Periodontal wound healing following GTR therapy of dehiscence-type defects in the monkey: short-, medium- and long-term healing

3D-Printed Soft Membrane for Periodontal Guided Tissue Regeneration

OBJECTIVES

The current study aimed to perform an in vivo examination using a critical-size periodontal canine model to investigate the capability of a 3D-printed soft membrane for guided tissue regeneration (GTR). This membrane is made of a specific composition of gelatin, elastin, and sodium hyaluronate that was fine-tuned and fully characterized in vitro in our previous study. The value of this composition is its potential to be employed as a suitable replacement for collagen, which is the main component of conventional GTR membranes, to overcome the cost issue with collagen.

METHODS

Critical-size dehiscence defects were surgically created on the buccal surface of the roots of canine bilateral mandibular teeth. GTR treatment was performed with the 3D-printed membrane and two commercially available collagen membranes (Botiss Jason® and Smartbrane-Regedent membranes) and a group without any membrane placement was considered as the control group. The defects were submerged with tension-free closure of the gingival flaps. Histologic and histometric analyses were employed to assess the periodontal healing over an 8-week experimental period.

RESULTS

Histometric evaluations confirmed higher levels of new bone formation in the 3D-printed membrane group. Moreover, in all defects treated with the membranes, the formation of periodontal tissues, bone, periodontal ligaments, and cementum was observed after 8 weeks, while in the control group, only connective tissue was found in the defect sites. There was no clinical sign of inflammation or recession of gingiva in any of the groups.

SIGNIFICANCE

The 3D-printed gelatin/elastin/sodium hyaluronate membrane can be safe and effective for use in GTR for periodontal tissue regeneration therapies, with better or comparable results to the commercial collagen membranes.

Pharmacological Activation of YAP/TAZ by Targeting LATS1/2 Enhances Periodontal Tissue Regeneration in a Murine Model

Due to their multi-differentiation potential, periodontal ligament fibroblasts (PDLF) play pivotal roles in periodontal tissue regeneration in vivo. Several in vitro studies have suggested that PDLFs can transmit mechanical stress into favorable basic cellular functions. However, the application of mechanical force for periodontal regeneration therapy is not expected to exhibit an effective prognosis since mechanical forces, such as traumatic occlusion, also exacerbate periodontal tissue degeneration and loss. Herein, we established a standardized murine periodontal regeneration model and evaluated the regeneration process associated with cementum remodeling. By administering a kinase inhibitor of YAP/TAZ suppressor molecules, such as large tumor suppressor homolog 1/2 (LATS1/2), we found that the activation of YAP/TAZ, a key downstream effector of mechanical signals, accelerated periodontal tissue regeneration due to the activation of PDLF cell proliferation. Mechanistically, among six kinds of MAP4Ks previously reported as upstream kinases that suppressed YAP/TAZ transcriptional activity through LATS1/2 in various types of cells, MAP4K4 was identified as the predominant MAP4K in PDLF and contributed to cell proliferation and differentiation depending on its kinase activity. Ultimately, pharmacological activation of YAP/TAZ by inhibiting upstream inhibitory kinase in PDLFs is a valuable strategy for improving the clinical outcomes of periodontal regeneration therapies.

Periodontal Wound Healing and Regeneration: Insights for Engineering New Therapeutic Approaches

Periodontitis is a widespread inflammatory disease that leads to loss of the tooth supporting periodontal tissues. The few therapies available to regenerate periodontal tissues have high costs and inherent limitations, inspiring the development of new approaches. Studies have shown that periodontal tissues have an inherent capacity for regeneration, driven by multipotent cells residing in the periodontal ligament (PDL). The purpose of this review is to describe the current understanding of the mechanisms driving periodontal wound healing and regeneration that can inform the development of new treatment approaches. The biologic basis underlying established therapies such as guided tissue regeneration (GTR) and growth factor delivery are reviewed, along with examples of biomaterials that have been engineered to improve the effectiveness of these approaches. Emerging therapies such as those targeting Wnt signaling, periodontal cell delivery or recruitment, and tissue engineered scaffolds are described in the context of periodontal wound healing, using key in vivo studies to illustrate the impact these approaches can have on the formation of new cementum, alveolar bone, and PDL. Finally, design principles for engineering new therapies are suggested which build on current knowledge of periodontal wound healing and regeneration.

