WO2016101082A1

WO2016101082A1 - Masterbatch composition that can be used in the production of dental prostheses and production method thereof

Info

Publication number: WO2016101082A1
Application number: PCT/CL2015/000068
Authority: WO
Inventors: Manuel Francisco MELÉNDREZ CASTRO; Paulo Andrés FLORES VEGA; Carlos Andrés MEDINA MUÑOZ; Eduardo Gerardo PÉREZ TIJERINA; Verónica Antonieta TORRES QUEZADA
Original assignee: Universidad de Concepción
Priority date: 2014-12-24
Filing date: 2015-12-24
Publication date: 2016-06-30
Also published as: CL2014003518A1

Abstract

The invention relates to a masterbatch composition that can be used in the production of dental prostheses, comprising: a nanoscale filler formed by between 0.05 - 0.20 wt.-% silver nanowires, between 0.05 - 0.20 wt.-% copper nanowires, and between 0.08 - 2.00 wt.-% zinc oxide nanowires; and liquid components comprising between 45 - 65 ppm methyl methacrylate monomer with an inhibitor, between 0.3 - 1.0 wt.-% ethylene glycol dimethacrylate-type crosslinking agent, and traces of a N,N dimethyl-p-toluidine-type activator. The invention also relates to the production method thereof.

Description

A COMPOSITION OF A USEFUL MASTERBATCH IN THE DEVELOPMENT OF DENTAL PROSTHESIS AND ITS PROCESSING PROCESS

Technical Sector

The technology is oriented to the chemical area, more specifically, it corresponds to a composition of a masterbatch useful in the elaboration of dental prostheses.

Prior art

The dentures are intended to replace the lost organs of the natural dentition, as well as the structures associated with the maxilla and the jaw with the aim of recovering the aesthetics and preserving the emotional health of the patient.

The material with which dental prostheses are currently manufactured is based on acrylic resins, mainly composed of a polymer called PMMA polymethylmethacrylate, whose monomer is MMA (methyl methacrylate). PMMA is a thermoplastic that can be of the linear type or with few ramifications. Acrylic resin is nothing more than a mixture of monomer (MMA), an initiator and a previously polymerized PMMA polymer. In addition, dyes in the form of threads are added to simulate blood vessels and give good appearance to the material when used for the manufacture of permanent dentures.

For the development of total prostheses, the physicochemical properties of PMMA play a fundamental role, mainly surface roughness, flexural strength, porosity and solubility. Since, being different properties from each other, they are closely related and contribute to microbial adhesion and retention on the surface of the prosthesis.

Acrylic resins have good mechanical properties and good chemical resistance which prevents corrosion of the prosthesis. However, one of the problems that present the most is the dimensional stability over time, property that certain materials have that when subjected to changes in temperature and humidity do not lose their shape and maintain their original dimensions. This causes the teeth of the prosthesis to be released or loosened and that the user has discomfort due to the deformation of the material.

Studies are constantly carried out on the modification of acrylic resins to improve the physicochemical properties, and decrease the adhesion of microorganisms present in the oral cavity such as Candida albicans. To overcome some limitations presented by the PMMA, reinforcement fibers have been incorporated into its composition, which increases its mechanical properties and thus prevents the propagation of fissures, since fracture of the denture bases is a recurring problem in the dental practice (Acosta et al, 2012). There are currently studies on the optimal components for making dental acrylic, focused on different

i compounds and in the elimination of microorganisms (Hanif et al., 2012; Jandt et al., 2009; Gómez et al, 2012).

On the other hand, many metals have been used for centuries as antimicrobial agents such as silver, copper, gold, titanium, zinc, which have attracted attention due to the different properties they can present for the application to which they are intended. With respect to nanoparticles, the antimicrobial properties of silver and copper have received the most attention, being used as a coating or incorporated in various materials, including PMMA. In addition, an inverse relationship between nanoparticle size and antimicrobial activity has been demonstrated. As a result of their small size, nanoparticles can offer other advantages for the biomedical field by improving biocompatibility. Even bacteria are less likely to acquire resistance against metal nanoparticles than other antibiotics.

