The International Journal of Oral & Maxillofacial Implants, 03/2010

Purpose: The aim of this study was to evaluate in vitro the microgap between different zirconia abutments and their titanium implants. Materials and Methods: Four systems were evaluated: Procera zirconia (Nobel Biocare) (Nb), Cercon Balance Anterior (Dentsply Friadent) (Ba), ZirDesign (Astratech) (Zd), and Straumann Cares ceramic (Straumann) (Ca). Five assemblies were assessed for each system. The assemblies were embedded in epoxy, cut along their long axes, and polished. Scanning electron microscopic observations were made along the first 100 µm of the gap on each side at maximal magnification. Images were combined and gap measurements were made 10 µm apart. A two-way analysis of variance was performed on the data. Results: Scanning electron micrographs showed a mean marginal microgap of 0.89 µm (SD 1.67) for all assemblies. Significant differences (P .001) were observed between mean (± SD) microgap measurements of the four tested systems: Ba = 0.38 ± 0.28 µm; Zd = 0.55 ± 0.23 µm; Nb = 1.83 ± 3.21 µm; Ca = 0.90 ± 0.59 µm. The mean microgap of the first 20 µm of the outer region (1.66 µm) was significantly (P .001) larger than the mean microgap (0.56 µm) of the inner region (30 to 100 µm). Conclusions: Within the limitations of this study, the mean microgap observed for all tested systems was less than 2 µm. For each system, the microgap decreased quickly from the outer region to the inner. The mean gap was larger for flat-to-flat connection systems, compared to internal-connection systems with a conical interface. These results demonstrate smaller microgaps compared to those described in the literature for titanium abutments. The precise fit of these abutments could lead to better biologic and biomechanical behavior. Keywords: dental implants, implant abutments, microgap, zirconia

Purpose: The inter-relationships between various implant and bone parameters were evaluated for their influence on the von Mises stress distribution within the mandible using the finite element procedure. The maximum compressive stresses in cancellous and cortical bone were compared to the published stress-strain data to determine bone fracturing status when the maximum (traumatic) loading is applied. Materials and Methods: Parameters considered herein include the implant diameter and length. Also considered are Young's modulus of cancellous bone and that of cortical bone, along with its thickness. The implant-bone system was modeled using two-dimensional plane strain elements, 50% osseointegration between implant and cancellous bone was assumed, and linear relationships were assumed between the stress value and Young's modulus of both cancellous and cortical bone at any specific point within the mandible. Results: Implant length was more influential than implant diameter within cancellous bone, whereas implant diameter was more influential in cortical bone. A ranking of all the parameters indicated that the applied masticatory force had a more significant influence on the stress difference, in both cancellous and cortical bone, than all other parameters. Young's modulus of cortical bone and implant length were least influential in cancellous and cortical bone, respectively. Under traumatic loading, cancellous bone fractured for all parameter combinations. When all parameters were set to their average values, the cortical bone did not fracture under traumatic loading. However, it fractured if all the parameters were all set to the minimum values. Conclusion: Quantitative evaluation and ranking of the major implant and bone parameters will help provide practical guidelines that are useful for the design and testing of dental implants. The study may also be of interest to dental professionals in evaluating possible implant placement options under various clinical scenarios. Keywords: bone density, finite element analysis, implant diameter, implant length, masticatory force, stress characteristics, traumatic loading

