cements used in the restorations in prostho

Cements

1. DENTAL CEMENTS AND CEMENTATION TECHNIQUES FOR FPD DR. AHMED FARGHALY PROFESSOR OF FIXED PROSTHODONTICS AHMED FARGHALY 1 CAIRO TOWER

2. AHMED FARGHALY 2 AGENDA - Introduction - Families of dental luting cements *Composition *Manipulation *Properties - Bonding mechanisms of dental cements - Desirable properties of dental cements - Proper Selection of Luting Cements Some Clinical Cases & Recommended Cements The correct selection of cement is the guarantee of successful restoration which is conditioned by the its durability

3. AHMED FARGHALY 3 D) Inlays & onlays 1- All ceramic 2- Metallic Precious Non precious Tooth supported restorations Implant supported restorations A) Crowns & bridges 1- All ceramic 2- Metallic & PFM Precious alloys Non precious alloys C) Posts 1- Fiber posts 2- Metallic posts 3 - Ceramic posts E) Resin bonded retainers 1- Metallic 2- All ceramic B) Laminate veneers 1-Heat pressed laminate veneer 2- Refractory die technique 3- Platinum foil matrix technique 4- Machine milled laminates FIXED RESTORATIONS

4. FAMILIES OF DENTAL LUTING CEMENTS I. Zinc oxide and eugenol: - Conventional. - Reinforced . II. Zinc phosphate. III. Zinc polycarboxylate. IV. Glass ionomer: - Conventional . - resin-modified glass ionomer. V. Composite, resin based: - Conventional . - Adhesive . AHMED FARGHALY 4

5. AHMED FARGHALY 5 Adhesive Cements Non adhesive ( Conventional cements) e.g. Zinc phosphate, zinc oxide Eugenol GIC based (Chemical bonding) Resin based ( Micro mechanical interlocking) 1- Composite resin - Smear layer removal via acid etching using 2 or 3 steps total etch adhesive cements e.g . Variolink II and nexus 2 - Smear layer preservation via self etching primer e.g. Panavia F Conventional GIC Resin modified GIC 2- Glass phosphonate (self etching adhesive cement) e.g. Rely X Unicem 3- Poly acid modified composite (smear layer preservation via self etching adhesive) e.g. Dyract Cem plus 4- Unfilled adhesive based on MMA resin Smear layer removal via acid etching e.g . Super bond C&B Smear layer preservation via self etching primer e.g . M-bond

6. Typical microscopic processes for formation of an adhesive joint Clean / stable / rough surface Good wetting of adhesive High contact in pores Strong cured / set adhesive AHMED FARGHALY 6

7. 1. Non-adhesive or mechanical = Attachment = Mechanical Interlocking = No actual bond , in which cement extend into small irregularities of adjoining surfaces ( Zinc phosphate). e.g. Amalgam, composite, zinc phosphate cement with irregularities of prepared tooth surface. 2. Micromechanical : By the flow and penetration of a liquid adhesive into microscopic or sub-microscopic irregularities in the surface of the adherent or substrate 3. Adhesive or Molecular adhesion, it is TRUE ADHESION = primary bonds = Adhesive dentistry = chemical bonding: Bonding between dissimilar materials through bonding between their atoms and molecules "chemical reaction" . e.g. Glass ionomer and zinc polycarboxylate with the tooth. AHMED FARGHALY 7 MECHANICAL CHEMICAL BONDING MECHANISMS OF DENTAL CEMENTS

8. CEMENT is a plastic paste of a fine powder and liquid which hardens to a solid mass. Cements are used to retain restorations and occupy marginal voids . AHMED FARGHALY 8 CEMENTATION is a procedure which allows full seating of fixed restorations with no damage to the oral tissues or the restoration. What is ……………. ?

