The International Journal of Oral & Maxillofacial Implants, 05/2015

Purpose: To assess the quality and quantity of newly formed bone around rough-surfaced titanium subperiosteal implants stabilized with two different fixation techniques and to investigate nanoindentation as a method for measuring the elastic properties of the bone around these implants. Materials and Methods: Ten 6-month-old white rabbits were used in this study. One femur received a subperiosteal implant fixed to the bone with screws. The other femur received a subperiosteal implant stabilized with a trough (bed) in the bone area, plus fixation screws. After a 3-month healing period, the animals were sacrificed and each titanium plate was resected along with the surrounding bone. Histometric measurements of osseointegration were performed on 16 titanium plates, and 16 titanium plates were evaluated qualitatively (hardness and modulus of elasticity) with nanoindentation. A regression model was used to analyze the data. Results: Subperiosteal implants placed into a trough performed significantly better than those placed on top of the cortical bone in terms of percentage of bone in direct contact with the titanium plate, length of new bone, and percentage of area of new bone. The mechanical properties (modulus of elasticity, hardness) of the newly formed bone above the plate measured at the microstructural level were significantly inferior to those of the mature cortical bone below the plate. Conclusion: Subperiosteal implants placed into a trough performed better than those placed on top of the cortical bone, but it seems that 3 months of healing is not enough to achieve optimal integration and bone maturation around them. Nanoindentation can offer valuable insight into the elastic properties of the microstructural component of the bone. Keywords: nanoindentation, subperiosteal, titanium implant

Purpose: To measure and compare the three-dimensional (3D) position of nine different abutments manufactured by different manufacturers after repeated torqueing on an internal-hexagon implant. Materials and Methods: Nine tapered implants were placed into an acrylic resin block. Five specimens each of nine different abutments (n = 45) were placed into one of nine implants. The abutments were handtightened and then torqued to the manufacturer-recommended torque of 30 Ncm. After 10 minutes, 30 Ncm of torque was reapplied. Another 10 minutes elapsed before testing was completed. Images were recorded in 12-second intervals. The spatial relationship of the abutments to the resin block was determined using 3D digital image correlation. Commercial image correlation software was used to analyze the displacements. Mean displacements for the abutments were calculated in three dimensions and overall for both torque applications. Statistical comparisons were done with a t test and a step-down Bonferroni correction. Results: The overall 3D displacement of the Atlantis Titanium abutment after the second applied torque was significantly greater than that of two of the eight other abutments. Displacement in all three dimensions for the Atlantis Titanium abutment changed direction between the first and second torque applications. All abutments moved further in the same direction except for the Atlantis Titanium abutment, which moved back toward its original hand-tightened position horizontally after the second torque application. Conclusion: Re-torqueing of abutments after a 10-minute interval leads to minor displacement of varying degrees between the abutment and a tapered implant. A potential effect of embedment relaxation and/or manufacturing errors should be taken into consideration when selecting an abutment for a cement-retained crown on a tapered implant. Accordingly, clinicians may benefit from adjusting cement-retained implant crowns after re-torqueing the abutments to prevent potential occlusal and interproximal contact problems. Keywords: abutment, cement, dental implant, displacement, embedment relaxation, retention

Purpose: The aim of this study was to evaluate the axial tightening force applied by conventional and diamondlike carbon (DLC)-coated screws and to verify, through three-dimensional finite element analysis (FEA), the stress distribution caused by different framework materials and prosthetic screws in overdenture frameworks with different misfit levels. Materials and Methods: The axial tightening force applied by the screw was evaluated by means of a titanium matrix connected to a load cell. Conventional titanium or DLC-coated screws were tightened with a digital torque wrench, and the load values were recorded. The values were applied in an FEA to a bar-clip attachment system connected to two 4.0 × 11-mm externalhexagon titanium implants placed in an anterior edentulous arch. DLC-coated and conventional screws were modeled with their respective axial forces obtained on the experimental evaluation for three bar framework materials (titanium, nickel-chromium, and cobalt-chromium) and three levels of misfit (100, 150, and 200 μm). Von Mises stresses for prosthetic components and maximum principal stress and microstrains (maximum principal strains) for bone tissue were measured. Results: The mean force applied by the conventional screw was 25.55 N (± 1.78); the prosthetic screw coated with a DLC layer applied a mean force of 31.44 N (± 2.11), a statistically significant difference. In the FEA, the DLC screw led to higher stresses on the framework; however, the prosthetic screw suffered lower stress. No influence of screw type was seen in the bone tissue. Conclusion: Titanium frameworks reduced the stress transmitted to the bone tissue and the bar framework but had no influence on the screws. Higher misfit values resulted in an increased stress/strain in bone tissue and bar framework, which was not the case for retention screws. Keywords: diamondlike carbon, finite element analysis, implant prosthesis, misfit, overdentures