Purpose: The aim of this study was to evaluate, through histomorphometric analysis, the effect that different loading times would have on the bone response around implants. Materials and Methods: Three Replace Select implants were placed on each side of the mandible in eight dogs (n = 48 implants). One pair of implants was selected for an immediate loading protocol (IL). After 7 days, the second pair of implants received prostheses for an early loading protocol (EL). Fourteen days after implant placement, the third pair of implants received prostheses for advanced early loading (AEL). Following 12 weeks of prosthetics, counted following the positioning of the metallic crowns for the AEL group, the animals were sacrificed and the specimens were prepared for histomorphometric analysis. The differences between loading time in the following parameters were evaluated through analysis of variance: bone-to-implant contact, bone density, and crestal bone loss. Results: The mean percentage of bone-to-implant contact for IL was 77.9% ± 1.71%, for EL it was 79.25% ± 2.11%, and for AEL it was 79.42% ± 1.49%. The mean percentage of bone density for IL was 69.97% ± 3.81%, for EL it was 69.23% ± 5.68%, and for AEL it was 69.19% ± 2.90%. Mean crestal bone loss was 1.57 ± 0.22 mm for IL, 1.23 ± 0.19 mm for EL, and 1.17 ± 0.32 mm for AEL. There was no statistical difference for any of the parameters evaluated (P > .05). Conclusion: Different early loading times did not seem to significantly affect the bone response around dental implants. Keywords: animal study, bone density, bone-to-implant contact, dental implants, early loading, immediate loading, osseointegration

Purpose: The objective of this study was to assess the influence of mandibular morphology on the stress and strain distributions in the bone supporting an implant. Materials and Methods: Subjects were selected from patients with missing mandibular premolar teeth. Computed tomographic scans of the premolar region were classified into nine groups based on the overall bone morphology and the relative position of the alveolar crest. Finite element models of the bone on the basis of this classification, with inserted implants and superstructures, were constructed. A load of 200 N applied 30 degrees buccal from the vertical axis was directed toward the occlusal surface. Results: One hundred two partially (n = 98) and completely (n = 4) edentulous subjects were recruited. Their ages ranged from 40 to 79 years (mean age, 60.5 years; 41 men and 61 women). Approximately 56% of the patients showed bone widening in the caudal direction. The maximum compressive stresses were shown in the lingual cervical regions. An influence of overall bone morphology on stress distribution was not observed; however, the alveolar crest contour clearly affected the maximum stress and strain values. Compressive microstrain above 4,000 was observed only when the alveolar crest was lingually located relative to the body of the mandible. These high strain levels were concentrated at the lingual cervical margin, with volumes ranging from 0.04 to 0.07 mm3. Conclusion: The contour of the alveolar crest potentially plays a critical role in maintaining the bone levels surrounding implants. Keywords: bone morphology, computed tomography, dental implant, mandible, stress

Purpose: Registration refers to the linkage of coordinates from an image with actual patient coordinates and has been shown to be the most influential factor in the accuracy of image-guided surgery. Invasive bone markers are the gold standard but require surgical placement prior to imaging. In contrast, registration templates or external registration frames are noninvasive, but their repositioning during imaging and surgery can be a source of error. The purpose of the present study was to determine whether noninvasive registration methods can achieve an accuracy similar to that of invasive bone marker registration. Materials and Methods: Computed tomographic slices (1 mm each) of a maxillary and mandibular dental stone cast that had been prepared with target markers on the buccal and oral surfaces were registered with an optical-based navigation system simulating invasive bone markers, noninvasive registration templates, and a noninvasive external registration frame. Predicted error of the navigation system, fiducial registration error, and target registration error were evaluated. The use of five and seven registration markers was compared. Results: A total of 696 error measurements was performed. The external registration frame showed significantly worse fiducial registration error compared with the other methods, but there was no significant difference in target registration error between invasive and noninvasive registration methods. The predicted error given by the navigation system significantly underestimated target registration error. Increasing the number of registration markers from five to seven resulted in no significant differences. Conclusions: Noninvasive registration based on registration templates or external registration frames showed accuracy that was equivalent to that of invasive registration. The use of five registration markers was sufficient. The predicted error given by a navigation system should not be mistaken as "navigation error" during clinical application. Keywords: accuracy, image-guided implant surgery, registration

