The International Journal of Oral & Maxillofacial Implants, 02/2008

Purpose: The aim of this study was to evaluate quantitatively and qualitatively the influence of estrogen deficiency on autogenous bone block grafts in aged ovariectomized rats. Materials and Methods: Fifty 12-month-old female Wistar rats were used in the study. They were divided into 2 groups, an ovariectomized group and a sham-operated group. After 30 days the animals received autogenous block bone grafts on the angle of the mandible, harvested from the calvaria. The animals were euthanized at 7, 14, or 28 days postoperatively. Results: Histologic analysis showed that at 7 days postsurgery, the interface between graft and recipient site in the sham-operated group appeared filled by a granulation tissue with angiogenic activity, whereas the ovariectomized group still exhibited a blood clot and a granulation tissue in organization. On the 14th postoperative day, the interface in the sham-operated group was partially filled by newly formed bone establishing a union between the graft and the recipient site. The interface in the ovariectomized group was typically filled by granulation tissue with discrete osteogenic activity in most specimens. On the 28th postoperative day, the graft in the sham-operated group appeared histologically integrated to the mandible. However, the interface in the ovariectomized group appeared partially filled by newly formed bone, with areas of interposed connective tissue. The statistical analysis revealed that bone neoformation was significantly greater in the sham-operated group (57.41% at 14 days and 68.35 at 28 days) in comparison with the ovariectomized group (40.82% at 14 days and 53.09 at 28 days) at the 5% level. Conclusion: The estrogen depletion caused by the ovariectomy hindered the healing process of autogenous block bone grafts placed in the mandibles of aged rats. Schlagwörter: autograft, bone transplantation, estrogen deficiency, menopause, ovariectomy

Purpose: The goal of this work was to analyze the stress distribution in 2 wedge-shaped implant designs, straight and angled, by means of a 3-dimensional finite element method (FEM) stress analysis. Materials and Methods: A model was generated from computerized tomography of a human edentulous mandible with the implants placed in the left first molar region. The model included boundary conditions representing the muscles of mastication and the temporomandibular joint. An axial load of 100 N and a horizontal load of 20 N were separately applied at the tops of the implant abutments, and system equilibrium equations were used to find each muscle intensity force based on its position and direction. The mandibular boundary conditions were modeled considering the anatomy of the supporting muscle system. Cortical and medullary bones were assumed to be homogeneous, isotropic, and linearly elastic. Results: The stress analysis provided results in terms of normal maximum tensile (s1) and compressive (s3) stress fields. The stress distribution was quite similar for both designs, indicating a good performance of the angled design. Conclusions: Stresses in the angled implant were in general lower than in the straight implant, and the differences between the 2 designs studied were more relevant for the vertical load. No indication was found that angled implants of the type described generate stress-induced problems compared to straight implants. Schlagwörter: biomechanics, dental implants, dental stress analysis, finite element analysis

Purpose: The purpose of this in vitro study was to compare the dimensional accuracy of a stone index and of 3 impression techniques (tapered impression copings, squared impression copings, and squared impression copings splinted with acrylic resin) associated with 3 pouring techniques (conventional, pouring using latex tubes fitted onto analogs, and pouring after joining the analogs with acrylic resin) for implant-supported prostheses. Materials and Methods: A mandibular brass cast with 4 stainless steel implant-abutment analogs, a framework, and 2 aluminum custom trays were fabricated. Polyether impression material was used for all impressions. Ten groups were formed (a control group and 9 test groups formed by combining each pouring technique and impression technique). Five casts were made per group for a total of 50 casts and 200 gap values (1 gap value for each implant-abutment analog). Results: The mean gap value with the index technique was 27.07µm. With the conventional pouring technique, the mean gap values were 116.97 µm for the tapered group, 57.84 µm for the squared group, and 73.17 µm for the squared splinted group. With pouring using latex tubes, the mean gap values were 65.69 µm for the tapered group, 38.03 µm for the squared group, and 82.47 µm for the squared splinted group. With pouring after joining the analogs with acrylic resin, the mean gap values were 141.12 µm for the tapered group, 74.19 µm for the squared group, and 104.67 µm for the squared splinted group. No significant difference was detected among Index, square/latex techniques, and master cast (P >.05). Conclusions: The most accurate impression technique utilized squared copings. The most accurate pouring technique for making the impression with tapered or squared copings utilized latex tubes. The pouring did not influence the accuracy of the stone casts when using splinted squared impression copings. Either the index technique or the use of squared coping combined with the latex-tube pouring technique are preferred methods for making implant-supported fixed restorations with dimensional accuracy. Schlagwörter: dental implantation, dental impression technique, dental models

