CONTROVERSIAS EN CIRUGÍA ORAL Y MAXILOFACIAL I

 

Bone cavity augmentation in maxillofacial surgery using autologous material

Relleno de cavidades óseas en cirugía maxilofacial con materiales autólogos

 

 

P. Infante-Cossío¹, J.L. Gutiérrez-Pérez¹, D. Torres-Lagares², A. García-Perla García¹, J.D. González-Padilla¹

1 Servicio de Cirugía Oral y Maxilofacial. Hospitales Universitarios Virgen del Rocío, Sevilla, España
2 Becario de Docencia e Investigación. Universidad de Sevilla, España

Dirección para correspondencia

 

 

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ABSTRACT

Although a large number of materials have been described for augmenting bone cavities, the best material is still autologous cortical-cancellous bone or bone chip, which can form new bone through osteogenesis, osteoinduction and osteoconduction mechanisms. The oral and maxillofacial surgeon needs to be familiar with the biological properties and the fundamental characteristics of autologous material, the different techniques for obtaining it and its clinical application. Donor sites should preferably be intraoral. Bone filters and scrapers should be used for small defects, and the iliac, tibial or calvaria bones [should be used] when more quantity is required. There are no conclusive studies with regard to combining bone grafts with membranes. The combination of autologous grafts with other augmentation material has led to multiple studies, although definitive conclusions cannot yet be established. Autologous bone should be chosen for augmenting bone cavities, as it is useful for solving a variety of clinical situations in a simple, fast and safe manner.

Key words: Bone regeneration; Autogenous bone chips; Bone graft; Craniofacial bone defect.

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RESUMEN

Aunque se han descrito numerosos materiales para rellenar una cavidad ósea, el mejor material sigue siendo el hueso autólogo corticoesponjoso o particulado, que puede formar hueso nuevo por mecanismos de osteogénesis, osteinducción y osteoconducción. El cirujano oral y maxilofacial debe conocer las propiedades biológicas y las características fundamentales de los materiales autólogos, las diferentes técnicas de obtención y sus aplicaciones clínicas. Como zonas donantes se emplean preferentemente las intraorales, el filtro de hueso y los raspadores para pequeños defectos, y el hueso ilíaco, tibia o calota cuando se requiere más cantidad. No existen estudios concluyentes respecto a la asociación de injertos óseos con membranas. La combinación de injertos autólogos con otros materiales de relleno, ha desembocado en múltiples estudios, sin que se puedan establecer conclusiones definitivas por el momento. El hueso autólogo es de elección para el relleno de cavidades óseas, ya que es útil para dar solución a variadas situaciones clínicas de forma simple, rápida y segura.

Palabras clave: Regeneración ósea; Hueso autógeno particulado; Injerto óseo; Defecto óseo craneofacial.

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Introduction

One of the greatest challenges that exists today in oral and maxillofacial surgery is the reconstruction with augmentation material of the cavities and bone defects of the maxillae. The aesthetic and functional possibilities that osteointegrated implants represent has led to bone augmentation procedures being used more and more, and to an increasing interest in bone regeneration techniques and the use a variety of osteoinductive materials. Different materials have been used for regenerating bone within a cavity, including autologous bone grafts, allogenic and xenogenic materials, bone substitutes, guided bone regeneration techniques, and more recently, the use of recombinant human bone morphogenic proteins. The election in clinical practice of augmentation material, or any other, requires knowledge of the complex mechanisms that are involved in bone regeneration, that allows us to evaluate, from a critical point of view, the avalanche of information regarding available materials.

Of all the materials, possibly the most used in our specialty continues being the autologous bone graft, which is useful in a variety of clinical settings such as dento-alveolar, oncological, malformation, traumatologic surgeries, etc. With regard to this debate we will revise in this article the clinical applications of augmentation material for bone cavities from the point of view of autologous materials. We would first like to state that our position will be that of defending autologous material as the treatment of choice for bone cavity augmentation, as it serves to solve a great multitude of problems in different clinical settings in a simple, fast and secure manner.

