e.monoblock revisited

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monoblocks in endo

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4 ENDODONTIC MONOBLOCKS: Revisited Dr. Asheesh Sawhney*, Dr. Lavanaya Verma**, Dr.Vinisha Pandey***ABSTRACTRemoval of tooth structure during restorative and endodontic treatments increases the risk of tooth fracture. In addition, an adhesion of root canal sealers to dentin is important to seal the root canal thoroughly & prevent dislodgement of filling materials. Recently the use of monoblocks created by bonding root filling materials to radicular dentin has become popular with dentinal bonding reaching the root canal. The aim of this article is to review new materials and different concepts of root canal filling that have been used in the past and present for rehabilitation of root canal space. Thus, the potential of these monoblocks is discussed with the possibility of their use in future.KEYWORDS: monoblocks, dentinal bonding, root filling material.INTRODUCTIONThe ultimate goal of endodontic obturation has remained the same for the past 50 years: a true hermetic seal. A seal where there is no leakage coronally, apically, or laterally. A seal that will help ensure endodontic success and thereby maintain root canal therapy as a preferred treatment modality. An additional goal has been to create a technique so user-friendly that it will result in the greatest majority of dentists performing the best possible obturation.Gutta-percha has for many years been widely used as a solid material in root fillings associated with different types of sealers. Even associated with a sealer, this material it is not capable of preventing leakage, as has been shown in many studies. In actuality, what creates the seal in all of these techniques (silver points, lateral condensation, and thermoplastic methods) is the sealer. Therefore, the sealer is the key to obtaining a true hermetic seal thus creating a true monoblock1, 13 The term monoblock literally means a single unit & its application in dentistry particularly in orthodontics in 1902 was a revolution. Introduced by Dr. Pierre Robin as MONOBLOC APPLIANCE, who united upper & lower acrylic appliances for the treatment of class II division 1 malocclusion. 1The term monoblock is now familiar to endodontics with the application of dentin adhesive technology to endodontics. Thus this article attempts to provide a broader meaning to the term monoblock & the potential of currently available bondable material to achieve a single unitwith root dentin.TYPES OF MONOBLOCKSMonoblocks created in the root canal spaces may be classified as primary, secondary, or tertiary depending on the number of interfaces present between the bonding substrate and the bulk material core (Fig. 1). But before we discuss each type of monoblock, there are 2 pre-requisites to create a mechanically homogeneous unit. First, the material should have the ability to bond strongly and mutually to one another.Second, these materials should have a modulus of elasticity that is similar to that of the substrate.1PRIMARY MONOBLOCKSA primary monoblock has only one interface that extends circumferentially between the material and the root canal wall. Example: HYDRON, MTA A).HYDRON: - introduced in 1970s for en masse filling of root canal.1Advantages: potential successor of gutta perchaDisadvantages: consists of HEMA (hydroxy ethyl methacrylate) which polymerizes in the presence of water.1* Reader **Professsor,* PG Student; Department of Conservative dentistry & Endodontics, Rama Dental College, Hospital & Research Centre, Kanpur.(B)Mineral trioxide aggregate (MTA):-represents a contemporary version of the primary monoblock in attempts to strengthen immature tooth roots. Advantages: root strengthening, stimulate cementogenesis in apexification and root end fillings.Disadvantages: lack of bonding to dentin and low strength in tension. SECONDARY MONOBLOCKSSecondary monoblocks are those that have two circumferential interfaces, one between the cement and dentin and the other between the cement and the core material. 1Most common type of endodontic monoblockExample: carbon fiberreinforced posts (i.e., carbon fiber posts), Resilon monoblock system (RMS).(A)Carbon fiber reinforced posts:Advantages: have a modulus of elasticity very similar to that of dentin, could achieve a toothpost core monoblock.1,5Help to distribute masticatory loads homogeneously and reduce stresses during function.Disadvantages: low stiffness. 