Purpose: Accurate measurement of alveolar bone and adjacent anatomic structures is of paramount importance in implant insertion. This study was conducted to compare the linear measurement accuracy of 64-channel computed tomography (CT) and cone-beam CT (CBCT). Materials and Methods: Twenty-seven sites were marked on three dry human skulls, with the positions of the buccal and palatal fiducial markers ensuring the representation of one plane by each buccal-palatal pair. The skulls were imaged using Somatom Sensation 64-channel CT (Siemens) and Pro Max 3D CBCT (Planmeca). The two fiducial markers and alveolar bone height were measured on the printed films of the cross-sectional views representing the best buccal and palatal markers. The maxillae were then sawed in marked locations, and direct measurements of the fiducial markers and alveolar bone height were then made. The Wilcoxon signed rank test was employed for statistical analysis. Results: The measurement errors for the buccal fiducial markers, palatal fiducial markers, and crest height for CBCT were 0.38 ± 0.39 mm, 0.37 ± 0.33 mm, and 0.58 ± 0.45mm, respectively; for the 64-channel CT they were 0.59 ± 0.61 mm, 0.37 ± 0.42 mm, and 0.72 ± 0.92 mm, respectively. There was no statistically significant difference in measurement error between the two methods (P > .05). Conclusion: There was no statistically significant difference in terms of linear measurement accuracy between the two systems; it could, therefore, be concluded that CBCT is a useful tool for a preliminary assessment of anticipated implant sites. Keywords: computed tomography, cone-beam computed tomography, dental implant, linear measurement

Purpose: This review critically compares the available clinical and laboratory methods for assessing the fit of an implant prosthesis. Materials and Methods: MEDLINE and PubMed databases were searched for studies related to the fit of implant prostheses or the effect of misfit. Different combinations of key words were used. The screening procedure was performed in two stages. In the first stage, the relevant articles were selected. In the second stage, from those articles, specific inclusion and exclusion criteria were applied. Results: Fifty-four articles were selected. Two different techniques were identified: in vitro and in vivo. The advantages, disadvantages, and limitations of each technique are discussed. There are clear limitations for the in vivo techniques. The in vitro techniques provide a more accurate measure of prosthesis misfit. Conclusions: Because of the variety of techniques and the different parameters assessed by each, it is useful to combine several techniques to assess the accuracy of fit, quantify the effect of misfit, and subsequently determine an acceptable level of fit. Keywords: dimensional measurements, implant framework, modeling methods, passive fit, prosthesis fit

Purpose: Osteoporosis and diabetes are physiologic determinants that affect the process of osseointegration. The demand for dental implants is high in these patients, who have benefited from progress in preclinical research. Osseointegration has been extensively studied in rat models of osteoporosis and diabetes. The aim of this study is to present an assessment of the published data and provide consideration for future studies. Materials and Methods: The present study summarizes information through a systematic review of the literature from 1997 to 2008 available through PUBMED. The authors found 20 and 13 articles that report on osseointegration of implants in osteoporotic and diabetic rats, respectively. The survey was extended to recent publications on relevant aspects related to species, strains, and quality of endpoint data. Results: Differences in experimental variables such as timing of implant insertion, location of implants, or duration of disease prior to implant placement were reported and can be justified based on the experimental questions. Moreover, heterogeneity was further caused by variations in the age of rats and in reporting of the main parameters of osseointegration in the cortical and medullary compartments. Regardless of these differences, the evidence indicates consistently that ovariectomy results in reduced osseointegration, while there is only moderate evidence for impaired osseointegration in diabetic rats. Conclusions: Selection of the appropriate protocol is critical when studying implant osseointegration in rats. This overview highlights the demand for quality endpoint data related to animal numbers, data collection, and the way to establish osseointegration. Because of the differences in research questions, general recommendations for uniform models for osteoporosis and diabetes cannot be made. Keywords: bone regeneration, diabetes, implants, osseointegration, ovariectomy, rat

