Koopman and Perron-Frobenius operators on reproducing kernel Banach spaces.

Koopman and Perron-Frobenius operators for dynamical systems are becoming popular in a number of fields in science recently. Properties of the Koopman operator essentially depend on the choice of function spaces where it acts. Particularly, the case of reproducing kernel Hilbert spaces (RKHSs) is drawing increasing attention in data science. In this paper, we give a general framework for Koopman and Perron-Frobenius operators on reproducing kernel Banach spaces (RKBSs). More precisely, we extend basic known properties of these operators from RKHSs to RKBSs and state new results, including symmetry and sparsity concepts, on these operators on RKBS for discrete and continuous time systems.

Stem Cell Transplantation and Cell-Free Treatment for Periodontal Regeneration.

Increasing attention has been paid to cell-based medicines. Many in vivo and in vitro studies have demonstrated the efficacy of stem cell transplantation for the regeneration of periodontal tissues over the past 20 years. Although positive evidence has accumulated regarding periodontal regeneration using stem cells, the exact mechanism of tissue regeneration is still largely unknown. This review outlines the practicality and emerging problems of stem cell transplantation therapy for periodontal regeneration. In addition, possible solutions to these problems and cell-free treatment are discussed.

Periodontal and peri-implant wound healing following laser therapy.

Laser irradiation has numerous favorable characteristics, such as ablation or vaporization, hemostasis, biostimulation (photobiomodulation) and microbial inhibition and destruction, which induce various beneficial therapeutic effects and biological responses. Therefore, the use of lasers is considered effective and suitable for treating a variety of inflammatory and infectious oral conditions. The CO2 , neodymium-doped yttrium-aluminium-garnet (Nd:YAG) and diode lasers have mainly been used for periodontal soft-tissue management. With development of the erbium-doped yttrium-aluminium-garnet (Er:YAG) and erbium, chromium-doped yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers, which can be applied not only on soft tissues but also on dental hard tissues, the application of lasers dramatically expanded from periodontal soft-tissue management to hard-tissue treatment. Currently, various periodontal tissues (such as gingiva, tooth roots and bone tissue), as well as titanium implant surfaces, can be treated with lasers, and a variety of dental laser systems are being employed for the management of periodontal and peri-implant diseases. In periodontics, mechanical therapy has conventionally been the mainstream of treatment; however, complete bacterial eradication and/or optimal wound healing may not be necessarily achieved with conventional mechanical therapy alone. Consequently, in addition to chemotherapy consisting of antibiotics and anti-inflammatory agents, phototherapy using lasers and light-emitting diodes has been gradually integrated with mechanical therapy to enhance subsequent wound healing by achieving thorough debridement, decontamination and tissue stimulation. With increasing evidence of benefits, therapies with low- and high-level lasers play an important role in wound healing/tissue regeneration in the treatment of periodontal and peri-implant diseases. This article discusses the outcomes of laser therapy in soft-tissue management, periodontal nonsurgical and surgical treatment, osseous surgery and peri-implant treatment, focusing on postoperative wound healing of periodontal and peri-implant tissues, based on scientific evidence from currently available basic and clinical studies, as well as on case reports.

Antimicrobial photodynamic therapy suppresses dental plaque formation in healthy adults: a randomized controlled clinical trial.

