Reliability of an Innovative Slab Shear versus Microtensile Bond Strength Test: Mechanical and Finite Element Analysis.

OBJECTIVE: The aim of this study was to evaluate the efficiency of slab shear bond strength test (Slab_SBS) versus the microtensile in evaluation of the bond strength of different substrates. MATERIALS AND METHODS: Forty-eight extracted caries-free human third molars were utilized for teeth specimens' preparation. After flattening of all molars' occlusal table, the specimens were divided into two groups based on the type of utilized restorative material: nanohybrid resin composite and resin-modified glass ionomer (RMGI). Each group was further subdivided into three subgroups according to the subsequently applied bond strength test and specimen width; microtensile bond strength test (µTBS), Slab_SBS [2 mm] and Slab_SBS [3 mm]. Both testing methods were additionally applied on CAD/CAM specimens, nanohybrid resin composite blocks (composite-to-composite), and ceramic blocks (ceramic-to-ceramic). CAD/CAM specimens were prepared and cemented and then sectioned and subdivided as followed for teeth specimens' preparation. Pretest failures (PTF), bond strength, and failure mode of each specimen were recorded. Representative three-dimensional (3D) finite element analysis (FEA) models were developed to simulate µTBS and Slab_SBS specimens. Data were statistically analyzed using Shapiro-Wilk test and Weibull analysis. RESULTS: Pretest failures were only noted in the µTBS subgroups. Slab_SBS provided comparable bond strength to the µTBS of all substrates with adhesive mode of failure. CONCLUSION: Slab_SBS is easier to prepare with consistent and predictable outcome with no pretest failures during specimen preparation and better stress distribution.

Assessment of biomechanical behavior of immature non-vital incisors with various treatment modalities by means of three-dimensional quasi-static finite element analysis.

The objectives of this study were to evaluate the stress distribution and risk of fracture of a non-vital immature maxillary central incisor subjected to various clinical procedures using finite element analysis (FEA). A three-dimensional model of an immature central incisor was developed, from which six main models were designed: untreated immature tooth (C), standard apical plug (AP), resin composite (RC), glass-fibre post (GFP), regeneration procedure (RET), and regeneration with induced root maturation (RRM). Mineral trioxide aggregate (MTA) or Biodentine® were used as an apical or coronal plug. All models simulated masticatory forces in a quasi-static approach with an oblique force of 240 Newton at a 120° to the longitudinal tooth axis. The maximum principal stress, maximum shear stress, risk of fracture, and the strengthening percentage were evaluated. The mean maximum principal stress values were highest in model C [90.3 MPa (SD = 4.4)] and lowest in the GFP models treated with either MTA and Biodentine®; 64.1 (SD = 1.7) and 64.0 (SD = 1.6) MPa, respectively. Regarding the shear stress values, the dentine tooth structure in model C [14.4 MPa (SD = 0.8)] and GFP models [15.4 MPa (SD = 1.1)] reported significantly higher maximum shear stress values compared to other tested models (p < 0.001), while no significant differences were reported between the other models (p > 0.05). No significant differences between MTA and Biodentine® regarding maximum principal stress and maximum shear stress values for each tested model (p > 0.05). A maximum strain value of 4.07E-03 and maximum displacement magnitude of 0.128 mm was recorded in model C. In terms of strengthening percentage, the GFP models were associated with the highest increase (22%). The use of a GFP improved the biomechanical performance and resulted in a lower risk of fracture of a non-vital immature maxillary central incisor in a FEA model.

A Case Report of a Maxillary Second Molar with Two Distinct Palatal Canals, Confirmed by CBCT.

Cases of unusual and complex root canal morphology could be difficult to diagnose and treat. This report describes the diagnosis and management of a rare maxillary right second molar (tooth #17) with two distinct palatal canals. The tooth was diagnosed with irreversible pulpitis and symptomatic apical periodontitis. Non-surgical root canal treatment was performed. Accurate diagnosis and comprehensive treatment of cases with unusual root canal morphology can be achieved by evaluation of periapical radiographs at different angulations, advanced magnification techniques, and the Cone Beam Computed Tomography (CBCT) scanning. Clinicians should be aware that two separate palatal canals could exist in maxillary second molar teeth.

Post-fatigue fracture resistance of premolar teeth restored with endocrowns: An in vitro investigation.

