Guided tissue regeneration

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Anti-inflammatory cytokines are IL-4, IL-10, IL-11, IL-13, IL-16, transforming growth factor , soluble TNF-receptor and soluble interleukin-1 receptor. ... The alveolar bone proper is 0.1 to 0.4 mm thick and is consisted of a Harversian system and lamellated and bundle bone. ... The immune response to infection is regulated by the balance between T helper (Th) 1 and Th2 cytokines. The differentiation of Th1 and Th2 T cell subsets is determined by a number of factors, including the antigen itself, antigen dose, route of administration, nature of the antigen-presenting cell and co-stimulatory molecules. ... Lymphocytes comprise 20-40% (1000 - 4000 cells/l) of all leukocytes. ... Markers/Receptors on B cells are Surface Immunoglobulin (IgM and IgD), CD40, B7, ICAM-1, LFA-1, MHC II, CD32 (Ig Fc receptor), CD35 (Receptor for complement component). ... Genes for HLA are clustered in MHC located on Chromosome 6: 6p21. ... Most leukotoxin producing strains of A. actinomycetemcomitans are of serotype b. ... Re-classification of Actinobacillus actinomycetemcomitans as Aggregatibacter actinomycetemcomitans has been done on the basis of Phylogenetic similarity of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus, Haemophilus paraphrophilus, and Haemophilus segnis. ... There are three types of elastic bers: elastin, oxytalan, and elaunin. Only oxytalan bers are present within the periodontal ligament. ... The main components of Basement Membrane are laminin, type IV collagen, fibronectin, type VII collagen and proteoglycans. ... Bone Morphogenetic Proteins (BMPs) are potent growth factors belonging to the Transforming Growth Factor- superfamily. ... Red complex of the microbial complexes includes Tannerella forsythia, Porphvromonas gingivalis and Treponema denticola.

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Guided tissue regeneration

Introduction:

The ultimate goal of periodontal therapy is restoring the periodontal health and regeneration of the lost periodontal structures. The conventional non-surgical and surgical periodontal therapies lead to cessation of the active periodontal disease but in most cases, it results in repair and not regeneration or new attachment. New attachment describes new cementum formation with inserting collagen fibers on a root previously denuded of its periodontal ligament 1. Periodontal regeneration is differentiated from new attachment in that it must include new bone formation. Studies have established that healing after conventional periodontal therapy includes the formation of a long junctional epithelial attachment 2.

As already discussed in The history of periodontal regenerative therapy, 1970s and 1980s can be considered as two decades when research work enlightened the basic fundamentals of periodontal regeneration. Studies done during this period aimed at discovering whether any of the periodontal tissues (periodontal ligament, alveolar bone or gingival connective tissue) possessed capacity to regenerate the lost periodontal structures by formation of new attachment. Melcher (1976) 3 put forward hypotheses according to which, certain cell populations residing in the periodontium have the potential to create new cementum, alveolar bone and periodontal ligament, provided they have the opportunity to populate the periodontal wound. These progenitor cell populations can be derived from four sources,

Research work done by Polson and Caton 4 (1982), Lindhe et al. 5 (1982), Karring et al. 6 (1980), Nyman et al. 7 (1980) Karring et al. 8 (1985), Nymen et al. 9 (1982) and Warrer et al. 10 (1993) clearly showed that new connective tissue attachment occurs from cells originating from periodontal ligament. The development of guided tissue regeneration (GTR) was created in order to selectively guide tissue regeneration in the periodontium following periodontal disease. The technique of using barrier to selectively guide the tissue regeneration was first introduced by Nyman et al. 9 in 1982 and the term GTR was coined by Gottlow et al. 11 in 1986. This procedure was also referred to as selective cell population 12 or controlled tissue regeneration 13.

Initial barriers used were cellulose acetate laboratory filters or expanded polytetrafluoroethylene (ePTFE) membranes. First human experiment providing evidence that GTR could enhance regeneration of the human periodontium was done by Nyman et al. using a cellulose acetate laboratory filter by Millipore 14. Subsequent studies reported successful treatment of periodontal defects using ePTFE barriers in humans and dogs 11, 15-17.