 

Objectives and clinical applications of augmentation materials

After the excision of a cyst or a benign bone tumor of the maxilla, the resulting bone cavity will heal primarily [showing] an inverse correlation to its size. This is known as the critical size defect and it refers to a certain size after which spontaneous healing will not take place.¹ Traditionally the augmentation of bone cavities was not considered as strictly necessary in small post-surgical defects, [as it was felt] closure of the flap would permit natural bone healing. The adequate design and handling of the flap, which results in the primary closure of soft tissues, influences the prediction decisively as to the primary ossification of the cavity. However, there is today a growing tendency to augment the cavities, including the smaller ones, in order to accelerate bone regeneration, or to make it more predictable, and in order to provide more appropriate bone quality.

On augmenting bone cavities, the principal objectives that a material should meet, are the restoration of the function and form of the maxilla, and for there to be stability over time. The ideal material should reinforce the resistance of the maxilla, reestablish its continuity and provide support for dental prostheses or the insertion of osteointegrated implants. In addition, the physiological ossification period should be shortened significantly, and it should be technically simple while supported by ample clinical experience. The material that possesses the majority of these characteristics is the autologous cortical-cancellous or cancellous bone chip graft.

The clinical application of cavity augmentation in maxillofacial surgery is varied. Most of the references in the literature are to alveolar clefts, elevation of the sinus or the nasal pit for the insertion of osteointegrated implants, and to postextraction alveolus, pre-prosthesis and periodontally treated crest defects. However, in clinical practice its use extends also to those situations resulting in a defect or post-surgical cavity in the maxilla, such as for example in apicectomies, cystectomies, odontogenic or bone tumors excision and even in craniofacial surgery for augmenting the frontal sinus.²

Bone regeneration of post-extraction alveolus. The augmentation of post-extraction alveolus is directed at faster and more predictable bone regeneration and an increase in the alveolar ridge, with the aim of compensating the postoperative bone atrophy in areas that are candidates for the posterior placement of osteointegrated implants. Morbidity is the principal inconvenience that can implicate an additional donor site. If multiple dental extractions are planned, the graft can be obtained by means of an alveoloplasty.³ Graft material can also be collected using filters, scrapers or gouge forceps, or it can be taken from an intraoral donor site if the patient wants to avoid a foreign material being implanted.

Augmentation of maxillary sinuses and nasal pits. When the height of the bone is insufficient in the lateral or anterior region of the upper maxilla, the bone chip graft with elevation of the maxillary sinus or nasal pit, permits obtaining the necessary volume of bone for the insertion of osteointegrated implants. Currently there seems to exist considerable consensus in the literature regarding the achievement of better results with autologous bone, and with cancellous bone in particular.^4,5

Congenital alveolar fissures. The reconstruction of alveolar clefts should ideally be carried out in the mixed dentition of the child in order to achieve the closure of the oronasal communication, union of the bone fragments separated by the cleft, and bone support for the nasal ala and for the definitive eruption of the permanent canine.⁶ The autologous bone chip graft is usually extracted from the iliac crest (Fig. 1) although the tibia has also been described as a donor site.⁷

 

Healing mechanisms of autologous material

Generally, augmentation material can be divided into two types: grafts that transport live cells (in clinical practice only the utility of autografts has been demonstrated, as they do not lead to an immunologic response), and bone regeneration materials that are placed in the recipient bed but that do not have any cellular viability. Three basic procedures intervene in the production of new bone that will be formed in the cavity. These may occur independently or simultaneously depending on the reconstruction material used, and these are known as osteogenesis, osteoinduction and osteoconduction. ⁸ The mechanisms involved in this procedure have become known over the last few years thanks to basic investigation that has permitted us to make a critical evaluation of the different materials available, to decide which of all of them is the most appropriate in each clinical setting, to use them with the best possible technique and to maintain realistic expectations regarding the new materials that are in clinical trials or in experimental stages.⁹

Osteogenesis. Is the formation of new bone by means of a transplant of augmentation material made up of live cells that directly produce bone regeneration. This mechanism is typical of autografts, and it is particularly important in cortical- cancellous and bone chip grafts due to faster revascularization.

