The International Journal of Oral & Maxillofacial Implants, 05/2011

Purpose: The vertical location of the implant-abutment connection influences the subsequent reaction of the peri-implant bone. It is not known, however, whether any additional influence is exerted by different microgap configurations. Therefore, the radiographic bone reactions of two different implant systems were monitored for 6 months. Materials and Methods: In eight mongrel dogs, two implants with an internal Morse-taper connection (INT group) were placed on one side of the mandible; the contralateral side received two implants with an external-hex connection (EXT group). On each side, one implant was aligned at the bone level (equicrestal) and the second implant was placed 1.5 mm subcrestal. Healing abutments were placed 3 months after submerged healing, and the implants were maintained for another 3 months without prosthetic loading. At implant placement and after 1, 2, 3, 4, 5, and 6 months, standardized radiographs were obtained, and peri-implant bone levels were measured with regard to microgap location and evaluated statistically. Results: All implants osseointegrated clinically and radiographically. The overall mean bone loss was 0.68 ± 0.59 mm in the equicrestal INT group, 1.32 ± 0.49 mm in the equicrestal EXT group, 0.76 ± 0.49 mm in the subcrestal INT group, and 1.88 ± 0.81 mm in the subcrestal EXT group. The differences between the INT and EXT groups were statistically significant (paired t tests). The first significant differences between the internal and external groups were seen at month 1 in the subcrestal groups and at 3 months in the equicrestal groups. Bone loss was most pronounced in the subcrestal EXT group. Conclusions: Within the limits of this study, different microgap configurations can cause different amounts of bone loss, even before prosthetic loading. Subcrestal placement of a butt-joint microgap design may lead to more pronounced radiographic bone loss. Keywords: bone morphology, crestal implant placement, implant-abutment microgap, radiographic study, subcrestal placement

Purpose: The aim of this comparative study was to investigate cell-based effective bone engineering and the correlation between the osseointegration of dental implants and tissue-engineered bone using dental pulp stem cells (DPSC), bone marrow stem cells (BMSC), and periosteal cells (PC). Materials and Methods: The first molar and all premolars were extracted from the mandibles of three dogs, and in each dog, six bone defects (three on each side) were prepared with a 10-mm-diameter trephine bur after 4 weeks. Different materials were implanted in the defects and the sites were allowed to heal. The experimental groups were as follows: (1) dog DPSC and platelet-rich plasma (PRP) (dDPSC/PRP), (2) dog BMSC and PRP (dBMSC/PRP), (3) dog PC and PRP (dPC/PRP), and (4) control (defect only). Eight weeks later, dental implants were placed in the defects. After another 8 weeks, the amount of bone regeneration was assessed by histologic and histomorphometric analyses (bone-implant contact). Results: The mean bone-implant contact values were 66.7% ± 3.6% for group 1 (dDPSC/PRP), 62.5% ± 3.1% for group 2 (dBMSC/PRP), 39.4% ± 2.4% for group 3 (dPC/PRP), and 30.3% ± 2.6% for the control group. Conclusions: DPSC showed the highest osteogenic potential and may be a useful cell source for tissue-engineered bone around dental implants. Keywords: bone marrow stem cells, bone regeneration, dental pulp stem cells, periosteal cells, platelet-rich plasma, tissue engineering

Purpose: The presence of pathogenic microorganisms associated with both chronic periodontitis and implant failure can induce a host immune response. The type of response is determined by an individual's genetic makeup. The aim of this study was to investigate the genetic relationship between interleukin-10 (IL-10) and tumor necrosis factor alpha (TNF-α) polymorphisms and patient susceptibility to chronic periodontitis or implant failure and to compare their immunogenetic functions. Materials and Methods: This study recruited subjects according to clinical diagnostic criteria for failing implants, chronic periodontitis, healthy implants, and healthy controls. Human DNA from buccal swabs was analyzed by amplification refractory mutation system-polymerase chain reaction and agarose gel electrophoresis performed for gene polymorphisms of IL-10 (IL-10, IL-1082, IL-819, and IL-592) and TNF-α (TNF-α-308). Differences in the polymorphisms between test groups and healthy controls were assessed by Pearson chi-square test. Results: A total of 95 patients (16 failing implants, 22 chronic periodontitis, 23 healthy implants, and 34 healthy controls) were enrolled in this study. No significant association of IL-10 and TNF-α alleles, genotypes, or haplotypes were observed in chronic periodontitis or failing implant patients (P > .005). However, both patient groups showed highly similar frequencies of alleles, genotypes, and haplotypes (P > .99). Conclusion: This study found no significant association of either IL-10 or TNF-α genes in the susceptibility to the development of chronic periodontitis or implant failure. Keywords: chronic periodontitis, cytokines, failing implants, interleukin-10, single nucleotide polymorphisms, tumor necrosis factor-alpha