1, 5(B) Resilon monoblock system: is a thermoplastic, synthetic, polymer composite root canal filling material.Designed based on polyester chemistry, Resilon contains bioactive and radiopaque fillers. Manipulated in the same manner as gutta-percha but possesses the potential for bonding with a resin based sealant or bonding agent. 1, 7Advantages: preventing bacterial micro leakage owing to enhanced sealing.Improves the fracture resistance of endodontically treated teeth.Disadvantages: bonding to root dentin is weak due to decreased bond strength & lack of free radical containing oxygen inhibition layer. 1,7TERTIARY MONOBLOCKSAre those in which a third circumferential interface is introduced between the bonding substrate and the abutment material.1Examples: DT Light post, Anatomic post, EndoRez system, ActiV GP (A)Endo Rez system: - conventional gutta-percha cones are coated with a proprietary resin coating.Advantages: no dentin adhesive is applied bonding takes place by incorporation of dentinal plugs.1Disadvantages: rapid polymerization of the adhesive, establishment of a mechanically homogenous unit with the root canal is difficult. 1 (B) ActiV GP: - conventional gutta-percha cones that are surface coated with glass-ionomer fillers.Advantages: chemically bonded.1Disadvantages: coronal leakage is more than that of gutta-percha.1 Microleakage & monoblocksStudies conducted on Hydron demonstrated extensive leakages as it consisted of HEMA (Hydorxyethyl methacrylate) which polymerizes in the presence of water to form soft hydro gels that is highly permeable & leachable. Thus, we know that one of the first monoblock was not an ideal root filling material. Different studies were conducted to assess the apical sealing ability of different core materials used with Epiphany sealer and to evaluate the effect of Resilon/Epiphany system on creating an apical mono-block seal.In a recent study, Raina et al found that there was no differences between the apical sealings of gutta-percha/AH Plus and Resilon/ Epiphany system and results concluded that both root canal fillings did not manage to create a monoblock root filling that does not leak, Paqu and Sirtes investigated the apical long-term sealing ability of gutta-percha/AH Plus and Resilon/ Epiphany and reported that Resilon/Epiphany root fillings prevented fluid movement to the same degree as gutta-percha/AH Plus counterparts. 1, 8Shipper et al investigated the bacterial leakage of roots filled using lateral and vertical condensation techniques with gutta percha and AH 26 sealer, with gutta-percha and Epiphany sealer and filled with Resilon and Epiphany sealer. Results showed that Resilon group was superior to gutta-percha groups. 6,8,10Mustafa ,Saglam, Yaman et al concluded Resilon and Epiphany sealer exhibited the least microleakage values and were found to be the best root-canal filling material and this finding may support the manufacturer thesis in which they stated that Resilon and Epiphany create a monoblock filling by bonding each other.8 Pashley,et al evaluated the sealing efficacy of three root-filling systems/techniques in preventing bacterial leakage and concluded that ActiV GP showed the highest bacterial leakage8, 10Dultra et al conducted a study to compare the apical sealing ability of four root canal sealers, Endofill, AH plus, EndoRez & Epiphany and low microleakege results of Endo REZ, which is a UDMA resin-based root canal sealer whereas zinc oxide-eugenol-based sealer had the highest microleakage means of all tested materials. 1,8,10Thus, Root canal microleakage is a complex subject because many variables may influence infiltration, such as root filling techniques, physical and chemical properties of sealers and presence or absence of smear layer. Bond strength & monoblocks Kaya et al compared the interfacial strength and failure mode of root fillings consisting of different technique material combinations (gutta percha or Resilon combined with AH Plus, Ketac Endo or Epiphany Group) and found Resilon had significantly less push-out bond strength than gutta-percha.14In another study by Palamara & Messer bond strength of dentin sealer interface with / without main cone was evaluated using 3 resin sealers , namely AH Plus , Endo REZ or Resilon sealer.Amongst the three resin sealers, AH Plus showed the highest bond strength compared with two UDMA-based root canal sealers. The Real Seal sealer and Resilon cone also showed low bond strength. This suggested that the monoblock concept of Resilon should be reconsidered. 