BACKGROUND: Oral care is important for oral and systemic health, especially for elderly institutionalized individuals and compromised patients. However, conventional mechanical plaque control is often difficult for these patients because of the pain or the risk of aspiration. Although antimicrobial photodynamic therapy (aPDT), which is considered an alternative or adjunct to mechanical approaches, has potential application as a less stressful method of daily plaque control, no clinical application of this technique has been reported. METHODS: We investigated the inhibitory effect of a combination of toluidine blue O (TBO), and a red light-emitting diode (LED) on dental plaque formation in healthy volunteers. The optimal concentration of TBO was determined in preliminary in vitro experiments to evaluate the bactericidal effect of aPDT on Streptococcus oralis and to clarify its safety in fibroblast cells. To survey the mechanism of TBO-mediated aPDT, the quality and quantity of reactive oxygen species (ROS) generated during aPDT were also examined using electron spin resonance (ESR) spectroscopy. Subsequently, the inhibitory effect of aPDT on dental plaque formation was investigated in eleven subjects as a clinical pilot study. The right or left mandibular premolars were randomly assigned to the treatment (with aPDT) or control (without aPDT) groups. In total, aPDT was applied six times (twice per day) to the teeth in the test group over a period of four days. On the fourth day, the study concluded and the analyses were performed. RESULTS: A combination of 500 or 1000 µg/ml TBO and LED irradiation for 20 s significantly decreased the number of colony forming units of Streptococcus oralis. The cytotoxicity of aPDT was comparable to that of standard antiseptics used in the oral cavity. Hydroxyl radicals were detected by ESR analysis, but singlet oxygen was not. A randomized controlled trial demonstrated that aPDT with 1000 µg/ml TBO and red LED irradiation significantly suppressed dental plaque formation without harming teeth or the surrounding tissues. CONCLUSIONS: aPDT has the potential to be a promising novel technical modality for dental plaque control. TRIAL REGISTRATION: This trial was registered with University Hospital Medical Information Network Clinical Trials Registry (number UMIN000012504).

Effect of PDGF-BB combined with EDTA gel on adhesion and proliferation to the root surface.

Periodontal regeneration using EDTA or PDGF showed promising results, but the effect of combined application was still unclear. This study aimed to verify the effect of EDTA and/or PDGF application on root adhesion and proliferation of PDL fibroblast cells. Eighty specimens were prepared from forty periodontitis teeth and made five groups: (1) diseased (untreated), (2) SRP (scaling root planing), (3) EDTA (24%), (4) PDGF (25 ng/ml) and (5) Combined application of EDTA and PDGF. Periodontal ligament cells were cultured on the above conditioned dentin plate, and SEM examination was preformed and cells were counted within a representative standard area for both cell morphology and density. All groups including untreated showed significantly increase of adhered cells from baseline to 7 days. Among them, rate of increase was much higher in EDTA, PDGF, and combined groups. ANOVA test indicated that the number of cells in PDGF and combined groups was significantly higher than diseased group at 1 day. On day 7, PDGF and combined groups showed significantly higher number of adhesion cells than that found in the diseased, SRP and EDTA groups. Thus, root conditioning with EDTA enhanced cell adhesion more than SRP alone. There was no significant difference of cell number between PDGF and combined group. Combined application of EDTA and PDGF increased significantly PDL cell adhesion than EDTA alone. PDGF alone, however, also showed comparable effect to combined application at all periods. Thus, synergistic effect between PDGF and EDTA was not observed.

Imaging of acquired cystic disease-associated renal cell carcinoma by contrast-enhanced ultrasonography with perflubutane microbubbles and positron emission tomography-computed tomography.

The preoperative assessment of renal cell carcinoma (RCC) complicated with acquired renal cystic disease in a 63-year-old male patient on long-term hemodialysis (30 years and 8 months) that was difficult because of no or poor contrast enhancement by dynamic CT scan is reported. Contrast-enhanced ultrasonography with perflubutane microbubbles and positron emission tomography-computed tomography (PET-CT) with 18F-fluorodeoxy glucose (FDG) in addition to dynamic CT were effective and useful for preoperative assessment of this patient. The pathological subtype of RCC in this patient was acquired cystic disease-associated RCC (ACD-associated RCC), which has been newly defined by Tickoo et al. (Am J Surg Pathol 30:141-153, 2006).

In vitro studies of the ablation mechanism of periodontopathic bacteria and decontamination effect on periodontally diseased root surfaces by erbium:yttrium-aluminum-garnet laser.

