Periodonta Regeneration

REGENERATION Restoration of structure and function is accomplished by "regeneration" while replacement with simpler nonfunctional tissues is "repair.“ Repair is the replacement of dead cells with fibrous connective tissue cells and fibers; depending on the cells affected, function is often not restored. • • • •

Factors Governing Regeneration Type of destroyed cells. Condition of the stroma. Number of remaining cells 1- Type of Cell Destroyed “Labile cells" continually divide; they will regenerate. Covering cells of the skin and gastrointestinal tract (oral mucosa) as well as bone marrow cells . "Stable cells" may divide; they may regenerate. Parenchymal cells of the liver as well as many connective tissue cells "Permanent cells" cannot divide; they cannot regenerate. Skeletal muscle cells, cardiac muscle cells, and nervous system neurons 2 - Condition of the stroma.

The stroma of an organ is its supporting and nourishing component. It is generally composed of fibrous connective tissue through which blood vessels and nerves pass. The stroma provides a framework or scaffolding upon which parenchymal cells are attached. It is composed of collagen and reticular fibrils Regeneration will be hindered if the stroma is destroyed. 3- Number of remaining cells Because regeneration depends on mitosis of nearby cells, a critical mass of remaining cells should be present. 3- Number of remaining cells Because regeneration depends on mitosis of nearby cells, a critical mass of remaining cells should be present. Wound Healing

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There are Four basic steps in repair of a wound Clot formation Inflammation Proliferation “Epithelialization, Granulation ,Organization Maturation ,Cicatrization

Clot is composed of a protein known as "fibrin Fibrin forms a protein meshwork that serves to hold the wound together, to prevent foreign materials from entering, and to form a scaffold into which reparative tissue can penetrate. Another protein, “Fibronectin" also appears in the early stages of wound healing. This substance is derived from blood plasma During the first several hours, a mild acute inflammatory reaction appears. Chemical mediators released from cells damaged during the incision initiate the inflammatory reaction. The reaction is a mild one

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Platelets, the first response cell, release multiple cytokines including; • •

Insulin-like growth factor-I (IGF-I), Platelet-derived growth factor-AB (PDGF-AB), PDGF-BB,

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Vascular endothelial growth factor (VEGF),

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Transforming growth factor-beta1 (TGF-beta1),

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Epidermal growth factor (EGF) .

Fibronectin, fibrinogen, histamine serotonin, and vonWillebrandactor Platelet degranulation also activates the complement cascade, specifically C5a, which is a potent chemoattractant for neutrophils Neutrophil •

The second response cell to migrate to the wound

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Responsible for debris scavenging

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Complement-mediated opsonization of bacteria.

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Bacteria destruction via oxidative burst mechanisms (i.e., superoxide and hydrogen peroxide formation). 3

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The neutrophils kill bacteria and decontaminate the wound from foreign debris (microphagocyte Elaborate IL-1 Macrophages The next cells present in the wound are the macrophages (monocytes). Macrophages secrete numerous enzymes as Collagenases, which debride the wound Interleukins and tumor necrosis factor (TNF), which stimulate fibroblasts (produce collagen) and promote angiogenesis.

• Growth factors Cytokine

Cell of Origin

Function

PDGF

Platelets Macrophages Endothelial cells

Cell chemotaxis Mitogenic for fibroblasts Stimulates angiogenesis Stimulates wound contraction

TGF-alpha

Macrophages T lymphocytes Keratinocytes

Mitogenic for keratinocytes and fibroblasts Stimulates keratinocyte migration

TGF-beta

Platelets T lymphocytes Macrophages Endothelial cells Keratinocytes

Cell chemotaxis stimulates angiogenesis and fibroplasia

EGF

Platelets Macrophages

Mitogenic for keratinocytes and fibroblasts Stimulates keratinocyte migration

Fibroblast growth factor

Macrophages Mast cells T lymphocytes Endothelial Ce

Chemotactic and mitogenic for fibroblasts and keratinocytes Stimulates angiogenesis

Keratinocyte growth factor

Fibroblasts

Stimulates keratinocyte migration, differentiation, and proliferation

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Growth factors normally are detectable only at a very low concentrations. They are deposited in response to specific stimuli. These stimuli can be major or minor wound healing events such as clot formation, cell damage, neovascularization, and the presence of inflammatory mediators.