Purpose: The purpose of this study was to compare the von Mises (vM), compressive, and tensile stresses occurring on implants, abutments, and surrounding bone using three-dimensional finite element analysis (FEA) in three simulations in the anterior maxilla: a single titanium implant with a titanium abutment, a single titanium implant with a zirconia abutment, and a single one-piece zirconia implant. Materials and Methods: Three types of implants (all were 4 × 12 mm) were modeled using FEA: Astra OsseoSpeed implant with titanium abutment (ATt), Astra OsseoSpeed with zirconia abutment (ATz), and White-SKY (WS) one-piece zirconia dental implant. The anterior maxillary bone was also simulated with FEA. The implants were placed into the maxillary left central incisor region. Loading was applied horizontally and obliquely and the stresses were examined. Results: The vM and compressive stresses that occurred on the implant and cortical bone in the ATz model were lower than those seen in the ATt model. The tensile stress values observed in the abutment and cortical bone in the ATz and ATt models and all the stress values occurring in trabecular bone were similar. The stresses that occurred in the WS implant were lower than the stresses exerted on the ATt and ATz implants, except for tensile stresses under oblique loading. Conclusion: Lower stresses occurred on the zirconia implant (WS), except for tensile stress under oblique loading. The zirconia implant generated the lowest stresses in cortical bone, and the zirconia abutment resulted in lower vM and compressive stresses than the titanium abutment in implant and cortical bone. Keywords: dental implants, finite element analysis, implant abutments, stress/strain, titanium, zirconia

Purpose: The purpose of this study was to use a clinical simulation to determine whether wear of the internal surface of a titanium implant was greater following connection and loading of a one-piece zirconia implant abutment or a titanium implant abutment. Materials and Methods: Two implants received zirconia abutments and two received titanium abutments. The implants were secured into four fiber-reinforced epoxy resin disks that had been prepared to receive the internal-connection implants. The assemblies were cyclically loaded off-axis for a total of 1,000,000 cycles. At various intervals, the abutments were removed, photographed, examined using scanning electron microscopy (SEM), and returned to the implants for further testing. The area of titanium transfer from the implants to the abutments observed in the SEM images was quantified using image analysis software. Results: The method was able to quantify the area of material transferred to the abutments. There was considerably more wear associated with the zirconia abutments, but the rate of wear slowed after about 250,000 cycles. Parabolic curves were fit to the data. The projected mean ± standard deviation maximum area (wear) values associated with the titanium and zirconia abutments were 15.8 ± 3.3 × 103 µm2 and 131.8 ± 14.5 × 103 µm2, respectively, and this difference was statistically significant (P = .0081). Conclusions: The implants with the zirconia abutments showed a greater initial rate of wear and more total wear than the implants with the titanium abutments following cyclic loading. The amount of titanium transfer seen on the zirconia abutment increased with the number of loading cycles but appeared to be self-limiting. The clinical ramifications of this finding are unknown at this time; however, the potential for component loosening and subsequent fracture and/or the release of particulate titanium debris may be of concern. Keywords: cyclic loading, fatigue testing, fretting wear, implant abutment, implant-abutment interface, titanium, zirconia

Purpose: Controversy exists regarding the "All-on-Four" concept for a mandibular full-arch fixed prosthesis. The purpose of this study was to examine photoelastically the effect of the inclination of the two distal implants according to the All-on-Four concept on the stress distribution within the supporting structure. Materials and Methods: Two photoelastic models of a human edentulous mandible were fabricated. Each model had four screw-type implants embedded in the interforaminal area. The two distal implants were placed axially in one model and tilted 30 degrees distally in the other model. Two cantilevered acrylic resin prostheses, which used angulated abutments for the distal tilted implants and straight abutments for the axial implants, were fabricated and delivered. Vertical loads of 13 kg were applied at three loading points on the prosthesis: the central fossa of the first molar, the distal fossa of the first premolar, and the distal fossa of the second premolar. Stresses that developed in the supporting structure were monitored photoelastically and recorded photographically. Results: Whereas all cantilever loadings concentrated the stresses at the distal crest of the distal implant sites in both models, the posterior tilting of distal implants splinted in a full-arch fixed prosthesis did not increase the stresses in bone around the distal implants versus the axial-implant model. Conclusion: Within the limitations of this photoelastic stress analysis, the use of tilted implants reduced the maximum stress in the distal crestal bone of the distal implant by approximately 17% relative to the axial implants. Keywords: All-on-Four concept, mandibular full-arch fixed prosthesis, photoelastic stress analysis, tilted implant