Evidence of attachment gain after guided tissue regeneration:

The research work done by above stated researchers acted as foundation for building evidence for effectiveness of guided tissue regeneration in achieving attachment gain. After it was demonstrated that cells for periodontal regeneration originate from periodontal ligament, a lot of research work has been done on intrabony and furcation defects, using various barrier membranes. A review given by Needleman et al. 18 highlights various clinical studies which demonstrate clinical attachment gain after guided tissue regeneration for periodontal infra-bony defects. Another systematic review given by Murphy and Gunsolley 19 on the treatment of periodontal intrabony and furcation defects clearly demonstrates clinically significant attachment gain after GTR procedure. Karring et al. 20 in their articles in Periodontology 2000 have enumerated various animal and human studies which prove the authenticity of the basic concept of guided tissue regeneration in achieving attachment gain. Recently, a systematic review concluded that many studies demonstrated a histological attachment gain and regeneration when grafting materials were combined with barrier membranes 21.

A meta analysis analysed studies.

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Biological basis of Guided tissue regeneration:

The guided tissue regeneration is based on the concept of selective growth of cells derived from periodontal ligament by placing a physical barrier which prevents the apical migration of the epithelium and gingival connective tissue cells along the root surface. Along with this, the physical barrier is also thought to provide protection to the blood clot during early phases of wound healing and ensures space maintenance for ingrowth of newly formed periodontal apparatus. The barrier membrane has no biological effect on wound healing and proliferation and migration of the mesenchymal and periodontal ligament cells.

Ideal requirements of barrier membrane:

Although no membrane used so far for GTR purpose is ideal, but there are some basic requirements ofa barrier membrane:

Bio-compatibility:

It should bebio-compatible. The interaction between membranes and host tissue should not induce adverse immunogenic reaction;

Space-making:

It is the ability to maintain a space for cells from surrounding periodontal ligament tissue to migrate for stable time duration.

Tissue integrity:

The membrane should have tissue integrity i.e. tissue should grow into the membrane without completely penetrating it all the way through. If the membrane does not integrate with the tissue, epithelium may grow downwards on the surface of the membrane to encapsulate it. Tissue integration also provides stability to the overlying flap.

Cell-occlusiveness:

It should prevent cells and fibrous tissue from invading the defect site which can delay the bone formation;

Mechanical strength:

It should have enough mechanical strength to allow and protect the healing process, including protection of the underlying blood clot;

Degradability:

It should have adequate degradation time which matches the regeneration rate of bone tissue to avoid a secondary surgical procedure to remove the membrane.

Membrane configuration and design:

The membrane should be provided in a configuration and design which easily adapts to the defect or it can be easily trimmed for the same.

Indications of guided tissue regeneration:

Guided tissue regeneration is indicated in following conditions,

Two or three walled vertical, interproximal and circumferential intrabony periodontal defects.Class II furcation defects.Class III furcation defects with less predictability of success.Treatment of gingival recession.Ridge augmentation (Guided bone regeneration).

Classification of barrier membranes:

The barrier membranes can be classified into two broad categories of resorbable and non-resorbable membranes as shown in the following flow chart.

Classification of barrier membranes

Non-resorbable membranes:

The initial barrier membranes used were non-resorbable. These were made up of methylcellulose acetate (Millipore, Bedford, MA, USA). The problem with these membranes was their fragility. They used to tear easily while manipulation, which limited their clinical use. Soon these were replaced by expanded, high-density and Titanium reinforced ethylene polytertafluoroethelene [ePTFE (e-, d-PTFE and Ti-e-PTFE)] membranes and titanium mesh (Ti-mesh) 24.

Polytetrafluoroethylene (PTFE) membrane:

PTEF membranes were introduced in dentistry in 1984. This membrane is composed of.

The surface of the PTFE membrane is rough, which facilitates bacterial adhesion. So, after placement no surface of the membrane should be exposed to oral cavity. The main disadvantage of using non-resorbable membranes is the requirement of a second surgical intervention to remove the barrier 4 to 6 weeks after implantation. It causes trauma to the newly formed tissue and also flap elevation results in a certain amount of crestal bone resorption 25.

To address this problem, membrane made of high-density polytetrafluoroethylene (dPTFE) was designed especially for use in socket grafting by Barry Bartee 26. The surface of this membrane is comparatively smoother and impenetrable by bacteria which does not facilitate the bacterial adhesion or invasion. So, primary closure is not required. After tooth extraction the socket is filled with bone graft and the membrane is placed to cover the opening of the filled socket with its margins pushed below the gingival margins. Sutures are placed to secure the membrane in place. The main advantages of this membrane are no need for primary coverage of membrane and no need for releasing incisions for additional freeing of the flap. The membrane can be easily removed without additional surgical procedure 27.

