Alloyed titanium has been studied extensively and found to have suitable qualities for use as a dental cast. While some combinations of metals with titanium may not yield desirable results, the Ti-Cu mixture has shown excellent properties and structural adaptation for applications in fabricating dental works.
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Dental Stone, which is more recently referred to as Dental Cast, is an accurate, 3-dimensional prototype of a patient's denture. It is obtained by pouring a dense material, solidifying under specified conditions, into an impression of a patient's oral tissue. Many materials have been developed and used as dental casts. However, most of them have challenges that have prompted scientists and dental technologists to keep up research to improve the technique.
Mechanical and Structural Advantages of Titanium in Dental Cast
Titanium is a lightweight transition metal with an excellent refractive property but a relatively high melting and boiling point. The metal is about 40% lighter than steel, even though both have almost the same strength and durability. Alloys of titanium are also known to possess high tensile strength and low weight and are exceptionally resistant to corrosion. They are also resistant to erosion and cavitation upon intense application of pressure.
Notably, the ability of titanium to resist corrosion has made it an essential material for denture analysis and fabrication. When oxygen attacks a titanium material, it forms a thin layer of TiO2 on its surface, which effectively inhibits further material degradation via corrosion.
Another property which makes titanium and its alloy an essential material in the dental cast is its low elasticity modulus. This property makes it quite flexible and allows it to return to its original shape after bending. Titanium alloys are among a group of alloys referred to as Memory Alloys. These metals can be deformed when cold but return to their original shape when heated.
Titanium is also a diamagnetic, biocompatible transition metal and is not toxic or allergenic to the human system. The metal density is relatively low, ensuring that it can easily be carried within the human buccal cavity. Below are the significant physical properties of titanium, which affect its mechanical and structural adaptation as a metal constituent of alloys used in dental cast fabrication:
- State of Matter under Standard Conditions - - Solid
- Atomic Mass - - - - - - 47.867 amu
- Density under Standard Conditions - - 4.506 g/cm3
- Melting Point - - - - - - 1670 0C
- Boiling Point - - - - - - 3287 0C
- Thermal Expansion - - - - - 8.6 mK
- Thermal Conductivity - - - - 21.9 W/mK
Mechanical and Structural Advantages of Copper in Dental Cast
Copper, like titanium, is a transition metal. It is ductile, malleable, and has relatively high thermal and electrical conductivity. Like titanium, copper is also very resistant to corrosion. The malleable and ductile nature of the metal makes it ideal for fabrication and joining.
Copper metal possesses enormous strength and durability and does not brittle under harsh environmental conditions. The metal is also a non-ferrous one, which means it is diamagnetic, just like titanium. The ability of copper to form alloys quickly is crucial in its application for making a suitable dental cast. It is also biocompatible to the human body and even shows strong antimicrobial activity. Studies are still ongoing to determine the actual mechanism of copper's antimicrobial action. However, elementary studies suggest that it could be related to its microstructure.
The significant mechanical and structural properties of copper are listed below:
- State of Matter under Standard Conditions - - Solid
- Atomic Mass - - - - - - 63.546 amu
- Density under Standard Conditions - - - 8.92 g/cm3
- Melting Point - - - - - - 1084 0C
- Boiling Point - - - - - - 2562 0C
- Thermal Expansion - - - - - 16.5 mK
- Thermal Conductivity - - - - 401 W/mK
Mechanical and Structural Advantages of Ti-Cu Alloy as a Dental Cast
Titanium metal has very desirable qualities for dental casting, but the alloy of titanium and copper presents improved mechanical properties. It has better corrosion resistance, advanced biocompatibility, and a relatively low melting point. However, the Ti-Cu alloy's properties depend on its microstructural properties, including growth formation, morphological features of the inter-metal structures, and the formation mechanism of the alloy precipitates.
What Determines the Microstructure of a TI-Cu Alloy
The microstructural properties of metallic alloys are primarily determined by the route through which the alloy was produced. In making Ti-Cu alloy, two basic methods are used. These are mechanical alloying (MA) of the pure elements and mechanical milling (MM) of intermetallic compounds.
In a study published in the Journal of Alloys and Compounds, samples of Titanium alloys produced by the two methods were structurally analyzed by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Differential Scanning Calorimetry (DCS). SEM results showed that the MM-alloy powder was deformed during the milling.
The XRD spectral analysis confirmed that the constituent metals were uniformly dispersed in both methods. In contrast, the result from both the XRD and DSC analysis suggests that the milling time required for the complete amorphization of the MA-alloy is longer than that required for the MM-alloy. It also reveals that the MA-alloy powder's activation energy and crystallization temperature are not the same as that of the MM-alloy powder.
Alternative Materials for Dental Casts
Many materials have been developed before and after introducing the Ti-Cu alloy for the dental cast. Each of these materials possesses unique advantages and limitations. Alloys of gold, platinum, and palladium were all used in the 1950s as dental casts, but the significant limitations of these alloys were that they were weak and had low sag resistance. However, the alloys were able to cast and solder without much difficulty. Nonetheless, the cost of this alloy was relatively high and was not affordable to a good number of patients.
Over the years, subsequent studies and research have thrown up other alloys containing a lesser amount of noble metals, which are very useful in dental casting. The Ti-Cu alloy is one of these discoveries.
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References and Further Reading
Xu V. W., Nizami M. Z. I., Yin I. X., Yu O. Y., Lung C. Y. K., Chu C. H. (2022). Application of Copper Nanoparticles in Dentistry. Journal of Nanomaterials, 12(5). pp: 805.
https://www.researchgate.net/publication/358911773_Application_of_Copper_Nanoparticles_in_Dentistry
Thongthammachat S., Moore B. K., Barco M. T., Hovijitra S., Brown D. T., Andres C. J. (2002). Dimensional Accuracy of Dental Casts: Influence of Tray Material, Impression Material and Time. Journal of Prosthodontics, 11(2). pp: 98 – 108.
https://pubmed.ncbi.nlm.nih.gov/12087547/
Papadiochos I., Papadiochou S., Emmanouil I. (2017). The Historical Evolution of Dental Impression Materials. Journal of Hist Dent. 65(2). pp: 79 – 89.
https://deepblue.lib.umich.edu/bitstream/handle/2027.42/67759/10.1177_08959374880020011701.pdf?sequence=2
Morecambe Metals. (2018). Metals and Their Properties: Copper. Accessed online on 3rd June 2022
https://www.morecambemetals.co.uk/what-are-the-properties-of-copper/
Kishimura H., Matsumoto H. (2011). Fabrication of Ti-Cu-Ni-Al amorphous alloys by Mechanical Alloying and Mechanical Milling. Journal of Alloys and Compounds 509(12). pp: 4386 – 4389.
https://www.sciencedirect.com/science/article/abs/pii/S0925838810031750
Asgar K. (1988). Casting Metals in Dentistry: Past – Present – Future. Journal of Advanced Dental Restoration, 2(1). pp: 33 – 43.
https://deepblue.lib.umich.edu/bitstream/handle/2027.42/67759/10.1177_08959374880020011701.pdf?sequence=2
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