Duffy, John. (2007) An overview of bone grafting techniques and materials in implant dentistry. BDS Elective Report.

Transcription

1 Duffy, John. (2007) An overview of bone grafting techniques and materials in implant dentistry. BDS Elective Report. 15th January 2008 Enlighten

2 An overview of bone grafting techniques and materials in implant dentistry Word count: 4310

3 Index 1. Introduction 3 2. Materials Autograft bone 4 Allograft bone 5 Xenografts 5 Alloplast materials 6 3. Techniques Localised deficiencies 7 Larger deficiencies 7 Onlay grafting (minor and major) 8 Maxillary sinus grafting 9 Guided bone regeneration Future Clinical experience Summary References and Acknowledgements Appendix 15 2

4 Introduction: The use of dental implants to provide support for replacement of missing teeth has become an important component of modern dentistry. As a result of advances in research in implant design, materials and techniques the use of dental implants has increased dramatically in the past few years and is expected to expand further in the future. Many types of implants have become available for application to different clinical cases, and an increasing number of dentists have become involved in this form of treatment. Dental implants are small, typically screw-shaped attachments, usually made from titanium. They are inserted into the jawbone to replace missing tooth roots. Following osseointegration(when the bone attaches firmly to the implant) a replacement tooth can be secured to the top of the implant. The replacement tooth can look, feel and perform like a natural tooth. Implants have several advantages over fixed bridgework or partial dentures in patients with gaps in their dentition. Unlike dentures, implant-stabilised teeth are integrated into the patient s natural bone, meaning that there is no slipping or movement. This can greatly improve confidence and function. Implant-secured teeth can also prevent further bone loss around edentulous areas and prevent excess forces being applied to abutment teeth. However, dental implant placement can be a difficult and expensive treatment option, and bone grafting procedures are often needed. Bone grafting is the process of surgically placing new bone into spaces around a broken bone or bone defect. Defects are replaced with bone from the patient s own body (autogenous bone), or an artificial, synthetic or natural alternative. The graft not only replaces missing bone, but also helps your body to regrow its own lost bone. For successful implant placement, a sufficient amount and quality of bone is essential around the site of insertion. However, many patients seeking implant treatment are deficient in bone volume, and hence bone grafting has become an integral part of implant surgery. In about 40% of all implantations, clinicians use regenerative procedures to build up bone and soft tissue. The use of bone substitutes and membranes is now one of the standard therapeutic approaches. Today, bone grafting procedures have become an almost integral part of implant reconstruction. In many instances, a potential implant site in the upper or lower jaw does not offer enough bone volume or quantity to accommodate a rootform implant of proper size or in the proper place. This is usually a result of bone resorption that has taken place following loss of one or more teeth. Bone grafting procedures usually try to re-establish bone dimension, which was lost due to resorption. 3

5 Materials: With respect to bone graft materials used, we have to differentiate between several choices. The complexity of the bone deficiency and the patient s decision will influence the graft material chosen. Autograft: The autograft remains the gold standard to which all other materials are judged. It is defined as tissue transplanted from one site to another within the same individual. It is basically your very own tissue, taken from a donor site and placed somewhere else in the body, into the recipient site. The best success rates in bone grafting have been achieved with autografts, because these are essentially living tissues with their cells intact. Autogenous bone has many advantages over the alternatives. It is osseoinductive/conductive, sterile, biocompatible/non-immunogenic, easy to manipulate and readily available from adjacent or remote sites. The microscopic architecture is perfectly matched. The main disadvantage of autografting is that is has to be harvested from a secondary (either intra- or extra-oral) site, which usually means more complicated surgery and higher morbidity. Favoured intra-oral sites include the chin, retro molar areas and other edentulous areas. Chin grafts are indicated for use in unilateral sinus lifting procedures or (buccal) onlay grafting for widening of a thin crest due to the limited amount of bone available. Chin bone is harvested from the parasymphyseal region, ensuring a minimum distance of at least 5mm from the anterior teeth apices is maintained. This is crucial to assure the vitality of the teeth and to avoid contact with the anterior branch of the inferior alveolar nerve. A very limited volume of cancellous bone can be harvested from this region, although the cortical bone is very hard but can be particulated if necessary. Mandibular angle grafts are also indicated for unilateral and occasionally bilateral sinus grafting procedures, and onlay grafting. It is useful in block or particulated form but there are certain limitations to the size of the graft, although more material is available than from the chin. However, almost no cancellous bone can be harvested from this site. Again great care has to be taken to avoid contact with the inferior alveolar nerve, which should be released from the cortical bone before harvesting. Iliac crest grafts are the most common form of extra-oral grafts used in implant dentistry. Iliac grafts are indicated when large amounts of bone are required to achieve the desired volume and shape for implant placement. Cortical and cancellous bone can both be collected in sufficient amounts to restore severely resorbed maxillae. Iliac crest bone is also used for larger grafting needs, such as bilateral sinus lift procedures combined with nasal inlays. Blocks and particulated bone can be grafted from this site. Tibial grafts are the other commonly used extra-oral grafting site, with a limited amount of cancellous graft material available, indicated for use as onlay graft material or for sinus lifts (unilateral). 4