Interleukin (IL)–1, IL-2, IL-6, and IL-8

Macrophages Mast cells Keratinocytes Lymphocytes

IL-1 - Induces fever and adrenocorticotropic hormone release, enhances TNFalpha and interferon (INF)– gamma, activates granulocytes and endothelial cells, and stimulates hematopoiesis IL-2 - Activates macrophages, T cells, natural killer cells, and lymphokineactivated killer cells; stimulates differentiation of activated B cells; stimulates proliferation of activated B and T cells; and induces fever IL-6 - Induces fever and enhances release of acutephase reactants by the liver IL-8 - Enhances neutrophil adherence, chemotaxis, and granule release

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INFs (IFN-alpha, -beta, and -delta)

Lymphocytes Fibroblasts

Activate macrophages Inhibit fibroblast proliferation

Angiogenesis, is stimulated by TNF-alpha, the new capillaries deliver nutrients to the wound and help maintain the granulation tissue bed. - The final part of the proliferative phase is granulation tissue formation. Fibroblasts differentiate and produce ground substance and then collagen. The ground substance is deposited into the wound bed; collagen is then deposited as the wound undergoes the final phase of repair. 4-- The final phase of wound healing is the maturational phase. Collagen deposition continues for a prolonged period, but the net increase in collagen deposition plateaus after 21 days. The wound undergoes contraction, ultimately resulting in a smaller amount of apparent scar tissue.

Healing of Periodontal Wound The healing of periodontal wounds following flap surgery is a more complex process than that which takes place in a skin injury. The flap of soft tissue is located over a hard tissue, the root, with an avascular surface, sometimes contaminated with bacteria and toxic materials. The most common healing of a periodontal wound is characterized fundamentally by the epithelialization of the internal face of the flap in contact with the radicular surface, forming the so-called long epithelial attachment. More apically, the maturation of the connective tissue reestablishes the connective attachment, and, at the deepest point of the injury, it is possible to detect a certain recovery of the bone architecture and the periodontal ligament

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Reattachment and New attachment. Reattachment is the attachment between two parts of previously separated tissue, whether due to periodontal injury or to the destructive process of periodontitis. This occurs when viable ligament tissue still exists on the radicular surface, in such a way that during healing this tissue is able to unite with the periodontal fibers on the opposite side of the wound. This phenomenon may arise during the healing of the deepest areas of the periodontal pocket. New attachment is used when this joining of tissues (epithelial and/or connective) is produced on an area of the radicular surface previously affected by periodontitis, and where no viable periodontal tissue remained Periodontal Regenerative TherapyWhen we speak of periodontal regeneration, we usually refer to the partial regeneration (in height) of the periodontium., complete regeneration of the periodontium around whole circumference of the tooth is not abt to occure in humanDuring tooth development, the periodontal stem cells originate from the dental follicle cells, and are able to differentiate in order to form radicular cementum, periodontal ligament, and alveolar bone.

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Some of these stem cells remain in the periodontal ligament after the tooth has fully developed. During the healing of a periodontal wound, these stem cells, together with those located in the perivascular region of the alveolar bone, are stimulated to proliferate, migrate into the defect and differentiate to form new cementoblasts, periodontal ligament fibroblasts, and osteoblasts Periodontal Debridement This basic approach, whether achieved by nonsurgical disinfection during closed debridement e.g., ( in periodontal pocket depths of up to 5 mm) or by surgical debridement, can lead to the development of a stable attachment apparatus, if not regeneration. In advanced cases (e.g., cases of severe loss of horizontal alveolar bone), healing after debridement procedures is not followed by significant gains in new attachment

Surgical debridement of intraosseous defects appears to lead predictably to an increase in periodontal attachment of about 2.5 mm, with variable amounts of bone filling (Polson 1978).

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Radicular

(Root) conditioners

The radicular surface exposed to a periodontal pocket or to the oral cavity presents bacteria, bacterial toxins or even changes in mineralization . Instrumentation of the root surface, however, results in formation of a smear layer of organic and mineralized debris. The thickness of this smear layer usually ranges from 2-15 μ is thought to serve as a physical barrier between the periodontal tissues and the root surface and may inhibit deformation of new connective tissue attachment to the root surface . 1- A saturated citric acid solution It is prepared by adding distilled water to the acid gradually until the PH reached 1 and the prepared solution is continuously stirred for 10 minutes .Acid is applied to root surface by cotton pellet for 3 minutes .

2- Tetracycline HCl solution It is freshly prepared by adding a 500 mg capsule to 5 ml of distilled water to result in 5% solution and the solution is continuously stirred for 10 minutes .The solution pH is about 3.3. 3 - Ethylenediamine tetra acetic acid EDTA (pH 7.0) solution or gel in 15%,- 20% concentration EDTA not only preserves the vitality of the remaining periodontal cells close to the root surface, but also removes calcium ions from the collagenous dentin matrix more selectively (chelation) than lowpH etching agents 4- Erebium Yttrium Aluminum Garne (Er:YAG laser) 9

Erbium laser ablates hard tissue through “microexplosion” rather than heating the tissue resulting in minimal thermal effects The results of histological studies in humans have been contradictory, A recent systematic review of the literature concluded that the evidence to date suggests that using these chemical agents has no significant clinical benefit for the patient with respect to the reduction in probing depth or gain in clinical attachment level (Mariotti 2003)).