Purpose: To evaluate the effects of low-level laser therapy (LLLT) on peri-implant bone regeneration by means of resonance frequency analysis and histologic analysis of bone-to-implant contact (BIC). Materials and Methods: Thirty-two male New Zealand rabbits were randomly divided into four groups of eight animals each, one control group (nonirradiated animals) and three experimental groups that received LLLT (group E5 = 5 J per session; group E10 = 10 J per session; group E20 = 20 J per session). The mandibular left incisor was surgically extracted in all animals, and a nanoparticle-treated-surface osseointegrated implant was placed immediately afterward. The experimental groups were irradiated with aluminum-gallium-arsenide laser diode every 48 hours over a 13-day period for a total of seven sessions. Implant stability quotients (ISQs) were measured at the time of implant placement and 30 days after the last LLLT session. The animals were then euthanized and dissected, and histologic slides of the implant region were obtained for BIC evaluation. Results: Significant differences in ISQ were detected between groups before and after LLLT, with group E20 showing significantly higher values than controls. The percentage of BIC was also significantly higher in group E20 than in control animals. Conclusion: Laser therapy at a dose of 20 J per treatment session, based on the irradiation protocol used in this study, was able to significantly increase ISQ values and BIC after implant placement, indicating that laser irradiation effected an improvement in peri-implant bone healing. Keywords: dental implants, laser therapy, osseointegration

Purpose: Achievement of primary stability upon surgical placement of dental implants is a key factor for successful osseointegration and depends mainly on implant-related factors. The aim of this study was to compare and assess the primary stability of implants with active and regular threads in type 2 as well as type 4 bone. Materials and Methods: Fresh cow vertebrae and a pelvis were used as models of type 4 bone and type 2 bone, respectively. Implants with two different designs-regular-threaded and active-threaded-both 4.3 mm wide and 13 mm long, were placed in both types of bone (n = 80). Stability measurements were completed by four prosthodontists using two different Periotest devices and resonance frequency analysis. Statistical analyses were performed with the Mann-Whitney U test. Results: No statistically significant differences were found between the implant types in either type of bone in the stability measured with different methods. For both implant types, the mean resonance frequency values in type 2 bone were statistically significantly higher than in type 4 bone, whereas the mean Periotest values in type 2 bone were statistically significantly lower than in type 4 bone. Conclusion: Within the limitations of this in vitro study in bone types 2 and 4, the active-threaded implant, which was invented to increase primary stability, did not show higher primary stability compared to a regular-threaded implant. Keywords: bone quality, bone-implant interface, immediate loading, implant design, implant stability

Purpose: To quantify the reliability of a new drilling system for implant osteotomy characterized by an eccentric sensor that automatically stops the drill upon contact with soft tissue. This safety mechanism aims to minimize surgical trauma to nerves, vessels, and the maxillary sinus mucosa. The benefits of the eccentric sensor position on planar and angulated surfaces were tested in vitro. Materials and Methods: Predicted drill protrusion after auto-stop was validated against experiments on four human cadaver mandibles (30 osteotomies with varying angles). Measurement of the drill's exit holes allowed calculation of the amount of drill protrusion, and postoperative computed tomographic scans of the mandibles were acquired to determine the drill's exit angles. Results: Mean drill protrusion into human jawbone was 0.46 ± 0.26 mm and differed significantly from expected drill protrusion, which was based on mathematical modeling, of 0.64 ± 0.3 mm. Detection of bone passage on angulated walls was seen up to 71 degrees. A central sensor position, by contrast, may result in significantly greater drill protrusion into soft tissue (mean difference: 0.55 ± 0.49 mm) that increases with the drill's exit angle (r = 0.93). Conclusion: Auto-stop drills may significantly enhance safety for the patient during osteotomy. The benefits of eccentric sensor positioning were particularly apparent when applied on angulated surfaces, whereas drill angulation was not found to influence this safety mechanism. Keywords: dental implants, drill device, osteotomy, resistance sensor, safety stop, sinus floor elevation, surgical complication

Purpose: To compare time-efficiency in the production of implant crowns using a digital workflow versus the conventional pathway. Materials and Methods: This prospective clinical study used a crossover design that included 20 study participants receiving single-tooth replacements in posterior sites. Each patient received a customized titanium abutment plus a computer-aided design/computer-assisted manufacture (CAD/CAM) zirconia suprastructure (for those in the test group, using digital workflow) and a standardized titanium abutment plus a porcelain-fused-to-metal crown (for those in the control group, using a conventional pathway). The start of the implant prosthetic treatment was established as the baseline. Time-efficiency analysis was defined as the primary outcome, and was measured for every single clinical and laboratory work step in minutes. Statistical analysis was calculated with the Wilcoxon rank sum test. Results: All crowns could be provided within two clinical appointments, independent of the manufacturing process. The mean total production time, as the sum of clinical plus laboratory work steps, was significantly different. The mean ± standard deviation (SD) time was 185.4 ± 17.9 minutes for the digital workflow process and 223.0 ± 26.2 minutes for the conventional pathway (P = .0001). Therefore, digital processing for overall treatment was 16% faster. Detailed analysis for the clinical treatment revealed a significantly reduced mean ± SD chair time of 27.3 ± 3.4 minutes for the test group compared with 33.2 ± 4.9 minutes for the control group (P = .0001). Similar results were found for the mean laboratory work time, with a significant decrease of 158.1 ± 17.2 minutes for the test group vs 189.8 ± 25.3 minutes for the control group (P = .0001). Conclusion: Only a few studies have investigated efficiency parameters of digital workflows compared with conventional pathways in implant dental medicine. This investigation shows that the digital workflow seems to be more time-efficient than the established conventional production pathway for fixed implant-supported crowns. Both clinical chair time and laboratory manufacturing steps could be effectively shortened with the digital process of intraoral scanning plus CAD/CAM technology. Keywords: conventional pathway, dental crown, dental implant, digital, time-efficiency, workflow