6 For minor procedures which require very little amounts of bone graft, bone collecting devices may be useful. These collect particles of bone during drilling of the implant site. This technique is conservative of other bone tissue and provides autogenous bone which functions well as a grafting material. Autogenous bone is the ideal material for bone grafting in dentistry. However, it adds further complications and the benefits/risks and alternatives must be discussed pre-operatively. There are no substitutes for autogenous bone; there are, however, synthetic alternatives. Allograft: Allograft material can also be used for dental implant treatment. An allograft is a tissue graft between individuals of the same specimen but of non-identical genetic composition. The source is usually cadaver bone, which is available in large amounts. This bone has to undergo many different treatment sequences in order to render it neutral to immune reactions and avoid cross contamination of host diseases. In practice, fresh allogenic bone is rarely used because of immune response and the risk of disease transmission. Human bone material in the form of freeze dried bone or demineralised freeze dried bone (DFDB) has been used widely in periodontology and implant dentistry. A wide range of grafts are available, which may be particulate, thin sheets of cortical plate or much larger bone blocks. Allografts have been used as an alternative, but have little or no osteogenicity, increased immunogenic and resorb more rapidly than autogenous bone. Allograft bone is a useful material in patients who require bone grafting of a non-union type but have inadequate autograft bone. It is predominantly used as a scaffold for bone repair and are resorbable. Xenografts: Defined as tissue grafts between two different species (i.e. bone of bovine origin). Some have received wide acclaim and are used to provide inert framework for bone regeneration either alone or in combination with autogenous bone graft. Currently, Bio-Oss and Bio-Gide are widely used as dental xenograft materials. Bio-Oss is a xenograft consisting of deproteinized, sterilized bovine bone with 75 80% porosity and a crystal size of approximately 10 μm in the form of cortical granules; it has a natural, non-antigenic porous matrix and is chemically and physically identical to the mineral phase of human bone; it has been reported to be highly osteoconductive and to show a very low resorption rate (Furst et al, 2003; Orsini et al, 2005). The organic material is completely removed to leave the mineralised bone architecture, which renders it non-immunogenic and presumably safe from possibility of infection. A more recent study (Orsini et al, 2005) demonstrated a favourable long-term tissue response to Bio-Oss particles with mainly woven immature bone shown at 20 months, which was replaced with lamellar bone with time. 5

7 Bio-Oss is becoming increasingly popular for use in bone grafting in implant dentistry, and is often used in combination with Bio-Gide. Bio-Gide is a membrane made of collagen which facilitates planned soft tissue management during augmentation. Bio-Gide is composed of highly purified natural collagen from pigs which has a natural bilayer design, has native collagen for soft tissue compatibility and forms a barrier for undisturbed bone regeneration. Studies have shown Bio-Gide to allow successful bone regeneration in combination with Bio-Oss (Wallace et al, 2005) and provide a barrier function lasting several months (Yamada et Al, 2002) Alloplast: Graft material which is synthetically derived and does not originate from humans or animals. Materials such as hydroxyapatite and similar formulations are easily used as fillers on their own or combined with autogenous bone. They provide an osteoconductive framework for bone but are not osteoconductive and are unable to contribute to osseointegration. Hydroxyapatite is available in a variety of forms. The most commonly used non-resorbable form becomes embedded in newly formed fibrous tissue and bone, and the resulting tissue combination is a less than ideal implant bed. The use of alloplastic grafting materials on their own is not routinely recommended. Hydroxyapatite and other bone substitutes require further clinical research and should not be used on their own as grafting material until their efficacy is evidence-supported. Growth factors are natural proteins found in our bodies that stimulate growth of certain tissues. With respect to bone, genetic engineers have been able to isolate and clone Bone Morphogenic Proteins (BMPs), which have been shown to induce tremendous bone growth in many animal and more recently human clinical studies. BMPs may very well become a potential substitute for autogenous graft material for certain applications in the future. 6

