**4. Discussion**

452 Biomaterials – Physics and Chemistry

materials. it does not have these common disadvantages, such as being concrete, visible during activation of mimics muscles, and having a temporary effect. For what concerns the skeletal tissue, for years we have used autologous bone grafts and cartilaginous tissues similar to many prosthetic materials. They showed plastic phenomenon and they were easy to infections and resorption instead of esthetic and functional aspects. In these years, porous polyethylene results to be a suitable material for bony integration; it is easy to use and has great reconstructive quality and low susceptibility to infections. A general problem of the same biomaterials is a lack of visibility on conventional radiographs; they can be seen using magnetic resonance imaging or computed tomography. These investigations are not suitable for the frequent examinations, because magnetic resonance imaging is a high-priced procedure and computed tomography has a high radiation dose. During the follow-up, we encountered some difficulties for their radiotransparency; therefore, in our study, we used a noninvasive technique such as ultrasonography (US) to estimate the filling conditions and eventually to characterize an eventual pathologic process during the early phase. The aim of this study was to examine the use of ultrasound imaging in detecting the changes in

All patients were grouped according to different kinds of diseases: malformative pathologies (patients with hemifacial microsomia), degenerative pathologies ( patients with scleroderma and with Romberg syndrome), results of skull-facial traumas, and pure aesthetic problems such as senile aclasia. They have been examined using US (in early and late postsurgical courses) with a highresolution probe (7.5-13 MHz, Astro; Esaote Biomedica, Genoa, Italy). The protocol of the study has foreseen almost 3 ultrasound controls; with a variable follow-up of 7 days to 36 months. After 7 days ofimplantation, we made the first

Polyethylene porous, being a semirigid material that needs rigid interns fixture, decreased migration and stabilization problems. The polyacrylamide is introduced as a gel. If it is not well positioned, it could migrate. Integration and migration progress can be studied by US investigations, such as object examination. Initially, in both treated groups, transplant may show a light inflammatory state that will disappear in the succeeding days. Correct evaluation to appraise for the stabilization of the materials is composed of evaluating clinical and US parameters. The clinical parameters were as follows: the alteration absence of the impending fabrics, the graft, the edema absence, manque´ mobilization, or migration of the implantation. The US parameters were as follows: absence of massive harvests of liquidate, inflammatory reactions of the surrounding fabrics, and good visualization of the implantation and the surrounding tissue. With this worktop, we have been able to appraise the diverged characteristics of the biomaterial and visualize the tissues reactions. In our results porous polyetylene showed strong ecogenic features such as the bone and vanishing margins; however, the implantation (like a titanium screw) appears as a reverberated ultrasound bundle. We could evidence the stability of the biomaterials, namely, its integration, eventual nearby tissue alterations, in the early and late phases. Therefore, polyacrilamide appears anecogenous with a water-like aspect in the recent implants and corpuscolated in the older ones. Sometimes, such as in connective tissue degenerative pathologies (such as scleroderma) with an increase of the fibrotic component, we can visualize more vacuolized structures not for a lack of fibrotic integration but for the pathologic fibrotic beams. Although the implant seemed to be surrounded by a fibrotic tissue envelope, US technique can be considered an excellent way to visualize the clinical

biomaterials.

ultrasound control.

A biomaterial is defined as a several composed structure, able to interface with the biological systems in order to increase the volume, to give support or to replace a tissue. The performances of the installed materials are evaluated on the basis of bio-functionality and bio-availability therefore bio-compatibility (**1)**.

The bio-functionality is the property of a bio-material to produce a determinate function from the physical and mechanical point of view while the bio-availability is the capacity of a bio-material to develop a determinate function during all the useful life of the plant (**2)**. The final properties of a material depend both on the intrinsic molecular structure of the polymer and on the chemical and physiques processes to which it is exposed and can be widely manipulated intervening on the 10 operating conditions of such processes and on the polimerizzation's reaction. The immediate answers of the human body to the action of a biomaterial is divided in two phases: an inflammation is initially developed because of the first defensive reaction of the organism to an foreign body; subsequently there is a restorative process of the damage. In general if the installed material is toxic, this causes the necrosys of the surrounding tissues; if it is not toxic and inert under the biological point of view a fibrous capsule around to the plant is formed (this answer is quite rare because the biomaterial is usually not completely inert); if, at last, the material is bioactive, it stimulates a precise biological answer and it is progressively supplemented with the surrounding tissue .

In most cases the material undergone some degradation form and the products of such process are released in the tissues. Such products, if they are not biologically active and they are not toxic, are removed with the normal metabolic processes, if however their concentration reaches high values they can locally accumulate and give an acute or chronic pathologies .In case, instead, of toxic products, a persistent inflammation developed; the products of the degradation processes, can stay in the releasing zone, with only local effects, or they can spread in the vascolare system and have so effects also on organs and tissues far from the releasing zone. The progress of the medical research has allowed the perfectioning and the development of new biomaterial in the reconstructive surgery, that has aesthetic licence to obtain excellent results by no much invasive surgical techniques and immediate results. An ideal bio-material presents these characteristics: absence of toxicities, anti-allergic properties, bio-compatibility (**2)**, biofunctionality, easy to use and easy to remove. In our study the porous polyethylene and the bio bone have been analysed as substitutive of the hard tissues and the polyacrylamide and polialkylimide for the soft tissues **(3)**. The bony reintegration is a complex and multi-factory process studied end analyzes in the time (**4)**. At present several substitutive alternatives of the bone by autologus and eterologus bone, biomaterial are possible. Since the past what better choice was considered the allograft bone (**5-6)** which was useful for replacement of big bony deficits even if with difficult 11 vascularization (16-50% of fractures)(**7)**. The bone-conductive, mechanical and

