The International Journal of Oral & Maxillofacial Implants, 06/2011

Purpose: Nanotechnology has been employed in attempts to enhance bone incorporation of dental implants. Often, nanoparticles are applied to the implant surface as particle coatings. However, the same properties that may increase the functionality may also lead to undiscovered negative effects, such as instability of the nanocoating. The aim of this study was to investigate the stability/instability of the nanoparticles using a radiolabeling technique. Materials and Methods: Twenty threaded and turned titanium microimplants were inserted in 10 rats. All 20 implants were coated with nanometer-sized hydroxyapatite (HA) particles. In order to trace the HA nanoparticles, the particles for 16 implants were labeled with calcium 45 (45Ca). After 1, 2, 4, and 8 weeks, the implants and surrounding bone were retrieved and analyzed using autoradiography with respect to particle migration from the implant surface. Samples from the brain, liver, thymus, kidney, and blood, as well as wooden shavings from the rats' cages, were also retrieved and analyzed using liquid scintillation counting. Results: The radioactivity representing the localization of 45Ca decreased over time from the vicinity of the implant. The amounts of 45Ca found in the blood and in the rats' excretions decreased with time and corresponded well to each other. After 8 weeks, the only trace of 45Ca was found in the liver. Conclusion: The results indicated that released particles leave the body through the natural cleaning system, and the probability that the nanocoating will assemble in vital organs and thus become a potential biologic risk factor is unlikely. Keywords: implant, in vivo, nanocoat instability

Purpose: To investigate the osseous repair in epiphyseal rabbit femur defects treated with organic bovine bone (OBB) cancellous block or OBB cortical granules. Materials and Methods: Forty-eight trephined defects were made bilaterally in 30 rabbits. In 18 animals, the defects were filled with OBB cancellous block (experimental group 1) or OBB cortical granules (experimental group 2), and in 12 animals (control group), the defects on both sides were filled only with blood clot. After 30, 90, and 180 days, the femur epiphyses were collected, fixed, radiographed both digitally and conventionally, and then processed for histologic analyses. The newly formed cortical bone was measured in the histologic sections using a digital image analysis system. Results: Histologically, both experimental groups showed total or partial closure of the defects with woven bone at 30 days, whereas in the control sites, a marked migration of connective tissue into the defect was apparent. At 90 and 180 days, a similar pattern of repair was observed in the experimental groups and the control group. Quantitatively, however, no significant differences between groups (P > .05) were observed throughout the experimental period. A significant reduction in newly formed cortical bone occurred at 90 and 180 days (P .05) in all groups. Radiographically, no statistically significant differences were seen among the groups (P > .05). Conclusions: The study showed minor descriptive differences at the first healing period that were not evident at later periods and that were not shown through histomorphometry and radiographic analysis. The only significant results were related to time. Keywords: bone repair, demineralized bone matrix, osteogenesis, rabbit, xenograft

Purpose: Because the evidence regarding the efficacy of splinting short implants on strain distribution is limited, this study aimed to measure and compare the strains generated by splinted and nonsplinted screw-retained implant crowns for short implants with internal connections. Material and Methods: Computed tomographic scan data of a patient missing all mandibular molar teeth were digitized using a software program, and stereolithography was then used to produce an acrylic resin cast. Two 4- × 6-mm implants were placed in the left side. One set of splinted crowns and one set of nonsplinted crowns were made to fit the two implants using screw retention. Three-dimensional image correlation was used for full-field measurement of strains and provided a synchronized stereo view of the cast during the experiment. Cameras recorded changes in random dot patterns that had been applied to the surface of the cast as the prostheses were loaded up to 400 N in vertical and oblique directions using a universal testing machine. Testing was repeated three times for splinted and nonsplinted crowns. An image correlation algorithm used the dot pattern to define correlation areas. Coordinates of these areas were determined for each recorded photograph and used to calculate the strains. Strain distribution data were compared for maximum and minimum principal strains. Results: Qualitative data showed evidence of increased load sharing for splinted, screw-retained prostheses regardless of the direction of the load applied. However, the only statistically significant difference between the two prosthesis types occurred for peak maximum principal strain under oblique loading. Conclusions: Splinting short implants may provide a more even strain distribution during functional loading. Clinical corroboration of these findings is needed. Keywords: screw-retained, short implants, splinted