Purpose: This systematic review examines the published findings on the clinical effectiveness and predictability of allogeneic bone blocks for the correction of alveolar ridge deformities to support dental implant placement in humans. Materials and Methods: A bibliographic search was conducted of the MEDLINE and EMBASE databases for studies in which allogeneic block grafts were used for alveolar bone augmentation. The search was limited to human studies in English-language publications between 1950 and September 2008. Data extraction included the following outcomes: (1) vertical and/or horizontal bone gain/loss, (2) graft failure rate and complications, and (3) implant survival rate. Results: The initial search identified 35 papers from the electronic databases, with nine publications meeting inclusion criteria: two case reports, six case series, and one prospective, multicenter, consecutive case series. No randomized controlled clinical trials were identified in the search. Observational studies (110 total patients) generally reported high rates of clinical graft incorporation (90% or greater) and implant survival (99% to 100%); however, the majority of reports involved selected defects in anterior regions with short-term follow-up (less than 3 years). Conclusion: Clinical evidence remains limited to case series and reports that differ with respect to alveolar ridge defect selection, treatment, and endpoints of therapy over short-term follow-up periods. Although case-based reports document the potential for allogeneic block grafts to support alveolar ridge augmentation and implant placement, insufficient evidence is available to establish treatment efficacy relative to graft incorporation, alveolar ridge augmentation, and long-term dental implant survival. Keywords: allograft, alveolar ridge, augmentation, bone, dental implant, onlay grafting

Purpose: Contradictory results have been reported on the comparability of implant stability measurements performed with the Periotest and the Osstell Mentor devices. The purpose of the present finite element analysis was to simulate the influence of the parameters implant length, bone quality (cortical thickness and damping factor), bone loss, and quality of transducer fixation on resonance frequency analysis (RFA) and damping capacity measurements. Materials and Methods: Three-dimensional finite element models of implants placed in human mandibular bone were designed for the simulation of Periotest (Periotest value; PTV) and RFA (implant stability quotient) measurements. Three values for each of the parameters implant length, damping capacity of cortical and trabecular bone, thickness of cortical bone, bone loss, and quality of transducer fixation were obtained. Measurements were simulated at four stages of osseointegration. Results: For all parameters, an increase in implant stability was found with increasing levels of osseointegration. Implant stability was positively correlated with implant length and thickness of cortical bone, with slightly converging values at increased levels of osseointegration. Varying the damping factor of bone had no significant effect. Implant stability was negatively correlated with bone loss, with slightly converging values at increased levels of osseointegration. Linear changes in implant length and bone loss caused nonlinear effects in implant stability values. Stiffness of transducer fixation had an impact on RFA measurements when values below 10 GPa were applied. Conclusion: Although both measuring devices reacted similarly when different parameters of implant stability were changed, good correlation between Periotest values and implant stability quotients was observed only when measurement values of implants without bone loss were considered. Keywords: damping capacity, finite element analysis, implant stability, Osstell Mentor, Periotest, resonance frequency

Purpose: It is unknown whether different microgap configurations can cause different peri-implant bone reactions. Therefore, this study sought to compare the peri-implant bone morphologies of two implant systems with different implant-abutment connections. Materials and Methods: Three months after mandibular tooth extractions in six mongrel dogs, two oxidized screw implants with an external-hex connection were inserted (hexed group) on one side, whereas on the contralateral side two grit-blasted screw implants with an internal Morse-taper connection (Morse group) were placed. On each side, one implant was inserted level with the bone (equicrestal) and the second implant was inserted 1.5 mm below the bony crest (subcrestal). Healing abutments were inserted immediately after implant placement. Three months later, the peri-implant bone levels, the first bone-to-implant contact points, and the width and steepness of the peri-implant bone defects were evaluated histometrically. Results: All 24 implants osseointegrated clinically and histologically. No statistically significant differences between the hexed group and Morse group were detected for either the vertical position for peri-implant bone levels (Morse equicrestal -0.16 mm, hexed equicrestal -0.22 mm, Morse subcrestal 1.50 mm, hexed subcrestal 0.94 mm) or for the first bone-to-implant contact points (Morse equicrestal -2.08 mm, hexed equicrestal -0.98 mm, Morse subcrestal -1.26 mm, hexed subcrestal -0.76 mm). For the parameters width (Morse equicrestal -0.15 mm, hexed equicrestal -0.59 mm, Morse subcrestal 0.28 mm, hexed subcrestal -0.70 mm) and steepness (Morse equicrestal 25.27 degree, hexed equicrestal 57.21 degree, Morse subcrestal 15.35 degree, hexed subcrestal 37.97 degree) of the peri-implant defect, highly significant differences were noted between the Morse group and the hexed group. Conclusion: Within the limits of this experiment, it can be concluded that different microgap configurations influence the size and shape of the peri-implant bone defect in nonsubmerged implants placed both at the crest and subcrestally. Keywords: bone morphology, equicrestal placement, histometric study, microgap, subcrestal placement

