•In the Name of Allah Who is the most Merciful and the most •Beneficial
MIXING TECHNIQUES OF FIVE DENTAL PRODUCTS • By Najib Ahmad Dawar Roll #: 66 Khyber College Of Dentistry Peshawar (Pakistan)
• The Process by which two or more components are mixed together in order to get a homogeneous mix. e.g.• Mixing of powder & liquid components,• Mixing of two pastes &• The mixing of paste & liquid components. Wor king Time• The time available for mixing and manipulating a material.
Mixing Techniques Of Five DentalProducts Which I Covered InPresentation 1 Gypsum 2 Glass Ionomer Cement 3 Alginate 4 Zinc Phosphate Cement 5 Zinc Polycarboxylate Cement
1-Gypsum mixinG:• Mixed by two pr ocess: • Manual Pr ocess ( Hand Mix) • Mechanical Pr ocess
Requirements:Robber Bowl, Spatula, Water & Powder.Pr ocedure:: • Take a measured quantity of water in the r ubber bowl • Add powder to the Bowl.
• Settle it for 30 sec with out spatulation.• This technique minimize the chances of Air interruption.• Then spatulation starts and wipe the powder with the inside of the bowl with a spatula to insure wetting of the powder and minimizes the Air entrapped.• Spatulation continues until all the powder is uniformly wetted and mix..• Mixing time is 1min at 2rev/sec.• Two setting Times:• Initial setting time• Final setting time
• Mechanical mixing is done under vacuum mixer.• It gives stronger and denser Mix.• No chances for Air to entrap in the Mix.
Precautions:• The mixing equipment must be clean.• Flexible plastic bowl should be used.• Wide bladed spatula should be used.• No air should be trapped in the Mix.• The material should be used as soon as possible after mixing since its viscosity increases and will reach a stage where the material is unworkable.
2-GLAss iOnOmER CEmEnT mixinGRequir ements:Powder & Liquid, Glass slab or Non absorbable Treated paper pad & plastic or ceramic spatula.• Consists of Powder & liquid• If the liquid is the viscous carboxylic acid then P/L ratio of 1.3:1 to 1.35:1 is used,• If the liquid is water then W/P ratio 3.3:1 to 3.4:1 is used.• The P/L ratio also depends on application of the cements… • lining consistency • luting consistency
• For lining consistency the P/L ratio is 3:1• And• For luting consistency the P/L ratio is 1.5:1• Powder should be divided into two equal parts….• Half of the powder will be carried and mixed with liquid with a stiff spatula so that powder is covered with liquid..• After this the 2nd half is added and keep on mixing. Until get the desired consistency.• mixinG TimE:• 30-60sec.• WORKinG TimE:• 2 minutes• Immediately carry to the prepared cavity b/c the working time after mixing is only 2min.
Encapsulated products are usually mixed for 10sec inmechanical mixer and dispensed directly onto thetooth restoration.
Precautions:• There should be no evaporation of water.• A good mix should have a glassy surface, this indicates the presence of poly acids which ensures bonding with the tooth, but a mix with a dull surface is discarded as it indicates prolong mixing which reduces the adhesion.• If the liquid contains polyacids, it should not be placed in a refrigerator as it becomes very viscous.• The glass slab should not be below the dew point, as moisture may condense on the slab and changes the acid water balance.• Never use stainless steel spatula as it is composed of metals which may react with Glass Ionomer cement .Always use plastic or ceramic spatula…
3-ALGinATE mixinG• Requirements: A clean flexible plastic Bowl,Wide bladed spatula and a Plastic tube containing water• Alginate are supplied as powder which are mixed with water• A plastic measuring cylinder is used for the correct volume of water• An alginate powder is also supplied in small sachets.• Each sachet are sufficient for one impression.
• After proportioning the water and powder are mixed together in a plastic mixing bowl using a wide bladed spatula• Rapid spatulation is required to give thorough mixing and an alginate sol of creamy consistency is formed.• Then pour a water in the measuring cylinder up to point 1 leaving 1 part in the cylinder…• Mixing is started with a stirring motion to wet all the powder.• Once the powder has been moistened then rapid spatulation with the side should be done…
• Spatulation with sides will help to: • Remove most of the air bubbles… • Dissolve alginate from the surface and complete their dissolution.• After the material gain creamy consistency …stop spatulation…• Mechanical devices are also available for spatulation alginate. their main advantage are… • Speed • Convenience • Elimination of human variables.
• Pr ecautions::• Rapid spatulation is required• Spatulation with the sides is done• Correct volume of water and powder is required.• The water powder ratio specified by the manufacturer should be used.
4-ZinC phOsphATE CEmEnT mixinGMixing Requirements:Large Narrow Bladed Stainless steelspatula, Cooled Thick Glass slab,mixinG::• Its Mixing is an exothermic process.• Incorporate the proper amount of powder into the liquid slowly on a glass slab to attain desired consistency… • For Cavity Lining P/L is 3.5:1 • For luting a more thinner
• We divide the powder into increments Smaller, larger and then smaller for proper dissipation of heat.• 1st incorporate a small increment of powder into liquid minimum heat is evolved.• Then larger increment of powder is added to further saturate the mix.• Finally a smaller increment of powder is added to achieve the desired consistency of cement.
• The mix procedure begins with a Small one, then larger one and ends with a small one to compensate heat and to achieve slow neutralization.• The reaction is neutralization type.• Always use thick glass slab to slow down the process of temperature change• For increasing the working time we use cold glass slab or frozen glass slab.• Mixing Time:• 60-90 sec are enough for mixing.• Working Time luting -2.5 minutes lining – 2 minutes
• Mix over a large area to dissipate the generated heat as this heat will accelerate the setting time.• The cap from the liquid bottle should be removed enough to dispense sufficient liquid for one mix. ,and then replaced immediately
• If the liquid is placed open for a long time the water will be either lost or gained depending upon the humidity. which will alter the setting characteristics and physical properties.
Mixing::• Available as powder and liquid or precapsulated form.• Powder is shaken gently• Powder is dispensed on paper pad or glass slab• A bulk of powder i.e. 90% Of the powder is added to the Liquid immediately so that the liquid particles do not evaporate.• P/L ratio is 1.1,1.5:1 or 2:1and it can be increased according to the demand.• The remainder of the powder is mixed in order to achieve the desired consistency.• It should be spread over a small area.
• It should be used immediately after mixing b/c working time is only 3min at 22 centigrade.• Working time can be increased by using a cool glass slab.• Normally it ranges b/w 2.5-6 mins but can be increased up to 10-15 mins by using chilled glass slab.