Computational protocol: Effect of ferrule on the fracture resistance of mandibular premolars with prefabricated posts and cores

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Protocol publication

[…] One hundred extracted mandibular premolars were selected by the inclusion criteria of free of caries, cracks, or fractures by visual inspections and radiographs, based on a power analysis (G*Power software version 3.1.3; Universitat Kiel, Tranz Faul, Germany). Correct handling of specimens was supervised by Chonnam National University Dental Hospital Institutional Review Board (IRB No.1304/004-001). Hard and/or soft dental debris of teeth were removed using hand scalers, and the teeth were kept in saline during the study except during the operative procedures.The specimens were randomly divided into 5 groups (n = 20): intact teeth restored with a crown (NR, no root canal treatment); ETT restored with a crown without a post (NP, no post); ETT restored with a prefabricated post, core, and crown incorporating a 0 mm ferrule (F0); ETT restored with a post, core, and crown incorporating a 1 mm ferrule (F1); and ETT restored with a post, core, and crown incorporating a 2 mm ferrule (F2) (, , ).In each group, the root length (L) from the buccal mid-point of cement-enamel junction (CEJ) to the apex and buccolingual (BL) and mesiodistal (MD) dimensions at the CEJ were measured with a digital caliper (Absolute Digimatic; Mitutoyo Corp, Kanogawa, Japan) (). The measurements were analyzed with a one-way analysis of variance (ANOVA) to determine significant differences between the groups (P > .05).Coronal tooth structure was reduced to a height of 6 mm occlusal to the CEJ in NR and NP, at the CEJ in F0, at a height of 1 mm occlusal to the CEJ in F1, and at 2 mm occlusal to the CEJ in F2 ().Teeth were embedded along the long axis in autopolymerizing acrylic resin (Vertex self-curing; Vertex-Dental B.V., Zeist, Netherlands) at 3 mm apical to the CEJ to simulate an acceptable biologic width between the clinical crown margin and alveolar bone ().A root canal treatment by the same clinician was applied to groups except for NR. The root canal was prepared within 1 to 2 mm of the apex on a radiograph. The root canal was instrumented with hand files and the step-back technique enlarging the canal to the average #35 K-file (DENTSPLY Maillefer, Ballaigues, Switzerland), irrigated with saline, and dried using paper points (Suredent, Sungnam, Korea). Each canal was obturated with gutta percha points (Suredent, Sungnam, Korea) and a canal sealer (AH plus; DENTSPLY DeTrey GmbH, Konstanz, Germany) by lateral condensation. shows the descriptions for the post and core system used in this study. NR had no post and core. NP was built up with a core at the access opening. The experimental groups (F0, F1, and F2) used prefabricated posts and cores.One week after the root canal treatment, the experimental groups was prepared with a # 2 Pesso reamer (MANI, Takanezawa, Japan) to remove 9 mm of gutta percha apical to the CEJ. Post space was prepared using a Parapost® drill (1 mm diameter) with a low speed handpiece. A new drill was used for each group during the procedure. The canals were irrigated with water and then dried with paper points and blown air. Paracore® (Coltène/Whaledent Inc., Cuyahoga Falls, OH, USA) build-up was performed according to the manufacturer's instructions, and NRC (non-rinsed conditioner) (Coltène/Whaledent Inc., Cuyahoga Falls, OH, USA) was applied to the canal for 30 seconds. After the material was removed with a dry paper point, air blowing proceeded for 2 seconds, and a mixture of bonding A and B (Coltène/Whaledent Inc., Cuyahoga Falls, OH, USA) (ratio 1:1) was applied for 30 seconds. The excess was removed with a dry paper point, and air blowing proceeded for 2 seconds. A dual polymerizing adhesive resin was applied in the canal with a syringe, and the post was inserted in the canal. After building up the coronal portion, it was set to self-cure for 4 minutes.All teeth were prepared for a metal ceramic crown with diamond rotary cutting instruments using a high speed handpiece. The same prosthodontist performed all the procedures. The buccal shoulder margin (depth of 1.5 mm) and lingual chamfer margin (depth of 0.5 mm) were prepared with a 6 mm axial wall height. The finish line for the crown was placed at the level of the CEJ. The teeth of the experimental groups were prepared with ferrule lengths of 0 mm, 1 mm and 2 mm, respectively.Custom trays were fabricated with light curing resin (Eazipan LC™; Vericom Co., Chuncheon, Korea). Impressions of prepared specimens were made with polyvinylsiloxane (Honigum® light; DMG, Hamburg, Germany) and poured with Type V stone (Suprastone; Kerr, Orange, CA, USA). As shown in , the wax-up for a working model was completed 8 mm above the buccal CEJ and 7 mm above the lingual CEJ for the metal crown. To reproduce the buccal cusp, a protuberance of 2 mm was created on the buccal marginal ridge. Loading was designed to be put on this notch. Wax patterns were sprued, invested, and casted with base metal alloy (Bellabond Plus; BEGO, Bremen, Germany) following the manufacturer's guidelines. The cast crowns were adjusted for passive fit with a silicone disclosing material (Fit Checker®; GC Dental Industrial Corp., Toyko, Japan), and corrected crowns were luted to the teeth with resin modified glass ionomer cement (RelyX luting cement; 3M ESPE, St. Paul, MN, USA) mixed according to the manufacturer's instructions. Each crown was placed for 5 minutes under finger pressure. After the setting was complete, the excess cement was removed with a dental explorer.The teeth were submitted to 1000 cycles between 5℃ and 55℃ using a thermal cycling machine (The 1100; SD mechatronik GmbH, Miesbacher, Germany) to simulate the degradation of restorations in the oral cavity during cyclic loading, with a dwell time of 10 seconds, as in previous studies.After the thermal cycling test, the teeth were loaded in a universal testing machine (Unitech RB301; R&B Inc., Daejeon, Korea) and placed at an angle of 135 degrees to the axis of the tooth. The load was applied on the protuberance of the buccal cusp with a crosshead speed of 2.54 mm/min (). The fracture load (in N) was measured as the first major load drop occurred.The data were analyzed with a one-way ANOVA in order to determine the difference of fracture load among groups. Tukey HSD test was used for post hoc analysis. A statistical program (IBM SPSS Statistics 21; IBM, Armonk, NY, USA) was used. A significance level of alpha equal to 0.05 was used for all statistical testing. […]

Pipeline specifications

Software tools G*Power, SPSS
Application Miscellaneous
Diseases Fractures, Bone