9. What is the Ideal Cement ???? . 9

10. DESIRABLE PROPERTIES OF DENTAL CEMENTS: AHMED FARGHALY 10 III . CLINICAL: 11- Adjustable working time and rapid set 12- Radio opacity 13- Easy removal of excess cement: II. PHYSICAL: 5- High strength in compression , tension and shear 6- Maximum adhesion and sealing 7- Low film thickness 8. Low viscosity and easy flow: 9- Insolubility in the oral fluids. 10- Low uptake of water I. BIOLOGICAL : 1- Non irritating to the tissues 2- Bactericidal and bacteriostatic 3- Anticariogenic property. 4- Absence of microleakage

11. AHMED FARGHALY 11 1- Non irritating to the tissues The luting cement should be non-irritant to the oral tissues eg (PULP AND GINGIVA) 2- Bactericidal and bacteriostatic ZOE cement and ZPC cement were most effective against some microorganisms followed by the newer resin cement. Patients with high caries index can be treated more effectively using the above mentioned cements . 2- Bactericidal and bacteriostatic ZOE cement and ZPC cement were most effective against some microorganisms followed by the newer resin cement. Patients with high caries index can be treated more effectively using the above mentioned cements .

12. AHMED FARGHALY 12 3- Anticariogenic property. The luting cement should contain fluoride in its composition. Fluoride ions are released for prolonged periods and taken up by the underlying tooth structure leading to increased resistance to recurrent decay . 4- Absence of microleakage Almost all cases marginal leakage is a function of the solubility and dimensional change of the cementing agent as well as its degree of adaptation to the surfaces involved .

13. AHMED FARGHALY 13 5- High strength in compression , tension and shear to resist the forces of mastication. B- TENSION C- SHEAR A- COMPRESSIVE

14. A) To the underlying abutment preparations, enamel AND dentin B) Core materials (amalgam, composite resin, glass ionomer, ceramic or a cast core of precious or non-precious alloys). C) To the restoration material which may be : - Metallic (precious or non-precious alloys). - Non-metallic (porcelain or resin ). AHMED FARGHALY 14 6- Maximum adhesion and sealing

15. 7- Low film thickness Acceptable range (20-40 microns) to permit crown to seat adequately. To obtain the thinnest possible cement film between the tooth and restoration it is important to bring about the greatest cement flow during the initial stage of the cementation process. AHMED FARGHALY 15 SEVERAL VARIABLES affect the thickness of the cement film remaining between the prepared tooth surface and a restoration . 1- Powder/Liquid ratio. 2- Amount and duration of the pressure applied during seating of the restoration. 3- The degree of taper of the preparation. 4- The viscosity of the cementing medium. 5- The thickness of internal relief:

16. AHMED FARGHALY 16 A) Enlargement of the interior of the casting by electrical or chemical stripping. B) Enlargement of the die by a spacing material or die relief before the wax build up . THE THINNER THE CEMENT FILM THE BETTER THE CEMENTING AND RETENTIVE ACTION AND THE GREATER CHANCE OF PERMANENCE OF THE RESTORATION BECAUSE AIR SPACES, VOIDS AND STRUCTURE DEFECTS ARE MINIMIZED IN A THIN FILM.

17. 8. Low viscosity and easy flow : The luting cement should have a suitable viscosity to enable it to flow easily over the adherent surface. The initial viscosity of the cementing medium had a major effect on the seating of the crown . AHMED FARGHALY 17 Low viscosity allows crowns to seat better than high viscosity fluids.

18. AHMED FARGHALY 18 9- Insolubility in the oral fluids. Resistant to solubility and disintegration in the oral cavity . 10- Low uptake of water Water sorption and resistance to disintegration in saliva. If the cement dissolves or deteriorates under a restoration, leakage can result in sensitivity and caries.

19. 11- Adjustable working time and rapid set It is an extremely important property. Working time is that time during which the viscosity or consistency of the mix is such that it flows readily under pressure to form a thin film. Short working time creates a problem when cementing a long span bridge (multiple units ). AHMED FARGHALY 19 Frozen slab technique: The glass slab is removed from a freezer. The technique uses a 50%-75% increased powder/liquid ratio. This technique is useful when multiple casts are to be cemented.

