 mm and -0.8 mm on the mesial and distal surfaces, respectively, at 12 months. The multivariate model revealed that radiolucency at or adjacent to implant site was associated with an increased risk of crestal bone loss (odds ratio, 1.88; 95% CI, 1.00 to 3.60). Twelve months after placement, 92.5% of implants had had = 1.5 mm of crestal bone loss. Discussion: The results of this study were comparable to the results of other studies comparing immediate loading to delayed loading. Further research to estimate long-term changes in crestal bone loss and to identify risk factors for bone loss with immediate loading is recommended. Conclusion: This study suggests that crestal bone level changes with immediately loaded implants were within the recommended range for 92.5% of the evaluated implants. The mandible showed a higher risk for crestal bone loss compared to the maxilla. Keywords: crestal bone levels, dental implants, immediate loading, multivariate models, retrospective cohort studies, risk factors

Purpose: To evaluate, by means of the polymerase chain reaction (PCR), the presence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia in the mandibular arch of completely edentulous subjects before implant placement and 4 and 6 months after the placement of mandibular implant-supported fixed prostheses. materials and methods: Fifteen patients had bacterial plaque collected with sterile paper points before implant placement (ie, when they were completely edentulous) and at 3 sites on the peri-implant sulci displaying the largest probing depths after placement of 5 implants. Results: For the edentulous arch, A actinomycetemcomitans was detected in 13.3% of subjects, P intermedia was detected in 46.7% of subjects, and there was no detection of P gingivalis. After 4 and 6 months of implant placement, A actinomycetemcomitans was detected in 60% and 73.3% respectively; P intermedia in 46.7% and 53.3% respectively; and P gingivalis in 46.7% and 53.3%, respectively. Discussion: Future diagnosis should not be restricted to distinguishing individuals at risk of peri-implant disease. Such individuals should be identified by the employment of microbiologic methods and knowledge of the multifactorial nature of the host response to the action of microorganisms. Conclusions: The longer the implants were in the oral cavity, the higher the occurrence of A actinomycetemcomitans, P gingivalis, and P intermedia in the peri-implant sulci of completely edentulous patients rehabilitated with mandibular implant-supported fixed prostheses was, without any clinical or radiographic evidence indicating peri-implant disease in the studied period. (Before-and-After Study)

Purpose: The purpose of the study was to compare the failure rates of implants with either a machined surface or a TiUnite surface used to replace failing implants. Materials and methods: The files of 578 patients, ie, of all patients who were treated at the Department of Periodontology of the University Hospital in Leuven by means of oral implants during 3 recent consecutive years, were analyzed. The implants included in the study had an observation time ranging from 9 to 49 months. All patients had been provided with Brånemark System implants. Only 2 types of implant surfaces were used: machined and TiUnite. Data collection and analysis focused on the replacement implants, ie, implants placed at sites where the original implants had failed. Data were statistically analyzed by means of Statistica for Windows Software version 5.1; a Fisher exact P test was used. The level of significance was set at P = .05. Results: A total of 41 patients experienced the nonintegration of 58 implants. Of those, 29 implants with a machined surface were replaced by implants with the same surface. Six of the replacement implants failed. Nineteen machined-surface implants were replaced by TiUnite surface implants; 1 failed. Ten TiUnite-surface implants were replaced by implants with the same surface; none failed. The difference in failure rate between machined-surface replacement implants and TiUnite replacement implants was statistically significant (P = .05). Discussion: In addition to the usual patient-related compromising factors, replacement of a failing implant involves the challenge of achieving osseointegration in a nonpristine bone site. In the present study, implants with TiUnite surfaces were associated with fewer failures than machined-surface implants under the same conditions. Conclusion: An improved implant surface such as TiUnite may offer a better prognosis when a failed implant has to be replaced at the same site. (Comparative Cohort Study) Keywords: dental implants, implant failures, implant surfaces, osseointegration

