Background/Objectives: Endodontically treated molars are structurally weakened due to internal tissue loss, increasing their risk of fracture. Endocrowns, developed as a conservative alternative to post–core systems, have gained popularity with the rise of digital dentistry, CAD/CAM workflows, and 3D-printed restorations. In this context, the aim of the present pilot study was to investigate the influence of cement layer thickness, intracoronal depth, and dentine wall thickness on the fracture resistance of molars restored with 3D-printed endocrowns. Methods: Twelve extracted human molars were endodontically treated and restored with endocrowns fabricated from a 3D-printed resin material, SprintRay Crown^TM (SprintRay Inc. Los Angeles, CA, USA), via masked stereolithography (MSLA) on a Prusa SL1 printer. Cementation was performed using RelyX Universal Resin Cement (3M, Maplewood, MN USA). Cone beam computed tomography (CBCT) was used to measure the dentine thickness and intracoronal depth before cementation and cement thickness after cementation. The fracture resistance was evaluated using a universal testing machine. For each variable (Td, Dp, Tc), the 12 specimens were divided into two groups (n = 6). Statistical analysis included Pearson correlation, a one-way ANOVA, and the non-parametric Mann–Whitney U test. Results: Within the limitations of this pilot in vitro study, cement thickness demonstrated a strong positive correlation with fracture resistance (r = 0.577) and was the only variable showing statistical significance in the ANOVA (F = 7.847, p = 0.019). In contrast, intracoronal depth and dentine wall thickness exhibited weaker and nonsignificant correlations. No significant mechanical advantage was observed from increasing the pulp chamber depth or peripheral dentine wall thickness. This result was further supported by nonparametric Mann–Whitney U testing (p = 0.015). Conclusions: Cement layer thickness is a key biomechanical factor influencing the fracture resistance of endocrown restorations. Preparation depth and dentine wall geometry appear to have a less direct impact.

Background/Objectives: This study investigates the temperature changes on the external root surface during root canal preparation using different rotary systems and assesses the impact of irrigation temperatures. Methods: Sixty extracted human maxillary incisors were divided into four groups based on the rotary system used: ProTaper Next (Dentsply Sirona, Ballaigues, Switzerland), Reciproc Blue (VDW GmbH, Munich, Germany), WaveOne Gold (Dentsply Sirona, Ballaigues, Switzerland), and TruNatomy (Dentsply Sirona, Ballaigues, Switzerland). These systems differ in cutting efficiency and design. Temperature measurements during instrumentation and irrigation were recorded using a FLIR E60bx thermal camera (Teledyne FLIR LLC, Hudson, NH, USA). Irrigations were conducted with sodium hypochlorite at room temperature and heated to 60 °C. Results: The ProTaper Next group exhibited the highest average temperature increase during instrumentation (5.2 °C), followed by WaveOne Gold (4.3 °C), Reciproc Blue (3.7 °C), and TruNatomy (2.8 °C). During irrigation with heated sodium hypochlorite, temperature rises recorded were 6.8 °C for ProTaper Next, 5.9 °C for WaveOne Gold, 5.2 °C for Reciproc Blue, and 4.1 °C for TruNatomy. Statistical analysis revealed a significant negative correlation between dentin thickness and temperature rise, with r-values ranging from −0.62 to −0.87 across the groups. No significant correlation was found between canal diameter and temperature change, indicating that the canal’s size does not influence the thermal impact as much as the properties of the rotary system and irrigation temperature. Conclusions: Different rotary systems produce varying levels of temperature increases on the external root surface, influenced significantly by the thickness of the dentin and the temperature of the irrigation solution. These variations necessitate careful selection of instrumentation and irrigation protocols to minimize potential thermal damage to surrounding periodontal tissues.