Purpose: The present study introduced the application of cytodetachment technology-the examination of single cell responses to implant material surfaces-to the analysis of implant surfaces with a view to significantly improving upon conventional methods of studying cell interactions with implant surfaces. Materials and Methods: With the new cytodetachment technology, osteoblasts (MG-63) were allowed to attach to a surface, and a nanoprobe was positioned adjacent to the cell. The probe was then moved using a piezo-actuator to completely detach the cell. The detachment forces were calculated and analyzed statistically for three different groups of implant disks: a titanium (Ti) grit-blasted (TiOblast) surface (n = 15, group 1), a fluoride-modified (OsseoSpeed) surface (n = 15, group 2), and a machined titanium surface (n = 6, group 3). Results: The detachment force was slightly higher for the OsseoSpeed surface than the TiOblast surface, but this difference was not statistically significant. The detachment force on the machined surface was statistically significantly lower than that seen in the other groups, thus supporting the rationale that changes in surface properties would be reflected in the measured detachment force. The OsseoSpeed and TiOblast surfaces demonstrated stronger osteoblast adhesion compared to the machined titanium surface. Conclusions: Within the limitations of this study, this report is a good proof-of-principle for the application of cytodetachment technology to testing implant surfaces. It might represent a new parameter to judge implant surface properties and might have broad applications in product development and research protocols for future implant surfaces. Keywords: cell, cellular, cytodetachment, dental implant, osseointegration, osteoblasts, surface properties, titanium

Purpose: Cathepsin-K is an enzyme involved in bone metabolism. This feature may make it important both for natural teeth and dental implants. The aims of the present study were to comparatively analyze cathepsin-K levels in gingival crevicular fluid (GCF) and peri-implant sulcus fluid (PISF) and to determine whether GCF and PISF cathepsin-K profiles reflect the clinical periodontal/peri-implant status. Materials and Methods: Clinical parameters (probing depth, Gingival Index, Plaque Index, and bleeding on probing) were recorded, and GCF/PISF samples were obtained from natural teeth (group T) and dental implants (group I), which were divided into groups based on health (clinically healthy, gingivitis/peri-implant mucositis, and periodontitis/peri-implantitis). Cathepsin-K activity was determined with a commercially available cathepsin-K activity assay kit (BioVision). Results: Sixty natural teeth and 68 dental implants were examined. Teeth with periodontitis (group T-3) showed significantly higher total cathepsin-K activity (10.39 units) than teeth with gingivitis (group T-2, 1.71 units) and healthy teeth (group T-1, 1.90 units). The difference in cathepsin-K activity between groups T-2 and T-1 was not significant. Implants with peri-implantitis (group I-3) had higher total enzyme activity (10.26 units) than healthy implants (group I-1) (3.44 units). Although the difference between clinical parameters was not significant, group I-3 had higher cathepsin-K levels than group I-2 (4.74 units). When natural teeth (T-1, T-2, T-3) were compared to implants (I-1, I-2, I-3), no significant differences were observed for cathepsin-K levels. Conclusion: More cathepsin-K activity was clearly observed with inflammatory periodontal and peri-implant destruction. The highest cathepsin-K levels detected in GCF and PISF samples, obtained from sites with periodontitis and peri-implantitis, suggests the potential involvement of cathespin-K in increased bone metabolism around natural teeth and dental implants. Keywords: cathepsin-K, dental implants, gingival crevicular fluid, natural teeth, peri-implant sulcus fluid

Purpose: To evaluate the osteogenic potential of commercially pure titanium after different surface treatments. Materials and Methods: Thirty commercially pure grade 2 titanium disks of similar designs and dimensions were divided into three groups. In the first group (group C), polished samples were used as the control group. In the second group (group SG), an oxide layer was coated on the samples using a sol-gel dip coating technique. In the third group (group SA), samples were sandblasted and treated with different acids in succession to etch the samples. Scanning electron microscopy with energy-dispersive x-ray spectroscopy of one sample from each group was performed to observe the surface morphology and surface composition. The surface roughness of the samples was evaluated with a surface profilometer. To evaluate the effect of the SA and SG treatments on the samples' osteogenic potential, samples from each group underwent cell culture study using human osteosarcoma osteoblast cell lines. Scanning electron microscopy of one sample from each group was performed to observe cell morphology and attachment. Results and Conclusion: The SA and SG surfaces were rougher than that of the control group. There was a significant increase in oxygen content in groups SG and SA. Cell sheets were able to penetrate into the pores and adhered inside the valleys of the SA samples, suggesting excellent attachment. Keywords: human osteosarcoma osteoblast cells, sandblasting and acid-etching, sol-gel dip coating, surface properties