13Homogeneity of monoblocksComplete Obturation without voids will ensure a more homogeneous and complete fill of the root canal system. It is desirable and would be ideal if all voids could be eliminated.Figure 1. A schematic diagram depicting the classification of endodontic monoblocks Cementum Root dentin Bondable coating Fiber post / Root filling material Resin cement / Root canal sealerSamuel R. Epley et al compared a new resin based obturation material with traditional gutta percha techniques in its ability to fill the prepared root canal spaces. The purpose of this in vitro study was to compare the presence of voids in root canals obturated with the new resin-based system versus voids present in canals obturated by two traditional methods using a zinc-oxide eugenol sealer .Roth sealer was found to have more voids as compared to Resilon & Epiphany group.15In another study Gulsahi et al compare the cross-sectional area of sealer plus voids of Epiphany sealer surrounding root fillings completed with Resilon cones and laterally compacted gutta-percha & found no significant differences between both the groups.16Interfacial strength & monoblocks Vertical root fractures of endodontically treated teeth are frequently encountered in the dental practice. Removal of tooth structure during endodontic and restorative treatments increases the risk of tooth fracture, with fatigue mechanisms mediating the fracture of root tissues over time. Recently, the use of monoblocks created by bonding root filling materials to radicular dentin has been proposed as a means to strengthen roots.A Study by Gesi, Pashley & Tay compared the interfacial strengths of Resilon/Epiphany and gutta-percha/AH Plus using a thin-slice push-out test design. They concluded that there was no difference in the interfacial strength of Resilon and gutta percha to inter radicular dentin. 17, 18The strength of an endodontically treated tooth is directly proportional to the amount of remaining sound tooth structure. As tooth structure is lost, the potential for tooth fracture increases. The modulus of elasticity of porous poly- (HEMA) hydro gels such as Hydron ranges from 180 to 250 MPa. To reinforce roots, the modulus of elasticity of a root filling material would need to approximate that of dentin (i.e., 14,000 MPa), thus Hydron was not stiff enough to strengthen roots even if it could have bonded to root canal surfaces. 1, 17In a study by Texiera et al, concluded that fracture resistance of root canal treated teeth is increased when filled with Resilon monoblock system. 18DISCUSSIONThree-dimensional sealing of the root canal is one of the main goals of endodontic treatment and is essential for preventing apical and coronal leakage in the root-canal system. Several test methods have been described to evaluate sealing quality of obturated root canals. The most popular method is the dye penetration test. Dye penetration studies are commonly used because they are easy to accomplish and do not require sophisticated materials. Pitt Ford, who compared the dye leakage of several sealers in vitro, found the differences seen did not produce noticeably different tissue responses in vivo.1, 7, 11 Cleaning the dentinal surface by removing the smear layer is an essential step in the process of successful root canal treatment. In the present study the smear layer was removed by the alternating use of NaOCl and EDTA in order to improve the adaptation of the sealer to the canal wall.Gutta-percha and sealer have been used for many years for root canal obturation. However, new materials and techniques are now available which may increase the potential for successful outcomes by creating a better interface between root canal walls and the filling material to decrease leakage. Some studies have shown a relationship between apical leakage and the bond strength of sealers. The sealers have an inverse relationship for adhesion to gutta-percha and to dentin. In contrast the attachment between the gutta-percha and the sealer AH26 and AH plus may allow an avenue for leakage.6,11 However, in the Epiphany root obturation system, Resilon sealers attachment to root canal walls and to the Resilon filling core material appears