Background and Objectives: Three-dimensional printing is increasingly used to fabricate dental restorations; however, limited evidence is available on the mechanical performance and fracture behavior of printable resin materials used for endocrown restorations. Fracture load alone may not fully describe material performance, particularly when brittle or defect-sensitive failure occurs. This in vitro study aimed to compare the fracture resistance, Weibull parameters, experimental Mode I fracture toughness parameter, and failure patterns of three 3D-printed resin materials used for endocrown restorations. Materials and Methods: Thirty anatomically identical molar replicas were produced from a single prepared tooth model and restored with endocrowns fabricated from NextDent C&B MFH (NextDent B.V., Soesterberg, The Netherlands), SprintRay Crown (SprintRay Inc., Los Angeles, CA, USA), and BEGO VarseoSmile Crown Plus (BEGO GmbH & Co. KG, Bremen, Germany) (n = 10/group). The restorations were cemented and subjected to compressive loading until fracture. Maximum fracture force values were analyzed using Welch’s ANOVA and Weibull statistics. In parallel, single-edge-notched bend (SENB) specimens were fabricated from the same materials and tested using an ASTM D5045-based configuration to calculate an experimental Mode I fracture toughness parameter. Representative fractured crowns and standardized specimens were examined using stereomicroscopy to assess visible failure morphology. Results: No statistically significant difference in maximum fracture force was found among the three materials (Welch’s ANOVA, p = 0.217). The mean fracture force values were 862.37 N for NextDent C&B MFH, 804.37 N for SprintRay Crown, and 699.43 N for BEGO VarseoSmile Crown Plus. In the complementary analyses, BEGO VarseoSmile Crown Plus showed the highest Weibull modulus (m = 9.36), indicating a narrower distribution of fracture values, and the highest mean experimental Mode I fracture toughness parameter (5.250 MPa·m^0.5) under the present experimental conditions. Qualitative stereomicroscopic analysis revealed material-dependent visible failure patterns: SprintRay Crown exhibited more extensive fragmentation, whereas BEGO VarseoSmile Crown Plus showed a more defined visible fracture pattern with less secondary fragmentation. Conclusions: Fracture load alone was insufficient to characterize the mechanical behavior of the tested materials fully. Weibull parameters, the experimental fracture toughness parameter, and failure morphology provided complementary information and should be considered when evaluating 3D-printed resin materials for endocrown restorations.

Background and Objectives: Warm injectable gutta-percha techniques may improve three-dimensional filling of complex canal anatomy, but heat transfer to the external root surface may threaten periodontal tissues when the 47 °C threshold is exceeded. This in vitro study quantified external root-surface temperature changes during obturation with the Woodpecker FI-G/FI-P system and compared manufacturer preset temperatures with actual device output. Materials and Methods: Twenty extracted single-rooted human teeth standardized to 18 mm were prepared and assigned to obturation at 180 °C (Group A, n = 10) or 230 °C (Group B, n = 10). Infrared thermography recorded coronal, middle, and apical root-surface temperatures. A second device-based experiment measured FI-G and FI-P output at preset temperatures of 150 °C, 180 °C, 200 °C, and 230 °C. Results: The 230 °C setting produced significantly higher middle-third temperatures than the 180 °C setting (41.84 ± 5.52 °C vs. 36.99 ± 3.21 °C; p = 0.027; Cohen’s d = 1.07), whereas coronal and apical differences were not significant. The highest external root-surface value was 49.6 °C, and 3/10 specimens obturated at 230 °C exceeded 47 °C in the middle third. A significant coronal-to-middle gradient reversal was observed at 230 °C (p = 0.045). Device measurements showed strong attenuation between preset and output temperatures: at 230 °C, the FI-G tip base reached 150.0 °C but the tip apex reached 51.3 °C, while FI-P plugger tips reached 120.0 °C. Conclusions: The 180 °C setting produced a more predictable thermal profile, whereas 230 °C increased localized middle-third overheating risk. These in vitro findings support cautious temperature selection, especially in teeth with reduced dentin thickness or compromised root anatomy.