20. Can we control the working time ??????? 1- P owder / L iquide ratio. 2- Addition of incremental powder 3- Spatulation time 4- Frozen glass slab (retards the chemical reaction between P & L ) 20

21. AHMED FARGHALY 21 12- Radiopacity The luting cement must be translucent and not opaque for esthetics of all ceramic restorations and laminate veneers. 13. Easy removal of excess cement : Interproximally and from the gingival sulcus, lack of thorough removal of excess cement leads to soft tissue irritation and serious periodontal problems.

22. AHMED FARGHALY 22 CONDITIONS THAT PREVENT PROPER ADHESION (BONDING) TO TOOTH SURFACES 1- THE INHOMOGENEOUS COMPOSITION OF ENAMEL AND DENTIN 2- SURFACE IRREGULARITIES OF THE PREPARED SURFACE 3- PRESENCE OF DEBRIS ON TOOTH SURFACE 4- PRESENCE OF WATER ON PREPARED SURFACE Good adhesion Poor adhesion Incomplete wetting (Air voids)

23. Some Clinical Cases & Recommended Cements Currently there is no single and superior cement material that can perform well in all the luting requirements of all restorations. In other words, a universal utilization cement is not yet available. The different cements should be properly selected according to their merits for the particular cementation utilization. Each dentist must decide which cement to use based on clinical application and specific patient needs . AHMED FARGHALY 23 WHY? Proper Selection of Luting Cements

24. Cement of choice: 1. Glass ionomer. 2. Zinc phosphate. 3. Adhesive composite resin particularly Panavia in which we can control the working time due to its anaerobic setting characteristics. N.B.: Polycarboxylate cement is not used in this case due to its extremely short working time and low strength properties . Reinforced zinc oxide eugenol is also not used due to its low strength properties and short working time. AHMED FARGHALY 24 I. Cementation of long span bridge: Cement requirements: 1. Long working time. 2. High mechanical properties. 3. Preferably to be adhesive.

25. II. Caries active patients (high caries index): Cement requirement: Must have an anticariogenic property by releasing fluoride ions and inhibiting secondary caries . Cement choice : 1. Glass ionomer cement (conventional and resin-modified). 2. Composite resin that releases fluoride (recent version e.g. Panavia F). AHMED FARGHALY 25

26. AHMED FARGHALY 26 Cement requirement: Should be non irritant, palliative to the pulp. Cement of choice: 1. Polycarboxylate. 2. Reinforced zinc oxide and eugenol. III. Deep preparation and over tooth reduction:

27. VI-Cementation of porcelain jacket crowns and porcelain laminates: Cement requirements: 1. Translucency . 2. Early high mechanical strength and fracture toughness. 3. Adhesive to the treated porcelain and tooth surfaces . Cement of choice: - Composite resin cement. - N.B .: Glass ionomer cement although it is translucent but has the disadvantage of slowness with which ultimate properties are developed. So when subjected to masticatory stress elastic deformation of the underlying cement could result in fracture of the brittle ceramic. AHMED FARGHALY 27

28. V. Cementation of a restoration to a core or crown base materials: Cement requirement : Adhesion to the core material . AHMED FARGHALY 28 C ement of choice: ACCORDING TO THE TYPE OF CORE MATERIAL. a ) Amalgam core: All cements are used currently for cementation against amalgam core. But, it is recommended to use high copper amalgam core with high tin concentration with polycarboxylate cement since the high tin concentration enhances the bonding between amalgam cores and polycarboxylate cements.

29. AHMED FARGHALY 29 b) Composite resin core: We choose a composite resin cement because of the chemical similarity in composition and therefore it bonds chemically to the composite core . c) Glass ionomer core: We choose a glass ionomer cement because of the chemical similarity in composition leading to chemical bonding to the glass ionomer core.

