Gelatin methacryloyl and Laponite bioink for 3D bioprinted organotypic tumor modeling.

Three-dimensional (3D)in vitrotumor models that can capture the pathophysiology of human tumors are essential for cancer biology and drug development. However, simulating the tumor microenvironment is still challenging because it consists of a heterogeneous mixture of various cellular components and biological factors. In this regard, current extracellular matrix (ECM)-mimicking hydrogels used in tumor tissue engineering lack physical interactions that can keep biological factors released by encapsulated cells within the hydrogel and improve paracrine interactions. Here, we developed a nanoengineered ion-covalent cross-linkable bioink to construct 3D bioprinted organotypic tumor models. The bioink was designed to implement the tumor ECM by creating an interpenetrating network composed of gelatin methacryloyl (GelMA), a light cross-linkable polymer, and synthetic nanosilicate (Laponite) that exhibits a unique ionic charge to improve retention of biological factors released by the encapsulated cells and assist in paracrine signals. The physical properties related to printability were evaluated to analyze the effect of Laponite hydrogel on bioink. Low GelMA (5%) with high Laponite (2.5%-3.5%) composite hydrogels and high GelMA (10%) with low Laponite (1.0%-2.0%) composite hydrogels showed acceptable mechanical properties for 3D printing. However, a low GelMA composite hydrogel with a high Laponite content could not provide acceptable cell viability. Fluorescent cell labeling studies showed that as the proportion of Laponite increased, the cells became more aggregated to form larger 3D tumor structures. Reverse transcription-polymerase chain reaction (RT-qPCR) and western blot experiments showed that an increase in the Laponite ratio induces upregulation of growth factor and tissue remodeling-related genes and proteins in tumor cells. In contrast, cell cycle and proliferation-related genes were downregulated. On the other hand, concerning fibroblasts, the increase in the Laponite ratio indicated an overall upregulation of the mesenchymal phenotype-related genes and proteins. Our study may provide a rationale for using Laponite-based hydrogels in 3D cancer modeling.

Comparing the Repair of Veneered Zirconia Crowns with Ceramic or Composite Resin: An in Vitro Study.

STATEMENT OF PROBLEM: Current techniques for repairing porcelain-chipped restorations have several limitations. With advances in CAD/CAM technology, the combination of resin cements and high-strength ceramic materials might offer new options for repairing the chipping of veneering ceramic. PURPOSE: The purpose of this study is to compare the load-to-failure of veneered zirconia crowns repaired by different materials. MATERIAL AND METHODS: Veneered zirconia crowns were made on aluminum dies (n = 10/group). Feldspathic porcelain (Vita VM9, Vident) was applied to the zirconia coping (Vita In-Ceram YZ, Vident) in a cylindrical shape (Ø 10.5 mm, height 7.5 mm). A bevel cut on the porcelain veneer (45 degree, 3 mm width) was made at one side of each crown to simulate porcelain chipping. The crowns were then divided into four different groups according to the repair materials: 1. Conventional resin composite (A; Tetric EvoCeram, Ivoclar Vivadent); 2. Flowable resin composite (B; G-aenial Universal Flo, GC america); 3. CAD/CAM milled feldspathic ceramic (C; Vita Trilux Forte, Vident); 4. CAD/CAM milled lithium disilicate glass-ceramic (D; IPS e.max CAD, Ivoclar Vivadent). Resin cement (Multilink Automix, Ivoclar Vivadent) was used to cement the CAD/CAM ceramic materials to the beveled crowns. Each crown underwent 5000 cycles of thermocycling. The strength test was performed on an Instron universal testing machine by loading force on the center of repaired part to record load-to-failure. Data were analyzed by ANOVA and Tukey HSD post-hoc tests (α = 0.05). RESULTS: Mean loads-to-failure (in Newton +/- SD) of repaired veneered zirconia crowns were: Gr. A: 660.0 ± 200.5; Gr. B: 681.7 ± 175.9; Gr. C: 1236.0 ± 188.8; Gr. D: 1536.3 ± 286.1. Catastrophic failure was the most dominant failure mode in every group. Few specimens exhibited cohesive failure. Only one specimen in group D had adhesive failure. CONCLUSIONS: Within the limitation of the study, veneered zirconia crowns repaired with CAD/CAM ceramic materials have significantly higher load-to-failure than veneered crowns repaired with resin composite (p ≤ 0.05). CLINICAL IMPLICATIONS: Traditionally, porcelain-chipped restorations are often repaired with resin composite and bonding technique. Repairing chipped porcelain with CAD/CAM ceramics fitting the fractured parts can be alternative option with potential advantages. More well-designed studies are necessary to justify this novel repair technique.

