Periodontal Ligament Formation Research Articles

Application of induced pluripotent stem (iPS) cells in periodontal tissue regeneration

Tissue engineering provides a new paradigm for periodontal tissue regeneration in which proper stem cells and effective cellular factors are very important. The objective of this study was, for the first time, to investigate the capabilities and advantages of periodontal tissue regeneration using induced pluripotent stem (iPS) cells and enamel matrix derivatives (EMD). In this study the effect of EMD gel on iPS cells in vitro was first determined, and then tissue engineering technique was performed to repair periodontal defects in three groups: silk scaffold only; silk scaffold + EMD; and silk scaffold + EMD + iPS cells. EMD greatly enhanced the mRNA expression of Runx2 but inhibited the mRNA expression of OC and mineralization nodule formation in vitro. Transplantation of iPS cells showed higher expression levels of OC, Osx, and Runx2 genes, both 12 and 24 days postsurgery. At 24 days postsurgery in the iPS cell group, histological analysis showed much more new alveolar bone and cementum formation with regenerated periodontal ligament between them. The results showed the commitment role that EMD contributes in mesenchymal progenitors to early cells in the osteogenic lineage. iPS cells combined with EMD provide a valuable tool for periodontal tissue engineering, by promoting the formation of new cementum, alveolar bone, and normal periodontal ligament.

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.

17β‐Estradiol Promotes Cementoblast Proliferation and Cementum Formation in Experimental Periodontitis

Periodontitis is a chronic inflammatory condition that leads to the destruction of the tooth-supporting tissues. Its treatment includes the arrest of the inflammatory process and, in some circumstances, the restoration of the lost anatomy and function, including the formation of new cementum, periodontal ligament (PDL), and bone. With this goal, we investigated the effects of low concentrations of 17beta-estradiol on human cementoblast proliferation and its possible regenerative potential in vivo. Human cementum-derived cells obtained from a healthy human premolar were isolated and characterized by immunocytochemistry. Cell proliferation assays were performed to test the effects of 100 nM 17beta-estradiol and enamel matrix derivative (EMD). Three-wall intrabony periodontal defects were created in beagle dogs. After 1 month of plaque accumulation, 0.225 mg 17beta-estradiol impregnated in a collagen sponge was applied to randomly selected defects (test group), whereas a collagen sponge impregnated in a culture medium was applied to the control group. After 3 months, specimens were obtained, and tissue regeneration was assessed by histometric analysis. Cells spreading out from human tooth-layer explants were able to form cell colonies, produce a mineral matrix, and express osteocalcin, indicating they were cementoblast-like cells. In contrast, PDL fibroblasts did not express osteocalcin. 17beta-estradiol, but not EMD, increased the rate of human cementoblast cell proliferation in vitro by 2.5-fold. Histometric results from the treated periodontal defects revealed that 17beta-estradiol promoted the formation of 2.94 mm of new cementum, (45% of the defects) compared to 1.54 mm of new cementum in the control group (28% of the defects). Furthermore, the test group showed an inhibition of epithelial downgrowth and a gain of new connective tissue attachment. 17beta-estradiol promoted human cementoblast cell proliferation in vitro and periodontal regeneration in an experimental periodontitis model.

The Bone Formation Capabilities of the Anorganic Bone Matrix–Synthetic Cell‐Binding Peptide 15 Grafts in an Animal Periodontal Model: A Histologic and Histomorphometric Study in Dogs

