Periodontal Pathogen Adhesion, Cytotoxicity, and Surface Free Energy of Different Materials for an Implant Prosthesis Screw Access Hole.

Background and Objectives: Oral implant restorations are an excellent treatment option for edentulous patients; however, periodontopathogenic bacteria have been found in the microgaps between implant-abutment junctions. Implant designs to limit the microgaps have been extensively studied. However, studies have shown microgaps continue to exist, allowing for the leakage of bacteria into the implant system. Screw access hole materials are used to fill the access hole void. The use of materials with beneficial properties could provide bacterial leakage prevention. The aim of this study was to examine the surface free energy, cytotoxicity, and bacterial adhesion of selected screw access hole materials such as cotton, polytetrafluoroethylene (PTFE) tape, paraffin wax-polyolefin thermoplastic (PF), paraffin wax (Wax), gutta-percha (GP), and caviton EX (CE). Materials and Methods: A sessile drop test was performed to observe the contact angle and calculate the surface free energy of each material in order to determine the level of hydrophobicity. Cytotoxicity was examined in a mouse gingival epithelial cell line for day 1 and day 3. Bacterial adhesion was tested with Porphyromonas gingivalis, Fusobacterium nucleatum, and Aggregatibacter actinomycetemcomitans. Results: PTFE, PF, and wax presented low surface free energies of 19.34, 23.041, and 24.883 mN.m-1, respectively. No cytotoxicity was observed, except for GP and CE. Concurrently, the bacterial adhesion was also the lowest in PTFE and PF. Conclusions: Within the limits of this study, PTFE and PF showed an excellent biocompatibility with few bacterial adhesions. These materials could be potential screw access hole materials in clinical settings.

Comparison of gingiva-derived and bone marrow mesenchymal stem cells for osteogenesis.

Presently, bone marrow is considered as a prime source of mesenchymal stem cells; however, there are some drawbacks and limitations. Compared with other mesenchymal stem cell (MSC) sources, gingiva-derived mesenchymal stem cells (GMSCs) are abundant and easy to obtain through minimally invasive cell isolation techniques. In this study, MSCs derived from gingiva and bone marrow were isolated and cultured from mice. GMSCs were characterized by osteogenic, adipogenic and chondrogenic differentiation, and flow cytometry. Compared with bone marrow MSCs (BMSCs), the proliferation capacity was judged by CCK-8 proliferation assay. Osteogenic differentiation was assessed by ALP staining, ALP assay and Alizarin red staining. RT-qPCR was performed for ALP, OCN, OSX and Runx2. The results indicated that GMSCs showed higher proliferative capacity than BMSCs. GMSCs turned more positive for ALP and formed a more number of mineralized nodules than BMSCs after osteogenic induction. RT-qPCR revealed that the expression of ALP, OCN, OSX and Runx2 was significantly increased in the GMSCs compared with that in BMSCs. Moreover, it was found that the number of CD90-positive cells in GMSCs elevated more than that of BMSCs during osteogenic induction. Taking these results together, it was indicated that GMSCs might be a promising source in the future bone tissue engineering.

Indirect osteoblast differentiation by liposomal clodronate.

Bisphosphonates impair function of osteoclasts and prevent bone resorption, the mechanism of which has been studied extensively. However, the possible effects of bisphosphonates on chondroblast differentiation and calcium deposition by osteoblasts have only been demonstrated recently. Moreover, cells from monocytic lineage are capable of stimulating osteoblast proliferation. Hence, susceptibility of osteoblasts to various factors requires further investigation. A primary culture of bone marrow-derived stromal cells was treated with liposomal clodronate (0.1, 0.5, or 1.0 mg/ml) or conditioned medium from liposomal clodronate. Liposomal clodronate (0.25 mg) was injected into mouse femur for in vivo experiments. The effects of liposomal clodronate were examined by alkaline phosphatase staining and/or activity assay, and real-time RT-PCR was used for studying the effect on osteogenic gene expression. Administration of liposomal clodronate to bone marrow-derived mesenchymal stromal cell culture enhanced alkaline phosphatase activity and mRNA levels of Runx2 and Dlx5. In addition, conditioned medium from liposomal clodronate also stimulated osteogenic characteristics similar to those of observed in vitro, and the number of exosomes in the conditioned medium was highest when pre-treated with liposomal clodronate. Western blot analysis revealed the presence of RANK proteins in exosomes collected from conditioned medium of liposomal clodronate. Identical observations were obtained in vivo, as liposomal clodronate-injected mouse femur showed increased alkaline phosphatase activity and Runx2 and Dlx5 mRNA expressions, even though the numbers of monocytes and macrophages were reduced. In conclusion, osteoblast differentiation was promoted via soluble RANK-containing exosomes in response to clodronates.

