Mechanical behaviour of composite resins for dental applications.

Ghiban, Brandusa ; Bortun, Cristina Maria ; Faur, Nicolae 等

1. INTRODUCTION

Development of nowadays dental techniques for repairing oral teeth is based on acrylic resins and their properties, such as: esthetic properties (translucidity, color similar to the replaced tissues and color maintaining both during elaboration and inside human mouth) and physical- chemical properties (dimension stability and shape maintaining during processing and inside human mouth, good elasticity, wear resistance in human mouth, impermeability for saliva and food, good polishing and hygiene, good connection to the other prosthesis components, superior plasticity temperature than human mouth temperature, non toxicity and non-irritating for the human tissue). According to EN ISO 1567 there are four types of resins: heat curing resins (upper 65[degrees]C) either bi-component, or mono-components, self curing (lower 65[degrees]C), thermoplastic materials in granulate form, light curing resins and microwave polymerized resins. Heat curing resins are now the most used materials for realization of partial or total dental prostheses.

World market of bi-component heat curing resins know a lot of product, such as Meliodent (Heraeus Kulzer), Vertex (Vertex), Superacryl (Spofa), Triplex (Ivoclar). Prosthetic restoration of edentulous patients must follow the recovery of dental arcades, functional almost partial mastication recovery, and why not aesthetic shape and form of teeth, occlusal equilibration, homeostasis of the prosthetic field. The problem of mechanical behavior of acrylic resins materials is a real one, being well and repeatedly presented in literature (Memon 2001; Messe 2008; Uzun 2002). The necessity of a minimum level of mechanical characteristic values guarantee may appear in order to assure the prosthesis viability on long term (Bortun 2008; Bortun 2009). The aim of presented paper is the necessity of processes grounding which takes place for integration maintaining of bicomponent heat curing resins, and also to structural characterization of four types of resins, with different behavior.

2. MATERIALS AND EXPERIMENTAL PROCEDURE

There were analysed four acrylic resins which are usually used in dental practice, respectively: MELIODENT, SUPERACRYL, TRIPLEX and VERTEX. In accordance with dental practice, there were made by polymerization samples with the following dimensions: 2 mm thickness, 30 mm length and 5 mm width. In order to define the mechanism of fracture, all amples were loaded in the same manner. Mechanical characteristics were determined by Zwick Roel equipment with data processing using testXpert system. The loaded stress was 50kN and the rezolution 0,1 [micro]m for all experimental samples.

The experimental samples were then analysed at stereomicroscope Olympus type SZX7, equipped with image processing soft QuickphotoMicro 2.2. There were analysed both longitudinal and transversal surfaces perpendicular to fracture surface.

3. EXPERIMENTAL RESULTS AND INTERPRETATION

The mechanical characteristics of the heat curing dental experimental resins are given in figure 1. As one may remark, the lowest value of the ultimate strength is for MELIODENT, than SUPERACRYL and TRIPLEX, the highest being for VERTEX. Considering the manner of fracture we may conclude that resin VERTEX has the best mechanical behavior among all the investigated heat curing dental resins.

Detailed analysis under the stereomicroscope revealed interesting observations. As a general remark, the entire sample has a brittle fracture, with a quasi crystalline aspect in transversal cross section. Each resin has its own structural characteristics. Resin type MELIODENT, given in figure 2, has in general a brittle aspect. One may remark in transversal cross section relative many chop fibers, about 3-4 red and short fibers. All the fibers cracked separately than the matrix, as a sign of a different fracture behavior between fiber and the matrix. There is no fragmented fracture of the samples. Resin type SUPERACRYL, given in figure 3, has a specific structural feature. The entire sample fractured in fragmented manner, resulting three parts after fracture (the so called 100% "fragmented fracture"). One may remark a small amount of short chop fibers on the transversal cross section, respectively one or two.

Resin type TRIPLEX, given in figure 4, has a proportion of fragmented fracture about 70%, in three pieces. Only 20% from the total number of fibers may crack in the same time with the matrix. This resin has intermediate values of reinforced fibers among all investigated resins.

Resin type VERTEX, given in figure 5, has a proportion of fragmented fracture about 60%, in two pieces. About 40% from the total number of fibers may crack in the same time with the matrix. This resin has the highest amount of reinforced fibers among all investigated resins.

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4. CONCLUSIONS

Comparative analysis of fracture behaviour for four heat curing dental acrylic resins may reveal the following aspects:

(i) all the heat curing dental acrylic resins present fragmented fracture, but in different proportion: 100% for MELIODENT and SUPERACRYL, 70% for TRIPLE* and 30% for VERTEX;

(ii) mechanical characteristic values of samples were in different ranges: ultimate strength is 63 MPa for Meliodent, 66 MPa for SUPERACRYL, 69 MPa for TRIPLEX, the highest value being for VERTEX, respectively 70MPa;

(iii) different behavior of dental acrylic heat curing resins is due to significant differences between mechanical characteristics of reinforced fibers and matrix. Red small chop fibers may or may not fracture in the same time with the matrix. So, at MELIODENT, VERTEX and SUPERACRYL samples fibers may not fracture in the same moment with matrix, in opposite with TRIPLEX samples, where only 20% from the total number of fibers are broken simultaneously with the matrix;

(iv) the best mechanical behavior of the investigated heat curing dental acrylic resin is for VERTEX, with the highest amount of reinforced fibers among the other resins.

5. ACKNOWLEDGMENTS

The present work has been supported from the CNCSIS PNII, ID 1878/2008-"Analytical evaluation of materials and dental prosthesis durability based on fracture toughness and cracks rate propagation".

6. REFERENCES

Bortun C., Ghiban B., Sandu L., Faur N., Ghiban N., Cernescu A. (2008). Structural investigations concerning mechanical behavior of two dental acrylic resins, Revista Materiale Plastice, Romania, 45, nr.4, 2008, pp 362-365, ISSN 0025-5289

Bortun C.,Ghiban B., Ghiban N., Jiga G (2009). Investigation concerning mechanical and structural behaviour of dental resins, Proceeding of ICSAAM, Tarbes France, ISBN pp 1-7

Memon M.S., Yunus N., Razak A.A. (2001). Some mechanical properties of a highly cross-linked, microwave-polymerized, injection-molded denture base polymer, Internationa. Journal of Prosthodontics, May-Jun;14(3):214-8

Mese A, Guzel Kg.(2008). Effect of storage duration on the hardness and tensile bond strength of silicone- and acrylic resin-based resilient denture liners to a processed denture base acrylic resi, J. ProsthetDent, Feb;99(2):153-9

Uzun G., Hersek N.(2002). Comparison of the fracture resistance of six denture base acrylic resins, J. Biomater Appl, Jul;17(1):19-29