As a way to reduce the adhesion of bacteria and fungi to oral materials and devices, silver nanoparticles are being evaluated to be incorporated into prosthetic materials and orthodontic adhesives. It has been shown that the amount of silver nanoparticles incorporated into the matrix of a polymer can influence the physical properties of these materials. However, Ahmad Sodagar et al., (2012), proposed to study the effects produced by silver nanoparticles (Ag-NPs) on the flexural strength of acrylic resins. Since nanoparticles have the possibility of imparting mechanical properties to some dental materials, they assumed that the addition of Ag-NPs to acrylic resins would affect their mechanical characteristics. Therefore, although the addition of Ag-NPs has an antimicrobial advantage, they were also disturbed by its effects on the flexural strength in the PMMA resin.

Zhihui Han, et al, 2014, studied the effect of Ag-NPs as a support material in an acrylic poly (methyl methacrylate) resin, which was reinforced with zirconium dioxide nanoparticles (2r02-NPs) and whiskers (nanobars ) aluminum borate (WsBA). It was found that Ag-NPs showed a synergistic effect when mixed with Zr02-NPs and WsBA; and where the latter could improve the flexural strength of composite materials compared to pure PMMA.

On the other hand, it is known that biofilm growth contributes to tooth decay and resin failure based on dental composite materials. Therefore, the oxide considered as antimicrobial agents has been used, including copper, zinc, titanium and tungsten (Allaker et al., 2014). Within this context, it has been tested in vitro with zinc oxide nanoparticles (ZnO-NPs) in biofilm culture test systems. Finding that these ZnO-NPs mixed in a variety of composite materials, have excellent properties to significantly inhibit the growth of Streptococcus sobrinus biofilms in concentrations of not less than 10% (w / w) in a three-day trial period. However, at this concentration, the impact of the structural characteristics of composite materials is pending. (Allaker, 2010). ZnO-NPs have also been tested on the mechanisms of antibacterial activity, which include the generation of reactive oxygen species and damage to the cell membrane, with the consequent interaction of nanoparticles with intracellular content, (Allaker et al. , 2014).

Other studies have been carried out with the purpose of reinforcing PMMA resin for prosthetic bases with zirconium dioxide nanotubes (ZrO2-NTs), (WeiYu, et al, 2014). Determining that these nanotubes have a better reinforcing effect than the ZrO2 nanoparticles. This oxide possesses a variety of advantageous properties such as excellent toughness and mechanical strength, resistance to abrasion and physical corrosion, and biocompatibility. It has been applied in clinical materials, especially for artificial denture and bone repair. However, there is still no study focused as a reinforcement of PMMA for prosthetic base.

Another emphasis has been to use different types of fiber (glass, polyethylene) as a reinforcement material for PMMA resins (Viswambaran et al., 2011), since they would allow an increase in mechanical properties (Acosta et al., 2012). An example of the above is the result obtained by T. Kanie et al. (1999), where the effect produced by the reinforcement with woven glass fibers on the mechanical properties of the acrylic resin was determined. In their investigation it was shown that for samples containing silanized glass fibers, the flexural strength and impact resistance were superior to those of samples without fiberglass (Kanie et al., 2000). In the same way, Paul Franklin et al., (2004) worked in similar conditions but with fiberglass scales obtaining results similar to those mentioned in the work of T. Kanie. Based on this background, there is still a need to find materials that ensure the quality and durability of dental prostheses, in addition to preventing the adherence of microorganisms in the oral cavity. Disclosure of the Invention

The present technology corresponds to a composition of a masterbatch (concentrate) of thermo-curable and self-curable composite acrylic resins that include within the polymer matrix nanowires of silver (Ag-NWs), copper (Cu-NWs) and oxide of zinc (ZnO-NWs), to increase the useful life of a final forming due to a better control in its dimensional stability. The nanowires reinforce the polymer matrix and provide antimicrobial, antifungal and photocatalytic properties to the final conformation. The applications of this masterbatch range from the manufacture of permanent dentures to implants for medical use, in addition to the manufacture of special and resistant parts also for medical use.

