1. DENTAL CEMENTS AS LUTING AGENTS

2. Numerous dental treatments necessitate attachments of indirect restorations and appliances to the teeth by means of a cement. These include metal ,metal- ceramic, and ceramic restorations provisional restorations, laminate veneers for anterior teeth , orthodontic appliances, pins and posts used for retention of restorations .

3. Characteristics of Abutment -Prosthesis Interface
When two relatively flat surfaces brought into contact, space exists on microscopic scale, there are peaks and valleys
There are only point contacts along the peaks
Main purpose of cement is to fill this space completely
If cement is not fluid enough voids can develop around deep valleys

5. Procedure for cementation of prostheses
To be effective a Type-I cement must be fluid and be able to flow into a continuous film of 25 um thick or less without fragmentation
The cement paste should coat the entire inner surface of the crown and extend slightly beyond the margin. It should fill about half of interior crown volume
Moderate finger pressure should be used to displace excess cement and to seat the crown

6. Variables that can facilitate seating of prosthesis include –
Using a cement of lower viscosity
Increasing the taper of preparation
Decreasing the height of crown preparation
Vibration

7. Removal of excess cement
Removal of excess cement depends on properties of cement used –
If cement sets to a brittle state and does not adhere to surrounding surfaces,tooth and prosthesis, it is best removed after it sets . This applies to Zinc phosphate and ZOE cements
For cements which are capable of adhering chemically like GIC, polycarboxylate and resin cement ,coat surrounding surface with petroleum jelly and remove excess as soon as seating is completeds

8. Dislodgment of prosthesis
Recurrent caries may occur
Disintegration of cement can result from fracture or erosion of cement
In oral environment , cement layer near the margin can dissolve and erode leaving a space. This space can be susceptible to plaque accumulation and recurrent caries

9. Loss of cement at marginal area resulting from exposure to oral fluid

10. CHOICE OF LUTING AGENT An ideal luting agent has- Long working time
Adheres well to both tooth structure and cast alloys
Provides a good seal
Is nontoxic to the pulp
Has adequate strength properties
Has low viscosity and solubility
Exhibits good working and setting characteristics
Any excess can be easily removed

11. ZINC PHOSPHATE CEMENT It is the oldest of cementation agents
It serves as standard by which newer systems can be compared
Zinc phosphate cement is still the luting agent of choice for otherwise normal, conservatively prepared teeth

12. Recommended powder:liquid ratio 1.4 gm powder to 0.5ml liquid
Working time- 5 min
Setting time-5-9 min
Manipulation-a cool mixing slab should be employed ,cool slab prolongs the working time
Recommended powder:liquid ratio 1.4 gm powder to 0.5ml liquid
Mixing is initiated by addition of small amount of powder with brisk spatulation
A considerable area of mixing slab should be used ,this reduces the amount of heat generated.

13. Two mixes of cement prepared with identical powder liquid ratio
Two mixes of cement prepared with identical powder liquid ratio. Temp in A is 18 degree C. temp in B is 29.5 degree C

14. Compressive strength -104 MPa Modulus of elasticity -13 GPa
Physical properties –
Compressive strength -104 MPa
Modulus of elasticity -13 GPa
It is quite stiff and resistant to elastic deformation even when employed for cementation of restorations that are subjected to high masticatory stress

15. The pH then increases rapidly but still is only about 5.5 at 24 hours
Retention
Primary bonding occurs by mechanical interlocking at interfaces and not by chemical interactions
Biologic properties
The acidity of cement is quite high at the time when prosthesis is placed on prepared tooth
The pH then increases rapidly but still is only about 5.5 at 24 hours
Thus if underlying dentin is not protected against infiltration of acid via dentinal tubules pulpal injury may occur

16. ZINC POLYCARBOXYLATE CEMENT
It was the first cement system that developed an adhesive bond to tooth structure
This agent is recommended on retentive preparartions when minimal pulp irritation is important e.g. in children with large pulp chambers

17. If good bonding to tooth structure is to be achieved ,the cement must be placed on the tooth surface before it loses its glossy appearance. The glossy appearance indicates a sufficient number of free carboxylic acid groups on the surface of mixture that are vital for bonding to tooth structure

18. Consistency of polycarboxylate on completion of 30 sec mix
Prolonged mixing or mix is allowed to remain on slab cement becomes dull and consistency becomes s tacky