Purpose: The purpose of this study was to exploit potential methods of surface modification for improving the seal between the neck portion of a dental implant and the surrounding soft tissue. Materials and Methods: Titanium surfaces were modified by machining (SM-Ti group); machining and acid etching (AE-Ti group); or machining, acid etching, and depositing 4.5 collagen/hyaluronic acid (col/HA) polyelectrolyte bilayers (CHC-Ti group). These were analyzed using scanning electron microscopy, scanning force microscopy, x-ray photoelectron spectroscopy, contact angle measurement, and quartz crystal microbalance measurement. The degradation behavior of the col/HA multilayer coating was measured. Next, human gingival fibroblasts (HGFs) were cultured on the different surfaces, and cell morphology and spreading were observed using fluorescence microscopy and a shape factor measurement. Cell proliferation was examined by fluorometric quantification of the amount of cellular DNA. Matrix formation of HGFs was determined via enzyme-linked immunosorbent assay. Gene expression was analyzed via reverse transcriptase polymerase chain reaction. Results: Similar surface topology for these three groups was observable on a microscopic scale, and morphologic differences were apparent on the nanoscale. Both acid etching and col/HA deposition improved the hydrophilicity of the titanium surface, in contrast to machining alone. Each col/HA bilayer was about 5 nm thick. The col/HA coating degraded in about a week. Attachment and spreading of HGFs was better on the CHC-Ti surface than on the SM-Ti or AE-Ti surfaces. Moreover, the proliferation and differentiation of HGFs were greatly stimulated when cultured on CHC-Ti. Conclusion: In contrast to two control surfaces (one machined, one machined and acid-etched), col/HA treatment of Ti improved the attachment, spreading, proliferation, and differentiation of HGFs. Keywords: coating, dental implant, implant neck, soft tissue integration, surface properties

Purpose: The purpose of this study was to evaluate the influence of reusing high-resistance drills on bone heating, immediate bone cell viability, and drill wear after performing implant osteotomies in rabbit tibias. Materials and Methods: Two hundred sequential implant osteotomies were created in the superior tibial cortex of 12 White male rabbits. Six groups were established (G1 to G6) according to the number of osteotomies performed with each drill (0, 10, 20, 30, 40, and 50). Drilling began with a spear drill, followed by 2.0-mm, 2.8-mm, 3.0-mm, and 3.15-mm helical drills. The receptor beds were collected for immunohistochemical analysis, thermal changes were quantified, and the drills were subjected to scanning electron microscopy analysis. Results: A high degree of correlation between drill wear and number of osteotomies was observed (Pearson correlation coefficient, r = 0.984). Spear drills underwent twice as much deformation as helical drills. The bone heating analysis concluded that there was no statistically significant relationship between the number of osteotomies and bone heating (P > .05), but there were greater thermal changes during drilling with the spear drill than during drilling with helical drills (ratio 3:1). Immunohistochemical analysis showed a physiologic balance of osteoprotegerin and RANKL (receptor activator of nuclear factor κB ligand) immunolabeling in all groups; however, there was greater immunolabeling of all proteins in group G6 (50 osteotomies). Conclusions: The tested drills did not cause significant bone heating after being reused 50 times; however, they caused more tissue trauma in the 50th osteotomy. Worn drills that are reused may be expected to cause excessive damage to the bone tissue and could adversely affect the osseointegration process. Keywords: cell survival, dental implants, immunohistochemistry, osteotomy, scanning electron microscopy

Purpose: This three-dimensional finite element analysis study evaluated the effect of different material combinations on stress distribution within metal-ceramic and all-ceramic single implant-supported prostheses. Materials and Methods: Three-dimensional finite element models reproducing a segment of the maxilla with a missing left first premolar were created. Five groups were established to represent different superstructure materials: GP, porcelain fused to gold alloy; GR, modified composite resin fused to gold alloy; TP, porcelain fused to titanium; TR, modified composite resin fused to titanium; and ZP, porcelain fused to zirconia. A 100-N vertical force was applied to the contact points of the crowns. All models were fixed in the superior region of bone tissue and in the mesial and distal faces of the maxilla section. Stress maps were generated by processing with finite element software. Results: Stress distribution and stress values of supporting bone were similar for the GP, GR, TP, and ZP models (1,574.3 MPa, 1,574.3 MPa, 1,574.3 MPa, and 1,574.2 MPa, respectively) and different for the TR model (1,838.3 MPa). The ZP model transferred less stress to the retention screw (785 MPa) than the other groups (939 MPa for GP, 961 MPa for GR, 1,010 MPa for TP, and 1,037 MPa for TR). Conclusion: The use of different materials to fabricate a superstructure for a single implant-supported prosthesis did not affect the stress distribution in the supporting bone. The retention screw received less stress when a combination of porcelain and zirconia was used. Keywords: finite element analysis, implant-supported dental prosthesis, metal-ceramic alloys, zirconium