These three nanomaterials will present an improved interface with the resin allowing a reinforcement of the resin, and consequently, substantially benefiting its mechanical properties. Especially, it improves the creep over time of the material avoiding deformations, which can be obtained a dimensionally stable prosthesis. In addition, they allow to obtain antimicrobial prostheses that control the bacterial flora that is housed in the spaces that are in contact between the gums and the prosthesis, avoiding the bad smell and also the bacterial plaque.

The metal nanowires correspond to a single crystal that has a preferential growth direction, and in particular, the Cu and Ag nanowires have shape memory (Mem-F) effect and pseudo-elastic behavior in single crystals with FCC structure (Cubic face centered). Mem-F is a behavior that is associated with a reversible network reorientation process of the crystalline structure and is driven by surface tension and the high reorientation process of the FCC crystalline structure and the large surface volume ratio of the nanowires The existence of this behavior depends on the twinnability of the material, size of the nanowires and the temperature. Mem-F and pseudo-elastic behavior are clearly a phenomenon that has not been observed in the bulk state of metals (Cu and Ag), and indicates that nanowires can be used as nano and microstructural materials with self- healed

Shape memory nanowires constitute an improvement over alloys with SMA shape memory in multiple aspects, including the ability to maintain greater traction, for example, tensions of the order of gigapascals (GPa), experiencing reversible stresses that may exceed 40% compared to 10% for bulk SMAs. Another advantage of this type of materials is that it is simple to synthesize unique crystals.

On the other hand, by incorporating the nanowires into self-healing and thermosetting resins, the properties of the nano scale are transmitted to the polymer matrix, with which multifunctional nanocomposites are manufactured. The above, allows the load to reinforce the matrix, incorporate the antimicrobial, photocatalytic properties, dimensional stability due to the effects of nano-wire shape memory, longer life time of final forming, resistance to thermal changes and prevents the propagation of fissures

Specifically, the composition of the acrylic resin masterbatch comprises at least the following components:

to. Nanometric Load:

• Silver nanowires (Ag-NWs) with diameters between 20 - 150 nm, shorter lengths between 1 - 30 μηι and load ratio between 0.05 - 0.20% (w / w);

• Copper nanowires (Cu-NWs) with diameters between 20 - 150 nm, shorter lengths between 1 - 30 μιη and load ratio between 0.05 - 0.20% (w / w); Y

· Zinc oxide nanowires (ZnO-NWs) with diameters less than 100 nm, lengths between 1 - 30 μιτι and load ratio between 0.08 - 2.00% (w / w).

b. Liquid Components:

• Methyl methacrylate monomer with inhibitor of the preferred type: hydroquinone, nitrobenzene (NB), butylhydroxytoluene (BHT), 2,2-diphenyl- 1-picrylhydrazyl (DPPH), dinitro-ortho-cresol (DNOC), dinitro-sec-butylphenol (DNBP) and dinitrophenols (DNOP), at a concentration between 45-65 ppm; Y

• Crosslinker of the preferred type EDMA (Ethylene Glycolmethacrylate) between 0.3 -2.0% w / v.

• Activator of type N, N dimethyl-p-toluidine in traces.

Where ZnO acts as a passivator of color due to its white color, for that reason the final dispersion obtained is slightly white. Using high proportions of Cu-NWs and Ag-NWs in the process is counterproductive, because each of these wires has a particular color (gray for Ag-NWs and reddish for Cu-NWs). Therefore, with permanent dentures being a direct application of the masterbatch, it must retain a good aesthetic appearance, which must be preserved when using the masterbatch for the preparation of the composite acrylic resin with which the prosthesis will be prepared.

The masterbatch is made with the liquid components of the composite acrylic resin and the nanometric charge, in a controlled atmosphere to avoid early polymerization. Silver and copper wires are obtained by hydrothermal synthesis and zinc oxide nanowires are obtained by microwave-assisted thermal decomposition. All the nanowires used as a charge have proven antimicrobial properties, in addition ZnO-NWs are photocatalytic so they can prevent fungal growth. In Figures 1, 2 and 3 it is possible to see an image of the silver, copper and zinc oxide nanowires, respectively.