The aim of this study is to verify the regenerative potential of particulate anorganic bone matrix-synthetic peptide-15 (ABM-P-15) in class III furcation defects associated or not with expanded polytetrafluoroethylene membranes. Class III furcation defects were produced in the mandibular premolars (P2, P3, and P4) of six dogs and filled with impression material. The membranes and the bone grafts were inserted into P3 and P4, which were randomized to form the test and control groups, respectively; P2 was the negative control group. The animals were sacrificed 3 months post-treatment. Histologically, the complete closure of class III furcation defects was not observed in any of the groups. Partial periodontal regeneration with similar morphologic characteristics among the groups was observed, however, through the formation of new cementum, periodontal ligament, and bone above the notch. Histologic analysis showed granules from the bone graft surrounded by immature bone matrix and encircled by newly formed tissue in the test group. The new bone formation area found in the negative control group was 2.28 + or - 2.49 mm(2) and in the test group it was 6.52 + or - 5.69 mm(2), which showed statistically significant differences for these groups considering this parameter (Friedman test P <0.05). There was no statistically significant difference among the negative control, control, and test groups for the other parameters. The regenerative potential of ABM-P-15 was demonstrated through new bone formation circumscribing and above the graft particles. The new bone also was accompanied by the formation of new cementum and periodontal ligament fibers.

Effect of recombinant basic fibroblast growth factor on reimplanted teeth in beagle dogs

This study assessed the effect of recombinant fibroblast growth factor (FGF-2) on reimplanted teeth. Premolars were reimplanted in dogs. Roots on the left side of the mandible were treated with FGF-2, whereas roots on right side served as controls. At 2, 4, or 8 weeks after treatment, animals were humanely killed and specimens collected and processed for histopathologic examination. After 2 weeks, proliferating cell nuclear antigen-positive cell ratios in the experimental group were significantly greater than those in the control group (P < .01). After 4 and 8 weeks, the experimental group showed formation of new cementum. Moreover, incidence of replacement resorption in the experimental group was significantly lower than that in the control group (P < .01). The results indicate that FGF-2 promotes formation of new periodontal ligament and prevents ankylosis and root resorption following reimplantation of teeth.

Growth factors in periodontal regeneration

Inflammatory periodontal disease is an almost ubiquitous disorder in the adult population. Cases or sites with moderate to advanced disease often continue to show signs of inflammation after non-surgical approach. Our current understanding of periodontal healing is based on a hypothesis by Melcher who proposed that the cell type that repopulates the exposed root surface at the periodontal repair site will define the nature of the attachment/repair that take place. If mesenchymal cells from periodontal ligament/perivascular region of the bone proliferate and colonize the root surface, regeneration occurs. Growth factors are natural cell products that are released or activated when cell division is needed. This action typically occurs during such events as wound healing or tissue regeneration. Activated platelets at the wound margins release several growth factors such as platelet-derived growth factor (PDGF), transforming growth factor (TGF)-alpha, epidermal growth factor etc. Cells adjacent to the injured site also are induced to release growth factors such as insulin-like growth factor-I, PDGF, TGF-alpha and TGF-alpha within a few hours after injury. In periodontal regeneration, the coronal re-establishment of the periodontal ligament (PDL) is required together with corresponding cementum and supporting alveolar bone. Thus, agents which promote periodontal ligament fibroblast (PLF) proliferation and migration as well as collagen biosynthesis would appear to be mediators for enhancing new PDL formation. When combinations or cocktails of different factors are used, greater repair is achieved than when individual factors are applied.

Regenerative potential and healing dynamics of the periodontium: a critical‐size supra‐alveolar periodontal defect study

The nature and characteristics of the newly formed periodontium obtained following regenerative procedures remain a matter of controversy. The objective of this study was to evaluate the regenerative potential of the periodontal attachment and healing dynamics as observed from the spatial distribution of newly formed cementum, periodontal ligament (PDL) and alveolar bone following optimal circumstances for wound healing/regeneration in a discriminating animal model. Critical-size, 6-mm, supra-alveolar, periodontal defects were surgically created in six young adult Beagle dogs. Space-providing ePTFE devices with 300-microm laser-drilled pores were implanted to support wound stability and space provision in one jaw quadrant/animal. Treatments were alternated between left and right jaw quadrants in subsequent animals. The gingival flaps were advanced to submerge the defect sites for primary intention healing. Histometric analysis followed an 8-week healing interval. Healing was uneventful in all animals. The histometric analysis showed that cementum regeneration (2.99 +/- 0.22 mm) was significantly greater than PDL (2.54 +/- 0.18 mm, p=0.03) and bone regeneration (2.46 +/- 0.26 mm, p=0.03). The wound area showed significant positive non-linear effect on cementum (log beta=1.25, p<0.001), PDL (log beta=1.24, p<0.001) and new bone formation (log beta=1.36, p<0.001). A high degree of concordance and significant linear relationship was observed between cementum, PDL and bone regeneration indicating that their formation virtually occurred in parallel. Cementum, PDL and alveolar bone virtually regenerate in parallel under optimal circumstances for periodontal wound healing/regeneration. Moreover, space provision positively influences the extent of periodontal regeneration.

