Ist Year - Dental Materials

1. ‫الرح‬ ‫الرمحن‬ ‫هللا‬ ‫سم‬‫ب‬‫مي‬

2. Zinc phosphate cement

3. Uses
•Cementation of fixed restorations
•Cavity base under metallic filing to protect the pulp
from thermal or electrical stimuli.
•Temporary filing.

4. Composition
Powder
ZnO (90%): main ingredient.
MgO (10%): aid in sintering by reduction of sintering temperature.
SiO2: filler.
Bi2O3: impart smoothness to the freshly mixed cement.

5. Liquid
H3PO4 (50%): main ingredient.
H2O (45%): it controls acid ionization
Al2(PO4) 3 and ZnPO4:-
They reduce the reaction rate ( retarder)
They stabilize the pH of the acid.

6. Setting reaction of Zinc phosphate cement

7. Manipulation
Powder/ liquid ratio.
Mix on thick walled and cool glass slab + stainless steel spatula.
To achieve slow neutralization of the liquid and allow heat
dissipation.
Mix over a large area.
Mix the cements in increments:
Add the small amount of powder into the liquid.

8. Mixing procedure
There are three steps
First add the small amount of powder into the liquid
•To achieve the slow neutralization of the liquid.
•To control the reaction.

9. Second Larger amount of powder is added to liquid
•For further saturation of liquid to newly form zinc
phosphate.
•This step may not effect by heat released from the
reaction.{because of the less amount of unreacted acid}
Finally the small amount of powder is added again
•To control the optimum consistency

10. Properties of Zinc phosphate cement
I) It is the standard against which to compare newer cements due to
•The long persistence of them in clinical performance.
•Their manipulation is easy.
•They have ideal rheological properties (set sharply to a relatively
strong mass from a fluid consistency) .

11. II) Working time and setting time
Working time commonly is 2-6 minute
Setting time is 2.5-8 minute
How to extend the setting time?
Reducing powder/ liquid ratio {not recommended}
Mixing on the cool glass slap {no moisture}
Mixing over a large area.
Mixing cements in increments.

12. Control of setting time at chair side (by operator)
1. Powder/liquid ratio
Reducing P/L ratio will increase working and setting times.
Drawbacks of this method:
•physico-mechanical properties.
•Lower initial pH (high acidity)

13. 2. Rate of powder incorporation
Add small quantity of powder into the liquid for the first few
increments to reduce the amount of heat generated and permits
more powder to be incorporated into mix. This method prolong
the working time without jeopardizing the physico-mechanical
properties, therefore it is a recommended method .

14. 3. Spatulation time
Increasing spatulation time, prolong the working and setting times.
Prolonging spatulation time effectively destroys the matrix that was formed;
that is, extra time is needed to rebuild the bulk of the matrix.
4. Temperature of the mixing slab
It is the most effective method. Cooling the slab markedly retard the
chemical reaction between the powder and the liquid so matrix formation is
retarded. This permits incorporation of optimum amount of powder into the
liquid without the mix developing an unduly high viscosity.

15. III) Viscosity
It has low initial viscosity giving it these advantages:-
•Easy flow during restoration seating.
•Give low film thickness.
•Its viscosity increase rapidly with time, therefore the restoration
should be cemented rapidly after completing mixing to make use of
the lower initial viscosity.

16. IV) Mechanical properties
High compressive strength that allows amalgam condensation. In
10 minutes it attains 50% of its final strength which is attained
after 24 hours. It has low tensile strength (brittle). Its E is similar
to that of dentine. So it can support the overlying restoration and
occlusal stresses.

17. V) Solubility
•It is an important property especially when used for luting. Dissolution
contributes to the marginal leakage around restorations and result in looseness
of restorations or caries recurrence.
They have high solubility rate especially thin mixes. Once they set, their
solubility decreases, therefore they must be kept unexposed to oral fluid during
their setting.
VI) Biocompatibility
Irritant (pH is 2 and reach neutrality after 24 hours) so in deep cavities,
chemical insulator is needed.

18. Advantages
1. Speed and ease of usage.
2. Sufficient flow to form a thin layer for cementing of closely adapted crowns,
fixed partial dentures and inlays.
3. Low thermal conductivity beneath a metallic restoration.
4. High compressive strength that allows amalgam condensation.
Disadvantages
1. Solubility in mouth fluids.
2. Opaque material not suitable for visible surfaces.

19. Zinc polycarboxylate cement (ZPC)

20. The first cements that bond chemically to tooth structures.
They combine the strength properties of Zn PO4 +
biological acceptability of ZnOE.
These materials have gone through several stages of
development since their inception and progress is continuing.

21. Uses
1. Cementation of cast alloy, porcelain restorations and orthodontic
bands.
2. Cavity liners or base materials.
3. Temporary filling material.