Purpose: The purpose of this study was to evaluate the radiographic bone level and stability changes around early loaded chemically modified sandblasted and acid-etched implants with and without a machined collar. Materials and Methods: Seventy-two chemically modified sandblasted and acid-etched implants 4.1 mm in diameter and 8 mm in length were placed in six dogs. Thirty-six implants had no machined collar (NMC) and 36 had a 2.8-mm machined collar (MC). Resonance frequency measurements were obtained at placement and weekly for 3 weeks. All implants were loaded 21 days after surgery. Standardized periapical radiographs were obtained at baseline, at 3 weeks, and at 3, 6, 9, and 12 months. The radiographs were randomized and digitized, and linear measurements of the distance from the first bone-to-implant contact to the shoulder of the implant were performed at the mesial and distal aspects of each implant. For statistical analysis, mixed-model repeated-measures analysis of variance was used. Results: All implants achieved hard and soft tissue integration clinically and radio-graphically and were clinically immobile. From placement to week 3, the mean implant stability increased for MC implants by more than 5 ISQs and for NMC implants by more than 7 ISQs. Radio-graphically, there were significant differences between treatment groups beginning at 3 months. After 12 months of loading, the MC implants presented a mean bone loss of 1.00 mm and the NMC implants presented a mean bone gain of 0.11 mm. Conclusions: Chemically modified sandblasted and acid-etched implants without a machined collar presented bone gain, and implants with a machined collar showed bone loss after a 1 year following early (21-day) loading. The tendency toward a coronal apposition of bone observed under these conditions may be attributed to the osteoconductive properties of the chemically modified surfaces of these implants and to the absence of the machined collar. Keywords: alveolar bone loss/etiology, dental implants, early loading, follow-up stability, osseointegration, resonance frequency analysis

Purpose: To evaluate the difference between the dental surgeon's perception of implant stability and the actual insertion torque and actual values obtained through resonance frequency analysis (RFA) during implant insertion surgery. Materials and Methods: One hundred fifty-two patients who needed one or more dental implants were selected. A total of 514 Xive implants was inserted. For all 514 implants, after insertion, the oral surgeon was asked to indicate the probable RFA values (implant stability quotient [ISQ]). For 483 implants, the surgeon was also asked to indicate the probable insertion torque values (N/cm). The actual values were then measured. The RFA and insertion torque values were grouped into low, medium, and high groups. Results: The mean perceived RFA was 72.2 ± 9.8 ISQ. The mean actual RFA was 73.5 ± 10.2 ISQ. This difference was statistically significant (P = .01). The mean perceived insertion torque was 39.1 ± 20.1 Ncm. The mean actual insertion torque was 39.9 ± 20.7 Ncm. The mean difference between actual and perceived ISQ values was -1 ± 14.9, with a range from -60 to 59; the mean difference between actual and perceived insertion torque values was -1.3 ± 9.9, with a range from -38 to 45. Conclusions: Xive implants obtained good primary stability in many different clinical situations with a standard protocol. Primary stability is generally underestimated, especially in the presence of low or medium ISQ and torque values. The accuracy of primary stability prediction is not good enough to prevent mistakes when using an immediate loading technique; therefore, a more systematic use of objective measurements is encouraged. Keywords: dental implants, immediate loading, implant stability, insertion torque, resonance frequency analysis

