Histologic evaluation of demineralized freeze-dried bone allografts in barrier membrane covered periodontal fenestration wounds and ectopic sites in dogs

BACKGROUND/AIM: The aim of this study was to investigate healing responses to demineralized freeze-dried bone powder allografts in standardized periodontal fenestration defects, compared with subcutaneous wounds in a dog model. METHODS: Circular periodontal fenestration defects were created buccally at all four canines in 14 mongrel dogs. Each site received one of the following underneath a barrier membrane: (a) ethylene oxide (EO)-sterilized demineralized freeze-dried bone allografts (DFDBA), (b) heat-treated DFDBA, (c) non-sterilized DFDBA and (d) ungrafted control. Twelve of the 14 dogs had three subcutaneous chest wall pouches created and one of the three DFDBA materials placed in each. The animals were necropsied at 4 weeks. Histologic sections were prepared through the center of the fenestration sites in an apico-coronal direction. Quantitative analysis using computer-assisted imaging technique was performed. Subcutaneous implants were evaluated histologically and quantified for associated inflammatory cell infiltrate. RESULTS: Fenestration defects healed by partial osseous fill and cementum regeneration with formation of a periodontal ligament. The graft particles generally appeared isolated from the site of osteogenesis and covered by cementum-like substance. Graft particles incorporated into newly formed bone at a distance from the root surface was the exception. No statistically significant differences in new bone formation were observed between treatment groups within animals, but significant inter-animal variation was found (p<0.01). Quantities of retained graft particles were limited, and without cellular resorption. A bone augmentation effect was associated with the barrier in the majority of sites. No bone formation was evident at the subcutaneous sites where graft particles displayed distinctly modified surface zones and multinucleated giant cell resorption. Significantly more inflammatory infiltrate was associated with EO-sterilized grafts compared with heat-treated grafts (p=0.05). CONCLUSION: Implantation of DFDBA neither enhanced osseous healing in periodontal fenestration defects, nor resulted in ectopic bone induction. DFDBA particles implanted in either periodontal fenestration or subcutaneous wounds evoked distinctly different healing responses.     

Changes in periodontal fibre organization in mature bone/tooth isografts in mice

Mature mouse mandibular third molars together with their periodontal ligaments and alveolar bone were isografted to two heterotopic sites: the renal subcapsular site and the tibial shaft medulla. The pulps and periodontal ligaments of the grafts underwent cellular degeneration after Transplantation but demonstrated signs of revascularization and cellular repopulation 7 days after Transplantation. Grafts obtained at 28, 60 and 100 days after Transplantation demonstrated a significant decrease in the width of the periodontal ligament, a decrease in the number and organization of mature periodontal fibre bundles, the appearance of fibres arranged parallel with the root surface and a decrease in the thickness of surrounding alveolar bone. These regressive changes in the periodontal ligament were considered to be due primarily to the nonfunctional status of the teeth at the two heterotopic sites.     

Potential of Periodontal Ligament Cells to Regenerate Alveolar Bone

Regeneration of periodontal tissues, lost as a result of periodontal disease, is a key objective of periodontal treatment. Although several periodontal regeneration therapies have been devised, the origin of the undifferentiated cells that regenerate periodontal tissues remains unknown. Therefore, in the present study, to clarify the existence of osteoblast progenitor cells in the periodontal ligament, as well as to investigate the mechanism of alveolar bone regeneration without any effects from the original bone, we evaluated osteoblast differentiation induced by transplantation of GFP-transgenic rat molars into the subcutaneous tissues of wild-type rats. Ten days after transplantation, initial alveolar bone was formed apart from the cementum in the bifurcation region. After 20 days, this bone tissue had expanded to almost all of the bifurcation. GFP localization showed that the osteoblasts were derived from the transplant. Alpha-SMA- and BMP4-positive cells were observed near the root surface at 5 days after transplantation. With the progress of alveolar bone regeneration, osteoblasts expressing Runx2 and Osterix appeared in the bone-forming region. These results indicate that periodontal ligament tissue remaining on the root surface after a tooth extraction contains undifferentiated cells that have the ability to regenerate alveolar bone. The process of osteoblast differentiation in this model might be similar to that for normal alveolar bone formation. Thus, periodontal ligament cells might be useful for the regeneration of alveolar bone in tissue engineering applications.     