Osteoinduction. Is the capacity that some materials have for releasing certain substances that are referred to as osteoinductive, and which are capable of encouraging the formation of bone through an endochondral mechanism in areas that are removed from the recipient bed. In practice, this type of bone regeneration is only achieved with autologous and allogenic grafts. Over the last few years a series of factors and substances have been identified as responsible for the osteoinduction process. Among these are Bone Morphogenetic Proteins (BMPs) that have recently been developed in a recombinant form (rhBMP).¹⁰ They have a pure osteoinduction mechanism eliminating the need for obtaining autogenic bone. Preliminary results have proved interesting while improving angiogenesis, bone healing and cartilaginous [tissue]. Currently there is a move to commercialize tissue-engineering techniques clinically.¹¹

Osteoconduction. This is the process by which implanted inorganic material provides a matrix permitting bone-producing cells to grow from the defect margins. This material can be permanent or reabsorbable. Pure osteoconductive material does not lead to bone being formed intrinsically. Ossification is not endochondral and the formation of bone always starts on the exterior.

 

Autologous bone augmentation material. Classification

For the correct use of augmentation material various characteristics should be evaluated: biocompatibility, availability, osteoinductive and osteogenic capacity and mechanical stability. Among the different options regarding available augmentation material there is:

Autologous or autogenous grafts (cancellous or cortical- cancellous bone chip grafts). This is the material of choice due to it having osteogenic potential but no antigenic capacity. Different intraoral donor sites can be used (chin, tuberosity of the maxilla, ascending ramus) or extraoral [sites] (iliac crest, tibia, calvaria). The extraoral donor sites are preferred because they provide a greater volume of medullar bone, but they have the inconvenience of requiring in most cases additional general anesthesia.

Homologous or allogenic grafts or allografts. These are [grafts] from an individual of the same species that is genetically different. A few incompatible antigens are transplanted. A process is required in order to eliminate the antigenic potential.

Heterologous grafts or xenografts. These are [grafts] from an animal of a different species and even more foreign antigens are therefore transplanted than with allogenic [grafts].

Alloplastic or synthetic grafts. The immune response that is created by an alloplastic material can vary from none to moderate. Some materials are susceptible to bacteriological contamination. The principal advantage is that the need for a donor site in the very [patient] is eliminated. A matrix is basically provided that allows bone growth in its interior. Its effect is only osteoconductive and very slightly osteoinductive. Hidroxyapatite has been the alloplastic material used traditionally, but others have later been introduced into clinical [practice] that have relegated it into the background.

The basic method for providing bone with osteogenic capacity in the maxillofacial area is through non-vascularized bone grafts. Block grafts can be used of cortical bone, cortical-cancellous bone, or cancellous bone chips. The cortical-cancellous graft provides more mineral bone matrix for the bed than osteocompetent cells, and less new bone is formed than with cancellous grafts. The main characteristic of the cortical bone block is that it supplies mechanical stability. However, its osteogenic and osteoinductive capacities are very limited due to the absence of porous structures. Bone chip grafts and cancellous grafts transfer a high density of osteocompetent cells and, due to their trabecular structure, rapid re-vascularization is produced from the recipient bed. However, due to their consistency adequate retention is needed in the bone cavity into which they are placed, otherwise a titanium mesh or a membrane may be required, and the periosteum has to protect the soft tissue flap adequately.

For augmenting cavities the grafts used are of [bone] chip, either cancellous grafts removed with spoons, gouges, trephines from the iliac crest or the tibia plateau, or grafts of corticalcancellous [bone] chips removed with a bone mill and taken from intraoral or extraoral donor sites (iliac crest or calvaria). If the graft is compacted carefully in the cavity, cellular density is increased, resulting in durable new bone formation. Once the graft has consolidated, these reconstructions prove to be very acceptable aesthetically and functionally, allowing also the insertion of osteointegrated implants.¹² A good number of clinical problems can also be solved in a simple form using small or moderate quantities of bone for small cavities with grafts from bone filters of scrapers.

 

Sources for obtaining non-vascularized autologous grafts

It is essential to know the advantages and limitations of every donor source, the results that can be achieved and potential morbidity. Formerly the classical sources for obtaining bone grafts for the reconstruction of maxillofacial defects were long bones. Today it is preferable to resort to the maxillas for small defects and to the iliac bone, tibia or calvaria when a larger amount is required. Choosing each approach depends on the type, size and form of the bone cavity, and the clinical experience and preferences of the surgeon.

