**3. Ultrasonography monitor follow-up**

The ideal biomaterial should be easy to implant and to remove, and simple to be identified by a low-dose radiation and low-cost radiologic technique. Authors wanted to evaluate ultrasonography (US) as a technique in monitoring biomaterial status after operation. Ultrasonography has been shown as an excellent way to visualize clinical features and a possible pathologic process of an implanted biomaterial; it is a non-invasive, low-radiation and low-cost dose radiologic technique. Reconstruction in facial deficit diseases needs adequate biomaterial to implant and a careful patients observation, that is, both clinical and radiologic. Ultrasonography is a fundamental component of the follow up of implanted biomaterial patients. the use of synthetic materials instead of an autolog tissue is codified from years and is widely diffused. In the last years, maxillofacial surgery has adopted poliacrilamide for the soft tissue, which is already used in esthetic surgery such as ''last generation filler'' to overwhelm the defects of the time such as wrinkles and furrows. Such material has replaced paraffin and silicone fluid used in the 1960s, and collagen and analogs used in the 1980s.In the same years, Conley and Baker experienced some slow-resorption synthetic materials that, when inserted in the derma, overwhelmed cutaneous imperfections. The biomaterials used until that moment were all very well tolerated, but they introduced the disadvantage of being ''statics'' materials, concrete, and above all, temporary. In the last few years, poliacrilamide has replaced, in part, the use of these

Facial Remodelling and Biomaterial 453

features and the pathologic process of implanted biomaterials. It represents a low-cost and low-radiation dose technique for a careful follow-up of patients affected by facial deficit disease after biomaterial implantation. The US technique shows a high radiologic sensibility in evaluating the features of the biomaterials. For its use, the limited cost and lack of

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

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

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

investigation on harmful US is the key for studying of the biomaterials. (18)

**4. Discussion** 

tissue .

bio-availability therefore bio-compatibility (**1)**.

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 biomaterials.

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 ultrasound control.

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

features and the pathologic process of implanted biomaterials. It represents a low-cost and low-radiation dose technique for a careful follow-up of patients affected by facial deficit disease after biomaterial implantation. The US technique shows a high radiologic sensibility in evaluating the features of the biomaterials. For its use, the limited cost and lack of investigation on harmful US is the key for studying of the biomaterials. (18)