Titanium mesh:

It is a suitable alternative for PTFE membrane. Effectively used in guided bone regeneration procedure, titanium mesh has exceptional properties of rigidity, elasticity, stability and plasticity. Rakhmatia et al. described four main advantages of Ti-mesh membranes over their alternative PTFE membranes 24:

These have mechanical properties (rigidity), which makes them suitable for space maintenance.Elasticity of the framework prevents mucosal compression.Stability prevents graft displacement.Plasticity permits bending.

Main disadvantage of using titanium mesh is stiffness of the material and a more complex surgery required to remove the mesh.

Bioresorbable membranes:

Bioresorbable membranes have been developed to avoid the need for surgical removal. These membranes can be broadly divided into two categories: natural and synthetic membranes. Natural membranes are made of collagen or chitosan, whereas synthetic products are made of aliphatic polyesters, primarily poly (glycolic acid) (PGA), poly (lactic acid) (PLA), poly (-caprolacton) (PCL) and their co-polymers 21. The main problem associated with the use of these membranes is their unpredictable resorption time and degree of degradation.

Natural bioresorbable membranes:

Collagen membranes:

Collagen is the major insoluble fibrous protein in the extracellular matrix and in connective tissue. It is one of the most abundant proteins in connective tissue. Most abundant collagens in body are Type I, Type II and Type III. These have a well defined triple helical structural configuration. Collagen Type I polymerizes to form aggregates of fibers and bundles. Collagen remodelling is a continuous process in the body and its degradation occurs specifically by collagen degrading enzyme collagenase. The collagen membranes are primarily made up of bovine and porcine Type-I collagen. There are many properties of collagen which make it a suitable choice to be used as barrier membrane.

Properties of collagen membrane which make it useful as a barrier:

It is a natural component of the periodontal tissue, so is well tolerated.It is a weak immunogen with favourable tissue response.

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Collagen is a weak immunogen and its immunogenicity is due to tellopeptide non-helical terminals which can be removed by enzymes such as pepsin, producing atellocollagen. One major problem associated with use of collagen membrane is rapid degradation of the membrane. The degradation time of the membrane should approximate the healing of periodontal apparatus. To overcome this problem, cross linked collagen membranes were developed. Cross-linking has been achieved by various methods including chemical treatment with aldehyde fixatives, imides and other treatments such as hydration and radiations. The problem associated with these procedures was toxicity and inability to control cross linkage. Bi-layered collagen membranes have been developed to overcome the problem of fast degradation. Presently, various collagen membranes are available commercially made up of both cross-linked and non cross linked Type-I and Type-III collagen of bovine and porcine origin.

Rothamel et al. 32 studied degradation time of various cross linked and non cross linked collagen membranes on rat model. Commercially available collagen membranes Biogide, BioMend, BioMendExtend, TutoDent and Ossix were investigated. They reported that non cross linked collagen membrane (Biogide: porcine type-I and type- III collagen) had very good compatibility with the host tissue. A rapid vascularisation and tissue integration caused their early degradation nearly within 4 weeks without any observable foreign body reaction. The cross linked collagen membrane (Ossix) underwent least amount of degradation after 6 months thereby maintaining space and cell occlusiveness. Its degradation was associated with foreign body reaction. So, it was inferred that cross-linkage prolongs the degradation time of collagen membrane.

Some commercially available collagen membranes:

BioMend (Zimmer, USA): (link)

This is a Type I collagen membrane manufactured from bovine Achilles tendon. The membrane is semi-occlusive (pore size 0.004 m) and resorbs in 4 to 8 weeks. The mechanical strength of the membrane varies from 3.522.5 MPa. Its fibrous network is proposed to modulate the cell activities improving healing.

BioGide (Osteohealth Company, SUI): (link)

This membrane is made up of Type-I and Type-III collagen of porcine origin. The resorption time is approximately 24 weeks. The mechanical strength of the membrane is upto 7.5 MPa. This membrane is usually used in combination with filler materials.

Ossix Plus (OraPharma, Inc., USA): (link)

This membrane is made up of Type-I porcine collagen. The membrane has the ability to maintain barrier functionality for 4-6 months, allowing sufficient time for osseous defects to achieve optimal bone regeneration. The membrane has good handling properties and adaptation.