Injectable simvastatin gel for minimally invasive periosteal distraction: In vitro and in vivo studies in rat.

OBJECTIVES: To evaluate whether the subperiosteal injection of simvastatin (SIM) with a novel in situ gel-forming system, SrHA/Alg (strontium hydroxyapatite/alginate), can stimulate vertical bone augmentation in a rat calvarial model. MATERIAL AND METHODS: The SrHA/Alg solution was synthesized and combined with different doses of SIM (0.01, 0.02, 0.1, and 0.2 mg) to form the following groups: (1) SrHA/Alg only, (2) SrHA/Alg/0.01, (3) SrHA/Alg/0.02, (4) SrHA/Alg/0.1, and (5) SrHA/Alg/0.2. The SIM release pattern was analyzed, and rat primary periosteum-derived cell (PDC) responses were investigated. Twenty male Wistar rats were enrolled in the calvarial subperiosteal injection experiment with each animal receiving a 200-µl single subperiosteal injection of SrHA/Alg with different amounts of SIM (0, 0.01, 0.02, and 0.1 mg) incorporated (n = 5). The 0.2 mg dose group was not tested in vivo due to the severe toxicity found in vitro. The new bone formation was assessed histologically and radiologically at 8 weeks. RESULTS: The slow release of SIM was confirmed, and PDC viability decreased in the SrHA/Alg/0.2 group. Alkaline phosphatase positive areas and mineralization areas were significantly greater in the SrHA/Alg/0.01 and SrHA/Alg/0.02 groups (p < .05). The mRNA expression level of Runx2 significantly increased in the SrHA/Alg/SIM-0.02 group by day 7 (p < .05) and significantly higher levels of VEGF were found in the SrHA/Alg/0.01 and SrHA/Alg/0.02 groups at different time points (p < .05). In vivo, no prominent clinical sign of inflammation was observed, and the most significant bone gain was shown in the SrHA/Alg/0.02 group (p < .05). The osteoclast formation within the newly formed bone area was reduced in the SrHA/Alg/0.1 group (p < .05). CONCLUSIONS: When combined with SrHA/Alg system, the 0.02 mg SIM seemed to be the optimal dose to stimulate subperiosteal bone formation without inducing inflammation. This combination may hold potential therapeutic benefits for clinical bone augmentation in a minimally invasive manner.

A diversity of peri-implant mucosal thickness by site.

OBJECTIVES: The objective of this study was to examine peri-implant mucosal thickness at different sites of peri-implant crevice around 70 implants placed in 35 patients. MATERIAL AND METHODS: The peri-implant mucosal thickness was defined as distance of the peri-implant mucosal margin and the coronal edge of bone/implant contact and measured using the cast models and dental radiography. RESULTS: The overall mean peri-implant mucosal thickness was 3.6 ± 1.4 mm, wherein maxillary anterior implants, maxillary posterior implants and mandibular posterior implants had significantly different dimensions of median thickness of 4.25, 3.75 and 3.0 mm, respectively. Furthermore, the mesial and distal sites of those positioned implants measured unevenness in the thickness especially in the maxillary posterior region with statistical significance. CONCLUSION: The proposed methodology to evaluate peri-implant mucosal thickness measured with a big variation from overall 3.6 mm with a big variation from 1.6 to 7.0 mm in healthy volunteers. And significant difference was found in the depth among the three regions and, statistically, dispersion of individual peri-implant mucosal thickness resulted in lack of consistency. Although dental implants have been well developed, predictable and prevailing prosthetics, onset of peri-implantitis might be inevitable in some cases. Therefore, establishment of a standardized dimensional diagnosis of peri-implant tissues followed by pathologic ascertainment could be taken into account for the prevention or curing of peri-implantitis.