Maxillae. The symphysis, body and ascending ramus of the mandible are a source of cortical grafts, and the area at the back of the maxillary tuberosity of cancellous bone. The limitations of block grafts are due to their size and structure, which is more or less cortical.

Grafts of granulated bone can also be collected easily through bone filters in aspirators (Fig. 2), or through scrapers. These can be a valid source for obtaining bone for small reconstructions in oral surgery, providing that the handling process for obtaining the graft is scrupulously performed in order to prevent any contamination from saliva.¹³

Iliac crest. This is the donor site that provides the greatest amount of volume of cancellous [bone] and which contains the largest proportion of cancellous to medullar bone. The iliac crest graft is commonly harvested from the anterior portion, as with this approach the position of the patient does not have to be altered. The maximum quantity of cancellous bone that can be harvested without causing significant morbidity is 50 cc.¹⁴ The advantage of the posterior approach is that the amount of cancellous bone that this provides is considerably superior (2.5 times) than with the anterior approach.¹⁵ The most frequent postoperative complication is gait disturbance. The incidence of this complication is minimized if the graft is harvested from the medial part of the iliac blade in stead of the external part. There can be changes in the nervous system that in any event do not produce sensory disturbances of any importance, and which disappear spontaneously shortly afterwards.¹⁶

Tibia. The grafting of bone proximal to the tibia is a technique which is gaining adepts as a donor site, as it requires a relatively simple procedure, having also a lower complication rate than the iliac crest graft. 5 to 30 cc of fragmented cancellous bone can be harvested (Fig. 3). Among the advantages of note is that it can be carried out using local anesthesia⁶ or intravenous sedation.¹⁷

Approaches using a trephine¹⁸ have been described for the iliac crest as well as for the tibial plateau when a large graft is not needed. The advantage of trephines is that they can be used with local anesthesia resulting in less morbidity.

Calvaria. This bone is widely accepted in maxillofacial surgery based on its proximity to the surgical site, its limited capacity for resorption compared with other sources (due to the great network of vessels that is possesses given its membranous origin that permits rapid revascularization and the maintenance of a large number of osteocompetent cells), and to low associated morbidity when in expert hands. The main complication is the tearing of the dura mater. The area of calvaria which is preferred is the area that corresponds to the parietal bone, which has a greater quantity of cancellous bone with a uniform thickness. Accessibility to this area is simpler, and there is hardly any postoperative pain. The cortical-cancellous graft is harvested respecting the internal cortical [layer] although the complete width can be used. It is currently indicated for the augmentation of alveolar clefts, orbital and midface reconstruction and for sinus lift augmentation.¹⁹

Rib. Currently the indications [for its use] are scarce as it has been substituted by the sources previously mentioned. The cortical-cancellous graft is harvested from the 5^th and 7th rib, using the complete width. It has less cancellous [bone], and a greater amount of it is reabsorbed with greater speed. Possible complications can be damage to the pleura consequently leading to pneumothorax.²⁰

 

Basic properties of autologous material

Autologous material is the most biocompatible material that exists as foreign antigen are not introduced into the cavity. These properties (being neither allergenic nor pathogenic) form precisely the best argument for using them. The disadvantage is that, for obtaining it, a donor site is needed. A decision has to be taken as to whether to use a proximal or distal location, which can entail new surgical sites and general anesthesia. However, graft harvesting rarely leaves significant lesions in the patient and morbidity in the donor site tends to be acceptable for the surgeon as well as for the patient.¹²

A characteristic that should be taken into account with regard to the autologous graft is its limited availability so, if it is indicated for the augmentation of large cavities and is insufficient, it can be mixed with other types of material. Different mixtures and proportions can be used so that its osteogenic, osteoinductive and osteoconductive capacities are used to the maximum. However, only the autogenous bone has osteogenic properties, that is, a capacity for introducing into the graft osteoblasts or osteocompetent undifferentiated cells which are able to form bone. But not all autologous bone has the same osteogenic capacity; cancellous [bone] provides the greatest amount of osteogenic cells. Allogenic, xenogenic, bone substitute and alloplastic material do not provide any osteocompetent cells. Their principal function consists in providing a scaffold or matrix that can be substituted by residual osteocompetent cells of the cavity bed. This type of bone formation is very limited and it is linked to the condition of the recipient bony bed.