Biosorb membrane (3M ESPE, USA): (link)

This is a Type-I bovine collagen membrane. The membrane is fully resorbed in 26 to 38 weeks. The handling characteristics of the membrane are good. The mechanical strength of the membrane improves its clinical handling due to long, interwoven collagen fibers.

Commercially available barrier membranes, their composition and properties

Non- resorbable membranes

CompositionCommercial name and providerPropertiesResorption timee-PTFEGore-Tex (W. L. Gore &

Associates, Inc., USA)e-PTFE membrane having good space maintanace properties-Titanium reinforced e-PTFEGore-Tex-TI (W. L. Gore & Associates, Inc., USA)Most stable space maintainer-d-PTFEHigh-density Gore-Tex (W. L. Gore & Associates, Inc., USA)0.2 m pores with no need for second surgery-Cytoplast (Osteogenics Biomedical.USA)-TefGen FD (Lifecore Biomedical, Inc.USA)0.20.3 m pores, easily removable membrane-Non-resorbable ACE (Surgical supply, Inc., USA)-Titanium meshTi-Micromesh ACE (Surgical supply, Inc., USA)1,700 m pores

0.1 mm thick-Tocksystem Mesh (Tocksystem, Italy)0.16.5 mm pore

0.1 mm thick-Frios BoneShields (Dentsply Friadent, Germany)0.03 mm pores

0.1 mm thick-Resorbable membranesSynthetic resorbable membranesResolut (W. L. Gore & Associates, Inc., USA)Poly-DL lactid/ Co-glycolid membrane10 weeksEpiGuide (Kensey Nash corporation, USA)Poly-DL lactic acid membrane.

Three layered membrane612 weeksVivosorb (Polyganics B.V. NL)DL-lactide--caprolactone

(PLCL) membrane8 weeksOsseoQuest (W. L. Gore & Associates, Inc., USA)Hydrolyzable polyester membrane with good tissue integration1624 weeksVicryl (Johnson & Johnson, USA)Polyglactin 910 Polyglicolid/

polyl actid 9:1412 weeksBiofix (Bioscience Oy, USA)Polyglycolic acid2448 weeksAtrisorb (Tolmar, Inc., USA)Poly-DLlactide and solvent3648 weeksNatural biodegradable membranesBio-mend (Zimmer, USA)Bovine I derived with Mechanical strength: 3.522.5 MPa8 weeksBio-Gide (Osteohealth Company, SUI)Porcine I and III derived24 weeksBiosorb membrane (3M ESPE, USA)Bovine I derived26-38 weeksNeomem (Citagenix, CAN)Bovine I derived

Double layered 26-38 weeksOsseoGuard (BIOMET 3i, USA)Bovine I derived2432 weeksOssix (OraPharma, Inc., USA)Porcine I derived1624 weeksPlasma rich in growth factors (PRGF Endoret) (BTI Biotechnology Institute, Vitoria, Spain)Derived from Patients own blood with abundent growth factors

Acellular dermal matrix allografts:

Acellular dermal matrix allografts have been used in periodontal plastic surgeries since 1994. As the name indicates, it does not contain cellular material; hence major histocompatibility complex class I and II antigens are not present in the graft thus eliminating chances of graft rejection. Other advantages of the membrane include: unlimited availability, optimum colour matching after healing, acceptable thickness of tissue after healing and formation of additional attached gingiva. Alloderm TM is commercially available acellular dermal matrix which has been used widely in soft tissue augmentation procedures.

Amniotic membrane:

Amniotic membrane is the innermost layer of the placenta consisting of..

It is tough and lacks blood vessels, lymphatic system and nerves. Immunohistochemically, collagen III, collagen IV, and laminin are expressed in the basement membrane of amniotic membrane. It also contains contains many growth factors 35 and exhibits anti-inflammatory 36 and anti-bacterial properties 37. The stem cell markers like epidermal marker CA125 38 and general epithelial markers such as cytokeratins and vimentin are present in large amount in the amniotic epithelial cells 39. It is very useful in management of burns, creation of surgical dressing, as well as reconstruction of oral cavity, tympanoplasty and arthroplasty. There is insufficient clinical data regarding its efficacy as GTR membrane compared to other membranes. However, some case reports and studies have been done using this membrane 40, 41.