Ligature induced peri-implantitis: tissue destruction and inflammatory progression in a murine model.

OBJECTIVES: The aim of this study was to investigate tissue destruction and inflammatory progression of ligature-induced peri-implantitis in mice and to establish an alternative murine model of peri-implantitis. MATERIAL AND METHODS: Sixty male C57BL/6NCrSlc mice (4-week-old) were used and the maxillary right first molars were extracted. Eight weeks after extraction, custom-made pure titanium machined screw type implants (0.8 × 1.5 mm) were placed, one implant per animal. Four weeks later, 5-0 silk ligatures were applied around implant necks to induce peri-implantitis. Animals were sacrificed at 0 (before ligature), 7, 14, 21 and 28 days after ligature. Half of the samples were analyzed radiologically and histologically to measure bone level change, osteoclast number, density, and distribution. The rest of the samples was used to determine the relative mRNA expression levels of IL-1 and TNF-α with RT-PCR analysis. RESULTS: Bone levels at all sites (buccal, palatal, mesial, distal) decreased 40-50% significantly 28 days after ligature (P < 0.01). Osteoclast number at all post-ligature time points increased significantly (P < 0.05). However, their density at day 28 decreased significantly compared to that of day 21 (P < 0.05). Accordingly, IL-1 and TNF-α mRNA expression increased significantly at the early time points but decreased significantly at day 28 after ligature (P < 0.05). CONCLUSIONS: Inflammatory response followed by significant peri-implant bone resorption suggested 28 days ligation is sufficient to successfully induce peri-implantitis in the current mice model. This model might open a new avenue to study the pathogenesis and mechanism of peri-implantitis.

Bioresorbable zinc hydroxyapatite guided bone regeneration membrane for bone regeneration.

OBJECTIVES: The aim of this study was to investigate the bone regenerative properties of a heat treated cross-linked GBR membrane with zinc hydroxyapatite powders in the rat calvarial defect model over a 6-week period. MATERIAL AND METHODS: In vitro physio-chemical characterization involved X-ray diffraction analysis, surface topology by scanning electron microscopy, and zinc release studies in physiological buffers. Bilateral rat calvarial defects were used to compare the Zn-HAp membranes against the commercially available collagen membranes and the unfilled defect group through radiological and histological evaluation. RESULTS: The synthesized Zn-MEM (100 µm thick) showed no zinc ions released in the phosphate buffer solution (PBS) buffer, but zinc was observed under acidic conditions. At 6 weeks, both the micro-CT and histological analyses revealed that the Zn-MEM group yielded significantly greater bone formation with 80 ± 2% of bone filled, as compared with 60 ± 5% in the collagen membrane and 40 ± 2% in the unfilled control group. CONCLUSION: This study demonstrated the use of heat treatment as an alternative method to cross-linking the Zn-MEM to be applied as a GBR membrane. Its synthesis and production are relatively simple to fabricate, and the membrane had rough surface features on one side, which might be beneficial for cellular activities. In a rat calvarial defect model, it was shown that new bone formation was accelerated in comparison with the collagen membrane and the unfilled defect groups. These results would suggest that Zn-MEM has the potential for further development in dental applications.

Effects of Abutment Removal and Reconnection on Inflammatory Cytokine Production Around Dental Implants.