The erbium:yttrium-aluminum-garnet (Er:YAG) laser is now increasingly used in periodontal therapy. The purpose of this study was to investigate the effect of Er:YAG laser irradiation on the morphology of periodontopathic bacteria and to compare the bacterial elimination effect of the laser and the ultrasonic scaler on diseased root surfaces in vitro. Colonies of Porphyromonas gingivalis were exposed to a single-pulse Er:YAG laser at 40 mJ and were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Also, 20 pairs of periodontally diseased root surfaces with subgingival calculi of freshly extracted teeth were treated by Er:YAG laser scaling at 40 mJ/pulse (14.2 J/cm(2) per pulse) and 10 Hz with water spray or ultrasonic scaling, or were not treated. The efficiency of each treatment was determined as the area treated per second, and the treated surfaces were examined by SEM. The material scraped from the treated root surfaces was cultured in aerobic and anaerobic conditions, and the numbers of colony forming units (CFUs) were compared. SEM and TEM showed that the Er:YAG laser had easily ablated the bacterial colony, leaving an ablation spot with a crater and the surrounding affected area showing melted branch-like structures. The laser irradiation was as equally effective and efficient as the ultrasonic scaler in performing root surface debridement. The CFUs after laser treatment were significantly fewer than those after ultrasonic scaling in aerobic and anaerobic culture conditions. Er:YAG laser ablates periodontopathic bacteria with thermal vaporization, and its bacterial elimination effect on the diseased root surfaces appears to be superior to that of the ultrasonic scaler.

Assessment of cell sheets derived from human periodontal ligament cells: a pre-clinical study.

Periodontal-ligament-derived cells (PDL cells) have stem-cell-like properties and, when implanted into periodontal defects in vivo, can induce periodontal regeneration including the formation of new bone, cementum, and periodontal ligament. We have previously demonstrated that PDL cell sheets, harvested from temperature-responsive cell culture dishes, have a great potential for periodontal regeneration. The purpose of this study has been to validate the safety and efficacy of human PDL (hPDL) cell sheets for use in clinical trials. hPDL tissues from three donors were enzymatically digested, and the obtained cells were cultured with media containing autologous serum in a cell-processing center (CPC). The safety and efficacy of hPDL cell sheets were evaluated both in vitro and in vivo. In vitro studies showed that the hPDL cell sheets had high alkaline phosphatase activity and periostin expression (known PDL markers) and no contamination with microorganisms. In vivo studies revealed that hPDL cell sheets, implanted with dentin blocks, induced the formation of cementum and PDL-like tissue in immunodeficient mice. The hPDL cells presented no evidence of malignant transformation. Thus, hPDL cell sheets created in CPCs are safe products and possess the potential to regenerate periodontal tissues.

Validation of human periodontal ligament-derived cells as a reliable source for cytotherapeutic use.

AIM: Periodontal ligament (PDL) is a reliable cell source for periodontal regeneration. In this study, an optimal protocol for the extraction, expansion, and characterization of human PDL (hPDL) cells was examined for clinical trials. MATERIALS AND METHODS: hPDL tissues were obtained from 41 surgically extracted teeth and digested with enzymes. Human adipose-derived stem cells (hADSCs), bone marrow-derived mesenchymal stem cells (hBMMSCs), and gingival fibroblasts (hGFs) were used for comparison. For each sample, the proliferative capacity, colony-forming ability, alkaline phosphatase activity, differentiation ability, the cell surface antigens, gene expression, and regenerative potential were examined. RESULTS: hPDL cells were more successfully extracted with collagenase/dispase [29/30 (96.7%)] than with trypsin/EDTA [8/11 (72.7%)], and exhibited osteogenic potential both in vitro and in vivo. The proliferation of hPDL cells was rapid at a low cell density. hPDL cells frequently differentiated into cementoblastic/osteoblastic lineage (∼60%). In contrast, their adipogenic and chondrogenic potentials were lower than those of hADSCs and hBMMSCs. Some genes (NCAM1, S100A4, and periostin) were preferentially expressed in hPDL cells compared with those of hBMMSCs and hGFs. Immunohistochemical studies revealed the expressions of S100A4 and periostin in hPDL tissue. CONCLUSION: A protocol for the successful cultivation and validation of hPDL cells is proposed for clinical settings.

