ZINC PHOSPHATE CEMENT - CLASSIFICATION,COMPOSITION,SETTING REACTION,MANIPULATION

 Zinc Phosphate Cement

• ADA Specification number of Zinc Phosphate is 96.

• Zinc phosphate cement was originally developed more than 100 years ago and was extremely popular during most of the twentieth century.

CLASSIFICATION:

TYPE 1 : Fine grained for luting

Type 2: medium grained for luting and restorative purpose.

COMPOSITION:

• Zinc Phosphate cement contains  powder and liquid containers which comes separately.

powder: zinc oxide 75%,magnesium oxide 13%,silicone dioxide-2%,bismuth trioxide-0.1%

liquid: phosphoric acid 38-59% in water 30-50% and is buffered with aluminium and zinc salts to control the ph.,zinc- 7%,aluminium-2%

CHEMISTRY AND  SETTING :

REACTION TYPE- ACID-BASE REACTION

SETTING REACTION:

Phosphoric acid dissolve in zinc oxide react with aluminum phosphate to form zinc aluminophosphate gel on undissolved zinc oxide particles 

set cement: unreacted zinc oxide particles gets encased in amorphous matrix of zinc aluminophosphate.

• loss of water from liquid increases the setting reaction
• addition of water during mixing accelerate reaction 

MANIPULATION:

• Powder should be divided into increments and added to liquid
• Brisk spatulation using considerable area of glass slab with each increment spatulated for 15-20 second
• Mixing time 1-5 to 2 minutes 
• Use of properly cooled thick glass slab will dissipate heat. 

METHODS TO INCREASE THE WORKING TIME OF CEMENT 

FROZEN SLAB TECHNIQUE:

•  Its, employed to increase the working time ,as zinc phosphate cement is a exothermic reaction in order to dissipate the heat and to cool down this technique is followed.
• In this method,a glass slab is cooled in refrigerator at 6 degree celsius or freezer at minus 10 degree celsius
• Employed during cementation of multiple orthodontic treatment ,long span bridges ,where longer working time and shorter setting time is required
• Powder and liquid are dispensed onto the slab without removing condensed moisture
• Amount of poder incorporated in this method is 50 to 75 %more than normal
• Lower viscosity cement facilitates the setting of multiple unit cast restoration.
• However ,incorporation  of condensed moisture into mix counteracts the higher powder to liquid ratio,hence compressive and tensile strength decreases 
• Working time is increased by 4 to 11 minutes 
• Setting time is shortened by 20 to 40%

POWDER LIQUID RATIO: 1.5g To 0.5mL

CLASSIFICATION OF CEMENT : 

1. STRENGTH; STRONG,WEAK
2. USES : RESTORATIVE,LUTING,PULP PROTECTION
3. PRIMARY COMPOSITION: PHOSPHATE,PHENOYLATE,RESIN BASED,POLYCARBOXYLATE 

BIOLOGICAL PROPERTIES

Pulp response is moderate pH IS 2 initial and 5 after luting.

ADVANTAGE:

• High compressive strength 120 mpa at 24 hours
• does not dissolve in oral fluid
• good thermal insulation ability

DISADVANTAGE:

• The molecular size of phosphoric acid is smaller than that of dentinal tubule,hence it can cause an adverse pulpal reaction when used in deep restoration

AIM OF THIS POST : 

zinc phosphate cement: classification,composition,setting reaction,methods to increase working time of cement , frozen glass slab, biological properties ,advantage and disadvantages of zinc phosphate cement .

Hope you all got enlightened about zinc phosphate if this post helped you do let me know in the comment section below 

For any product endorsement contact : stencildent@gmail.com.

                              THANK YOU