SURFACE ENERGETIC CHARACTERISTICS OF ACRYLIC BIOMATERIALS

Transcription

1 Biomaterials SURFACE ENERGETIC CHARACTERISTICS OF ACRYLIC BIOMATERIALS Mihaela-P\pu[a Vasiliu (Diaconu) 1, Daniela Ivona Tomi]a 2, Delia Spridon 3, Nicoleta Dumitra[cu 4, G. Costin 5, Carmen Stadoleanu 6 1. PhD Student, Gr. T. Popa UMF Ia[i, Univ. Assistant, Faculty of Medical Dentistry, Apollonia University Ia[i 2. Lecturer, PhD., Faculty of Medical Dentistry, Apollonia University Ia[i 3. PhD Student, Faculty of Physics, Al. I. Cuza University Iasi 4. Prof. PhD., Faculty of Physics, Al. I. Cuza University Iasi 5. Prof. PhD., Faculty of Medical Dentistry, Apollonia University Ia[i 6. Prof. PhD., Faculty of Medical Dentistry, Apollonia University Ia[i Corresponding author: Mihaela Papusa Vasiliu mihapapy@yahoo.com Abstract Introduction: Surface energetic characteristics of biomaterials influence their adherence to cells and bacteria, surface adsobtion of plasmatic proteins, as well as the capacity of such surfaces of immobilizing some biological species extremely important in medicine. Materials and method: Acrylic surfaces with an area of approximately 2 cm 2 were employed for the experiments: Duracryl Plus (Spofa/Dental Product, Czechia), Duracryl Plus covered with Palaseal (Heraeus Kulzer GmbH, Wehrheim, Germany); artificial saliva AFNOR S (ph 8.01) was used as a working solution. Results and discussion: Drops of distilled water and artificial saliva, deposited on the working materials: Duracryl and Duracryl covered with Palaseal, were photographed with an optical device, after which each drop was computer-processed, and the contact angle for each liquid surface on the surfaces of the biomaterials here under investigation was determined. On the basis of the determinations made for each material in part, the arihtmetic mean was established. Conclusions: The wettability of dental materials is wholly characterized by the values of the contact angle between the drop of biological liquid and the surface. Low values of the contact angles indicate a good wettability. The results obtained support the conclusion that the surface energy of the solid and rugosity are essential for controlling the adhesive properties of saliva unto dental materials. Keywords: dental acryclic biomaterials, energetic characteristics, saliva, protection lacquers INTRODUCTION As generally known, the surface energetic characteristics of biomaterials influence their adherence to cells and bacteria, surface adsobtion of plasmatic proteins, as well as the capacity of such surfaces of immobilizing some biological species extremely important in medicine. The processes occurring at the dental material biological fluids (oral medium) interface result in diseases generated by the materials utilized in stomatology, and their erroneous application. Both the natural and artificial materials present in the oral cavity, occurring in temporary or permanent contact with various substances are tested under various conditions. Both the teeth and the dental materials are subjected to large temperature ranges, starting from 0 C up to more than 50 C. Also, the ph values, varying between 0.5 and 8, may influence the behaviour of the dental materials in the oral cavity [1]. Each dental material has its own characteristics and manageability capacities, which recommend it for various applications. The stress caused by the masticatory forces and the abrasive nature of saliva determine the characteristics of such materials. That is why, the materials employed in stomatology should possess some proprieties, capable of reducing as much as possible their secondary effects and of prolonguing, again as much as possible, their life time.the mechanical requirements of the dental materials refer to their resistance to various types of forces and stresses, to surface hardness, to abrasion and compression forces [2-4]. Biocompatibility is required for all materials employed in stomatology. Their physical properties include a low thermal conductivity and the capacity of assuring a perfect joint between the restoration material and the tooth. In time, all such properties should be stable in the oral medium, without inducing negative effects upon the neighbouring tissues, while satisfying the aesthetic requirements [5]. 242 volume 15 issue 3 July / September 2011

