Monoblock

monoblock in endodontics

1. MONOBLOC CONCEPT IN ENDODONTICS Presented By Dr. Laxmi Murkey Dr. Vibha Hegde Dr . Sharad Kokate Dr . Ushaina Fanibunda Dr . Ashwin Jain Guided By Journal club

2. Monoblocks in root canals - a hypothetical or a tangible goal J Endod . 2007 The term monoblock , literally meaning a single unit Franklin R. Tay first described the concept of monoblock in endodontics . 2

3. MONOBLOCK ONE UNIT- GAP FREE ROOT FILLING MATERIALS POST AND CORE 3

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5. A primary monoblock has only one interface that extends circumferentially between the material and the root canal wall. HEMA containing root filling material Hydron ( Hydron Technologies) was marketed commercially for en masse filling of root canals 5

6. Disadvantage of H ydron Hydron was injected - presence of residual moisture within the root canals . Chirila TV et al stated that HEMA polymerizes in the presence of water to form soft hydrogels that are highly permeable and leachable. Moduli of elasticity of porous poly(HEMA) hydrogels such as Hydron ranges from 180–250 MPa 6

7. Orthograde obturation with mineral trioxide aggregate -primary monoblock in attempts to strengthen immature tooth roots 7

8. The compressive elastic moduli of Portland cement increase after 14 days to 15 GPa (i.e. 15,000 MPa ) . MTA does not contribute in root strengthening, apart from its ability to stimulate cementogenesis in apexification and root end fillings. L ack of bonding to dentin, and that although it has high stiffness in compression, it has little strength in tension Baek SH, Plenk H Jr , Kim S. Periapical tissue responses and cementum regeneration with amalgam, SuperEBA , and MTA as root-end filling materials. J Endod 2005 Tay and Pashley 8

9. MTA interacts with dentin by releasing calcium and hydroxyl ions results in the formation of apatite-like interfacial deposits . orthograde obturations and perforation repair 9

10. Secondary Monoblocks Secondary monoblocks are those that have two circumferential interfaces, one between the cement and dentin, the other between the cement and the core material. 10

11. T he materials that constitute a monoblock should have the ability to bond strongly and mutually to one another, as well as to the substrate with which the monoblock is intended to reinforce. T hese materials should have moduli of elasticity that are similar to the substrate. 11

12. Modulus elasticity of gutta-percha points (ca. 80 Mpa ) is 175–230 times lower than that of dentin (ca. 14,000–18,600 Mpa ), making them too plastic (i.e. not stiff enough) to reinforce roots after endodontic therapy. 12

13. I n 2004 with the advent of bondable root filling materials that are advocated as alternatives to conventional gutta- percha were introduced. Resilon ( Resilon Research LLC, Madison, CT) is a bondable root filling material that may be used for either lateral or warm vertical compaction techniques 13

14. Resilon - polycaprolactone -based, dimethacrylate resin– contains Bioactive glass Epiphany Sealer . Primer & a dual cure sealer 14

15. Initial studies on Resilon -filled root canals were highly favorable. Resilon Monoblock System (RMS ) that produces ideal root obturations in terms of coronal sealing and fracture resistance 15

16. It was studied later that large polymerization stresses during their setting that may cause debonding and gap formation along the periphery of the root filling . The extremely high C- factor(above 1000) in root canals has been cited as a possibility for not achieving perfect seals in Resilon -filled root canals Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentin bonding in root canals: a theoretical modeling approach. J Endod 2005;31:584–9 16

17. Also it lacks a free radical-containing oxygen inhibition layer - its bondability to resin- based sealers has further been questioned Tay FR, Hiraishi N, Pashley DH, Loushine RJ, Weller RN, Gillespie WT, Doyle MD. Bondability of Resilon to a methacrylate-based root canal sealer. J Endod 2006;32:133–7 . Gesi A, Raffaelli O, Goracci C, Pashley DH, Tay FR, Ferrari M. Interfacial strength of Resilon and gutta-percha to intraradicular dentin. J Endod 2005;31:809–13. 17

18. T here is no difference between Resilon and gutta-percha in strengthening and reinforcement of immature roots. The modulus of elasticity of Resilon was found to be 86.6 ± 43.2 MPa under dry conditions and 129.2 ± 54.7 MPa after one month of water sorption . Thus, similar to gutta-percha, Resilon is not stiff enough to achieve a mechanically homogeneous unit with root dentin Williams C, Loushine RJ, Weller RN, Pashley DH, Tay FR. A comparison of cohesive strength and stiffness of Resilon and gutta-percha. J Endod 2006;32:553–5 18