Purpose: The aim of this study was to develop a novel bone graft material that used extracted teeth. Materials and Methods: Thirty-six 10-week-old male Wistar rats were used. The incisors were extracted, immediately frozen and milled, mixed with hydroxypropyl cellulose (HPC), and injected into the socket. The remaining rats received HPC alone, or the socket was left to heal untreated. Socket healing and bone formation in all three groups were evaluated by three-dimensional image analysis from microcomputed tomography examination and histologic observation. Results: Quantitative morphologic measurements demonstrated that bone formation was significantly stimulated in the group that received milled tooth and HPC at 2 and 4 weeks after extraction compared to that of the control (untreated) group, which showed normal healing without any intervention. Histologic observation revealed that the compound of milled tooth and HPC promoted early healing of the socket and initiation of bone formation in the surrounding area. Interestingly, HPC injection alone decreased bone formation and bone mineral content at 2 weeks and then increased bone formation at 4 weeks. Conclusion: A bone graft material composed of milled tooth promotes early healing and bone formation, while HPC, which is chemically stable in vivo, affects bone formation in the extraction socket. Keywords: bone graft material, hydroxypropyl cellulose, milled tooth, socket healing, three-dimensional image analysis

Purpose: This study attempted to establish three-dimensional average curves of the gingival line of maxillary teeth using reconstructed virtual models to utilize as guides for dental implant restorations. Materials and Methods: Virtual models from 100 full-mouth dental stone cast sets were prepared with a three-dimensional scanner and special reconstruction software. Marginal gingival lines were defined by transforming the boundary points to the NURBS (nonuniform rational B-spline) curve. Using an iterative closest point algorithm, the sample models were aligned and the gingival curves were isolated. Each curve was tessellated by 200 points using a uniform interval. The 200 tessellated points of each sample model were averaged according to the index of each model. In a pilot experiment, regression and fitting analysis of one obtained average curve was performed to depict it as mathematical formulae. Results: The three-dimensional average curves of six maxillary anterior teeth, two maxillary right premolars, and a maxillary right first molar were obtained, and their dimensions were measured. Conclusions: Average curves of the gingival lines of young people were investigated. It is proposed that dentists apply these data to implant platforms or abutment designs to achieve ideal esthetics. The curves obtained in the present study may be incorporated as a basis for implant component design to improve the biologic nature and related esthetics of restorations. Keywords: cementoenamel junction, dental implants, esthetics, gingival line, scalloped design, three-dimensional scanner

Purpose: A biochemical approach to implant surface modification may offer an alternative to physicochemical and morphologic methods for obtaining desirable bone-implant interfaces. The objective of this study was to investigate the bone tissue response to anodized titanium implant surfaces coated with a poly(D,L-lactide-co-glycolide) (PLGA) solution mixed with 1α,25-diydroxyvitamin D3 (1α,25-(OH)2D3) via an electrospray technique. Materials and Methods: Threaded implants were manufactured and anodized under 300 V at 660 Hz for 3 minutes (control group). Half of the implants were then coated with 0.15 mL of the PLGA/1α,25-(OH)2D3 solution (5 µg/implant) via electrospray (experimental group). Surface topography was evaluated using field-emission scanning electron microscopy and optical interferometry. Forty-eight implants (12 implants per group per healing period) were surgically placed in random sites in the tibiae of 12 New Zealand white rabbits. After 4 and 12 weeks of healing, undecalcified ground sections were subjected to histologic and histomorphometric analyses. Results: At week 4, the mean bone-to-implant contact ratio (BIC%) over the entire length of the implant in the experimental group was 37.08% ± 10.18%, versus 28.01% ± 8.70% in the control group. The mean BIC% value in the first four consecutive threads of the experimental group was 48.64% ± 15.92%, compared to 36.11% ±13.49% in the control group (P .05). At week 12, the mean overall BIC% values were 39.10% ± 7.68% in the experimental group and 29.53% ± 9.49% in the control group. The mean BIC% value in the first four consecutive threads of the experimental group was 51.80% ± 16.41%, versus 37.35% ± 11.77% in the control group (P .05). Conclusion: The current study demonstrated that the PLGA/1α,25-(OH)2D3 solution coating resulted in submicron-sized particles, which may stimulate bone formation adjacent to the surface of implants inserted into bone. Keywords: 1α, 25-dihydroxyvitamin D3, anodized titanium implant, histomorphometry, poly(D, L-lactide-co-glycolide)

