Comparative characteristics of the physical and mechanical properties of the self-etchangeable self-adhesive composite cement for indirect restorations "Maxcem Elite

% and Relyx by 30 %, and the significance level of the advantage is very high (P <0.001). The peel strength looked approximately the same for the “Maxcem Elite TM” (5.32±0.27) MPa and Relyx (5.0±0.25) MPa and was 13.6 % better with respect to Bifix. Therefore, the advantage of "Maxcem Elite TM" in relation to Relyx U 100 can be affirmed at a satisfactory significance level of p<0.01. A high level of adhesion strength to tooth hard tissues and peel strength ensures reliability and durability of the enamel-composite-metal system.


Introduction.
One of the most important problems in the use of adhesive fixation bridges, which reduces the level of their widespread use, is the lack of high-quality and affordable fixation material [2,5].
Therefore, using the modern achievements of chemical science and the requirements for clinical application, it can be considered relevant to select the components of the material and their rational ratio, which would combine the low viscosity of the polymer matrix and the high dispersion of the hybrid filler, which makes it possible to achieve high plasticity and prevent the formation of a thick layer of material between the adhesive pad and the tooth surface [1,3].
Objective. To analyze in a comparative aspect the physical and mechanical properties of the polymer material "Maxcem Elite TM " as a fixing material for bridges of the adhesive fixation system.
Material and methods. The composite material "Maxcem Elite TM " is made on the basis of a monomeric matrix consisting of organic components: Bis-GMA, urethane dimethacrylate triethylene glycol dimethacrylate -18.8 % by weight, inorganic fillers -81.0 % by weight, a small amount of catalysts, stabilizers and pigments -0.2 % by weight. The amount of inorganic fillers is 81 % by weight and 68 % by volume. Particle size 0.04 -7.0 microns [4,6].
The study of the physical and mechanical properties of the material "Maxcem Elite TM " was carried out according to the following indicators: the appearance of the paste and adhesive, their consistency; the appearance of the polymer; diametrical strength; water absorption and water solubility; strength and conical yield point according to Heppler; tensile strength; adhesive strength of connection with hard tissues of the tooth, etc.
Results and discussion. On the basis of the laboratory studies it was found that absolutely all characteristics of "Maxcem Elite TM " comply with the requirements of ISO 4046-81 and TU.U.24.4-00481318-022-2002 [6]. Improved cement formula provides adhesion strength comparable to total-etch adhesives to tooth tissues and all types of dental materials without the use of an adhesive system (MPa enamel -25.5, dentin -25.8, titanium -41, zirconium -32.1 gold -33.2, E. max -34, ceramics -33. 6). An optimized matrix and filler system enhances lubricity, resulting in better adhesion to dentin [4].
In terms of the main quality indicators, such as high bond strength to hard tooth tissues, which is 1.6 times higher than the requirements in combination with a high level of peel strength and 1.5 times higher than the requirements, it allows you to obtain reliable fixation, which is a prerequisite when using this type of prosthetics. The high value of the hardening depth (4.6 mm) is 2.3 times higher than the standards, thereby expanding the possibilities of using adhesive bridges with metal frames. Our comparative analysis of the physical and mechanical properties of the investigated material "Maxcem Elite TM " "with analogues (Bifix VOCO, Relyx U 100 3M ESPE), allowed us to reveal the following regularities (table 1).
All investigated materials during the tests showed themselves as high-viscosity, homogeneous pastes in which there are no foreign impurities and inclusions. Although in terms of the depth of hardening "Maxcem Elite TM " is reliably (p <0.05) inferior, Bifix is by 14.9 % and by 13.3 % Relyx U 100, this does not significantly affect the quality of the bond of the adhesive structure with hard tooth tissues, especially due to the developed by us method of preparation of abutment teeth for adhesive onlays of bridges.
Therefore, the level of reliability of these comparisons can only be asserted by conducting an appropriate statistical analysis. None of the samples that were analyzed corresponded to the sample from the normally distributed general population (according to the Kolmogorov-Smirnov test), therefore, in our calculations, we used the methods of nonparametric statistics (table 2).