Periodontal tissue engineering by transplantation of multilayered sheets of phenotypically modified gingival fibroblasts

In periodontal tissue engineering, the sourcing of most of the relevant cells is limited by poor accessibility, whereas the use of readily available gingival fibroblasts is hampered because of their inhibitory effects on bone formation. To address the latter drawback, we developed a new graft composed of fibronectin (FN) matrix-based multilayered cell sheets of human gingival fibroblasts modified to express alkaline phosphatase (ALP). This study was undertaken to investigate the effects of this graft, called the FN-ALP transplant, on the healing of periodontal defects in a rat model. The FN-ALP transplants were grafted into periodontal fenestration bone defects in immunosuppressed rats. The process of periodontal healing was examined by histology, histomorphometry and immunohistochemistry. Grafted cells were tracked by immunostaining with human-specific antibodies. Control groups included non-transplanted empty defects and defects to which cell sheets without ALP induction had been grafted. After implantation, the FN-ALP transplants healed alveolar bone defects by intramembranous ossification, with formation of cementum and periodontal ligament. Moreover, FN-ALP transplants increased new bone formation, by endochondral ossification, on the mandibular cortex adjacent to the defect. Grafted fibroblasts were located near host osteoblasts and chondrocyte precursor cells early in the ossification process but were undetectable on and in newly formed bone and cartilage. These results indicate that the FN-ALP transplants support alveolar bone regeneration within the defect and augment bone formation outside the defect through the recruitment of host osteo/chondrogenic cells, suggesting their potential for periodontal tissue engineering applications.

Cementum and Periodontal Ligament–like Tissue Formation Induced Using Bioengineered Dentin

Stem cell-mediated root regeneration offers opportunities to regenerate a bio-root and its associated periodontal tissues to restore tooth loss. Periodontal ligament (PDL) and cementum complex and dentin pulp complex have been tissue engineered using human dental pulp stem cells and PDL stem cells, respectively. The aim of this study was to explore whether dentin formation could be induced using an inductive substrate and whether bioengineered dentin could induce cementum and PDL formation. First, dentin was bioengineered from tooth papillae of Sprague-Dawley (SD) rats with an inductive substrate, and its phenotype was characterized; then primarily cultured human PDL cells were seeded on the surface of dentin and transplanted under the skin of immunocompromised mice. Histological, immunohistochemical, and scanning electronic microscopy examinations results showed that bioengineered dentin could induce cementogenesis and PDL formation, and condense PDL arranged perpendicularly on the dentin surface via a layer of cementum-like tissue. The results indicated that tissue-engineered dentin could be induced using an inductive substrate and could be used as a further substrate for cementum and PDL tissue engineering.

