A short characteristic of new type of foreign dental cements Mineral Trioxide Aggregate (MTA)  for root canal dressing is presented. The results of experimental researchesdealing with the development of the composition and method of producing of the national dental cement of the similar purpose.  The effect of modifying additions (CaF2, P2O5, Bi2O3, MgO) on the sintering process of clinkers was  studied and the demonstration of metastable paragenesis in the of solid phase interaction in the system  CaO – Al2O3 – SiO2  was found. The obtained results provide more reliable designing of the mineralogical composition of cement clinker

Kuzmenkov, M. I.

Manak, T. N.

Shalukho, N. M.

Sushkevich, A. V.

A short characteristic of new type of foreign dental cements Mineral Trioxide Aggregate (MTA) for root canal dressing is presented. The results of experimental researchesdealing with the development of the composition and method of producing of the national dental cement of the similar purpose. The effect of modifying additions (CaF2, P2O5, Bi2O3, MgO) on the sintering process of clinkers was studied and the demonstration of metastable paragenesis in the of solid phase interaction in the system CaO – Al2O3 – SiO2 was found. The obtained results provide more reliable designing of the mineralogical composition of cement clinker

Belarusian State Technological University

ISSN 1683-0377. Proceedings of BSTU. 2012. Issue 3. Chemistry and Technology of Inorganic Substances 48 UDC 666.949:616.314 A. V. Sushkevich, PhD student (BSTU); M. I. Kuzmenkov, D. Sc. (Engineering), professor (BSTU);  N. M. Shalukho, PhD (Engineering), assistant lecturer (BSTU); T. N. Manak, PhD (Medicine), assistant professor (BSMU) DEMONSTRATION OF METASTABLE PARAGENESIS IN THE PROCESS  OF SOLID PHASE INTERACTION IN THE SYSTEM OF СаО – Al2O3 – SiO2 A short characteristic of new type of foreign dental cements Mineral Trioxide Aggregate (MTA) for root canal dressing is presented. The results of experimental researchesdealing with the develop-ment of the composition and method of producing of the national dental cement of the similar purpose. The effect of modifying additions (CaF2, P2O5, Bi2O3, MgO) on the sintering process of clinkers was studied and the demonstration of metastable paragenesis in the of solid phase interaction in the system CaO – Al2O3 – SiO2  was found. The obtained results provide more reliable designing of the minera-logical composition of cement clinker. Introduction. This work is a systematic re-search carried out at the Department of Chemical Technology of Binding Materials of Belarusian State Technological University in collaboration with the Department of General Dentistry of Belarusian State Medical University devoted to the the devel-opment of dental materials for various purposes. There is a need for surgical treatment to save the tooth at a time of the high prevalence of Bela-rusian patients dental caries (15-year-old popula-tion tooth decay is 91.7% and 35–44 years age group reaches 100%). The success directly de-pends on the right choice of filling material [1]. Theoreticallythe filling material must guaran-tee the tight root canal insulation. It must prevent the penetration of infection from the cavity. But it doesn’t have to cause any irritation to the sur-rounding tissue, to dissolve under the influence of tissue fluid. It must be easily removed from the channel because in the case oftreatment failure may be required a second sealing. Over the years amalgam,zinkoksideugenol, polimeric, glass ionomer cements, sealers contain-ing calcium hydroxide, polydimethylsiloxanes, etc were used for these purposes. But none of them doesn’t fully meet all the requirements for dental materials of the mentioned destination. A common shortcoming of all of these materials is their hy-drophobicity. That’s why it is necessaryto provide a completely dry workspace when they are used. But the problem is that quite often it cannot be achieved in the process of surgery root perfora-tions, retrograde fillings, etc. [2]. New material Mineral Trioxide Aggregate (MTA) has been developed in 1993 in the USA. This mate-rial represents the calcialuminosilicatecementcapable harden and gain strength in wet conditions [3, 4]. Such kinds of cements are not being produced in Belarus, so the demand for them is met by the imported materials like “ProRoot MTA” (Dentsply (USA)), “Trioksident” (“VladMiVa” (Russia)), “Restapex” (Ukraine), etc. However the experience of application of these cements in dental clinics of the Republic of Bela-rus has shown that they do not fully meet the grow-ing requirements. Thus the major shortcomings of the material “Trioksident” (Russia) is a long-time of the final curing (24 h) which makes it impossi-ble to root canal fillings within one patient visit. It also contains some large particles of theradiopaque filler (100–150 μm). Itisalsotypicalfor “Restapex” (Ukraine). Thus it makes difficult the penetration of cement paste into the narrow curves of root ca-nals and thenecessary seal isn’t provided.  Time of the final “ProRoot MTA” (USA) ce-ment hardening is 4–6 h. But its operating time takes only 4–5 min. It is not sufficient for good sealing. Inadditionitdoesn’t have the necessary plasticity. Therefore the aim of this research is the devel-opment and manufacturing process of receiving as well as holding technical and clinical testing of this type of dental cement. That is  free of the men-tioned drawbacks of similar foreign anlogs. Main part. Literature and patent analysis of the data showed that the composition of MTA cement contains such minerals as (3СаО · SiO2, 2СаО · SiO2, 3СаО · Al2O3). Being mixed with water they can be subjected to the hydrolysis and hydration with sub-sequent conversion to the lithoid material. There-forethree-component system CaO – Al2O3 – SiO2 was taken as aa base for their production. To define the scope of the clinker formation the reagents CaCO3 (class “p”), Al(OH)3 (class “c.p.”) and SiO2 · nH2O (class “c.p.”) some ex-perimental mixtures have been prepared. The molded samples pills with diameter 50 mm and height 5 mm have been formed from the batch mixtureby semi-dry pressing. Burninghas been carried out in an electric furnace in the temperature range of 1,300–1,450°C for 4 h. It was followed by rapid cooling ofobtained sinters (clinker) in air. The concentration limits of oxides (wt %: СаО – 75–85; SiO2 – 15–25; Al2O3 – 5–25)  Chemistry and Technology of Inorganic Materials and Substances 49forming clinkers under heat treatment  have been established during the first stage of the experi-mental work To estimate the binding properties the fired clinkers were finely grinded in a ball mill. It en-sured the passing of cement through the sieve N 0045 without a trace. The grinded cement mixedwiththedistilled water of water-cement ratio of 0.45. It helped to obtained the necessary consis-tency of cement paste that was molded into cubes with an edge of 10 mm. The compressive strength of the hardened material in accordance with ISO 9917 was measured at 3 and 28 days. Table 1 shows the cement characteristics which are derived from clinkers fired at 1,450°C and pos-sess the best strength properties. The Table shows that the cement production as a strength (23.3 MPa) as well as working time (6.0–6.5 min) is inferior to foreign analogs whose compressive strength is 65 MPa (“Pro-Root MTA”) and working time is 10–15 min (“Trioksident”). That’s why the the next stage of the experi-mental work was to improve the service properties of dental cement. To effect it we had to intensify the process of clinker formation. Fe2O3 is known to improve the STI-calcination of cement clinker in industry. It is widely and ef-fectively used for these purposes. Being a smooth it substantially reduces the temperature of clinker formation. However in addition to dental material strength high requirements are lodged for its whiteness. The dark color cement is not suitable from an aesthetic point of view. Therefore the effi-cient qualities of the mentioned addition cannot be used in this case. Therefore, CaF2, P2O5, Bi2O3 were takenas modifiers for the 3-component system. Their selec-tion was based on the following reasons. Calcium fluoride is known to accelerate the processes oc-curring between the components of a calcinable mixture, to lower the temperature of the formation of the basic eutectic melt. Thereby it reduces the clinker melt viscosity. The mobility of the ions is increased, the diffusion processes are accelerated. The formation of clinker is speeded up. Phospho-rus pentoxidestabilizes β-C2S and C3S thereby in-creasing their hydraulic properties. It should be explained by their loosening under the influence of ion P5+ and corresponding increasing of the supply of the potential energy of the crystal lattice of sili-cates [5–8]. As bismuth oxide isa low-melting (870°C) it simultaneously provides radiopaque of dental cement. The results of the experimental data (Table 2) showed that the separate addition of the CaF2 and Bi2O3 failed to achieve lower burning temperature (up 1,340oC) because clinkers spillage occurred in the process of cooling as a result of their silicate disinte-gration, i.e. the transformation of the active hydraulic dicalcium silicate β-2СаО · SiO2 to the inactive modi-fication γ-2СаО · SiO2. With the addition of P2O5 and burning temperature 1,340°С this effect was avoid-edbut the strength of the cement based on such clinker was minimal. It happened because the melt process of clinker formation was slowed down in deficiency of the resultingeutectic melt. Reducing of the clinker formation temperature up to 1,340°C was achieved by the addition both Vi2O3 and CaF2. To prevent further silicate decay P2O5 was additionally added. Besides to increase the strength properties of dental cement MgO was added, since magnesium ions partially replaced in the crystal lattice of Ca2+ makethe high-tempera-ture forms of tricalcium silicate more stabilize that can best contribute to the increase in the strength of cement. Table 2 shows that the cement received by the simultaneous additionof mineralizing adds has the highest strength characteristics. However the den-tal cement should also have the necessary time of final curing and working time.  Table 1 Composition of experimental cements and their properties Oxides mass content, wt %  Compressing strength, MPa,  at the age, 24-hour period Composition number CaO Al2O3  SiO2 3  28  Worktime, min 22 60  20  20  12.7 22.7  1.5  22.1 65  15  20  14.5  21.3  2  21 70  20  10  12.4  17.8  3  21.1 75  5  20  8.3  10.8  6.5  21.2 75  10  15  10.65  16.2  4.5  21.3 65  10  20  6.2 19.5 4  21.4 70  5  25  13.2  23.3  6  ISSN 1683-0377. Proceedings of BSTU. 2012. Issue 3. Chemistry and Technology of Inorganic Substances 50 Table 2 Strength of cement depending on the input of additives and firing temperature Compressing strength, MPa, at burning temperature, °С 1,300  1,340  1,400  at the age,  24-hour period at the age,  24-hour period at the age,  24-hour period Mineralizer Addition mass  content, wt % 3  28  3  28  3  28  P2O5 0.6  4.2  8.57  4.7  9.2  12.4  24.4  CaF2 1.5  9.7  18.1  10.3  19.4  14.6  27.1  Bi2O3 5.0 6.7  18.3  12.5  20.2  16.4  28.2  Combined introduction P2O5 CaF2 Bi2O3 0.8  1.5  3.0  10.1  19.2  12.9  24.3  18.6  29.8  Combined introduction P2O5 CaF2 Bi2O3 MgO 1.0 1.5 3.0 0.3 11.5 22.8 14.9  29.4  21.4  32.1   As you know the paramount influence on the properties of cement has its mineral composition. Therefore for the structurally-controlled synthesis, i.e. the formation of the desired mineral composi-tion it was necessary to examine the sequence of formation of the crystalline phases in the dynamic conditions like those that are used in the cement industry. There is no any informationon this subject in the literature. At the same time, we know that the sequence of the formation of crystalline phases during the “top” crystallization taking place on cooling magmatic meltthe effect of metastable par-agenesisappears. It refers to natural co-location of minerals connected by general physico-chemical and thermodynamic conditions of formation [9]. Thus the establishment of a metastable par-agenesis in the case of the “bottom” crystallization would establish a physical-chemical basis for the structure-controlled synthesis of dental cement clinkers. Relatively recently performed researches pre-sented in the doctoral dissertation of E. N. Pota-pova [10] show that the cement properties (com-pressive strength, working time, setting time, etc.) do not only depend on the mineralogical composi-tion of the clinker, but also on its melting history. Therefore for a more reliable design of clinker composition to produce dental cement it was nec-essary to establish on its base the genetic relation-ship in a line “charge → clinker → melt” and its effect on phase formation in the silicate system. Predict the sequence of formation of phases in the solid phase reactions and their realization al-lowed the results of thermodynamic calculations and experimental data on the determination of the phase composition of cakes (clinker) at different burning temperatures by X-ray fluorescence analy-sis (XFA).  The direct reactions of interaction with СаСО3 can take place at temperatures up to 800°C in the absence of CaO [11].  At temperatures above 800°C when CaCO3 de-carbonization takes place, Al2О3 and SiО2 react with CaOand with some formedelementarylow-basic compounds with subsequent saturation to a highly-basic ones. Analysis of changes of the Gibbs energy of solid phase reactions shows that the formation of the main clinker phases (3СаО · SiO2, 2СаО · SiO2, 3СаО · Al2O3) is the most probable through the intermediate phase. In reality the process of clinker formation can be traced by X-ray diffraction study. The analysis of samples obtained at different temperatures showed that their phase composition differs from the state showed on the diagram. It was found that the crystallization process of compositions in non-mineral phase in non-equilibrium conditions affect neighboring phases formed at lower temperatures. Fig. 1 shows a fragment of the constitution diagram of CaO – Al2O3 – SiO2 illustrated with studied composition points and location of the phase composition depending on the burning up temperature of the samples (Table 3).  Fig. 1 shows that the composition points of the experimental compositions in the crystallization field of the same phase depending on the location (center or periphery) will differ. The mode of sam-ples burning up also influence on it. Chemistry and Technology of Inorganic Materials and Substances 5119232117 181321.122.121.4CaO~2,570°С3CaO · SiO2limeCa2SiO42CaO · Аl2O3 · SiO23CaO · Аl2O3Ca3Аl2O6Al2O3SiO2heleniterankinite2080~2,070°С~2,050°С~2,130°С2CaO · SiO23CaO · 2SiO21,464°С1,460°С1,545°1,593°~1,310°~1,315°1,265°1,318°1,335°1,455°1,350° Fig. 1. Сonstitution diagram of CaO – Al2O3 – SiO2  illustrated  with experimental composition points    Table 3 Changes of the phase composition depending on the burning up temperature Phase compositionin the process of burning up, °С Composition number Crystallization field  on the constitution diagram  1,300 1,400 1,450 19 H H H H 17 C2S C2S, A C2S, C3A C2S, C3A, C3S 13 C2S − R R, C2S, A, H, P R, C2S, H, P R, C2S, H 18 C2S − H H, C2S, A H, C2S H, C2S 23 C2S − H C2S, H, A C2S, H C2S, H, C3S 22 C2S C2S, H, А, C3A C2S, C3S, C3A, G C2S, C3S, C3A 22.1 C2S − C3S C2S, H, А, C3А C2S, C3А, C3S  C2S, C3S, C3А 21.4 C3S C2S, C3A, C3S, М C2S, C3S, C3A C3S, C2S, C3A 21 C3S − CaO C2S, C3A, C3S,  H C2S, C3A, C3S C3S, C2S, C3A 21.1 C3S − CaO C2S, C3A, H, М C2S, C3A, C3S C3S, C2S, C3A Notes. H – helenite; A – anorthite; R – rankinite; P – pseudowollastonite; М – mullite; C3S – 3CaO · SiO2; C2S – 2CaO · SiO2; C3A – 3CaO · Al2O3.  Fig. 2 shows the change of the composition of clinker N 21.4 at the center of crystallization 3SaO · SiO2 depending on the burning up tem-perature.  Fig. 3 and 4 show the percentage of phases of clinker N 21.4 depending on the burning up tem-perature and input supplements. It can be seen that some intermediate phases are formed at lower temperatures. They convert to the basic ones at higher temperatures. By studying the change in the ratio of clinker phases depending on the burning up temperature and the introduction of additions you can get dental cement which will have the necessary properties. ISSN 1683-0377. Proceedings of BSTU. 2012. Issue 3. Chemistry and Technology of Inorganic Substances 52 Fig. 2. Sequence of crystal phase formation: а – composition N 21.4; b – modified P2O5, CaF2, Bi2O3, MgO  600°C 1,450°C1,400°C1,300°C1,200°C1,000°CCaCO3SiO2·nH2OAl(OH)3SiO2Al2O3CaCO3CO2 CO2CO2CO2CO2CaOCaOCaOCaOCaOС2S С3А С3АС2S С3АС3S С2S С3АС3АС3S С2S С2S С3S Rawmaterials Fig. 3. Sequence of phase composition formation of sample N 21.4   Fig. 4. Sequence of phase composition formation of sample N 21.4,  modified P2O5, CaF2, Bi2O3, MgO: C3S – 3CaO · SiO2; C2S – 2CaO · SiO2; C3A – 3CaO · Al2O3;  – silicates and calcium aluminates Chemistry and Technology of Inorganic Materials and Substances 53Conclusion. Based on the systematic investi-gations of solid-phase interaction in the system  CaO − Al2O3 − SiO2 as well as the modified CaF2, Р2О5, Bi2O3, MgO the dental cement to seal the root canalswas developed. It possesses all best properties of the foreign analogues. The results of thermodynamic calculations and experimental data on the phase formationby XRD re-vealed the manifestation of metastable paragenesis during crystallization in dynamic environments. It was the basis for the development of the parameters of the structural-controlled synthesis of dental cement. 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Demonstration of metastable paragenesis in the process of solid phase interaction in the system of СаО – Al[2]O[3] – SiO[2]

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Demonstration of metastable paragenesis in the process of solid phase interaction in the system of СаО – Al[2]O[3] – SiO[2]

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