Autologous material is the best suited for tolerating the forces of mastication, prostheses or muscular forces, and it adapts best to the area surrounding the bone. The material grafted has to withstand surgical manipulation and it has to maintain its stability once implanted into the cavity. Cortical grafts provide the most stability, even though for cavity augmentation this is of least importance as there is no break in the continuity of the maxilla.

A property of interest is stability over time. The capacity for resorption is lower in cancellous autologous grafts, especially if the augmentation material is covered adequately by the periosteum of the flap favoring vascularization and the incorporation of the transplanted bone at an early stage. On the other hand,cancellous bone has shown itself as being more infection-resistant, which is a very important characteristic should the graft come into contact with oral contamination.

Although it is true that there is no augmentation material capable of possessing all the ideal properties, on considering the election of one or the other, certain factors have to studied such as antigenicity, morbidity, economic factors, etc. From the point of view of biological properties, the best augmentation material is without doubt autologous cancellous bone chips. In addition, there are very few problems that cannot be solved with autologous material, and if the results are not satisfactory the procedure can be repeated.

 

Bone grafts and membranes

An important factor that has to be considered is that of maintaining the graft in position so that soft tissue does not interfere with the bone healing [process]. During the first healing phase of the grafted material, there is competition between bone tissue and soft tissue for filling the cavity. Due to soft tissue formation being faster, the cavity becomes obstructed. The development of guided bone regeneration membranes has demonstrated its usefulness for assisting and helping in the grafting of bones²¹ and its efficiency has been proved as it protects, by means of a barrier effect, the augmentation material in the oral medium, preventing the rapid growth of soft tissue towards the graft. However, the routine use of membranes and bone grafts does not guaranty success. Problems with membranes that have been documented include: dehiscence of soft tissue and exposure, displacement and collapse of the membrane. The membranes behave like foreign bodies and they can lead to infections and healing delays, and if they have to be removed prematurely, bone regeneration is less predictable.

The most controversial point is centered on whether or not to place a membrane when the periosteum of the mucoperiosteal flap is undamaged. It is clear that membranes can be useful when onlay²² type cortical grafts are used, or when alloplastic materials are used exclusively,²¹ because the formation of new bone is permitted by means of an osteoinductive mechanism in the first place, and osteoconduction in the second. However, the allograft of cancellous bone, which has a high percentage of osteocompetent cells, consolidates rapidly favoring vascular supply which comes principally from the overlying periosteum and from the osteogenic properties in the inner most layers of the periosteum. Adding a membrane to separate the graft form the periosteum could lead to a delay in the healing process of the graft.

 

Bone grafts and plasma rich in growth factors

One of the characteristics of bone chip grafts is that they can easily be mixed with plasma rich in growth factors. It would seem that the adding of plasma rich in growth factors accelerates soft tissue healing and bone regeneration. Marx and cols. published in 1998²³ a study of 88 patients in whom, after excising malignant as well as benign tumors, they proceeded to reconstruct using bone grafts enhanced with platelet-rich plasma for continuity defects of the mandible, alveolar clefts and sinus elevation surgery. This study concluded that the grafts into which platelet-rich plasma had been added had a higher rate of graft maturity, and this was shown by means of radiological analysis of monoclonal and histomorphometric antibodies on placing the implants. Its efficiency for enhancing osteogenesis and for diminishing the postoperative resorption of the grafts of cancellous bone from the iliac crest placed in patients with alveolar clefts, has also been described.²⁴

The growth factors obtained with platelet-rich plasma that is introduced at the same time as an autologous bone graft, constitute a useful and convenient procedure for enhancing the rate of newly formed bone, eliminating the possibility of transmitting disease and immunological reactions associated with allogenic and xenogenic substances.²⁵

 