19. Working time –much shorter than for zinc phosphate ,2.5 min
Setting time – ranges from 6-9 min
Manipulation-
P:L ratios parts of powder to 1 part of liquid
Cool the slab and powder but under no circumstances should the liquid be cooled
Powder is rapidly incorporated into liquid in large quantities.30 sec mixing time is adequate

20. Compressive strength -55 MPa Modulus of elasticity - 5.1 GPa
Physical Properties –
Compressive strength -55 MPa
Modulus of elasticity GPa
At manufacturers’ recommended powder: liquid ratios ,mixed polycarboxylate cement is very viscous .however polycarboxylate have different rheological or flow properties than zinc phosphate , exhibiting thinning with increased shear rate .this means they are capable of forming low film thicknesses despite their viscous appearance

21. Bonding to tooth structure –it bonds chemically to tooth structure ,the polyacrylic acid is believed to react via the carboxyl groups with calcium of hydroxyapatite

22. Biologic properties- The excellent biocompatibility with the pulp is a major factor in the popularity of this cement system .this is due to larger size of polyacrylic acid which may limit its diffusion through the dentinal tubules

23. GLASS IONOMER CEMENT
Glass ionomer is generic name of group of materials that use silicate glass powder and an aqueous solution of polyacrylic acid . It is also referred to as polyalkenoate cement

24. TYPES OF GIC Type-I Luting applications Type-II Restorative material
Type-III Liner or Base
Type-IV Pit and Fissure Sealant
Type-V Orthodontic Bracket
Type-VI Core build up

25. Working time-range is 3-5 min Setting time- 5-9 min Manipulation-
The powder is introduced into the liquid in large increments and spatulated rapidly for 30 to 45 seconds
Recommended P:L ratio is 1.25 to 1.5 g of powder per 1ml of liquid

26. Compressive strength -86 MPa Modulus of elasticity-7.3 GPa
Physical properties-
Compressive strength -86 MPa
Modulus of elasticity-7.3 GPa
A disadvantage is that during setting , glass ionomer appears particularly susceptible to moisture contamination and should be protected with a foil or resin coat or by leaving a band of cement undisturbed for 10 min

27. Biologic Properties- the glass ionomer cement bond adhesively to tooth structure and they inhibit infiltration of oral fluids at the cement tooth interface
In addition because it releases fluoride it may have an anticariogenic effect although this has not been documented clinically

28. ZINC OXIDE EUGENOL CEMENT
ZOE is extremely biocompatible and provides an excellent seal .however its physical properties are inferior to those of other cements ,which limits its use
Type-I is used for temporary cementation
Type-II is intended for permanent cementation of restorations

29. Type I ZOE Cements –it has a pH of 7 and is biocompatible with pulp .
It seals the cavity well against ingress of oral fluids , hence irritation caused by microleakage is minimized
The strength of a temporary cement must be low to permit removal of the restoration without trauma to the teeth

30. Type-II ZOE Cements- The 2-ethoxy benzoic acid (EBA) modifier replaces a portion of eugenol in conventional ZOE cement ,it improves the strength ,but it should be used only in restorations with good inherent retention form where emphasis is on biocompatibility and pulpal protection

31. RESIN CEMENTS
Composite resin cements with greatly improved properties were developed for resin retained prosthesis and are extensively used for bonded ceramic technique
Resin cements are available with adhesive properties i.e. they are capable of bonding chemically to dentin

32. Bonding is achieved with organophosphonates , HEMA (hydroxy ethyl methacrylate ) or 4-META (4-methacrylethyl trimellitic anhydride )
Resin based cements are irritating to pulp especially if they are not fully polymerized

33. RESIN MODIFIED GLASS IONOMER
They were introduced in an attempt to combine some of the desirable properties of glass ionomer i.e. fluoride release and adhesion with the higher strength and low solubility of resins .
These materials are less susceptible to early moisture exposure than glass ionomer

34. Currently among the most popular luting agents ,resin modified glass ionomer have low solubility , adhesion and low microleakage also perceived benefit of reduced post cementation sensitivity

35. Resin modified glass ionomers should be avoided with all ceramic restorations because they have been associated with fracture which is probably due to their water absorption and expansion

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