Purpose: The purpose of this investigation was to compare the efficacy of two therapeutic options-immediate implant placement and ridge preservation with delayed implant placement-in maintaining the position of the soft tissue margins following tooth extraction. Materials and Methods: This randomized controlled study evaluated apicocoronal changes in the midbuccal and proximal mucosal positions at implant placement sites from tooth extraction to 3 and 6 months following extraction. Twenty-four patients (26 sites) randomly received either immediate implant placement or ridge preservation (grafting with freeze-dried bone allograft and a collagen membrane) followed by implant placement 3 months later. Immediate placement sites received bone grafting for horizontal defects > 2 mm (from implant to cortical wall). Soft tissue measurements, vertical measurements, and ridge width measurements were performed and compared for immediate versus delayed implants and thin versus thick biotype. Results: The midbuccal soft tissue margins showed minimal recession over 6 months from the time of extraction (mean 0.17 ± 0.47 mm), with no differences between treatment groups. Interproximal tissue height decreased significantly from extraction to 6 months (mesial, 1.73 ± 0.71 mm; distal, 1.48 ± 0.80 mm), with no significant differences between immediate and delayed placement. Immediate implant sites had greater reductions in ridge width 6 months after extraction than delayed placement sites. Tissue biotype failed to show any significant relationship with the changes identified. Conclusions: This randomized controlled study comparing soft tissue changes following extraction failed to identify differences between patients treated with immediate or delayed approaches for midbuccal or interproximal soft tissue margins, although greater decreases in ridge width were observed in sites lacking bone grafting. Both immediate and delayed treatment approaches appear to be appropriate following tooth extraction, with the preferred treatment based on factors other than resultant soft tissue changes. Keywords: dental implant, esthetics, immediate implants, randomized controlled trial, ridge preservation, tooth extraction

Purpose: The aim of the present retrospective clinical study was to compare the efficacy of two piezoelectric cutting inserts for the incidence, size, and types of sinus membrane perforations, and to evaluate their various advantages for lateral window osteotomy. Materials and Methods: The study consisted of 127 maxillary sinus augmentation procedures performed at two centers. A bony window was made on the lateral wall of the maxillary sinus with either the piezoelectric saw or the round diamond insert and repositioned over the bone graft as a homologous bony barrier. The rate of membrane perforation during sinus augmentation between the two groups was compared and analyzed statistically by the chi-square test and the two-sample t test. Results: Seven perforations were seen in the 127 maxillary sinus procedures in this study (5.51%). Six perforations in 84 cases (7.14%) occurred with the piezoelectric saw and one perforation in 43 sites (2.32%) occurred while using the round insert. No statistically significant difference was found between the rates of membrane perforation between the two inserts. Conclusion: The lateral bony window was created effectively with either of the two kinds of piezoelectric inserts. The membrane perforation rate was not significantly affected by the type of piezoelectric insert. The piezoelectric saw insert was more advantageous than the round diamond due to its greater precision and easier repositioning of the lateral bony window as a barrier. Keywords: maxillary sinus augmentation, piezoelectric round diamond insert, piezoelectric saw, replaceable bony window, sinus membrane perforation

