Evaluation of axial displacement and torque loss of Morse-type prosthetic abutments of different angular tapers to their respective implants.

STATEMENT OF PROBLEM: The biomechanical stability of the implant-prosthesis assembly and its maintenance under function is a determining factor in the success of implant prosthesis rehabilitation, but studies of different angular tapers are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the axial displacement and torque loss of prosthetic abutments with Morse-type connections of different angular tapers after thermomechanical cycling by using microcomputed tomography (µCT) and a digital torque wrench. MATERIAL AND METHODS: Eighteen Ø3.5×11.5-mm implants were embedded in polyvinyl chloride cylinders, and the 3 different types of abutments (n=6) with angular tapers of 11.5 degrees - Alvim Cone Morse (ACM-11.5), 16.0 degrees - Helix Gran Morse (HGM-16), and 24.0 degrees - Nobel Replace Conical Connection (NRC-24) were installed with the torque recommended by the manufacturers. To calculate the axial displacements of the abutments about the implants, zirconia maxillary canine crowns were fabricated using a computer-aided design and computer-aided manufacturing (CAD-CAM) system and cemented onto the abutments. Before and after thermomechanical cycling, the assemblies were scanned using microtomography (micro-CT) to assess axial displacement, and the torque losses were calculated after the abutments were finally unscrewed. A load of 100 N, frequency of 2 Hz, and 106 cycles with temperature variation of 5 °C to 55 °C were used for the thermomechanical cycling. Analysis of variance and the Tukey post hoc test (α=.05) were used for analysis. RESULTS: A significant difference was observed between the abutments for axial displacement, measured after thermomechanical cycling (P=.002). The ACM-11.5 abutment showed the highest mean value (134.1 ±58.7 µm), different from HGM-16 (63.3 ±26.1 µm) (P=.013) and NRC-24 (42.7 ±8.7 µm) (P=.002); the 2 latter groups were similar to each other (P=.618). For the torque losses, no significant difference was found among the abutments (P=.928), but there were significant differences for the thermomechanical cycling (before and after) (P<.001) in that the loss of torque was greater after thermocycling. CONCLUSIONS: The smaller the taper angle of the Morse-type prosthetic abutment, the greater its axial displacement, and the thermomechanical cycling significantly reduced pretorque, regardless of taper.

Bond strength and quality of bond interface of multifilament fiberglass posts luted onto flat-oval root canals without additional dentin wear after biomechanical preparation.

STATEMENT OF PROBLEM: An intraradicular retainer formed by multiple independent glass fiber filaments was developed aiming to allow better adaptation in flattened root canals; however, the performance of the new posts is unclear. PURPOSE: The purpose of this in vitro study was to compare the bond strength (BS) and adhesive interface quality achieved in flattened root canals restored with conventional glass fiber posts (CFPs) and multifilament glass fiber posts (MFPs). MATERIAL AND METHODS: The distal roots of mandibular molars with long oval root canals were endodontically treated, and the obturation material was removed and assigned to 2 groups (n=11) according to the type of retainer used: CFP (WhitePostDC#0.5; FGM) or MFP (CometTail#4; Synca). The posts were cemented with self-adhesive resin cement. The specimens were sectioned (2 slices per third). The most cervical slice in each third was used to evaluate the BS, while the adhesive interface in the apical slices was analyzed by scanning electron microscopy. BS data were analyzed by using a multilevel generalized linear model, and adhesive interface SEM data were analyzed by using a multilevel ordinal logistic regression model (α=.05). RESULTS: Multilevel regression showed a statistically significant difference for the "type of retainer" factor (P=.001; CFP 2.61 ±1.30>MFP 1.59 ±1.54). No statistically significant differences were found for the "root thirds" factor (P=.346) or for the interaction of both factors (P=.114). The failure pattern was predominantly mixed or adhesive for CFP and adhesive to dentin for MFP. A better adaptation of the restorative material was observed in the cervical third for CFP and in the apical third for MFP (P<.001). CONCLUSIONS: MFP resulted in lower BS values than CFP, with a higher prevalence of adhesive failures to dentin and better adaptation of the adhesive interface in the apical third.

Effect of Intracoronal Depth of Teeth Restored with Endocrowns on Fracture Resistance: In Vitro and 3-dimensional Finite Element Analysis.

INTRODUCTION: Endodontically treated teeth have an increased risk of biomechanical failure because of significant loss of tooth structure. The biomechanical behavior of endodontically treated teeth restored was evaluated using different extensions of endocrowns inside the pulp chamber by in vitro and 3-dimensional finite element analysis (FEA). METHODS: Thirty mandibular human molars were endodontically treated. Standardized endocrown preparations were performed, and the teeth were randomly divided into 3 groups (n = 10) according to different endocrown extensions inside the pulp chamber: G-5 mm, a 5-mm extension; G-3 mm, a 3-mm extension; and G-1 mm, a 1-mm extension. After adhesive cementation, all specimens were subjected to thermocycling and dynamic loading. The survival specimens were subjected to fracture resistance testing at a crosshead speed of 1 mm/min in a universal testing machine. All fractured specimens were subjected to fractography. Data were analyzed by 1-way analysis of variance and the Tukey post hoc test (P < .05). Stress distribution patterns in each group were analyzed using FEA. Qualitative analyses were performed according to the von Mises criterion. RESULTS: After dynamic loading, a survival rate of 100% was observed in all groups. For static loading, statistically significant differences among the groups were observed (P < .05) (G-5 mm = 2008.61 N, G-3 mm = 1795.41 N, and G-1 mm = 1268.12 N). Fractography showed a higher frequency of compression curls for G-5 mm and G-3 mm than for G-1 mm. FEA explained the results of fracture strength testing and fractography. CONCLUSIONS: Greater extension of endocrowns inside the pulp chamber provided better mechanical performance.