Purpose: Human mesenchymal stem cells (hMSCs) hold the potential for bone regeneration because of their self-renewing and multipotent character. The goal of this study was to evaluate the influence of collagen membranes on the proliferation of hMSCs derived from bone marrow. A special focus was set on short-term eluates derived from collagen membranes, as volatile toxic materials washed out from these membranes may influence cell behavior during the short time course of oral surgery. Materials and Methods: The proliferation of hMSCs seeded directly on a collagen membrane (BioGide) was evaluated quantitatively using the cell proliferation reagent WST-1 (4-3-[4-iodophenyl]-2-[4-nitrophenyl]-2H-[5-tetrazolio]-1, 3--benzol-disulfonate) and qualitatively by scanning electron microscopy. Two standard biocompatibility tests, namely the lactate dehydrogenase and MTT (3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazoliumbromide) tests, were performed using hMSCs cultivated in eluates from membranes incubated for 10 minutes, 1 hour, or 24 hours in serum-free cell culture medium. The data were analyzed statistically. Results: Scanning electron microscopy showed large numbers of hMSCs with well-spread morphology on the collagen membranes after 7 days of culture. The WST test revealed significantly better proliferation of hMSCs on collagen membranes after 4 days of culture compared to cells cultured on a cover glass. Cytotoxicity levels were low, peaking in short-term eluates and decreasing with longer incubation times. Conclusion: Porcine collagen membranes showed good biocompatibility in vitro for hMSCs. If maximum cell proliferation rates are required, a prewash of membranes prior to application may be useful. Keywords: biocompatibility, collagen membrane, guided bone regeneration, human mesenchymal stem cells

Purpose: The aim of this study was to determine the accuracies of implant-level impressions for internal-connection dental implants with various angles of divergence. Materials and Methods: Five groups were created according to the angles of divergence (0, 5, 10, 15, and 20 degrees) between two implant analogs in a master model. A master stone model for each group was fabricated. The divergent angle in each master model was verified with a profilometer. Study models (n = 10) from each master model were constructed through the implant-level impression technique. The divergent angle in each study model was verified with the profilometer. The splinted metal framework with passive fit was cast with base metal and cast-on abutments in each master model. The metal framework was tried in the study models and the fit of each framework was evaluated. One-way analysis of variance and the Tukey Honestly Significant Difference test were used for statistical analysis. Results: Statistically significant deformations of the impressions were found in the study models with divergently placed implant analogs. A larger divergence angle resulted in a larger gap between the framework and the implant analogs. The gap in the 20-degree divergence group differed significantly from that measured in the master model (P .01). Conclusions: Internal-connection implants were accurate when the divergence angle was less than 15 degrees. Inaccuracy of impressions increased as the divergence angle increased. The inaccuracy was significantly greater for the 20-degree-divergent implants than the other groups. Keywords: deformation of impression, divergent angle, implant impression, implant-level impressions, impression accuracy, internal-connection implant

Purpose: This study aimed to evaluate the effect of different screw-tightening sequences, torques, and methods on the strains generated on an internal-connection implant (Astra Tech) superstructure with good fit. Materials and Methods: An edentulous mandibular master model and a metal framework directly connected to four parallel implants with a passive fit to each other were fabricated. Six stone casts were made from a dental stone master model by a splinted impression technique to represent a well-fitting situation with the metal framework. Strains generated by four screw-tightening sequences (1-2-3-4, 4-3-2-1, 2-4-3-1, and 2-3-1-4), two torques (10 and 20 Ncm), and two methods (one-step and two-step) were evaluated. In the two-step method, screws were tightened to the initial torque (10 Ncm) in a predetermined screw-tightening sequence and then to the final torque (20 Ncm) in the same sequence. Strains were recorded twice by three strain gauges attached to the framework (superior face midway between abutments). Deformation data were analyzed using multiple analysis of variance at a .05 level of statistical significance. Results: In all stone casts, strains were produced by connection of the superstructure, regardless of screw-tightening sequence, torque, and method. No statistically significant differences in superstructure strains were found based on screw-tightening sequences (range, -409.8 to -413.8 µm/m), torques (-409.7 and -399.1 µm/m), or methods (-399.1 and -410.3 µm/m). Conclusions: Within the limitations of this in vitro study, screw-tightening sequence, torque, and method were not critical factors for the strain generated on a well-fitting internal-connection implant superstructure by the splinted impression technique. Further studies are needed to evaluate the effect of screw-tightening techniques on the preload stress in various different clinical situations. Keywords: internal-connection dental implant, screw-tightening sequence, splinted impression technique, strain, tightening method, tightening torque