Purpose: The purpose of this clinical trial was to evaluate whether the crestal bone height around dental implants could be influenced by the use of a platform-switching protocol. Materials and Methods: All implants placed in the year 2006 in healed bone without any need for ridge augmentation were included in this study. The following groups were created: (1) wide-diameter implants were placed subcrestally and regular-diameter cover screws were connected; (2) regular-diameter implants were placed at the crest and regular-diameter cover screws were connected. Standardized radiographs were obtained after insertion of the definitive prosthesis and after 1 year. Calibrated measurements were conducted initiating from the mesial and distal bone peaks to the implant-abutment junction. The average value of the mean medial and mean distal values was calculated and analyzed with an unpaired two-tailed t test. P values .05 were regarded as statistically significant. Results: In all, 89 dental implants in 36 patients were evaluated. The implants with a platform-switched configuration (n = 75) exhibited statistically significantly less bone loss at time of insertion of the definitive prosthesis (0.30 ± 0.07 mm versus 0.68 ± 0.17 mm; P .05) and at 1 year (0.39 ± 0.07 mm versus 1.00 ± 0.22 mm, P .01) when compared to the nonplatform-switched implants (n = 14). Conclusion: Platform-switched implants seem to limit crestal bone remodeling. Keywords: bone preservation, crestal bone level, platform switching

The following case reports describe the use of computer-assisted image-guided surgery to plan and place craniofacial bone-anchored implants (CBAI) for facial prosthetic reconstructions. During virtual planning, the soft tissue and bone visualizations are segmented from spiral computed tomography data and the patient's normal anatomy is mirrored onto the skull of the defect side, thus providing the ability to visualize the future prosthetic form. CBAI are planned in the anatomical area that leads to the best cosmetic results. Bone quantity is directly assessed at the surgical sites with the integrated instrumentation while the clinician navigates within the images and virtual planning scheme in real time. The aim of this report is to show a technique that incorporates computer-assisted image-guided surgery into the preoperative planning and surgical placement of CBAI. The use of this technology to plan and place implants in the most ideal location for facial prosthetic treatment eliminated the need for a conventional or prototyped surgical guide. Keywords: anaplastology, auricular prosthesis, computer-assisted image-guided surgery, craniofacial bone-anchored implant, navigation, preoperative planning

Purpose: The present study evaluated implant and peri-implant outcomes as well as prosthodontic maintenance efforts for implant/bar-supported mandibular prostheses with different prosthesis anchorage systems. Materials and Methods: Seventy-six patients who received two or four interforaminal implants were assigned to one of three different bar designs and subsequently to different prosthesis supporting systems. Forty-nine patients received implants and a mucosa-supported implant-retained overdenture (OD) with an ovoid bar (two implants; design 1) or multiple ovoid bars (four implants; design 2). Twenty-seven patients received four implants and a rigid implant-supported prosthesis (ISP) with a milled bar (design 3). Implant survival, peri-implant parameters (marginal bone resorption, pocket depth, and plaque, bleeding, gingival, and calculus indices), and postinsertion prosthodontic maintenance were followed over a 5-year period and compared among the different retention modalities. At the most recent follow-up examination, subjective patient satisfaction was additionally evaluated using a simplified scoring system (ranging from 1 = not satisfactory to 5 = excellent). Results: Implant survival rates (100%) and all peri-implant parameters evaluated showed no differences among the three designs used for implant prosthesis anchorage. Prosthodontic maintenance did not differ between the different ODs (OD design 1: average of 1.04 maintenance visits/year/patient; OD design 2: 1.2 maintenance visits/year/patient), but it was significantly lower for the dentures that were rigidly stabilized with milled bars (ISP: 0.37 maintenance visits/year/patient). A high subjective satisfaction rate (range: 4.5 to 5.0) was registered at the final examination, without any differences among the designs used. Conclusions: Rigid anchorage with milled bars on four-implant prostheses combined with a metal-reinforced framework showed a lower extent of prosthodontic maintenance issues than round bars on two- or four-implant overdentures with resilient denture stabilization. Nevertheless, implants and peri-implant structures were not negatively affected by either resilient or rigid anchorage mechanisms. Keywords: edentulous mandible, implant-supported overdentures, milled bar, prosthodontic maintenance, round bar