The masterbatch process includes at least the following stages:

to. addition of liquid components of the resin: in a dry chamber, under nitrogen atmosphere, the MMA monomer and the inhibitor are added, to prevent the monomer from polymerizing in the mixing process;

b. washing of the nanometric charges: the loads of Cu-NWs and Ag-NWs must be repeatedly washed with analytical grade ethanol to eliminate synthetic waste and growth precursor molecules preferably polyvinylpyrrolidone (PVP). The above is due to the fact that the nanowires obtained by the hydrothermal method, unlike the microwave-assisted thermal decomposition method, produce residues that stick to the surface of the nanowires. Where the determination of the concentration of the dispersions is performed by atomic absorption for both Cu-NWs and Ag-NWs. On the contrary, ZnO-NWs do not need to be washed since a physical method is used in their synthesis, which does not require preferential growth precursors;

C. feeding of nanowires in the dry chamber: purified silver and copper nanowires should be dispersed in the MMA monomer; then ZnO-NWs must be weighed and dispersed in the solution. The addition is in this order because the ZnO is white in color, so it allows the resin color to be adjusted with the addition of the ZnO nanowires; Y d. crosslinking addition! -: the solution containing all the nanometric charges must be stirred for 15-25 min, during which time the crosslinker is added and finally the activator, then the solution is closed until it is used under a nitrogen atmosphere to avoid possible initiation or retardation of the mixture due to oxygen.

Finally, this masterbatch can be mixed to obtain dental prostheses with a solid component of the Polymethylmethacrylate (PMMA) type having an alkyl group with 1 to 20 carbon atoms, n-butyl polymethacrylate, acrylic copolymer, Poly (cyclohexyl methacrylate), poly (glycidyl methacrylate), poly (hydroxyalkyl methylmethacrylate), resins derived from acrylic acid and methacrylic acid.

The incorporation of nanometric loads (Ag-NWs, Cu-NWs and ZnO-NWs) to thermo-curable acrylic resins allows to improve aspects of the final forming when used in the manufacture of permanent dentures. Being 1 D nanostructures reinforce the matrix avoiding the propagation of cracks, improve the dimensional stability of the matrix in the final forming, avoid excessive formation of porosities and the deterioration of the resin. The materials used are biocompatible, so they do not pose a risk to people's health and are chemically stable. Compared to conventional resin without charge, the composite acrylic resin has better thermal diffusivity, conductive, antimicrobial and dimensional stability properties as it is reinforced by nanowires. In relation to the mechanical properties these do not vary significantly compared to the conventional acrylic resin, which is good, since in general the nanocomposites based on nanostructures within a polymeric matrix decrease the mechanical properties of the matrix. The curing process is similar to the conventional one, with minimal differences in the mixing of the solid component with the masterbatch with the nanowires. The PMMA / NWs nanocomposites also have antifungal properties, which benefits the development of dentures. In Figure 4 it is possible to see a fixed dental prosthesis and (b) a removable prosthesis made with composite acrylic resin based on PMMA and the MMA Masterbatch with Cu, Ag and ZnO nanowires. Application examples

Example 1. Procedure for the elaboration of nanocomposites with nanowires of copper, silver and zinc oxides.

For the trial process with the masterbatch from a monomer and nanometric loads, molds and sized cells were made to replicate the conventional procedure followed in dental laboratories until the formation of a permanent prosthesis. First, specimens were made with the composite acrylic resins made with the liquid component that is the concentrate or masterbatch that contained the MMA and the three different types of nanowires. The masterbatch preparation process comprised the following stages: a. addition of liquid components of the resin: in a dry chamber under nitrogen atmosphere 60 ppm of MMA monomer and 50 ppm of hydroquinone were added;

b. washing of the nanometric charges: the Cu-NWs and Ag-NWs loads were washed 5 times to eliminate synthetic wastes and polyvinylpyrrolidone precursor growth molecules (PVP);

C. feeding of nanowires in the dry chamber: the purified nanowires of silver (0.1 w / w) and copper (0.1 w / w) were dispersed in the MMA monomer; and then 1.0 w / w ZnO-NWs were dispersed in the solution .; Y

d. cross-linking the solution containing all the nanometric charges was stirred for 20 min, during which time 2% w / v of the EDMA crosslinker was added, then the solution was closed under nitrogen atmosphere to avoid possible initiation or retardation of the mixture due to oxygen.