Regeneration of dentin‐pulp complex with cementum and periodontal ligament formation using dental bud cells in gelatin‐chondroitin‐hyaluronan tri‐copolymer scaffold in swine

The purpose of this study is to use a tissue engineering approach for tooth regeneration. The swine dental bud cells (DBCs) were isolated from the developing mandibular teeth, expanded in vitro, and cultured onto cylinder scaffold gelatin-chrondroitin-hyaluronan-tri-copolymer (GCHT). After culturing in vitro, the DBCs/GCHT scaffold was autografted back into the original alveolar socket. Hematoxylin and eosin (H&E) staining combined with immunohistochemical staining were applied for identification of regenerated tooth structure. After 36-week post-transplantation, tooth-like structures, including well-organized dentin-pulp complex, cementum, and periodontal ligament, were evident in situ in two of six experimental animals. The size of the tooth structure (1 x 0.5 x 0.5 cm(3) and 0.5 x 0.5 x 0.5 cm(3) size) appeared to be dictated by the size of the GCHT scaffold (1 x 1 x 1.5 cm(3)). The third swine was demonstrated with irregular dentin-bony like calcified tissue about 1 cm in diameter without organized tooth or periodontal ligament formation. The other three swine in the experimental group showed normal bone formation and no tooth regeneration in the transplantation sites. The successful rate of tooth regeneration from DBCs/GCHT scaffolds' was about 33.3%. In the control group, three swine's molar teeth buds were removed without DBCs/GCHT implantation, the other three swine received GCHT scaffold implants without DBCs. After evaluation, no regenerated tooth was found in the transplantation site of the control group. The current results using DBSs/GCHT scaffold autotransplantation suggest a technical breakthrough for tooth regeneration.

Acellular Dermal Matrix as a Membrane for Guided Tissue Regeneration in the Treatment of Class II Furcation Lesions: A Histometric and Clinical Study in Dogs

The purpose of this study was to evaluate acellular dermal matrix (ADM) as a membrane for guided tissue regeneration (GTR) in the treatment of mandibular Class II furcation lesions and to compare it to a bioabsorbable membrane. Class II furcation lesions were created surgically and chronified in six mongrel dogs on the buccal surfaces of mandibular third and fourth premolars, bilaterally. After 1 month, GTR was performed. Each side was assigned randomly to the control group (CGr: bioabsorbable membrane made of polyglycolic acid: trimethylene carbonate) or the test group (TGr: ADM as a membrane). Clinical measurements of the width and thickness of the keratinized tissue (WKT and TKT, respectively) were made before GTR. The dogs were sacrificed 12 weeks following GTR, and histomorphometric analysis was performed. Area measurements were taken of new tissue, epithelium, connective tissue, and new bone; bone height and new cementum were measured. The formation of new bone, cementum, and periodontal ligament were similar in both groups. There were no statistically significant differences between the groups for any histomorphometric measurement. The TGr had a statistically significant increase in WKT and TKT after 3 months. The mean TKT gain was 1.03 mm for the TGr and 0.26 mm for the CGr (P <0.05). The ADM demonstrated histomorphometric results similar to the bioabsorbable membrane and resulted in a greater increase in the thickness of the keratinized tissue.

Enamel Matrix Derivative Stimulates Human Gingival Fibroblast Proliferation via ERK

Emdogain, a formulation of Enamel Matrix Proteins, is used clinically for periodontal regeneration to stimulate PDL (periodontal ligament), cementum, and bone formation. Its effects on gingival fibroblasts and tissue have not been thoroughly studied. Therefore, we investigated the mechanisms by which Emdogain affects the cell cycle of human gingival fibroblasts. Without serum, Emdogain (50 microg/mL) induced human gingival fibroblast entry into the S phase and DNA synthesis, but not completion of the cell cycle. With low serum concentrations (0.2-0.5%), Emdogain synergistically induced completion of the cell cycle, resulting in increased cell numbers. The mitogenic response to Emdogain depended on Extracellular Regulated Kinase (ERK) activation, which occurred in two waves, peaking after 15 min and 4 to 6 hrs, since it was abolished by U0126, a specific MAPK inhibitor. Inhibition of the second wave was sufficient to abrogate mitogenesis. This study characterized the mitogenic effect of Emdogain on primary human gingival fibroblasts, its cooperation with serum growth factors, and the key mediatory role of the ERK cascade.

