STUDIES AND RESEARCHES ON THE OBTAINING OF CAST TITANIUM IMPLANTS

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1 STUDIES AND RESEARCHES ON THE OBTAINING OF CAST TITANIUM IMPLANTS Mariana DUMITRU a Marius BIBU a Cristian DEAC a a "Lucian Blaga" University of Sibiu, Emil Cioran str. 4, Sibiu, Romania, cristian.deac@ulbsibiu.ro Abstract The paper presents the authors researches on titanium implants obtained through casting, especially for dentistry purposes. There are presented different constructive forms of implants used in this domain and the particular results obtained by the authors in casting such small pieces of titanium on an experimental device designed and realised by them. The casting method used for this purpose is that of lost-wax investment molds, showing the difficulties met in the process, considering the special properties of titanium a very high melting temperature (over 1670 C) and a great interaction capability with many chemical elements at these temperatures. 1. CONSTRUCTIVE SHAPES OF DENTAL IMPLANTS MADE OF TITANIUM AND TITANIUM ALLOYS Titanium dental implants used at present can be of very different shapes, such as those presented in figures 1 and 2 [1]. Fig. 1 Various constructive shapes of titanium dental implants 1

Fig. 2 Various constructive shapes of titanium dental implants As can be noticed from these pictures, implants which must be obtained have elaborate shapes and very small dimensions, since they have

A very important condition for the acceptance of any implant by the human body is the socalled bone integration.

2 Fig. 2 Various constructive shapes of titanium dental implants As can be noticed from these pictures, implants which must be obtained have elaborate shapes and very small dimensions, since they have to be introduced in the patients mouths. That is why implants must have very precise dimensions. A very important condition for the acceptance of any implant by the human body is the socalled bone integration. It has been shown that titanium is well tolerated by living tissues due to the fact that the superficial oxides are electric isolators, slowing down the exchange of ions and electrons between the implant and the tissue. Also, it has been shown that hydroxy-apatite crystals tend to form on the titanium implant's surface, facilitating the bonding between collagen fibres and implant surface [2]. Another condition is the quality of the metallic surface. Studies carried out in this regard [2] have shown that dental implants with a rougher surface (inside certain limits) present a better bone integration than those with plane surface. Therefore, titanium dental implants should have a rough metal surface and present also a striated profile which assures a better bone integration. Considering these aspects, the authors decided to design and cast a particular shape of titanium implant, presented in figure 3. This implant has a single screw and have the surface characteristics presented forward. In order to better observe the quality of surface and the striations of the implant, figure 4 presents the same titanium dental implant studied with a microscope, with magnifications of 10x, 30x and 3000x. 2

These have a double goal: to minimise the implant's mass and to help bone integration. Such an implant as that presented in fig.

3 Fig. 3 Dental titanium implant proposed for casting (magnification 10x) (magnification 30x) (magnification 3000x) Fig. 4. Microscopic images of the titanium implant surface In the pictures above there can be observed another characteristic of dental implants, namely the presence of holes in the implant body. These have a double goal: to minimise the implant's mass and to help bone integration. Such an implant as that presented in fig. 3 was experimentally cast by us using an original machine for melting and casting titanium. 2. EXPERIMENTAL TITANIUM CASTING FOR OBTAINING SMALL DIMENSIONS PIECES AS IMPLANTS 2.1. Pattern design and proposed technology Following a thorough analysis of the existing implant types, usually obtained by machining, and of the technologies needed for their realising, from titanium pellets, through casting, it was decided to realise an implant whose shape and dimensions are presented in figure 5 (magnification scale 2.5: 1). 3

4 Fig. 5 The designed titanium implant (magnification scale 5:1) In order to cast this implant, we considered the method of lost wax. For this purpose, adequate wax patterns were prepared from special dentistry wax, which were then coated with a ceramic investment material. These patterns are presented in figure 6. Fig. 6 Patterns of dentistry wax made for casting 4

5 One of the great problems of the designed technology of casting was the special ceramic material used for coating the patterns, because this material should not interact with the molten titanium and also should resist at very high casting temperatures (over 1700ºC). The optimal recipe for this material was obtained after several experiments and consists of a mixture of oxides (96% MgO, 1.5% SiO 2, 1.5 Fe 2 O 3, 0.5% Na 2 O, 0,5 Al 2 O 3 ) Experimental melting and casting titanium device For obtaining dental implants as those presented above, we used an experimental equipment for melting and casting titanium and its alloys, which was designed and realised by the authors of this paper. In principle, this machine works by melting in vacuum and casting in a protective gas atmosphere consisting of argon of high purity, conditions required by the chemical characteristics of molten titanium. This machine has 2 chambers, placed one below the other. The upper chamber is for melting titanium, and has a copper crucible cooled in water, in which titanium melts. The melting process is realised with electrical arc generated with the help of a welding source. In the second chamber is placed the special ceramic mold, in which the molten titanium is poured at the right moment. The casting process takes place in 5 phases [5]. 3. CONCLUSIONS The paper presents the possibility of obtaining titanium implants used in dentistry, such as those presented in figure 3, which were obtained through casting by the authors. The casting technology is that of lost wax ceramic investments with static casting in special conditions required by the special characteristics of titanium and its alloys. It is also presented the experimental device with which the casting was possible, device designed and realized by this paper authors. REFRENCES 1. DUMITRU, M., Studies and researches on technologies and equipments for casting titanium and its alloys in pieces of small dimensions, Doctorate thesis, Brasov, Romania, BREME, J., Titanium and titanium alloys, biomaterials of preference. In the Proceeding of the Sixth World Conference on Titanium, Paris, France, 1988, pages LYON, S.R., INOUYE, S., The interaction of titanium with refractary oxides, In Titanium and Titanium alloys, p , New York, LI, J., High Strength Ceramics with Potential Bioactivity, In Interceram, vol. 29, IDA, K., KURODA, T., YAMAGA, R., Casting force in several casting methods, Part II. Comparison of casting time in several casting methods, Journal of Osaka University Dental School,

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