Zinc phosphate cement
Zinc phosphate cement, or phosphate cement for short, is one of the most frequently used materials in dentistry . The cement is mixed from a powder (zinc oxide and 10% magnesium oxide) and a liquid (orthophosphoric acid H 3 PO 4 ) and, after setting, results in a crystalline zinc phosphate . In dentistry, cement is used to fix crowns (fixation cement ), as an underfill as a thermal and chemical insulator and as a temporary filling.
Outside of dentistry, phosphate cement is also used as an insulating coating and as a fixation for wire resistors .
composition
Phosphate cement is made up of two components: a cement powder and a liquid.
- The cement powder has the following components
- ≥ 80–90% zinc oxide (ZnO)
- ≥ 10% magnesium oxide (MgO)
- ≥ 6% calcium fluoride (CaF 2 )
- ≥ 4% silicon dioxide (SiO 2 )
- ≥ 1% aluminum oxide (Al 2 O 3 )
- The liquid consists of 45-64% phosphoric acid (orthophosphoric acid), supplemented with aluminum and zinc buffers, to which Ca, Mn, Mg and Zn oxides have been added to reduce the setting speed.
processing
For dental processing, the cement powder is mixed with the liquid on a cool and dry surface (usually a glass plate - on the rough side of the glass plate) with a spatula made of corrosion-resistant steel, agate or ceramic. The processing temperature should be room temperature (18–20 ° C).
The mixing ratio of powder to liquid depends on the degree of fineness of the grinding ( grain size ) of the powder, the water content of the acid and the intended use as cement or underfill. The powder / liquid ratio influences not only the consistency, but also the mechanical strength, the solubility and the film thickness of the cement. The tooth must be blown dry before the cement is inserted.
A creamy consistency is required for use as a luting cement so that the crown, bridge or inlay can be pressed completely onto the prepared tooth without raising the bite. The consistency can be checked with the "tick test" by pulling a tip out of the mass with the spatula. The correct underfill consistency is achieved when the resulting tip turns into a tick and does not sink back into the mass. The fastening consistency is achieved when the drawn tip slowly sinks back into the mass. Usually the mixed cement is poured into the crown to be cemented. After inserting it with cement, the patient bites (on a cotton roll) for a few minutes (4-6 minutes). During this time the cement sets. Then the cement residues are removed.
As an underfill, the cement should be processed with a consistency of putty, i.e. mixed with more powder. The putty can be pressed into the smallest of cavities by tamping pressure without containing air pockets.
properties
Zinc phosphate cement is the classic dental cement par excellence (conventional luting cement). In recent years, newer adhesive cements on a different chemical basis have been added (e.g. glass ionomer cement ), but have not displaced the classic phosphate cement , which continues to assert itself on the dental market with its simple and safe processing and its good price-performance ratio. Zinc phosphate cement has only a low flexural strength and does not stick to the dentin (it is a cement and not an adhesive).
Zinc phosphate cement has a high compressive strength, a low film thickness, minimal shrinkage and thermal expansion and is biocompatible. Compared to other luting materials such as glass ionomer cement or composites, zinc phosphate cement is less sensitive to moisture. The excess produced when cementing dental restorations can be easily removed.
Zinc phosphate cement has a high adhesive capacity on teeth, on metal, or on zirconium oxide .
Despite the strong acid, the zinc phosphate cement does not damage the pulp (or the dental nerve) during the setting phase. It is therefore used as an underfill under composite fillings to protect the pulp.
Well-known dental brands in Germany for zinc phosphate cement are Harvard-Zement and Hoffmann's Cement . Otto Hoffmann invented this cement in 1892 and had it patented. Until the beginning of the First World War he had a worldwide monopoly with his cement.
Manufacturing
The red zinc oxide is burned into solid clinker with flux , then rubbed into powder and oxidized (roasted) in the air . Metal oxides (iron and manganese oxide) are added to the white powder to achieve a tooth color. Phosphoric acid is obtained from minerals containing calcium phosphate using sulfuric acid.
history
Initially intended as a filling material, the Dresden Sylvestre Augustin Rostaing de Rostagni (1794–1866) and his son Charles Augustin Rostaing (* 1831) developed zinc phosphate cement, which they brought onto the market in 1858 and which was ultimately used to fasten crowns, bridges and inlays has been. After Sylvestre Augustin Rostaing did not pass on his recipe, the chemist, inventor and entrepreneur Carl Franz Otto Hoffmann set about recreating the dentin agent. He brought the fastening material onto the market as Hoffmann's phosphate cement. The Dentinagene mixture was also marketed as Harvard cement by the Berlin Harvard Dental Company from 1892 onwards .
Individual evidence
- ^ D. Raab: Fixation of all ceramic restorations - the advantages of cementation. DENTAL INC 2008: March / April, pp. 50-53.
- ^ D. Raab: Fixation of all ceramic restorations - the advantages of cementation.全 瓷 修复 的 粘接 - 水门汀 的 优势. DENTAL INC Chinese Edition 2008: Reprint.
- ↑ D. Raab: Conventional cementation of all-ceramic restorations. In: Zahn Prax. 12, 2009, pp. 84-86.
- ↑ Bernd Reitemeier: Introduction to dentistry . In: Tooth-Oral-Maxillofacial Medicine . Georg Thieme Verlag, Stuttgart, New York 2006, ISBN 3-13-139191-X , p. 5 ( limited preview in Google Book search).
- ↑ The pioneer of the dental industry , Hoffmann's. Retrieved February 26, 2016.
- ^ Fritz Ullmann, Wolfgang Gerhartz, Y. Stephen Yamamoto, F. Thomas Campbell, Rudolf Pfefferkorn, James F. Rounsaville: Ullmann's encyclopedia of industrial chemistry . VCH, 1987, ISBN 0-89573-158-4 ( limited preview in Google book search).
- ↑ The Harvard company ( Memento of the original from February 27, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. . Retrieved February 26, 2016.