Purpose: To evaluate the effects on bone of forced insertion of self-tapping orthodontic mini-implants and thus obtain biomechanical data to develop insertion protocols and optimize drills for implant site preparation. Materials and Methods: After implant site preparation, 39 orthodontic mini-implants (OMI), 1.6 × 7.5 mm each, were inserted into the hard bone of sheep mandible; 24 were placed with a 1-mm bone drill and 15 were placed with a standard-diameter (1.2-mm) drill. Removal torque was measured immediately (group A) and 8 weeks after insertion (group B). Eight OMIs (group C) were removed from the mandible in block sections of appropriate size for microcomputed tomographic morphometric and morphologic analyses. Results: All OMIs were placed without complications, with mean insertion torque of 17.625 (± 1.71) Ncm (test groups) and 17.70 (± 1.41) (control groups) and were stable at reentry. Group A implants showed a reduction in removal torque of 5.66%, while in group B, removal torque was reduced by 43.25%. In the control groups (ie, OMIs placed with a 1.2-mm drill), removal torque immediately after placement was reduced by 5.64%, and 8 weeks after insertion, removal torque had declined by 18.2%. Microcomputed tomographic bone morphometric analysis for both test and control groups showed that bone-implant contact was lower than expected in cortical bone 8 weeks after insertion. Morphologic analysis revealed cavities in the cortical bone close to the surface and microcalli in soft bone. Cavities in the cortical bone may have been caused by bone trauma during insertion. Conclusions: The use of a narrow drill for site preparation increased orthodontic screw insertion torque, but it also damaged the bone and decreased removal torque. Standard histologic examination may clarify whether cavities in hard bone are actually signs of bone resorption that results from the activation of remodeling. Keywords: anchorage, bone, bone biomechanics, microcomputed tomography, mini-implants, orthodontic implants

Purpose: To compare the effect of implant abutment modification on the amount of cement extruded at the crown-abutment margin and to evaluate the vertical discrepancy after cementation. Materials and Methods: Access openings of titanium abutments were modified with an opening (open) and placement of two vent holes 3 mm from the occlusal edge and 180 degrees apart (internal vent). Access openings were filled with resin material (closed) and used as controls. Each abutment was secured to an implant analog. Eugenol-free zinc oxide cement (TempBond NE) was selected to cement the cast crowns (n = 9) onto test abutments. The amount of cement extruded out of the margin was calculated, and vertical seating discrepancies were determined with a linear transducer device before and after cementation. Differences among groups were analyzed statistically. Results: The mean amount of extruded cement ranged from 36% to 90% of the total cement placed within the crowns. The order, from least to greatest amount of excess cement extrusion at the margins, was internal vent, open, and closed; significant differences were observed between test groups. The net vertical discrepancies of tested specimens ranged from -7 µm to +6 µm (mean, 0 µm). No statistically significant differences in vertical discrepancy were found between the groups. Conclusions: Venting the hollow abutment resulted in the least amount of cement extrusion when compared to closing off the screw access channel or leaving it open. Within the limitations of this study, it may be concluded that the use of two, 0.75-mm radius vent holes placed 3 mm apical to the occlusal area of the abutment and 180 degrees apart will limit the amount of cement extruded into the gingival sulcus of implant-retained crowns. Keywords: cementation, cement retention, customized abutment, implant restorations, seating discrepancy, temporary cement

Purpose: The aim of this study was to investigate the cellular response of human gingival fibroblasts (HGFs) cultured on smooth or rough zirconia (Zr) or titanium (Ti) disks. Materials and Methods: Disks fabricated from four different materials-smooth Zr (Zr-S), rough Zr (Zr-R), smooth Ti (Ti-S), and rough Ti (Ti-R)-were used, and surface roughness was analyzed by atomic force microscopy. After HGFs were cultured on these disks, cell morphology was examined by scanning electron microscopy, cell proliferation activity was evaluated by a monotetrazolium assay, and gene expression levels of various collagens and integrins were measured by real-time polymerase chain reaction. Results: The Ti-R disks were the roughest, followed by Zr-R, Ti-S, and Zr-S, in that order. The cells cultured on the Zr-S and Ti-S disks appeared to be more aligned with the fine irregularities at later time points, whereas the cells cultured on the Zr-S showed the weakest spreading compared to the other surfaces after 3 hours of culture. With respect to proliferation, cells proliferated significantly faster on the Zr-S surface than on the other surfaces. Gene expression of integrin α2 at 3 hours and integrin α5 and type I collagen at 48 hours on Zr-S was significantly up-regulated compared to Ti. Conversely, the expression of integrins ß1 and ß3 and type III collagen was significantly decreased on Zr-S at 1 hour compared to the other materials. Conclusion: These data indicate that different surface materials and topographies may induce a distinct HGF morphology, proliferation, and gene expression. Keywords: fibroblasts, gene expression, integrins, titanium, zirconia

