types of investment bonds
There are three types of investment material the refectory material in three types are common is silica but the binder is different so depending upon the type of binder used .
There are three types of investment material first is gypsum bonded investment material in which the binder used is gypsum product that is dental stone this kind of investment is ideal for gold alloys and that they can withstand the temperature up to 700 degree Celsius.
Gypsum bonded investment classified into three types:-
Type one is used to preparation in inlays and crowns and the compensation mold for casting shrinkage in type one gypsum bonded investment is through thermal expansion of the investment material so type one is associated with thermal expansion of investment material while type two also used for the preparation of inlays and crowns but the compensation of casting shrinkage is by hygroscopic expansion and type three is suitable for the partial denture with alloys
Composition of gypsum bonded investment:-
There are three basic constituents the refectory material, binder, and chemical modifiers
the refectory material is in the form of silica mainly silicon dioxide
the form of silica may be quartz, tridymite, cristobalite or a mixture of all these
the binder which used in gypsum bonded investment is dental stone or alpha calcium sulfate hem hydrate this bonded bind together to form a coherent mass the chemical modifiers which are used are sodium chloride and boric acid potassium sulfate graphite, magnesium oxide all these chemical modifiers modify physical properties of the investment material.
The silica or the refectory material is in a concentration of 60 to 50% the binder is an alpha Hema hydrate in a concentration of 30 to 35% and chemical modifiers 5% are used.
The function is each constituent
The gypsum binder or alpha Hema hydrate or dental stone it binds together the investment material and it imparts strength to the mold and this gypsum bonder it contributes to mold expansion by pausing sitting expansion now when gypsum product or alpha Hema hydrate is heated at very high temperature it has a property to shrink and that fracture but what's happens above 700 °C there slight expansion in the gypsum material but this expansion is very low in comparison to the high amount of contraction which occurs also with contraction there is a release of sulfur dioxide gases these gases react with the metal to form silver sulphide and copper sulphide.
The second constituents of the gypsum investment are the refectory material like silica.
silica is used in the form of quartz and cristobalite, silica it regulates the thermal expansion and it contributes to the mold expansion.
there are four forms of silica is cristobalite and fused quartz these, when heated up to transition temperature there is a change in the crystalline structure of it.
low quartz which is an alpha form at 575 °C may turn into high quartz which is beta form
low cristobalite which is an alpha form at 200 to 270°C form high cristobalite or the beta form
so when this transition of alpha to beta form occurs there is a decrease in the density of the material and increased in the volume and linear expansion of the material.
now this beta form is stable just about the transition temperature it's cool below the transition temperature it returns back to its alpha form.
the third component of the gypsum bonded investments are the chemical modifiers which may be reducing agent modifying chemicals are the coloring agents the reducing agent they reduce the exercises on the metal and it provides or non-oxidizing atmosphere in the mold the reducing agent which are used are carbon and copper powder the modifying chemicals which are used in the gypsum bonded investments are boric acid and sodium chloride which they regulate the sitting expansion and the sitting time and it prevents the shrinkage of the mold about 300°C.
setting time
the setting time of gypsum bonded investments according to the to ADA specification number two the setting time of gypsum bonded investments is about 5-25 minutes.
the affecting sitting time is the manufacturer process mixing time and mixing rate and water powder ratio and temperature and accelerators and retarders which are added to it.
sitting expansion
sitting expansion of gypsum bonded investments has the purpose of enlarging the mold and this enlarging mold compensate for the casting shrinkage.
there are three types of sitting expansion: -
1. normal sitting expansion.
2. hydroscobic sitting expansion.
3. thermal sitting expansion.
in normal sitting expansion when gypsum product is mixed with silica there's an expansion which is more than what caused by gypsum alone this is called normal sitting expansion, there are interlocking and intermeshing between gypsum and silica.
the ADA specification number two:-
the normal sitting expansion should be a maximum of 0.5% and this can be regulated using accelerators and with retarded of sitting.
the second type of sitting expansion is hydroscobic sitting expansion in which the investment material is allowed to set in contact with water so when these water molecules you can see cause outward growth of the crystals resulting in hydroscobic expansion which is 1.2 - 2.2% acceptable.
the factors affecting the sitting expansion:-
-composition: if the particles size is very small there's increased in the hydroscobic sitting expansion and alpha Hema hydrate show more sitting expansion than beta Hema hydrate and then increase in the quantity of silica increases the hydroscobic sitting expansion then increase the water powder ratio causes decrease in the hydroscobic sitting expansion.