Periodontal Ligament Cell Sheets and RGD-Modified Chitosan Improved Regeneration in the Horizontal Periodontal Defect Model

Objective  The aim of this study was to examine the potential of periodontal ligament (PDL) cells sheet and arginine-glycyl-aspartic acid (RGD)-modified chitosan scaffold for periodontal tissue regeneration in horizontal periodontal defect model.

Materials and Methods  PDL cell cytotoxicity was tested with 3–[4,5- dimethylthiazol-2yl]–2,5-diphenyl-2H-tetrazolium bromide assay. Cell migration toward the chitosan-based materials was analyzed with trans-well migration assay. Horizontal periodontal defect model was created in four maxillary and mandibular lateral incisors of Macaque nemestrina . Following periodontal therapy, the sites were transplanted with various regenerative materials: (1) chitosan, (2) RGD-modified chitosan, (3) PDL cell sheet with chitosan, (4) PDL cell sheet with RGD-modified chitosan. The periodontal tissue regeneration was evaluated clinically and radiographically. Gingival crevicular fluids were collected each week to evaluate cementum protein-1 (CEMP-1) expression with enzyme-linked immunosorbent assay, while the biopsies were retrieved after 4 weeks for histological and microcomputed tomography evaluation.

Statistical Analysis  Data was statistically analyzed using GraphPad Prism 6 for MacOS X. Normality was tested using the Shapiro–Wilk normality test. The Kruskal–Wallis test was used to compare the groups. Significance was accepted when p < 0.05.

Results  Clinical examination revealed more epithelial attachment was formed in the group with PDL cell sheet with RGD-modified chitosan. Similarly, digital subtraction radiography analysis showed higher gray scale, an indication of higher alveolar bone density surrounded the transplanted area, as well as higher CEMP-1 protein expression in this group. The incorporation of RGD peptide to chitosan scaffold in the group with or without PDL cells sheet reduced the distance of cement–enamel junction to the alveolar bone crest; hence, more periodontal tissue formed.

Conclusions  Horizontal periodontal defect model could be successfully created in M. nemestrina model. Combination of PDL cell sheet and RGD-modified chitosan resulted in the higher potential for periodontal tissue regeneration. The results of this study highlight the PDL cell sheet and RGD-modified chitosan as a promising approach for future clinical use in periodontal regeneration.

A New Technique for Research on Wound Healing through Extraction of Mandibular Lower Incisors in Wistar Rats

Objective The aim of this study was to explain a new technique for research on wound healing through extraction of mandibular lower incisors in Wistar rats.

Materials and Methods Fifty Wistar rats were used from studies using the experimental animal to investigate the effects of wound healing drugs on alveolar bone. The mandibular incisors of the Wistar rats were extracted using a special modified bein and special pulling pliers under general anesthesia. The tooth socket after extraction was closed using a 5.0 suture nylon needle.

Results The results of this technique used in this extraction showed 2% incisor tooth fracture and 3% bleeding, and that all fractured teeth could be removed properly, and bleeding could be stopped after suturing.

Conclusion The new techniques we use can be useful for research on mucosal and alveolar bone healing, specifically finding new types of drugs to accelerate wound healing after alveolar bone post extraction.

Evaluation of Efficacy of Surgical Periodontal Therapy with the Use of Bone Graft in the Treatment of Periodontal Intrabony Defects

INTRODUCTION

One of the most important goals of periodontitis therapy is the elimination of deep periodontal pockets. In regenerative periodontal therapy, different types of bone grafts, membranes, growth factors, etc. are used to improve regeneration of lost periodontal tissue. The aim of this study was to evaluate the effect of surgical therapy supported by the use of bone replacement material in the treatment of deep intrabony pockets, compared to surgical treatment (flap surgery) without the use of bone replacement in advanced periodontitis.

METHODS AND MATERIALS

The study included 50 patients of both sexes with advanced periodontitis, divided into two groups. After initial periodontal therapy was performed, plaque index (PI), papillary bleeding index (PBI) were verified, and depth of periodontal pockets was measured in both groups. One group (group 1) of the patients underwent surgical therapy, open flap surgery, while the other group (group 2) underwent the same surgical treatment method (open flap surgery), during which bone defects were filled with bone replacement material.