Purpose: Hydrophilicity is gaining increasing interest as a factor that might influence the osseointegration of dental implants. Therefore, in this study the dynamic wetting behavior of currently marketed dental titanium implants was analyzed by tensiometry, and its relationship to surface topography was examined. Materials and Methods: Nine screw-type implant systems from eight manufacturers were evaluated. Dynamic water contact angles were analyzed by tensiometric multiloop Wilhelmy experiments (10 loops, 10 mm/min immersion speed). The wetted length (perimeter) of the immersed samples was estimated by three-dimensional picture profile measurement of the thread height of the respective implant screws. Wettability was quantified by first advancing contact angles. Additionally, static contact angles were determined using the sessile drop technique. All implant surfaces were characterized by scanning electron microscopy (SEM). Contact angle data were subjected to one-way analysis of variance followed by the Student t test. Results: SEM revealed different types of surface morphology resulting from the different manufacturing processes. The first advancing mean contact angles of all implants ranged from 0 degrees (SLActive) to 138 degrees (OsseoSpeed), demonstrating statistically significant differences between implants. Because of kinetic hysteresis, initially hydrophobic implants became hydrophilic during following immersion loops. Conclusions: The tensiometric method was used to compare wettability of dental implants. A range from fully wettable/superhydrophilic to virtually unwettable/hydrophobic was observed on the implant surfaces examined. Keywords: dental implant, dynamic contact angle, hydrophilicity, surface topography, tensiometry, wettability

Purpose: The effect of different implant impression techniques on the accuracy of casts has been investigated mostly in vitro, and clinically relevant evidence is scarce. The purpose of this study was to investigate the effect of implant impression techniques-specifically, splinted versus nonsplinted-on the accuracy of fit of fixed implant prostheses in edentulous patients. Materials and Methods: This clinical study included 12 edentulous patients (13 edentulous arches). All patients had undergone computer-guided, prosthetically driven implant surgery. Splinted (with acrylic resin) and nonsplinted pickup implant impression techniques were used to generate two different casts. Intraoral verification jigs were made to fabricate a third index cast (prosthesis fabrication cast); these made up a control group. All patients were definitively rehabilitated with one-piece zirconia prostheses. The accuracy of fit of each prosthesis was evaluated indirectly by examining them clinically and radiographically while they were fit on the generated casts. Results: Of the 13 splinted casts, 12 presented with accurate clinical fit when the zirconia prosthesis was seated on its respective cast. Only 6 of the 13 nonsplinted casts showed accurate clinical fit. The zirconia prostheses fit accurately on all respective casts of the control group (prosthesis fabrication cast) as well as intraorally. The differences between the test groups and between the nonsplinted and control groups were statistically significant. No statistically significant differences were found between the splinted and control groups. Conclusion: There is clinical evidence that the splinted impression technique generates more accurate implant impressions and master casts than the nonsplinted technique for complete-arch, one-piece fixed prostheses. Keywords: accuracy of fit, dental implants, implant impressions, nonsplinted techniques, splinted techniques

Purpose: This study was designed to investigate the prevalence and course of the vascular canals in the maxillary sinus walls and to measure the distance between the sinus floor, the edentulous alveolar crest, and the vascular canal using cone beam computed tomography (CBCT). Materials and Methods: The maxillary sinus CBCT scans of 250 patients scheduled for implant surgery were examined. The vertical and mediolateral positions of the vascular canals or notches were investigated on the CBCT images. The location of each tooth was confirmed using a diagnostic template for implant placement. Statistical analyses were performed to verify whether the mean artery position was significantly different according to each tooth location, gender, and age. Results: A maxillary arterial endosseous anastomosis was observed in 52.8% of patients. The mean perpendicular distance from the sinus floor to the vascular canal was shortest in the first molar region (7.58 ± 3.19 mm) and longest in the first premolar region (9.2 ± 3.22 mm). The mean distance from the alveolar crest to the vascular canal was shortest in the first molar region (14.79 ± 4.04 mm) and longest in the first premolar region (18.92 ± 4.86 mm). These distances were significantly different according to tooth position. The mean distances from the alveolar crest and the sinus floor to the vascular canal did not decrease with age. The mediolateral position of the canals was also significantly different depending on tooth position. Conclusion: With this information about the branch of the posterior superior alveolar artery from CBCT, unnecessary bleeding during implant placement should be more easily preventable. The use of CBCT is recommended as a routine procedure prior to sinus floor elevation. Keywords: cone beam computed tomography, maxillary artery, maxillary sinus, sinus elevation