-temperature: if the temperature in which the material is immersed is more if the water is hot there is a decrease in the surface tension causes increase expansion.
-time of immersion: if the investment material is immersed in water before the initial set there is increased hydroscobic sitting expansion.
-spatulas: if there's decrease maturation there is a decrease in the hydroscobic sitting expansion.
-shelf life: older products show decreased in height sitting expansion.
-confinement: if you use any confinement for example wall of the container decrease the hydroscobic sitting expansion.
-water: amount of water which is added to the investment material if this water is more this results in increased sitting expansion.
The third type of sitting expansion is the thermal expansion which depends on the amount and type of silica, the thermal expansion is 1-1.6 %.
-increases in the water powder ratio causes a decrease in the thermal expansion
-sodium chloride and potassium chloride and lithium chloride it increases the thermal expansion
the properties of gypsum bonded investment:-
-the first properties are strength, the compressive strength after two hours of sitting should not be less than 2.5 MPa.
- porosity increases in the gypsum crystals reduced porosity also decreases in the Hema hydrate causes more amount of gauging water used so this causes more porosity so ideally there should not a decrease water powder ratio so if the water is used is less is it causes less porosity and if powder use is more this causes less porosity.
- a mixture of coarse particles whit fine particles reduces the porosity.
- fineness:- fine particles of the investment material results in decreased surface irregularities.
- storage:- the investment material should be stored in airtight containers to prevent contamination.
there is alpha hydroscobic plus thermal inlay casting investment material: -
this type of investment is used as hydroscobic or thermal type it contains mainly quartz and cristobalite mixture when used in hydroscobic technique this investment material is heated up to 482 °C and immersed in water when used thermal technique it is heated to 649°C without immersed in water.
there is another type of investment material that is used for casting higher melting alloys, the alloys which have a very high melting point.
these alloys have melting temperatures at around 850 - 1100°C we have already discussed that about 700°C the gypsum bonded investment they disintegrate so in this cases the investment material should be used with different binder these binder are either phosphor of phosphate or silica and the names of the investment material are phosphate bonded investment and the silica bonded investments.
The second type is the phosphate bonded investment material in which the binder is phosphate and it's ideal for cobalt-chromium alloys and this phosphate bonded investment material can withstand even higher temperatures.
it consists of three components:-
-the ammonium diacid phosphate this ammonium diacid phosphate gives strength to the investment material this ammonium diacid phosphate soluble in water and provides phosphate ions and it reacts with silica at high temperature to increase the strength at casting temperature.
-the silica is the refractory material.
- magnesium oxide is there which reacts with phosphate ions.
So this ammonium diacid phosphate reacts magnesium oxide and at room temperature, the ammonium diacid phosphate it combines with magnesium oxide and this combination gives the green and strength of the material.
ammonium diacid phosphate is used at very high temperatures so that the remaining part of it reacts with silica at a higher temperature to form silica phosphate this silicon phosphate gives strength at a higher temperature.
these phosphate bonded investment materials are supplied with a special liquid which is silica sol in the water this silica sol helps in thermal expansion.
Then the third type of investment material is the silica bonded investment material which bonded by silica and it's ideal for base metal alloys partial denture this silica bond with bonded can be used as an alternative to phosphate bonded investment .
it consists of: the silica bonded investment material contains silica bonder which is derived either from ethyl silicate or aqueous dispersion colloidal silica or sodium silicate.
ethyl silicate has inflamed components so most common binders are derived from either sodium silicate or colloidal silica.
this silica bonded investment material is provided with two bottles one containing a diluted hydrochloric acid and other containing water-soluble silica.
the solution of sodium silicate.
just before use an equal quantity of these two solutions are mixed so that hydrolysis takes place and freshly formed silicic acid you can get other important ingredient systems are the alloys which do not contain noble metals these alloys have high fusion and melting temperature so special investment materials such as zircate investment and magnesia investment are used and soldering investment is used for restoration whose parts are soldered for example an RPD the clasps are soldered it so this type of soldering investment consists of quartz and calcium sulfate Hema hydrate these investment materials have low sitting expansion and low thermal expansion so that the assembled parts do not shift during the sitting and also these have final particles size so here we complete with the entire discussion of dental casting investment material get thorough with this topic.
Then the third type of investment material is the silica bonded investment material which bonded by silica and it's ideal for base metal alloys partial denture this silica bond with bonded can be used as an alternative to phosphate bonded investment .