OBJECTIVES: The purpose of this study was to examine effects of abutment change on inflammatory cytokine production around implants. MATERIALS AND METHODS: Ten partially edentulous patients with a mean age of 60 years were recruited and divided into 2 groups. External Brånemark implants with anodic oxidized surface were installed and submerged in all patients. In the control group, the healing abutments were delivered at the second surgery, and they were removed more than 3 times till the final prosthesis delivery. In the test group, the final abutments were delivered at the second surgery. At different time points during the treatment, periimplant crevicular fluid was collected, and proinflammatory cytokines (interleukin-1ß [IL-1ß] and tumor necrosis factor [TNF]-α) were measured with enzyme-linked immunosorbent assay. The bone level was measured on the radiograms and clinical indices were also taken. RESULTS: All implants were osseointegrated. In the test group, IL-1ß level and probing depths were less in test group patients compared with the control group patients, whereas TNF-α level and bone level were not different between the groups. CONCLUSION: Although TNF-α and bone levels were not significantly different, delivering final abutment at the second surgery would induce less inflammation in the tissues around the implant.

Bone regeneration of rat tibial defect by zinc-tricalcium phosphate (Zn-TCP) synthesized from porous Foraminifera carbonate macrospheres.

Foraminifera carbonate exoskeleton was hydrothermally converted to biocompatible and biodegradable zinc-tricalcium phosphate (Zn-TCP) as an alternative biomimetic material for bone fracture repair. Zn-TCP samples implanted in a rat tibial defect model for eight weeks were compared with unfilled defect and beta-tricalcium phosphate showing accelerated bone regeneration compared with the control groups, with statistically significant bone mineral density and bone mineral content growth. CT images of the defect showed restoration of cancellous bone in Zn-TCP and only minimal growth in control group. Histological slices reveal bone in-growth within the pores and porous chamber of the material detailing good bone-material integration with the presence of blood vessels. These results exhibit the future potential of biomimetic Zn-TCP as bone grafts for bone fracture repair.

A modal analysis of implant-supported overdentures installed on differently positioned sets of dental implants.

This study evaluated the three vibration characteristics, namely, natural frequency, damping ratio, and natural mode, together with maximum displacement of a two-implant-supported overdenture (IOD) at different locator attachment positions using experimental modal analysis (EMA). Edentulous mandibular models with a gingival thickness of 1 mm or 3 mm were prepared, into which dental implants were placed using a fully guided surgical template designed with simulation software, the locator abutments were fastened, and the IODs were then fabricated. The implant positions were bilaterally marked at the lateral incisor, first premolar, and first molar regions. EMA was performed by hammering the test structures to measure the impulse response and obtain the vibration characteristics (n = 5). The Kruskal-Wallis test was performed for natural frequency and maximum displacement, and the Games-Howell test for damping ratio. The significance level was set at α = 0.05. The study indicated that the gingival thickness had a significant effect on the vibration characteristics. Moreover, the natural frequency and damping ratio results showed that the vibration subsided faster when the attachment was placed on the molar implants in the thick gingival model. Furthermore, according to the effect of lateral force on IODs, the difference in maximum displacement between the anterior and posterior regions of the IOD was smaller when the attachments were designed on the pair of lateral incisors. Thus, within the limits of this experiment, our results suggested that two anterior implant-supported IODs are preferable treatment designs in terms of vibration engineering, especially when the gingiva is thick; the molar attachment design could be considered for thin gingival conditions. The differences in gingival thickness and abutment position affected the vibration characteristics of the IOD. Further in vivo studies would be necessary to validate the implant positions and their IOD designs for the mandibular edentulous shapes and the occlusal relationship.

An In Vitro Evaluation of Selenium Nanoparticles on Osteoblastic Differentiation and Antimicrobial Properties against Porphyromonas gingivalis.