Effect of citric acid conditioning on fibroblast cell density in periodontal wounds

The present experiment was undertaken to study the repopulation of curetted root surfaces by fibroblast-like cells in experimental periodontal wounds. 6 beagle dogs were used. After reflecting mucoperiosteal flaps, fenestration wounds were made through the buccal cortical plate exposing roots of maxillary canines in 6 beagle dogs. Exposed root surfaces were curetted to remove cementum and periodontal ligament. On 1 side, the exposed root surface was conditioned with citric acid (pH 1) for 3 min while the contralateral root was treated with distilled water. Millipore filters were placed over the wounds to prevent flap connective tissues from contacting the exposed root surface. Histometric analysis was made 10 days after wounding. Fibroblast-like cells were seen migrating into the fenestration space and were primarily aligned along the root surface. Cell densities measured at the borders and central part of the wound showed significantly lower values (p less than 0.01 and p less than 0.05) in acid-conditioned wounds compared to controls. No significant difference in cell density was noted between the borders and central part of the wound in the acid-conditioned group. In the controls, the cell density at the borders was significantly greater than at the center, suggesting active cell migration from the borders. The present findings suggest that citric acid conditioning of root dentin may result in a low cell density during the early stages of healing in experimental periodontal wounds.     

Periodontal regeneration of transplanted rat molars after cryopreservation

The effects of cryopreservation on periodontal regeneration of transplanted rat molars were investigated histologically and histochemically in rats. Bilateral first and second maxillary molars of 4-week-old Wistar rats were gently extracted and transplanted into the abdominal subcutaneous connective tissue immediately or after cryopreservation in liquid nitrogen overnight. Donor teeth were slowly frozen by a rate-controlling freezer (program freezer) using 5% dimethylsulfoxide (DMSO) and 6% hydroxyethyl starch (HES) as cryoprotectants. One-four weeks after transplantation, they were carefully excised with the surrounding tissues. Regeneration of acellular cementum, periodontal ligament, and alveolar bone were observed 2 weeks after immediate transplantation. The pulp was repaired by the ingrowth of granulation tissue from the root apex followed by the formation of calcified tissue. The regenerated periodontal ligament was positive for alkaline phosphatase (ALP). Small or mononuclear tartrate resistant acid phosphatase (TRAP) positive cells were scattered on the newly formed alveolar bone and on the hard tissue in the pulp, but there was no external or internal progressive root resorption at 4 weeks. Cryopreserved teeth had acellular cementum with a rough surface at 1 week, but with the increase of cementoblasts and the appearance of periodontal ligament and alveolar bone, the surface became smooth at 3 weeks. Epithelial rests of Malassez (ERM) also revived. After regeneration of the periodontal tissues at 4 weeks, there was no evidence of root resorption. Although the process proceeded slowly, the cryopreserved teeth showed the periodontal regeneration substantially similar to that of the immediately transplanted teeth without progressive root resorption, indicating that they could be applicable for clinical use.     

The potential coronal migration of periodontal ligament tissue following experimental regeneration

The aim of the present study was to determine if the periodontal ligament cells can migrate onto curretted root surfaces following an experimental regeneration procedure. Buccal mucoperiosteal flaps were elevated in all three premolar regions in 5 mongrel dogs. The buccal bone was reduced to approximately 7 mm from its original level on 30 roots. Before the elevated flaps were replaced and sutured, Gore-Tex filters were adjusted to cover exposed root surfaces. No membranes were placed over 10 root surfaces, which served as controls. After 7 weeks of healing, the animals were sacrificed and all the roots were examined for histological evaluation of contralateral experimental and control teeth. With polychrome staining, the new periodontal ligament fibers of the curetted root surfaces were dyed methyl blue and the adjacent gingival collagen fibers were dyed red. On the experimental surface, coronal migration of periodontal ligament cells and connective tissue attachment were identified over long distances of curetted root surface. Periodontal ligament spaces were more prevalent in experimental sites than in control root surfaces. The results of the experiment suggest that the periodontal ligament cells actually migrated onto the curetted root surfaces when a periodontal space was created by physical barriers.     