Cargile membranes:

These barrier membranes are derived from cecum of an ox. After isolation the membrane is subjected to chromatization, similar to suture materials. This procedure prolongs its degradation time and improves the mechanical properties of the membrane. The proposed resorption time of cargile membrane is 30-60 days. Little data is available regarding the efficacy of these membranes in periodontal regeneration. A study done on dogs using this membrane, reported that many sites underwent uneventful healing, significant attachment gain and bone growth. This study also reported inflammation and resorption of coronal edge of the membrane in many sites within 2 weeks. The authors concluded that inflammation adversely affects the regeneration of periodontal apparatus 42. The major problem associated with this membrane is difficulty in handling and manipulation during placement.

Oxidized cellulose mesh:

Oxidized cellulose mesh is widely used as a haemostatic dressing. It converts into a gelatinous mass upon blood incorporation. It has been reported that this material is absorbed naturally and does not show any harmful effects. There is insufficient clinical data to authenticate the clinical efficacy of this biomaterial when used as barrier membrane. A study by Galgut who used this barrier membrane in furcation and interdental infrabony defects, demonstrated reduction in probing depth and gain in clinical attachment. However similar results were obtained after conventional surgical procedures 43. Further research is required to investigate efficacy of this membrane in periodontal regeneration.

Chitosan:

It is the deacylated derivative of chitin, which is widely used as food preservative. Chitosan is a

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Freeze-dried dura mater allograft:

The freeze-dried dura mater allograft (FDDMA) has been used as a barrier membrane for guided tissue regeneration. This material has been used since 1954 in various fields of surgery including general surgery, neurosurgery, gynaecological surgery and cardiovascular surgery. In oral surgical procedures it has been used for vestibuloplasty, mucogingival procedures, repair of oroantral fistula and periodontal regeneration. Since, it is a collagen based barrier, all the properties of a collagen membrane apply to dura mater allograft. One animal study demonstrated an optimal cell occlusive potential of this membrane when used in mandibular defects 47. Another study this membrane was used in combination with bone graft in periodontal intra-osseous defects. Results of the study demonstrated mean attachment gain of 4.33 mm and mean defect fill of 3.91 mm. No adverse reaction or delayed wound healing was noted throughout the study 48.

Synthetic bioresorbable membranes:

Synthetic materials are widely used for making bioresorbable barrier membranes. They are usually organic aliphatic thermoplastic polymers and most commonly used materials are poly--hydroxy acids, which include polylactic polyglycolic acid and their copolymers. These were developed by Kulkarni et al. 49 and were originally used in orthopaedic surgeries. Magnusson et al. 50 (1988) subsequently used them over buccal dehiscence in dogs and reported 2.5 mm gain of new attachment above the defect. Since then a lot of research has been done on these membrane highlighting their clinical efficacy.

Upon degradation, the end products of their breakdown are carbon dioxide and water. The degradation may take place upto 20 weeks or more depending upon their polymeric composition. Although considered biocompatible, a local inflammatory response is associated with their hydrolysis. To what extent this inflammatory response affects the healing process still need to be investigated. Following is description of commercially available synthetic bio-resorbable membranes,

Some commercially available synthetic bioresorbable membranes:

Resolute (W. L. Gore & Associates, Inc., USA): (link)

It is an occlusive membrane made up of glycolide and lactic copolymer and a porous web of polyglycolide fiber. The occlusive membrane prevents cell ingrowth, and porous part promotes tissue integration. Its resorption time is around 10 weeks. This membrane shows a good integrity with the tissue. The space maintenance with this membrane is good favouring regeneration. The membrane is degraded via hydrolytic and enzymatic pathways.

Atrisorb (Tolmar, Inc., USA): (link)

It is the only GTR membrane which is made chairside. It is made up of a polylactic polymer present in flowable form, dissolved in N-methyl-2-pyrrolidone. When the polymer is exposed to 0.9% saline for 4-6 minutes in a special cassette, an irregularly shaped membrane is formed. The membrane is then cut in a desired form and is placed into the defect by applying gentle pressure. The resorption of the membrane takes place within 3648 weeks.

Epi-Guide (Kensey Nash corporation, USA): (link)

it is made up of a bioresorbable polymer synthesized from D,D-L,L-polylactic acid. The membrane has three layers designed to stop and keep away epithelial cells and fibroblasts. The microscopic structure of the membrane is made up of void spaces which are connected to each other. The membrane is hydrophilic and exhibits good tissue integration properties. The membrane is slowly degraded into CO2 and H2O. The degradation time of the membrane is from 6-12 weeks.

Vicryl Periodontal Mesh (Johnson & Johnson, USA):

The Vicryl (polyglactin 910) woven mesh is prepared from a synthetic absorbable copolymer of glycolide and lactide, derived respectively from glycolic and lactic acids. The membrane loses its structure after 2 weeks, and completely resorbs in 4 or more weeks. The membrane is available in four fabricated shapes which can be adapted according to shape of the defect.

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Difference between Bio-degradable, Bio-resorbable and Bio-absorbable terminologies:

Bio-degradableBio-resorbableBio-absorbable

Macromolecular degradation of the material takes placeMacromolecular degradation of the material takes placeNo macromolecular degradation seenDegradation byproducts move from their site of action but not necessarily from boby Degradation byproducts are eliminated through natural pathways by simple filtrationPolymer molecules undergo dissolution in body fluids which may or may not be excreted

Clinical procedure for guided tissue regeneration:

The periodontal bone defects are formed due to periodontitis. The objective of guided tissue regeneration is to regenerate the lost tissue. Before we go for GTR procedure, appropriate treatment for periodontitis should be completed. Following steps are followed during the surgical procedure,

After achieving profound local anaesthesia, the area to be operated is disinfected with antimicrobial solution such as povidone iodine by doing intrasulcular irrigation.Sulcular or marginal incision is made and it is extended to one tooth anterior and/or one tooth posterior to the tooth where the procedure is to be performed.Vertical releasing incisions are made in such a way that the interdental papillae are preserved.Full thickness flap is reflected and all pocket epithelium is excised from the inner flap surface with the help of sharp curved scissors.The granulation tissue present within the defect is removed with the help of curettes and the root surfaces are meticulously scaled and planed to remove bacterial deposits and calculus. For scaling and root planing hand instruments, ultrasonic instruments, rotating finishing diamond stones and carbide burs may be used 51. Make sure that the defect is free of all the granulation tissue and debris. The bony walls of the defect may be decorticated to enhance new bone formation. The rationale behind doing decortication is to facilitate the ingrowth of vessels and bone forming cells from underlying bone marrow. The defect should be thoroughly irrigated with normal saline solution before placement of barrier membrane.The scaled and planed root surfaces may be.

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Interrupted sutures are placed to secure the flap at its position.Patient is instructed to gently clean the area with a soft tooth brush post-operatively and chlorhexidine (0.2%) mouth rinses are prescribed. The systemic antibiotic is administered immediately prior to the surgery and is continued for one week post-operatively.When non-resorbable membrane is used, it should be removed 4-6 weeks post operatively. To remove it, an incision is made starting from mesial surface of the tooth, posterior to the membrane and extending it to distal surface of tooth, anterior to the membrane. The flap is gently reflected and the membrane is detached from the flap using a sharp blade. Then, the membrane is gently pulled out. Every effort should be made not to injure the newly regenerated tissue. The flap covering the membrane may have pocket lining which is removed with a sharp curved scissors and the flap is sutured back. The flap should completely cover the newly formed tissue after suturing.The patient is instructed to do gentle brushing with soft tooth brush and is put on chlorhexidine (0.2%) mouth wash for another 2-3 weeks.

Grade II furcation involvement

After bone graft placement

Barrier membrane in place

After suture placement

Periodontal dressing in place

GTR procedure for furcation areas:

While doing GTR procedure in class-II furcation areas, accessibility to the defect is very important. The desired outcome of treating a furcation defect with GTR is obliteration of the defect by new bone formation. The defect is debrided to clean all the granulation tissue and deposits on the root surface. In cases where the furcation is narrow, it may be widened with the help of a flam shaped diamond stone to get complete access to the defect. The defect debridement, root scaling, root planing and root surface conditioning is done in the same way as described in the previous section. The barrier membrane is placed to cover the defect and is stabilized with the help of sling suture. Flaps are closed and sutured in their position. If recession is present or the flap is not covering the membrane completely, coronally displaced flap should be done to cover the defect and the membrane.