Bone Grafting It was thought that bone regeneration constituted a prerequisite for the formation of a new attachment, and that the formation of new bone would induce the formation of new cementum and periodontal ligament S0,different types of bone grafts and other materials have been used to enhance bone regeneration Indications Periodontal pockets (intrabony) greater than 5 mm following phase I therapy are difficult for patients to maintain and may be susceptible to further breakdown. These areas should be evaluated and considered for either pocket reduction or bone fill regenerative surgery Vertical bone loss with a resultant intrabony defect can result in moat-shaped defects. These lesions, especially those with two or three walls, respond well to bone fill regenerative procedures. Most notably, guided tissue regeneration (GTR) with or without bone graft materials Furcations

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In areas with furcations where there has been bone loss extending apically less than 4 mm from the crotch of the furca, the defect can be well managed with osseous surgery and apically positioned flaps. This will result in a papillalike projection of gingival tissue in the furcation with pocket depths of 2 to 3 mm. Bone fill regenerative procedures do not provide significant advantages for the Class I furcation defect with minimal bone loss. Class III furcation defects do not respond well to bone fill regenerative procedures. If a tooth has lost 70% or more of its supporting bone volume and has significant mobility (class 2+ or greater) following initial therapy, then bone fill regenerative procedures have little, if any, chance of success. Patients with periodontal pockets that are not associated with vertical bone loss (ie, intraosseous defects) should be managed with surgery directed at reducing the suprabony pockets, such as flap curettage, open flap débridement, or gingivectomy. In the anterior portion of the mouth, it may be better to maintain these areas with a nonsurgical approach if postsurgical gingival recession would create an aesthetic compromise.

Bone-grafting materials •

Autograft ("Autogenous") the gold standard grafting material

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Allograft transplant within the same species

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Xenograft a cross-species transplantation

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Alloplast implantation of a synthetic material Intraoral sources include

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Edentulous ridges, exostoses, tori,

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Healing extraction sites (8 to 12 weeks after extraction to allow newly forming bone to mature), 11

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Surgically created osseous defects,

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Implant osteotomy site,

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Maxillary tuberosity, and the Periodontal surgical site

Extraoral autogenous bone grafts may be harvested in large quantities from the iliac crest. •

Frozen specimens are preferred because of the greater bone apposition they demonstrate, a result of the cellular breakdown and release of inductive substances that occurs during the freezing process

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The postoperative complications associated with autogenous iliac grafts, make autogenous iliac crest grafts an undesirable alternative.

Autogenous graft may be cortical or cancellous. •

Cancellous bone contains a higher percentage of cells, and therefore has more osteogenic potential.

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Cortical bone is believed to have higher levels of BMP's, and is useful when structural support or three-dimensional augmentation is required.

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Osseous coagula are grindings of cortical intraoral bone that were mixed with blood Advantage of autogenous bone graft:

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1 - Presence of viable osteogenic cells within the graft

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2- The remaining non-vital bone matrix serves as an osteoconductive scaffold and is gradually replaced by "creeping substitution", 12

3- It have osteoinductive activity As autogenous bone matrix is broken down, bone morphogenetic proteins are released, resulting in the attraction, differentiation and proliferation of bone forming cells. 4- Autogenous grafts are nonimmunogenic • •

Trephines for harvesting autografts 1- The edentulous maxillary tuberosity may be harvested where a small amount of bone is required using small rongers

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2- The use of an osseous coagulum trap

3- The use of a bone "scraper"

4- Trephines For use in harvesting bone

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After harvest, the bone is morselized into small fragments less than 1.0 mm in size and kept moist in sterile saline until ready for use.

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Osteo-Crusher Hand-held bone mill used to create particulate bone from harvested autogenous bone

Allografts An allograft is a graft between genetically dissimilar members of the same species. Allografts used in periodontics are primarily in 2 forms: Ffreeze dried bone allograft

(FDBA)

Decalcified freezedried bone allograft (DFDBA). The demineralization of the cortical bone improves the osteoinductive potential by exposing bone morphogenic proteins, and other inductive factors known to increase bone formation.