Purpose: Implants shorter than 10 mm can be a long-term solution for sites with limited bone height. The purpose of this study was to determine the influence of some prosthetic factors on the survival and complication rates. materials and methods: Two hundred sixty-two short machined-surface Brånemark System implants were consecutively placed in 109 patients and followed for a mean of 53 months. The prosthetic parameters were recorded, and the data were examined for relation to peri-implant bone loss and biologic or biomechanical complications. Results: Relatively few crown-to-implant (C/I) ratios were 1 or > 2 (16.2%). Occlusal table (OT) width ranged from 5.4 to 8.3 mm. Opposing dentition was most often natural teeth, a fixed prosthesis supported by natural teeth, or an implant-supported fixed restoration. Occlusion with a normal buccolingual maxillomandibular relationship was found in 72.7% of the cases. No significant difference in peri-implant bone loss was correlated with C/I ratio or OT. Neither cantilever length nor bruxism had a significant effect on peri-implant bone loss. Mean bone loss was 0.74 ± .65 mm. The difference in the complication rate (15% overall) between the bruxer and the nonbruxer group was not statistically significant (P = .51). One implant was lost in a heavy bruxer after 7 years of function. Discussion: Increased C/I and OT values do not seem to be a major risk factor in cases of favorable loading. In 67% of the cases, the mesiodistal length of the prosthesis was less than the corresponding natural tooth length, which may have contributed to better load distribution and more favorable results. Conclusions: Short implants appear to be a long-term viable solution in sites with reduced bone height, even when the prosthetic parameters exceed the normal values, provided that force orientation and load distribution are favorable and parafunction is controlled. (Case Series) Keywords: crown-implant ratios, implant complication rates, prosthetic parameters, short implants

Purpose: Implant anchors such as miniscrews and miniplates have been loaded immediately for anchorage during orthodontic treatment. The purpose of this study was to measure the removal torque of immediately loaded miniscrews after clinical usage and to determine the possible factors associated with this value. materials and methods: From 29 patients with malocclusions, 46 miniscrews were removed, and removal torque was measured with a torque gauge. Removal torque values were subjected to statistical analysis for possible association of different clinical characteristics. Results: The mean removal torque value was 1.10 kg•cm, and removal torques for 50% of the implants were greater than 0.89 kg•cm (8.7 N•cm). Removal torque values were significantly higher in the mandible than in the maxilla. The removal torques of 15-mm and 17-mm miniscrews were significantly higher than those of 13-mm miniscrews. Therefore, the site of implantation and miniscrew length were important factors associated with removal torque. However, there was no significant correlation between the removal torque value and age, gender, healing time, or time in function. Discussion: When miniscrews are used as anchorage for uprighting tipped molars, excessive torque in a counterclockwise direction may loosen them. From the measurements obtained in this investigation, miniscrews can sufficiently sustain an uprighting moment. Conclusion: The removal torque values of the majority of miniscrews in this study population when loaded immediately as orthodontic anchorage were greater than 0.89 kg•cm, and this was sufficient for these implants to fulfill their purpose as anchors in 3-dimensional tooth movements. Keywords: dental implants, miniscrews, osseointegration, removal torque

Purpose: The primary aims of this retrospective study were to: (1) evaluate bone quality in different segments of the edentulous jaw and correlate it with demographic data and (2) establish a quantitative and objective assessment of bone quality based on the Hounsfield scale. materials and methods: One hundred one randomly selected computerized tomographic (CT) scans were used for the analysis. Edentulous segments ranging from 10 to 30 mm were selected for evaluation, and the findings were analyzed and correlated to demographics. Implant recipient sites were evaluated visually for bone classification by 2 independent examiners. The same sites were subsequently evaluated digitally using the Hounsfield scale, and the results were correlated with the visual classification. Results: The 4 quadrants of the mouth displayed Hounsfield unit (HU) values ranging from -240 HU to 1,159 HU. The highest unit/mean density value (559 ± 208 HU) was found in the anterior mandible, followed by 517 ± 177 HU for the anterior maxilla, 333 ± 199 HU for the posterior maxilla, and 321 ± 132 HU for the posterior mandible. There was no association between the Hounsfield value and density and age or gender. When subjective bone quality was correlated to Hounsfield index findings, only the relationship between HU and type 4 bone was found to be significant. Conclusions: Knowledge of the Hounsfield value as a quantitative measurement of bone density can be helpful as a diagnostic tool. It can provide the implant surgeon with an objective assessment of bone density, which could result in modification of surgical techniques or extended healing time, especially in situations where poor bone quality is suspected. Keywords: bone density, bone quality, dental implants, Hounsfield index