Despite numerous treatment methods, there is no gold standard for the treatment of peri-implantitis-an infectious peri-implant disease. Here, we examined selenium nanoparticles (SeNPs) at a wide range of concentrations to investigate their cytotoxicity, regulation of osteoblastic differentiation, and assessed the antibacterial effect against Porphyromonas gingivalis. SeNPs (mean size: 70 nm; shape: near-spherical; concentration: 0-2048 ppm) were tested against the MC3T3-E1 osteoblast precursor cell line and P. gingivalis red complex pathogen. Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) analysis was used to evaluate the bone morphogenetic protein 2 (BMP-2) signaling pathway. SeNPs at concentrations of 2-16 ppm showed no obvious cytotoxicity and promoted good mineralization and calcification. SeNPs at concentrations 64 ppm and below influenced gene expression promoting osteoblastic differentiation, whereas at high concentrations inhibited the expression of Runt-related transcription factor 2 (Runx2). The growth of P. gingivalis was significantly inhibited at SeNP concentrations of more than 4 ppm. SeNPs at low concentrations promoted osteoblastic differentiation while strongly inhibiting peri-implantitis pathogen growth. This study represents one of the few in vitro assessments of SeNPs against a red complex pathogen and the regulatory effect on osteoblastic differentiation. The findings demonstrate SeNPs could potentially be used for future application on implant coating.

Fluctuation of salivary alpha-amylase activity levels and vital signs during dental implant surgery.

BACKGROUND: Salivary alpha-amylase (sAA) activity level is thought to be an indicator of mental stress. However, the relationship between sAA activity levels and mental stress in patients during dental implant treatment has not been studied. In the present study, we aimed to examine the correlation between sAA activity levels and changes in patients' vital signs during dental implant surgery. RESULTS: Levels of sAA activity were higher after surgery when compared to before-surgery measurements. A significant positive correlation was found between sAA activity and heart rate (HR) (rs=0.434, p=0.007) as well as a positive correlation with oxygen level (rs=0.392, p=0.016). CONCLUSION: Levels of sAA activity tended to increase after the surgical procedures, as did patients' stress levels. SpO2 and sAA activity levels were inversely correlated. There was a positive significant correlation between HR and sAA activity, though there was no correlation between blood pressure and sAA activity levels. Salivary alpha-amylase may be a valuable indicator of stress and anxiety in dental patients undergoing dental implant surgery.

Evaluation of a Cetylpyridinium Chloride-, Dipotassium Glycyrrhizinate-, and Tranexamic Acid-based Mouthwash after Implant Placement: A Double-blind Randomised Clinical Trial.

PURPOSE: To evaluate the positive effects of a CPC-, GK2-, and TXA-based (CPC/GK2/TXA) mouthwash after implant placement. MATERIALS AND METHODS: Twenty patients (n = 20) who underwent posterior implant-placement surgery were randomly and evenly allocated to the study or the placebo group. After the mouthwash was used 3x/day for 7 to 10 days postoperatively, sutures were analysed by counting the colony-forming units (CFU) for total aerobes, total G [-] anaerobes, total enterobacteria and total H. influenzae, followed by Real-Time PCR of bacterial-specific DNAs of A. actinomycetemcomitans, P. gingivalis, T. forsythia, T. denticola, P. intermedia, P. micra, F. nucleatum, C. rectus, and E. corrodens. In vitro resistance of P. gingivalis, S. aureus, and P. aeruginosa was analysed. The compatibility of the mouthwash with Straumann SLA implant surfaces was evaluated by scanning electron microscopy (SEM). RESULTS: Sixteen patients (n = 16) completed the trial. A statistically significantly greater number of CFU was found in the placebo group for almost all species, especially for total G [-] anaerobes. No statistically significant in vitro resistance was found for P. gingivalis, S. aureus, and P. aeruginosa. SEM revealed no surface alteration after exposure to the mouthwash. CONCLUSION: The use of a CPC/GK2/TXA mouthwash inhibited propagation of the bacteria extracted from the post-surgical sutures after implant placement.

Low-Intensity Pulsed Ultrasound Stimulates Osteogenic Differentiation of Periosteal Cells In Vitro.