Low-level Er:YAG laser irradiation enhances osteoblast proliferation through activation of MAPK/ERK.

Although the use of high-level Er:YAG laser irradiation has been increasing in periodontal and peri-implant therapy, the effects of low-level Er:YAG laser on surrounding tissues and cells remain unclear. In the present study, the effects of low-level Er:YAG laser irradiation on osteoblast proliferation were investigated. Cells of the osteoblastic cell line MC3T3-E1 were treated with low-level Er:YAG laser irradiation with various combinations of laser settings (fluence 0.7-17.2 J/cm(2)) and in the absence or presence of culture medium during irradiation. On day 1 and/or day 3, cell proliferation and death were determined by cell counting and by measurement of lactate dehydrogenase (LDH) levels. Further, the role of mitogen-activated protein kinase (MAPK) pathways in laser-enhanced cell proliferation was investigated by inhibiting the MAPK pathways and then measuring MAPK phosphorylation by Western blotting. Higher proliferation rates were found with various combinations of irradiation parameters on days 1 and 3. Significantly higher proliferation was also observed in laser-irradiated MC3T3-E1 cells at a fluence of approximately 1.0-15.1 J/cm(2), whereas no increase in LDH activity was observed. Further, low-level Er:YAG irradiation induced the phosphorylation of extracellular signal-regulated protein kinase (MAPK/ERK) 5 to 30 min after irradiation. Although MAPK/ERK 1/2 inhibitor U0126 significantly inhibited laser-enhanced cell proliferation, activation of stress-activated protein kinases/Jun N-terminal kinase (SAPK/JNK) and p38 MAPK was not clearly detected. These results suggest that low-level Er:YAG laser irradiation increases osteoblast proliferation mainly by activation of MAPK/ERK, suggesting that the Er:YAG laser may be able to promote bone healing following periodontal and peri-implant therapy.

Association between periodontitis and anti-cardiolipin antibodies in Buerger disease.

AIM: Anti-cardiolipin (CL) antibodies can be induced in Buerger disease (BD), an inflammatory occlusive disorder affecting peripheral blood vessels, in response to bacteria bearing homology to the TLRVYK peptide of a phospholipid-binding plasma protein beta-2-glycoprotein I. TLRVYK homologies are present in Porphyromonas gingivalis (TLRIYT) and Treponema denticola (TLALYK). This study investigated the association between periodontal infection and anti-CL antibodies in BD patients. MATERIAL AND METHODS: Periodontal conditions were examined in 19 BD patients and 25 systemically healthy control subjects. All subjects were heavy smokers. Serum anti-CL, anti-TLRVYK, anti-TLRIYT, and anti-TLALYK antibodies were assessed using the enzyme-linked immunosorbent assay. RESULTS: BD patients had a significantly higher prevalence of periodontitis, more severe periodontal destruction and increased titres of serum anti-CL, anti-TLRVYK, anti-TLRIYT, and anti-TLALYK antibodies compared with healthy subjects. The levels of anti-CL antibodies positively correlated with those of the three anti-peptide antibodies. Anti-CL antibody titres were significantly associated with the percentage of sites with clinical attachment level >or=4 mm in BD patients. CONCLUSION: Elevated anti-CL antibody levels were associated with periodontal destruction in BD patients. Periodontopathic bacteria may serve as exogenous antigens that stimulate the anti-CL antibody production through molecular mimicry between the bacterial peptides and a host plasma protein.

Long-term histologic analysis of bone tissue alteration and healing following Er:YAG laser irradiation compared to electrosurgery.