Purpose: To determine if contamination of abutment screws with titanium nanoparticles affects the preload by measuring the reverse torque after multiple cycles of screw closing-opening. Materials and Methods: The study included 30 internal hex implants, titanium abutments, and titanium abutment screws. Fifteen abutment screws were contaminated with 60- to 80-nm titanium nanoparticles (contamination group), and the remaining 15 screws did not receive titanium nanoparticle contamination (noncontamination group). Each abutment screw was initially tightened to 25 Ncm with a digital torque gauge to stabilize the abutment to the implant. The second torque, 25 Ncm, was applied 10 minutes after the initial torque. After an additional 5 minutes, the screw was loosened to measure the reverse torque. Ten cycles of screw insertion and removal were conducted, and reverse torque values were measured in each cycle. Repeated measures analysis of variance and the Student t test were used for statistical analysis. The level of significance was set at α = .05. After 10 cycles of closure-opening, abutment screw threads were observed under ×40 magnification. Results: Abutment screws at every cycle generally showed preload values less than the initial applied torque. The mean reverse torque values in both groups had a tendency to decline as the test cycle progressed, except at the 6th, 9th, and 10th cycle in the contamination group. The noncontamination group always had higher mean reverse torques than the contamination group at the same test cycle with significant differences at the 1st, 2nd, 4th, 5th, 7th, and 8th cycles. The preload loss in percentages were 7.83% and 12.57% after the 1st cycle, 14.48% and 19.77% after 5 cycles, and 18.83% and 19.83% after 10 cycles in the noncontamination and contamination group, respectively. Abutment screws in both groups showed various degrees of wear and metal debris on screw surfaces. Conclusion: Contamination of abutment screws with titanium nanoparticles decreased screw reverse torque values because of a settling effect, though this effect seemed minimal after five cycles. A future clinical study is indicated to validate if cleaning of contaminated screws before the delivery of the prosthesis will increase preloads. Keywords: preload, screw loosening, settling effect

Purpose: Many different attachment systems (eg, bars, studs, magnets, telescopic copings) have been used to retain overdentures. The current study aimed to investigate the load transfer characteristics and to compare the stress levels of four attachment designs for mandibular overdentures retained by one central implant and two inclined distal implants. Materials and Methods: Photoelastic mandibular models fabricated with three screw-type implants (Tapered Screw-Vent, 3.75 × 13 mm) were placed in the parasymphyseal area. The center implant was vertically oriented to the midline, and the other implants were embedded in the canine areas with a 20-degree angulation relative to the center implant. Four overdentures with different attachment designs (bar, bar/ball, bar/distally placed Rk-1s, and Locators) were studied in the context of this model. Vertical loads (100 N) were applied to the central fossa of the right first molar area of each overdenture. Stress levels that developed in the denture-bearing areas and around the implants were observed photoelastically and evaluated visually. Results: The studied attachment designs showed low and moderate stress levels. The greatest stress was found with the bar/ball design, while the lowest stress levels were observed with the Locator attachment design. Conclusion: Stresses were concentrated on the loaded side for each design. All tested designs experienced moderate stress around the posterior edentulous area. None of the designs experienced more than moderate stress. The lowest stress was noted with the Locator attachments, which transmitted little discernible stress around the implants. Keywords: implant-retained overdenture, photoelastic stress analysis, precision attachment

Purpose: Implant design and the implant-abutment interface have been regarded as key influences on crestal bone maintenance over time. The aim of the present study was to determine crestal bone changes around implants placed at different depths in a dog model. Materials and Methods: Thirty-six two-piece dental implants with a medialized implant-abutment interface and Morse taper connection (Ankylos, Dentsply) were placed in edentulous areas bilaterally in six mongrel dogs. On each side of the mandible, three implants were placed randomly at the bone crest, 1.5 mm subcrestally, or 3.0 mm subcrestally. After 3 months, the final abutments were torqued into place. At 6 months, the animals were sacrificed and samples taken for microcomputed tomographic (micro-CT) and histologic evaluations. Results: Micro-CT analysis revealed similar crestal or marginal bone loss among groups. Both subcrestal implant groups lost significantly less crestal and marginal bone than the equicrestal implants. Bone loss was greatest on the buccal of the implants, regardless of implant placement depth. Histologically, implants placed subcrestally were found to have bone in contact with the final abutment and on the implant platform. Conclusion: Implants with a centralized implant-abutment interface and Morse taper connection can be placed subcrestally without significant loss of crestal or marginal bone. Subcrestal placement of this implant system appears to be advantageous in maintaining bone height coronal to the implant platform. Keywords: subcrestal, dental implant, bone levels, histology

