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Background: Conventional full-coverage crowns are used after endodontic treatment to enhance the fracture toughness of these teeth. However, these crowns lead to extensive loss of tooth structure. Continuous trials to develop a biomimetic conservative direct restorative material that can be used as a dentine substitute led to the development of the short fiber reinforced resin composite., Methods: Fifty extracted intact upper premolar teeth were selected. Ten teeth serve as positive control without any treatment (Group 1). The remaining forty teeth were received root canal therapy. Standardized MOD cavities were prepared in 30 teeth of them, then they were randomly divided into three groups: Group 2: teeth received no coronal restorations; Group 3: MOD cavities restored with packable short fiber reinforced composite (EverX Posterior), followed by 2 mm nanocomposite; and Group 4: MOD cavities restored with flowable short fiber reinforced composite (EverX Flow), followed by 2 mm nanocomposite. For the remaining ten teeth, MOD cavities were prepared, and cusps were reduced to receive ceramic overlays (CeraSmart 270). After thermocycling, fracture load is applied using the Instron Universal machine until samples fracture. Fracture loads were recorded, and fracture mode was evaluated. All data were subjected to statistical analysis., Results: Teeth restored with CeraSmart 270 overlays and those restored with high aspect ratio short fiber-reinforced resin composite recorded the highest resistance to fracture with no significant differences between them., Conclusions: EverX Posterior may be considered a conservative substitute for indirect overlays to restore endodontically treated teeth with MOD cavities., Clinical Relevance: Clinically, using fiber reinforced composite as a substitute for indirect restorations preserves the tooth structure and provides proper resistance to fracture., Competing Interests: Declarations. Ethics approval and consent to participate: This study was performed after approval of scientific research Ethics Committee, Kafr Elshiekh University. Informed consent was obtained from all patients to donate their extracted teeth for the research. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Purpose: The aim of this in vitro study was to assess and compare three different preparation designs of minimally invasive occlusal onlays on the trueness and precision of three different intraoral scanners under two different scanning conditions., Materials and Methods: Three maxillary premolars were prepared in three different designs and divided accordingly into three groups, Group 1: Anatomical (n = 60), Group 2: Flat (n = 60), and Group 3: Ferrule (n = 60). The samples were then further divided into subgroups according to scanners as subgroup A: Medit i500 (n = 20), subgroup B: 3Shape TRIOS 4 (n = 20), and subgroup C: Cerec Primescan (n = 20). Last, the samples were further divided according to scanning conditions: Division i: As prepared (n = 10) and Division ii: Sprayed - scan spray (n = 10). An industrial 3D scanner was used to obtain the reference STL files. Accuracy was assessed in terms of trueness and precision and recorded in terms of root mean square in micrometers. Numerical data were explored for normality using Shapiro-Wilk test and were analyzed using 3-way ANOVA followed by Tukey's post hoc test., Results: Regarding trueness, 3-way ANOVA showed that all tested variables had a significant effect on trueness. Significant interactions were found between the different variables (p < 0.001). For preparation design the highest value was found in ferrule preparation (27.88 ± 7.11), followed by flat preparation (22.99 ± 7.56), while the lowest value was found in anatomical preparation (18.83 ± 5.71) (p < 0.001). For scanner type, the highest value was found in Primescan (25.36 ± 10.66), followed by TRIOS 4 (22.75 ± 5.98), while the lowest value was found in Medit i500 (21.59 ± 5.03) (p < 0.001). As for the scanning condition, sprayed samples (26.54 ± 8.24) had a significantly higher value than non-sprayed samples (19.93 ± 5.53) (p < 0.001). Regarding precision, both preparation design and scanner type had a significant effect on precision. Scanning conditions had no significant effect. There was a significant interaction between the three tested variables (p = 0.012)., Conclusions: Anatomical preparation of minimally invasive occlusal onlays produced the most accurate scans. Within the tested preparation designs, Medit i500 and 3Shape TRIOS 4 have better trueness than Cerec Primescan. Cerec Primescan is more precise than 3Shape TRIOS 4 and Medit i500 Scan spray application causes a higher deviation in the trueness of the tested intraoral scanners while it does not affect their precision., (© 2023 by the American College of Prosthodontists.)

Objectives: To compare the stress distribution and crack propagation in cracked mandibular first molar restored with onlay, overlay, and two types of occlusal veneers using two different CAD/CAM materials by Finite Element Analysis (FEA)., Materials and Methods: A mandibular first molar was digitized using a micro CT scanning system in 2023. Three-dimensional dynamic scan data were transformed, and a 3D model of a cracked tooth was generated. Finite element models of four different models (onlay, overlay, and two types of occlusal veneer restored teeth) were designed. Two different CAD/CAM materials, including Lava Ultimate (LU) and IPS e.max CAD (EMX), were specified for both models. Each model was subjected to three different force loads on the occlusal surfaces. Stress distribution patterns and the maximum von Mises (VM) stresses were calculated and compared., Results: Compared to the base model, all restorations showed that high-stress concentration moved from the lower margin of the crack area towards the top of the crack area. The EMX-restored onlay, overlay, and occlusal veneer 2 had the lower stress in the cracked area and the lower average von Mises stress levels at the lower margin along the cracked line, especially under the 225N lateral force (P < 0.05). The occlusal veneer 1 filled with resin had a poorer stress distribution and higher stress concentration of stress at the remaining crack than the occlusal veneer 2 without resin filled inside., Conclusions: The EMX restorations with onlay, overlay, and occlusal veneer 2 showed lower stress concentration at the lower margin of crack surface compared to the LU-restored models. The occlusal veneer with internal resin filler exhibited higher stress on the end of the lower margin of the crack surface., Clinical Relevance: Our results suggest that onlay, overlay ceramic restorations and occlusal veneer (without resin filling inside) may be a favorable method to prevent further crack propagation., Trial Registration: A protocol was specified and registered with the Chinese Clinical Trial Registry (ChiCTR) on 2022-04-12 (registration number: ChiCTR2200058630)., Competing Interests: Declarations. Ethics approval and consent to participate: All the procedures were approved by the Ethics committee of Nanjing Stomatological Hospital (No. NJSH-2023NL-014–1) and conducted by the relevant guidelines and regulations. Informed consent was obtained from the subject. A protocol was specified and registered with the Chinese Clinical Trial Registry (ChiCTR) on 2022–04-12 (registration number: ChiCTR2200058630). Consent for publication: Patients signed informed consent regarding publishing their data and photographs. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)