Establishment of immortalized dental follicle cells for generating periodontal ligament in vivo

The dental follicle is a mesenchymal tissue that surrounds the developing tooth germ. During tooth root formation, periodontal components, viz., cementum, periodontal ligament (PDL), and alveolar bone, are created by dental follicle progenitors. Here, we report the presence of PDL progenitors in mouse dental follicle (MDF) cells. MDF cells were obtained from mouse incisor tooth germs and immortalized by the expression of a mutant human papilloma virus type 16 E6 gene lacking the PDZ-domain-binding motif. MDF cells expressing the mutant E6 gene (MDF( E6-EGFP ) cells) had an extended life span, beyond 150 population doublings (PD). In contrast, normal MDF cells failed to proliferate beyond 10 PD. MDF( E6-EGFP ) cells expressed tendon/ligament phenotype-related genes such as Scleraxis (Scx), growth and differentiation factor-5, EphA4, Six-1, and type I collagen. In addition, the expression of periostin was observed. To elucidate the differentiation capacity of MDF( E6-EGFP ) cells in vivo, the cells were transplanted into severe combined immunodeficiency mice. At 4 weeks, MDF( E6-EGFP ) cell transplants had the capacity to generate a PDL-like tissue that expressed periostin, Scx, and type XII collagen and the fibrillar assembly of type I collagen. Our findings suggest that MDF( E6-EGFP ) cells can act as PDL progenitors, and that these cells may be a useful research tool for studying PDL formation and for developing regeneration therapies.

Inflammatory external root resorption following surgical treatment for intra‐bony defects: a report of two cases involving Emdogain® and a review of the literature

Enamel matrix-derived proteins have been shown to regenerate periodontal tissues lost as a result of disease in humans. Emdogain, a commercial preparation of porcine enamel matrix derivative (EMD), has been shown to induce new cementum, periodontal ligament and bone formation in human periodontal defects. Although a number of studies have reported successful outcomes, local adverse effects have so far not been reported in the literature. This case report describes two examples of external inflammatory resorption following surgical root surface debridement and the use of Emdogain. The treatment in both cases involved raising a full-thickness flap following completion of non-surgical therapy. The granulation tissue from the defect was removed and the root surfaces debrided. Emdogain was applied following the manufacturers' instructions and involved conditioning the root surfaces with Pref-Gel and applying the Emdogain to the defect. The flaps were sutured and the site reviewed regularly. Radiographs were taken before the treatment was undertaken and also at 6 months to assess the healing of the defect. External inflammatory root resorption was observed on the treated teeth 6-24 months after therapy. External inflammatory root resorption may be an unusual adverse event following Emdogain treatment.

Use of Enamel Matrix Protein Derivative Before Dental Reimplantation: A Histometric Analysis

The use of enamel matrix protein in the treatment of periodontal defects has shown a favorable action on the proliferation of periodontal ligament cells, as well as on collagen formation and mineralization. The goal was to evaluate, histologically and histometrically, periodontal tissue regeneration after dental reimplantation using enamel matrix protein derivative (Emdogain, Biora AB, Malmö, Sweden). Male rats (Albinus, Wistar), weighing between 180 and 200 g, were divided in 3 groups. Animals in group I (control) had the upper right incisors extracted, the root canal was sealed with calcium hydroxide, and teeth were reimplanted in their alveoli. Group II underwent the same procedure, but the remaining periodontal ligament was removed from the root surfaces by root planing before reimplantation. In group III,following removal of the periodontal ligament, Emdogain was applied to the root surfaces. Animals were sacrificed 7, 20, and 60 days after reimplantation, and the alveoli were fixed, processed, and stained with hematoxylin and eosin. Formation of periodontal ligament, resorption areas, and ankylosis were analyzed. The results showed that group I (control) was better than groups II and III, with statistically significant differences on days 7 and 20 after reimplantation for formation of periodontal ligament. It may be concluded that with the methodology used, Emdogain was unable to stimulate tissue repair in reimplanted teeth.