There are three types of investment material first is gypsum bonded investment material in which the binder used is gypsum product that is dental stone this kind of investment is ideal for gold alloys and that they can withstand the temperature up to 700 degree Celsius.
Gypsum bonded investment classified into three types:-
Type one is used to preparation in inlays and crowns and the compensation mold for casting shrinkage in type one gypsum bonded investment is through thermal expansion of the investment material so type one is associated with thermal expansion of investment material while type two also used for the preparation of inlays and crowns but the compensation of casting shrinkage is by hygroscopic expansion and type three is suitable for the partial denture with alloys
Composition of gypsum bonded investment:-
There are three basic constituents the refectory material, binder, and chemical modifiers
the refectory material is in the form of silica mainly silicon dioxide
the form of silica may be quartz, tridymite, cristobalite or a mixture of all these
the binder which used in gypsum bonded investment is dental stone or alpha calcium sulfate hem hydrate this bonded bind together to form a coherent mass the chemical modifiers which are used are sodium chloride and boric acid potassium sulfate graphite, magnesium oxide all these chemical modifiers modify physical properties of the investment material.
The silica or the refectory material is in a concentration of 60 to 50% the binder is an alpha Hema hydrate in a concentration of 30 to 35% and chemical modifiers 5% are used.
The function is each constituent
The gypsum binder or alpha Hema hydrate or dental stone it binds together the investment material and it imparts strength to the mold and this gypsum bonder it contributes to mold expansion by pausing sitting expansion now when gypsum product or alpha Hema hydrate is heated at very high temperature it has a property to shrink and that fracture but what's happens above 700 °C there slight expansion in the gypsum material but this expansion is very low in comparison to the high amount of contraction which occurs also with contraction there is a release of sulfur dioxide gases these gases react with the metal to form silver sulphide and copper sulphide.
The second constituents of the gypsum investment are the refectory material like silica.
silica is used in the form of quartz and cristobalite, silica it regulates the thermal expansion and it contributes to the mold expansion.
there are four forms of silica is cristobalite and fused quartz these, when heated up to transition temperature there is a change in the crystalline structure of it.
low quartz which is an alpha form at 575 °C may turn into high quartz which is beta form
low cristobalite which is an alpha form at 200 to 270°C form high cristobalite or the beta form
so when this transition of alpha to beta form occurs there is a decrease in the density of the material and increased in the volume and linear expansion of the material.
now this beta form is stable just about the transition temperature it's cool below the transition temperature it returns back to its alpha form.
the third component of the gypsum bonded investments are the chemical modifiers which may be reducing agent modifying chemicals are the coloring agents the reducing agent they reduce the exercises on the metal and it provides or non-oxidizing atmosphere in the mold the reducing agent which are used are carbon and copper powder the modifying chemicals which are used in the gypsum bonded investments are boric acid and sodium chloride which they regulate the sitting expansion and the sitting time and it prevents the shrinkage of the mold about 300°C.
setting time
the setting time of gypsum bonded investments according to the to ADA specification number two the setting time of gypsum bonded investments is about 5-25 minutes.
the affecting sitting time is the manufacturer process mixing time and mixing rate and water powder ratio and temperature and accelerators and retarders which are added to it.
sitting expansion
sitting expansion of gypsum bonded investments has the purpose of enlarging the mold and this enlarging mold compensate for the casting shrinkage.
there are three types of sitting expansion: -
1. normal sitting expansion.
2. hydroscobic sitting expansion.
3. thermal sitting expansion.
in normal sitting expansion when gypsum product is mixed with silica there's an expansion which is more than what caused by gypsum alone this is called normal sitting expansion, there are interlocking and intermeshing between gypsum and silica.
the ADA specification number two:-
the normal sitting expansion should be a maximum of 0.5% and this can be regulated using accelerators and with retarded of sitting.
the second type of sitting expansion is hydroscobic sitting expansion in which the investment material is allowed to set in contact with water so when these water molecules you can see cause outward growth of the crystals resulting in hydroscobic expansion which is 1.2 - 2.2% acceptable.
the factors affecting the sitting expansion:-
-composition: if the particles size is very small there's increased in the hydroscobic sitting expansion and alpha Hema hydrate show more sitting expansion than beta Hema hydrate and then increase in the quantity of silica increases the hydroscobic sitting expansion then increase the water powder ratio causes decrease in the hydroscobic sitting expansion.
