They serve for the relief of the impressions And theprincipal constituent one is the sulfate of calciumSemi-hydrated β With the incorporation of additives.It is in the habit of being made of white color. Fig.5
For the model construction of study preparation ofthe muffles in the construction of the total protheses. Fig.6
It serves for the model construction, which they mustpresent high resistance to the compression and to thegraze. This plasters they are used for modelsantagonists or for mobile protheses. Fig.7
For the model construction, The resistance fromwhich to the compression And to the graze it isparticularly high. Minimal quantity of H2O, they arethe resistant mas and the dense mas of all. Fig.8
There are extra hard of high hardness for stumps, Butwith an expansion mas raised still. And also formetallic protheses. Fig.9
All the plasters have the same chemical formula his difference: It takes root principally in his physical properties. In the Stucco they are comparatively irregular and porous. In others they are denser and of more regular form. This difference allows to have the same consistency with less water in the cements stone and of great resistance, That in the stucco.
Advantages DisadvantagesThey do not need sophisticated They need a place fresh air to beequipment for his manipulation. stored and without dampness.Handling them adequately, there The properties are critical to obtaincan be achieved a complete, the physical results of agreementsmooth model and without with the type.bubbles.It is an economic product that one A vibrated excessive or inadequatefinds easily in the dental mechanic favors that the plasterwarehouse. catches bubbles.It is compatible with all thematerials of impression ofodontologic use.
Material and equipment to realizethe manual mixture of the plasterPlaster Manometer Cup SpatulaFig.10 Fig.11 Fig.12 Fig.13
To place in the container the necessary water, according tothe quantity of mixture that is needed toprepare, remembering that to minor quantity of water for acertain quantity of powder, major hardness of the plaster assoon as it has set.To beat energetically 1 min manually or 20-30 seconds withfood-mixer to the emptiness of plasters, the componentswithout adding not even any more powder any more doesnot even water down, since this would cause weakness inthe plotted material.
To avoid the incorporation of air bubbles during themixture, to prevent the porosity, which he carries to theappearance of weak points and superficial irregularities.Not to change the relation plaster waters down oncebegun the mixture, because a disorder takes place in thecrystals. If one adds water later they affect the cores ofcrystallization, since different stages of hardening takeplace and since not the whole mass crystallizes at the sametime, tensions are generated.
After finished the espatulado, places the materialbefore frague in the place where there is claimed that ithardens, once fact this has to be kept the immobility ofthe same one, since any movement during the work ofplotted causes faults and weak zones.It is suitable to hope that the plaster has set completelybefore submitting it to any manipulation.
To the 48 hrs of plotted it is considered that the plasterhas acquired his maximum hardness andresistance, being variable the time according to therelative dampness of the environment. Nevertheless forcommon uses one can work on the plaster an hour afterthis one has set, remembering that the resistance isincreasing in agreement with the step of the followinghours.