Purpose: The effect of type 2 diabetes mellitus (adult-onset non-insulin-dependent), which is the most common form of diabetes in humans, on osseointegration capacity has not been addressed in an appropriate animal model. This study histologically and histomorphometrically examines bone healing around titanium implants in the type 2 diabetes rat model. Materials and Methods: Titanium implants with a chamber were placed into the femurs of normal male rats and genetically modified male rats with a close symptomatic resemblance to human type 2 diabetes, as characterized by late-onset hyperglycemia and obesity. Cross-sectional histology for the tissue grown into the implant chamber was examined. Results: Bone volume around implants was consistently (from weeks 4 to 8 postimplantation) smaller for the diabetes group than for the control group in the cortical area, while the bone volume in the marrow area was not affected by the diabetes. Bone-implant contact percentage was considerably lower for the diabetes group in both the cortical and marrow areas, with the week 4 bone-implant contact in the cortical area being 12% for the diabetes group and 61% for the control group. A 2-fold difference remained at week 8. Bone morphogenesis in the diabetic rats was characterized by fragmented bone tissues and extensive soft tissue intervention. Conclusions: Type 2 diabetes mellitus impaired osseointegration capacity disproportionally between the cortical bone and bone marrow areas. The reduction of the bone quantity in the cortical area and the bone-implant contact in both the cortical and marrow areas was remarkable. Schlagwörter: blood glucose, bone histomorphometry, bone-titanium integration, endosseous titanium implant, risk factor

Purpose: The purpose of this study was to assess the precision at the implant interface of gold-machined UCLA-type abutments and computer-assisted design and manufacture (CAD/CAM) titanium abutments with both external-hexagonal connection and internal-hexagonal connection. Materials and Methods: Fifteen gold-machined UCLA-type abutments with external-hexagonal connection, 15 gold-machined UCLA-type abutments with internal-hexagonal connection, 15 CAD/CAM titanium abutments with external-hexagonal connection, and 15 CAD/CAM titanium abutments with internal-hexagonal connection were produced. The rotational freedom of all the abutments was assessed to detect the precision of fit of each abutment on the top of the implant platform. Measurements of rotational freedom were compared among groups. The quantitative differences among groups were assessed using 1-way analysis of variance (a = .05). Results: Significant differences relative to rotational freedom were not found among the 4 groups (P > .19). Conclusion: Both types of abutments (gold-machined UCLA-type and CAD/CAM titanium) consistently showed 1 degree of rotational freedom between the implant and abutment in both cases of external-hexagonal connection and internal-hexagonal connection. Schlagwörter: CAD/CAM titanium abutments, gold-machined UCLA-type abutments, hexagonal external connection, internal connection, single implant-cemented restorations