30. d) Cast core: 1. Precious cast core: All cements used currently does not provide a good adhesion to gold alloys. But polycarboxylate cement showed a bond strength which is 4 times greater than that of zinc phosphate and is directly proportional with the percentage of copper present in the alloy. Adhesive composite resin cement has superior bonding to gold alloys . AHMED FARGHALY 30 2. Non precious cast core: Adhesive composite resin, glass ionomer and polycarboxylate cements provide good adhesion to non precious alloys. 3. Ceramic core: We choose a composite resin cement after sandblasting of the ceramic core with aluminum oxide, followed by silane application.

31. AHMED FARGHALY 31 VI. Cementation of post crowns: Cement requirements: 1. High flow and ease of post cementation. 2. High strength properties. 3. Preferable to be adhesive. Cement of choice: 1. Glass ionomer. 2. Zinc phosphate. 3. Adhesive composite resin is used for cementation of non-metallic posts such as zirconium oxide ceramic posts and carbon fiber epoxy posts. (N.B. Because of the lack of oxygen in the canal, Panavia tends to set more rapidly)

32. VII. Cementation to a questionable preparation: ( Short, over convergence or to a continually dislodged restoration): Cement requirements: 1. Adhesive . 2. Extremely strong cement (high mechanical properties). 3. Insoluble . Cement of choice: Adhesive composite resin with pulp protection over deep dentinal areas. AHMED FARGHALY 32

33. VIII. Cementation of resin-bonded retainers (Maryland bridge): Cement requirements: 1. Adhesive to the treated metal surface and impregnation into etched enamel areas . 2. High mechanical properties. 3. Insoluble in the oral fluids. Cement of choice: The only cement of choice is the composite resin cement. AHMED FARGHALY 33

34. AHMED FARGHALY 34 THE ADHESIVE COMPOSITE RESIN SYSTEM NAMED RELY-X- UNICEM IS DISTINGUISHED BY: a . Its unique moisture tolerance. b. Little risk for postoperative hypersensitivity. c. Dimensional stability. d. Fluoride ions release. e. Available in several shades.

35. IN GENERAL, STEPS FOR CEMENTATION WORKFLOW 1 . The restoration after being checked for fitness, marginal seal, contact with adjacent teeth and occlusion, is thoroughly cleaned and washed then dried. 2. Application of local anaesthesia if it is proposed to eliminate pain from phosphoric acid and to decrease salivary flow . 3. Inspect all preparation surfaces for cleanliness. Remove any temporary cement with a pumice wash or hydrogen peroxide. 4. Isolate the area with cotton rolls and place the saliva ejector or high suction. 5. The tooth is gently dried, and avoid excessive dryness of the prepared tooth to prevent damage of the odontoblasts and post operative sensitivity. 6. Apply several thin layers of cavity varnish to seal the dentinal tubules and protects the pulp from irritation from phosphoric acid of phosphate cement. But with the adhesive cements (polycarboxylate, glass ionomer and adhesive composite resin) varnish should not be applied since it would prevent their adhesion to dentin . AHMED FARGHALY 35

36. 7. The luting cement of choice is mixed according to the manufacturers recommendation to the proper consistency. 8. Apply the cement by painting inside the clean internal surface of the restoration and most effectively to paint the axial walls only with fine brush which decrease the hydrodynamic pressure of the cement leading to more complete seating and decrease post operative sensitivity. 9 . To extend the working time, the cement should be applied to a cool restoration rather to a warm tooth. 10. Dry the tooth once again gently and push the restoration into place. Final seating is best achieved by rocking or vibrations until all excess cement is seen to have escaped. 11. After the crown is seated, check the margins to verify the complete seating of the restoration. 12. Removal of excess cement. 13. protect the setting cement which is susceptible to moisture contamination (initial high solubility, in case of glass ionomer) with varnish. 14. Check the occlusion and the patient is advised to chew carefully for a day because cements take at least 24 hours to develop their final strength. AHMED FARGHALY 36

