Conclusion of first part of dental materials

Conclusion

1/ Why is better to use dental alloys than pure metals?

- the composition of individual chemical elements or metal in alloy are so, that the properties of whole alloy are the best

2/ When was began to use dental alloys?

-the development of metal alloys arrived at the ending of 19. Century, when Mr. Bing constructed the first inlay°s bridge

3/ What is the main criterium for distribution of dental alloys?

-the main criterium for this distribution and for assigning of ISO standard is hardness of material- the hardness of dental material can characterised by the Vickers and by the Brinell

Conclusion

4/ Write the distribution of dental alloys – according to standard ISO (hardness material)- The alloys with the high content of aurum and platinum ( ISO 1562)

- The alloys with flat content of aurum and platinum, they are the alloys of argentum and palladium ( ISO 8891)

- The alloys of general metals ( cobalt, nickel ) ( ISO 6871)

- The alloys for ceramic burning ( titanium too) ( ISO 9693)

- The alloys as a aluminium bronze

Conclusion

5/ Characterise the properties of gold-platinum, ISO ( ISO 1562).

-they are indicated for large bridges

- they contetnt of aurum 75-90 %, 8-19% pllatinum, 4-10 % palladium, iron, iridium-iridium easy oxidate and make adhesion to the ceramic

- palladium has a high temperature of melting, higher mechanical resistence and lower price

- disadvantage is that palladium discolors the yelllow color of aurum

-typical color of these alloys after oxidation is grey or brown-grey

6/ Write the main characteristic of general metal alloys

- the basic of these alloys is cobalt or nickel

- next they include chrom (min 20-25 %), molybdenum (4%), iron, mangan, wolfram, berilium, titanium, carbon, nitrogen, silicium

- the content of nickel or cobalt, must be minimally 85%

- chrom very increased the hardness of material

- these alloys are indicate for metal construction of removable partial denture, large bridges, metaloceramic construction

- very heavy disadvantage is volumetric contraction by the freezing

Conclusion

7/ What is the galvanism?

- it is a complex of processes, which are result from elektrochemical reactions

- in general, it is rise of electric tension between two electrodes, which are coupled with fluid

-the basic of galvanism is ability of metals to release the cations from surface of metal alloy

8/ How can you characterise the stomatitis galvanica?

-they are clinical manifestation of galvanic stimulus on the mucosa surface

- to the symptoms belong : parestesia, stripes, disorders smack, strog attack of pain neuralgiform character

- it is glossitis or stomatitis 

Conclusion

9/ Describe the chemical chracteristic of cobalt-chrom alloys.-after standard ISO, cobalt alloys have to contain at least 25% Cr, 4% Mo

-reorganisation of atoms into the atomic lattice are the cause of volume expansion

- the casting temperature of cobalt alloys is 1400°C

10/ Explain the mechanical properties of cobalt alloys.

- the Co-Cr dental alloys are very strong and hard, because size of atoms of Co, Cr and Mo is similar (Co 0,25; Cr 0,26; Mo 0,28 mikrometra)

- atomic lattice is very resistant to the external forces

Conclusion

11/ What is the cause of resistance before corrosion.

- protection before corrosion is passive layer, which create by the chrome

- the cobalt alloys are more resistant before corrosion than nickel alloys, because the cobalt alloy dont make easy free cations

12/ Why the nickel alloys support hypersensitievity? -

metal cations react with anions surrounding medium. So they can make macromolekules. These elementary parts from alloys are trasported to the various parts of body.

- solubile compound of Ni-alloys are absorbed very quick and ca make change in structure of DNA and so support damage

Conclusion

13/ Describe the main characteristic of solders for Ni-Cr alloys.

- the solder must have the melting temperature about 100°C decreased than is the melting temperature of origin alloy ( for protect of origin alloy)

- a chemical composition of solder is similar as a composition of origin alloy

- from it results, that the place of connection is not very different from whole cast

- the different composition solder and origin alloy produces the base for galvanic current

Conclusion

14/ How can you describe the fineness of gold alloys?- it is the proportion of gold in gold alloys.- into the fineness belong the rate of platinum too- the main measurement of fineness is thousandth or carats- we distiguish 5 gradus of fineness

15/ Explain the chemical properties of gold alloys.

- they are without change on air and in water

- they are resistant before oxidation, it means they are resistant before corrosion

- they do not react with all of acids ( as a concentrate or as a solutions)

- only one solution , which can dissolve gold alloys, is solution of nitric acid and hydrochloric acid in volumetric rate is 1:3

 

Conclusion

16/ Write the distribution of gold alloys according to hardness of material.

