Background: This study evaluated the effects of milling (CADCAM), 3D printing, preparation taper angles (10 -degree and 20 -degree), auxiliary retentive features (groove and box), and provisional cement types (conventional and resin -based) on the adhesive failure stress of 3 -mm short provisional crowns (PC). The research was motivated by the need to understand how digital dentistry technologies impact the retention and durability of provisional crowns. Material/Methods: A total of 160 working models (3D -printed) and PCs [80 milled (CopraTemp)/80 printed (Asiga)] were fabricated from two 10- and 20 -degree typodont master models and two 20 -degree 3D -printed master models (groove and box), simulating a 3 mm high all -ceramic short PC. After provisional cementation with conventional (Kerr TempBond) and resin -based (ProviTemp) cements, 16 subgroups (n=10 each) underwent thermocycling (10 000 cycles; 5-55 degrees C) and pull -off tests on a universal testing machine. Statistical analysis was performed using oneway ANOVA and post hoc Tukey test. Results: Conventional cement failed at lower stress for milled (47.68 to 73.54) and printed (48.40 to 77.91) as compared to resin cement for milled (104.2 to 137.27) and printed (184.85 to 328.84), respectively, with significant differences. Increased taper and groove decreased failure load except for the printed PC/resin cement combination. Use of proximal box preparation increased retention significantly. Except for 20 -degree taper cemented with conventional cement, the differences in auxiliary retentive features for milled and printed provisional crowns were statistically significant at P 0.05 pound. Conclusions: 3D -printed PC, resin -based cement, 10 -degree taper, and proximal box preparation were associated with higher retention than milled, conventional cements, 20 -degree taper, and vertical groove.

BACKGROUND:Finite element analysis (FEA) for endocrown restorations (ER) on maxillary molars has rarely been investigated, despite its high incidence in gross decay and being treated endodontically. This study aimed to analyze the influence of various preparation features (margin type, pulp chamber extension, occlusal thickness) and restorative material (zirconia, lithium disilicate, nanoceramic resin) on the stress distribution pattern of maxillary first molar ER using three-dimensional FEA. MATERIAL AND METHODS:Six three-dimensional finite element models (models A-F) were created for ER maxillary molars, considering preparation features – margins (flat butt, 20° bevel, shoulder), pulpal extension (2 mm/4 mm), and occlusal thickness (3 mm) – for 3 ER materials (zirconia, lithium disilicate, nanoceramic resin). The closing phase of mastication was loaded with 600 Newtons of functional load from an apple bolus. Von Mises Stress (VMS) was used to calculate tooth component and ER stress distributions. Standard criteria were used to calculate cement layer failure risk. RESULTS:Resin nanoceramic shoulder margins with 2- and 4-mm PE (models E and F) had higher stress concentrations on the tooth preparation surface, cervical enamel, buccal roots, and ER intaglio surface. Higher elastic modulus (ME) materials had higher stress concentrations inside ER and less stress in the cement layer, facilitating tooth bonding. Resin nanoceramic distributed stresses more uniformly on ER/tooth tissues. CONCLUSIONS:Different margin and pulpal extension preparation features and restorative materials cause varied ER stress distribution. Shoulder margin created considerably larger stresses in dental tissue and ER than flat butt margin, regardless of material type. Increased pulpal extension reduced tooth tissue stresses but increased ER.

Background: This study investigates the effect of artificial aging of direct resin nanohybrid composites on mean bond strength values for veneer ceramic samples. Material/Methods: Ninety direct nanohybrid composite resin (Tetric N-Ceram) cylindrical discs were divided into 5 groups (n=18 each) based on aging cycles (thermocycling), as follows: TC=no aging (control), T1=850, T3=2500, T6=5000, and T12=10000 cycles, representing 1, 3, 6, and 12 months of clinical usage, respectively. Lithium disilicate glass ceramic (IPS e.max Press) cylindrical discs were cemented to resin discs using resin cement (Variolink N) after surface treatments (ceramic etching, silaning, composite abrasion). Differences in means between subgroups were calculated using one-way ANOVA, followed by the Tukey honestly significant differences post hoc test. Differences were considered statistically significant with a P value <= 0.05. Results: The highest SBS between ceramic and aged composite was observed at 1 month (m=20.35) but did not differ significantly from the control group (m=20.97). For all other subgroups (3, 6, 12 months) SBS was significantly less than that of the control (P <= 0.05). P <= 0.05). At 1 and 3 months, cohesive failures were more common, whereas adhesive failures were more common in 6- and 12-month-old composites. Conclusions: SBS of aged composites was less than that of non-aged composites, with SBS decreasing proportionally as the resin aged. When cementing a ceramic restoration over existing composite restorations, those older than 1 month should be removed and replaced with new ones.

Background: The implant–abutment interface has been thoroughly examined due to its impact on the success of implant healing and longevity. Removing the abutment is advantageous, but it changes the biomechanics of the implant fixture and restoration. This in vitro three-dimensional finite element analytical (FEA) study aims to evaluate the distribution of von Mises stress (VMS) in abutment-free and three additional implant abutment connections composed of various titanium alloys. Materials and methods: A three-dimensional implant-supported single-crown prosthesis model was digitally generated on the mandibular section using a combination of microcomputed tomography imaging (microCT), a computer-assisted designing (CAD) program (SolidWorks), Analysis of Systems (ANSYS), and a 3D digital scan (Visual Computing Lab). Four digital models [A (BioHorizons), B (Straumann AG), C abutment-free (Matrix), and D (TRI)] representing three different functional biomaterials [wrought Ti-6Al-4Va ELI, Roxolid (85% Ti, 15% Zr), and Ti-6Al-4V ELI] were subjected to simulated static/cyclic static loading in axial/oblique directions after being restored with highly translucent monolithic zirconia restoration. The stresses generated on the implant fixture, abutment, crown, screw, cortical, and cancellous bones were measured. Results: The highest VMSs were generated by the abutment-free (Model C, Matrix) implant system on the implant fixture [static (32.36 Mpa), cyclic static (83.34 Mpa)], screw [static (16.85 Mpa), cyclic static (30.33 Mpa), oblique (57.46 Mpa)], and cortical bone [static (26.55), cyclic static (108.99 Mpa), oblique (47.8 Mpa)]. The lowest VMSs in the implant fixture, abutment, screw, and crown were associated with the binary alloy Roxolid [83–87% Ti and 13–17% Zr]. Conclusions: Abutment-free implant systems generate twice the stress on cortical bone than other abutment implant systems while producing the highest stresses on the fixture and screw, therefore demanding further clinical investigations. Roxolid, a binary alloy of titanium and zirconia, showed the least overall stresses in different loadings and directions.