Purpose: To evaluate the influence of different implant designs on the biomechanical environment of immediately placed implants. Materials and Methods: Computed tomography (CT)--based finite element models comprising a maxillary central incisor socket and four commercially available internal-connection implants (SIN SW, 3i Certain, Nobel Replace, and ITI Standard) of comparable diameters and lengths were constructed. Biomechanical scenarios of immediate placement, immediate loading, and delayed loading protocols were simulated. Analysis of variance at the 95% confidence level was used to evaluate peak equivalent strain (EQV strain) in bone and bone-to-implant relative displacement. Results: Loading magnitude (77.6%) and the clinical situation (15.0%) (ie, presence or absence of an extraction socket defect, condition of the bone-to-implant interface) presented the highest relative contributions to the results. Implant design contributed significantly to strains and displacements in the immediate placement protocol. Whereas a greater contribution of implant design was observed for strain values and distributions for immediately placed and immediately loaded protocols, a smaller contribution was observed in the delayed loading scenario. Conclusion: Implant design contributes significantly to changing biomechanical scenarios for immediately placed implants. The results also suggest that avoiding implant overloading and ensuring high primary implant stability are critical in encouraging the load-bearing capability of immediately placed implants. Keywords: dental implant design, finite element analysis, immediate implant loading, immediate implant placement

Purpose: Stress caused by a non-passively fitting implant superstructure may induce bone adaptation, thereby changing the magnitude of static implant loading. Materials and Methods: In a previous investigation, repeated in vivo strain measurements were conducted on an implant-supported bar to evaluate changes in the magnitude of misfit resulting from bone remodeling processes. Both maximum (445 µm/m) and minimum (383 µm/m) strain values were simulated using a three-dimensional finite element model. The horizontal misfit needed to simulate experimentally determined strain values and the resulting stresses occurring in the restoration and the bone were quantified as von Mises equivalent stress. Additionally, different stages of osseointegration were modeled by altering the elastic modulus of bone immediately surrounding the implants. Results: To simulate the maximum strain value, a horizontal misfit of 83.3 µm had to be introduced, whereas the minimum strain value could be simulated via a horizontal misfit of 71.5 µm. Maximum misfit caused stress magnitudes of 105 MPa in cortical bone and 5.3 MPa in trabecular bone. Minimum misfit caused stress magnitudes of 90 MPa in cortical bone and 4.6 MPa in trabecular bone. The difference between maximum and minimum horizontal misfit was 12 µm and led to a reduction in maximum stress levels of 15 MPa in cortical bone and 0.7 MPa in trabecular bone. Progressing osseointegration affected the stress situation of the supporting implants. Conclusions: Within the limitations of this investigation, it can be concluded that bone adaptation may lead to implant site displacement in the range of several micrometers. Early fixation of non-passively fitting superstructures on implants may lead to greater passivity of fit. Keywords: bone remodeling, finite element analysis, loading protocol, passive fit, static implant loading, strain gauge

Purpose: This 3-year study evaluated the implant survival rate, peri-implant tissue response, prosthetic maintenance, and prosthetic complications in a series of patients who received two immediately loaded unsplinted threaded implants to retain a mandibular overdenture. Materials and Methods: Eight completely edentulous patients were evaluated clinically and radiographically immediately after implant placement, at 3 months, and at 1, 2, and 3 years after implant placement. Data were analyzed using repeated-measures one-way analysis of variance and the Wilcoxon signed rank test at a significance level of α = .05. Results: At 3 years, all implants remained osseointegrated (16/16), with an overall mean marginal bone change of -0.58 ± 0.39 mm and a mean Periotest value of -7.19 ± 0.54. The modified Plaque Index scores showed marked improvement in oral hygiene during the first year, but some relapse was observed thereafter. Prosthetic maintenance and complications included replacement of the attachment inserts, abutment loosening, dislodgement of the attachment housing, overdenture reline, denture tooth fracture, and overdenture base fracture. Conclusions: This 3-year study suggests that, despite less than ideal oral hygiene and a high incidence of complete/partial fracture of overdentures, favorable implant survival rate and peri-implant tissue responses can be achieved in mandibular overdentures retained with two immediately loaded unsplinted threaded implants. Keywords: immediate loading, implant-retained prosthesis, mandibular overdenture, prosthetic attachments, prosthetic complications, prosthetic maintenance, unsplinted implants