Purpose: Biomechanical load-fatigue performance data on single-tooth implant systems with different implant-abutment interface designs is lacking in the literature. This study evaluated the load fatigue performance of 4 implant-abutment interface designs (Brånemark-CeraOne; 3i Osseotite-STA abutment; Replace Select-Easy abutment; and Lifecore Stage-1-COC abutment system). The number of load cycles to fatigue failure of 4 implant-abutment designs was tested with a custom rotational load fatigue machine. The effect of increasing and decreasing the tightening torque by 20% respectively on the load fatigue performance was also investigated. Materials and Methods: Three different tightening torque levels (recommended torque, -20% recommended torque, +20% recommended torque) were applied to the 4 implant systems. There were 12 test groups with 5 samples in each group. The rotational load fatigue machine subjected specimens to a sinusoidally applied 35 Ncm bending moment at a test frequency of 14 Hz. The number of cycles to failure was recorded. A cutoff of 5 3 106 cycles was applied as an upper limit. Results: There were 2 implant failures and 1 abutment screw failure in the Brånemark group. Five abutment screw failures and 4 implant failures was recorded for the 3i system. The Replace Select system had 1 implant failure. Five cone screw failures were noted for the Lifecore system. Analysis of variance revealed no statistically significant difference in load cycles to failure for the 4 different implant-abutment systems torqued at recommended torque level. A statistically significant difference was found between the -20% torque group and the +20% torque group (P .05) for the 3i system. Conclusions: Load fatigue performance and failure location is system specific and related to the design characteristics of the implant-abutment combination. It appeared that if the implant-abutment interface was maintained, load fatigue failure would occur at the weakest point of the implant. It is important to use the torque level recommended by the manufacturer. Schlagwörter: abutment screw failure, implant-abutment interface, load fatigue, preload, torque

Purpose: The purpose of this study was to investigate the validity of the current Periotest system when measuring implant systems and to present a new system to monitor implant interface integrity. Materials and Methods: The new system records an impact accelerometer signal and utilizes software for data analysis to determine the resonance frequency of an implant-abutment system. The new system uses the handpiece from the Periotest to acquire an impact signal but makes no use of the rest of the device. Tests were completed to determine the repeatability of the new system along with the effects clinical variables such as abutment torque, angulation of the handpiece, striking height, and distance handpiece is held from the abutment have on the measurement results. Accuracy of the current Periotest method as well as the new system was independently evaluated through the use of an abutment with a strain gauge attached. Results: The new system for impact testing is shown to have greater accuracy than that of the Periotest device. Additionally, the effects of handpiece distance from abutment and torque (when above 15 Ncm) were found to be negligible while angulation of the handpiece and striking height affected the resonance frequency of the new system. Conclusion: The results of the in vitro testing indicate that greater resolution and accuracy can be achieved from an impact test that utilizes a clinical measurement protocol and independent analysis of the impact accelerometer signal. Schlagwörter: biomechanics, clinical assessment, diagnosis, impact test, implant interface, implant stability, resonance frequency analysis

Purpose: Restorative therapy of edentulous mandibles with residual ridge resorption is still a great challenge. Even though implant-supported stabilization of dentures has proved to be of value in these cases, treatment is sometimes problematic, not only due to narrow width of the denture-bearing areas but also because elderly patients are often averse to surgery. Implants with a normal length but a reduced diameter might facilitate therapy in patients with implant-supported dentures. The aim of the present study was to evaluate the clinical success of implants with a small diameter. Materials and Methods: In a prospective study, patients were provided with 2 implants 2.5 mm in diameter (MicroPlant; Brasseler, Lemgo, Germany) in a 2-stage procedure in the intraforaminal area of the edentulous mandible. Subsequently, the patients were monitored in periodic recalls. Periotest value, Gingival Index, and attachment level were monitored at these recall evaluations. Peri-implant bone loss was measured using panoramic radiographs. Patients rated the functionality of their denture using questionnaires administered before and after treatment. Results: Sixty-seven patients were monitored during an average observation time of 6 years (SD 2.7). The cumulative survival rate of the implants was 95.5%. Clinical and radiographic parameters yielded results comparable to those of implants with a larger diameter. The questionnaire revealed sharp and significant improvement in denture retention and chewing ability after denture stabilization with the implants. Conclusion: The clinical data and the results of the questionnaire clearly indicated that the patients were satisfied with the concept of stabilization of complete mandibular dentures with small-diameter implants. (Case Series) Schlagwörter: dental implants, elderly patients, implant-supported dentures, magnetic abutment, narrow implants, O-ring abutment, severe ridge resorption, slightly raised ridges