2 SURFACE ENERGETIC CHARACTERISTICS OF ACRYLIC BIOMATERIALS MATERIALS AND METHOD Acrylic surfaces with an area of approximately 2 cm 2 : Duracryl Plus (Spofa/Dental Product, Czechia), Duracryl Plus covered with Palaseal (Heraeus Kulzer GmbH, Wehrheim, Germany) were employed in the experiments. Duracryl is a self-polymerizable acrylic resin occurring as a bicomponent system: polymer and monomer. The polymer is a methyl polymethacrylate, in the form of low powder particles, while the monomer is methyl methacrylate, a volatile, bactericide liquid with aromatic fragrance. The monomer is not chemically stable so that, under the influence of light and heat, it tends to polymerize spontaneously, which restricts its utilization exclusively to transitory and urgent prosthesis systems. It has a low water absorbtion, low solubility, excellent colour stability, it may be easily prepared, finished and polished, and its manageability time is appropiate. Palaseal, a protection lacqueur for prostheses, crowns and temporary dental bridges (made of polymethacrylate), evidences high abrasion strength and resistance to the solvents from the bacterial plaque. After the final acrylate polymerizayion of Duracryl, Palaseal was applied with a brush, allowed to act for 20 sec, after which it was introduced in the photo-polymerization oven for 90 sec. The AFNOR S artificial saliva employed as a working solution was prepared with compounds of analytical purity, its ph=8.01, being measured on a ph 5/6 OAKTON ph-meter. The whole operation was performed in the Dept. of Biochemistry, at the Gr. T. Popa UMF of Ia[i (table I). Table I: Chemical composition of artificial saliva (AFNOR S90-701) Substance Chemical formula Concentration (g/l) Natrium chloride NaCl 0,7 Potassium chloride KCl 1,2 Disodic phosphate Na2HPO4 0,26 hydrogen Natrium bicarbonate NaHCO3 1,5 Potassium thocianate KSCN 0,33 Urea 1,35 The substances listed in table I were weighed, mixed and dissolved în 1000 ml of distilled water. The main parameters characterizing the surface properties of the materials surface energy, the polar and dispersive components, surface rugosity, as the mechanical work of adhesion - may be calculated by means of some physical models, starting from measurements of the contact angles between various liquids and the material under investigation. One of the important properties of a liquid (in this case, saliva), manifested in the interaction with a solid material (dental material) is the ability of freely wetting the surface of the object under analysis. If the liquid molecules show a more intense attraction towards the solid molecules than towards themselves (meaning that the adhesion forces are higher than the cohesion ones), surface wetting occurs on the liquid-solid interface surface. Alternatively, if the liquid molecules show a stronger attraction towards themselves and not towards the solid molecules (i.e., the cohesion forces are higher than the adhesion ones), the liquid forms drops, without wetting the surface. Experimental determination of the contact angle was made by an adequate optical method, and the drop images were processed with the ImageJ program. Drops of liquid (water and saliva) with an 1 µl volume were employed, the value representing the mean of 10 drops. Surface morphology and rugosity were analyzed by atomic force microscopy (AFM), while qualitative information on the chemical uniformity of the surfaces was obtained from phase AFM images. RESULTS AND DISCUSSION Selection of distilled water as a reference sample for the estimation of the contact angle for the materials under study is based on the fact that water represents 70% of the human organism and 99.4% of saliva. One of the essential roles played by saliva is its ability to moisten the mucous membrane and the dental structures, a characteristic checked out by measurement of the contact angle. International Journal of Medical Dentistry 243

3 Mihaela-P\pu[a Vasiliu (Diaconu), Daniela Ivona Tomi]a, Delia Spridon, Nicoleta Dumitra[cu, G. Costin, Carmen Stadoleanu The drops of distilled water and artificial saliva, deposited on the working materials: Duracryl (figs.1,2) and Duracryl covered with Palaseal (figs. 3, 4), were photographed with an optical device. Each drop was photographed and computerprocessed, after which the contact angle for each liquid surface on the surfaces of the biomaterials here under investigation was determined. Fig. 4. Aspect of artificial saliva drops on Duracryl with Palasial Following the determinations performed for each material in part, their arihtmetic mean was calculated, the obtained values being listed in table II, while the graphical representation of the contact angles is given in figure 5. Fig. 1. Aspect of distilled water drops on Duracryl Table II: Arithmetic mean resulting from measurements of the contact angle on acrylic surfaces Contact angle on acrylic surfaces Measured values saliva Arihtmetic mean Fig. 2. Aspect of artificial saliva drops on Duracryl Measured values water Arihtmetic mean Fig. 3. Aspect of distilled water drops on Duracryl with Palasial 244 Duracryl Acrylate Duracryl+Palaseal The wetting degree of a liquid on some surface may be measured by the contact angle between the liquid drop and the solid surface. Maintainance of the liquid on the surface in an almost spherical shape gives a higher value of the contact angle and a low moistening capacity. When the contact angle is low, the surface of the solid is covered by the liquid, wettability in- volume 15 issue 3 July / September 2011