- It is distribution at four classes ( type 1 – 4)

-Type 1 is smooth alloys with high content of gold; type 4 is very strong alloys with high content of pllatinum and palladium

17/ How can be changed the physical properties in gold alloys, when is added palladium and pllatinum?

- palladium and pllatinum provide higher casting temperature, higher mechanical resistance and narrower price- their disadventages is decoloration from yellow on white color -typical color of these alloys after oxidation is grey or grey-brown  

Conclusion

18/ Describe the general properties of titanium.- titanium is very good biocompatible material

- it has a exeptional resistance before corrosion

- it can be use as a bioactive material, which can make adhesion with vital tissue

- It is one metal, which is in nature as binary alloys and in dental prax is used as a pure metal

19/ When began the indutrial production of titanium?

- at 1932y. – as a chemical reaction between TiO2 and calcium or magnesium

- it was in America, Japan and in Russia

Conclusion

20/ Characterise the physical properties of titanium.

-titanium is the metal of steel color with high brightness

- difference from steel is in the weight. It is result from unequal density

- the density of pure titanium is about 4,51 g/cm3 , and Ti – alloys is 4,40 – 4,80 g/cm3 .

- in equation with cobalt alloys, which have density about 8,2 g/cm3 , the weight of the metal titanium cast is less about 43% than weight of similar cobalt cast ( according to large and shape)

Conclusion

21/ What is the main principle of melting titanium ?- the melting of titanium is by the mercury arc in vacuum

- this metod names as a „skull melting“

- other type of melting titanium is during the induction current

- this melting is running in the vacuum with special inert gas, argon (colorless and odorless gas)

22/ Explain the soldering of titanium.

- soldering of titanium parts is by the welding - according to very strong chemical reaction of titanium by the temperature above than 500°C, must be soldering very quick and with high thermal energy, by laser ray

Conclusion

23/ Which type of plaster is the main type for using in dental practice, for making others type of plaster.

- It is plaster of Paris

24/ What is the chemical base of plaster of paris?

- it is anhydric beta polyhydrate of gypsum: CaSO4 . 1/2H2 O

- it is produced by the process of dehydration of gypsum

- chemical reaction is following

CaSO4 .2H2 O CaSO4 . 1/2H2 O + 1/2H2 O

Conclusion

25/ Write the dividing of dental plaster according to chemical properties:-

from chemical view can be divided :

1. plaster of Paris ( soft plaster)

2. hydrocal plaster ( hard plaster)

3. densite plaster ( super hard plaster)

26/ Characterise the hydrocal plaster

- the base of this plaster is the alfa polyhydrate plaster of paris

- this plaster is more hardness than plaster of paris

- chemical and physical properties of both type are similar, but atomic lattice is different

- the beta plaster has a high porosity, but hydrocal plaster has nonporosity crystals

Conclusion

27/ Explain the setting of plaster. - Setting is exotermic reaction, it is hydration:

CaSO4 . 1/2H2 O + 1,5 H2 O CaSO4 .2H2 O + heat

- by the setting is mixed the powder with water

- by the setting create the volume expansion- the condition of this expansion is mashing of rising crystals- the name of this expansion is hydroscopic expansion

28/ How can be accelerated the setting of plaster?

- accelerating of setting can be secured with the :

- hot water

- chemical regulators of setting

- change of mixing speed (intensive mixing)

- changen of mixing rate

Conclusion

29/ Why is important the hydroscopic expansion at the setting of plaster? - it is necessary for compensation of contraction of metal alloys at the cooling

30/ What is the base for determination of plaster hardneess?

-the hardness is depend on character , large and shape of atomic crystals

- the plaster of paris is adorned with a crystals in shape of needles , this atomic lattice need for mixing a lot of water and from physical properties it is soft type of plaster

- superhard plaster is squars as a shape of atomic lattice and for mixing need a very little volume of water

Conclusion

31/ Explain the mixing rate W/P (water/powder).

it is volume of water to content of powder, which is necessary for making slurry plaster matter, for making prosthetic models

32/ Which type of plaster is the best for dental use and why?

- it is superhard plaster, type IV

- mixing rate is V/P 18,5-24

- hardness is 60 MPa

- volume expapnsion at the setting is 0,1%

-according to high hardness and mechanical resistance it is a good type for working models at fixed bridge and crown

Conclusion

End.