Interdisciplinary Approach to Treat Patients With Tooth Agenesis: A Case Report.

INTRODUCTION: Tooth agenesis is a type of dental anomaly in which individuals are missing teeth due to developmental failure as a result of genetic or environmental factors. With approximately one fourth of the population missing ≥1 third molar, tooth agenesis is considered a common dental anomaly. However, the severity of tooth agenesis can range from a missing single tooth to multiple teeth. When suffering from severe tooth agenesis, the patient's health and social relationships are often affected. CASE PRESENTATION: The patient in this report congenitally lost 11 teeth and suffered from compromised esthetics and impaired chewing function. In such a severe tooth agenesis case, interdisciplinary treatments involving orthodontics, periodontics, and prosthodontics were engaged to reconstruct the ideal biology, function, and esthetics for the patient. With an interdisciplinary approach, the periodontist played an important role in the rehabilitation of the edentulous regions with implants in combination with various hard and soft tissue augmentation procedures. In addition, the patient with severe tooth agenesis presented with additional dental anomalies. The periodontist, therefore, had to collaborate with other specialists to provide early detection and intervention to avoid future complications, such as the management of infraoccluded ankylosed deciduous molars and aberrant frenum. The patient at the end of treatment had a good occlusion with improved function and esthetics. CONCLUSION: This case report describes the interdisciplinary treatment approach used and points out the role of periodontists in the treatment of a patient with severe tooth agenesis.

Effect of Glazing on Flexural Strength of Full-Contour Zirconia.

OBJECTIVE: The purpose of this study was to evaluate the effect of glazing on flexural strength of highly translucent zirconia materials. MATERIALS AND METHODS: Specimens of three brands of zirconia bars (Prettau Zirconia, Zirkonzahn; inCoris TZI, Sirona; and Zirlux FC, Pentron Ceramics) were prepared and polished according to manufacturers' instructions. Final specimen dimensions were 20 × 4 × 2 mm. The specimens from each brand were divided into 3 groups (N = 10): control, heat-treated, and glazed. Heat-treated specimens were fired without the application of the glaze material. The glaze material was applied to the glazed specimens before being fired. A three-point bending test (15 mm span) was performed in an Instron universal testing machine (ISO 6872). Data were analyzed by ANOVA and Tukey's HSD post hoc test (α = 0.05). RESULTS: Two-way ANOVA showed a significant influence of surface treatments on flexural strength of zirconia materials (P ≤ 0.05). There was no significant difference in flexural strength among the different brands of highly translucent zirconia (P ≥ 0.05). Tukey's HSD post hoc test showed that specimens in the "glazed" group had significantly lower flexural strength than the control and heat-treated groups (P ≤ 0.05). CONCLUSION: Within the limitations of the study, external glazing decreased the flexural strength of highly translucent zirconia.

Effect of margin location on crown preparation resistance form.

STATEMENT OF THE PROBLEM: The location of preparation margins may compromise the fixed prosthodontic restoration's resistance form. Purpose This study evaluated changes of opposite wall margin position on rotational resistance form compared to the equal-height margin configuration. MATERIAL AND METHODS: The trigonometric computation of the minimal resistance form preparation taper, alpha1 , was determined using a previously described formula. The alpha1-values for different tooth sizes with variation of base widths (range 4 to 10 mm) and vertical wall heights (range 4 to 9 mm) were calculated. The alpha1-values represent resistance form with both opposing wall margins at the same vertical height position. The alpha2-values were calculated with additional formulas to address uneven margin heights. Calculated alpha2-values of 10 degrees or less were considered clinically significant due to the known level of difficulty for the clinician. RESULTS: As a general trend, the alpha2-values were reduced compared to the alpha1-values with shortening opposing vertical wall heights in all tooth-size categories. Clinically significant changes in the resistance form taper were shown in all tooth size categories except the smallest 4-mm tooth base size. CONCLUSION: Fixed prosthodontic restoration resistance form is negatively affected by uneven vertical margin placement. This phenomenon reduces the resistance form of the restoration compared to equal-height margin placement.