8 Techniques: Localised deficiencies: Simple techniques can be used to treat small deficiencies in the alveolar ridge. Implants can be placed at the same stage as augmentation (1 step surgery) or following bone regeneration (2 step surgery). It is important to consider whether grafting is necessary to achieve a stable implant at the time of placement or whether it is being used to promote bone repair over areas of the implant. Depending on the particular situation, 1 step surgical implant placement technique may be used. Usually, a round piece of the gum in the area of projected implant is cut off (punch technique) rather than making a line incision and opening a flap. Osteotomy is performed through this opening and the implant is placed directly. In this method, the implant remains exposed and there is no need for re-opening of the implant (second stage). When a tooth has to be extracted, and implant treatment is the preferred choice of treatment for substitution of the removed tooth, immediate placement of implant into the extracted site can be performed. There are several advantages to this method. Immediate implant placement into the extraction site prevents the time needed for bone regeneration following grafting (~3-6 months) as is required in 2 step surgery. The healing process of the implant (osseointegration) runs as a natural process - the body builds up the new bone in the extracted site where the implant was placed. There are also contra-indications to immediate implant placement at extraction sites, such as cortical bone loss and severe infection. 2 step surgery is the most common treatment method for dental implant placement. Bone augmentation before implantation is generally the preferred option. This is particularly the case for non-submerged or single stage implants. Alveolar defects should be augmented at least 3 months before implant placement but delays greater than 6 months may result in resorption of the graft. Larger deficiencies: Larger deficiencies in bone quality or amount usually arises due to progressive resorption following: -tooth loss and trauma -developmental anomalies -pathological conditions (e.g. cysts) Techniques to resolve the lack of appropriate bone can involve the entire edentulous jaw, aim to improve the height and/or width of the bone available as well as to provide bone of sufficient quality to provide implant anchorage. There are several different implant placement techniques commonly used, each dependant on the individual patient s circumstances. 7

9 Onlay grafts: Minor grafts: Onlay grafts are versatile in that they are able to augment the bone in either the vertical or lateral dimension or a combination of the two. Onlay grafting is a method of increasing bone volume but can also be used to level deformities in the bone contour or to cover dehiscences. In cases where only small amounts of one material is needed it may be enough to collect bone during preparation of the fixture site or take small pieces of bone from an adjacent area (e.g. tuberostiy). Small grafts may be harvested from the chin or retro molar area, although large cortico-cancellous grafts are usually taken from the iliac crest. Miniscrews and plates or wires should be used to secure grafts to the recipient bed. The host bed is perforated with a small bur to allow blood clot to form between the 2 bone surfaces and allow communication with the cancellous bone which contains osteoproginetor cells. Any remaining voids may be packed with cancellous bone chips to maximise the healing potential. The bone particles are placed over the defect with or without a covering membrane. Healing before abutment connection is dependant upon the initial stability of the fixture and may take 3-6 months. The bone used for the onlay technique can be particulated or in the form of a block. Onlay block grafts are indicated where there is a need to improve the width of the thin alveolar process or to increase the height in localised defects. Minor onlay grafts used to increase widths are often placed bucally on the crest (buccal onlays) and secured with titanium plate screws. Cortical bone is best used as onlay while particulated bone can be used as a filler around the onlay bone. As mentioned, it is advisable to drill small holes with a round bur to stimulate bleeding and improve healing potential. Implants can be placed simultaneously but it is advisable to let the bone heal before implant insertion, especially if the original crest is too thin for implant site preparation. Good closure of the flap is also essential to prevent contamination of the bone graft material with saliva and bacteria from the oral cavity. Major onlay bone grafts (block form): Larger block bone grafts are indicated where there is an edentulous maxilla or almost edentulous maxilla with severe bone deficiency. The height and width of the alveolar process should be improved by this procedure, enabling appropriate implant positioning. A flap technique which does not jeopardize the healing of such a large bone graft volume is essential. Tension-free closure of the flap is also indicated. Bone from the iliac crest is most commonly used for major onlay bone grafts. The whole block can be attached to the maxilla, or it can be divided into 2 or 3 blocks and then attached. The blocks should be trimmed to fit the alveolus as tightly as possible. Again, a large number of small holes should be drilled to allow for good healing. The block(s) can then be attached to the residual bone with titanium plate screws or by the implants (usually 6 or more). The remaining alveolus must be capable of stabilising the grafted bone and implants but, when used appropriately, this technique can be very useful in altering jaw relations with simultaneous implant placement. 8