Purpose: Pneumatized sinuses in the posterior maxilla often make implant placement difficult or impossible. A sinus lifting procedure can reliably augment the bone height, with the highest success rates reported when two-stage implants are placed 6 to 9 months later. The aim of this study was to evaluate the clinical reliability of a shortened approach in which nonsubmerged implants were placed at the time of sinus augmentation. Materials and Methods: All patients treated with sinus floor elevation and simultaneous implant placement at the authors' institution from 1999 to 2004 were retrospectively selected for a long-term follow-up study. Sinus elevation was considered when the remaining subantral bone height did not reach 6 mm in one or more implant sites. The lateral window technique was performed using bovine hydroxyapatite as a filler, and nonsubmerged implants were placed immediately. Implant and prosthodontic survival rates, as well as biologic and prosthodontic complications, were evaluated 2 to 6 years after loading. Results: In a sample of 40 patients, 50 subantral bone augmentations were performed and 102 implants were placed using the one-stage approach. One implant remained submerged because of a lack of primary stability. No sinusitis was noted. Only two implants were lost before loading. No implants failed after the definitive restorations were placed, leading to a 98% implant survival rate and 100% prosthodontic survival rate after 2 to 6 years. Conclusions: Subantral bone regeneration with bovine hydroxyapatite as a space filler is an effective and safe procedure allowing high survival rates of implants placed in the posterior maxilla. If the remaining bone is sufficient to ensure primary stability, implant placement can be performed simultaneously with sinus lifting, and even in a nonsubmerged fashion. Keywords: biomaterials, bone regeneration, bovine hydroxyapatite, implants, sinus lift, subantral augmentation

Purpose: The aim of this study was to compare the long-term success rates of wide-diameter implants in the mandibular molar region placed immediately after extraction and loaded either immediately or after a 3-month healing period. Materials and Methods: In 71 patients, 120 implants were positioned immediately after tooth extraction; 60 implants (immediate loading group) were loaded immediately and 60 were loaded after 3 months (delayed loading group). Radiographic examinations were made at baseline and at 1, 2, 3, 4, and 5 years after implant placement. Results: After 5 years, a survival rate of 96.67% was reported for all implants (failure rate, 3.33%). Four implants were lost, two from the immediate loading group and two from the delayed loading group. There were no patient dropouts in either group. Conclusions: Wide-diameter implants placed in fresh extraction sockets and loaded immediately or after a delay showed no significant clinical or radiographic differences after 5 years. Keywords: extraction sockets, immediate loading, wide-diameter dental implants

Purpose: To assess the long-term behavior of 980 implants placed in a private practice and evaluate the influence of periodontitis history and smoking habit on implant survival rates. Materials and Methods: A retrospective review of clinical records of consecutively treated patients with Astra Tech implants was conducted. This review included all patients treated between February 1994 and January 2005. Clinical histories were reviewed, and data were gathered on clinical and radiographic examinations. A record was kept on smoking habits, periodontitis history, length and diameter of implant(s), and whether the sinus was elevated. Cumulative survival proportions analysis was performed, and Cox regression multivariate analysis modified for correlated dependent observations was also used, with the implant as the unit of analysis. Results: A total of 323 patients (185 [57.3%] female; mean age, 55.4 ± 15.2 years) received 980 implants. Of the implants evaluated in this study, 71.1% were placed in patients who were undergoing periodontal maintenance care and 38.8% were placed in smokers. The cumulative survival rate was 96.2% at 5 years; 4.3% of implants failed; 57.1% of failures occurred before implant loading. Tobacco use and periodontitis did not affect the risk of failure, and their interaction did not show significance (P = .386). Implants from individuals with many implants and those placed in patients with sinus elevation showed a higher risk of failure (P .05). Regression analysis showed no significant interaction between periodontitis history, tobacco use, and implant failure. Conclusions: Implant placement is an effective and reliable long-term treatment, even in periodontal patients under maintenance care and with a smoking habit. Combined analysis of tobacco use and history of periodontitis showed no significant interaction with implant failure in this sample. Keywords: dental implants, periodontitis, regression analysis, risk factors, survival, tobacco use