Purpose: The aim of this study was to compare the pain experienced after implant placement with 2 different surgical procedures: a flapless surgical procedure using an image-guided system based on a template and an open-flap procedure. materials and methods: The study population consisted of 60 patients who were referred for implant placement. One group consisted of 30 patients who were referred for the placement of 80 implants and treated with a flapless procedure. The other group consisted of 30 patients who were referred for the placement of 72 implants with a conventional procedure. Patients were selected randomly. They were requested to fill out a questionnaire using a visual analog scale (VAS) to assess the pain experienced and to indicate the number of analgesic tablets taken every postoperative day from the day of the surgery (D0) to 6 days after surgery (D6). Results: The results showed a significant difference in pain measurements, with higher scores on the VAS with open-flap surgery (P .01). Pain decreased faster with the flapless procedure (P = .05). The number of patients who felt no pain (VAS = 0) was higher with the flapless procedure (43% at D0 versus 20%). With the flapless procedure, patients took fewer pain tablets (P = .03) and the number of tablets taken decreased faster (P = .04). Discussion: Minimally invasive procedures may be requested by patients to reduce their anxiety and the pain experienced and thus increase the treatment acceptance rate. Conclusion: With the flapless procedure, patients experienced pain less intensely and for shorter periods of time. Keywords: computer-aided surgery, dental implants, minimally invasive surgical procedures, pain

The objective of this article was to review the different factors and limitations influencing the accuracy of computer-aided implant surgery. In vitro and in vivo accuracy studies of articles and congress proceedings were examined. Similar results using bur tracking as well as image-guided template production techniques have been reported, and both methods allow for precise positioning of dental implants. Compared to the conventional technique, this sophisticated technology requires substantially more financial investment and effort (computerized tomographic imaging, fabrication of a registration template, intraoperative referencing for bur tracking, or image-guided manufacturing of a surgical template) but appears superior on account of its potential to eliminate possible manual placement errors and to systematize reproducible treatment success. The potential for the protection of critical anatomic structures and the esthetic and functional advantages of prosthodontic-driven implant positioning must also be considered. However, long-term clinical studies are necessary to confirm the value of this strategy and to justify the additional radiation dose, effort, and costs. (More than 50 references) (Literature Review) Keywords: dental implant surgery, image-guided bur tracking, image-guided template production

This article presents a technique for the removal of the screws used to fix a bone graft and for the placement of dental implants in a flapless approach that utilizes the tracking technology of a computerized navigation system. A 24-year-old female patient injured in a terrorist bombing suffered from tooth loss and a bone defect in the maxilla. The area was grafted with bone from the chin in preparation for the placement of dental implants. Four months following the grafting procedure, the fixing screws were removed and the dental implants were placed in a flapless approach by the application of a specialized computerized navigation system. This technique emphasizes the potential of computerized navigation approaches in the facilitation of minimally invasive oral surgery. Keywords: bone grafting, computer-assisted surgery, dental implants, flapless implant surgery, navigation surgery, screws

Esthetic demands and nonparallel situations between the axial direction of the suprastructure and the implant require angulation of the abutment. The Conical Seal design avoids microleakage and micromovements after the abutment has been seated and finally retained via screw. However, there is no protection against rotation during the fixation procedure. Therefore, a control device and/or method for a reproduction of correct seating during each treatment step of permanent prosthesis fabrication is desirable. The purpose of this investigation was to develop a device to ensure the correct seating by less expensive, safer, easier, and more precise methods. The sequence of components and the standard procedure required modification: in the modified procedure, the impression is made at the implant level, and the straight implant replica is embedded in the laboratory cast. The angled abutment needs modification by grinding to create small margins in the mesial, distal, and palatal walls. Three materials that are used in daily dental practice are combined to fabricate an individual transfer device. Direct waxup of the restoration onto the angled abutment without a prefabricated component shortens the laboratory processing. The modified sequence and procedure, small alterations of the angled abutment, and an individual transfer device can simplify the transfer procedures, improve clinical performance and applicability, and shorten chair time. (Technical Note) Keywords: angled abutment modification, individual transfer devices, prosthetic procedures