BACKGROUND: The erbium-doped:yttrium, aluminum, and garnet (Er:YAG) laser is reportedly useful for periodontal therapy. However, the potential thermal damage that Er:YAG laser irradiation can produce on bone tissue has not been fully clarified. The purpose of this study was to histologically examine the effects of the Er:YAG laser on bone tissue and subsequent wound healing compared to electrosurgery in a long-term study. METHODS: Calvarial bone from 30 rats was exposed to contact and non-contact Er:YAG laser irradiation (115 mJ/pulse, 10 Hz) without water coolant, or electrode contact. The treated surfaces were analyzed by scanning electron microscopy (SEM), and the healing process was histologically observed until 12 months post-surgery. RESULTS: Contact irradiation resulted in substantial bone ablation, whereas non-contact irradiation produced slight tissue removal. Histologic and SEM analyses of the lased surface showed no severe thermal damage, except for the production of a superficially affected layer with a microstructured surface. The layer did not inhibit new bone formation, and the ablated defect was repaired uneventfully. Although the thickness of the layer gradually decreased, it generally remained in the cortical bone through the observation period. Electrosurgery produced a large area of thermal necrosis without ablation, and the damaged area was not replaced with new bone. CONCLUSIONS: Unlike electrosurgery, Er:YAG laser irradiation without water coolant easily ablated bone tissue, and thermal alteration in the treated surface was minimal. The superficially affected layer did not interfere with the ensuing bone healing, resulting in favorable repair of the defect.

Energy output reduction and surface alteration of quartz and sapphire tips following Er:YAG laser contact irradiation for tooth enamel ablation.

BACKGROUND: Despite the recent increase in application of Er:YAG laser for various dental treatments, limited information is available regarding the contact tips. This study examined the changes in energy output and surface condition of quartz and sapphire contact tips after Er:YAG laser contact irradiation for tooth enamel ablation. MATERIALS AND METHODS: Ten sets of unused quartz or sapphire contact tips were employed for contact irradiation to sound enamel of extracted teeth. The teeth were irradiated with Er:YAG laser at approximately 75 J/cm(2)/pulse and 20 Hz under water spray for 60 minutes. The energy output was measured before and every 5 minutes after irradiation, and the changes in morphology and chemical composition of the contact surface were analyzed. RESULTS: The energy output significantly decreased with time in both tips. The energy output from the sapphire tips was generally higher on average than that of the quartz. The contact surfaces of all the used quartz tips were concave and irregular. Most of the sapphire tips also appeared rough with crater formation and fractures, except for a few tips in which a high energy output and the original smooth surface were maintained. Spots of melted tooth substances were seen attached to the surface of both tips. CONCLUSION: In contact enamel ablation, the sapphire tip appeared to be more resistant than the quartz tip. The quartz tips showed similar patterns of energy reduction and surface alteration, whereas the sapphire tips revealed a wider and more characteristic variation among tips. Lasers Surg. Med. 41:595-604, 2009. (c) 2009 Wiley-Liss, Inc.

Application of cell-sheet engineering for new formation of cementum around dental implants.

Periodontal disease involves the chronic inflammation of tooth supporting periodontal tissues. As the disease progresses, it manifests destruction of periodontal tissues and eventual tooth loss. The regeneration of lost periodontal tissue has been one of the most important subjects in periodontal research. Since their discovery, periodontal ligament stem cells (PDLSCs), have been transplanted into periodontal bony defects to examine their regenerative potential. Periodontal defects were successfully regenerated using PDLSC sheets, which were fabricated by cell sheet engineering in animal models, and for which clinical human trials are underway. To expand the utility of PDLSC sheet, we attempted to construct periodontal tissues around titanium implants with the goal of facilitating the prevention of peri-implantitis. In so doing, we found newly formed cementum-periodontal ligament (PDL) structures on the implant surface. In this mini review, we summarize the literature regarding cell-based periodontal regeneration using PDLSCs, as well as previous trials aimed at forming periodontal tissues around dental implants. Moreover, the recent findings in cementogenesis are reviewed from the perspective of the formation of further stable periodontal attachment structure on dental implant. This mini review aims to summarize the current status of the creation of novel periodontal tissue-bearing dental implants, and to consider its future direction.

Periodontal ligament cell sheet promotes periodontal regeneration in athymic rats.