4 SURFACE ENERGETIC CHARACTERISTICS OF ACRYLIC BIOMATERIALS creases and adhesion occurs. Table II shows that the highest value of the arithmetic mean is registered for the contact angle of distilled water on the Duracryl surface 72.97, whereas the lowest one for the Duracryl covered with Palaseal, which means a low adherence of saliva to this surface. b) Fig. 6. AFM image of Duracryl-type acrylate: a) Topography 3D morphology Duracryl (30µm x 30 µm); b) Phase imagine of the Duracryl sample Fig. 5. Graphical representation of the contact angle at acrylic surfaces with artificial saliva and distilled water a) Surface morphology and chemical composition influence the adhesion and wettability properties of the surface. In this respect, a comparative study of these dental materials was developed, on the basis of AFM images (figs. 6.a, 7.a), while the values of surface rugosity (Rrms) are listed in table III. Table III: Rugosity of acrylic surfaces Sample Duracryl Duracryl+Palaseal Rrms (nm) a) b) Fig. 7. AFM image of the Duracryl-type acrylate covered with Palaseal: a) 3D topography morphology Duracryl covered with Palaseal (30µm x 30 µm); b) Phase image of the Duracryl sample covered with Palaseal The lowest rugosity is registered for Duracryl+Palaseal, which confirms the idea that International Journal of Medical Dentistry 245

5 Mihaela-P\pu[a Vasiliu (Diaconu), Daniela Ivona Tomi]a, Delia Spridon, Nicoleta Dumitra[cu, G. Costin, Carmen Stadoleanu this material is the most recommended one for dental applications. Worth mentioning is that a higher rugosity involves a higher absorbtion probability (as due to a larger specific surface) and stronger physico chemical interactions of the elements from the biological liquid (artificial saliva) with the surface of the material (as due to a higher number of physical-type, non-covalent links). Qualitative analysis of the phase image (figs. 6. b, 7. b) shows that all materials employed are chemically uniform. CONCLUSIONS One of the most important characteristics of saliva in the oral medium is its ability of wetting both teeth and the mucous membrane. Practically, the moistening capacity of the dental materials is exclusively characterized by the values of the contact angle between the drop of biological liquid and the surface. Low contact angles indicate a good wetting ability. Appropiate wetting of the surfaces appears when the surface tension of the liquid is lower than the surface energy of the solid. The energetical characteristics of the materials employed for fixed and mobile prostheses were analyzed, for the determination of the contact angle. Another important physical characteristic is the surface rugosity of the dental biomaterials (R rms ), providing some correlations between the value of the mechanical work of adhesion and the adsorbtion of molecules of biological liquid. The rugosity of such surfaces was analyzed on an atomic force microscope. A higher rugosity of the classically-polished Duracryl was registered, which was nevertheless 3.6 lower after the application of a Palaseal layer, which improved the physical properties, and reduced the adherence of the oral microorganisms to the material surface. The obtained results support the conclusion that the surface energy of the solid and rugosity are essential for controlling the adhesive properties of saliva onto dental materials. References 1. Erik Asmussen, Anne Peutzfeldt and Alireza Sahafi, Finite element analysis of stresses in endodontically treated, dowel-restored teeth, The Journal of Prosthetic Dentistry, , October K. Pflug, C. Weber, Dental materials having a nanoscale filler, Smart Materials Bulletin, Volume 2002, Page 13, 1 Iulie Edward C. Combe, Brandon A. Owen, James S. Hodges, A protocol for determining the surface free energy of dental materials, Dental Materials 20, , Linda Wang, Paulo Henrique Perlatti D Alpino, Lawrence Gonzaga Lopes, José Carlos Pereira Mechanical properties of dental restorative materials: relative contribution of laboratory tests, J Appl Oral Sci; 11(3): , Dumitra[cu Nicoleta, Biomateriale [i Biocompatibilitate, Ed. Univ. Al. I. Cuza Ia[i, 28-87, volume 15 issue 3 July / September 2011