Purpose: To analyze the indications and frequency for three-dimensional (3D) imaging for implant treatment planning in a pool of patients referred to a specialty clinic over a 3-year period. Materials and Methods: All patients who received dental implants between 2008 and 2010 at the Department of Oral Surgery and Stomatology at the University of Bern were included in the study. The influence of age, gender, and time of treatment (2008 to 2010) on the frequency of use of two-dimensional (2D) radiographic imaging modalities alone or in combination with 3D cone beam computed tomography (CBCT) scans was analyzed. Furthermore, the influence of the indication, location, and need for bone augmentation on the frequency of use of 2D imaging modalities alone or in combination with CBCT was evaluated. Results: In all, 1,568 patients (792 women and 776 men) received 2,279 implants. Overall, 633 patients (40.4%) were analyzed with 2D imaging procedures alone. CBCT was performed in 935 patients (59.6%). There was a statistically significant increase in CBCT between 2008 and 2010. Patients older than 55 years received a CBCT scan in addition to 2D radiographic imaging statistically significantly more often. Additional 3D imaging was most frequently performed in the posterior maxilla, whereas 2D radiographs alone exhibited the highest frequency in the anterior mandible. The combination of 2D with CBCT was used predominantly for implant placement with simultaneous or staged guided bone regeneration or sinus elevation. Conclusion: Based on these findings from a specialty clinic, the use of additional CBCT imaging for implant treatment planning is influenced by the indication, location, local anatomy (including the need for bone augmentation), and the age of the patient. Keywords: cone beam computed tomography, conventional radiographic imaging, dental implants, frequency, indications

Purpose: To assess the methodologic quality of systematic reviews on the effect of platform switching upon peri-implant marginal bone loss. Materials and Methods: An electronic literature search of several databases was conducted by two reviewers. Articles were considered for quality assessment if they met the following inclusion criterion: systematic reviews that aimed at investigating the effect of platform switching/mismatch on marginal bone levels around dental implants. Two independent examiners evaluated the review publications using two quality-ranking scales (assessment of multiple systematic reviews [AMSTAR] and Glenny checklist). Descriptive statistics were used to summarize the results, and Cohen's kappa coefficients were calculated to appraise interrater agreement of each checklist. Results: Overall, five systematic reviews (including three of them with meta-analysis) were evaluated. The mean AMSTAR score ± standard deviation was 8.4 ± 2.6 (range, 4 to 11), and the mean Glenny score was 10.8 ± 2.9 (range, 6 to 14), showing high statistical correlation (rs = 0.98, P = .005). Cohen interexaminer test yielded values of κ = 0.88 and κ = 0.86 for the AMSTAR and Glenny checklist, respectively. The AMSTAR items rated positive in 78%, whereas 18% met the criteria for "no" and 4% were "not applicable." Only one review article met all criteria. Items of the Glenny checklist rated positive in 73% and negative in 27%. All but one study with the lowest quality scores (finding no difference) demonstrated a clinical benefit of implant platform switching in preserving the peri-implant marginal bone loss. Conclusion: According to the quality-ranking scales appraised, substantial methodologic variability was found in systematic assessment of benefits with the platform switching concept to preserve peri-implant bone level. High-quality systematic reviews, however, generally favored platform switching over platform matching. Keywords: bone regeneration, dental implants, dental implant-abutment design, evidence-based dentistry, platform switching, systematic review

The emerging literature has recently reported an alarming increase in peri-implantitis. This disease is typically described as the result of an imbalance between host response and bacterial load, supported by gram-negative anaerobic microflora. The current literature on the prevention and treatment of peri-implantitis does not allow for the extraction of applicable clinical information. In fact, the lack of efficacy of the current treatment methods may be a result of insufficient understanding of the biology. The aim of this position paper was to try to reevaluate the etiopathogenesis of peri-implantitis, highlighting the principal clinically induced triggering factors of the disease. The consensus conference provided strong evidence to suggest that a different microbiologic flora (slightly different from that collected around teeth affected by periodontitis) could support peri-implantitis. However, the evidence to support a consensus statement regarding clinically triggering factors (surgical, prosthetic, and biomechanical) for peri-implantitis is only of moderate strength (cohort studies or consistent results from long-term, well-populated case series). Expert opinion led the consensus group to support the following: rectifying the number of peri-implant inflammatory situations caused by surgical, restorative, or material complications may lower the number of infections to a more realistic figure and may suggest different and more appropriate treatment plans. At the same time, it can be stated that implant material, shape and surface characteristics, procedures and biomaterials used for bone augmentation, and incorrect prosthetic procedures and biomechanical plans could also be risk factors for the occurrence and progression of periimplantitis. Keywords: crestal bone loss, microbiologic factors, peri-implantitis, prosthetic factors, surgical factors

