Controversias en Cirugía Oral y Maxilofacial: Parte I

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Maxillofacial osteosynthesis with titanium
Osteosíntesis maxilofacial con titanio

 

S. Martínez-Villalobos Castillo

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Abstract: Titanium is an element whose properties have made possible impressive advances in the aerospace and chemical industry of our days. We could say that it is already the metal of the future. As biomaterial used in the osteosynthesis techniques one has consolidated like of first choice in front of the steel. Its extraordinary biocompatibility and the possibilities that biometallurgy offers to us are opening the doors in numerous fields of medical application like for example the Odontology. In our speciality, and with the reservations that we will analyze for the paediatric surgery, it continues being of first choice by virtue of its properties and of the refined manufactures that the industry makes our available. The resorbables biomaterials, to the margin of the paediatric midface and craniofacial surgery, are at the less safe and resisted alternative in the present time and in our opinion, with a hopeful future that little by little lays way in indications like orthognathic surgery and midface trauma of the adult. In any case the relation costs/benefits is an aspect that also would be due to consider in our election. Key words: Maxillofacial osteosynthesis; Titanium. Biomaterials; Paediatric facial osteosynthesis; Titanium plates; Resorbable plates.

Resumen: El Titanio es un elemento cuyas propiedades han posibilitado avances impresionantes en la industria aerospacial y química de nuestros días. Podríamos decir que ya es el metal del futuro. Como biomaterial utilizado en las técnicas de osteosíntesis se ha consolidado como de primera elección frente al acero. Su extraordinaria biocompatibilidad y las posibilidades que la biometalurgia ofrece le están abriendo las puertas en numerosos campos de aplicación médica como por ejemplo la Odontología. En nuestra especialidad, y con las salvedades que analizaremos para la cirugía pediátrica, continua siendo de primera elección en virtud de sus propiedades físico-químicas y de las refinadas manufacturas que la industria pone a nuestra disposición. Los biomateriales reabsorbibles, al margen de la cirugía pediátrica de tercio medio y craneofacial, son en la actualidad y a nuestro juicio alternativas menos seguras y contrastadas, con un futuro esperanzador que se abre camino poco a poco en indicaciones como la cirugía ortognática y en la traumatológica del tercio medio facial del adulto. En cualquier caso, la relación coste/beneficio es un aspecto que también se debería considerar en nuestra elección. Palabras clave: Osteosíntesis maxilofacial; Titanio. Biomateriales; Osteosíntesis facial pediátrica; Placas de titanio; Placas reabsorbibles.

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Miembro AO-CFM España. European AO Faculty,
Médico Adjunto Servicio de Cirugía Oral y Maxilofacial.
Hospital Universitario Virgen de las Nieves, Granada, España

Correspondencia:
Sergio Martínez-Villalobos Castillo
Servicio de Cirugía Oral y Maxilofacial
Hospital Universitario Virgen de las Nieves, Granada, España
E-mail: smvillalobos@terra.es

 

Introduction

The beginning of fixation with plates and screws for osteosynthesis (active repair of fractured bones) goes back to 1886 when the German man Karl Hansmann presented his clinical experience in which two cases of mandibular fractures treated with this system were included. However, they were designed for the treatment of fractures in the body’s long bones.

The two important world wars, for obvious reasons, meant a great advance in the development of bone repair techniques and systems. However, in the maxillofacial territory, this advance was not so significant, since the use of the fixation techniques developed for long bones was accompanied by a high index of complications and failures. Thus its use has remained very limited, the classical orthopedic treatments being the ones used routinely. Up to recently, in especially complex situations, a more evolved technique was used, but it was designed for general traumatology in an attempt to repair serious maxillary bone lesions, attempts that almost always failed or at least were associated to high morbidity (Figs. 1 and 2).

Thus, specific techniques and systems are needed for the maxillofacial territory given its anatomic, physiological and biomechanical characteristics, with a dual objective: anatomical repair with functional restoration as early as possible and a drastic decrease in morbidity.

Osteosynthesis and biomaterilas

Different experimental studies in the field of biomechanics and physiopathology of bone consolidation as well as the investigation and improvement of the biomaterials used have led to a very rapid advance in the last 25 years in regards to techniques and systems, thanks to which a considerable decrease has occurred in the complications indexes and therapeutic failures in the management of the different craniofacial osteosynthesis techniques.