Purpose: This study evaluated possible publication bias and its related factors in implant-related research over time. Materials and Methods: Articles published in Clinical Implant Dentistry and Related Research, Clinical Oral Implants Research, Implant Dentistry, Journal of Oral Implantology, and The International Journal of Oral & Maxillofacial Implants between 2005 and 2009 were reviewed. Nonoriginal articles were excluded. For each article included, study outcome, extramural funding source, type of study, and geographic origin were recorded. Descriptive and analytic statistics (α = .05), including the chi-square test and logistic regression analysis, were performed where appropriate. Results: From a total of 2,085 articles, 1,503 met the inclusion criteria. Of the articles analyzed, 1,226 (81.6%), 160 (10.6%), and 117 (7.8%) articles reported positive, negative, and neutral outcomes, respectively. In vitro studies, studies from Asia, and funded animal studies were more likely to report positive outcomes compared to others (P = .02, P .0001, and P = .009, respectively). Industry-funded studies represented the lowest frequency of positive outcomes versus studies funded by other sources. Conclusions: There were a high number of implant-related studies reporting positive outcomes in the five selected journals. Some selected factors were associated with positive outcome bias. In general, funding was not associated with a positive outcome, except for animal studies. Industry-supported research did not show any association with the publication of positive outcomes. Keywords: dental implants, funding, industry, publication bias

Purpose: The aim of this animal study was to evaluate, through immunochemical analysis, new bone formation in rabbit maxillary sinuses with and without bone grafts. Materials and Methods: Bilateral sinus augmentation procedures were performed in rabbits. Bony windows were created with a piezoelectric surgical device with a saw insert. In the first group, the bony window was repositioned after careful elevation of the sinus mucosa without bone grafting. A miniscrew was inserted into the bony window to support the elevated sinus membrane. In the second group, anorganic bovine graft (Bio-Oss) was grafted after very careful elevation of the sinus membrane. Collagen membrane was placed over the bone graft. Rabbits were sacrificed after 1, 2, 4, 6, and 8 weeks. The augmented sinuses were evaluated by immunochemical analysis of proliferating cell nuclear antigen (PCNA), type I collagen, and osteocalcin content. Results: Immunochemically positive cells for PCNA were present along the floor of the replaced bony window and the elevated sinus membrane from 1 to 4 weeks in the graftless group. In the grafted group, immunochemically positive cells for PCNA were not present after 1 week. In the ungrafted group, the expression of type I collagen was present from week 1. However, the expression of type I collagen was present after 2 weeks in the grafted group. Osteocalcin was observed in both groups after 1 week. Osteocalcin was observed along the floor of the replaced bony window in the graftless group but was not observed along the collagen membrane in the grafted group. Conclusion: According to this immunochemical study, faster and greater new bone formation was observed in sites that received no grafting material. The repositioned bony window may accelerate new bone formation earlier during healing versus the placement of a collagen membrane grafting material in the sinus. Keywords: bone grafting, immunochemical study, maxillary sinus augmentation, new bone formation, replaceable bony window, sinus membrane elevation, sinus mucosa

Purpose: The aim of this retrospective study was to evaluate implant survival/success rates and peri-implant parameters as well as patient satisfaction for uniformly designed implant-supported anterior maxillary or mandibular fixed partial dentures (FPDs). Materials and Methods: A retrospective study was conducted on patients with maxillary or mandibular anterior partial edentulism (all incisors missing) treated between 2002 and 2006 with a two-implant-supported four-unit FPD. All FPDs were of the same design: two implant abutments in the lateral incisor positions and two ovate pontics in the central incisor positions. Cumulative implant survival rates and peri-implant conditions (marginal bone loss, pocket depth, Plaque Index, Gingival Index, Bleeding Index, Periotest values) as well as the incidence and type of prosthodontic maintenance were evaluated. The patients' subjective satisfaction rate was surveyed using multiple questionnaires with a 10-point scoring system (0 = not satisfied to 10 = highly satisfied). Results: Thirty-six of 38 patients (dropout: 5%) with 72 implants (50 maxillary and 22 mandibular implants, 25 maxillary and 11 mandibular FPDs) were available for follow-up after a mean observation period of 56.2 ± 10.3 months. High cumulative implant survival and success rates (100%) and healthy peri-implant parameters (mean marginal bone resorption: 1.8 ± 0.3 mm; mean pocket depth: 2.5 ± 1.0 mm; Periotest value: -4.5 ± 1.1; and Plaque/Bleeding/Gingival indices of 0 in 70% of sites [with significantly better results in the maxilla than in the mandible]) were achieved. The most frequent required prosthodontic maintenance efforts were maxillary recementation (3/25; 12%) and mandibular rebasing (2/11; 18.2%). A high score for satisfaction was obtained, although slightly better overall results were seen for maxillary than for mandibular FPDs. Conclusion: For all parameters evaluated, these FPDs proved to be a viable treatment procedure for anterior partial edentulism with good clinical and esthetic outcomes. Keywords: anterior region, clinical outcome, dental implants, fixed partial dentures, patient satisfaction