22. Forms
• Conventional type: powder and liquid in two separate bottles.
•Water settable (anhydrous) type:
Its powder is the same like that of conventional type + freeze-dried
powder of the polyacid in one bottle. Its liquid is either distilled
water or weak solution of NaH2PO4.

23. Composition
Powder
Their composition and manufacturing are similar to those of zinc phosphate
cement.
Liquid
•30-40% aqueous solution of Polyacrylic acid or acrylic acid copolymer.
•Other organic acids such as:-
Itaconic acid to prevent gelation during storage.
Tartaric acid to control setting reaction.
•NaH2PO4 which  viscosity of polyacid and  S.T.

24. Setting reaction
The setting reaction is the same, whether the polyacid is freeze-dried and
subsequently mixed with water, or if the conventional aqueous solution of the
polyacid is used as liquid.

25. Properties
Working and setting times
It has shorter working time than zinc phosphate .
Lowering the temperature of glass slab increase the working time.
Cooling the powder only will retard the reaction without thickening the liquid.
Mechanical properties
Its compressive strength < zinc phosphate.
Tensile strength > phosphate cement
Solubility: It has low solubility in water.

26. Bonding to tooth structure
•Bonds chemically to E & D.
•The polycarboxylic acid reacts via COOH groups with calcium of
hydroxyapatite forming chemical bonding .

27. •Bonding to enamel is higher than to dentine, probably
because of the greater inorganic content and its greater
homogeneity from a morphologic standpoint.
•Smear layer removal by conditioning tooth surface with
10% polyacrylic acid for 10 seconds, will increase the bond
strength.
•It sticks to clean stainless steel.

28. Biocompatibility
•The effect of polycarboxylate cements on the pulp is comparable to or
less than that of zinc oxide-eugenol.
•pH of polycarboxylate cement (1.7) is higher than that of a zinc
phosphate cement (2) but polycarboxylate cement is more compatible
due to :-
•The rapid rise of the cement pH toward neutrality (few minutes for ZPC
but 24 hours for ZNPO4.
•Has bigger molecular size that block dentinal tubules.

29. Anticariogenicity
The fluoride containing cements release
fluoride, which is taken up by the neighboring
enamel, thus increasing its resistance against
caries.

30. Mechanism of action of fluoride in caries fitting
•Fluoride inhibits the enzymes responsible for carbohydrates fermentation.
•Fluoride shifts the equilibrium balance between demineralization and
remineralization toward remineralization.
•Fluorides act as a catalyst for uptake of calcium and phosphate ions.

31. Glass-ionomer cements (GICs)
Uses
•Restoration of erosion lesions
•Luting agent for crown and bridge
Types of GICs
•Conventional GICs.
•Metal reinforced GICs.
•Resin modified GICs.

32. Conventional GIC
Composition
Powder
Calcium aluminosilicate glass:-
•Silica (SiO2)
•Alumina (Al2O3)
•Calcium fluoride (CaF2) and NaF.

33. Function of the glass powder
•Releasing ions responsible for setting and properties of hard cement.
•Contributes to aesthetics.
Liquid is a Copolymer of
•Acrylic acid: main reactant.
•Itaconic acid: decrease viscosity of the liquid and inhibit gelation caused
by intermolecular hydrogen bonding.
•Tartaric acid: important hardener& controls pH during setting process.

34. Forms
•Powder/liquid form (conventional).
•Anhydrous cements (water settable).
•Capsules: pre-proportioned so achieve the correct p/l
ratio.

35. It occurs in three steps:
Dissolution
Gelation and hardening
hydration

37. Properties of GICS
Working and setting times
•It is less than that of ZnPO4.
•Water settable systems have longer working time and slower initial set than the
hydrous systems.
Mechanical properties
•Compressive strength: comparable to that of ZnPO4 cement.
•Tensile strength: slightly higher than that of ZnPO4 cement but still very low
(brittle behavior). Modulus of elasticity: less than that of ZnPO4 cement, i.e.
less rigid and more prone to elastic deformation.

38. Film thickness
Similar to or less than that of ZoPO4 cement (25 μm or less).
Solubility
Good resistance to dissolution under oral conditions and improved by
varnish protection.
Bonding
The same as Zinc polycarboxylate cement.
Anticariogenic properties
GICs possess anticariogenic properties as a result of fluoride release

39. Biocompatibility
GICs are as compatible as zinc polycarboxylate cements for the same reasons
discussed before with polycarboxylate.
Aesthetics
1. GICs are considered inferior to many composite resins in aesthetic
appearance.
2. GICs appeared dull and lifeless, and this limited their application to the
restoration of erosion lesions and non-critical class III cavities.
3. In facts, the translucency of the GICs was more closely matched to that of
dentine than that of enamel.