GTR is a treatment of choice when class II furcation defects are encountered. However, Novaes and Novaes 52 listed 8 different situations of class II furcations in which GTR is not indicated:

Lack of access for adequate debridement of the furcation,Endodontic or prosthetic perforations in the furcation areas of the roots,Crown lengthening procedures that invades the furcations,Root proximities untreatable by the restorative alveolar interface (RAI) technique,Extensive gingival recessions,Deep caries involving the roots,Untreatable endo-perio lesions,Longitudinal root fractures where hemisection is recommended.

Errors which may happen during GTR procedure:

Excessive trauma to the flap:

A full thickness flap is gently reflected during GTR procedure. Excessive manipulation of the flap may traumatize the flap thereby delaying its healing or it may also cause sloughing of the tissue.

Perforation of the membrane:

If the margins of the bone defect are sharp, they may cause membrane perforation during placement. Any sharp edge of the bone should be smoothened out with minor osetoplasty.

Tearing of the membrane while placing a sling suture:

The bioresorbable membranes become delicate when they come in contact with blood. While placing it around the tooth with the help of sling suture, excessive force may tear the membrane.

Exposed margins of the membrane:

After suturing the flap in its position, no margin of the membrane should be exposed to oral cavity because it promotes bacterial aggregation and faster membrane degradation. In an animal experimental study, it was demonstrated that in areas with membrane exposure, large inflammatory infiltrate and necrotic tissue were found even when the animals received systemic antimicrobial therapy and daily rinses with a chlorhexidine gluconate solution 53.

Wound healing following GTR procedure:

The basic cellular and molecular events that take place during wound healing after guided tissue regeneration are essentially the same as that of wound healing in any other non-oral site. As in any injury clot formation is the first event that takes place. The main functions of clot are; protection of the denuded tissues and serving as a provisional matrix for cell migration 54. After clot formation within few hours, the early inflammatory response is initiated with the recruitment of inflammatory cells (predominantly neutrophils and monocytes). These cells clean the wound by releasing their enzymes and reactive oxygen species and also by phagocytosis. Within three days the late inflammatory response is marked by migration of macrophages into the wound area and secretion of chemical mediators which attract fibroblasts, endothelial cells, and smooth muscle cells into the wound area. These chemical mediators are growth factors and cytokines which play a key role in wound healing. The cell rich granulation tissue thus formed undergoes maturation andremodeling.Wound epithelisation is initiated within few hours after injury which is characterized by proliferation and migration of cells from basal layer towards surface.

In guided tissue regeneration, our main focus is to find out the.

In subsequent studies they covered the heparin treated root surface with polylactic acid or expanded polytetrafluoroethylene (ePTFE) membranes. Connective tissue formation rather than long junctional epithelium was demonstrated in these areas showing importance of wound stability and space maintenance 60, 61. One study evaluated regeneration in the absence of strict cell occlusion 62. A tissue expanding gold mesh was applied in surgically created horizontal periodontal defects in the mandibular premolar region in dogs. The contralateral defect served as control which was closed without gold mesh. Results of the study demonstrated new bone formation in test sites as compared to control sites demonstrating that new bone formation may proceed in the presence of space without strict occlusion of the gingival connective tissues.

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GTR therapy around endodontically treated teeth:

The prime requirement of regenerative therapy is that the area should be totally free from any kind of infection. A properly done endodontic treatment in endodontically involved teeth is pre-requisite for GTR procedure. It has been seen that an endodontically treated tooth responds in the same way to GTR therapy as the natural tooth.

Factors affecting periodontal regeneration:

Defect morphology:

As explained in Patterns of bone loss in inflammatory periodontal diseases, the periodontal bone defects can be classified as one wall, two wall and three wall defects or their combination. This classification indicates only the bony wall remaining around tooth and does not indicate about status of periodontal ligament. The cells for regeneration are derived from the remaining periodontal ligament space. In general, more the walls of the bone remaining around the defect more is the periodontal ligament space surrounding the diseased root surface. For example, in a three wall bone defect involving one to three root surfaces, the diseased root surface is surrounded by PDL form three aspects. Thus, the chances of formation of new attachment are highest for three wall defect and least for one wall defect. In other words we can say that more is the ratio between remaining and lost periodontal ligament, more are the chances of regeneration.

Innate regenerative potential:

Innate regenerative potential varies from individual to individual. In some patients the results of periodontal regenerative therapy are as desired and in others they are not in spite of an accurate surgical procedure. This can be explained on the basis of innate regenerative potential of an individual.