Engineered autologous bone marrow mesenchymal stem cells: alternative to cleft alveolar bone graft surgery

ABSTRACT: Human recombinant bone morphogenetic protein 2 (rhBMP-2) accelerates bone regeneration but is associated with limited cementum and periodontal ligament regeneration, local root resorption, and ankylosis. This study assessed a new approach to the regeneration of the alveolar bone and periodontal attachment apparatus using a combination of ex vivo autologous bone marrow mesenchymal stem cells (MSCs) engineered by replication defective adenovirus to express the BMP-2 gene and pluronic F127 (PF127) in a large mammalian animal model. Bilateral maxillary periodontal defects were created over the premolar area in 9 mature male miniature swine. The 18 defects were randomly assigned to receive either BMP-2-expressing MSCs in the advBMP-2 group or MSCs alone in the MSC group. The regenerated periodontal attachment apparatus was evaluated histologically, and the total regenerated bone volume was calculated from three-dimensional computed tomography analysis. Three months after implantation, significant bone volume was regenerated in the advBMP-2 group. Periodontal apparatus regeneration was significantly better in the advBMP-2 group. New cementum and Sharpey fibers were observed on the denuded root surfaces in the advBMP-2 group, whereas incomplete healing with localized root surface resorption was noted in the control group. The use of ex vivo BMP-2-engineered autologous MSCs enhanced bone and periodontal apparatus regeneration in maxillary alveolar and periodontal defects in swine. This novel integrated approach might be suitable for clinical periodontal apparatus repair. This may be an alternative for cleft alveolar bone graft surgery.     

Healing following devitalization of sites within the periodontal ligament by ultralow temperatures

Healing of specific rat periodontal ligament (PDL) sites following freezing injury was monitored histologically to evaluate repair potentials of this tissue. Buccal alveolar plates supporting the first mandibular molar in 15 adult rats were surgically exposed. The coronal 3 mm of plate covering the buccal surface of the mesiobuccal root and underlying periodontal ligament and cementum were subjected to ultralow temperature using a gas expansion micro/cryoprobe, diameter 2 mm, cooled to -81 degrees C for 5 seconds. Tissues were repositioned and sutured in layers. Animals were sacrificed at 1, 24 and 72 hours and at 2, 5 and 7 weeks following surgery and mandibles removed for histologic analysis. Microscopic evaluation of 24-hour specimens showed loss of cellular vitality in the PDL, adjacent bone and cementum at experimental sites. Cellularity of the gingiva coronal to the crest, and of the PDL apical to the experimental zone, appeared to be within normal limits. Transition between experimental and nonexperimental sites was abrupt. After 72 hours cells from the PDL and gingiva appeared to migrate into and repopulate the noncellular PDL. Few capillaries surrounded by mesenchymal cells and limited polymorphonuclear neutrophil infiltration were observed within the injured PDL site. Marginal gingival inflammation was minimal. At 14 days, collagen lysis, resorption of alveolar bone and root resorption were evident. In the PDL space, nonfunctionally oriented, cellular connective tissue elements were abundant. At 5 and 7 weeks, root resorption was marked. At this time interval, osteogenesis at seams of nonvital bone, repair cementum at sites of root resorption, and at times, ankylosis, were noted.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth factors in periodontal regeneration

Abstract:  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)-α, 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-α and TGF-α 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.     

Guided periodontal regeneration using bilayered collagen membranes and bovine bone mineral in fenestration defects in the canine

