1. Rola Shadid, BDS, MSc, Associate fellow AAID
4/17/2017
Luting Cements
Rola Shadid, BDS, MSc, Associate fellow AAID

2. Key Terms
Cement : Substance that hardens to act as a base ,liner , filling material , or adhesive to bind devices & prostheses to tooth structure or to each other
Luting agent : A viscous material placed between tooth structure & prostheses that hardens through chemical rxn to seal a space or to cement two components together.

3. Key Terms
Film thickness : Height of space betw. two surfaces that are separated by the cement layer. This dimension is measured after pressure is applied betw. two flat surfaces that are separated by a cement layer.
For temporary & final cementation, the maximum thickness is typically about 40µm
The size of particles & P/L ratio significantly affect FT.

4. Continue/
A thinner film has fewer internal flaws compared with a thicker one ( increase retention)
Excess cement can be expressed more easily when thin film thickness is provided

5. Key Terms
Working time: The time from the start of mixing to the maximum time at which the viscosity of the mix is still low enough to flow readily under pressure to form a thin film
Setting time :The elapsed time from the start of mixing to a point at which an external physical disturbance will not cause permanent dimensional change

6. Question
During the initial seating of three-unit bridge, if the prosthesis fits the prepared tooth perfectly that removal requires a great deal of force .Why is a cement required for retention under this condition ?

7. Answer
When two flat surfaces are brought into contact, a space exists betw. them on a microscopic scale ; the surfaces exhibit peaks & valleys so there are only point contacts along the peaks. The open spaces can be substantial in terms of oral fluid flow & bacterial invasion.

9. The luting cement can seal the space & provide void- free sealed continium; so it resists shear stress acting along the interface (mechanical retention)
It can also bind chemically to tooth structure & restoration so it improves the retention of prosthesis.

10. Continue/Answer
In mechanical retention , failure occurs at interfaces . While in chemical retention , failure occurs cohesively through the cement itself.

11. Ideal Luting Cement Adheres to tooth structure & cast alloys
Long working time
Low viscosity & solubility
Nontoxic to the pulp
Adequate strength properties
Compressible in thin layers
Provides good seal
Any excess can be easily removed

12. Zinc Phosphate cement
Powder : Zinc oxide (90%) & magnesium oxide (10%)
Liquid : Phosphoric acid , water , aluminium phosphate , zinc phosphate.
Acid content 33 ± 5 wt%

13. Zinc Phosphate cement Reduction in P/L ratio produces weaker cement
Loss or gain in water content of liquid leads to weaker cement
film thickness is about 25µm
Bonding occurs by mechanical interlocking at interfaces
Working time 1.5 to 5 min .Setting time 2.5 – 8 min

14. Zinc Phosphate cement
Excess cement can be easily removed after it has set
Maturation (It is advisable to place a layer of varnish to margin to allow the cement more time to mature )

15. Zinc Phosphate cement Limited biocompatibility :
2 minutes after mixing pH is 2
pH is 5.5 at 24 hr
irritation depends on the thickness of residual dentin, because of this irritation cavity varnish may be used to protect against the pulp irritation

16. Zinc Phosphate cement
Successful use over many years suggests that its effect on dental pulp is clinically acceptable
The luting agent of choice for otherwise normal conservatively prepared tooth

17. Question
How can we increase the working time of zinc phosphate cement at chairside ?

19. Zinc Polycarboxylate cement
Liquid is an aqueous solution polyacrylic acid or a copolymer of acrylic acid with other carboxylic acids , such as itaconic acid
Powder is similar to that of zinc phosphate cement ± stannous flouride

20. Zinc Polycarboxylate cement
1st cement system that developed an adhesive bond to tooth structure
Bonding to tooth structure is explained by :
Polyacrylic acid reacts with calcium ions via carboxyl groups on the surface of E or D.
Binds chemiclly to Stainless Steel crowns .

21. Zinc Polycarboxylate cement
Zinc polycarboxylate mix is classified a pseudoplastic (thixotropic)& undergoes thinning at increased shear rate…25µm .

22. Zinc Polycarboxylate cement
Working time 2.5 min compared with approx. 5 min of zinc phosphate
( refrigerate powder before mixing)
Compressive s. 55 to 67
MOE 2.4 to 4.4 GPa

23. Zinc Polycarboxylate cement
Removal of excess cement is more difficult than zinc phosphate cement after it has set
Avoid removing excess cement in the rubbery stage because cement may be pulled out from beneath the margins leaving a void
You can remove it after it has set or ASA seating is completed

24. Zinc Polycarboxylate cement
Relatively biocompatible (equivalent to ZOE) because :
pH rises more rapidly
Larger size of polyacrylic acid molecule so less diffusion into dentinal tubules.
Recommended on retentive preparation when mimimal pulp irritation is important ( in children with large pulp horns)

25. Glass Ionomer Cement
Powder is an acid-soluble calcium flouroaluminosilicate glass(15 to 50µm)
Liquid is an aqueous solutions of polyacrylic acid 40 to 50%wt + tartaric acid
Water-settable glass ionomer : freeze-dried polyacid powder & glass powder are placed in the same bottle as a powder, the liquid consists of water .When mixed, acid dissolves to a liquid acid & this is followed by acid-base rxn.