Application of periodontal ligament cell sheet for periodontal regeneration: a pilot study in beagle dogs

The ultimate goal of periodontal treatment is to regenerate the damaged periodontal support. Although periodontal ligament (PDL) cells are essential for periodontal regeneration, few studies have reported the transplantation of periodontal ligament cells to periodontal defects. We developed a new method to apply periodontal ligament cells as a sheet to the defect. The aim of this study was to investigate the periodontal healing after application of the periodontal ligament cell sheet in beagle dogs. Autologous periodontal ligament cells were obtained from extracted premolars of each beagle dog. Periodontal ligament cell sheets were fabricated using a temperature-responsive cell culture dish. Dehiscence defects were surgically created on the buccal surface of the mesial roots of bilateral mandibular first molars of each dog. In the experimental group (five defects), periodontal ligament cell sheet with reinforced hyaluronic acid carrier was applied to the defect. Only the hyaluronic acid carrier was applied to the contralateral side as a control (five defects). Eight weeks after surgery, the animals were sacrificed and decalcified specimens were prepared. Healing of the periodontal defects was evaluated histologically and histometrically. No clinical signs of inflammation or recession of gingiva were observed in both experimental and control groups. In the experimental group, periodontal tissue healing with bone, periodontal ligament and cementum formation was observed in three out of five defects. In the control group, such periodontal tissue formation was not observed except in one defect. Histometric analysis revealed that the formation of new cementum in the experimental group was significantly higher than that in the control group. The periodontal ligament cell sheet has a potential to regenerate periodontal tissue and may become a novel regenerative therapy.

Mandibular Bone Deficit With a Histologic Study in Man

The aim of this study was that to determine the clinical and histologic results of a new hydroxyapatite, with innovative properties compared with the other alloplastic materials used in the regenerative treatment of grade 3 bony defects of the mandibular furcations in the human. The hydroxyapatite used in our research is characterized by a scarce density and crystallinity, while from a microstructural point of view, the granules have nanometric dimensions (0.05-0.1 microm). The patient reported here by the authors had a grade 3 infrabony defect into a mandibular furcation. The surgical procedure used consists of the creation of a flap, roots planing, the conditioning of the roots with tetracycline HC, the accurate positioning of the granules of the hydroxyapatite in the furcation area, the crown replacing of the flap, and finally the suture of the same. Six months after the insertion of hydroxyapatite, the clinical effect was studied, comparing the variations found in probing the insertion of depth. At the end of the treatment, a block section of the molar was performed, with part of the surrounding soft tissues, whose histologic analysis underlined the moderate and initial formation of bony tissue, periodontal ligament, and radicular cement in the middle and lower portion of the furcation. In light of these results, the authors conclude that the use of this new hydroxyapatite is promising in the treatment of the mandibular furcations in the human, even if it will be necessary to continue to test its effectiveness through more studies.

Effect of recombinant human bone morphogenetic protein-12 (rhBMP-12) on regeneration of periodontal attachment following tooth replantation in dogs.

Subcutaneous and intramuscular implants of bone morphogenetic protein-12 (BMP-12) have been shown to induce formation of tendon and ligament tissue. BMP-12 induced a new attachment with a distinct fibrocartilaginous zone at the tendon-bone interface in the rat tendon-bone attachment model. Surgical controls showed poor healing and failure to reform the appropriate tendon-bone attachment morphologically. Application of recombinant human BMP-12 (rhBMP-12) to periodontal defects suggests that rhBMP-12 has the potential to support regeneration of the periodontal ligament (PDL). The objective of this pilot study was to evaluate this effect of rhBMP-12 in a tooth replantation model. Six, young adult, male Hound Labrador mongrel dogs were used. Maxillary and/or mandibular incisor and premolar teeth were extracted and the PDL was either left "intact" or removed by root planing. rhBMP-12 (1.0 mg/ml) or a buffer control was topically applied to teeth with "intact" PDL in contralateral jaw quadrants in each of 3 animals. The teeth were immersed in 1.0 ml of the rhBMP-12 or the buffer solution for 10 min and then replanted. The remaining three animals received rhBMP-12 (1.0 mg/ml) and the buffer control in a similar fashion applied to teeth instrumented to remove the PDL and cementum, and surface demineralized with citric acid. The animals were euthanized at 8 weeks postsurgery and block sections were collected and processed for histopathologic analysis. No dramatic differences were found between teeth receiving topical rhBMP-12 and the buffer control. Application of rhBMP-12 did not have an apparent effect on new cementum and PDL formation in the tooth replantation model. Moreover, application of rhBMP-12 did not increase nor did it decrease the apparent presence and extent of ankylosis along the root surface compared to the control. The observations from this study do not support the use of topical rhBMP-12 to support the reestablishment of the PDL including regeneration of cementum and functionally oriented fibers, and to prevent ankylosis and root resorption following replantation of teeth.