Purpose: The aim of the present study was to determine bone density in designated implant sites using cone beam computed tomography (CBCT) and to evaluate possible correlations between age, gender, insertion torque measurements, and resonance frequency analysis (RFA) values. Materials and Methods: Completely and partially edentulous patients were treated with implants between 2007 and 2008 and evaluated retrospectively. The preoperative examination included a panoramic radiograph, CBCT, diagnostic casts, and a clinical examination of the jaws. With the CBCT scans, bone densities were recorded in Hounsfield units (HU). Insertion torque values and implant stability measurements (via RFA) were also noted. Results: Mean bone density and insertion torque values were 623 ± 209 HU and 42.4 ± 4 Ncm, respectively, for the 82 implants placed. Mean primary stability (implant stability quotient) was 62.4 ± 8. The differences in mean bone density at implant sites in the mandible (717 ± 204 HU) and the maxilla (490 ± 128 HU) were statistically significant for all patients (P .05). There was a statistically significant relationship between bone density values and insertion torque measurements for implant sites in the anterior mandible (r = 0.562, P .05), as well as between bone density and RFA values for men (r = 0.412, P .05). Conclusions: Bone density measurements using preoperative CBCT may be helpful as an objective diagnostic tool. These values, in conjunction with RFA values and insertion torque measurements, can provide the implant surgeon with an objective assessment of bone quality and may be especially useful where poor-quality bone is suspected. Keywords: bone density, insertion torque, primary stability, resonance frequency analysis

Purpose: Different graft materials have been proposed to minimize the reduction in ridge volume after tooth extraction. The aim of the present study was to compare the use of synthetic magnesium-enriched hydroxyapatite (MHA) with porcine bone (PB) grafts in fresh sockets by histologic and histomorphometric analyses. Materials and Methods: Forty-five fresh extraction sockets were selected in 15 patients. A split-mouth design was used: 15 sockets received MHA in one side of the jaw (MHA group), 15 sockets on the other side received PB (PB group), and 15 random unfilled sockets were considered the control group. Four months after surgery, cylindric bone specimens were harvested for histologic and histomorphometric analyses. Results: Histologic examinations revealed an absence of inflammatory cells, bone formation in all treated sites, and the presence of biomaterial particles and connective tissue. Mean vital bone measurements for the MHA, PB, and control groups were 36.5% ± 2.6%, 38.0% ± 16.2%, and 30.3% ± 4.8%, respectively. Statistically significant differences were found between the MHA and control groups and between the PB and control groups; differences between the MHA and PB groups were not significant. Connective tissue percentages averaged 33.3% ± 1.5% for the MHA group, 25.3% ± 9.4% for the PB group, and 58.3% ± 7.1% for the control group. Statistically significant differences were found between all groups. Residual graft material occupied 32.2% ± 3.2% of the MHA-grafted sites and 36.6% ± 4.8% of the PB sites. This difference was not statistically significant. Conclusions: Within the limits of this study, histologic examination showed the same biologic behavior in bone formation and resorption processes for the two examined biomaterials. Keywords: alveolar ridge preservation, hydroxyapatite, porcine bone, tooth extraction, wound healing

Purpose: To identify factors associated with crestal bone gain around single-tooth implants. Materials and Methods: A retrospective cohort study was conducted. More than 90 different local and systemic factors were documented. Descriptive statistics and univariate and multivariate mixed-effects regression models, adjusted for multiple implants in the same patient, were used to identify predictors of crestal bone gain after insertion of definitive restorations. Results: Eighty-one subjects who received 326 Bicon implants were followed for an average of 70.7 months. Eighty-one implants in 46 patients showed varying degrees of apparent bone gain over time. Variables associated with peri-implant bone gain in the first multivariate model were: type of opposing structure, tooth (P = .02); type of restoration, crown cemented on a prefabricated titanium abutment with a spherical base (P = .006); hydroxyapatite coating (P = .0005); implant size 5 × 8 mm (P = .02); and daily intake of nonsteroidal anti-inflammatory drugs (NSAIDs) (P =.04). NSAIDs remained significantly correlated to crestal bone gain in the second multivariate analysis; an implant was significantly more likely to gain bone if the patient was taking NSAIDs daily (P = .02), but this effect was specific to hydroxyapatite-coated implants (P = .01). Conclusion: Daily doses of NSAIDs were correlated with a significant increase in crestal bone levels around single-tooth hydroxyapatite-coated implants following crown insertion. Keywords: dental implants, nonsteroidal anti-inflammatory drugs, peri-implant bone gain, prospective cohort study, risk factors