The results obtained relate to all comparisons of the material "Maxcem Elite TM " in terms of the indicators included in table 2. For example, we came to the conclusion (see table 1) about a high reliable advantage in terms of Heppler's conical yield point over the best of comparable materials Relyx U 100 (C = 1489.3±74.5 MPa). Since it is the best, the preference of the material "Maxcem Elite TM " over others can be asserted in no way at a lower level of reliability. By comparing the indicators of water absorption, water solubility and peel strength, the situation was the opposite.
The study of the level of water absorption indicates the probable absence of variability of the indicator of the studied material in comparison with comparable analogs. The value of the water solubility index of all the studied composites practically does not differ from the value of "Maxcem Elite TM " (within (2.5±0.1)%), and comply with the requirements of ISO 4046. These conclusions are also confirmed statistically, since none of the applied criteria indicated for the presence of significant differences. Note that the last two indicators affect the stability of the glue line and the toxic effect on the human body.
Analyzing the indicators of the diametrical strength of the materials under study, we can reliably (p<0.001) note the indicators of "Maxcem Elite TM " higher than Bifix by 17.2 %, and higher than Relyx U 100 by 17.3 %. Also, other physical and mechanical properties of the material "Maxcem Elite TM " have a significant (p<0. The study of the level of water absorption indicates a significant absence of variability of the indicator of the studied material in comparison with a comparable analogue. This indicator for "Maxcem Elite TM " is significant and reliable (at the level of p>0.0001), less compared to Relyx U 100 (by 20 %). The value of the water solubility index of all the composites under study practically does not differ from the value of "Maxcem Elite TM " (within (2.5±0.1) %), and comply with the requirements of ISO 4046. We believe that statistical analysis confirms this, since the difference between " Maxcem Elite TM "and Relyx Note. * -significant difference (p<0.05) "Maxcem Elite TM " in comparison with the best analogue. U 100 could be asserted only at an extremely low level of significance (p>0.18). Among the most important strength characteristics for luting materials are the adhesive strength of the bond to the hard tissues of the tooth and the peel strength. In terms of adhesive strength of bonding to hard tissues, the undisputed leader was "Maxcem Elite TM ", which significantly (p<0.001) and significantly surpasses Bifix by 37.2 %, and Relyx U 100 by 30 %. Relative to the peel strength index, which was approximately the same for "Maxcem Elite TM " (5.32±0.27) MPa and Relyx U 100 (5.0±0.25 MPa) and the best by 13.6 % in relation to Bifix. But, as shown by an accurate analysis (table 2), the advantage of "Maxcem Elite TM " in relation to Relyx U 100 can be asserted at a high level of significance P<0.013. The high level of adhesive strength of the connection with hard tooth tissues and peel strength ensures the reliability and durability of the enamel-composite-metal system connection, which makes it possible to use this material for fixing adhesive structures.
The high level of adhesive strength of the connection with hard tissues of the tooth and the peel strength ensures the reliability and durability of the connection of the enamel-composite-metal system.
Thus, on the basis of laboratory tests and statistical analysis of their results, we made the following conclusions.
Conclusions. In a comparative aspect, a study was made of the physicomechanical properties of composite cements for indirect restoration. It was found that in terms of adhesive strength of bonding with hard tissues, Maxcem Elite TM turned out to be the undisputed leader, which by average measurements exceeds Bifix by 37.2 % and Relyx by 30 %, and the significance level of the advantage is very high (P <0.001). The peel strength looked approximately the same for the "Maxcem Elite TM" (5.32±0.27) MPa and Relyx (5.0±0.25) MPa and was 13.6 % better with respect to Bifix. Therefore, the advantage of "Maxcem Elite TM" in relation to Relyx U 100 can be affirmed at a satisfactory significance level of p<0.01. A high level of adhesion strength to tooth hard tissues and peel strength ensures reliability and durability of the enamel-composite-metal system.