Purpose: The aim of the present study was to test the association between transmucosal depth of 2-stage dental implants and malodor production. Materials and Methods: Fifty-nine 2-stage implants were tested in 14 patients. Measurements were conducted 3 to 4 weeks following second-stage surgery. Measurements included healing abutment malodor scored using a subjective scale, volatile sulfide compounds levels measured using a sulfide monitor (Halimeter), and microbial sampling for anaerobic growth and malodor production. Results: All the malodor-related parameters measured in this study were significantly associated with the transmucosal depth. A significant increase in severity was observed concomitant with the increase in transmucosal depth. Conclusion: Based upon the data from this study of 59 two-stage implants in 14 patients, it appears that transmucosal depth of 2-stage dental implants may be an important factor affecting the presence of anaerobic bacterial population and resulting malodor production within the implant-abutment interface. (Case Series) Schlagwörter: bacteria, dental implants, malodor, transmucosal

Purpose: The objective of this study was to determine changes in interdental papillae, alveolar bone loss, esthetics, and initial healing survival when 1-piece narrow-diameter implants were immediately loaded in sites with limited tooth-to-tooth spacing. Materials and Methods: One-piece titanium alloy implants with a maximum diameter of 3.0 mm and a resorbable blast surface texture on a square-thread form were evaluated. Digital photographs were made at each clinical visit to assess soft tissue healing. Interproximal soft tissue fill of the embrasure was assessed with a modified Jemt index. Standardized radiographs were made at baseline (implant placement) and at 6 and 12 months postsurgery. Radiographic bone height was measured from a consistent landmark on the implant. A 1-sided t test was used to determine statistical differences of bone height. Results: Thirty-one implants were placed in 17 subjects. One implant had clinical mobility and was removed, for an overall survival rate of 96.7%. Mean bone height on the day of placement and restoration was 2.33 + 0.73 mm above the first thread. Mean bone height was 1.75 ± 0.78 mm at 6 months postrestoration and 1.63 ± 0.81 mm at 12 months postrestoration. There was a statistically significant loss of bone support over the initial 6 months (0.58 mm; P .01), with no significant progression thereafter (0.12 mm; NS). Complete fill of papillae was found in 92% of maxillary lateral incisor sites and 60% of mandibular incisor sites. Conclusion: The use of 1-piece narrow-diameter immediately loaded implants appears to be an effective prosthetic treatment for areas of limited space. (Case Series) Schlagwörter: esthetics, implants, interdental papillae

Purpose: The objective was to compare implants in the posterior maxilla with or without sinus floor augmentation. Materials and Methods: A retrospective study was conducted of patients who received implants in the posterior maxilla. All patients received solitary, implant-retained fixed partial dentures or crowns. A standardized form for implant treatment was used to document the follow-up examination. The different parameters were initially analyzed descriptively by frequency distribution, measure of central tendency, and statistical spread. A 95% level of significance was set for all tests. Results: A total of 76 patients with 141 dental implants in the posterior region of the maxilla were evaluated. Fifty-one patients with 71 implants received prior no augmentation (sinus floor elevation) and composed the control group. Twenty-five patients with 70 implants received an additional bone transfer prior to implant placement. The mean age of the patients at time of the follow-up examination was 49.7 years in the overall group, 52.6 years for men and 46.7 years for women. The implants inserted in an augmented area had similar implant stability and implant loss results after a mean functional observation period of 1.6 years (range, 0.5 to 4.7 years) compared to those inserted without augmentation. Augmented implants exhibited less peri-implant bone resorption. Conclusions: The outcomes for implants with augmentation were similar to those without augmentation. (Comparative Cohort Study) Schlagwörter: comparative study, peri-implant bone resorption, posterior maxillary region, sinus floor elevation