Example 2. Preparation of the composite acrylic resin to make permanent dentures.

For the elaboration of the nanocomposites (acrylic resin with nanostructures) it was necessary to design a stainless steel acrylization mold (MACRIL), in which a plaster base and a wax mold with the dimensions of 10 x 1, 3 x were placed 0.3 cm This wax mold was placed in the middle of the MACRIL and underwent heating (60 - 80 ° C) so that a mask remained on both sides of the plaster. Then, the wax residues were removed and the mask that remained on both the top and bottom of the MACRIL was adjusted. At the end of this stage, the mold was ready for the acrylization process, which was composed of 4 stages: preparation, pressing, polymerization and demolition.

i) Preparation: the nanobatch loading masterbatch was previously stirred for 5 minutes using a magnetic stirrer. During the whole process of mixing with the PMMA (which had 0.5% Fe2Ü3 pigments), the sample had to be agitated and homogenized to provide a good dispersion of the load, for which a glass rod and agitation were used vigorous manual. The mixing ratios of the masterbatch and acrylic resin were those conventionally used, that is, 1/3 of masterbatch per 2/3 of resin. Upon reaching the plastic phase of the process, when the material was detached from the walls of the container approximately 20 minutes after mixing, the material was ready for the pressing and subsequent polymerization process. To do this, the mixture was separated from the mixture of the plaster that filled the MACRIL with a film of HDPE (High Density Polyethylene) and covered until the curing process was finished, the working temperature was 20 ° C. ii) Pressing: MACRIL was placed in a special press with its dimensions and a pressure of 1500 kg / cm ² was exerted for 2 minutes.

iii) Polymerization (acrylic): for this stage a digital vibrating screen of 53 liters capacity was conditioned, which was filled with water halfway. Stirring prevented the formation of temperature gradients within the system. The MACRIL was placed in the middle of the vibrating screen and the temperature was increased at a rate of 5 ° C / min to 90 ° C to avoid excessive porosity formation. Most of the MACRIL was filled with plaster to facilitate a proper resin curing process. The acrylization time (curing) was 60 minutes at 90 ° C, then the system was brought to 100 ° C for an additional 60 minutes. After this time, the system was removed and cooled to room temperature (20 ° C).

iv) Demuflado: the cured piece was carefully removed from the MACRIL so as not to damage it, since it could be glued to the plaster.

The procedure described above is the same one used for shaping permanent dentures (PDP). This process was selected to facilitate the study of the thermo-mechanical properties of the material, since each analysis requires different types of specimens. Volumetric, antimicrobial, mechanical and photoacoustic resistivity studies were conducted to determine the thermal diffusivity of the resin, always comparing with a standard that was the conventional resin without nano-wire loading. In addition, water absorption and verification of the residual monomer was determined. All procedures performed until obtaining the reinforced acrylic nanocomposite, followed the requirements and conditions required by ISO 1567 and standard No. 12 of the American Dental Association, which specify the tests to be performed on resins for denture bases .

A. Antimicrobial Activity of Nanoalambres de Cu, Ag and ZnO

Antimicrobial assays were carried out by the hydrothermal method and the method of decomposition assisted by microwaves to the nanowires separately, to verify if these materials had antimicrobial activity. The results of the antimicrobial susceptibility assays by agar diffusion against the Escherichia Coli and Staphylococcus Aureus strains showed positive results (see Table 1).

Table 1. Nano-wire antimicrobial activity

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It was determined that the activity of the metal nanowires was lower compared to that of ZnO-NW. This was due to the fact that in the method used in the synthesis no type of growth precursor molecule of preference was employed. The differences found between the Cu-NWs and Ag-NWs, are due to the fact that the interaction of the Ag-NWs with the PVP molecules is much stronger, making it difficult to remove it. With this test it was shown that the three nanomaterials used in the preparation of the composite acrylic resin have antimicrobial activity.

B. Results and Analysis of Acrylic Nanocomposites prepared using the Masterbatch and PMMA resin.

B.1. Water absorption.