37. FAMILIES OF DENTAL LUTING CEMENTS I. Zinc oxide and eugenol: - Conventional. - Reinforced . II. Zinc phosphate. III. Zinc polycarboxylate. IV. Glass ionomer: - Conventional . - resin-modified glass ionomer. V. Composite, resin based: - Conventional . - Adhesive . AHMED FARGHALY 37

38. I. Zinc oxide-Eugenol cement: Type I: Unmodified zinc oxide eugenol cement which is designed for temporary cementation because of the palliative effect on the pulp and the low strength properties allowing non traumatic removal of the restoration. On many occasions it is advisable to cement a restoration temporarily so that the patient and dentist can have a chance to assess its appearance and function over a longer time than can be provided in a single visit. Type II: Reinforced zinc oxide-eugenol for final cementation either by incorporation of a polymer or by the addition of alumina to the powder and EBA (orthoethoxy benzoic acid) to the eugenol liquid . Composition of EBA: The powder is composed of zinc oxide, fused quartz or alumina and hydrogenated resin. The liquid is eugenol and orthoethoxy benzoic acid . AHMED FARGHALY 38

39. Manipulation : Rapid incorporation of the powder into the liquid and then continue spatulation for 60 seconds . Properties of EBA: 1. Adhesion (only mechanical): It is not adhesive and do not form chemical bond with tooth structure or the restoration. 2. Biological compatibility : It is extremely biocompatible and provides a palliative and sedative effect on the pulp. 3. Mechanical properties : It has limited strength properties. The mechanical properties are inferior to other cements . 4. Solubility : It is a soluble cement mainly due to elution of eugenol. 5. Working time : It has a short working time. 6. Film thickness: It has a high film thickness (50 µm). 7. Viscosity and flow: It has a good flow. 8. Translucency: It is not translucence, because the set cement is opaque. 9. Anticariogenic property : It has no anticariogenic property. 10. Removal of excess cement: Difficult to remove excess cement . AHMED FARGHALY 39

40. II. Zinc phosphate cement: Composition: The powder is composed of about 90 percent zinc oxide and 10 percent magnesium oxide. The liquid is an aqueous solution of phosphoric acid containing about 30 to 40 percent water. Manipulation: • Dispense the proper amount of powder and liquid on a cool, dry, clean and thick glass slab. • The powder is divided into small quantities (each about one sixth of the total mix) and add them one at a time to the liquid. • After the first increment of powder has been incorporated for 15 to 20 seconds, a second increment is added, and so on. • During mixing, a large surface area (60% of the slab) should be used so that the heat of the exothermic setting reaction will be dissipated. • The mixing continues until all powder has been incorporated (about 90 seconds). • The cement is of proper consistency if it pulls into a thread of about 20 mm in length before snapping back onto the slab. AHMED FARGHALY 40

41. Properties : 1. Adhesion (only mechanical): It is not adhesive and do not form chemical bond with tooth structure and the restoration. The retention depends on the mechanical interlocking of the set material with surface roughness on the preparation and restoration. 2. Biological compatibility : It is irritant to the pulp due to the initial acidity at the time of placement which leads to pulp irritation. Application of several successive thin layers of varnish will protect against pulpal irritation from infiltration of the phosphoric acid. Frozen slab technique have the benefit of accelerating pH rise of the cement and decreasing the irritation to the pulp. 3. Mechanical properties: Has high mechanical properties particularly the compressive strength. The use of cool glass slab or frozen slab technique allows an additional powder to be incorporated in the liquid and improving the compressive strength of the cement. AHMED FARGHALY 41

42. 4. Solubility : It is a soluble cement, greater resistance to solubility is obtained by incorporating more powder into the liquid (cool glass slab and frozen slab technique). 5. Working time: It has a reasonable and long working time about 5 minutes. 6. Film thickness: has a thin film thickness. The maximum film thickness is 25 µm. 7. Viscosity and flow: Zinc phosphate cement is dilatant, i.e. viscosity increased with increase shear rate of mixing. The viscosity rise steadily during setting. The cement provides a good flow. 8. Translucency : It is not translucent but the set cement is opaque. 9. Anticariogenic property: It has no Anticariogenic property. 10. Removal of excess cement : Easy removal of excess cement because it develops brittle properties. AHMED FARGHALY 42