This study was performed to evaluate the effect of deproteinized bovine porous bone mineral (BBM) and BBM-collagen (BBMC) used alone or in combination with a bilayer collagen membrane in guided periodontal regeneration. In 12 dogs, contralateral surgical circular fenestration defects 5 mm in diameter were produced at the midbuccal aspect of the alveolar bone in 24 maxillary canines. Bone, periodontal ligament, and cementum were completely removed. Experimental sites were filled with BBM or BBMC. Bilayered collagen membranes covered half the experimental sites (BBM+M and BBMC+M), and the other half were left uncovered. Control sites remained empty; half were covered with collagen membranes (cont+M) and the underlying space spontaneously filled with blood, and half were left uncovered (cont). Three months postsurgery, undecalcified sections were prepared. Measurements were made using a caliper on a projection microscope, and the surface area of new bone and BBM particles within the healed surgical defect was evaluated using the point-counting method. In the experimental defects, new cementum covered 31% to 67% of the exposed dentin, with a significant difference between defects covered with membranes and defects that were not covered (P < .05). New cementum in the control (unfilled) defects also differed significantly between covered and uncovered defects. New bone growth presented a pattern similar to the cementum. There was no statistical difference between defects treated with BBM and BBMC, within both covered and uncovered groups. There was less connective tissue in the covered defects than in the uncovered defects (P < .05). The defects were filled with new bone, new connective tissue/bone marrow, and bovine bone particles. New bone area fraction was 23.4% to 25.2% in defects filled with BBMC and BBM, respectively (P = NS). Bone fraction area in membrane-covered defects ranged from 34.4% to 36.8% in experimental defects (P = NS). All membrane-treated defects showed higher values for bone area fraction in comparison to the uncovered control defects. Particle area fraction ranged between 17.4% and 26.2%, with only BBMC and BBM+M defects showing a statistically significant difference (P < .05). Defects filled with submembranous blood clot exhibited significantly more new cementum and bone regeneration than experimental defects filled with BBM or BBMC. Treatment of defects with BBM or BBMC showed similar influences on bone and cementum regeneration in fenestration periodontal defects. The presence or absence of bilayered collagen membranes was the predominant factor influencing bone and cementum regeneration.     

Experimental intrabony and periodontal defects treated with natural mineral combined with a synthetic cell-binding Peptide in the canine: morphometric evaluations

BACKGROUND: A synthetic peptide (P-15) analog of collagen added to anorganic bovine bone mineral (ABM) has recently been used as an enhanced bone graft material (ABM/P-15). The objective of this study was to test the contribution of ABM/P-15 in a new putty form (PEP) in two experimental membrane-protected defects: periodontal and intrabony. Its efficacy as filler biomaterial in guided tissue regeneration (GTR) and guided bone regeneration (GBR) procedures was evaluated histologically and morphometrically. METHODS: In the maxillary canines, a facial mucoperiosteal flap was raised bilaterally in nine dogs. Two circular defects, 5 mm in diameter and 2 mm in depth, were made on each side: a fenestrated periodontal on the canine root and an intrabony in the alveolar diastema, anteriorly. PEP particles filled both defects on one side; the contralateral side was blood filled (control). All surgical sites were covered with a bioabsorbable membrane. Histologically, at 4 months, tissue blocks were made using the cutting/grinding non-decalcification method followed by morphometric analysis. In the periodontal fenestration root surface, the linear percentage of new cementum (%CEM), area percentage of new bone (%NB), and residual biomaterial particles (%PEP) were calculated. These same measurements were calculated at the intrabony sites, except cementum. The amount of direct NB to PEP contact was measured to assess the osteoconductivity level (OSC). The Pearson correlation test was used to evaluate any significant relationship between the different measured parameters. RESULTS: In the grafted and non-grafted fenestration root surface defects, %CEM averaged 59.5% and 73.9% (P <0.02), respectively; %NB averaged 36.1% and 31.4%, respectively; and %PEP averaged 20.6%. The mean percentage of OSC was 52.4%. In the intrabony grafted and non-grafted sites, %NB averaged 50.7% and 60.1%, respectively (P <0.02). Residual %PEP averaged 26.1%, and OSC averaged 35.6%. At the intrabony sites, higher %NB and lower %OSC were found compared to the fenestration sites (P <0.001 and P <0.03, respectively). Correlation analysis showed a negative correlation between %NB and %PEP at the fenestration defects. In between the two defect types, %OSC was significantly correlated (P <0.05). CONCLUSIONS: ABM/P-15 putty showed osteoconductive and biocompatible qualities. However, at 4 months in this model, no enhanced regeneration was present compared to a higher CEM and NB growth detected at non-grafted membrane-protected sites.     