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They are available in unlimited amounts, and have osteoinductive potential comparable with autogenous bone Grafting with DFDBA has been shown to result in new attachment apparatus characterized by new bone, cementum, and periodontal ligament fibers

MinerOss® is a mixture of mineralized allograft cancellous and cortical chips that provide an osteoconductive scaffold to encourage bone growth.DFDBA

DFDBA

Grafton DBM Putty - network of DBM Fibers in a glycerol carrier

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Reginafil DFDBA

Xenografts Derived from animal sources. Anorganic bovine bone is chemically treated to remove its organic components, leaving a trabecular and porous architecture similar to human bone. Studies show that xenografts may have osteoinductive capabilities, and there appears to be no difference between the clinical healing of anorganic bovine bone and DFDBA. Anorganic bovine bone may result in a gain in clinical attachment accompanied by regeneration, especially when combined with the use of an occlusive membrane 16

Xenografts PepGen P-15 (received ADA Seal of Acceptance in May 2002) Dentsply CeraMed Dental, Lakewood, Colo. PepGen P-15 is a bone-grafting material that is composed of anorganic bovine-derived hydroxyapatite bone matrix, or ABM, combined with a synthetic cell-binding peptide, P-15. The P-15 peptide is a synthetic clone of a 15 amino acid sequence of the α1 chain of Type I human collagen (residues 766-780). Pep-Gen P-15 combines 200 nanograms of P- 15 with 1 gram of ABM and is available in particulate and gel form Alloplasts They are osteoconductive, inert biologic fillers. They include : •

Ceramics such as calcium phosphate (hydroxyapatite) and tricalcium phosphate,

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Calcium sulfate (plaster of Paris),

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Calcium carbonates (coral)

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Bbioactive glass ceramics.

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“Calcium Hydroxide (oily solution) Osteora®MetaCura GmbH,Munich)

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Hard tissue replacement Polymer (HTR polymer) BioplantTM All these materials are biocompatible with host tissues, nontoxic, nonallergenic and noninflammatory..

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Alloplasts are easy to obtain in large quantities and are relatively inexpensive.

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Depending on the porosity and particle size, these materials may allow bone conduction (bone growth in and around the alloplast), 17

but are generally not used for periodontal regeneration because they become encapsulated by connective tissue and act only as biocompatible space fillers. •

Healing adjacent to the root surface is mainly by a long junctional epithelium, without restoration of periodontal structures. These materials, therefore, are reserved for instances when autogenous bone is not available and the patient objects to the use of an allograft Deeper lesions respond better than shallow defects

Success of Bone Replacement Grafts •

The outcome from bone replacement graft procedures depends upon : Type of graft material used

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Initial defect morphology.(defect morphology is characterized by the number of remaining osseous walls

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Three-walled defects respond better than 2- or 1-walled defects,

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Deeper lesions respond better than shallow defects

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The wider the angle between the root surface and the defect wall, the less the potential for repair or regeneration .

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Optimal plaque control by the patient and appropriate surgical management also are considered critical factors to success

Nanomaterials.

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Nanomaterials are those materials with components less than 100 nm in at least one dimension, including clusters of atoms, grains less than 100 nm in size, fibers that are less than 100 nm diameter, films less than 100 nm in thickness, nanoholes, and composites that are a combination of these.

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Nanocomposites usually exhibit much better performance properties than traditional materials

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Another important feature of nanostructured materials is the development of self-assembly.

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Nanomaterials are of interest from a fundamental point of view because the properties of a material (e.g. melting point, electronic properties, optical properties) change when the size of the particles that make up the material becomes nanoscopic.

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Recently a synthetic Nanocrystalline hydroxyapatite (nano-HA) paste (Ostim ,Heraeus Kulzer,Hanau ,Germany) containing 65% water and 35% nanostructured apatite particles has been itroduced for augmentation procedures in osseous defects

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Advantages of a nanostructured material are its close contact with the surroundig tissues, quick resorption characteristics and a high number of molecules on its surface

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It has been found that undisturbed osseous integration and complete resorption of nano-HA paste occurs within 12 weeks,

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It increases the prolifration of human PDL fibroblasts significantly

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Its effect is linked to activation of EGF-R(Kasaj et al J Oral Sci 2008) In intrabony defects, bone replacement grafts, result in increased bone levels, less crestal bone loss, increased clinical attachment gain, and greater probing depth reduction (PDR) compared with open-flap debridement. With the use of DFDBA, one of the most studied ,2.2 mm of mean defect fill can be expected from bone grafting procedures. Other reviews suggest an average bone fill of 65%, 19

Furcation defect fill depends on the morphology of the defect and root configuration. Increasing vertical bone loss, horizontal bone loss, and root divergence results in a decrease in the expected percentage of bone fill in the furcation. The best results are in Class 2 furcations. Bowers et al 2003 Autografts, DFDBA, and possibly xenografts result in new attachment.. On the other hand, open flap debridement and alloplasts result in periodontal repair characterized by a long junctional epithelium.(Reynolds et al 2003)

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