AIM: The primary goal of periodontal treatment is regeneration of the periodontium. Current theories suggest that the periodontal ligament (PDL) cells have the capacity to participate in restoring connective and mineralized tissues, when appropriately triggered. We evaluated whether human PDL cell sheets could reconstruct periodontal tissue. MATERIAL AND METHODS: To obtain the cell sheet, human PDL cells were cultured on temperature-responsive culture dishes with or without osteogenic differentiation medium. The cell sheets were transplanted on periodontal fenestration defects of immunodeficient rats. Forty rats were divided in two groups: in one group, cell sheets cultured with control medium were transplanted and in the other, cell sheets cultured with osteogenic differentiation medium were transplanted. The defects were analysed histologically and histomorphologically after healing. RESULTS: Most of the experimental group exhibited a new cementum-like layer and new attachment of collagen fibres to the layer. Histomorphological analyses indicated significant periodontal regeneration. The control group revealed dense extracellular matrix and fibre formation, but an obvious cementum layer was not observed. CONCLUSIONS: Transplanted PDL cell sheets cultured with osteogenic differentiation medium induced periodontal regeneration containing an obvious cementum layer and Sharpey's fibres. Thus, the method could be feasible as a new therapeutic approach for periodontal regeneration.

Changes in serum interleukin-6, C-reactive protein and thrombomodulin levels under periodontal ultrasonic debridement.

AIM: This study aimed to compare the effect of single-visit full-mouth mechanical debridement (FMD) and quadrant-wise mechanical debridement (QMD) on the levels of serum interleukin (IL)-6, C-reactive protein (CRP) and soluble thrombomodulin. MATERIAL AND METHODS: Thirty-six subjects with chronic periodontitis were randomly allocated to three groups: undergoing QMD, single-visit FMD with povidone iodine or with water. Serum IL-6 and soluble thrombomodulin were measured by enzyme-linked immunosorbent assay, and serum CRP was measured by the latex-enhanced nephelometric method. RESULTS: Serum IL-6 level increased significantly immediately after debridement in all the three groups, with this increase being greatest in the full-mouth groups. However, the increase in the full-mouth groups was not significantly higher than that of quadrant-wise group. In the quadrant-wise group, serum IL-6 level decreased significantly 1 month after debridement compared with baseline. Serum-soluble thrombomodulin decreased significantly in the full-mouth groups but not in the quadrant-wise group. Changes in CRP level were not significant at baseline or after debridement in all the three groups. CONCLUSIONS: FMD increased serum IL-6 and reduced serum-soluble thrombomodulin to a greater extent than QMD, suggesting that the former technique has stronger transient effects on systemic vascular endothelial functions than the latter.

Clinical application of erbium:YAG laser in periodontology.

Various lasers have been introduced for the treatment of oral diseases and their applications in dental clinics have become a topic of much interest among practitioners. Technological advances and improvements have increased the choices of the available laser systems for oral use. Among them, a recently developed erbium-doped:yttrium aluminum garnet (Er:YAG) laser system possesses suitable characteristics for oral soft and hard tissue ablation. Due to its high absorption in water, an effective ablation with a very thin surface interaction occurs on the irradiated tissues without any major thermal damage to the irradiated and surrounding tissues. In the field of periodontics, the application of Er:YAG laser for periodontal hard tissue has begun with studies from Japanese and German researchers. Several in vitro and clinical studies have already demonstrated an effective application of the Er:YAG laser for calculus removal and decontamination of the diseased root surface in periodontal non-surgical and surgical procedures. However, further studies are required to better understand the various effects of Er:YAG laser irradiation on biological tissues for its safe and effective application during periodontal and implant therapy. Randomized controlled clinical trials and more basic studies have to be encouraged and performed to confirm the status of Er:YAG laser treatment as an adjunct or alternative to conventional mechanical periodontal therapy. In this paper, the advantages and current clinical applications of this laser in periodontics and implant dentistry are summarized based on current scientific evidence.

Periodontal regeneration with autologous periodontal ligament-derived cell sheets - A safety and efficacy study in ten patients.