Surface topography and porosity of barrier membrane:

The pore size of the barrier membrane is important because it should prevent excessive penetration of fibrous tissue into the bone defect (soft tissue ingrowth) but at the same time it should allow neovascularization and bone formation. It has been shown that a pore size more than 100 m is required for penetration of highly vascular connective tissue. If the pore size is less than 100 m, primarily avascular tissue grows because the pores are inadequate for penetration of capillaries. A study has shown greater bone formation with macro-porous membranes as compared to micro-porous membranes 63. But, increasing the pore size adversely affects the mechanical properties of the membrane. Along with this, the surface topography of the membrane is also important as it may affect the biological behaviour of the cells towards membrane and cell occlusion capability of the membrane. Further research is required to find out the optimum pore size of the barrier membrane to achieve best results of the procedure.

Mechanical stability of the membrane:

Any kind of micro movement in the membrane adversely affects.

Soft tissue ingrowth in membrane:

The barrier membrane is an occlusive membrane, not allowing ingress of any kind of cells or soft tissue. A thin layer (up to 1 mm thickness) of soft tissue may be formed under the membrane which may be due to shrinkage of the initial blood clot under the membrane, entrapment of air or membrane micromovements. The clinical significance of this membrane is not known.

Stabilization of blood clot:

Stabilization of the blood clot is primary requirement for GTR success. The defect should be free of all granulation tissue and soft tissue. The membrane should extend 2-3 mm beyond the defect so that any migration of the epithelium and soft tissue below the membrane should be prevented. While flap closure it should be ensured that no part of the membrane is exposed. The most important period of cell migration and proliferation are the first 30 days. If the membrane is stable and doing its desired function of defect isolation from overlying tissue, optimum regeneration can be expected during this period.

Tooth mobility:

Tooth mobility may adversely affect the healing process mainly due to the fact that wound stabilization is a primary requirement for healing. Hyper mobile tooth may jeopardise the clot stability, hence healing. The membrane attached to a hyper mobile tooth moves along with the tooth thus compromising flap healing. Hepermobility may temporarily increase after surgery causing discomfort to the patient. keeping all these factors in mind, the hypermobile teeth should be splinted before performing GTR procedure.

Patient factors:

A patient scheduled for GTR procedure should be well motivated and should have undergone thorough hygienic phase of treatment. Patient must maintain a good oral hygiene during the healing period. Any inflammation of tissue surrounding the membrane causes early degradation of the membrane, thus causing partial or complete failure of GTR procedure.

Cigarette smoking has been associated with a reduced healing response following GTR treatment 23, 66, 67. It has been shown that most significant effects of smoking on periodontal healing occur during tissue maturation phase 66, 67. So, it has been suggested that when guided tissue regeneration treatment is done for class II furcations in smokers, an anti-infective therapy should be incorporated into the treatment protocol to enhance the regenerative outcome 66.

Stress is another patient related factor which may adversely affect the outcome of GTR therapy. The proposed mechanism of negative effects of stress on healing after GTR therapy are, neglect of oral hygiene, changes in diet, increase in smoking and other pathogenic oral behaviors, bruxism, alterations in gingival circulation, changes in saliva, endocrine imbalances and lowered host resistance 68.

Systemic conditions like diabetes mellitus also adversely affects the outcomes of GTR therapy. Susceptibility to periodontal microbial colonization and impaired wound healing after surgical therapy are the main reasons for compromised results of GTR therapy in diabetic patients. Other systemic conditions which affect the outcome of GTR therapy include HIV infection, other diseases with impaired immune response, patients with rheumatoid arthritis, and other immune-complex diseases.

Assessment of regeneration:

As explained in History of periodontal regenerative therapy the assessment of guided tissue regeneration is usually done by one of a few methods. They include periodontal probing, radiographic analysis, re-entry, and histological evaluation are all techniques employed to assess the results of guided tissue regeneration.

Conclusion:

Guided tissue regeneration has evolved as a promising technique for periodontal regeneration. Since introduction of concept of GTR, various bioresorbable and non- bioresorbable membranes have been introduced. The bioresorbable membranes are more extensively used today because they do not require a separate surgical procedure for removal. Although god results can be achieved with this procedure, complete periodontal regeneration is still far. Future research is directed towards developing new techniques to achieve this goal.

Periobasics: A textbook of Periodontics and Implantology

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Periobasics: A textbook of periodontics and implantology

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