These tests were carried out because the curing process that was selected was by immersing the stainless steel mold in the thermostatic bath, so that water filtration may exist, which would affect the curing, and therefore, the mechanical properties of the test tubes These tests were based on ASTM D570, for which samples taken in two dental laboratories and one prepared as blank were taken as standard.

Table 2 shows the result of the FTIR spectrum, where M1 corresponds to the dental laboratory sample, M2 standard resin without elaborated nanowires, M3 and M4 corresponds to the PMMA / NWs nanocomposites made with the masterbatch (performed in duplicate) . From the analysis of the FTIR spectrum it can be seen that there is no significant difference in any of the samples tested. This could also be verified by the consistency and appearance of the samples, which were very similar to the samples made in dental laboratories. The possible oxidation of the Ag-NWs and Cu-NWs due to the humidity of the plaster and the water that was filtered was avoided by the HDPE film.

Table No. 2. FTIR analysis of PMMA / NWs based nanocomposites compared to unfilled resins.

On the other hand, the FTIR spectrum of the thermosetting MMA monomer (Marche brand) was compared with each of the FTIR spectra of the prepared PMMA / NWs nanocomposites prepared with the masterbatch, where no fingerprints corresponding to residual monomer were found. Similarly to each of the liquid samples where the water absorption tests were performed, they were concentrated in a rotary evaporator and FTIR was performed, resulting negative for residual monomer. Therefore, it was concluded that in the curing process and the proportions used of PMMA and masterbatch are optimal for the curing reaction.

B.2. Photoacoustic spectroscopy.

With this analysis the thermal diffusivity of the material is determined, corresponding to the rate of change with which a material increases in temperature, when it is brought into contact with the heat source. Therefore, the product of the value of its density and the heat capacity of it is determined through the thermal conductivity of the divided material. Thermal diffusivity is a parameter to determine the ability of the material to blur the temperature.

The results are presented in Table 2, where the cured resins of the dental laboratory (M1) were compared. An increase in the thermal diffusivity was found in the PMMA / NWs nanocomposites prepared with the masterbatch, this was due to the fact that the three nanowires are good conductors of heat which allowed an easy transfer of heat in the sample volume, achieving balance with the environment more quickly. This benefits the durability of the prosthesis and better dimensional stability.

Table 3. Determination of thermal diffusivity of cured resins and

prepared nanocomposites based on nanowires.

B.3. Volumetric Resistance (p _v ).

The volumetric resistivity is an intrinsic property of each material, it is defined as the opposition to the passage of current inside a material, for this a Mega Ohm meter Model 1550B FLUKE was used. The results are presented in Table 3, where it is possible to observe that the material reinforced with nanowires is still an insulator, because the volumetric resistance was high. However, the trend shows that as the metal nanowires were added to the thermostable matrix there was a decrease in this. Otherwise it happens when ZnO-NWs are added, because the electrical properties of the material were not substantially improved compared to resins without nanowires. All sample values are expressed in GQ, so the composite acrylic resins (M6) continue to behave with electrical insulation. This benefits the prosthesis against possible corrosive effects and in the protection of artificial teeth.

Table 3. Determination of the volumetric resistance of nanocomposites and resins prepared in the laboratory.

B.4. Flexion tests.

The bending test was carried out on the Machine Per Prove Materiali No. 2710 of the Metro Com Comazzi Oscar Novara Italia company, according to ASTM 790. Rectangular specimens of approximate size 90 mm long, 20 mm wide and 7 were prepared. , 5 mm thick, as shown in Table 4. According to the results, the increase in nanowires within the polymer matrix decreased the mechanical properties of the material, but not significantly, which was probably due to the degree of crosslinking. of the nanocomposite. The PMMA / Cu-NWs and PMMA / Ag-NWs nanocomposites did not change significantly compared to the resin without nanowires, this was mainly due to the low charge of nanowires within the matrix. On the contrary, with the addition of all the nanowires the material decreased its resistance from 235.02 MPa to 180.00 MPa, maintaining the same order of magnitude. So, the material PMMA nanocomposite / nanowires prepared with the masterbatch, can be used without problem in the manufacture of permanent prostheses, since it improves the dimensional analysis of the pieces with a constant effort as a function of time.