26. Glass Ionomer Cement
Both dessication & contamination compromise the integrity of freshly mixed material(should be protected with a foil of resin coat or varnish or by leaving a band of cement undisturbed for 10 minutes)

27. Glass Ionomer Cement
The adhesive mechanism to tooth structure is comparable to that of zinc polycarboxylate cement.
F ions released from GIC inhibit the progression of secondary caries(not documented clinically)

28. Glass Ionomer Cement
Removal of excess cement is the same as for polycarboxylate cement.

29. Glass Ionomer Cement Relatively biocompatible
The set cement is somewhat translucent
Relatively biocompatible
( Zinc phosphate<GIC<ZOE )
Compressive s. is comparable to that of zinc phosphate cement , tensile s. is higher

30. Resin-modified glass ionomer cement (Hybrid Ionomer)
Among the most popular materials in general practice
Less susceptible to early moisture exposure
Low solubility & low micoleakage
Less post-treatment sensitivity
Should be avoided with all-ceramic restorations because they have been associated with fracture (due to water absorption & expansion)

31. Resin Cements
The composition is similar to that of resin –based composite filling material: resin matrix with silane-treated inorganic fillers
Most of them require dentine bonding agent
The adhesive monomer incorporated in bonding agent & resin cement includes HEMA , 4-META
Chemical-cure , light-cure , dual-cure system

32. Resin Cements Insoluble in oral fluids strongest in compression
Less biocompatible than glass ionomer cement , especially if they are not fully polymerized (the monomeric component)
Greater film thickness

33. Resin Cements
Luting agent of choice for all ceramic inlays, crowns , bridges (because of their ability to reduce fracture of ceramic structure & because of the range of shades available to produce an optimal esthetic result)
Indicated when a casting has become displaced through lack of retention

34. Resin Cements Chemical-cure resin cements
The two components are mixed on a paper pad for 20 to 30 s
It is best to remove excess cement immediately after the prosthesis is seated
It is suitable for all types of prostheses

35. Resin Cements Light –curable cements Single component system
Indicated for cementation of thin ceramic prostheses, resin-based prostheses, & direct bonding of ceramic and plastic orthodontic brackets when the thickness is less than 1.5mm
Excess cement should be removed ASA seating is completed

36. Resin Cements Dual-cure cements Two- component systems
Chemical activation is v slow & provides extended working time until the cement is exposed to curing light
Should not be used with light –transmitting prostheses thicker than 2.5mm

37. Zinc Oxide –Eugenol Cement
Setting rxn:
Zinc oxide hydrolysis & subsequent rxn betw. zinc hyroxide & eugenol to form a chelate
Water is needed to initiate the rxn & it is a by-product of rxn (rxn proceeds more rapidly in a humid environment)

38. Least irritating of all dental cements (pH 7) & excellent seal, free eugenol has bacteriocidal & obtudent effect

39. Zinc Oxide –Eugenol Cement
Should be used only in restorations with good inherent retention form where emphasis is on biocompatibility & pulpal protection

40. Zinc Oxide –Eugenol Cement
Residual free eugenol interferes with proper setting of resin cements ;carboxylic acid can be used to replace eugenol & produce zinc oxide-noneugenol cements

41. Zinc Oxide –Eugenol Cement
Temporary ZOE Restorations
Last for a few days to few weeks at most
Intermediate ZOE Restorations
Last for 1 year
Sufficient powder must be added to achieve a stiff, puttylike restorative material.

42. Comparison between cements

43. Solubility & disintegration of cements
In vivo studies :
ZOE > Zinc phosphate / Zinc polycarboxylate > GIC > Resin-modified GIC > Resin cement

44. Comparison of film thickness

45. Comparison of retention

46. Compressive Strength

47. Patient sensitivity

48. Radioopacity

49. Comparison of microleakage

50. Antibacterial prop.

52. How does the adaptation of restoration affect selection of cement ?

53. How does the type of restoration affect selection of cement?

54. Answer
Adhesion of Zinc polycarboxylate to stainless steel is excellent
Metal restoration requires chemical cure resin cements , resins formulated for cementing conventional casting must have lower film thickness than materials designed for ceramics

55. Resin modified glass ionomer luting agents should be avoided with all ceramic restorations because they have been associated with fracture , which is probably due to their water absorption and expansion

56. Adhesive resins are the luting agents of choice for all ceramic inlays, crowns , bridges (because their ability to reduce fracture of ceramic structure & because of the range of shades available to produce an optimal esthetic result)
the mechanism of all ceramic crown strengthening is due to prevention of crack propagation from the internal surface by the bonded resin

57. Dual cure is used in ceramics, but it is not used for veneers because the amine accelerator can cause the color of luting agent to change , for veneers a light -cured resin is preferred
Light curable cements are indicated for cementation of thin ceramic prosthesis , the thickness of the restoration in the bonded area is less than 1.5 mm
For inlays, a chemical or dual cure resin cement is preferred

58. Zinc phosphate and polycarboxylate cements are not recommended to be used with all ceramic restorations because the materials are opaque due to high concentration of unreacted zinc oxide , this will detract from the appearance of porcelain crowns , particularly if the cement luting margin is visible

59. Procedure

62. Thank You