10 Maxillary sinus grafting (sinus lift): Lack of bone volume beneath the maxillary sinus cavity often causes difficulties in placing implants in the posterior maxilla region. Following loss of posterior maxillary tooth support, resorption of the alveolar process occurs either at the oral side, or by expansion of the sinus cavity into the alveolar process, or both. This often results in a lack of adequate amount and quality of bone available for implant placement, and hence a sinus lift is required. Maxillary sinus grafts, a procedure which can be performed under local anaesthesia, involves carefully cutting a window in the lateral antral wall using surgical burs but retaining the integrity of the sinus membrane. It is well known that foreign particles passing into the maxillary sinus will usually cause an inflammatory reaction, leading to loss of graft material. This can lead to failure of both the graft and the implants placed, hence it is vital to maintain the integrity of the sinus membrane. The condition of the maxillary sinus must be assessed pre-operatively. It may be impossible to avoid mucosa perforation. If the sinus membrane is torn it is not advisable to graft particulate material although blocks or corticocancellous bone can be secured in position. After a window has been cut in the lateral antral wall, the window may be in-fractured to create a discrete cavity on the superior aspect of the residual alveolus. Graft material can then be inserted which serves to keep the bone trap-door in it s elevated position. This technique is often used as a pre-implant procedure when the residual alveolar ridge has to a point where initial implant stability is compromised. Maxillary ridges with less than 5mm of available bone height should be augmented at least 3 months prior to implant placement. This improves the likelihood of stable implants and the success rates. A fairly recent study (Zitzmann et al. 1998) indicated the choice of approach for sinus floor augmentation. A 2-step procedure should be carried out if residual bone height is less than 4-5mm whereas a residual bone height greater than 5mm with sufficient primary stability suggests a simultaneous procedure. An osteotome technique should only be indicated where residual bone height is greater than 6mm. If necessary, block graft material can be fixed by wire osteosynthesis or by titanium screw plates if the stability is insufficient. If block grafts are used in the procedure, the blocks can be combined with artificial bone material to cover small defects and allow for adequate healing. Research has indicated that coverage of the lateral window with a membrane results in a significantly higher graft survival rate (Wallace S, Froum S 2003). Maxillary sinus grafting is sometimes combined with nasal inlay grafting if it is also necessary to increase the bone volume in the sub nasal area for placement of implants. 9

11 Guided bone regeneration: One of the most popular methods for treating localised ridge deficiencies is GBR. The concept of treatment is simple. A biocompatible barrier membrane is placed between the gum and bone. This barrier prevents downgrowth of the gum into the underlying bone as it heals. Bone progenitor cells then migrate into the defect, instead of the soft tissues. This allows bone to form within the void. This technique can be used before or at the same time as implant placement. Barrier membranes can be non-resorbable (e.g. Gore-Tex ) or resorbable, meaning a second surgical procedure to remove the membrane is not necessary. GBR can be used to promote bone fill of a defect before implant placement or used to regenerate bone in dehiscences around implants at the time of placement. Recent research (Hammerle CH, Lang N 2001) has demonstrated the successful combination of implantation and GBR in a single procedure without the need for further surgical interventions. 10

12 Future: Research and studies have identified new techniques and materials for bone grafting in dentistry. Piezo surgery is a recent development which has many uses for bone surgery in dentistry. In implantology, piezosurgery can be used for implant site preparation, bone harvesting (chips and blocks), osteoplasty, ridge expansion, bony window osteotomy in sinus lifts, as well as many other applications. There are a variety of insert tips available depending on the treatment required. Piezosurgery allows selective cuts to be made, allowing for maximum safety of the soft tissues. Micrometric cuts allow for maximal surgical precision and intra-operative sensitivity. The cavitation effect in piezosurgery give maximal intra-operative visibility (blood free surgical site). Although expensive, piezosurgery units are being used increasingly in bone grafting procedures for many applications, and their use may well expand in the future. Nobel Biocare has created the Teeth-in-an-Hour process. The name is self-explanatory, but what is so unique is the state-of-the-art process this product employs. This system is all computer enabled. The majority of work is done in the planning stage, so the patient only needs surgery for quite literally one hour. Once complete, the patient goes from totally toothless to a full mouth of functioning permanent teeth. The pre-surgery visit is very important and involves CT scans of the jaw bones and use of CAD/CAM. Bioactive glasses have also been the subject of considerable investigation. Bioactive glass is a synthetic, non-toxic biocompatible material (Wilson et Al 1981) which has been shown to be highly osteoconductive in animal studies (Turunen et al. 1997). They may also be used more widely in the future. 11