Facial Remodelling and Biomaterial 455

of the facial soft tissue: in order to choise the biomaterial as much as more suitable and-bio compatible with the host organism. To a careful evaluation of every single case, the results have not been completely uniforms; in the patients treated with polialkylimide, adverse reactions have happened: in two cases has verified a multi-capsule formations around the biomaterial , with relative capsule formation and an only case the rejection, with adverse cutaneous reaction. In particular the case of rejection has verified in subject with Hemi-facial atrophy. The phenomenon of compartimentalizzazione was verified in only two cases, it was not due to the absence of integration of the biomaterial with the organism but it was consequent to the 13 autoimmune pathology. For the subjects treated with polyacrilyamide adverse reactions have not happened; the material has shown a good integration in patients with various pathologies . This biomaterial turns out to be of easier utilization and provided with greater fluidity injection. For what concerns the patients affected with infectious pathologies like HIV, their treatment with filling biomaterial has given both recent and after 3 year distance good results; rejection events have not happened. Such patients are constantly evaluated by the infective point of view; we have experiences of biomaterial's utilization in HIV+ patients with HAART treatment which present lipodystrophy lesions . The malleability and easy application of the hydrogel, an utilization of theirs has made possible in combination to other biomateriali. The use of different biomaterials in the same patient is necessary when the deficit to fill was high and when the simple application of an only one biomaterial was turning out insufficient. The treated cases have given good results and good tolerance between the installed material. Porous polyethylene, bio-bone, Polyalkylimide, Polyacrylamide offer a good alternative in selected cases to the traditional reconstructive surgery, for the immediate results and easy way of application. A follow up of at last six years through echography and Computed Tomography exams shows their biocompatibility, stability and inactivity, The restoring of symmetry and harmony of a face can be reached through both traditional surgery and also using biomaterials, that can substitute tissues graft or osteotomy with an easy way of application, their stability and their long

Bulbulian AH. Maxillofacial prosthetics: evolution and practical application in patient

Fini Hatzikiriakos G. Uno sguardo al passato, curiosita` sulle protesi nasali. Il Valsala

Tjellstrom A. Osteointegrated implants for replacement of absent or defective ears. Clin

Tjellstrom A, Granstrom G. One stage procedure to establish osteointegration: a zero to five

Schaaf NG. Maxillofacial prosthetics and the head and neck cancer patients. Cancer

Labbe´ D, Be´nateau H, Compe`re JF, et al. Implants extra-oraux: indications et contre-

Be´nateau H, Crasson F, Labbe´ D, et al. Implants extra-oraux et irradiation: tendances

Granstrom G, Jacobsson M, Tjellstrom A. Titanium implants in irradiated tissue: benefits from hyperbaric oxygenation. Int J Oral Maxillofac Implants 1992;7:15Y25

rehabilitation. J Prosthet Dent 1965; 15:554Y569

years follow-up report. J Laryngol Otol 1995;109:593Y598

indications. Rev Stomatol Chir Maxillofac 2001;102:239Y242

actuelles. Rev Stomatol Chir Maxillofac 2001;102:266Y269

lasting, not last a good esthetic result.14

Plast Surg 1990;17:355Y366

1985;61:61Y64

1984;54:2682Y2690

**6. References** 

immunological properties were good but correlated to the seat of the withdrawal and to the type of bone processing (**5-7-8-9)**. The Demineralized Bone Matrix can be easily extracted with 0.5 or 0.6 NHCL (**10-11)** 

from the allograft bone so as to obtain an increase in the bone-inductive capacities, the loss of the immunological power and an increase in his supplementary effectiveness (**12)**. One of the limits of the Demineralized Bone Matrix is his malleable consistency which makes him suitable for the bony filling most than to the bony replacement, above all in districts of the face that is not subject to the traction of the soft tissues (**13)**. Everybody notice the porous polyethylene, used for the reconstruction of the hard tissues of the face; This material presents bio-compatibility with the human organism and easy malleability (**14)**. This includes that the surgical time are considerably reduced and the surgical procedure are not much invasive. One of the advantages of this material is his property to restore big bony deficits, contributing to give volume to the absent structures . It is fixed by screws, which contribute to the maintenance of a fixes position in the time, as it is also taken back in literature (**15).** His utilization can be corollary of the orthognathic surgery in the restoration of the facial harmony or in the treatment of facial asymmetries from pathologies.Sharpen for this big variety of applications the porous polyethylene exists in various forms concerning the various facial places to restore: orbital margin (**15),** nasal dorsum, mandibular ramus. The injectable filler are very commonly used for the treatment of soft alterations of the tissues of the face; these can be of different nature and composition. Are commonly divided in temporary and permanent; in our work take the permanent filler into consideration like the plyacrylamide and polialkylimide. These are also defined of the "hidrogel", for the high water content; their use has prevalently aimed at the filling of soft tissues, whit satisfactory results. Their principal properties are: elasticity, permeability and high bio-compatibility with the organism. Of these we remember the polialkylimide, injective bio-material formed by 2.5% of synthetic polymer of polyalkylimide and for 97.5% from apirogen water. Studies have been also executed in 12 vitro and they have shown a low toxicity and cutaneous sensibilization, following prolonged treatment. The polyacrilyamide (**16- 17)** is an injectable bio- material, formed by 3% of reticulate polymer of polyacrylamide and 97% from not pirogenic water. It is an hydrophilus absorbent gel, what comes infiltrated in deficit of the soft tissue. His mechanism of action is to add volume to the soft tissues, restoring the normal structures of the face. This bio material has an easy applicability also in different pathologies; important is not to use in post herpetic phase. It needs several applications for the partial absorption which can verify.