RESULTS

The results showed that both group 1 and group 2 experienced improvements after periodontal surgical therapy. In group 1, there are no statistically significant changes in all three plaque index measurements (PI), while there has been a significant reduction in PI in group 2 following the surgery. For the PBI index, it was determined that there were statistically significant changes in values in group 1, both after surgical procedures and six months later, as well as in group 2. Statistical analysis of the results of the probing depth of pockets has shown that there are significant changes in the measurement of the depth of periodontal pocket one month after the surgery, as well as six months later, meaning that there has been a significant reduction in the depth of the periodontal pocket one month following the surgery as well as six months later, for both groups. However, we did not determine a statistically significant difference in the probing depth of pockets between these two groups.

CONCLUSION

Six months after a surgical therapy, clinical parameters showed a reduction of the probing depth of the periodontal pocket in both examined groups. The use of bone replacement did not yield significantly better results in reducing the depth of probing compared to the standard flap surgery. We believe that future research should focus on testing the effectiveness of new regenerative methods and materials (bone replacements with various properties, membranes, and surgical methods) that will result in better treatment results with predictable outcomes.

The influence of root surface distance to alveolar bone and periodontal ligament on periodontal wound healing

PURPOSE

The purpose of this animal study was to perform a 3-dimensional micro-computed tomography (micro-CT) analysis in order to investigate the influence of root surface distance to the alveolar bone and the periodontal ligament on periodontal wound healing after a guided tissue regeneration (GTR) procedure.

METHODS

Three adult Sus scrofa domesticus specimens were used. The study sample included 6 teeth, corresponding to 2 third mandibular incisors from each animal. After coronectomy, a circumferential bone defect was created in each tooth by means of calibrated piezoelectric inserts. The experimental defects had depths of 3 mm, 5 mm, 7 mm, 9 mm, and 11 mm, with a constant width of 2 mm. One tooth with no defect was used as a control. The defects were covered with a bioresorbable membrane and protected with a flap. After 6 months, the animals were euthanised and tissue blocks were harvested and preserved for micro-CT analysis.

RESULTS

New alveolar bone was consistently present in all experimental defects. Signs of root resorption were observed in all samples, with the extent of resorption directly correlated to the vertical extent of the defect; the medial third of the root was the most commonly affected area. Signs of ankylosis were recorded in the defects that were 3 mm and 7 mm in depth. Density and other indicators of bone quality decreased with increasing defect depth.

CONCLUSIONS

After a GTR procedure, the periodontal ligament and the alveolar bone appeared to compete in periodontal wound healing. Moreover, the observed decrease in bone quality indicators suggests that intrabony defects beyond a critical size cannot be regenerated. This finding may be relevant for the clinical application of periodontal regeneration, since it implies that GTR has a dimensional limit.

Long-term Observation of Regenerated Periodontium Induced by FGF-2 in the Beagle Dog 2-Wall Periodontal Defect Model

The long-term stability and qualitative characteristics of periodontium regenerated by FGF-2 treatment were compared with normal physiological healing tissue controls in a Beagle dog 2-wall periodontal defect model 13 months after treatment by assessing tissue histology and three-dimensional microstructure using micro-computed tomography (μCT). After FGF-2 (0.3%) or vehicle treatment at the defect sites, serial changes in the bone mineral content (BMC) were observed using periodic X-ray imaging. Tissues were harvested at 13 months, evaluated histomorphometrically, and the cortical bone volume and trabecular bone structure of the newly formed bone were analyzed using μCT. FGF-2 significantly increased the BMC of the defect area at 2 months compared with that of the control group, and this difference was unchanged through 13 months. The cortical bone volume was significantly increased by FGF-2, but there was no difference between the groups in trabecular bone structure. Bone maturation was occurring in both groups because of the lower cortical volume and denser trabecular bone than what is found in intact bone. FGF-2 also increased the area of newly formed bone as assessed histomorphometrically, but the ratios of trabecular bone in the defect area were similar between the control and FGF-2 groups. These results suggest that FGF-2 stimulates neogenesis of alveolar bone that is of similar quality to that of the control group. The lengths of the regenerated periodontal ligament and cementum, measured as the distance from the defect bottom to the apical end of the gingival epithelium, and height and area of the newly formed bone in the FGF-2 group were larger than those in the control group. The present study demonstrated that, within the limitation of artificial periodontal defect model, the periodontal tissue regenerated by FGF-2 was maintained for 13 months after treatment and was qualitatively equivalent to that generated through the physiological healing process.