Purpose: The purpose of the present study was to determine whether intravenous sedation during dental implant surgery contributed to stabilization of hemodynamics. Materials and Methods: Two hundred fifty-five consecutive patients treated with dental implants were randomly assigned to receive either intravenous sedation with local anesthesia (sedation group, n = 123) or local anesthesia only (nonsedation group, n = 132). Midazolam and propofol were used synergistically as sedative agents. Systolic blood pressure, diastolic blood pressure, and pulse rate were measured every 2.5 minutes during dental implant surgery. On the basis of these data, the coefficient of variation, percentage of change, maximum values, and incidences of a larger increase were analyzed and expressed as cardiovascular changes. Results: A comparison of percentages of change, maximum values, and incidences of a greater increase showed that systolic and/or diastolic blood pressure were significantly higher in the nonsedation group than in the sedation group. The combination of midazolam and propofol sedation prevented excessive increases in blood pressure. The circulatory suppression induced by the intravenous sedation regimen not only reduced mental stress arising from the state of sedation but also exerted a pharmacologic effect. The application of this intravenous sedation regimen stabilized hemodynamics and contributed to the safety of the patient in dental implant surgery. Conclusion: The application of intravenous sedation had a beneficial effect for hemodynamic changes during dental implant surgery. Keywords: dental implant surgery, hemodynamics, intravenous sedation, midazolam, propofol

Purpose: A clinical evaluation of the long-term survival rate of three subtypes of a dental tube-in-tube implant with special emphasis on peri-implant bone resorption was conducted and is presented here. Materials and Methods: A retrospective follow-up examination of patients treated with tube-in-tube implants between August 2001 and August 2005 was conducted. For patients available for clinical recall, success criteria according to Albrektsson and Buser were evaluated. Differences in peri-implant bone resorption with regard to implant subtype and depth of implant placement (supracrestal or crestal) were calculated via the Student t test. Results: One hundred twenty-seven patients were provided with a total of 382 Camlog implants. Of the implants placed, 239 were root-line (RL), 129 were screw-line (SL), and 14 were cylindric. One hundred four patients with 318 implants could be contacted. In 59 cases, bony augmentation was performed. After an average time in situ of 32 months (range, 8 to 56 months), 307 of 318 surveyed implants (96.5%) remained in function. Six implants were lost as a result of absence of osseointegration, four following peri-implantitis, and one owing to hypesthesia. Two patients with eight implants have died since 2005, and 21 patients with 47 implants could not be contacted. In 75 patients with 240 implants, clinical success rates were 94% (Albrektsson) and 97% (Buser). A significant difference in bone resorption was found between RL and SL implants (P .0001). Implants that had been placed supracrestally showed significantly less bone resorption than crestally inserted implants, both overall and in subgroup analyses (RL, P = .015; SL, P .0001). Conclusion: The internal tube-in-tube implant system showed promising long-term results. Significantly less bone resorption was seen for RL implants as well as for implants that were placed supracrestally. Keywords: bone resorption, dental implants, implant-abutment interface, implant design, long-term study

Purpose: Augmentation of the sinus floor with autogenous bone often requires an extra donor site, which is associated with a risk of morbidity, and current grafting protocols involve healing times of up to 9 months. In this prospective in vivo study, the time-dependent efficacy of PepGen P-15 Putty, a combination of bovine hydroxyapatite and synthetic peptide in a sodium hyaluronate carrier, was evaluated in sinus grafting. Materials and Methods: Twenty-four edentulous patients received bilateral sinus augmentations with PepGen P-15 Putty, which mimics the cell-binding domain of type I collagen responsible for cell migration, differentiation, and proliferation. The patients were randomly divided into four groups of six patients each, corresponding to 2, 4, 6, and 9 months of healing postaugmentation. After these time intervals, bone biopsy specimens were retrieved through the alveolar bone crest into the augmented sinus, and subsequently oral implants were placed. The specimens were immersed in buffered formalin, scanned with a desktop microcomputed tomography machine, and processed for histologic and histomorphometric evaluation. A mixed model was used for statistical analysis. Results: Three-dimensional microcomputed tomography depicted the distinct structure of trabecular bone encompassing remnants of PepGen, and histologic evaluation revealed osteoblasts and osteoid with osteocytes in the vicinity of the PepGen particles at all healing stages. Histomorphometric results indicated an increase in the newly formed bone fraction in the specimens as follows: 21.3% (± 2.33) at 2 months, 21.9% (± 8.9) at 4 months, 28.5% (± 6.9) at 6 months, and 29.8% (± 11.8) at 9 months. The differences were statistically insignificant. All implants placed in the augmented sites integrated and were restored prosthetically. Conclusions: PepGen can be used successfully for maxillary sinus augmentation. These data provide evidence that implant placement, even after only 2 months of healing, may be possible. Keywords: bone substitute, dental implants, histology, maxillary sinus augmentation, microcomputed tomography, synthetic cell-binding peptide