19. Is Resilon the Solution? Studies have shown conclusive evidence of Resilon being equally effective or even superior to gutta-percha based systems however long-term studies on leakage comparing gutta-percha and Resilon -based systems have shown they showed more fluid movement when tested at 16 months . IEJ 2007 19

20. The question of biocompatibility of periapical tissues with resin-based systems and leaching of resin by-products still exists. So , due to the nonresorbable nature of resins, the removal of obturating material in the cases of overfills is a major concern. 20

21. Tertiary Monoblocks An additional circumferential interface is introduced by coating the non-bondable gutta-percha points with materials that render them bondable to the root canal sealers. 21

22. Diisocyanate isocyanato group - the hydroxyl group of a hydroxyl-terminated polybutadiene - hydrophobic component- binds to the gutta-percha cones Isocyanato group – binds to the hydrophilic methacrylate functional group producing a gutta-percha resin coating that is bondable to a hydrophilic, methacrylate-based dual-cured resin sealer. In the EndoRez system ( Ultradent , South Jordan, UT ) 22

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24. To -date, leakage and morphologic studies showed that the seal of system is mediocre. polymerization shrinkage of the methacrylate-based sealer . sealer bonds weakly to the pre-polymerized proprietary coating – absence of oxygen inhibition layer. Since the external proprietary resin coating is uneven there can be partial detachment J Adhes Dent 2005 24

25. In ActiV GP ( Brasseler )- used with conventional gutta-percha cones that are surface-coated with glass ionomer fillers using a proprietary technique. It can be bonded to the root dentin via a glass- ionomer sealer Dent Today 2006 25

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27. However, being a single cone technique, coronal leakage of the ActiV GP system to fluid filtration was worse than that achieved with gutta-percha/AH Plus. Monticelli F, Sword J, Martin RL, Schuster GS, Weller RN, Ferrari M, Pashley DH, Tay FR. Sealing properties of two contemporary single-cone obturation systems. Int Endod J. in press 27

28. H ydrophilic polymer in the root canal, The Smart-Seal System ( endotechnologies,USA ). The system consists of premade obturation points ( C - Points) containing a polyamide core with an outer bonded hydrophilic polymer coating. The polymer coating is a cross-linked copolymer of acrylonitrile and vinylpyrrolidone which has been polymerised and cross- linked using allyl methacrylate and a thermal initiator 28

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30. The inner core is composed of two proprietary nylon polymers: Trogamid T and Trogamid CX . Smartpaste bio is a resin based sealer designed to swell through the addition of bioceramic filler particles. 30

31. Smartpaste bio produces calcium hydroxide and hydroxyapatite as by- products of the setting reaction, rendering the material both anti-bacterial while setting and very biocompatible once set. Also , it is hydrophilic in nature, allowing the C- point to hydrate and swell to fill any voids. 31

32. The use of expandable obturating materials to improve the seal of the root-filled canals Hydrophilic obturations of the root canal shows a better resistance to bacterial leakage as compared to hydrophobic obturations . JCD 2015 32

33. Monoblock in post and core 33

34. A customized polyethylene fibre post- core system such as Ribbond ( Ribbond Inc., Seattle, WA ,USA ) can create a primary monoblock in a root It has a elastic modulus of 23.6 GPa ( Eskitascioglu et al. 2002 ) therefore, too high elastic modulus creates interfacial stresses along the resin dentin interface. 34

35. POLYETHYLENE FIBRE POST-CORE 35

36. Microleakage studies comparing different dowel systems was done using fluild filtration test. Glass fibre and ribbond posts should least microleakage when compared to zirconia and stainless steel. Fracture resistance was better in glass fibre post as compared to ribbond posts J Prosthet Dent 2004 Clin oral investig 2012 36

37. Prefabricated post systems bonded to root canal dentine via resin cements represent a secondary monoblock First implied existence of a mechanically homogeneous monoblock is reported in 1996 with the bonding of epoxy resin– based, carbon fiber–reinforced posts to root dentin . 37

38. Epoxy- resin based matrices – did not bond to methacrylate cements Carbon - fibre posts are black in colour and do not lend themselves to aesthetic restorations with all-ceramic units. These posts are also called glass- fibre and quartz- fibre 38

39. In the fibre posts the epoxy resin matrix are replaced with highly cross-linked , methacrylate resin matrices that have the potential to bond to methacrylate-based resin cements 39