Purpose: The purpose of this work was to investigate the effect of a hydroxyapatite (HA) coating doped with zinc (Zn), magnesium (Mg), or strontium (Sr) on implant osseointegration in ovariectomized rats. Materials and Methods: The HA coating doped with trace elements was produced by electrochemical deposition. Surface properties were tested by field emission scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and measurement of ionic release. A total of 36 ovariectomized rats were randomly divided into four groups: the HA coating group, the Zn-HA coating group, the Mg-HA coating group, and the Sr-HA coating group. The corresponding implants were then inserted into the tibiae. Histomorphometric analysis was performed after 4, 8, and 12 weeks. Results: HA coatings doped with 2.5% Zn, Mg, or Sr by electrochemical deposition showed almost identical surface morphologies. Bone-implant contact (BIC) in the Zn-HA group was significantly greater than that in the HA group for all time periods. BIC values in the Sr-HA group significantly exceeded those in the HA group at 8 and 12 weeks after implantation. Bone ingrowth area values of both the Zn-HA and Sr-HA groups were statistically significantly different from those in the HA group after 8 and 12 weeks. Conclusion: The Zn-HA and Sr-HA coatings have the potential to improve implant osseointegration in osteoporosis. Keywords: electrochemical deposition, hydroxyapatite, osseointegration, trace elements

Purpose: The aim of this study was to introduce a novel method of flap advancement without a vertical releasing incision for guided bone regeneration (GBR) and to discuss its clinical outcomes. Materials and Methods: This retrospective study involved patients who had received GBR for dental implants between April 2012 and April 2013. In all patients, a typical midcrestal incision was made on the edentulous alveolar ridge, and a sulcular incision was extended to the adjacent two teeth; however, no vertical incision was performed. Instead, a wide periosteal releasing incision and an additional releasing incision that selectively cut part of the facial expression muscles (the orbicularis oris or the buccinator) were used. Postoperative complications, such as swelling, pain, paresthesia, signs of infection, and membrane exposure, were evaluated at 1, 2, 4, 12, and 24 weeks after surgery. Results: Forty sites in 34 patients were evaluated. At all surgical sites, flap advancement of more than 7 mm was attained, and clinically passive primary closure was achieved. All patients experienced slight or mild postoperative swelling without functional limitation or discomfort during mouth opening, eye opening, and swallowing. No long-lasting pain (more than a week), paresthesia, or signs of infection occurred during the follow-up period of 6 months. However, delayed exposure of titanium mesh after 4 months was observed in two patients who had used a provisional removable prosthesis. Within 2 weeks, the exposures closed spontaneously after prosthesis use was halted and careful daily dressing was undertaken. Conclusion: The flap advancement technique presented in this study easily enables clinically passive primary closure, and there was no obvious failure of primary closure. This technique could be used successfully in GBR procedures. Keywords: flap advancement, guided bone regeneration, tension-free primary closure

Purpose: Diabetes mellitus is considered a relative contraindication for dental implant therapy, depending on levels of glycemic control. The purpose of this research was to evaluate the peri-implant conditions and measure the levels of interleukin 1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in the peri-implant crevicular fluid (PICF) in patients with glycemic-controlled type 2 diabetes (T2DM). Materials and Methods: Thirteen patients with well-controlled T2DM and seven systemically healthy patients were recruited for this study. Clinical measurements were recorded, and samples of gingival crevicular fluid (GCF) and PICF were collected from the sulci of both adjacent teeth and implants at baseline (after implant placement), 1 month, 4 months, and 7 months. Levels of IL-1β and TNF-α in the GCF and PICF were analyzed by enzyme-linked immunosorbent assay. Standardized intraoral radiographs were taken at baseline (after implant placement), 4 months, and 7 months. Implant stability was assessed by resonance frequency analysis at baseline, at 1 month, and at 4 months. Results: Glycosylated hemoglobin levels in the T2DM group were significantly increased at 7 months compared to baseline levels. Implant stability quotient levels at 4 months were increased significantly compared to baseline in both groups. Alveolar bone levels around implants were statistically lower at 4 and 7 months compared to baseline and statistically decreased at 7 months compared to 4 months in the T2DM group. There were no significant differences between groups in bone levels around implants, and no significant differences were found in levels of IL-1β and TNF-α at either teeth or implants or between the groups. Conclusion: The results suggest that dental implant therapy can be offered to patients with well-controlled T2DM, as there were no significant differences between control and diabetic patients in terms of clinical parameters or GCF and PICF cytokine levels. Keywords: alveolar bone loss, dental implant, diabetes mellitus, glycosylated hemoglobin, interleukin 1 beta, tumor necrosis factor alpha

Purpose: The aims of this study were to investigate the best two of five common methods of collecting autologous bone (preliminary study [PS]) and to test clinically the effects of autografts harvested using a trephine bur or bone scraper for sinus augmentation surgery (main study [MS]). Materials and Methods: In the PS, five autograft samples from five patients (n = 25) were harvested with a bone scraper, round bur, piezoelectric device, implant bur, and trephine bur and were processed for histomorphometric analysis. In the MS, sinus augmentation was performed on 20 patients using bovine-derived bone substitute and autograft collected with a trephine bur (group A, n = 10) or collected with a bone scraper (group B, n = 10). Narrow implants were also placed. At 6 months, changes in graft volume were evaluated with cone beam computed tomography. The amounts of regenerated bone, residual graft, and osseointegration of the implants were assessed histologically. Results: In the PS, the trephine bur and bone scraper harvested bone chips that were medium to large and more vital than those obtained with the other tools. In the MS, no significant differences were seen between groups in terms of the amount of residual biomaterial, regenerated bone, change in graft volume, and osseointegration. Conclusion: Biologic differences between these two bone particulates may not influence regeneration and implant osseointegration in sinus augmentation when mixed with xenograft bone. Keywords: autograft, bone regeneration, cone beam computed tomography, sinus augmentation, tissue harvesting, xenograft

Purpose: To compare volumetric changes after sinus augmentation of completely edentulous maxillae with either autogenous or allogeneic fresh-frozen bone particles. Materials and Methods: This split-mouth study in patients who required bilateral sinus grafting used autograft particles for one sinus and allograft particles for the contralateral sinus. The grafted sinuses were left to heal for 6 months prior to implant insertion. All patients underwent four computed tomography scans: prior to augmentation and 1 week, 6 months, and 12 months after grafting. Computer software was used to analyze bone graft volume in each scan. Results: Fifteen patients (8 men, 7 women) with a mean age of 54 ± 5 years (range, 48 to 60 years) took part and underwent 30 sinus augmentation procedures. Mean autograft and allograft volumes were not statistically significantly different at each time point (1 week: 2.01 ± 0.43 cm3 vs 2.46 ± 0.79 cm3; 6 months: 1.53 ± 0.49 cm3 vs 1.75 ± 0.64 cm3; and 12 months: 1.38 ± 0.43 cm3 vs 1.59 ± 0.56 cm3, respectively). Mean volumetric reductions of 31.35% and 35.36% (23.9% and 29.9% in the 6 months prior to implant insertion, followed by an additional 9% and 9% in the following 6 months), relative to 1 week postgrafting, were noted for the autograft and allograft groups, respectively, after 12 months. Conclusion: On the basis of this split-mouth study of 15 patients, there was no statistically significant volumetric difference after 12 months between the use of autograft or allografts for sinus augmentation. Fresh-frozen bone allograft may serve as an alternative that avoids the morbidity associated with autograft harvesting. Keywords: autogenous bone, computed tomography, fresh-frozen bone allograft, sinus augmentation

Purpose: To compare the oral health-related quality of life (OHRQoL) in a prospective, randomized crossover trial in patients with mandibular overdentures retained with two or four locators. Materials and Methods: In 30 patients with edentulous mandibles, four implants (ICX-plus implants [Medentis Medical]) were placed in the intraforaminal area. Eight weeks after transgingival healing, patients were randomly assigned to have two or four implants incorporated in the prosthesis. After 3 months, the retention concepts were switched. The patients with a two-implant-supported overdenture had four implants incorporated, whereas patients with a four-implant-supported overdenture had two retention locators taken out. After 3 more months, all four implants were retained in the implant-supported overdenture in every patient. To measure OHRQoL of the patients, the Oral Health Impact Profile 14, German version (OHIP-14 G), was used. Results: A considerable increase in OHRQoL could be seen in all patients after the prosthesis was placed on the implants. Also, a statistically significant difference of OHRQoL could be seen in the OHIP-14 G scores between two-implant and four-implant overdentures. Patients had a higher OHRQoL after incorporation of four implants in the overdenture compared with only two implants. Conclusion: Patients with implant-retained overdentures had better OHRQoL compared with those with conventional dentures. The number of incorporated implants in the locator-retained overdenture also influenced the increase in OHRQoL, with four implants having a statistically significant advantage over two implants. Keywords: intraindividual comparison, locator-retained overdenture, oral health-related quality of life, two- versus four-locator

Purpose: To evaluate changes in marginal bone levels around maxillary and mandibular mini-implants stabilizing complete dentures and to explore possible risk factors associated with bone loss. Materials and Methods: All eligible patients from nine private dental practices were invited to participate. Panoramic radiographs were obtained postoperatively and at the follow-up examination. The changes in bone level were estimated with linear mixed models that included the factors sex, age, jaw, region (anterior versus posterior), smoking habits, and loading concept. Results: Of the 180 invited patients, 133 participated in the followup (response rate: 73.9%). Of 336 mini-implants in 54 maxillas and 402 mini-implants in 95 mandibles, 15 maxillary implants and 11 mandibular implants were lost after insertion, and 4 mandibular implants fractured. Radiographic evaluations in 11 participants were not possible. The mean marginal bone loss at the remaining 634 mini-implants in 122 patients was 0.8 mm in the maxilla and 0.5 mm in the mandible over a mean observation time of 2.2 ± 1.0 years. This difference in univariate estimation lost significance after adjusting for the other variables. Implants in former smokers showed more bone loss than implants in participants who had never smoked. Implants that were loaded 3 to 4 months after placement (delayed loading) showed more marginal bone loss than immediately loaded implants. No statistically significant differences were found between men and women, different age groups, or anterior and posterior implants. Conclusion: Mean marginal bone loss around mini-implants used to stabilize complete dentures was insignificantly higher in the maxilla than in the mandible after a mean observation period of 2.3 years. These values are comparable with marginal bone loss around standard-diameter implants. A previous smoking habit and delayed loading after implant placement with a low insertion torque were shown to be possible risk factors for bone loss. Keywords: bone loss, edentulism, mini-implant, overdenture, risk factor