Table 4. Results of the flexural properties of nanocomposites based on PMMA resins and Cu, Ag and ZnO nanowires.

B.5. Microbial Susceptibility by Agar Diffusion.

This assay is commonly used to measure the sensitivity of a microbial agent against some antimicrobial compound in antibiotics and drugs. In this case, polymeric nanocomposites were analyzed in order to know if they possessed antimicrobial activity.

The bacterial strain used for the tests was Staphylococcus Aureus. In Figure 4 it is possible to see in (a) the bacterial strain Staphylococcus Aureus incubated for 24 hours in Mueller Honton agar and in (b) the sample M6 fitted for the test showing the inibition halo is shown by way of example. The antimicrobial agent diffused from the sample to the outside of the culture producing an inhibition zone, in which a critical concentration of the agent inhibited bacterial growth.

The results in Table 5 show that the PMMA resin without nanowires did not show antimicrobial activity against Staphylococcus Aureus. The antimicrobial effect was mild for the PMMA / Cu-NWs, PMMA / Ag-NWs nanocomposites; which was due to the small amount of nanowires in the matrix since there was a percentage of the metal surface passivated with PVP and CTAB. However, an important result was achieved with the PMMA / Cu, Ag and ZnO NWs nanocomposites, where the halo of inhibition in the 11 mm agar diffusion susceptibility test. This means that the composite acrylic resins prepared with the masterbatch had antimicrobial properties. Table 5. Results antimicrobial activity of PMMA resins and PMMA / NWs nanocomposites, against Staphylococcus Aureus strain.

Claims

1. A composition of a masterbatch useful in the elaboration of CHARACTERIZED dental prostheses because it comprises at least the following components:

to. nanometric charge: composed of silver nanowires between 0.05 - 0.20% w / w; copper nanowires between 0.05 - 0.20% w / w; and zinc oxide nanowires between 0.08-2.00% w / w; Y

b. liquid components: composed of methyl methacrylate monomer with an inhibitor between 45-65 ppm; crosslinker of the ethylene glycol dimethacrylate type between 0.3 - 2.0% w / v and an activator of the N, N dimethyl-p-toluidine type in traces.

A composition of a masterbatch useful in the preparation of dental prostheses according to claim 1, CHARACTERIZED in that the nanowires have diameters between 20-150 nm and lengths between 1-30 pm.

A composition of a masterbatch useful in the preparation of dental prostheses according to claim 1, CHARACTERIZED in that the inhibitor is of the hydroquinone, nitrobenzene, butylhydroxytoluene, 2,2-diphenyl-1- picrilhydrazyl, dinitro-ortho-cresol, dinitro-sec-butyl type -phenol and dinitrophenols.

A process for preparing a masterbatch from the composition of claim 1 CHARACTERIZED because it comprises at least the following steps: a. addition of liquid resin components: in a dry chamber the MMA monomer and the inhibitor are added;

b. washing of nanometric charges: copper and silver nano-wire charges should be washed;

C. feeding of nanowires in the dry chamber: first they must be dispersed in the purified silver and copper nanowires in the MMA monomer; and then zinc oxide nanowires; Y

d. crosslinker addition: the solution containing all nanometric charges should be stirred for 15-25 min, during which time the crosslinker is added, then the solution is closed under a nitrogen atmosphere.

A process for preparing a masterbatch from the composition of claim 1 CHARACTERIZED because step "a" operates under a nitrogen atmosphere.

A thermo-curable composite acrylic resin useful in the preparation of dental prostheses, according to claim 3 CHARACTERIZED because it comprises the masterbatch obtained in the process of claim 3 and a resin of the type polymethylmethacrylate, n-butyl polymethacrylate, acrylic copolymer, poly (cyclohexyl methacrylate), poly (glycidyl methacrylate), poly (hydroxyalkyl methyl methacrylate), resins derived from acrylic acid and methacrylic acid, in a 1: 2 ratio

7. A thermo-curable composite acrylic resin useful in the preparation of dental prostheses, according to claim 3 CHARACTERIZED because it has antifungal and antimicrobial properties.