43. III . Zinc Polycarboxylate cement: Composition: The powder is composed of zinc oxide containing less than 10% magnesium oxide. The liquid is a 40% aqueous solution polyacrylic acid. Water settable versions of this cement is available . Manipulation : All powder should be incorporated to the liquid quickly and at once, and the spatulation should be completed within 30 seconds to provide the maximum lengths of working time. The proper consistency of the cement if follow the cement spatula about 20 mm in length when the spatula is rapidly moved upward. AHMED FARGHALY 43

44. Properties: 1. Adhesion ( chemical and mechanical): It is the first truly adhesive cement which is introduced by Smith in 1968. It adheres to enamel and in a lesser way to dentine due to chemical bond between the cement and the contained calcium of the tooth structure. To achieve good adhesion to tooth structure, a clean surface is necessary in order to attain intimate contact and interaction between the cement and the tooth. A recommended procedure is to apply a 10 percent polyacrylic acid solution (conditioner) for 10 to 15 seconds followed by rinsing with water to remove the smear layer. The mixed cement should be applied to the tooth as soon as possible and be used only as it still appears glossy on the surface otherwise poor adhesion may result. The cement does not adhere well to gold or porcelain. Techniques of tin plating of the fitting surface of the restorations have been developed to improve the adhesion. The cement provides strong adhesive bond to non-precious alloy. AHMED FARGHALY 44

45. 2. Biologic compatibility: Excellent biocompatibility because the cement is not irritant and there is lack of post operative sensitivity: a) There is rapid rise of pH to a value of 6 and 7. b) The large molecular size and low toxicity of the polyacrylic acid. c) Its ability to complex with proteins limits diffusion through the dentinal tubules . 3. Mechanical properties: Lower compressive and modulus of elasticity but higher tensile strength compared to zinc phosphate. 4. Solubility : It is a soluble cement. 5. Working time: It has an extremely short working time about 2.5 minutes, which makes the seating of a long-span bridge difficult. 6. Film thickness: it has a low film thickness (25 µm). 7. Viscosity and flow: Polyacrylic acid solutions are viscous which affects the ease of mixing of the cement. The cement is pseudoplastic i.e. the viscosity decreased with increase shear rate of mixing. 8. Translucency : It is not translucent but the set cement is very opaque because of the large quantity of unreacted zinc oxide that is present. 9. Anticariogenic property: It has no anticariogenic property. AHMED FARGHALY 45

46. 10. Removal of excess cement: It is difficult to remove excess cement because the cement does not develop brittle properties. During setting, the cement passes through a rubbery stage. The excess amount that has extruded at the margins should not be removed while the cement is in the rubbery stage since there is danger that some of the cement may be pulled out from beneath the margins, leaving a void, and leading to recurrent caries. Excess is not removed until the cement becomes hard. AHMED FARGHALY 46

47. IV. Glass ionomer cement: Composition: A. Conventional glass ionomer: The powder is a calcium fluoro-aluminosilicate glass. The liquid is polyacrylic or polymaleic acid. The glass ionomer cements are supplied as a powder and a liquid or as a powder that is mixed with water. The polyacrylic acid is formulated in the powder. The liquids of these products may be water or a dilute solution of tartaric acid in water (water settable cement). Several products are encapsulated. B. Resin-modified glass ionomer cement: They are glass ionomer cements with the addition of a small quantity of resin components such as (HEMA) or BIS-GMA some of the water component of the conventional glass ionomer cement is replaced by a water /HEMA mixture. The amount of resin in the final set cement is between 4.5% to 6%. AHMED FARGHALY 47