Adequate bone volume is required for osseointegrated implants to restore lost teeth and oral function. Several studies have demonstrated potential advantage of stem cells in regenerative medicine using osteoblasts. The periosteum is composed of osteoblasts, fibroblasts, and osteoprogenitor cells. It may be an alternative source for bone tissue engineering because of easy isolation and rapid proliferation in vivo and in vitro. Low-intensity pulsed ultrasound (LIPUS) has proved successful in recoveries from nonunions, delayed unions, and fracture of the bone in both animal experiments and clinical treatments. The study was to investigate the influence of LIPUS on the osteogenic differentiation in murine periosteum-derived cells (PDCs) and the underlying mechanism of LIPUS. PDCs were treated daily with LIPUS for 20 min up to 21 days with 3 MHz frequency, 30 mW/cm2 intensity, and pulse repetition frequency of 1 kHz. The effects of LIPUS on cell proliferation and viability were investigated. Osteogenic differentiation was analyzed by alkaline phosphatase (ALP)-positive cell staining, ALP activity assay, mineralized nodule formation, real-time reverse transcription-polymerase chain reaction, as well as western blotting. The results indicated that ultrasound stimulation did not significantly affect the proliferation of PDCs. But LIPUS significantly increased ALP activity on day 7 and markedly promoted formation of mineralized nodules on day 21. mRNA expression of ALP and osteocalcin was significantly upregulated by stimulation with LIPUS. LIPUS enhanced gene expression of both bone morphogenetic protein-2 (BMP-2) and osterix only in the presence of osteogenic medium. LIPUS stimulation did not affect Smad 1 and Smad 5 protein expression, but significantly upregulated protein levels of BMP-2 and phosphor-Smad 1/5/9 in PDCs. Thus, LIPUS stimulation increased early osteogenic differentiation in a normal medium and further enhanced expression of BMP-2 and subsequent osterix expression through the canonical Smad-signaling pathway in an osteogenic medium, leading to mineral apposition. Therefore, LIPUS might have potential to promote osteogenesis in PDCs. Impact statement There are few studies on periosteum-derived cells (PDCs) because conventional methods of their isolation are relatively difficult to procure abundant cells for cell culture and the total cell numbers are limited. In this study, a modified isolation technique of murine calvarial PDCs using gelatin is described. PDCs were initiated to emerge as early as day 3 and showed increased proliferation, which can be used for further studies. Low-intensity pulsed ultrasound stimulation increased early osteogenic differentiation in a normal medium and further enhanced expression of bone morphogenic protein-2 and subsequent osterix expression through the canonical Smad-signaling pathway in an osteogenic medium, leading to mineral apposition.

Evaluation of residual contamination on healing abutments after cleaning with a protein-denaturing agent and detergent.

OBJECTIVE: This study evaluated the cleaning potential of a protein-denaturing agent with or without anionic detergent by monitoring the residual contamination on healing abutments used for dental implant treatment. METHOD AND MATERIALS: Forty contaminated healing abutments removed from patients were randomized and immediately treated with differing cleaning methods; either Method A (presoaking in 1% sodium dodecyl sulfate followed by ultrasonication with 4 mol/L guanidine hydrochloride), or Method B (soaking in distilled water followed by ultrasonication with 4 mol/L guanidine hydrochloride) was used. Samples were stained with phloxine B and photographed using a light microscope. The proportion of stained and contaminated areas on each healing abutment was then calculated using Image J. The surface was examined with a scanning electron microscope and energy-dispersive x-ray spectroscopy. RESULTS: The percentages of contaminated surfaces of the screwdriver engagement region, upper body, and lower body for methods A and B were 50% and 38%, 10% and 80%, and 38% and 18%, respectively. There was a statistically significant difference (engagement region [P < .001], upper body [P = .043], and lower body [P = .017]; Mann-Whitney) regarding the residually stained areas between the two cleaning methods. No surface alterations were seen by scanning electron microscopy. Energy-dispersive x-ray spectroscopy confirmed that the cleaned surfaces of the healing abutments revealed no signs of organic contamination. CONCLUSION: Although the combination of a strong denaturing agent and detergent effectively cleaned contaminated healing abutments, perfect cleaning was not always possible, indicating that the reuse of healing abutments in different patients is not recommended.

Comparison of splinted and non-splinted superstructures of three implants placed in a mandibular distal extension model with missing teeth using modal analysis.

This study evaluated the effects of two types of superstructures (splinted crown and non-splinted crown) on four vibration characteristics (natural frequency, damping ratio (DAR), vectors in antiphase, maximum displacement (MDP)) by using modal analysis. These structures were fabricated on three implants placed in the mandibular free-end defect model. After placing three implants on a mandibular distal extension model with missing teeth, the three-unit splinted and non-splinted crowns were designed on the CAD software. Subsequently, the zirconia disc was milled using a milling machine to produce the superstructures (n = 5). After establishing four measurement points on each crown of the prostheses, a vibration was applied to the mandible model with an impact hammer, and the transfer function of each measurement point was identified. Using the modal analysis software, the natural frequency and damping ratios were calculated from the transfer function, modal shapes at each natural frequency were observed, and maximum displacement that takes into account the lateral force during mastication was simulated. The t-test was performed for each of the averaged values of natural frequency, maximum displacement, and damping ratio (p < 0.05). Mann-Whitney U test was performed on the average of the number of vectors in antiphase (p < 0.05). The mean natural frequency was significantly higher in the splinted crown (758.2 ± 2.8 Hz) than that in the non-splinted crown (752.8 ± 3.7 Hz) (P = 0.047). The mean damping ratio was not significantly different for the splinted (3.3 ± 0.2%) and non-splinted crowns (3.2 ± 0.3%) (P = 0.535). The average number of vectors in antiphase was significantly smaller in the non-splinted crown (4.4 ± 0.9) than in the splinted crown (10 ± 2.5) (P = 0.008). The mean value of the maximum displacement was significantly smaller in the splinted crown (6.7 ± 1.1 µm) than that in the non-splinted crown (7.3 ± 0.6 µm) (P = 0.048). Within the limitations of this study, the vibration characteristics of the superstructures differed between designs with splinted and non-splinted crowns. Crown splinting increased the rigidity and natural frequency and decreased the MDP. However, the higher number of vectors in antiphase indicated more twists in the superstructures during vibration. The non-splinted crowns showed a lower natural frequency and a greater maximum displacement; however, they comprised fewer vectors in antiphase, indicating that the twist during vibration was less than that observed with the splinted crowns. Thus, our results suggest that crown splinting reduces the deformation of the superstructure, implants, and the surrounding tissues in comparison to the deformation observed when no splinting is performed.

Modal analysis of two different types of fixed implant-supported prostheses embedded in edentulous maxillae.

PURPOSE: Modal analysis has been used to monitor and quantify the vibration of each component of a prosthesis at its natural frequency. An understanding of the vibrational characteristics of a prosthesis can guide selection of the appropriate prosthesis configuration to prevent excessive stress. In this study, modal analysis of fixed implant-supported prostheses with 4 or 6 abutments in edentulous maxillae was performed. METHODS: Sixteen patients underwent maxillary dental implant treatment and received screw-fixed implant-supported prostheses (9 patients received 4-abutment prostheses and 7 patients received 6-abutment prostheses) in edentulous maxillae. An impact hammer was used for excitation of the prostheses, and vibration was detected on every crown of the prostheses. The modal parameters were determined in each subject. Furthermore, the modal shapes were compared at each natural frequency. RESULTS: The median natural frequencies of subjects with 4- and 6-abutment prostheses were 697 and 781Hz, respectively. The mean damping ratios did not differ significantly between 4- (8.2±1.7%) and 6-abutment (6.6±1.7%) prostheses (p=0.125). The mean maximum displacements of fixed prostheses were significantly lower for 6-abutment (10.3±3.3µm) than for 4- (20.3±9.1µm) prostheses (p=0.004). The median number of vectors in antiphase was significantly lower for 6- (4) than for 4-abutment prostheses (14) (p=0.001). CONCLUSIONS: The current study demonstrated less adverse vibration in the 6-abutment prostheses than in the 4-abutment prostheses, suggesting that modal analysis can contribute to novel future developments in the designs of dental implant prostheses.