Purpose: To evaluate the survival rate of dental implants replacing failed implants in grafted maxillary sinuses using the lateral approach vs nongrafted posterior maxillae. Materials and Methods: A retrospective analysis was conducted to study the survival of secondary dental implants inserted in the posterior maxilla in previously failed implant sites between the years 2000 and 2010. The study group consisted of patients who had also undergone maxillary sinus augmentation, and the control group consisted of patients in whom implants in the posterior maxilla had failed. Clinical and demographic data were analyzed using a structured form. Results: Seventy-five patients with a total of 75 replaced implants were included in the study. The study group comprised 40 patients and the control group, 35 patients. None of the replaced implants in the study group failed, resulting in an overall survival of 100%; three replaced implants in the control group failed (92% survival). The main reason for the primary implant removal was lack of osseointegration (35 [87.5%] of 40 study group implants and 23 [65.7%] of 35 control group implants [P = .027]). The difference between the groups with regard to the timing of primary implant failure was statistically significant. The study group had more early failures of the primary implant than did the control group (77% vs 62%; P = .038). Conclusion: Dental implants replaced in the posterior maxilla had a high survival rate. A higher rate of survival was found in augmented maxillary sinus sites. Within the limits of the present study, it can be concluded that previous implant failures in the grafted maxillary sinus should not discourage practitioners from a second attempt. Keywords: failed implants, grafted maxillary sinuses, primary implants, re do implants, secondary implants

Purpose: To conduct a histomorphometric investigation comparing the use of enzyme-deantigenic equine bone (EDEB) and anorganic bovine bone (ABB) for maxillary sinus augmentation. Materials and Methods: Forty patients with Cawood Class V atrophic ridges who required maxillary sinus augmentation randomly received EDEB (n = 20) or ABB (n = 20) granules. Six months later, biopsy specimens were obtained, and implants were placed. Bone specimens were subjected to histomorphometric analysis, and newly formed bone (NFB) and residual biomaterial (RB) percentages were calculated. Patients were followed up for 3 years after definitive prosthetic rehabilitation, and implant success and survival rates were determined according to the criteria of Albrektsson and Zarb. Results: All patients healed uneventfully. Histomorphometric results for the EDEB were as follows: NFB = 46.86% ± 12.81% and RB = 11.05% ± 9.27%. For ABB, they were: NFB = 25.12% ± 7.25% and RB = 28.65% ± 9.70%. The difference was significant at a .05 level of confidence both for NFB and RB. At the 3-year follow-up, the implant survival rate was identical in the two groups (100%). Conclusion: Grafting with EDEB resulted in a greater quantity of NFB at implant insertion. No significant clinical differences were observed between the two patient groups at the 3-year follow-up. EDEB was as effective as ABB for sinus augmentation. Keywords: bone remodeling, biomaterial, sinus augmentation, xenograft

Purpose: Peri-implantitis is a disease characterized by soft tissue inflammation and continued loss of supporting bone, which can result in implant failure. Peri-implantitis is a multifactorial disease, and one of its triggering factors may be the presence of excess cement in the soft tissues surrounding an implant. This descriptive study evaluated the composition of foreign particles from 36 human biopsy specimens with 19 specimens selected for analysis. The biopsy specimens were obtained from soft tissues affected by peri-implantitis around cement-retained implant crowns and compared with the elemental composition of commercial luting cement. Materials and Methods: Nineteen biopsy specimens were chosen for the comparison, and five test cements (TempBond, Telio, Premier Implant Cement, Intermediate Restorative Material, and Relyx) were analyzed using scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. This enabled the identification of the chemical composition of foreign particles embedded in the tissue specimens and the composition of the five cements. Statistical analysis was conducted using classification trees to pair the particles present in each specimen with the known cements. Results: The particles in each biopsy specimen could be associated with one of the commercial cements with a level of probability ranging between .79 and 1. TempBond particles were found in one biopsy specimen, Telio particles in seven, Premier Implant Cement particles in four, Relyx particles in four, and Intermediate Restorative Material particles in three. Conclusion: Particles found in human soft tissue biopsy specimens around implants affected by peri-implant disease were associated with five commercially available dental cements. Keywords: dental cement, inflammation, foreign body particles, peri-implantitis