Purpose: To assess the treatment outcome (implant survival, surgical complications, patient satisfaction) of vertical distraction of the severely resorbed edentulous mandible. Materials and Methods: Forty-six patients with severe resorption of the edentulous mandible (bone height 5 to 8 mm, median 6 mm) participated in this study. The anterior segment of the mandible was vertically augmented using the Groningen distraction device. One or 2 months after the last day of distraction, 2 implants (n = 92) were placed. Standardized clinical and radiographic assessments were performed annually, and patient satisfaction was scored on a 10-point rating scale (0 = completely dissatisfied; 10 = completely satisfied). Results: Three implants were lost during the healing phase, but none were lost for the rest of the follow-up period (72 ± 10.3 months), resulting in an implant survival rate of 97%. One patient developed a fracture of the mandible 3 days after the last day of distraction; it healed uneventfully. The mean mandibular bone resorption during follow-up as measured on radiographs in the midline and distal of the implants was 9.8% ± 0.6% and 10.2% ± 0.8%, respectively. In 4 patients radiolucency in the distracted area persisted during the follow-up period. Four patients reported a slight sensory disturbance at the final evaluation visit. All patients functioned well with their prostheses. The mean patient satisfaction score after treatment was 8.1 ± 1.2. Conclusion: Vertical distraction of the anterior segment of a severely resorbed alveolar ridge of the mandible can provide a proper basis for insertion and osseointegration of endosseous load-bearing implants with good implant survival, few surgical complications, and good patient satisfaction. (Case Series) Schlagwörter: augmentation, dental implants, distraction osteogenesis, edentulous mandible

Purpose: To evaluate the success rate of immediately loaded conventional implants placed in the premaxilla in association with 2 zygomatic implants. Materials and Methods: All patients included had worn complete maxillary dentures for at least 2 years. They were required to have no severe systemic pathologies and could not be on any drugs. They could not have any oral infection, uncontrolled periodontal disease, sinusitis, parafunctional signs, alteration of the occlusal plane, or smoking habits. They had to be good candidates for the insertion of 4 or 5 traditional implants in the premaxilla and 2 zygomatic implants without guided bone regeneration. Primary stability had to be achieved. Impressions for prosthetic rehabilitation were made during first-stage surgery. Temporary fixed cross-arch prostheses were inserted 12 to 24 hours after surgery. Permanent cross-arch screw-retained prostheses were placed after 6 months. Results: Seven patients met all the inclusion criteria and were enrolled in the study (Caucasian, 4 males and 3 females, mean age 56.8 years). In total, 14 zygomatic and 34 conventional implants were placed. The survival rate for zygomatic and conventional implants and fixed prostheses was 100% after 24 months of functional loading. Conclusion: The preliminary results are encouraging, but the long-term clinical prognosis remains to be determined. (Case Series) Schlagwörter: edentulous maxilla, immediate loading, resorbed maxilla, single-stage surgery, zygomatic implants

Purpose: The purpose of the present prospective clinical study was to evaluate the radiographic and clinical outcome of immediately loaded implants in the partial edentulous mandible over a 4-year follow-up period using a modified surgical protocol, primary implant stability criteria, and splinting for inclusion. Materials and Methods: Patients in need of implant treatment in the partial edentate mandible were consecutively included in the study. The implant sites were underprepared to obtain maximal stability. Inclusion criteria for the study were torque of a least 30 Ncm before final seating of the implant and an ISQ greater than 60. A provisional fixed partial denture was delivered within 24 hours and a definitive fixed partial denture within 3 months. The patients were monitored with clinical and radiographic follow-up examinations for up to 4 years. Stability of the implants was measured with resonance frequency analysis at placement and after 6 months. Results: Ninety-six patients were evaluated, and 77 patients who met the inclusion criteria were included. A total of 111 fixed partial dentures supported by 257 Brånemark System implants (77 turned and 180 TiUnite implants) were delivered. Four (1.6%) of the 257 implants did not osseointegrate, giving an overall survival rate of 98.4% after 4 years. Three turned (3.9%) implants and 1 oxidized implant (0.6%) failed after 4 to 13 months. The average marginal bone resorption was 0.7 mm (SD 0.78) during the first year in function. Turned implants showed an average bone loss of 0.5 mm (SD 0.8) and oxidized implants an average of 0.7 mm (SD 0.8). Resonance frequency analysis showed a mean implant stability quotient of 72.2 (SD 7.5) at placement and 72.5 (SD 5.7) after 6 months of loading. Conclusion: It is concluded that immediate loading of implants with firm primary stability in partially edentulous areas of the mandible appears to be a viable procedure with predictable outcome. (Comparative Cohort Study) Schlagwörter: dental implants, immediate loading, insertion torque, partially edentulous mandible, primary stability, prospective study, resonance frequency analysis