Purpose: The present study was performed to evaluate the 5-year status of immediately placed implants subjected to maxillary sinus elevation without grafting. Materials and Methods: Implants were placed in 2004 and 2005. A minimum of 3 mm of residual bone height (RBH) was required. All implants were placed with a sinus elevation performed through a lateral approach by the trap-door, open-window method without placement of any grafting material. Regular follow-up included oral hygiene instruction, periodontal charting, panoramic radiographs, and cone beam computed tomographic scans. The gained bone height (GBH) in the sinus, peri-implant sulcus depth, and marginal bone loss were analyzed statistically. Results: Forty-four patients (26 men, 18 women) with an average age of 58 years received 80 implants, which were followed for 5 years after prosthesis delivery. No patients developed sinusitis or other complications leading to implant loss. The average RBH was 5.06 ± 1.51 mm and the average intrasinus implant length was 7.77 ± 1.69 mm. Survival rates for the implants were 100% after 2 and 5 years. Average GBH was 7.24 ± 1.83 mm at 2 years (range, 3 to 12 mm) and 7.44 ± 1.94 mm at 5 years (P > .05). The average peri-implant sulcus depths were 2.5 ± 0.4 mm at 2 years and 3.1 ± 0.5 mm at 5 years (P .05). The mean peri-implant marginal bone loss was 1.3 ± 0.3 mm at 2 years and 2.1 ± 0.5 mm at 5 years (P .05). Conclusions: New bone formation in the sinus was confirmed, and good survival of implants with maxillary sinus elevation by the lateral approach without grafting was observed after 5 years. Attention should be focused on oral hygiene maintenance to ensure peri-implant gingival health. Keywords: graft, implant, lateral approach, maxillary sinus, sinus elevation, survival

Purpose: The present study provides an inventory of the number of fractures that occurred in conjunction with implant placement in edentulous patients in the Dutch population from 1980 to 2007 and estimates the incidence with which this might occur. The study also sought to define the factors that increase the risk of fracture. Materials and Methods: Questionnaires were sent to all 198 oral and maxillofacial surgeons working in 56 hospitals in the Netherlands. Questions were asked regarding the causes of fractures, the height of the edentulous mandible, and the methods of fracture treatment. Results: Responses were received from 53 of the 56 departments. During the study period, 157 edentulous mandibles fractured in conjunction with implant treatment. All fractures occurred in mandibles with less than 10 mm of height, as measured in the symphysis. An incidence of less than 0.05% was estimated based on an estimated number of 475,000 patients treated with at least two implants during this time to support an overdenture. Reasons for early implant failures were insufficient bone volume, iatrogenic causes, nonintegration, and a narrow arch. Peri-implantitis, trauma, and explantation were associated with fractures occurring 1 year or more after implant placement. Several methods were employed to treat the fractured mandibles, including closed reduction, rigid fixation using osteosynthesis plates, and bone grafts with fixation. In 52% of patients, fracture healing was uneventful; however, in 48% of patients, complications were encountered, including osteomyelitis, nonunion, plate fracture, screw loosening, and dehiscences with subsequent infections. Conclusions: Mandibles with a height of 10 mm or less, as measured at the symphysis, are at risk of fractures and associated complications. The provision of proper informed consent regarding the advantages and disadvantages of placing implants in thin mandibles is essential. Keywords: dental implants, fracture treatment, implant placement, mandibular fracture, mandibular resorption

Purpose: The aim of this study was to evaluate the effectiveness of a modified surgical technique to extend the keratinized gingiva around implants in augmented mandibles and the stability of the technique after 1 year. Materials and Methods: Implants were inserted in mandibles in combination with ridge augmentation and extension of deficient buccal keratinized gingiva (BKT) with free gingival grafts (FGGs), in which the keratinized local gingiva (KLG) was transferred toward the lingual. In group 1, implants were placed simultaneous with ridge augmentation, and FGGs were performed at the time of uncovering the implants. In group 2, the implants were placed after ridge augmentation, and FGGs were performed at the time of implant placement with nonsubmerged healing. The width of KLG and FGG, as well as the width of the BKT and lingual keratinized gingiva (LKT), were measured 4 weeks, 3 months, and 1 year after soft tissue grafting. Results: Seventy implants (46 in group 1, 24 in group 2) were placed in 29 patients with a mean age of 54.4 years. The mean width of KLG was 2.90 mm preoperatively (3.00 mm for group 1, 2.75 mm for group 2). Mean FGG was 4.60 mm in group 1 and 4.70 mm in group 2. For group 1 the mean width of BKT was 3.70 mm after 1 year. In contrast, group 2 showed mean BKT of 3.30 mm after 1 year. The resultant overall gain in BKT was 3.50 mm at 1 year. The LKT exhibited significantly more atrophy in group 1 (0.35 mm at 1 year) than in group 2 (0.05 mm at 1 year). Conclusions: The combination of ridge augmentation with the presented modified surgical technique resulted in the stable extension of keratinized gingiva around implants for 1 year. Keywords: alveolar ridge management, dental implants, extension of keratinized gingiva, free gingival grafts, soft tissue management