Clinical and radiographic evaluation of periodontal intrabony defects by open flap surgery alone or in combination with Biocollagen(®) membrane: A randomized clinical trial

BACKGROUND

Guided tissue regeneration (GTR) is often incorporated in regenerative periodontal surgical procedures. However, the actual benefits of adding GTR to such a procedure remain undocumented. The purpose of this randomized controlled trial was to investigate the contribution of GTR to the outcomes of open flap debridement (OFD) in the treatment of intrabony defects.

MATERIALS AND METHODS

A total of 16 patients of both sexes satisfying the criteria of chronic periodontitis and each of whom displayed one intrabony defect were randomly assigned to two groups, i.e. either treated with open flap surgery and GTR (group 1) or with open flap surgery alone (group 2), in this parallel-arm study. The soft tissue and hard tissue measurements, including probing pocket depth (PD), clinical attachment level (CAL), and bone mineral density were recorded at baseline and 3,6 and 12 months after surgery. The differences with a P < 0.05 were considered significant.

RESULTS

Results showed that the membrane group showed significant difference when compared with open flap surgery alone, in relation to the degree of periodontal pocket, clinical attachment loss, and bone density.

CONCLUSION

The findings of this study suggest that biocollagen membrane could be considered as an option in the treatment of intrabony defects. Biocollagen membrane alone gives favorable clinical results in the treatment of intrabony defects. Open flap debridement resulted in acceptable clinical results in the treatment of intrabony defects.

Interproximal periodontal defect model in dogs: a pilot study

OBJECTIVE

This study aimed to evaluate the validity of a surgically created interproximal periodontal defect in dogs.

MATERIALS AND METHODS

Surgery was performed in the interproximal area between the maxillary second and third premolars in two beagle dogs. Following an incision and reflection of the gingival flap, a 3-mm wide and 5-mm high defect was prepared surgically at the interproximal area. A thorough root planing was performed and the flap was coronally positioned and sutured. The contra-lateral area was served as the control with no surgical intervention. After 8 weeks of healing, the animals were killed and the defect was analysed histometrically and radiographically.

RESULTS

The interproximal periodontal defect resembled a naturally occurring defect and mimicked a clinical situation. After healing, the defect showed limited bone (0.89±0.02mm) and cementum regeneration (1.50± 0.48mm).

CONCLUSIONS

Within the limitations of this pilot study, the interproximal periodontal defect showed limited bone and cementum regeneration. Thus, it can be considered as a standardized, reproducible defect model for testing new biomaterials.

Wound healing following regenerative procedures in furcation degree III defects: histomorphometric outcomes

Degree III furcation involvements were surgically created at four first molars in each of three monkeys. Following 6 weeks of healing, full-thickness flaps were elevated. Following 24% EDTA gel conditioning, the defects were treated with one of the following: (1) enamel matrix proteins (EMD), (2) guided tissue regeneration (GTR) or (3) a combination EMD and GTR. The control defects did not receive any treatment. After 5 months of healing, the animals were sacrificed. Three 8 μm thick histological central sections, 100 μm apart, were used for histomorphometric analysis in six zones of each tooth either within the furcation area or on the pristine external surface of the root. In all specimens, new cementum with inserting collagen fibres was formed. Following GTR or GTR + EMD, cementum was formed up to and including the furcation fornix indicating complete regeneration on the defect periphery. Periodontal ligament fibres were less in all four modalities compared to pristine tissues. In the teeth treated with GTR and GTR + EMD a higher volume of bone and periodontal ligament tissues was observed compared to EMD. After 5 months of healing, regenerated tissues presented quantitative differences from the pristine tissues. In the two modalities where GTR alone or combined with EMD was used, the regenerated tissues differed in quantity from the EMD-treated sites.

Evaluation of an injectable rhGDF-5/PLGA construct for minimally invasive periodontal regenerative procedures: a histological study in the dog

AIM

To evaluate the injectability, biocompatibility, safety, and periodontal wound healing/regeneration following application of a novel bioresorbable recombinant human growth/differentiation factor-5 (rhGDF-5)/poly(lactic-co-glycolic acid) (PLGA) construct.