In 1949, the Belgian man Robert Danis presented the principle of axial compression of the fracture focus. Beginning with this idea, the Swiss group ASIF developed different research lines that were successful at the beginning of the 1960’s for their clinical application in the treatment of long bone fractures. In 1968, Luhr designed an axial compression plate for mandibular osteosynthesis. In 1973, Michelet and in 1975 Champy described the principles of non-compressive monocortical osteosynthesis for the maxillofacial territory. Thanks to these technical progresses, and to the development of biometallurgy, obtaining good clinical results with minimum associated morbidity began to be reachable objectives.

Minimum properties are required for all plate osteosynthesis, basically adequate resistance (to provide stability), sufficient ductility (to allow for anatomic molding) and biocompatibility (to not produce local or systemic adverse effects). The materials from which the implants for osteosynthesis are made vary; pure or alloyed stainless steel, cobaltchrome- molybdenum and titanium are mainly used. For many years, stainless steel was the material of choice. It consists in an alloy of the iron, chrome, nickel and molybdenum metals in well-defined proportions (62.5%-17.5%- 14.5% and 2.8 % respectively) associated to other components in less proportion. Its resistance, compatibility and anticorrosive properties (proportionally linked to the presence of chrome) are adequate, although, in 1977, Steinemann described certain anticorrosive potentially by interaction between different metallic components of the implant «fretting corrosion». This circumstance advises the systematic withdrawal of stainless steel materials once the fracture is consolidated and mineralized, at approximately one year of the intervention.

In this technological development that we are referring to, Titanium as a biomaterial has become one of the undoubtable protagonists, given its extreme chemical passivity (and thus excellent biocompatibility) and because it has adequate physical properties for good long term biomechanical behavior. Because of its density, the implants have about 45% less density than the iron and cobalt implants, an important factor regarding comfort of the patient, above all in long fixations. Its low elasticity module is another advantage, since it minimizes the protection against pressure and this is transferred to the bone. The relative importance of the protection against the pressure is increased as the implant size increases. Thus, since the middle of the 1989’s, the implants made with pure titanium are of choice for osteosynthesis in the cranial-maxillofacial territory.

Titanium

Titanium (Ti) was discovered in 1791, and was assigned no. 22 on the Periodic Table of Elements. It is the ninth element in abundance of the earth’s crust, it being found in significant concentrations, above all, in the rutile (in form of TiO₂) and in ilmenite (FeO.TiO₂). At present, its «synthesis» as pure metal is performed from these minerals by the technique developed by Kroll in 1937: reduction of titanium tetrachloride with magnesium in argon atmosphere to avoid its oxidation.

In the middle of the 1950’s, the studies related to titanium and its alloys underwent an important impulse, basically in the USA, given the great importance that its physical-chemical properties grant it in the development of military and aerospatial technology, above all: low density, low elasticity module, excellent mechanical resistance/density relationship, good behavior at high temperatures, great resistance to corrosion and magnificent biocompatibility. In the following decade, its applications were extended to the chemical and biomedical industry

Titanium is considered as a light metal, the only one that presents dimorphism. In pure state, its crystalline and stable microstructure is hexagonal, becoming cubic and unstable after 882ºC (transfer temperature). This transformation makes it possible to perform combinations with different elements and, consequently, obtain alloys with different crystallographic structures and thus physical-chemical properties. We distinguish three types.

• Alloy a are those that present a hexagonal structure at environmental temperature, and the alloying effect consists in increasing the transfer temperature. Commercially pure titanium belongs to this group

• Alloys b are those that present cubic structure at room temperature and the effect of the alloy in them is precisely that of making this microstructure stable at this temperature.

• The microstructure is mixed (globular) and stable in the alloys a/b ; the TAV (Titanium/6% Aluminium/ 4% Vanadium alloy) belongs to this group.

The «commercially pure» titanium (Ti CP) is simply titanium and oxygen, together with other «impurities». In fact, pure metallic titanium reacts very rapidly with oxygen, nitrogen, hydrogen and carbon of the atmosphere, so that when it is obtained for commercial purposes, it presents these impurities in its composition in different proportions, which gives rise to up to four types of combinations with different resistance and ductility grades (Grades 1 to 4 of the A.S.T.M. F67 guideline) (Tables 1 and 2).