to be superior. The Resilon System may be attributed to the monoblock provided by the adhesion of the filling material to the sealer, which also adheres and penetrates into the dentin walls of the root-canal system.11 The question arises regarding whether these materials are bonded along the entire length of the canal especially in the apical area. Similar to using current materials, there will be areas - including some complicated apical regions - where bonding to the canal wall either will not exist or be less than ideal.CONCLUSIONAlthough the concept of creating mechanically homogenous units with root dentin is excellent in theory, accomplishing these ideal monoblocks in the root canal space is easier said than done. Removal of thick smear layers & attempts to infiltrate these smear layers with mild self-etching adhesives is not currently achieved. To date, there are no data on how this may be performed efficaciously inside root canals without avoiding over thinning of the adhesive or introducing air /water forcefully beyond the root apex. Entrapment of these water droplets between the adhesive and resin cements/sealer is analogous to introducing crack tips can act as stress raisers that promote crack growth and propagation during loading along the interface. Highly unfavourable cavity geometry within the root canal space is detrimental during the polymerization of the resin cements or sealers.1, 9, 11 The pursuit of an ideal monoblock for reinforcing the root canal may still be viewed as an ideal goal. These issues become increasingly more complex as additional interfaces are incorporated from the primary to the tertiary monoblocks.REFERENCESFranklin R. Tay and David H. Pashley. Monoblocks in root canals: A Hypothetical or a Tangible Goal, J Endod 2007; 33: 391-98.Rhome, Solomon, Rabinowitz. Evaluation of sealing properties of lateral condensation, vertical condensation, & Hydron, J Endod 1981; 7:458-61.Reader, Foreman, Meyers. Hydron versus gutta-percha and sealer: a study of endodontic leakage. J Endod 1997Andreasen JO, Munksgaard EC, Bakland LK. Comparison of fracture resistance in root canals of immature sheep teeth after filling with calcium hydroxide or MTA. Dent Traumatol 2006; 22:1546.Sidoli GE, King PA, Setchell DJ. An in vitro evaluation of a carbon fiber-based post and core system. J Prosthet Dent 1997; 78:59.Shipper G, rstavik D, Teixeira FB, Trope M. An evaluation of microbial leakage in roots filled with a thermoplastic synthetic polymer-based root canal filling material (Resilon). J Endod 2004; 30:3427.Teixeira FB, Teixeira EC, Thompson JY, Trope M. Fracture resistance of roots endodontically treated with a new resin filling material. J Am Dent Asso 2004; 135:646 52.Mustafa Murat Kocaka, Ozgur Erb, Baran Can Saglamc, Sis Yamand. Apical Leakage of Epiphany Root Canal Sealer Combined with Different Master Cones. Eur Jour of Dent;2008; 2:91-5.Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentin bonding in root canals: a theoretical modelling approach. J Endod 2005; 31:584 9.Tay FR, Loushine RJ, Monticelli F, et al. Effectiveness of resin-coated gutta-percha cones and a dual-cured, hydrophilic methacrylate resin-based sealer in obturating root canals. J Endod 2005; 31:65964.Koch K, Brave D. A new endodontic obturation technique. Dent Today 2006 25:102,104 7.Monticelli F, Sword J, Martin RL, et al. Sealing properties of two contemporary single-cone obturation systems. Int Endod J , 2005;31;122-27.A. Jainaen, J. E. A. Palamara & H. H. Messer . Push-out bond strengths of the dentinesealer interface with and without a main cone. IEJ, 2007;40;882-90.B. U reyen Kaya, A. D. Kececi, H. Orhan & S. Belli Micropush-out bond strengths of gutta-percha versus thermoplastic synthetic polymer-based systems an ex vivo study , IEJ, 2007;41;211-18.Samuel R. Epley, D MD, Jacob Fleischman, DMD, Gary Hartwell, DDS, and Carmen Cicalese , Completeness of Root Canal Obturations: Epiphany Techniques versus Gutta-Percha Techniques , JOE, 2006 ;32;6;541-44.Kamran Gulsahi, Comparison of the Area of Resin-based Sealer and Voids in Roots Obturated with Resilon and Gutta-Percha JOE, 2006;33;11;1338-41.Andrea Gesi ,David Pashley & Franklin R.Tay Interfacial Strength of Resilon and Gutta-Percha to Intraradicular Dentin .J Endod 2005;31;809-13.Texiera et al Fracture resistance of roots endodontically treated with a new resin filling material. , JADA, 2007; 135; 646-52.