MATERIAL AND METHODS

Periodontal pockets (3 x 6 mm, width x depth) were surgically created over the buccal roots of the second and fourth mandibular pre-molars in eight adult Hound Labrador mongrel dogs. Surgeries including injection of the rhGDF-5/PLGA construct into the pockets were sequenced that four animals provided 2-/4-week and four animals 6-/8-week observations of sites receiving rhGDF-5/PLGA or serving as sham-surgery control.

RESULTS

The rhGDF-5/PLGA construct was easy to prepare and apply. Approximately 0.2 ml (93 microg rhGDF-5)/tooth was used. Clinical and radiographic healing was exemplary without adverse events. Healing was characterized by a non-specific connective tissue attachment, acellular/cellular cementum, periodontal ligament (PDL), bone regeneration, and a junctional epithelium. PLGA fragments were observed in 4/7, 2/8, and 1/8 sites at 2, 4, and 6 weeks, respectively. Associated inflammatory reactions exhibited no limiting effect on periodontal wound healing/regeneration. Root resorption/ankylosis was not observed. Bone formation showed apparent increased maturity (lamellar bone) at 6 weeks in sites receiving rhGDF-5/PLGA compared with the control. Both protocols exhibited significant increases in PDL, cementum, and bone regeneration over time, without significant differences between treatments. In time, PDL and cementum regeneration was twofold greater for the control at 4 weeks (p=0.04) while increased bone formation was observed at sites receiving rhGDF-5/PLGA (p<0.01).

CONCLUSIONS

In conclusion, the rhGDF-5/PLGA construct appears to be a safe technology for injectable, ease-of-use application of rhGDF-5-stimulated periodontal wound healing/regeneration. Additional work to optimize the polymer carrier and rhGDF-5 release kinetics/dose might be required before evaluating the efficacy of this technology in clinical settings using minimally invasive approaches.

Histological characteristics of newly formed cementum in surgically created one-wall intrabony defects in a canine model

PURPOSE

Periodontal regenerative therapies for defects created by severe periodontitis are mainly focused on bone regeneration. Although cementum regeneration needs to be better understood, it is believed to play an important role in periodontal regeneration. The first step toward a full understanding of cementum regeneration is to compare repaired cementum to pristine cementum. This study, which used histological techniques, was designed to focus on cementum regeneration and to compare pristine cementum to repaired cementum after surgical procedures with 8 and 24 week healing periods in a canine model.

METHODS

Buccal and lingual mucoperiosteal flaps of 10 beagle dogs were surgically reflected to create critical-sized defects. Intrabony one-wall defects, of which dimension is 4 mm width and 5 mm depth, were made at the distal aspect of mandibular second premolars and the mesial aspect of mandibular fourth premolars in the right and left jaw quadrants. Animals were sacrificed after 8 and 24 weeks post-surgery for histological specimen preparation and histometric analysis.

RESULTS

The repaired cementum was composed mostly of acellular cementum and cellular mixed fiber cementum and was thicker in the apical area than in the coronal area. The acellular cementum of the supracrestal area appeared to be amorphous. The newly formed cellular cementum was partially detached from the underlying circumpulpal dentin, which implied a weak attachment between new cementum and dentin, and this split was observed to a lesser extent in the 24 week group than in the 8 week group. The vertical height of the repaired cementum was greater in the 24 week group than in the 8 week group.

CONCLUSIONS

Within the limitations of this study, we can conclude that repaired cementum after root planing was mainly acellular cementum and cementum tissue that matured to a shape similar to pristine cementum as the healing progressed from 8 to 24 weeks.

Pre-clinical models for oral and periodontal reconstructive therapies

The development of new medical formulations (NMF) for reconstructive therapies has considerably improved the available treatment options for individuals requiring periodontal repair or oral implant rehabilitation. Progress in tissue engineering and regenerative medicine modalities strongly depends on validated pre-clinical research. Pre-clinical testing has contributed to the recent approval of NMF such as GEM 21S and INFUSE bone grafts for periodontal and oral regenerative therapies. However, the selection of a suitable pre-clinical model for evaluation of the safety and efficacy of a NMF remains a challenge. This review is designed to serve as a primer to choose the appropriate pre-clinical models for the evaluation of NMF in situations requiring periodontal or oral reconstruction. Here, we summarize commonly used pre-clinical models and provide examples of screening and functional studies of NMF that can be translated into clinical use.