40. Advantages of GICs
• Chemical bonding to tooth structures.
•Biocompatible.
•Long term fluoride release.
•Good compressive strength.
•Low solubility in oral fluids

41. Disadvantages of GICs
•Technique sensitive as they are very sensitive to
either water contamination or dehydration
•Low abrasion resistance.
•Short working time and long setting time.
•Brittleness (low tensile strength) and low fracture
toughness.

42. Resin modified glass ionomer cements (Hybrid GICs)
The aim: is to overcome some of the drawbacks of the
conventional GICs that result from the slow acid base
reaction such as:-
1. Short working time and long setting time.
2. Cracking on desiccation and moisture sensitivity.
3. Poor resistance to acid attack.

43. Composition
These products are hybrid of the two groups of materials, namely composite resin
and GIC.
Liquid
•Methacrylate resin which enables setting to occur by polymerization.
•Polyacid & ion-leachable glass to bring about setting by an acid-base mechanism.
•HEMA: a hydrophilic methacrylate which enables both resin and acid
components to co-exist in aqueous solution, the HEMA also takes part in the
polymerization.
•Water acid ionization enabling the acid-base reaction to occur.

44. Setting reaction of the Hybrid GICs
•The acid-base reaction
Free radical polymerization

45. Properties of resin modified GICs cement
•Release of fluoride.
•Ability to bind chemically to tooth structures.
•A prolonged working time and a rapid setting time.
•High strength.
•Higher resistance to desiccation and acid attack.

46. Metal reinforced glass ionomer cements
The aim of reinforcing the cement with metal is
•To overcome the drawbacks of conventional GICs which are:
Brittleness
Low abrasion resistance
Low fracture toughness
•To enable using them as posterior filling materials.

47. Methods of metal reinforcements
Silver alloy admix:
It is performed by simply mixing of silver amalgam alloy powder to the
conventional GIC (hand mix material).
Cermet cement
by sintering the silver only to the cement powder.
Uses of metal reinforced GICs
•Core build up material.
Posterior filling material for deciduous teeth

48. Disadvantages of metal reinforced GICs
•Reduction in fluoride release.
•Reduction in bond strength with tooth structures.
Advantages of metal reinforced GICs
•Increase in abrasion resistance.
•Little increase in compressive strength.
•Reduction in solubility.

49. Resin Cements
History
Introduced 1950’s as an unfilled resin
Current resin cements, introduced in late 1980’s
Problems of Resin
•High polymerization shrinkage.
•High thermal expansion.
•Lead to high microleakage.

50. Classification of Resin Cement (RC)
According to filler content
•Unfilled or filled (inorganic/glass filler particles)
•Resin cement vs Resin composite cement
According to polymerization reactions
•Light-activated (Light-cure);
•Chemical-activated (Chemical-, Self-cure);
•Dual-activated (Dual-cure)

51. According to use of dentin bond agent (DBA)
•Some resin cements do not require DBA, bonds directly to tooth (Adhesive RC).
•Resin cements require DBA applied prior to the RC; DBA bonds to tooth, resin
cement bonds to DBA (non-adhesive RC)

52. 4-META/MMA-TBB resin cement product
4-META/MMA-TBB resin cement (unfilled)
Chemical-activation
Composition:
Base: 4-META/MMA (4-methyloxy ethyl trimellitic anhydride/
Methylmethacrylate)
Catalyst: TBB (tributyl boron oxide)
Powder: Polymethylmethacrylate powder (NO glass filler particles)

53. Manipulation
•Etch, rinse, and dry
•Mix Base + Catalyst , Apply 1st mix to tooth
•Add 2 scoops powder (PMMA) to 2nd mix of Base/Catalyst
•Apply 2nd mix to restoration
•Seat restoration
Application: metal-based restorations

54. Advantages
•Direct bond to tooth, No DBA
•Medium-high strength bond (~17 MPa)
Disadvantages
•Bond strength NOT long-term: ~10 MPa at 1 year.
•Higher solubility-- related to decreased bond strength.

55. Resin Composite Cements
Basic description
• Bis-GMA based resin (Bis-type methacrylate/TEGDMA resin )
• Filler: Silanated glass, silica particles
• Polymerization activation: Light, Chemical, Dual
• 10 MDP: Phosphate ester, Adhesive monomer for tooth structure.
• Brand dependent use of DBA
Ex: Resin Composite Cement: Panavia 21 (Available at UMKC)
• Chemical-activation .

56. Manipulation
• Etch and prime tooth structure with self-etch ED primer
• Apply for 60 sec, then dry. Do not rinse.
• Acidic HEMA primer: pH ~2-3; Do not use conventional phosphoric acid etch
• Mix catalyst & base pastes, 20 sec (Spread thin on pad, prevent premature set)
• Apply to restoration, seat restoration
• Clean excess cement using;
microbrushes, gauze.
Floss between teeth to remove inter-proximal excess.