Purpose: This cross-sectional study was performed to determine whether an association exists between the width of keratinized mucosa and the health of implant-supporting tissues. Materials and Methods: Data on 200 dental implants were collected. Periodontal parameters measured included Plaque Index, Gingival Index, width of keratinized mucosa, thickness of keratinized mucosa, radiographic bone level, and bleeding on probing. Statistical analysis was accomplished with the t test, Wilcoxon rank sum test, and logistic and linear regression models. Significance was established when P was less than .05. Results: The mean Gingival Index score, Plaque Index score, and radiographic bone loss were significantly higher for those implants with a narrow zone ( 2 mm) of keratinized mucosa. Implants with a narrow zone of keratinized mucosa also were more likely to bleed upon probing, even after adjusting for Plaque Index, smoking, thickness of the gingiva, and time since implant placement (adjusted odds ratio, 2.37; 95% confidence interval, 1.04 to 5.83). Significant independent association also was found between the width of keratinized mucosa and radiographic bone loss in favor of wider zone of keratinized mucosa. Conclusion: Increased width of keratinized mucosa around implants is associated with lower mean alveolar bone loss and improved indices of soft tissue health. (Cross-sectional Study) Schlagwörter: dental implants, keratinized gingiva, peri-implant tissues

Purpose: The aim of the present study was to establish a noninvasive method for quantitative analysis of supra- and subgingival biofilm formation on dental implants considering different surface modifications. Materials and Methods: Patients of both sexes were included. They had to be in generally good health, partially edentulous, and the recipient of at least 1 screw-type implant with an abutment possessing supra- and subgingival areas. Healing abutments were inserted for 14 days. The abutment surfaces were divided into quadrants that were sandblasted, ground, acid-etched, and untreated (with the latter surface as a control). Biofilm formation on the healing abutments was analyzed using scanning electron microscopy, including secondary-electron and Rutherford backscattering-detection methods. Calculation of biofilm-covered surfaces was performed depending on grey-values, considering supra- and subgingival areas. After calculating absolute and relative biofilm-covered surfaces depending on localization, the influence of surface modification on biofilm formation was analyzed. Results: Fifteen healing abutments were inserted in 11 patients. In all surface properties plaque adhesion in supragingival areas was significantly higher (17.3% ± 23.1%) than in subgingival areas (0.8% ± 1.0%). Biofilm accumulation in supragingival areas was significantly increasing by higher surface roughness, whereas this influence was not detected in subgingival areas. Conclusion: The described method is valuable for investigation of supra- and subgingival biofilm adhesion on surface-modified implant abutments. There was a significant influence of surface localization (supra- and subgingival) as well as surface modification on biofilm formation. (Case Control Study) Schlagwörter: abutment, biofilm, implant, scanning electron microscopy, surface roughness

Purpose: The aim of the present study was to histomorphometrically investigate crestal bone changes at nonsubmerged implants (Camlog) with different machined collar lengths in a dog model. Materials and Methods: One-stage insertion of sandblasted acid-etched screw-type implants with machined neck sizes of 1.6 mm (CAM) and 0.4 mm (CAM+) was performed in the mandibles of 4 beagle dogs. Both types of implants were inserted so that the implant shoulder (IC) exceeded the alveolar crest for 0.4 mm. Placement was followed by the connection of standard abutments. The animals were sacrificed after 2 and 12 weeks. Dissected blocks were processed for histomorphometric analysis (eg, distance between IC and the coronal extension of bone-implant contact [CBI], the distance between IC and the apical extension of the inflammatory cell infiltrate, and the percentage of bone-implant contact). Results: Histomorphometric analysis revealed significantly increased mean IC-CBI (CAM: 2.4 ± 0.3 mm; CAM+: 1.6 ± 0.1 mm) and BIC (CAM: 77%; CAM+: 80%) values in both groups at 12 weeks. However, mean IC-CBI values were significantly higher in the CAM group (P .01). An inflammatory cell infiltrate was localized to the implant-abutment interface of both CAM and CAM+ implants, and BC was clearly separated from aICT by a subepithelial connective tissue zone. Conclusions: Within the limits of the present study, it was concluded that (1) rough-surfaced implant necks reduced crestal bone level changes after 12 weeks of healing, and (2) microbial leakage apparently did not contribute to the marginal bone resorption in either group. Schlagwörter: animal study, histomorphometry, machined neck, marginal bone level, microbial leakage, rough neck

