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Prof. Dr. Moustafa Fakhry Khalil
Dr. Naguib El-Fawal For more than 100 years, the restoration of endo treated teeth has been a concern of dentists. They are subjected to a significant loss of tooth structure accompanied by reduction in toughness, flexibility of the remaining dentin, and tensile forces. These changes weaken the teeth due to irreversible changes in dentin microstructure. Introduction Failures involving the post and the crown can result in fracture of the post and the root, and loss of retention of the post. Vertical root fracture constitutes the most serious type of failure in post-restored teeth because it prevents retreatment, and indicates tooth extraction. Introduction INTRODUCTION Introduction Traditionally, metallic alloys have been used to fabricate dental posts and cores due to their suitable physical properties, and their ability to be casted or machined into précised forms. However, these systems have a number of drawbacks; concerns have been raised with respect to the biocompatibility of certain alloys, and removal of metallic posts might be difficult. They also might alter the optical properties of the overlying restoration. Root fracture is commonly associated with this type of posts. Introduction So, the controversy today would be which material or combination of materials is the most efficient concerning strength, esthetics, reliability and ease of manipulation to restore endo treated teeth. AIM OF THE WORK Aim of the work The objective of this in vitro study was to compare the fracture resistance and failure modes of endo treated teeth restored with: MATERIALS AND
•Twenty freshly extracted sound single rooted human maxillary central incisors were collected with about the same dimensions in width and length, free of root surface caries, fractures and defects. They had no previous endodontic treatment and no previous restorations that might affect fracture resistance to experimental compressive loading. II.Post and Core Materials: A.Fiber Reinforced Composite Post and Core:
•FRC Evolution Post is a stepped cylindrical, metal-free root canal post. It consists of high density glass fibers embedded in epoxy resin and appears radiopaque in x-rays. Each group of teeth has its special design of posts, and each design has 3 different sizes “Small, Medium and Large”. Large size was used here.
•Evolution Drill size F3 was used for reshaping the root canal to receive the FRC Evolution Post size Y3 to ensure accuracy of fit in the root canal. II.Post and Core Materials B.Custom Made Pressable Ceramic Post and Core:
•IPS e.max Press is a Lithium disilicate glass ceramic material, and it is presented as ingots with four different degrees of opacity (HT, LT, MO, HO).
•The shape of the post will be the same as the shape of the fiber reinforced composite post used in this study. And the post space will be created using the same drill used for the fiber posts. III.Luting Materials V.Materials Used For Mounting the Teeth VI.Materials Used For Making the Impression For Custom Made All-Ceramic Posts METHODS IV.Materials Used For Root Canal Treatment: A)Manual canal instrument K-File type.
B) Gutta Percha Points.
C) Absorbent paper points.
D) Resin Sealer “Adseal”. A.Acrostone cold cure denture base material.
B.Special Tray self cure acrylic material.
C.Custom made split brass mold.
D.PTFE “PolyTetraFluoroEthyline” tape.
I.Stomaflex® Gel Catalyst. A.Express STD Impression Material. B.Pattern Resin LS. 1-Specimens Preparation 1-Specimens Preparation 3-Root Canal Preparation and Filling Twenty freshly extracted sound single rooted human maxillary central incisors were obtained. External debris were removed from all the specimens with an ultrasonic scaler. They were examined to exclude root surface cracks under 20X magnification. Radiographs were made for the specimens to ensure that there was no internal resorption or any canal abnormalities. •The buccolingual and the mesiodistal dimensions at cementoenamel junction of each tooth were measured using digital caliper (accurate to 0.01mm) to ensure an even size distribution within the specimen groups. The mean buccolingual and mesiodistal dimensions were 6.6 mm and 6.3 mm respectively. 1-Specimens Preparation The coronal portions of all teeth were sectioned perpendicular to the long axis of the teeth at a level of 2 mm coronally to the most incisal point of the cementoenamel junction to obtain the ferrule length by using a diamond disc under water cooling system. The remaining lengths were 16 ± 1 mm in all specimens. The specimens were randomly divided into two groups according to the type of post used. Each group consists of ten teeth.