Purpose: To investigate whether bone regeneration can be accelerated by using a conditioned medium (CM) and guided bone regeneration (GBR) technique. Materials and Methods: CM was harvested from rat bone marrow stromal cells (BMSCs). The components of CM were immobilized using a polylactide-co-glycolide (PLGA) membrane treated with and without 0.5 mol/L sodium hydroxide (NaOH) to elevate the hydrophilicity. Four experimental groups were prepared: PLGA membrane treated with (1) phosphate-buffered saline (PBS; PBS-M), (2) PBS and 0.5 mol/L NaOH (hydrophilic treatment; PBS-HM), (3) CM (CM-M), and (4) CM and 0.5 mol/L NaOH (CM-HM). These experimental membranes were observed using scanning electron microscopy. Proteins derived from BMSCs immobilized on the PLGA membrane were detected with liquid chromatography-tandem mass spectrometry (LC/MS/MS). Cell proliferation and alkaline phosphatase (ALP) activity were measured to analyze the effect of CM on the BMSCs. Experimental membranes were transplanted into a rat calvarial bone defect model. Microcomputed tomography and histologic analyses were performed 4 and 8 weeks after transplantation. Results: The CM derived from BMSCs can be immobilized on the PLGA membrane. Hydrophilic treatment of the PLGA membrane enhanced the amount of CM immobilization. LC/MS/MS analysis showed that the immobilized proteins on the surface of PLGA membrane were extracellular matrix, such as collagen, decorin, and fibronectin. The proteins in the CM, which were released from the PLGA membrane, enhanced cell proliferation and ALP activity in rat BMSCs. Newly formed bone area at the bone defects that had been treated with CM-HM was significantly high compared with those at bone defects treated with the other membranes. Conclusion: The PLGA membrane treated with 0.5 mol/L NaOH and CM promoted bone regeneration in this rat calvarial defect model. Keywords: conditioned medium, guided bone regeneration, tissue engineering

Purpose: Concentrated growth factor (CGF) is an autologous leukocyte- and platelet-rich fibrin biomaterial that has recently been used for bone healing therapy. Previous studies used fibrin membrane or CGF extract without fibrin without soluble factors in vitro. This study investigated the effects of CGF that contained soluble factors on cultured rat bone marrow (RBM) cells in vitro. Furthermore, the effects of CGF implanted in rat calvarial bone defects in vivo were also investigated. Materials and Methods: CGF and platelet-poor plasma (PPP) gel, which both have fibrin networks, were prepared from rat blood. For the in vitro study, CGF and PPP gel were frozen, and thin sections approximately 30 μm thick were cut and coated onto the surfaces of cell disks. RBM cells were then harvested and cultured on the coated disks in serum-free medium. For the in vivo study, rat calvarial bone defects (3.8 mm in diameter) were created and implanted with CGF, PPP gel, or left unfilled. Results: In vitro, the actin stress fibers of RBM cells cultured on disks coated with CGF or PPP gel tended to extend more than cells cultured on uncoated disks. However, no significant difference was observed in terms of cell morphology between RBM cells cultured on CGF- and PPP gel-coated disks. Cell proliferation and osteoblastic differentiation were significantly higher in cells cultured on the CGF-coated disks than on the PPP gel-coated disks. In vivo, more new bone had formed in defects treated with CGF than in defects treated with PPP gel. Conclusion: In this preliminary study, fibrin and soluble factors in CGF promoted initial cell stretching, proliferation, and osteoblastic differentiation of RBM cells in vitro and bone regeneration in rat calvarial bone defects in vivo. Keywords: bone healing, bone marrow, calvarial bone defect, concentrated growth factor, platelet-poor plasma gel

Purpose: The aim of this study was to determine the effect of collagenated biphasic calcium phosphate (CBCP) loaded with fibroblast growth factor-2 (FGF-2) on bone regeneration in a rabbit sinus model. Materials and Methods: Bilateral sinus augmentations were performed using either FGF-2-loaded CBCP (FGF-2 group) or CBCP only (control group) in 10 rabbits. The experimental animals were euthanized at 2 weeks (n = 5) or 4 weeks (n = 5) postoperatively. Volumetric analyses were done by means of microcomputed tomography and histomorphometry. Results: The volumes of total augmentation, new bone, residual material, and fibrovascular tissue were significantly greater in the FGF-2 group than in the control group at 2 weeks, but the differences between the two groups had disappeared by 4 weeks. Histologically, the healing patterns, such as new bone formation and the resorption of residual material, did not differ notably between the two groups. The results of the histometric analysis did not correspond to those of the volumetric analysis. The areas of total augmentation, new bone, residual material, and fibrovascular tissue, and the number of blood vessels did not differ significantly between the FGF-2 and the control groups at either time point. Conclusion: CBCP loaded with FGF-2 resulted in the early promotion of new bone; however, it failed to produce superior bone regeneration in a later stage of healing. Keywords: animal model, bone regeneration, bone substitute, fibroblast growth factor-2, maxillary sinus