Effect of doxycycline-treated hydroxyapatite surface on bone apposition: A histomophometric study in murine maxillae.

Improved osseointegration of dental implants is imperative in clinic. Effect of doxycycline on promoting bone formation after implant placement was expected due to its inhibitory properties on inflammation and osteoclastogenesis. To evaluate new bone formation on the hydroxyapatite (HA)-coated implant surface, which was treated with doxycycline, in comparison with the untreated HA surface, half of the HA-coated implants were soaked in doxycycline solution (DOX group) whereas the other HA-coated implants were untreated (HA group). Eight weeks after extracting the maxillary first molars of 4-week-old male mice, the implants of both groups were placed at the extracted site. 4 and 8 weeks after surgery, the samples were evaluated radiologically and histomorphometrically. Bone-implant contact of DOX group was statistically higher than the one of HA group at 4 and 8 weeks. New bone area between the threads of the implants also statistically increased at 8 weeks in DOX group compared to HA group.

Liposome-encapsulated plasmid DNA of telomerase-specific oncolytic adenovirus with stealth effect on the immune system.

Oncolytic virotherapy has the disadvantage of being unsuitable for systemic delivery due to immune elimination. Liposomal encapsulation is well-recognized to reduce immune elimination and enhance the stability of drugs in the bloodstream. In the present study, the potential of liposome-encapsulated plasmid DNA of telomerase-specific oncolytic adenovirus (TelomeScan) expressing GFP (Lipo-pTS) as an oncolytic adenoviral agent suitable for systemic delivery was investigated. Lipo-pTS, which has a diameter of 40-50 nm, showed potent antitumor effects on HCT116 colon carcinoma cells in vitro and in vivo. Tumor selectivity of Lipo-pTS was independent of coxsackie and adenovirus receptor (CAR). Importantly, Lipo-pTS reduced production of adenovirus-neutralizing antibodies (AdNAbs) after intravenous administration into immune-competent mice compared to TelomeScan, and even in the presence of AdNAbs, Lipo-pTS maintained strong cytotoxicity. In conclusion, Lipo-pTS has the potential to become an oncolytic adenoviral agent suitable for systemic delivery with the characteristics of CAR-independent antitumor activity and a stealth effect on the immune system.

Local application of rhTGF-beta2 modulates dynamic gene expression in a rat implant model.

Various anabolic agents, including transforming growth factor-beta (TGF-beta), have been shown to enhance intramembranous bone regeneration and strengthen the mechanical connection between implant and host skeleton, a prerequisite for clinical success with orthopedic and dental implants. Mechanisms underlying these observations at the level of the gene have received little attention. A rat model was used to examine levels of gene transcription for 21 "osteogenic" genes by real-time polymerase chain reaction at days 1, 3, 5, 7, 10, 14, and 28 in a control group and a group in which the implant was treated with 1 microg recombinant human TGF-beta2 (n = 42, equally divided among the 2 groups and 7 time points). Genes were chosen to represent three functional categories: (1) growth factors, their receptors and antagonists; (2) bone differentiation markers; and (3) inflammation markers. Examination of the transcription profiles showed that nine genes had up-regulated or down-regulated expression levels without a change in timing and 12 genes had accelerated or delayed expression profiles with or without a concomitant change in maximal or minimal expression. The earliest changes (days 1-3) involved accelerated expression profiles for IGF-1R and VEGF and up-regulation of TGF-beta2, TbetaRI, BMP-2, BMP-7, and Cbfa1. Furthermore, principal components analyses showed that some subsets of genes were co-expressed in both groups, although the temporal relationship of these subsets was altered following growth factor treatment. Thus, in addition to changes in individual transcription profiles, the regulatory connections between sets of co-expressed genes may also be affected by exogenously delivered anabolic agents during bone regeneration.