The different physical procedures used to obtain and manipulate Titanium CP (temperature, cooling rate, etc.) make it possible to obtain up to three different crystalline microstructures with different properties; equiaxial (the titanium of the dental implants and for osteosynthesis), martensitic and Widmanstätten (Fig. 3). The «mechanization» process is finally a fundamental step to obtain high quality implants on surface, characteristics that may be analyzed with the scanning electron microscope and whose defects may have a repercussion on the biomechanical properties of the implant in service (Figs. 4 and 5).

On the other hand, this elevated reactivity with oxygen leads to the spontaneous and rapid formation of titanium oxide layers on its surface, that vary from TiO to Ti7O₁₂, layers that, although they are thin, are impermeable, with the consequence that their anticorrosive properties have excellent resistance to the action of the inorganic acids and of almost all the organic ones (Contzen-1967). Thus, no corrosion has been seen even in cases of osteosynthesis failure in which the surrounding tissue is darkened by abrasive particles of pure titanium (Pohler, 1988). Therefore, it is extremely insoluble so that its biocompatibility is excellent, it behaving as a chemically inert material that does not interact with the body (on the contrary to steel). For Steinemann (1988), there is a physiological saturation of titanium in the body, so that the possibility of interaction with additional soluble titanium does not exist. No toxic or allergic reactions have been described.

TAN (Titanium/6% Aluminium/ 7% Niobium) is a relatively new alloy selected by the AO/ASIF for future generations of implants designed for the fixation of fractures. The alloy was conceived by a research team in Sulzer Bros (Winterthur-Switzerland) and introduced in 1985 in the clinical practice (total hip replacement prosthesis). The mechanical properties of the TAN alloy are very similar to the Ti-6Al-4V alloy, used as a biomaterial for many years. Vanadium has been substituted by Niobium, a metal discovered by Hatchett in Connecticut in 1801 and initially called Columbium, which was assigned no. 41 on the Periodic Table of Elements.

Its composition is shown in Table 3, it being extremely important for the hydrogen contents to be minimum to prevent the fracture of the alloy. Its microstructure is mixed globular a/b, very similar to TAV, so that its physical properties are also very similar (sensitivity, elasticity module, sensitivity to tension, rotational fatigue, corrosion, etc). In regards to Grade 4 Ti CP, it has substantial advantages, that we could summarize for practical effects in a better relationship with manageability/resistance binomial. From the biocompatibility point of view, TAN follows the principle of only using non-toxic elements for implants indicated in USA 4,029,129 assigned to the Straumann Institute (Waldenburg-Switzerland).

Numerous in vivo and in vitro experimental studies support the excellent biocompatibility of this alloy and certain advantages (at least in the theoretical and experimental field) in regards to the compounds with Vanadium. Finally, the photoelectron spectroscopic analysis has determined that the TAN surface is a mixed layer of titanium oxide, aluminum oxide and niobium oxide, that is more stable chemically than the titanium oxide layers formed in the Ti CP, so that the resistance to corrosion is, if possible, better. Surface treatments such as the anodized one of the implants makes it possible to determine the thickness of this mixed oxide layer, that is the one which conditions the color that the implants have due to the diffraction of the light inside the oxide (typically golden in the AO implants).

An example of these last generation implants in our territory is made up of the screws for fixation for the UNILOCK 2.0 type blocking systems.

Osteosynthesis and radiotherapy

At present, the mandibular osteosynthesis with titanium plates after oncological ablative procedures is a routine and perfectly systematized technique. Fixation techniques in osteotomy approach are usually used to reinforce the marginal mandibulectomies, in the bridging of bone defects after segmental mandibulectomies and in microvascularized or free bone graft fixation. According to the case, different types of fixations are used, and the presence of pre- or postoperative radiotherapy is a determining factor in its choice. As a general rule, rigid fixation, that is sufficiently stable, should be attempted on those radiated areas or that will be included in the radiation fields (Fig. 6).

It is well known that radiotherapy conditions an increase in the index of local complications, including, among others, osteosynthesis failures. However, a direct and significant causal relationship not been solidly established in the references between the presence of osteosynthesis material and the appearance of these complications, their genesis being multifactorial.

Different local factors have been established as responsible for this phenomenon, among which the anatomic location of the mandibular defect and the presence or not of adequate coverage of the implants with vascularized flaps stand out. Typically, the complications are more frequent in absence of this coverage and in the symphysial regions and the mandibular body, just in front of the masseteric «case.» The tissue factors related with this increase in morbidity are fundamentally alterations that radiotherapy causes in bone microvascularization and connective tissues, that condition a delay in the curing process and tissue regeneration. Finally, biochemical harmful effects such as those that are produced on the activity of the BMP (bone morphogenetic protein) have also been established. Consequently, consolidation of an osteotomy and the osteointegration process between screws and bones are slowed down with an increase in the possibilities of failure, especially if we consider that the risk of infection is also increased for the same local and tissue reasons. Under these circumstances, the use of a fixation that is not sufficiently stable almost guarantees the presentation of complications.

A second aspect to consider is the interaction that occurs between the implant metal and radiation. It is well known that the dose distribution is altered, producing an increase of it due to a dispersion phenomenon in front of the implant and a decrease due to the effect of distal absorption of it. From the experimental point of view, it has been established that these changes are directly proportional to the atomic number of the interposed metal and to the «profiles » (in terms of thickness and width) of the implant, it being limited to an area between 1-5 mm around the plate, with a dosimetric mean of less than 3% for the dispersion phenomenon at 2 mm and of 4% for the absorption phenomenon at 5 mm. These variations are, however, «compensated» when parallel and opposite fields (Ryu-1995) are used. In the clinical practice, these phenomena could have two important repercussions: on the oncological control, due to the lessening and infradose, and on the tissue radionecrosis due to overdose.

In the first case, and with the data available, it seems unlikely that after the performance of oncological surgery ad hoc with gross oncological margins of safety and with the possible use of reconstructive flaps, the interposition of a plate could interfere on the therapeutic dose that the tumor surgical bed should receive. There is no scientific evidence of an increase in the local relapse rate for this reason.

In the second aspect, the dispersion may have clinical repercussion, since a focal osteoradionecrosis may occur due to overdose in the bone-screw interphase, with the consequent failure of the osteosynthesis system applied, or a greater tissue, mucous or cutaneous radionecrosis with major risk of intra- or extraoral plate exposure (Fig. 7).

In summary, and given that head and neck radiotherapy generally uses parallel and opposite fields, the variations in the therapeutic dose due to dispersion and absorption are compensated without having a significant repercussion on the local oncological control and even, for most of the authors, on the focal radionecrosis phenomena. In any event, and based on the atom number, the titanium alloys are also, in this aspect, less interactive and thus of choice in presence of adjuvant radiotherapy in regards to those of iron. In the clinical practice, the option of a Block plate (UNILOCK type) would be of choice in all the cases that must coexist with radiotherapy, not due to its lower profiles but, above all, to minimize the ischemia provoked on the bone cortical by the compression of a traditional plate as much as possible (Fig. 8).

Finally, it can be stressed that the complication and failure indexes attributed to the Radiotherapy/Osteosynthesis binomium are minimized in the presence of adequate tissue coverage and by the anatomic restoration with microvasclarized bone grafts of the mandibular defects. The option of the osteosynthesis bridge, with the adequate implant, should be reserved for very posterior defects or for patients with a very unfavorable oncological prognosis.

Withdrawal of osteosynthesis

Once the fracture or osteotomy is consolidated, the osteosynthesis materials lose their biomechanical effect of interfragmentary fixation and become mechanically inert bodies. The underlying bone is remodeled in a reactive way to the vascular stress caused by having the plate attached. This process occurs in the first months of the post-operative period and occurs with an initial phase of some porosity that is resolved if the intracortical circulation is unharmed, a circumstance that occurs when the osteosynthesis technique has been adequate. After the necessary time, the osteointegration grade is such that new bone formation sometimes occurs on the osteosynthesis plate (Fig. 9). In this situation, one year after the surgery, it is difficult to make the decision to withdraw the osteosynthesis material, if titanium has been used. It means a new surgical intervention, often with general anesthesia, that is not exempt from certain local and systemic risks. In addition, on many occasions, the osteointegration is such that ostectomies must be performed to be able to withdraw the material, the heads of the screws may become detached, the remnants remaining in the bone thickness, etc. Finally, a situation of local extreme aggression, with risk of complications, that should be justified, may occur. We cannot overlook that, on many occasions, and in some countries more than in others, the systematic withdrawal of the osteosynthesis is due more to social-health care and economic criteria than to strictly biomedical ones.

The principal indications, almost always relative, to proceed to the withdrawal of the fixation material would be:

• Intolerance to cold

• Subcutaneous palpation and sensitivity

• Intra-extraoral exposure

• Interference with prosthesis

• Interference with dental implants

• Instability. Mobility of the plate and/or loosening of the screws, due to infection and/or by technical error.

• Local or general adverse reactions (toxic): stainless steel hardware.

Another possible disadvantage (mentioned in the literature) that could well justify either the withdrawal of metallic osteosynthesis material or the use of resorbable osteosynthesis is interference with the CT scan imaging tests during oncological conditions follow-up. This question would depend on the craniofacial territory and the pathological condition in question and acquires special importance in the tumor pathology of the cranial base. In these cases, and given that the biomechanical requirements of the area make it possible without added risks, fixation with resorbable implants would be of choice. The profile of the implants to be used in the midface (miniplates) minimizes these effects, so that our choice could be individualized based on the biomechanical and functional needs of each patient and on the presence of adjuvant radiotherapy. On the mandibular level, the need for osteosynthesis during the surgical procedure is generally associated to an advanced stage of the oncological disease and thus to the almost inevitable presence of radiotherapy. Under these circumstances, a safe, sufficiently stable, usually rigid fixation that provides a functional rehabilitation as early as possible and minimizes the possibility of complications is imposed. At present, the resorbable implants do not guarantee these premises, so that osteosynthesis with titanium is of choice, even assuming the disadvantage of the possible delay in the diagnosis of a relapse due to interference with the CT scan imaging tests.

In fact, since the incorporation of the MRI to our routine diagnostic armamentarium, this disadvantage has become obviated, given that titanium implants do not cause interferences or artifacts in this type of examination, but only an empty sign that is limited to the exact location and decrease of the implant. This is because the titanium alloys do not have residual magnetism and the implants thus may be subjected to Magnetic Nuclear Resonances routinely (the magnetic permeability, in the case of not very permeable materials, may be measured with an instrument called Severn Gauge whose lowest calibrated test is equal to 1.01, having registered lower permeabilities in the TAN alloy).

The follow-up of the consolidation and mineralization processes of fractures or osteotomies does not pose any disadvantage, since the CT scan examinations with bone window are not artifacted by the titanium implants, or, of course, by the plain X-rays or tomographic examination.

The controversy continues in the case of growing patients, although in general, as we will see later on, they tend to be withdrawn although they are not causing problems, invoking the uncertainty on the possible very long term adverse effects.

The migratory phenomenon that occurs during growth is well known. Metallic osteosynthesis in the cranial territory, for this reason, should be systematically withdrawn, due to their possible endocranial penetration with the consequent meningeal interaction. The indication of resorbable osteosynthesis in these cases is by choice.

Plate fracture

The plates may «become fractured». The cause is the so-called metallic fatigue (Pohler and Straumann- 1975), a situation that occurs when the plate supports an excessive and prolonged mechanical load, almost always due to the absence of underlying bone reconstruction (reconstruction plates with bone defect bridging). If the plate has also been excessively manipulated during the molding process, this phenomenon may be favored (Fig. 10).

However, the most frequent cause of the metallic rupture is the error in its choice, that is, when we require that a plate has biomechanical benefits for which it has not been designed. At present, this situation frequently occurs in the treatment of edentulous mandible factures with miniplates, in which we underestimate the functional force that must be counteracted. On the other hand, when the defects in bone continuity are not restored, the extreme bone remains tend to be reabsorbed, so that there may be loosening and loss of screws, that are initially stable and osteointegrated, and that should be removed, in the long term.

Osteosynthesis with titanium children

Fortunately, most of the maxillary fractures that occur in the pediatric age are subsidiary to conservative treatment, understanding this to be from the therapeutic abstinence to intermaxillary fixation. The choice of one alternative or another depends on the intrinsic characteristics of the fracture and the patient’s age, above all in regards to the teething stage present. On other occasions, open surgery is required to reduce the fracture, although interfragmentary fixation is not essential finally. In those cases, the exquisite surgical management of the soft tissues is essential to minimize the vascular damage and the possible repercussion that this could have on growth.

In general, there is a tendency to be more conservative when the patient is younger, but there are cases in the clinical practice that do not permit it. There are situations in which an open reduction with active fixation of the foci is necessary for adequate curing of the fractures, fundamentally in the cases having an important degree of displacement, in presence of multiple foci and/or of fractures of both maxillaries and regardless of the patient’s age group (Fig. 11). Classically, wire osteosynthesis (stainless steel) has been used to solve most of these cases, associated or not to intermaxillary fixation. The evolution in the design of titanium miniplates and microplates with very low profiles (1-1.5 mm) and very short and selfthread screws have generalized their use in the situations, displacing wire fixation almost completely, since the primary stability that it makes possible is very superior. Thus, in many occasions, intermaxillary fixation can be obviated, a situation to is important in relationship to children (Fig. 12).

In the case of mandibular fractures, the final objective of the treatment in these cases is similar to that of the adult population, that is, obtaining an anatomic reduction and stabilization of the focus that permits an anatomic as well as functional correct and immediate repair. Based on this premise, it is clear that the mandible of these patients is subjected to a series of characteristics, in large part, common to the rest of the facial skeleton, that conditions the therapeutic solution: bone in growth, maxillo-mandibular combined growth, presence of tooth buds (different teething phases) and baseline position of the inferior dental nerve. Thus, the growth dynamics leads us to different clinical situations in the surgical treatment of the mandibular fractures in children. This heterogeneity, together with the low incidence of facial fractures in childhood, justifies the nonexistence of a treatment reached by consensus. As basic principles, the degree of displacement will condition the need for osteosynthesis, the teething phase will determine the immobilization techniques and the osteosynthesis to be used and the site of the fracture the duration of the immobilization (Hardt-Gottsauner- 1993).

The advantages of open surgery with fixation not only are based on obtaining an exact reduction of the fracture foci. This type of action makes it possible for the airway to remain permeable, anticipating potential serious complications such as vomit aspiration (that is not rare in children) and obtaining a rapid return to the usual diet of the child, with maintenance of maxillomandibular and cranial-mandibular functionalism (TMJ) early. This passive physiotherapy is beneficial for all the stomatognatic system in growth (Fig. 13).

The disadvantages described in the literature include the possible damage of the tooth buds, the interruption of the osteogenic potential of the periosteum on exposing the mandible with the consequent alteration of the growth pattern, appearance of hypertrophic scars, fundamentally in adolescents, and the possible interference of the osteosynthesis material in the mandibular growth that we will refer to later on. It must be stressed that all these disadvantages, except the last one, are common for the resorbable osteosynthesis systems, and it could even be thought that somewhat more important due to the greater profiles of their plates and screws (Champy- 1992). The indications for open surgery with semirigid fixation in the mandibular fractures in childhood are, in our opinion, and in agreement with other authors, the following:

1. High energy traumatisms, that cause multiple mandibular fractures, especially if they accompany midface fractures. Open fractures are included within this section (Fig.14). The energy released frequently causes comminution of the fragment; the fixation with miniplates makes it possible to recover the architecture of the mandible, minimizing the functional and esthetic damage.

2. Deficient fixation of the metallic splints with intermaxillary blocking. During the first two year of life, the primary dentation does not supply sufficient stability. After, the mixed dentation sometimes makes obtaining adequate immobilization difficult. The open reduction in mandibular fractures, single but with important displacement, makes it possible to avoid precarious intermaxillary fixation.

3. Association of condyle and mandibular body fractures. Fundamentally before 12 years of age, the condyle makes up the most frequent site of mandibular fractures. Conservative treatment, based on a bland diet and early mobilization, is sometimes hindered by the existence of another fracture focus, basically in the contralateral mandibular body. Fixation with osteosynthesis material allows for early oral opening, minimizing the risk of ankylosis risk in the damaged joint (Fig. 15).

4. Situations in which the traumatism consequences are not limited to facial fractures. In the first stages of childhood, the presence of intracranial or thoracic-abdominal lesions are unpleasantly common. In these situations, it is advisable to use open treatment of the mandibular fractures, that makes it possible to adequately reduce and stabilize the fracture, maintaining the airway free, which facilitates the work of the pediatric intensive care units and avoids the undesired tracheotomy (Fig.16).

In the case of displaced orbito-zygomatic fractures, much more uncommon, an intraoral approach and fixation by titanium miniplate on the zygomatic maxillary buttress is advised. If an approach of the infraorbital ridge or orbital floor is necessary, a subtarsal or transconjunctival pathway can be used. The infraorbital ridge may be stabilized by wire osteosynthesis or by titanium microplates. The orbital floor can be restored by pure reduction of the displaced fragment, or by autologic grafts without any type of fixation. Finally, if the eyebrow approach is necessary to perform a fronto-zygomatic osteosynthesis, titanium mini-microplates or wire osteosyntehesis may be used if the zygomatic maxillary buttress has been well fixed. In Lefort type fractures, in spite of their rareness, most of the cases (80%) require open surgery and semirigid fixation. Only those cases with minimum displacement are subsidiaries of a therapeutic abstention (bland diet and control) or of the application of an intramaxillary blocking during 3 weeks. In the rest of the cases, stabilization of the naso-maxillary and zygomatic maxillary buttress will be done by miniplates.

At present, both for orbito-zygomatic fractures as well as for the midface, the indication of the resorbable osteosynthesis can be of choice, since its results are comparable to osteosynthesis with titanium and the possibility of a future withdrawal is obviated. We believe that the decision depends on, above all, the experience of the surgeon with one system or another.

In regards to the orbital-nasal-ethmoidal fractures, it must be considered that the growth of the midface is conditioned by the development of the anterior cranial fossa, orbital cavity and septum. The fractures of this region, although rare, have, on the one hand, a high potential to alter facial development, but on the other hand, they may be accompanied by important esthetic sequels due to inadequate reduction. Thus, in spite of the important deperiostization that its treatment has, most of the authors maintain the idea of performing an anatomic reduction of all the displaced fractures by coronal approach in absence of facial wounds that permit a direct approach. The semirigid fixation should be performed preferentially with resorbable miniplates (if the conditions of the soft tissues make it possible), with steel wires, with titanium microplates or if the stability of the fracture allows it, with biological glues (cyanocrylate). The use of metallic plates in this territory means certain risk of intracranial migration and requires a close follow- up until growth has ended and, if necessary, of a second approach for its withdrawal (Fig. 17).

Conclusions

The interference of titanium osteosynthesis in the growth of facial bones has been repeatedly invoked in the literature. As we have already stated, it is difficult to discriminate between the harmful effects derived from the fracture itself, the indirect trauma on TMJ, of the traumatic or surgical lesions on the soft tissues (Moss and Rankow growth matrix) and those due to the application of titanium miniplates for osteosynthesis on growth.

Fixation with titanium miniplates and microplates, excluding the pericranial territory, thus poses the controversy derived from the need for a second operation for its withdrawal, a need that is argued to indicate the fixation with resorbable systems. The authors who maintain this position generally proceed to its withdrawal at 2-3 months of its application. When the approaches are intraoral, the consequences of a second surgery may be considered to be acceptable, but in extraoral approaches (i.e. coronal or submandibular), these consequences cannot be scorned. On the other hand, some surgeons postulate that the new surgical approach has a repercussion on facial growth in a similar way to the primary treatment of the fracture, so that, considering the recognized biocompatibility of the titanium plates, they recommend their maintenance, above all in patients over 13 years, except if an objective alteration is produced. It must be considered, as we have already said, that the osteosynthesis manifest as biomechanically active until the fracture has consolidated. After this time, they behavior as inert bodies on which, and in the absence of complications, bone remodeling and osteointegration are produced, it being possible to see how the material «accompanies» the mandible in its growth (Fig. 18).

Following the assumptions of Evidence Based Medicine, no contrasted scientific evidence that establishes a direct causal relationship between the presence of titanium implant and a growth alteration on the facial bone is found in the literature. The clinical experience of many surgeons, among them us, speak against this possibility, so that once the pertinent critical assessment is made in terms of validity and utility, we could conclude that this hypothesis does not justify the lack of use of these implants in children when necessary, or the systematic withdrawal of them when it is not necessary (Figs. 19 and 20).

In any event, a prolonged follow-up is essential in these patients on whom the decision will be individualized.

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