Extracellular matrix expression and periodontal wound-healing dynamics following guided tissue regeneration therapy in canine furcation defects

AIM

Temporal and spatial expression pattern of extracellular matrix (ECM) components in furcation defects following guided tissue regeneration (GTR) compared with open-flap debridement (OFD).

MATERIAL AND METHODS

In 21 dogs, mandibular second and fourth pre-molars were treated with one non-resorbable and three different resorbable membranes. Third pre-molars were treated by OFD. After 2, 4, 8 weeks and 3, 6, and 12 months, tissues were analysed by immunohistochemistry for collagen I (Col-I) and III (Col-III), fibronectin (FN), bone sialoprotein (BSP), and osteopontin (OPN).

RESULTS

At 2 weeks, the defect was mainly occupied by FN+ granulation tissue (GT), which was sequentially replaced by new connective tissue expressing FN, Col-I, and increasingly Col-III. Following superficial resorptions by OPN+ osteoclasts and odontoclasts, cementum and bone formation ensued with strong expression of BSP and OPN along bone and tooth surfaces. Deposition of Col-I, FN, BSP and OPN+ cementoid and osteoid became evident after 4 weeks. Extrinsic fibres of cementum and bone stained intensely for Col-III. The newly formed periodontal ligament expressed FN, Col-I, and Col-III, but no BSP or OPN.

CONCLUSIONS

The spatial ECM expression was similar for OFD and the different GTR methods, although the timing and quantity of ECM expression were influenced by wound stabilization and inflammatory reactions.

Gene expression profiling of cells involved in periodontal regeneration

Understanding the molecular mechanisms involved in periodontal regeneration is important for the development of more predictable clinical techniques. This study aimed to identify these mechanisms by comparing the gene expression profiles of cells derived from regenerating defects with patient-matched periodontal ligament cells. Gene profiling was carried out via Affymetrix U133A arrays containing probes for 22,000 genes. Robust differences in gene expression were obtained by identifying genes that consistently changed by a minimum of 2-fold. Analysis of molecular function as designated by gene ontology (GO) identified differentially regulated mechanisms including protein metabolism, tyrosine kinase activity, and skeletal development. The differentially expressed genes could be broadly divided into the categories of protein biosynthesis and turnover, structural constituents of the cytoskeleton and extracellular matrix, and signal transduction. The differential expression of 4 genes (EGR-1, elastin, osteoprotegerin, and IGFBP3) was confirmed via real-time polymerase chain reaction (PCR). Further, the expression of another 2 differentially expressed transcripts, decorin and biglycan, was immunohistochemically confirmed in a periodontal wound healing model and the protein expression was consistent with the pattern of gene expression. This study gives insight into the molecular processes involved in periodontal regeneration and identifies cell markers that are characteristic of regenerating periodontal tissues.

The structure of periodontal tissues formed following guided tissue regeneration therapy of intra-bony defects in the monkey

OBJECTIVE

To describe the periodontal tissues formed following guided tissue regeneration (GTR) therapy of intra-bony defects (IBD).

METHODS

Eight adult Macaca fascicularis monkeys were used. Proximal IBD were created at the mandibular second pre-molars and second molars. After 3 months, GTR surgery was performed. The animals were euthanized at 6 months and 2 years after surgery. Block biopsies were harvested, and prepared for histological analysis.

RESULTS

At 6 months the defect had healed with new cementum (NC), periodontal ligament (PDL) and bone. The NC seemed to be firmly anchored to the dentin. Supra-crestally, the NC consisted of a 10 microm thick layer of acellular extrinsic fibre cementum (AEFC). Sub-crestally, the NC was considerably thicker and consisted of an inner layer of AEFC and an outer thicker layer of cellular mixed fibre cementum (CMFC). The extrinsic fibre density amounted to about 10 fibres per 100 microm. The PDL was wider than the pristine PDL and widened in coronal direction. After 2 years of healing, the thickness of the NC in the sub-crestal compartment had increased by about 20 microm and the fibre density had increased by about 50%.

CONCLUSION

After 2 years of healing the structure of the regenerated tissues resembled that of pristine periodontal tissues.