Discussion

Autologous cancellous bone chips continue being the material of choice for augmenting cavities, despite efforts to achieve similar results with other materials, especially with allogenic and xenogenic bone, bone substitute and biomaterials. There are probably two principal reasons as to why autologous materials maintain their superiority today in oral and maxillofacial surgery. Firstly, there is the fact that an ideal alternative material has not been found after 25 years of intense investigation and clinical application. The potential advantages (avoiding donor site morbidity and its unlimited availability) have not surpassed the inconveniences: intolerance, lack of adaptability, resorption, lack of patient acceptance and economic cost. Secondly, the versatility, survival and adaptability of autologous materials have been backed by the simplification and increased knowledge of bone harvesting methods, especially for small and medium sized defect cases.

In biological terms, the bone autograph is the best augmentation material for a cavity, as new bone can be formed in the bed by means of osteogenesis, osteoinduction and osteoconduction. The remaining materials which are known alternatives for autografts lack a capacity for producing bone progenitor [cells] and, in general, they have good osteoconductive capacity but their osteoinductive potential is variable. Rejection is the immunologic factor determining the result of augmentation materials, and intervention is primarily due to the activation of an antigen-specific immune response. Autologous material does not introduce any antigens into the bed so, from the immunologic point of view, autologous material is the best and the safest [option], and it should be considered as a first choice whenever possible.

Harvesting an autologous bone graft successfully depends on extracting the [correct] amount and quality of bone required for each reconstruction. It should be planned with the knowledge of donor site anatomy, in such a way that blood loss and morbidity is as limited as possible. Bone chip grafts can be obtained in simpler ways: by means of trephines, vacuums with bone collection filters or bone scrapers.

Cancellous bone chips can be mixed with different types of materials such as xenografts, demineralized human bone or bioactive glass [granules]. Numerous mixtures have been described and with differing proportions, which makes revision of the literature impossible in this sense. Most of the studies are centered on the augmentation of the maxillary sinus.²⁶ They are indicated in situations where there is little autologous bone available or in small defects. In this way, the amount of autologous bone required is inferior. The inconveniences are the risk of transmitting disease and the increase in costs.

Bone filters and other systems for the intraoral collection of bone are an aid for obtaining autogenous bone, which is very useful for augmenting small bone cavities such as such as in sinus elevation, periodontal defect cavities or postextraction alveolus, either on their own or combined with other products. These systems for collecting autologous bone chips are inexpensive, and due to their high predictability, they have become a valid alternative for small sized bone cavities.²⁷

Guided bone regeneration membranes can be used for covering bone defects and post-extraction alveolus, acting as a biocompatible barrier that impedes the growth of soft tissue, connective [tissue] and epithelial cells towards the interior of the underlying bone during the bone healing period. If autogenous bone is used for augmentation, a membrane can be added optionally to stabilize and maintain the position of the bone chip graft although, if the mucoperiosteal flap is intact and if it completely covers the alveolus in a tension- free fashion, this is not necessary. However, if alloplastic materials are used, the use of a membrane is advisable.

In short, although there are many augmentation materials for bone cavities, the material that will replace the autologous cortical-cancellous bone or bone chip has yet to be described. Neither are there conclusive studies as to the usefulness of membrane placement reflected in satisfactory and real clinical results and, in consequence, the indications for their use are limited at the present time. The controversies surrounding the combining of autologous grafts with other augmentation material has led to multiple studies, some in favor of this combination and others against, while no definitive conclusions can be established at the moment.²⁸ Alloplastic material is probably being over indicated, perhaps because surgeons are not obtaining enough training to enable them to carry out the different grafting techniques safely.²⁹ It is essential that the oral and maxillofacial surgeon know the biological properties and fundamental characteristic of autologous material, the different harvesting techniques and their clinical applications as augmentation material for bone cavities.

 

 

Dirección para correspondencia:
Pedro Infante Cossío
Servicio de Cirugía Oral y Maxilofacial
Hospitales Universitarios Virgen del Rocío
Avda Manuel Siurot s/n
41013 Sevilla, España
E-mail: pinfante@us.es

Recibido: 02.08.04
Aceptado: 06.10.04

 

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