Periodontal repair in dogs: effect of recombinant human bone morphogenetic protein-12 (rhBMP-12) on regeneration of alveolar bone and periodontal attachment.

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to stimulate alveolar bone and cementum formation in periodontal defects but not a functionally oriented periodontal ligament (PDL). Subcutaneous and intramuscular implants of BMP-12 have been shown to induce tendon formation and ligament-like tissue. The objective of this study was to evaluate rhBMP-12 for periodontal regeneration, in particular PDL formation. Six young adult Hound Labrador mongrel dogs were used. Routine supraalveolar periodontal defects were created around the mandibular premolar teeth. Three animals received rhBMP-12(0.04 mg/ml) in an absorbable collagen sponge (ACS) carrier vs. rhBMP-12(0.2 mg/mL)/ACS in contralateral defects. Three animals received rhBMP-12(1.0 mg/ml)/ACS vs. rhBMP-2(0.2 mg/ml)/ACS (total implant volume/defect approximately 1 ml). The animals were euthanized 8 weeks postsurgery and block biopsies were processed for histometric analysis. Bone regeneration appeared increased in sites receiving rhBMP-2/ACS compared to sites receiving rhBMP-12/ACS. Cementum regeneration was similar comparing sites implanted with rhBMP-2/ACS to sites implanted with rhBMP-12/ACS. In contrast, sites receiving rhBMP-12/ACS exhibited a functionally oriented PDL bridging the gap between newly formed bone and cementum whereas this was a rare observation in sites receiving rhBMP-2/ACS. Ankylosis appeared increased in sites receiving rhBMP-2/ACS compared to those receiving rhBMP-12/ACS. The outcomes of this study suggest that rhBMP-12 may have significant effects on regeneration of the PDL. Additional preclinical evaluation is needed to confirm these initial observations prior to clinical application.

Formation of new periodontal ligament around transplanted teeth with proliferating tissue in periodontal osseous defect under barrier membrane

The present study evaluated whether transplanted proliferating tissue in periodontal osseous defects can form new periodontal ligament. A periodontal osseous defect was created in dogs by removing alveolar bone around the circumference of the premolar, and was covered with the membrane or without the membrane at control sites. After two weeks, the proliferating tissue in the periodontal osseous defect under the barrier membrane was excised, while at each control site, the connective tissue was dissected. The proliferating tissue and tooth were transplanted to holes drilled in the alveolar bone, while at the control sites, the connective tissue and tooth were transplanted. After one, two and four weeks, the dogs were sacrificed and examined histologically; a LightCycler was also used to measure the mRNA expression of vascular endothelial growth factor (VEGF) and alkaline phosphatase (ALP) in the transplanted tissues. VEGF and ALP mRNA expressions were significantly increased in the transplanted proliferating tissue compared with the connective tissue (control). The root transplanted bearing the proliferating tissue formed new periodontal ligaments, whereas connective tissue could be observed on the root surface in the controls. The results of this study show that transplanted proliferating tissue promotes the formation of new periodontal ligaments around the root.