ZINC PHOSPHATE CEMENT.pptxptesentqtion cons

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1. ZINC PHOSPHATE CEMENT 1

2. CONTENTS Introduction Composition Mode of supply Types Setting reaction Manipulation Setting time Properties Advantages Disadvantages 2

3. INTRODUCTION ADA specification n o. 96 O ldest luting cement introduced way back in 1800s by Dr. Otto Hoffmann. G old standard for comparative studies in dental cements. Earlier, some researchers have regarded this cement as the first “self-etch” cement due to its capability of demineralizing the dentin surface. 3

4. COMPOSITION POWDER Zinc oxide: Approximately 90.2% Magnesium oxide: 8.2% (reduces temperature of calcination process during manufacture) Other oxides: 1.6% (alter the working characteristics and final properties of the cement) Bismuth trioxide (imparts smoothness to the freshly mixed cement mass) Silicon dioxide (acts as inactive filler and aids in calcination process during manufacture) 4

5. MANUFACTURE The ingredients are heated together at a temperature of 1000°C–1300°C for several hours. M agnesium oxide - white color to the cement besides improving the strength. Magnesium oxide and silica - help in the calcination process during manufacturing. Bismuth trioxide - prolongs the setting time. 5

6. LIQUID 1. Aqueous solution of phosphoric acid: 50%–60% (main ingredient) Free acid: 38.2% Combined with Zn and Al: 16.2% 2. Aluminum and zinc: Up to 10% (act as buffers and partially neutralize phosphoric acid, thus tempering the reactivity of the liquid) 3. Water (33%) 6

7. MODE OF SUPPLY Powder and liquid 7

8. TYPES 1. Type I—Fine grained: Film thickness less than 25 mm Luting permanent metallic restorations Cementation of orthodontic bands 2. Type II—Medium grained: Film thickness of 40 mm High strength thermal insulating base 8

9. SETTING REACTION When the powder is mixed with the liquid - the phosphoric acid attacks the surface of the powder particles and releases zinc ions into the liquid. Aluminum from the liquid reacts with these zinc ions and forms zinc aluminophosphate gel, which covers the surface of the unreacted powder particles. Exothermic reaction S et material - an amorphous matrix network of zinc aluminophosphate that surrounds incompletely dissolved particles of zinc oxide. 9

10. Unbound water - forms globules within the material - makes the cement highly permeable resulting in a porous structure. E xhibits some shrinkage on setting. The reaction can be presented as: 3ZnO + 2H 3 PO 4 + H 2 O → Zn 3 (PO 4 ) 2 + 4H 2 O 10

11. MANIPULATION A properly cooled thick glass slab will help to dissipate the exothermic heat of reaction. C ool glass slab - longer working time I deal cooling range - 18°C–24°C Powder/Liquid ratio: Base - P/L ratio of about 3.5:1 Luting - more fluid mix with a lower P/L ratio 11

12. MIXING PROCEDURE Powder: D ivided into four to six increments. 12

13. Incrementally incorporated into the liquid while spatulating over a large area to dissipate the heat produced during the reaction. 13

14. Initially, smaller portions of powder are incorporated into the liquid because: The powder quantity being minimal, the heat generated is less. Large increment - the temperature rise is very rapid and leads to a rapid approach of initial set. Mixing time - 60–90 seconds 14

15. HANDLING CHARACTERISTICS P roper luting consistency - when the mix is fluid yet springs up from the slab 2–3 cm as the spatula is lifted up from the freshly mixed cement (string test). 15

16. Base - the consistency is like heavy putty. Third consistency - Band seating consistency - retention of orthodontic bands. 16

17. SETTING TIME T ime period from the start of the mix to the time when the mix reaches its desired consistency/hardness. Z inc phosphate cement is between 2.5 and 8 minutes. FROZEN GLASS SLAB TECHNIQUE: During the cementation of multiple orthodontic bands, long span bridges, etc., - longer working times and shorter setting times are required. T he glass slab is cooled in a refrigerator at 6°C or in a freezer at −10°C. 17

18. The powder and liquid are dispensed onto this slab without removing the condensed moisture. The amount of powder incorporated in this method is 50%–75% more than normal W orking time - increased by 4–11 minutes for slab temperatures ranging from 6°C to −10°C as compared with the working time for a slab temperature of 23°C. Setting times - shortened by 20%–40% as compared to the normal mixes. 18

19. RETARDERS FOR SETTING REACTION: Calcination of powder during manufacturing. Buffering agents in the liquid - control the number of phosphate groups available for reaction. Use of a cool glass slab. Adding the increments in small quantities. 19

20. ACCELERATORS: Increasing the P/L ratio. Adding water to the liquid. Decreasing the particle size of the powder. Increasing the temperature of the mixing atmosphere. 20

21. PROPERTIES Strength: Initial rapid rise in strength reaching 50% of its final strength (100–160 MPa) in the first 10 minutes and the final strength is reached after 24 hours. L ow tensile strength (5–8 MPa) - brittle in nature. Adhesion: N o adhesion to tooth structure. D epends on the microirregularities of the tooth surface to achieve frictional retention. 21

22. Solubility: H ighly soluble in water for the first 24 hours after setting and loss of material can range from 2.4% to 3.3%. After this, the solubility is negligible (0.2%). Cement with a high P/L ratio exhibits less solubility. Biocompatibility: H as the potential to cause inflammation of the pulp, especially in deep cavities - presence of acid - mandatory to place cavity varnish prior to placement of zinc phosphate cements. 22

23. pH rises rapidly - pH of 4.2 within 3 minutes after the start of mix. pH of 6 by the end of 1 hour. The pH reaches neutral at 48 hours. Insulation: Excellent thermal insulator but in thickness of 1 mm or more. Poor electrical insulator due to its porosity. Optical properties: Zinc phosphate cement is opaque 23

24. ADVANTAGES Zinc phosphate cement has high compressive strength - used as a base under amalgam restorations. A good thermal and electrical insulator. Effective in reducing galvanic shock. H as relatively low solubility compared to GIC and ZOE cements. 24

25. DISADVANTAGES L ow tensile strength - brittle in nature. H igh modulus of elasticity. C annot be used to lute all ceramic restorations since it lacks flexibility. L acks chemical adhesion; retention is only by mechanical means. P ulpal irritant due to the low initial Ph. L ow pH causes gross decalcifications - observed after removal of orthodontic bands luted with zinc phosphate. 25

26. REFERENCES S.Mahalaxmi . Direct restorative materials: Dental cements. Materials Used in Dentistry,2 nd edition. New Delhi: Wolters Kluwer Health. 2018;240-244. 26

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