BACKGROUND: Periodontitis results in the destruction of tooth-supporting periodontal tissues and does not have the ability to heal spontaneously. Various approaches have been introduced to regenerate periodontal tissues; however, these approaches have limited efficacy for treating severe defects. Cytotherapies combine stem cell biology and tissue engineering to form a promising approach for overcoming these limitations. In this study, we isolated periodontal ligament (PDL)-derived cells from patients and created cell sheets with "Cell Sheet Engineering Technology", using temperature responsive culture dishes, in which all the cultured cells can be harvested as an intact transplantable cell sheet by reducing the temperature of the culture dish. Subsequently, the safety and efficacy of autologous PDL-derived cell sheets were evaluated in a clinical setting. METHODS: A single-arm and single-institute clinical study was performed to verify the safety and efficacy of autologous PDL-derived cell sheets in patients with periodontitis. Wisdom teeth were extracted from patients diagnosed with chronic periodontitis, ranging in age from 33 to 63 years (mean [±SD], 46 ± 12), and periodontal tissues were scraped for cell sources. Three-layered PDL-derived cell sheets were constructed using temperature-responsive culture dishes and transplanted in an autologous fashion following standard flap surgeries. Bony defects were filled with beta-tricalcium phosphate granules. Clinical variables were evaluated at baseline, 3 months, and 6 months. Cone-beam computed tomography was performed at baseline and 6 months. Additionally, mid-long-term follow-up has been performed with patients' agreements. RESULTS: Our method was found to be safe and no severe adverse events were identified. All the findings, including reduction of periodontal probing depth (mean ± SD, 3.2 ± 1.9 mm), clinical attachment gain (2.5 ± 2.6 mm), and increase of radiographic bone height (2.3 ± 1.8 mm), were improved in all 10 cases at 6 months after the transplantation. These therapeutic effects were sustained during a mean follow-up period of 55 ± 19 months, and there were no serious adverse events. CONCLUSIONS: The results of this study validate the safety and efficacy of autologous PDL-derived cell sheets in severe periodontal defects, and the stability of this efficacy during mid-long-term follow up. This cytotherapeutic approach, based on cell sheet engineering, offers an innovative strategy to treat the recognized unmet need of treating severe periodontal defects.

In Vivo Periodontium Formation Around Titanium Implants Using Periodontal Ligament Cell Sheet.

Osseointegrated implants have been recognized as being very reliable and having long-term predictability. However, host defense mechanisms against infection have been known to be impaired around a dental implant because of the lack of a periodontal ligament (PDL). The purpose of our experimental design was to produce cementum and PDL on the implant surface adopting cell sheet technology. To this aim we used PDL-derived cells, which contain multipotential stem cells, as the cell source and we cultured them on an implant material constituted of commercially pure titanium treated with acid etching, blasting, and a calcium phosphate (CaP) coating to improve cell attachment. Implants with adhered human PDL cell sheets were transplanted into bone defects in athymic rat femurs as a xenogeneic model. Implants with adhered canine PDL-derived cell sheets were transplanted into canine mandibular bone as an autologous model. We confirmed that PDL-derived cells cultured with osteoinductive medium had the ability to induce cementum formation. The attachment of PDL cells onto the titanium surface with three surface treatments was accelerated, compared with that onto the smooth titanium surface, at 40 min after starting incubation. Results in the rat model showed that cementum-like and PDL-like tissue was partly observed on the titanium surface with three surface treatments in combination with adherent PDL-derived cell sheets. On the other hand, osseointegration was observed on almost all areas of the smooth titanium surface that had PDL-derived cell sheets, but did not have the three surface treatments. In the canine model, histological observation indicated that formation of cementum-like and PDL-like tissue was induced on the titanium surface with surface treatments and that the PDL-like tissue was perpendicularly oriented between the titanium surface with cementum-like tissue and the bone. Results demonstrate that a periodontal-like structure was formed around a titanium implant, which is similar to the environment existing around a natural tooth. The clinical application of dental implants combined with a cell sheet technique may be feasible as an alternative implant therapy. Furthermore, application of this methodology may play an innovative role in the periodontal, prosthetic, and orthodontic fields in dentistry.