40. Since resin cements exhibits less microleakage and bond to the tooth structure as compared to other cements 40

41. Fiber posts that contain an external silicate coating (DT Light SL, VDW GmbH, Munich, Germany), Anatomic Post R(TD , St. Egéve , France) may be considered as tertiary monoblocks Tertiary monoblock = Fibre post + external silane 41

42. Coating made of silane and silicate is applied to the post DT Light SL 42

43. J.dent mater 2005 The adhesion between prefabricated FRC posts and composite resin cores with and without post- silanization was studied. For better adhesion , salinization is advisable Choi et al . found that no additional surface treatment is needed . 43

44. ‘ANATOMIC POST’ 44

45. Theoretically, a reduction of the resin cement thickness should result in a reduction of volumetric shrinkage. Polymerization shrinkage stresses along the cavity walls are also present in a low compliance environment Introduction of a tertiary interface is problematic in that gaps were found to be present between the fiber post and the relining composite. These gaps may can act as stress raisers and result in eventual adhesive failure and dislodging of the fiber post from the relining composite. 45

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47. Thus, until non-shrinking composites are available the pursuit of an ideal monoblock for reinforcing the root canal may be viewed as an ideal goal . CONCLUSION 47

48. Monoblocks in root canals: a finite elemental stress analysis study Aim To investigate using finite element stress analysis ( FEA) primary, secondary and tertiary monoblocks created either by adhesive resin sealers or by different adhesive posts and to evaluate the effect of interfaces on stress distribution in incisor models 2011 International Endodontic Journal 48

49. primary monoblock - Mineral Trioxide Aggregate ( b) Secondary monoblock - ( MetaSEAL ) and Resilon (c)tertiary monoblock – EndoREZ ( d) primary monoblock - polyethylene fibre post-core ( Ribbond ) ( e ) secondary monoblock - glass- fibre post and resin cement ( f) tertiary monoblock - bondable glass - fibre post ( g) tertiary monoblock - silane - coated ceramic post 49

50. A 300 N load was applied from the palatal surface of the crown with a 135 angle to the tooth long axis. Measured in von Mises stress unit 50

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52. RESULT 52

53. Stresses within roots increased with an increase in the number of the adhesive interfaces . Creation of a primary monoblock within the root canal reduce the stresses that occur inside the tooth structure. DISCUSSION 53

54. The palatal side of the MTA - decreased stress accumulation (8.33–13.3 MPa ) Composite resin in the access cavity has increased stress at the coronal region. The MTA-treated model revealed that the material kept the stress inside of the material body (1.67 –3.33 MPa ) and directed towards the root. 54

55. The polyethylene fibre post-core system is considered to create primary monoblocks in the present study. Von Mises stress values indicated that the stress occurring coronally was high in primary monoblock model N o stress was directed towards the root. 55

56. secondary monoblock model revealed stress accumulation at the interface between the Resilon and MetaSEAL (13.3–20 MPa ) Even the adhesive procedures alone are not sufficient to strengthen dentine if the material is not stiff enough (Grande et al . 2007 ) 56

57. Debonding of posts because of contraction stress of ( Cagidiaco et al . 2008 ). Shrinkage stresses that occur with polymerization of methacrylate -based resins specially in deep, narrow canals In the present study it was demonstrated that as the number of interface increases the stresses also increase but the distribution of stresses were close to that of natural tooth. 57

58. F ibre posts that contain an extra silicon coating such as DT Light ( VDW) or ceramic posts that require a silane coating such as Cosmopost ( Ivoclar ) - tertiary monoblocks . Stress values along the cement glass - fibre or ceramic interface ranged from 1.67 to 15 Mpa for tertiary monoblock models Furthermore , the stress was directed through the root. 58

59. C eramics used for post fabrication present moduli of elasticity that are above that of dentine ( Dietschi et al . 2007 ) . T he failure mode is mostly non-restorable ( Eskitascioglu et al. 2002, Maccari et al. 2003 ). Catastrophic fractures 59

60. Concept of monoblock is hypothetical Accomplishing these “ideal monoblocks ” in the root canal space is easier said than done. 60

61. Over-thinning of the adhesive Even the entrapment of water droplets between the adhesive and resin cements/sealer introduces crack tips in fracture toughness testing . They can act as stress raisers that promote crack growth and propagation during loading along the interface. J Biomed Mater Res B Appl Biomater 2006 J Endod 1998 Problems associated 61

62. “The goal of being able to bond a canal from the minor constriction to the canal orifice to the occlusal surface is a desirable one” 62

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