DENTAL CEMENTS AS LUTING AGENTS

1. DENTAL CEMENTS AS LUTING AGENTS www.rxdentistry.net

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 . www.rxdentistry.net

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 www.rxdentistry.net

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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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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

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 www.rxdentistry.net

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 www.rxdentistry.net

12. 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. www.rxdentistry.net

13. 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 www.rxdentistry.net

14. 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 www.rxdentistry.net

15. 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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

19. Working time –much shorter than for zinc phosphate ,2.5 min • Setting time – ranges from 6-9 min Manipulation- • P:L ratios - 1.5 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 www.rxdentistry.net

20. Physical Properties – • Compressive strength -55 MPa • Modulus of elasticity - 5.1 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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

26. 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 www.rxdentistry.net

27. Biologic Properties- the glass ionomercement 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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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 www.rxdentistry.net

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