13 Clinical experience: A wide variety of clinical procedures were carried out during my elective. I have selected five different cases to present, with a brief explanation of the procedures carried out, and photographs to help illustrate the cases. Case 1 (Mrs Clark) This case shows the full sequence of the restoration of a missing lower left first molar tooth. Following tooth extraction, bone grafting was placed (Bio-Oss ) and the area allowed to heal for 5 months. Following this the implant was placed and again allowed 3 months healing prior to being restored with an abutment and crown. The final picture shows a two year review. Case 2 (Sinus Lift) This case shows a pre-operative OPG radiograph showing large maxillary air sinuses bilaterally. Pneumatisation over the years since the tooth loss has led to bone deficiency with increasing sinus volume. The second OPG shows the patient after bilateral sinus lift surgery. This was carried out under local anaesthesia using the Piezo surgery system. Graft material used was chin harvested chips and Bio-Oss. The case has since been restored using NobelGuide Teeth in an Hour. Case 3 (Int. Sinus Lift) This case demonstrates the use of internal sinus elevation. This is also known as bone added osteotome sinus floor elevation. Part of the implant osteotome is drilled, with the apical portion being prepared with osteotomes and a mallet to in fracture the sinus floor, thus tenting the sinus membrane. Graft material is then pushed into the tented area and the implant placed. Where possible this technique avoids the need for the full invasive sinus floor elevation. Case 4 (J Hammond) This case shows the complex rehabilitation of the severely atrophic maxilla. Severe bone loss has occurred after many years of tooth loss. Chin grafting is utilized with Bio-Oss to restore the maxillary bulk. Following this the area is restored using two implants and Zirconia bridgework. Case 5 (C Edgar) This case demonstrates immediate loading in the aesthetic zone. It utilizes bone harvested during the preparation of the implant osteotomy. The tooth is extracted atraumatically using periotomes and the socked debrided. The implant is placed using flapless surgery and harvested bone graft packed bucally. An immediate temporary abutment is then used to retain a temporary crown. The final photographs show the same case at 2 month review. It will be restored in 3 months time. This is a difficult technique to perfect, but can be used in this case to fully support the soft tissues with a superb aesthetic result in the aesthetic zone. All patient have consented to their names and photographs being used. Clinical photographs of each case shown in appendix. 12

14 Summary: Dental implants have provided an additional treatment option for patients who have lost one or more teeth. They have several advantages over the alternatives of fixed or removable prosthesis, and their use is widely growing. Advances in the ability to increase bone volume before or during treatment has allowed implants to be carried out in a wider variety of clinical cases. Small bone defects can easily be corrected with simple grafting techniques, to allow effective implant insertion. Various inlay, onlay and grafting techniques can be utilized to allow bone reconstruction in cases where large defects exist, meaning patients with very little bone levels can also benefit from implants. There also advances in the materials used for grafting. Traditional materials like autogenous bone are still routinely used for grafting, while newer materials have been scientifically proven and also play an important role in modern day grafting. Other grafting materials may well be used in the near future, once scientifically proven, potentially making bone grafting for dental implants less difficult. The various implant cases I observed clinically has greatly enhanced my knowledge of both bone grafting and implants in dentistry. I have developed an understanding for the indications for bone grafting, and when and how to apply the different techniques and materials in practice. The clinical experience has been both valuable and enjoyable, and I have learned about a component of dentistry that is expected to expand in the near future. 13

15 References and Acknowledgments: A Clinical Guide to Implants in Dentistry, R M Palmer. Bone Grafting In Oral Implantology, Federico Hernandez Alfaro Geistlich Professional Information for Implantology Guide. Introducing Dental Implants, John A. Hobkirk, Roger M. Watson, Lloyd J. Searson Bone Grafting Techniques for Maxillary Implants, Karl-Erik Kahnberg The Sinus Bone Graft, Second Edition, Jensen, Ole T. The A-Z of materials, accessed 18/8/07 Dental Implants by S.Robert Davidoff, accessed 18/8/07 Teeth-in-an-Hour, accessed 10/09/07 Piezosurgery, accessed 30/09/07 Dental Implant Professional, accessed 20/09/07 A special thanks to Dr Philip Friel, for all the help with this elective project. 14

16 Appendix: Case 1: Case 2: 15

17 Case 3: Case 4: 16

18 Case 5: The full range of clinical photographs are provided on disc. 17