48. Manipulation: The powder is divided into two equal parts and mixed with the liquid using the spatula. The first increment is rapidly incorporated in 10 seconds and the second increment incorporated for a further 10 seconds. The proper consistency of the cement is reached if it follows the cement spatula about 20 mm in length when the spatula is rapidly moved upward. Properties: 1. Adhesion (chemical + mechanical): It is the second truly adhesive cement which is introduced by Wilson and Kent in 1972. It adheres to enamel and to a lesser way to dentin due to chemical bond between the cement and the contained calcium of the tooth structure. The cement does not adhere to gold or porcelain. It provide strong bond to non-precious alloys specifically after sandblasting with 50 µm alumina. AHMED FARGHALY 48

49. 2. Biological compatibility: The cement is not irritant because the liquid is polyacrylic acid. It may cause prolonged postoperative sensitivity varying from mild to severe. To reduce the incidence of post operative sensitivity the following procedure is suggested: a) Slight hydration of the tooth before cementation by placing a drop of water on the tooth during mixing, this is gently blown off just before placing restoration on the tooth. b) Allowing the cement to set hard to the touch, plus one minute before removing the excess. c) Placing a varnish on the margins of the restoration after removing the excess cement. AHMED FARGHALY 49

50. 3. Mechanical properties: High compressive and tensile strength but lower modulus of elasticity. A disadvantage of glass ionomer cement is the slowness with which the ultimate properties are developed. N.B .: The resin modified glass ionomer cement provides rapid early development of strength. 4. Solubility : It is a soluble cement. The cement has a high initial solubility, therefore we have to protect the setting cement from moisture by applying a varnish at the margin of the restoration. N.B.: The resin modified glass ionomer cement has the advantage of resistance to initial solubility. 5. Working time: It is not too long about 3.5 minutes. The use of water settable cement will improve and prolong the working time. N.B.: The resin modified glass ionomer cement allows for longer working time. AHMED FARGHALY 50

51. 6. Film thickness: Low film thickness (20 µm). 7. Viscosity and flow: Glass ionomer showed an initial slow rise in viscosity with a subsequent increase. It has a high and excellent flow. 8. Translucency : It is translucent due to the presence of glass. The refractive index of glass ionomer is similar to enamel and dentine and is an advantage when it is used with the porcelain labial margin technique. N.B.: A disadvantage of the resin-modified glass ionomer cement is the decrease of translucency because of difference in refractive index between the polyacid matrix and polymerized monomer. 9. Anticariogenic property: It has an anticariogenic property and is related to its fluoride content. 10. Removal of excess cement: Easy removal of excess cement because it develops brittle properties. AHMED FARGHALY 51

52. V. Composite Resin Cement: ( A) Conventional composite resin (powder/liquid or two paste systems): One major component is a diacrylate oligomer diluted with lower molecular weight dimethacrylate monomers. The other major component is silanated silica or glass. The initiator accelerator is peroxide-amine. (B) The adhesive composite resin systems: 1. Panavia : the powder consists of 75% quartz filler and initiators. The liquid consists of aromatic methacrylates , aliphatic methacrylates , phosphate monomer activators and stabilizers. 2. 4-META cement: Is formulated with methyl methacrylate monomer and acrylic resin filler and is catalyzed by tri-butyl- borone . 3. Rely-X- Unicem : Is a self adhesive dual-cure resin cement. Conditioning of the prepared tooth structure is not necessary with the Rely-X- Unicem (no etching-priming or bonding). AHMED FARGHALY 52

53. Composition: Monomer : Phosphorulated methacrylates , which can generate self-adhesion. The acidic nature of the monomer allows for demineralization of the tooth surface and then penetration of the cement into the tooth surface. Once polymerized micromechanical retention is achieved between the cement and the tooth. Filler technology: Inorganic alkaline fillers 72% by weight. AHMED FARGHALY 53 RELY-X- UNICEM IS DISTINGUISHED BY : a . Its unique moisture tolerance. b. Little risk for postoperative hypersensitivity. c. Dimensional stability. d. Fluoride ions release. e. Available in several shades.