Purpose: For dental implants to be successful, osseointegration must occur, but it is unknown how much time must pass for osseointegration to be established. Preclinical studies suggested that titanium implants with a sandblasted and acid-etched (SLA) surface were more osteoconductive and allowed more rapid osseointegration than machined or turned implant surfaces. The hypothesis of this study was that implants with an SLA surface could be loaded in half the conventional healing time of machined-surface implants and that, after loading, the implants would be successful for 5 years. Materials and Methods: A prospective multicenter clinical study was conducted with 439 implants placed in native bone in 135 edentulous and partially edentulous patients. Abutments were attached to the implant with 35 Ncm of torque without countertorque after 6 weeks in type I to III bone and after 12 weeks in type IV bone. The patients were carefully evaluated for 5 years. Results: Most implants were placed in nonsmoking, nondiabetic patients with a mean age of 55 years (range, 21 to 82 years). Eighty percent of the implants were 10 or 12 mm long, 96% had a diameter of 4.1 mm, and 78% were placed in type II or III bone. Patients maintained good oral hygiene and were satisfied with the restorations. Four implants failed, and one implant was deemed unsuccessful between surgery and the 1-year postloading visit. No implants failed or were unsuccessful in subsequent years. The cumulative survival and success rates for 385 implants in 120 patients after 5 years were 99.1% and 98.8%, respectively. Conclusion: Implants with an SLA surface can be restored in 6 weeks for type I to III bone and 12 weeks for type IV bone. Furthermore, they can be maintained after loading for 5 years with very high success and survival rates. Keywords: clinical trial, dental implants, early loading, implant-supported prostheses, multicenter study

Purpose: The purpose of this retrospective study was to evaluate the medium- to long-term clinical outcome of single-tooth implants placed into fresh extraction sockets using a low-insertion-torque protocol and immediately restored with acrylic resin provisional crowns. Materials and Methods: Sixty-one patients consecutively referred for the replacement of one or more failing teeth were planned for treatment by means of extraction and immediate implant placement and provisionalization using a low-insertion-torque protocol of = 25 Ncm. Low rotational stability was not a contraindication to treatment unless there was a lack of axial stability. Implant survival and marginal bone levels were documented. A statistical analysis was performed to discover any correlations between insertion torque, age, gender, implant size and tooth position and marginal bone loss. Results: Sixty-eight implants were placed. Three implants failed to osseointegrate; one was replaced and immediately restored and has been successful for more than 5 years. The overall survival rate for all implants was 95.5%, which have been in function for a period of 1.25 to 9.5 years. The mean marginal bone loss of the 54 implants followed for at least 24 months was 0.23 ± 0.60 mm mesially and 0.20 ± 0.72 mm distally. Overall, 78% of implants showed no marginal bone loss, 9% experienced 0.1 to 0.5 mm of bone loss, and 13% demonstrated > 0.5 mm of bone loss. There were no significant correlations between the various parameters analyzed and marginal bone loss. Conclusion: A torque of only 25 Ncm would seem more than sufficient to yield a favorable clinical outcome, and there may be a misconception as to what actually represents adequate primary stability. Immediate provisionalization of single-tooth implants placed with a relatively low insertion torque can yield favorable survival rates and optimal maintenance of marginal bone levels compared to the generally accepted norm. Keywords: dental implants, immediate placement, insertion torque

Purpose: Despite the development of novel and more precise fabrication methods, absolute passive fit of implant-supported superstructures has yet to be consistently achieved. In the past, several laboratory techniques have been described to analyze fit. The purpose of this study was to assess two methods of fit evaluation with a control (well fitting) prosthesis and an intentionally misfit prosthesis. Materials and Methods: In this in vitro study, two comparable implant-supported superstructures (control and test misfit) were fabricated after scanning a test cast of a maxilla with four implants (two on each side). The test structure was fabricated with a known minor misfit on one of the inserted implants by manipulating the coordinates on the scanned files. The control superstructure was fabricated as accurately as possible without manipulating any scanned information. Both superstructures were evaluated using optical scanning and strain gauge measurements by an investigator who was blinded to the designed misfit. Results: Optical scanning demonstrated an accuracy of 10 µm for the control frame, while the misfit frame demonstrated greater discrepancies, both at the intentionally misfit connection (connection #2, misfit of 29 µm) and at the other connections (#1, 4 µm; #3, 5 µm; #4, 4 µm), although the latter connections showed less misfit. The strain gauge measurement showed a higher mean deviation of 26.2 µm (± 5.9 µm) in the test model, versus 15.3 µm (± 4.3 µm) in the control model. Conclusion: Optical scan analysis was able to detect the misfit in the test superstructure and the manipulated implant. The strain gauge measurements confirmed these findings, indicating that both methods of assessing inaccuracy are effective. Optical scan analysis may be used as a simplified and clinically applicable method to detect minor misfits in implant-supported superstructures. Keywords: implant superstructure, optical scan analysis, passive fit, prosthesis, prosthetic misfit, strain gauge