Purpose: The aim of the present retrospective investigation was to evaluate implant-supported maxillary overdentures using either anterior (group 1) or posterior (group 2) maxillary implant placement. Material and Methods: Maxillary overdentures were planned with support by either 4 implants placed in the maxillary anterior region (group 1) or 6 to 8 implants placed in augmented maxillary posterior regions (group 2, bilateral sinus augmentation) and anchored either on an anterior or on 2 bilaterally placed milled bars. Cumulative implant survival rate, peri-implant conditions (marginal bone loss, pocket depth, Plaque Index, Gingival Index, Bleeding Index, and Calculus Index) and the incidence and type of prosthodontic maintenance were assessed and compared for the 2 groups. In addition, the cumulative survival rate for implants placed in grafted regions was compared with that of implants placed in nongrafted regions. esults: Thirty-four patients (16 for group 1 and 18 for group 2) with 179 implants were available for follow-up examination after a mean period of 42.1 ± 20.1 months. Four initially placed implants failed to osseointegrate and were replaced, but no further losses were seen during the loading period, for a 5-year cumulative implant survival rate of 97.8%. No differences in implant survival rates were seen between either the group-1 (98.4%) and group-2 (97.4%) concepts or nongrafted (98.0%) and grafted (97.5%) implants. The peri-implant parameters showed a healthy soft tissue, good oral hygiene, and an acceptable degree of peri-implant marginal bone loss. The rigid fixation of all overdentures was associated with a low incidence of prosthodontic maintenance, without any significant differences between the 2 groups. Conclusions: In well-planned overdenture treatment programs, a high survival rate and excellent peri-implant conditions can be achieved for implants placed in the anterior or posterior maxilla. Rigid anchorage of maxillary overdentures either on an extended anterior milled bar or on 2 bilateral posterior milled bars provides for a low incidence of prosthodontic maintenance. (Comparative Cohort Study) Schlagwörter: dental implants, edentulous maxilla, maxillary overdentures, milled bars

Objective: Resonance frequency analysis (RFA) is a method of measuring implant stability. However, little is known about RFA of implants with long loading periods. The objective of the present study was to determine standard implant stability quotients (ISQs) for clinical successfully osseointegrated 1-stage implants in the edentulous mandible. Materials and Methods: Stability measurements by means of RFA were performed in regularly followed patients who had received 1- stage implants for overdenture support. The time interval between implant placement and measurement ranged from 1 year up to 10 years. The short-term group comprised patients who were followed up to 5 years, while the long-term group included patients with an observation time of > 5 years up to 10 years. For further comparison RFA measurements were performed in a matching group with unloaded implants at the end of the surgical procedure. For statistical analysis various parameters that might influence the ISQs of loaded implants were included, and a mixed-effects model applied (regression analysis, P .0125). Results: Ninety-four patients were available with a total of 205 loaded implants, and 16 patients with 36 implants immediately after the surgical procedure. The mean ISQ of all measured implants was 64.5 ± 7.9 (range, 58 to 72). Statistical analysis did not reveal significant differences in the mean ISQ related to the observation time. The parameters with overall statistical significance were the diameter of the implants and changes in the attachment level. In the short-term group, the gender and the clinically measured attachment level had a significant effect. Implant diameter had a significant effect in the long-term group. Conclusions: A mean ISQ of 64.5 ± 7.9 was found to be representative for stable asymptomatic interforaminal implants measured by the RFA instrument at any given time point. No significant differences in ISQ values were found between implants with different postsurgical time intervals. Implant diameter appears to influence the ISQ of interforaminal implants. (Case Series) Schlagwörter: implant stability, mandible, 1-stage implants, resonance frequency analysis