54. AHMED FARGHALY 54 Manipulation: Chemical , light cured and dual-cured (chemical + light cure) systems are available in composite resin cement. The chemically activated, is supplied as powder and liquid or two pastes systems. The two components are combined by mixing on a treated paper and for 20 to 30 seconds. For the adhesive composite resin (Panavia). The entire amount of powder is rapidly wetted and incorporated with the liquid. Spatulate the mix for 60-90 seconds. The mix will appear very dry at first but will approach a smooth creamy consistency after about 30 seconds. Once the cement has been thoroughly mixed, it should be spread out in a thin layer over the entire pad, this keeps Panavia exposed to oxygen thereby keeping it fluid.

55. Properties: 1. Adhesion : a) Conventional composite resin (only mechanical) it is not adhesive and do not form chemical bond with tooth structure and the restoration. The bond to acid-etched enamel has been far stronger than the dentine bond. Adhesion to dentine presents a more difficult problem because it is a living, wet tissue and contains less mineralized tissue than enamel. Any material which bonds to dentine must first attach to, then be stable on a wet surface. This surface also consists of a smear layer which is an adherent amorphous calcified debris, produced by the action of any cutting instruments. Modern bonding agents have been developed to adhere to dentine, via this smear layer, by modifying or totally removing it and infiltrating the exposed dentine . AHMED FARGHALY 55

56. Effect of acid etching on dentin: The main problem of dentine bonding is that a hydrophobic (Water repellent) resin is required to stick to a watery substrate. A hydrophilic resin primer solution is applied to infiltrate the dentine . Phosphoric acid etching causes alterations in the morphology of the dentine surface, removes the smear layer, opens and widens the dentinal tubules and demineralizes the surface. The tubule has a funnel- shaped appearance and some of the peritubular dentine near the surface has been dissolved. Collagen fibers are evident in the demineralized dentine . The tags extend from an acid-resistant zone of primer/resin infiltrated dentine called the Hybrid layer. AHMED FARGHALY 56

57. b) Adhesive composite resin (chemical + mechanical): Panavia bonds chemically as well as mechanically due to the addition of phosphate ester to the monomer. It is adhesive to tooth structure, silanated porcelain, composites and to the oxide layer on the metal surface . For non-precious alloys, such as nickel chromium and cobalt chromium should be sandblasted with 50 µm alumina oxide powder . For precious alloys, the gold alloys should be sandblasted and then tin-plated (0.2-0.4 microns layer of tin). The cement bonds to the tin oxide layer which develops on the tin-plated surface. 2. Biological compatibility: Conventional and adhesive composite resin cements are irritant to the pulp. 3. Mechanical properties: Excellent mechanical properties for the conventional and adhesive composite resin cement . 4 . Solubility: Composite resin cement is the only insoluble cement in oral fluids . 5. Film thickness: a) Conventional: High film thickness. b) Adhesive: Low film thickness (19 microns ). AHMED FARGHALY 57

58. 6. working time: a) Conventional : Short working time. b) Adhesive (Panavia): Controlled working time. It has a unique anaerobic setting characteristic. The cement will not polymerize or cure as long as it is in contact with oxygen. This enables the clinician to control the working time before applying the oxygen-inhibiting gel (oxygaurd). 7. Viscosity and flow : the viscosity increases rapidly. 8. Translucency : It is translucent. 9. Anticariogenic property : It has no anticariogenic property except the most recent version that releases fluoride (e.g. Panavia F ). 10. Removal of excess cement: a) Conventional: Very difficult. The time of removal of excess cement is critical. It is best to remove the excess cement immediately after the restoration is seated. If it is done while the cement is in a rubbery state, cement may be pulled from beneath the margin of the restoration leaving a void and leading to secondary caries. b) Adhesive (Panavia): Easy removal of excess cement before applying the oxygen-inhibiting gel: oxygaurd (polyethylene glycol gel ). AHMED FARGHALY 58

59. Thank You … AHMED FARGHALY 59