Purpose: The present study was designed to compare the long-term outcome and complications of cemented versus screw-retained implant restorations in partially edentulous patients. Materials and Methods: Consecutive patients with bilateral partial posterior edentulism comprised the study group. Implants were placed, and cemented or screw-retained restorations were randomly assigned to the patients in a split-mouth design. Follow-up (up to 15 years) examinations were performed every 6 months in the first year and every 12 months in subsequent years. The following parameters were evaluated and recorded at each recall appointment: ceramic fracture, abutment screw loosening, metal frame fracture, Gingival Index, and marginal bone loss. Results: Thirty-eight patients were treated with 221 implants to support partial prostheses. No implants during the follow-up period (mean follow-up, 66 ± 47 months for screw-retained restorations [range, 18 to 180 months] and 61 ± 40 months for cemented restorations [range, 18 to 159 months]). Ceramic fracture occurred significantly more frequently (P .001) in screw-retained (38% ± 0.3%) than in cemented (4% ± 0.1%) restorations. Abutment screw loosening occurred statistically significantly more often (P = .001) in screw-retained (32% ± 0.3%) than in cement-retained (9% ± 0.2%) restorations. There were no metal frame fractures in either type of restoration. The mean Gingival Index scores were statistically significantly higher (P .001) for screw-retained (0.48 ± 0.5) than for cemented (0.09 ± 0.3) restorations. The mean marginal bone loss was statistically significantly higher (P .001) for screw-retained (1.4 ± 0.6 mm) than for cemented (0.69 ± 0.5 mm) restorations. Conclusion: The long-term outcome of cemented implant-supported restorations was superior to that of screw-retained restorations, both clinically and biologically. Keywords: cementation, implant-supported restoration, partial edentulism, screw retention

Purpose: To review the clinical outcomes of immediate, early, and conventional single-tooth implant placement in mandibular or maxillary first molar sites. Materials and Methods: The charts of patients treated consecutively for first molar replacement according to unconventional (immediate = group 1, early = group 2) or conventional (late = group 3) surgical protocols were examined. All available clinical parameters were reviewed to calculate implant survival and success rates according to well-established criteria. Periapical radiographs obtained upon delivery of the definitive crown (T2) and 1 year later (T3) were digitized and assessed to evaluate marginal bone loss (MBL). Clinical photographs were evaluated to determine soft tissue health. Results: Forty-seven patients were treated with a total of 53 immediate, early, or late single implants. The last follow-up examination was at 38.84 ± 16.14 months (mean ± SD) for group 1, 32.91 ± 18.49 months for group 2, and 42.66 ± 12.41 months for group 3. The implant survival rate was 100% for all groups. The success rates were 91.7% for early implants, 95.0% for immediate postextraction implants, and 100% for implants placed in healed sites. MBL and soft tissue parameters did not differ significantly among the three groups at definitive restoration delivery or 1 year later; a thin gingival biotype, irrespective of treatment timing, was the only covariate that was able to slightly affect the outcome variables. Conclusions: Short-term implant survival and success rates, as well as MBL values for immediate, early, and conventional implants, appear similar for maxillary and mandibular first molar sites. Early placement should be considered as a suitable alternative to immediate placement when unfavorable conditions at the time of extraction could affect the clinical outcome of immediate placement. Keywords: clinical study, dental implants, early placement, first molar site, immediate placement, marginal bone loss

Immediate placement of a definitive metal-resin implant-fixed complete prosthesis on four implants after flapless computed tomographic (CT)-guided surgery was compromised because of misfit due to a discrepancy in the position of an implant. However, the definitive prosthesis could be delivered on the day of surgery with the help of laser-welding procedures. Immediate loading of four maxillary implants with a definitive prosthesis might be a viable option using the laser-welding technique in case of misfit of the prosthesis. Keywords: All-on-Four, CT-generated surgery, immediate loading, misfit, Nobel Guide

In the past few decades, the rehabilitation of maxillary defects has posed a significant challenge for prosthodontists. The advent of zygoma implants presents a unique alternative for maxillary reconstruction while minimizing prosthetic complications. However, the placement of zygoma implants is not without risk. This report describes the application of a special self-developed surgical navigation system, AccuNavi, for the planning and subsequent precise placement of zygoma implants in patients with maxillectomy defects. The superimposition of the preoperative planning and the real placement demonstrated that all of the three zygoma implants were appropriately positioned and oriented. In the phantom experiment, the mean distance and angular deviations were 0.58 ± 0.18 mm and 1.12 ± 0.39 degrees, respectively. This preliminary use of the AccuNavi for the placment of zygomatic implants appears to be a reliable method for transferring the planning of a complex osteotomy to the actual surgical procedure. However, further multicenter clinical evaluations should be conducted to establish the predictability of this surgical technique. Keywords: intraoperative navigation, maxillary defects, zygoma implants