Group A: Teeth restored with one-piece fiber-reinforced composite post and core (Evolution Post) covered by an all-ceramic crown (IPS e.max Press)
Group B: teeth restored with custom made one-piece pressable ceramic post and core (IPS e.max Press) covered by an all-ceramic crown (IPS e.max Press). 2-Grouping of Teeth 4-Mounting 4-Mounting 4-Mounting 5-Preparation of Posts Space 5-Preparation of Posts Space 6-Fabrication of Custom-made Ceramic Posts and Cores Each specimen was embedded in its acrylic resin block fabricated by the specially designed split brass mold. This mold consists of split brass cylindrical ring (the inner diameter is 15mm, the outer is 25mm, and the length is 20mm) surrounded by an outer complete ring with two locking screws for support; the blocks were designed to fit precisely in load cell of the testing machine. The mold was designed in order to hold and centralize the specimens with their long axis by using the following steps: I.The root surfaces were covered with polytetrafluoroethylene (PTFE) tape (Teflon Tape) to the level of 2mm below the CEJ to create a layer of thickness of 0.2-0.3mm to simulate the periodontal ligament space and to minimize microleakage. II.The acrylic resin was mixed and inserted to the split brass mold, then the tooth was mounted in the acrylic block by the aid of a dental surveyor, to ensure that the long axis of the specimen was parallel to the axial surface of the mounting ring. III.The acrylic resin was extended to a level of 2mm below the CEJ to imitate the biological width. IV.During the course of polymerization, the acrylic resin block was cooled in water to avoid dehydration of the dentin and deformation of the acrylic resin so that the embedded depth could remain unchanged. V.After complete setting of the acrylic resin, the Teflon tape was removed from the teeth, and then a light body silicon impression material (Stomaflex Light; SpofaDental) was injected into acrylic resin block. VI.The tooth was reinserted firmly into the acrylic resin block; excess silicon material was moved away after material set. I.Pesso reamer burs were used to remove 8mm of gutta percha from the sectioned surfaces. At least 5mm of gutta percha was left inside the apical part of the canal. II.A master drill (evolution drill) was used to prepare the post space by inserting it till it reaches the full length of the drill which is 8mm. III.Drilling was accompanied with copious saline irrigation. IV.The Evolution post and core was tried in the post spaces for both groups, the retention and fit were checked. The custom-made ceramic post and core must be an exact replicate for the evolution post. The replicate was created as the following: I. A key (consisting of a sunk and a countersunk) was created by using heavy body additional silicon material as the following: A.The sunk: it was made by mixing small portions of base and catalyst and making the mix oval in shape, then we inserted the labial half on the evolution post and core into the mix till the mix setting. B.Five triangular grooves were made on the sunk by using a blade ( two on the right side of the post, two on the left, and one below the apical part of the post) to provide the correct path for the countersunk. 6-Fabrication of Custom-made Ceramic Posts and Cores 6-Fabrication of Custom-made Ceramic Posts and Cores 7-Cementation of the Posts and Cores
A.FRC Evolution Post and Core: 7-Cementation of the Posts and Cores
A.FRC Evolution Post and Core: 7-Cementation of the Posts and Cores
B. IPS e.max Press Custom Made post and Core: 6-Fabrication of Custom-made Ceramic Posts and Cores C. A separating medium was applied to the sunk and the lingual half of the evolution post to prevent the adhesion of the sink and countersunk. D.The countersunk: it was made by mixing small portions of base a catalyst and making the mix oval in shape, then it was applied and adapted on the sunk till the material sets. II.The evolution post was removed from the key. III.A standard post and core resin pattern was created by using Pattern Resin LS; the powder and monomer were mixed according to the manufacturer’s instructions. The mix was applied on the space created by the evolution post and core in the key, and then it was sandwiched between the sunk and the countersunk. IV.The key was pressed by a tightened rubber band until the full setting of the pattern resin. V. The pattern resin was removed from the key, and the excess material was removed by a blade. VI.The pattern resin was tried in the post spaces of the teeth in group B to check the fit and retention. VII.The post and core patterns were invested and then casted by ceramic (IPS e.max Press) using Ivoclar furnace and following the manufacturer’s instructions. VIII.The resulting ceramic post and core was tried in again in the post spaces of the teeth in group B. 8-Fabrication of All-Ceramic Crowns 8-Fabrication of All-Ceramic Crowns 8-Fabrication of All-Ceramic Crowns 9-Cementation of the Crowns:
Group A "Evolution Post and Core" 9-Cementation of the Crowns:
Group A "Evolution Post and Core" 10-Thermocycling: 11-Mechanical Testing a)The teeth were prepared with a round-end tapered diamond bur to create a deep chamfer finish line that is located 2mm below the cores to create the ferrule effect. b)One coat of die spacer was applied on the core surface before each crown construction. c)Crown wax patterns for one tooth from each group were fabricated on the core with a 9mm height. A palatal notch was milled in the waxed crown with the surveyor at an angle of 135° to the long axis of the tooth, measuring 1mm depth, 2mm width and 6mm above the cervical margin of the crown. This notch served as a standard loading point. d)The crown wax was invested then casted by IPS e.max Press ceramic. e)The crown was tried on the tooth and the palatal notch was temporarily blocked with wax. f)An index of heavy body additional silicone material was created to standardize the morphology of all the twenty crowns. g)The other 18 crowns wax patterns were created using the heavy body index. And the palatal notch was recreated in all of them. 9-Cementation of the Crowns:
Group B "IPS e.max Press Post and Core" All the test specimens were stored in incubator at 37°C for 24 hours prior to the mechanical testing. The test specimens were thermocycled using thermocycling machine for 500 cycles at 55°C and 5°C with a dwell time of 1 minute, and transfer time of 30 seconds. 12-Statistical Analysis All measurements and observations in all steps were performed by the same investigator. Data were collected from each group and according to each test, and then statistically analyzed with one way analysis of variance to compare the two groups. Results Results Results Results RESULTS Table (I): Fracture loads of the two groups in Kilograms (Kg): Mean fracture resistance of two test groups. Table (II): Comparison of failure modes among the two groups: •There was no statistically significant difference in failure modes between Evolution post (Group A) and custom made IPS e.max Press post (Group B). (P value = 0.329) •30% of all samples represented type I failure mode (favorable) and 70% represented type II failure mode (catastrophic). Results Distribution of failure modes of the two test groups. Favorable Results Catastrophic Conclusions Recommendations CONCLUSIONS Within the limitations of this in vitro study; the following conclusions were obtained: 1.The endodontically treated anterior teeth restored either by one-piece FRC post and core, or custom made ceramic post and core have comparable fracture resistance. 2.The Evolution FRC post and core had slightly more favorable failure modes and slightly more predictable results than the custom made ceramic post made from IPS e.max Press. RECOMMENDATIONS Within the limitation of this study we recommend that: 1.Fiber reinforced composite posts and cores are preferable to restore endodontically treated teeth because they are less expensive and more time saving. 2.Further clinical studies should be conducted to confirm these in vitro results. 3.Further clinical studies should be conducted to compare between these two types of post and core regarding their effect on esthetics. Strength and esthetics are the main factors affecting the choice of an appropriate restoration for endo treated teeth. They are commonly restored with a post, core and a crown. The main functions of the post are: to create coronoradicular stabilization, and retaining the core. Fracture susceptibility of teeth restored with posts are due to many factors such as: the amount of the remaining healthy tooth structure, which provides resistance to the fracture of the tooth, as well as the characteristics of the post, such as the material composition, modulus of elasticity, diameter and length. So, the above difficulties associated with metal posts ( coupled with developments in fields of ceramic and polymeric technology, advances in adhesive dentistry and the increased esthetic demand from patients) have prompted the development of tooth-colored, metal-free post and core systems. These can be broadly divided into composite (Epoxy-resin fiber) and ceramic post systems. Thus the purpose of this study was to compare the effect of glass fiber reinforced post and core and pressable ceramic post and core on vertical root fracture resistance of endo treated upper central incisors. 1-One piece glass fiber post and core, covered by an all-ceramic crown. 2-One piece ceramic post and core made of IPS e.max Press, covered by an all-ceramic crown. MATERIALS The root canals were endodontically treated in all the specimens with step-back technique using K-files, and obturated using lateral condensation technique. 1-Specimens Preparation
I. Specimens Selection: 4-Mounting Same as group "A" EXCEPT: Same as group "A" EXCEPT: