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Objectives: To proof the feasibility of direct colour printing on 3Y-TZP using 222 nm UV-C through investigating the degree and durability of the colour changes, and testifying whether surface, mechanical and biological properties are influenced by the treatment., Methods: 222 nm UV-C light (Irradiance: 1.870 mW/cm 2 ) was used to treat 3Y-TZP for durations from 15 min to 24 h. ΔE*, TP, crystalline structure, surface morphology, S a , BFS and biological activities were investigated before and after irradiation. SPSS 28.0 was used for statistical analysis (α = 0.05)., Results: 222 nm UV-C irradiation was capable to shade white 3Y-TZP into tooth colours. With the increase of ΔE*, TP decreased, such that the longer the irradiation time, the higher the ΔE* (logarithmic relationship) and lower the TP. Despite the induced optical changes being prone to fade, the process can be predicted by inversely proportional relationships between ΔE*, TP and the testing points. The treated surface exhibited enhanced hydrophilicity, while the recovery phenomenon was observed. Other properties were not altered by the treatment., Significance: This is the seminal study demonstrating the feasibility of direct colour printing on 3Y-TZP using 222 nm UV-C. The new relationship between the colour centre and E g of 3Y-TZP was established, whereas the induced optical changes were stabilised after a certain period and were highly predictable by controlling the irradiation periods. The irradiation was only correlated to the electron excitation and oxygen vacancies, and would not lead to any changes of other properties. A simple, safe and promising approach to achieve satisfactory colours on 3Y-TZP in clinical practice can be developed., Competing Interests: Declaration of Competing Interest There are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Objectives: This study utilised an Artificial Intelligence (AI) method, namely 3D-Deep Convolutional Generative Adversarial Network (3D-DCGAN), which is one of the true 3D machine learning methods, as an automatic algorithm to design a dental crown., Methods: Six hundred sets of digital casts containing mandibular second premolars and their adjacent and antagonist teeth obtained from healthy personnel were machine-learned using 3D-DCGAN. Additional 12 sets of data were used as the test dataset, whereas the natural second premolars in the test dataset were compared with the designs in (1) 3D-DCGAN, (2) CEREC Biogeneric, and (3) CAD for morphological parameters of 3D similarity, cusp angle, occlusal contact point number and area, and in silico fatigue simulations with finite element (FE) using lithium disilicate material., Results: The 3D-DCGAN design and natural teeth had the lowest discrepancy in morphology compared with the other groups (root mean square value = 0.3611). The Biogeneric design showed a significantly (p < 0.05) higher cusp angle (67.11°) than that of the 3D-DCGAN design (49.43°) and natural tooth (54.05°). No significant difference was observed in the number and area of occlusal contact points among the four groups. FE analysis showed that the 3D-DCGAN design had the best match to the natural tooth regarding the stress distribution in the crown. The 3D-DCGAN design was subjected to 26.73 MPa and the natural tooth was subjected to 23.97 MPa stress at the central fossa area under physiological occlusal force (300 N); the two groups showed similar fatigue lifetimes (F-N curve) under simulated cyclic loading of 100-400 N. Designs with Biogeneric or technician would yield respectively higher or lower fatigue lifetime than natural teeth., Significance: This study demonstrated that 3D-DCGAN could be utilised to design personalised dental crowns with high accuracy that can mimic both the morphology and biomechanics of natural teeth., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Objective: To seek dentine analogue materials in combined experimental, analytical, and numerical approaches on the mechanical properties and fatigue behaviours that could replace human dentine in a crown fatigue laboratory test., Methods: A woven glass fibre-filled epoxy (NEMA grade G10; G10) and a glass fibre-reinforced polyamide-nylon (30% glass fibre reinforced polyamide-nylon 6,6; RPN) were investigated and compared with human dentine (HD). Flexural strength and elastic modulus (n = 10) were tested on beam-shaped specimens via three-point bending, while indentation hardness (n = 3) was tested after fracture. Abutment substrates of G10, RPN and HD were prepared and resin-bonded with monolithic lithium disilicate crowns (n = 10), then subjected to wet cyclic loading in a step-stress manner (500 N initial load, 100 N step size, 100,000 cycles per step, 20 Hz frequency). Data were statistically analysed using Kruskal-Wallis one-way ANOVA followed by post-hoc comparisons (α = 0.05). Survival probability estimation was performed by Mantel-Cox Log-Rank test with 95% confidence intervals. The fatigue failure load (FFL) and the number of cycles until failure (NCF) were evaluated with Weibull statistics. Finite Element Models of the fatigue test were established for stress distribution analysis and lifetime prediction. Fractographic observations were qualitatively analysed., Results: The flexural strength of HD (164.27 ± 14.24 MPa), G10 (116.48 ± 5.93 MPa), and RPN (86.73 ± 3.56 MPa) were significantly different (p < 0.001), while no significant difference was observed in their flexural moduli (p = 0.377) and the indentation hardness between HD and RPN (p = 0.749). The wet cyclic fatigue test revealed comparable mean FFL and NCF of G10 and RPN to HD (p = 0.237 and 0.294, respectively) and similar survival probabilities for the three groups (p = 0.055). However, RPN promotes higher stability and lower deviation of fatigue test results than G10 in Weibull analysis and FEA., Significance: Even though dentine analogue materials might exhibit similar elastic properties and fatigue performance to human dentine, different reliabilities of fatigue on crown-dentine analogues were shown. RPN seems to be a better substrate that could provide higher reliability and predictability of laboratory study results., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Objectives: The purpose of this study was to estimate the fatigue life of premolars restored with two dental ceramics, lithium disilicate (LD) and polymer infiltrated ceramic (PIC) using the numerical method and compare it with the published in vitro data., Methods: A premolar restored with full-coverage crown was digitized. The volumetric shape of tooth tissues and crowns were created in Mimics ® . They were transferred to IA-FEMesh for mesh generation and the model was analyzed with Abaqus. By combining the stress distribution results with fatigue stress-life (S-N) approach, the lifetime of restored premolars was predicted., Results: The predicted lifetime was 1,231,318 cycles for LD with fatigue load of 1400N, while the one for PIC was 475,063 cycles with the load of 870N. The peak value of maximum principal stress occurred at the contact area (LD: 172MPa and PIC: 96MPa) and central fossa (LD: 100MPa and PIC: 64MPa) for both ceramics which were the most seen failure areas in the experiment. In the adhesive layer, the maximum shear stress was observed at the shoulder area (LD: 53.6MPa and PIC: 29MPa)., Significance: The fatigue life and failure modes of all-ceramic crown determined by the numerical method seem to correlate well with the previous experimental study., (Copyright © 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.)