-temperature: if the temperature in which the material is immersed is more if the water is hot there is a decrease in the surface tension causes increase expansion.
-time of immersion: if the investment material is immersed in water before the initial set there is increased hydroscobic sitting expansion.
-spatulas: if there's decrease maturation there is a decrease in the hydroscobic sitting expansion.
-shelf life: older products show decreased in height sitting expansion.
-confinement: if you use any confinement for example wall of the container decrease the hydroscobic sitting expansion.
-water: amount of water which is added to the investment material if this water is more this results in increased sitting expansion.
The third type of sitting expansion is the thermal expansion which depends on the amount and type of silica, the thermal expansion is 1-1.6 %.
-increases in the water powder ratio causes a decrease in the thermal expansion
-sodium chloride and potassium chloride and lithium chloride it increases the thermal expansion
the properties of gypsum bonded investment:-
-the first properties are strength, the compressive strength after two hours of sitting should not be less than 2.5 MPa.
- porosity increases in the gypsum crystals reduced porosity also decreases in the Hema hydrate causes more amount of gauging water used so this causes more porosity so ideally there should not a decrease water powder ratio so if the water is used is less is it causes less porosity and if powder use is more this causes less porosity.
- a mixture of coarse particles whit fine particles reduces the porosity.
- fineness:- fine particles of the investment material results in decreased surface irregularities.
- storage:- the investment material should be stored in airtight containers to prevent contamination.
there is alpha hydroscobic plus thermal inlay casting investment material: -
this type of investment is used as hydroscobic or thermal type it contains mainly quartz and cristobalite mixture when used in hydroscobic technique this investment material is heated up to 482 °C and immersed in water when used thermal technique it is heated to 649°C without immersed in water.
there is another type of investment material that is used for casting higher melting alloys, the alloys which have a very high melting point.
these alloys have melting temperatures at around 850 - 1100°C we have already discussed that about 700°C the gypsum bonded investment they disintegrate so in this cases the investment material should be used with different binder these binder are either phosphor of phosphate or silica and the names of the investment material are phosphate bonded investment and the silica bonded investments.
The second type is the phosphate bonded investment material in which the binder is phosphate and it's ideal for cobalt-chromium alloys and this phosphate bonded investment material can withstand even higher temperatures.
it consists of three components:-
-the ammonium diacid phosphate this ammonium diacid phosphate gives strength to the investment material this ammonium diacid phosphate soluble in water and provides phosphate ions and it reacts with silica at high temperature to increase the strength at casting temperature.
-the silica is the refractory material.
- magnesium oxide is there which reacts with phosphate ions.
So this ammonium diacid phosphate reacts magnesium oxide and at room temperature, the ammonium diacid phosphate it combines with magnesium oxide and this combination gives the green and strength of the material.
ammonium diacid phosphate is used at very high temperatures so that the remaining part of it reacts with silica at a higher temperature to form silica phosphate this silicon phosphate gives strength at a higher temperature.
these phosphate bonded investment materials are supplied with a special liquid which is silica sol in the water this silica sol helps in thermal expansion.
Then the third type of investment material is the silica bonded investment material which bonded by silica and it's ideal for base metal alloys partial denture this silica bond with bonded can be used as an alternative to phosphate bonded investment .
it consists of: the silica bonded investment material contains silica bonder which is derived either from ethyl silicate or aqueous dispersion colloidal silica or sodium silicate.
ethyl silicate has inflamed components so most common binders are derived from either sodium silicate or colloidal silica.
this silica bonded investment material is provided with two bottles one containing a diluted hydrochloric acid and other containing water-soluble silica.
the solution of sodium silicate.
just before use an equal quantity of these two solutions are mixed so that hydrolysis takes place and freshly formed silicic acid you can get other important ingredient systems are the alloys which do not contain noble metals these alloys have high fusion and melting temperature so special investment materials such as zircate investment and magnesia investment are used and soldering investment is used for restoration whose parts are soldered for example an RPD the clasps are soldered it so this type of soldering investment consists of quartz and calcium sulfate Hema hydrate these investment materials have low sitting expansion and low thermal expansion so that the assembled parts do not shift during the sitting and also these have final particles size so here we complete with the entire discussion of dental casting investment material get thorough with this topic.
Then the third type of investment material is the silica bonded investment material which bonded by silica and it's ideal for base metal alloys partial denture this silica bond with bonded can be used as an alternative to phosphate bonded investment .