OBJECTIVES: To evaluate the post-fatigue load-to-failure and failure modes of endodontically treated premolar teeth restored with endocrowns fabricated from different CAD/CAM materials. MATERIALS AND METHODS: A total of 60 extracted human, single-rooted premolar teeth were endodontically treated and sectioned horizontally 2 mm above the cementoenamel junction. Sectioned teeth were restored using two reconstruction designs: endocrowns (Cendo) or post-crowns (Cpost) (n = 30 p/g). In each group, reconstructions were fabricated from 3 different CAD/CAM substrates (n = 10 p/g); a resin-based composite (Cera), a lithium disilicate glass ceramic (LiSi) and a monolithic, translucent zirconia (Zir). Additional 10 intact teeth were used as control. Restored teeth were subjected to dynamic fatigue test (10-50 N, 600,000 cycles) and thermocycling (5-55 °C, 1500 cycles). Load-to-failure and failure mode was determined following application of a static, 45° oblique compressive load on each specimen. One-way and Two-way analysis of variance (ANOVA), Tukey's post hoc and chi-square tests were used to determine statistically significant interactions among experimental and control groups. RESULTS: All specimens survived the mechanical and thermal fatigue tests. A statistically significant interaction between reconstruction design and material type was observed (p  <  0.001). CpostZir and CendoCera groups exhibited significantly higher post-fatigue load-to-failure when compared to other materials of the same reconstruction design (p ≤ 0.001). The highest frequency of catastrophic failures was observed with Zir reconstructions in both designs. Intact teeth exhibited significantly higher load-to-failure when compared to all groups (p ≤ 0.042) except CpostZir (p = 0.345). CONCLUSION: Single piece, CAD/CAM resin composite endocrowns can present a reliable option for restoring endodontically treated premolar teeth. CLINICAL SIGNIFICANCE: Endocrowns can be as effective as post-crowns provided appropriate preparation; material selection; and bonding protocols are utilized. Clinicians need to be cautious when prescribing zirconia endocrowns to restore premolar teeth owing to the low fracture resistance and high risk of catastrophic failures.

Dissolution of a mineral trioxide aggregate sealer in endodontic solvents compared to conventional sealers.

The aim of this study is to evaluate the solubility of a Mineral Trioxide Aggregate sealer (MTA-Fillapex) compared with five other sealers, calcium hydroxide (Sealapex), resin (Realseal), zinc oxide-eugenol (Tubli-Seal), and two epoxy resins (AH-26 and AH-Plus), in chloroform and eucalyptoil in static and ultrasonic environments. Samples of each sealer were prepared (n = 180) and then divided into 12 groups that were immersed in solvents for 5 and 10 min in static and ultrasonic environments. The mean weight loss was determined, and the values were compared using Student's t-test, One-way ANOVA, and Tukey's HSD post-hoc test (p < 0.05). In chloroform, MTA-Fillapex, AH-26, and Sealapex displayed moderate solubility with no significant difference in dissolution (p = 0.125); however, their dissolution was significantly lower than that of AH-Plus (p < 0.001), which was almost fully dissolved after 10 minutes. Realseal was significantly less soluble than all sealers (p < 0.001). In eucalyptoil, MTA-Fillapex showed low solubility, as all of the sealers did, but Tubli-Seal was significantly more soluble than other sealers (p < 0.001). Using ultrasonic activation resulted in a significantly higher dissolution rate in chloroform for all sealers except MTA-Fillapex after 10 min (p = 0.226). In eucalyptoil, ultrasonic activation significantly increased the dissolution rate of all sealers except MTA-Fillapex after 5 and 10 min, Sealapex at 10 min, and AH-Plus at 5 min (p > 0.05). In conclusion, MTA-Fillapex was not sufficiently dissolved in either solvent. Ultrasonic activation had limited effectiveness on MTA-Fillapex dissolution, whereas it significantly increased the efficiency of solvents in dissolving a number of endodontic sealers.

Dissolution of a mineral trioxide aggregate sealer in endodontic solvents compared to conventional sealers

Abstract The aim of this study is to evaluate the solubility of a Mineral Trioxide Aggregate sealer (MTA-Fillapex) compared with five other sealers, calcium hydroxide (Sealapex), resin (Realseal), zinc oxide-eugenol (Tubli-Seal), and two epoxy resins (AH-26 and AH-Plus), in chloroform and eucalyptoil in static and ultrasonic environments. Samples of each sealer were prepared (n = 180) and then divided into 12 groups that were immersed in solvents for 5 and 10 min in static and ultrasonic environments. The mean weight loss was determined, and the values were compared using Student's t-test, One-way ANOVA, and Tukey's HSD post-hoc test (p < 0.05). In chloroform, MTA-Fillapex, AH-26, and Sealapex displayed moderate solubility with no significant difference in dissolution (p = 0.125); however, their dissolution was significantly lower than that of AH-Plus (p < 0.001), which was almost fully dissolved after 10 minutes. Realseal was significantly less soluble than all sealers (p < 0.001). In eucalyptoil, MTA-Fillapex showed low solubility, as all of the sealers did, but Tubli-Seal was significantly more soluble than other sealers (p < 0.001). Using ultrasonic activation resulted in a significantly higher dissolution rate in chloroform for all sealers except MTA-Fillapex after 10 min (p = 0.226). In eucalyptoil, ultrasonic activation significantly increased the dissolution rate of all sealers except MTA-Fillapex after 5 and 10 min, Sealapex at 10 min, and AH-Plus at 5 min (p > 0.05). In conclusion, MTA-Fillapex was not sufficiently dissolved in either solvent. Ultrasonic activation had limited effectiveness on MTA-Fillapex dissolution, whereas it significantly increased the efficiency of solvents in dissolving a number of endodontic sealers.