Tooth auto-transplantation with double periodontal ligament stimulation to replace periodontally compromised teeth

BACKGROUND: The healing process of autotransplantation puts 2 different tissues in competition: the ligament on the root surface and the bone tissue of the alveolus. This study shows the effects of a protocol with 2 surgical stages, which promote ligament repair, inhibit adhesion between bone and dental root, and reduce the occurrence of the ankylosis-root resorption phenomenon. METHODS: Forty-three patients, 33 to 73 years old, received 47 transplantations of mature teeth (including retained teeth) during a 5-year period. During the first surgical step, the transplanted tooth is extracted, measured, immediately replaced in its origin site, and maintained with an original suture technique. The alveolus to which the tooth will be transplanted is adapted after extraction of the periodontally compromised tooth. The second surgery occurs at day 14, when regeneration of periodontal ligament (PDL) is at a maximum (first stimulation). The tooth is transplanted in its new alveolus and retained using the same suture technique to avoid a rigid splint and to create mechanical stimulation of the PDL (second stimulation). RESULTS: The results were 95.75% positive with normal PDL, with a 4.25% failure rate (transplant loss) and no ankylosis. Mean probing reduction was 8.37 +/- 3.0 mm. Mean radiographic bone gain was 7.73 +/- 4.32 mm. CONCLUSIONS: This study suggests that auto-transplantation with double PDL stimulation can be a viable treatment in clinical practice, especially to replace teeth with large periodontal lesions, deep furcation defects, and/or root fractures. This study shows the high potential of stimulated PDL to regenerate alveolar bone and periodontal structures in severe destruction sites.     

A technique for treatment of extensive periodontal defects: a case study

This case study describes the use of oxidized cellulose mesh to improve healing of periodontal defects of poor regenerative capacity. Circumferential defects with horizontal bone loss were treated by surgical exposure of the root surface followed by scaling and root planing. Prior to flap replacement, oxidized cellulose mesh was positioned in incremental layers over the defects so as to replace the lost alveolar bone. It was to act also as a barrier to the ingress of epithlial cells and gingival fibroblasts into the healing wound using the principles vof guided tissue regeneration. Healing was good, with minimal post-operative recession. Whether regeneration of alveolar bone and periodontal ligament occurred as a result of using this technique could not be determined in this clinical case study.     

Confidence region of alveolar bone level on xeroradiography

Dental radiographs can be important for examination, evaluation and diagnosis of periodontal disease, and they have been widely used by dentists. However, discrepancies between radiographs and existing clinical periodontal tissue have been found. The purpose of this study was to investigate the relationship between the existing alveolar bone level on a Xeroradiograph and the root surface area covered with a periodontal ligament. Alveolar bone blocks from human skulls (total 34 teeth) and 60 patients (total 165 teeth) were used for this study. Each human skull bone block was taken Xeroradiograph under three types of conditions. 165 teeth from patients with severe periodontal disease were taken Xeroradiograph by a parallel method. The following equation was used for measuring the teeth on the Xeroradiograph. alpha = Root area supporting the existing alveolar bone/Root area from periapical to C-E junction x 100 The root surface area of each of the teeth extracted from bone blocks and of the extracted teeth from patients were measured by the membrane technique and calculated as follows: beta = Root surface area covered with periodontal ligament/Root surface area x 100 There was no significant difference in equation alpha calculated on three types of Xeroradiographs in the human skull. Significant positive correlations between alpha and beta were obtained, and an empirical regression line was constructed to estimate the ratio of the root surface area covered with periodontal ligament from the existing alveolar bone level on the Xeroradiograph. The results suggest that the ratio of the area of periodontal ligament to the root surface area given by these methods provides useful data for examination, diagnosis and evaluation of periodontal disease.     

Effect of recombinant human bone morphogenetic protein-2/absorbable collagen sponge (rhBMP-2/ACS) on healing in 3-wall intrabony defects in dogs

BACKGROUND: Recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge (ACS) carrier is being evaluated as a candidate therapy for periodontal regeneration. The objective of this study was to evaluate regeneration of alveolar bone and cementum, and associated root resorption and ankylosis following surgical implantation of rhBMP-2/ACS in a canine clinical model. METHODS: Bilateral 3-wall intrabony periodontal defects were surgically induced in the premolar region in the maxilla and mandible in 8 young adult Korean mongrel dogs. The defects in each animal received rhBMP-2/ACS (rhBMP-2 at 0.2 mg/ml, total implant volume/defect approximately 0.1 ml) or buffer/ACS, or served as sham-operated controls. Surgeries were sequenced for each animal to provide postmortem observations following 8- and 24-week healing intervals. Treatment outcomes were evaluated using clinical, radiographic, and histometric parameters. RESULTS: Surgical implantation of rhBMP-2/ACS resulted in accelerated enhanced bone formation in the 3-wall intrabony periodontal defects but in no apparent enhancement of cementum regeneration. rhBMP-2/ACS did not appear to be associated with aberrant healing events such as root resorption and ankylosis under these simulated clinical conditions. CONCLUSIONS: Surgical implantation of rhBMP-2/ACS may be used safely to support regeneration of alveolar bone in intrabony periodontal defects in dogs without aberrant events such as root resorption or ankylosis complicating the regenerative procedure. rhBMP-2/ACS does not appear to have a significant effect on cementum regeneration and formation of a functional periodontal ligament in this model.     

Effect of surgical implantation of recombinant human bone morphogenetic protein-2 in a bioabsorbable collagen sponge or calcium phosphate putty carrier in intrabony periodontal defects in the baboon

BACKGROUND: Recombinant human bone morphogenetic protein-2 (rhBMP-2) in a proper carrier has been shown to induce clinically relevant bone formation for several oral/maxillofacial and periodontal indications and to stimulate regeneration of the periodontal attachment. The objective of this study is to evaluate regeneration of alveolar bone, cementum, periodontal ligament, and associated root resorption and ankylosis following surgical implantation of rhBMP-2 in an absorbable collagen sponge (ACS) or a calcium phosphate putty (alphaBSM) carrier in 3-wall intrabony periodontal defects in the baboon. METHODS: rhBMP-2/ACS and rhBMP-2/alphaBSM were implanted in surgically produced, maxillary and mandibular, large size, 3-wall intrabony defects in 4 baboons. Contralateral jaw quadrants were implanted with buffer/ACS, buffer/ alphaBSM, or served as sham-operated surgical controls. Treatments were allocated to left and right, maxillary and mandibular, jaw quadrants following a randomization schedule. Four months following implantation, block biopsies of defect sites were obtained, processed, and subjected to histologic and histometric analysis. RESULTS: Defect sites receiving rhBMP-2/ACS and rhBMP-2/alphaBSM demonstrated significantly greater regeneration than controls. No significant differences were observed between defect sites receiving rhBMP-2/ACS or rhBMP-2/alphaBSM regarding epithelial migration and connective tissue attachment and new bone formation. However, rhBMP-2/ACS supported significantly greater new cementum formation. Ankylosis or root resorption were not observed. CONCLUSIONS: The results of this study support the use of rhBMP-2 to enhance periodontal regeneration of intrabony periodontal defects. While this novel technology holds promise, refinement in carrier systems may provide the key to enhancement of the regenerative potential.     

Experimental study of periodontal tissue regeneration. Changes in the periodontium after tooth implantation with and without periodontal ligament

The role of the periodontal ligament in periodontal tissue regeneration was evaluated. The materials included bilateral upper 1st premolars and lower 2nd, 3rd, and 4th premolars of 11 adult Beagle dogs, aged from 3 to 6 years. Before implantation, the right teeth were extracted and kept for a period of more than 3 months in "a solution for reserving teeth". The left teeth on the other hand, were extracted and soon implanted thus retaining the periodontal ligament into the newly created bone cavities prepared in the right edentulous areas. At the same time, the right reserved teeth were implanted into the left tooth sockets. Implanted teeth were periodically observed macroscopically, radiographically, and histologically for a 6-month period. Macroscopical observation showed good clinical repair in the bilateral sides of the tooth implantation with and without a periodontal ligament. After a 6-week experimental period, radiographic observations of the implanted lower right teeth having a periodontal ligament revealed lamina dura-like findings. Histopathological investigation revealed ankylosis and root resorption on the left side, where the reserved teeth without a periodontal ligament were implanted. But regeneration of the periodontal tissue complex, which consisted of the gingiva, alveolar bone, cementum, and periodontal ligament, was generally observed in the implanted right teeth having a periodontal ligament. These results suggest that the periodontal ligament cells play a significant role in periodontal tissue regeneration.     

Connective tissue reattachment as related to presence or absence of alveolar bone

The present study was designed to examine if alveolar bone, located adjacent to a root surface deprived of its periodontal ligament and cementum layer, can stimulate the reformation of a connective tissue attachment. The maxillary and mandibular incisors in 3 monkeys were extracted. Immediately after tooth extraction, the buccal root surfaces of the incisors from the left side of the jaws were planed by means of curettes to a level corresponding to half the root length. All teeth were then reimplanted into their original sockets. However, before tooth reimplantation, the buccal alveolar bone plate was removed in 2 of the monkeys to a level corresponding to half the depth of the sockets. The animals were sacrificed 6 months after the reimplantation procedure. The jaws were removed and histological sections of the experimental teeth and adjacent periodontal tissues were produced. The sections were analyzed in the microscope and subjected to histometric measurements. The results demonstrated that, irrespective of the presence or absence of alveolar bone, a fibrous reattachment failed to form on that part of the reimplanted teeth which had been deprived of their periodontal ligament. This indicates that alveolar bone located adjacent to a root surface may have limited influence on the biological conditions which determine whether periodontal healing results in connective tissue reattachment or new attachment.     

The regenerative potential of the periodontal ligament

The current decline in the incidence of dental caries indicates that patients will retain most of their dentition. Reconstruction or regeneration of the entire attachment apparatus, including the periodontal ligament, cementum, and bone, is an attainable therapeutic goal. Clinical treatments designed to reattach connective tissue to exposed root surfaces commonly result in the formation of a long junctional epithelial attachment. This attachment is probably not an effective barrier to bacterial toxins and may allow recurrent pocket formation. To enhance reattachment of connective tissue, root-conditioning agents have been used but their clinical efficacy is questionable. Restoration of destroyed alveolar supporting bone by means of allogenic and autogenous bone-grafting materials has been recommended, but these procedures do not restore the cementum and PDL. Attempts to promote regeneration of the entire attachment apparatus have included clinical studies that used mechanical means to promote repopulation of affected root surfaces by periodontal ligament fibroblasts and prevent contact of epithelial or gingival connective tissue cells. Results thus far have been encouraging, but the practicality of these techniques may be limited. However, these studies have demonstrated that if only PDL cells contact the root surface during healing, a normal PDL can re-form. Dental follicle tissue is capable of inducing the formation of cementum-like structures and is clearly the cell population responsible for cementum and PDL formation. Recent research has demonstrated that the dental papilla probably shares the same inductive capabilities as the dental follicle.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vivo differentiation of progenitor cells of the periodontal ligament

The present study was designed to test the hypothesis that during regeneration of cementum, the progenitor cells from periodontal ligament must come in contact with root dentin in order to differentiate into cementoblasts. After reflecting mucoperiosteal flaps, fenestration wounds were made in the buccal cortical plates of mandibular canines in 6 beagle dogs. The exposed root surfaces were curretted to remove all cementum. The exposed root surface on one side was demineralized with citric acid while the contralateral wound had saline treatment. The exposed root surfaces were then dried and pieces of Nuclepore membrane (pore size 0.1 mu) were attached to part of the exposed root surface to prevent contact of progenitor cells with root dentin. The fenestration wounds were then covered with Millipore filter to facilitate the population of wounds by progenitor cells from the periodontal ligament. Histologic analysis was performed after 3 months of healing. In specimens where the Nuclepore membrane had remained attached to root dentin, no new cementum was seen over the membrane. At the borders of the wounds and in specimens where the Nuclepore membrane had detached from root dentin, new connective tissue attachment was consistently seen. Also, root resorption was very rarely observed in both the acid-treated and control specimens. The present findings suggest that contact with root dentin may be necessary for progenitor cell differentiation into formative cells like cementoblasts.