Mechanical Properties of Polymer-Based Blanks for Machined Dental Restorations

The tremendous technological and dental material progress led to a progressive advancement of treatment technologies and materials in restorative dentistry and prosthodontics. In this approach, CAD/CAM restorations have proven to be valuable restorative dental materials in both provisional and definitive restoration, owing to multifarious design, improved and highly tunable mechanical, physical and morphological properties. Thus far, the dentistry market offers a wide range of CAD/CAM restorative dental materials with highly sophisticated design and proper characteristics for a particular clinical problem or multiple dentistry purposes. The main goal of this research study was to comparatively investigate the micro-mechanical properties of various CAD/CAM restorations, which are presented on the market and used in clinical dentistry. Among the investigated dental specimens, hybrid ceramic-based CAD/CAM presented the highest micro-mechanical properties, followed by CAD/CAM PMMA-graphene, while the lowest micro-mechanical features were registered for CAD/CAM multilayered PMMA.

Evaluating the masking ability of CAD/CAM hybrid ceramics with different thicknesses

Aim: A discoloration existing under the restoration can affect the final restoration color, and various techniques can be used to address this situation. The aim of this study was to investigate the masking ability of the substructure, color of different hybrid CAD/CAM ceramics in various thicknesses. Methodology: A total of 120 samples were produced from 4 different CAD/CAM hybrid ceramic blocks (Cerec blocs, GC Cerasmart, Vita Enamic, 3M Lava Ultimate) in 1, 1.5 and 2 mm thickness. The samples were sliced with 100 N pressure in a low-speed precision cutting device under water cooling. The specimens were placed over the neutral grey background for initial spectrophotometric measurements. A3 color posterior nanohybrid composite (14 X 7 X 1 mm) was preferred to mimic discoloration in the substructure. The cementation procedure of composite and the CAD/CAM hybrid ceramic complex was standardized under 10 N continuous pressure and was performed using a dual cured resin cement. All samples were incubated at 37 °C for 24 hours in incubator after cementation. And the second spectrophotometeric measurement was done via the L*, a*, and b* color attributes of the complex specimens. Additionally, ΔE* values were calculated to determine the color differences between each group. Kruskal Wallis test was used for statistical analysis and Dunn’s test was used for group comparison. Significance was evaluated at least p <0.05. Results: It was found that thickness of the ceramics increases, the substructure color is better masked and the thickness made a statistically significant difference on the masking ability (p<0.01). For 1 mm thick samples, the highest ΔE* value was found in Cerec blocs with 9.36, while the lowest value was found in GC Cerasmart as 4.27. Conclusion: Within the limitations of this study, it was concluded that the tested CAD/CAM hybrid ceramics showed better masking ability than Cerec blocs. How to cite this article: Ünalan Değirmenci B, Wahid WF. Evaluating the masking ability of CAD/CAM hybrid ceramics with different thicknesses. Int Dent Res 2021;11(2):114-20. https://doi.org/10.5577/intdentres.2021.vol11.no1.9 Linguistic Revision: The English language in this manuscript has been checked by at least two professional editors, both native speakers of English.

Mechanical and thermal stress analysis of hybrid ceramic and lithium disilicate based ceramic CAD-CAM inlays using 3-D finite element analysis

Objectives: The aim of this study was to analyze mechanical and thermal stresses of hybrid ceramic and lithium disilicate based ceramic of CAD/CAM inlays using 3D Finite element analysis. Material and Methods: A three dimensions finite element model of permanent maxillary premolar designed according to standard anatomy with class II cavity preparation for inlay restored with two different ceramic materials:- 1- Hybrid ceramic (Vita Enamic), 2- Lithium disilicate based ceramic (IPS e.max CAD). Totally six runs were performed on the model as: One loading case for each restorative material was tested in stress analysis; seven points of loading with 140N vertically applied at palatal cusp tip and cusp slop, marginal ridges and central fossa while the models base was fixed as a boundary condition in the two cases. Two thermal analysis cases were performed for each restoration material by applying 5ºC and 55ºC on the crown surface including the restoration surface. Results: The results of all structures were separated from the rest of the model to analyze the magnitude of stress in each component. For each group, maximum stresses on restorative materials, cement, enamel, and dentin were evaluated separately. Both ceramic materials generated similar stress distribution patterns for all groups when a total occlusal load of 140 N was applied. Conclusion: Thermal fluctuations of temperature have a great influence on the stresses induced on both restoration and tooth structure. IPS e.max CAD produced more favorable stresses on the tooth structure than Vita Enamic. KEYWORDS Ceramics; Finite element analysis; IPS e.max CAD; Lithium disilicate; Vita Enamic.

Superficial Effects of Different Finishing and Polishing Systems on the Surface Roughness and Color Change of Resin-Based CAD/CAM Blocks

Objective: CAD/CAM blocks are widely used in dental restorations around the world. This study aimed to investigate the effects of different polishing and finishing systems on surface roughness and color change of resin-based CAD/CAM blocks. Material and Methods: In this study, material samples of 2×7×12mm were prepared. In three different experimental groups, surface polishing was carried out with one-step, two-step and multi-step polishing systems. The samples in one subgroup of each experimental group were polished with the diamond paste. Once the initial roughness and color values of the samples were measured using a profilometer and a spectrophotometer, the samples were immersed in coffee. Surface roughness and color change (∆E00) results were statistically analyzed using two-way variance analysis (ANOVA). Results: Finishing and polishing systems created significantly different levels of surface roughness on the hybrid ceramic block (Vita Enamic) but not on the composites block (Brilliant Crios, Grandio Blocs). While the two-step and multi-step finishing and polishing systems produced the lowest color change on hybrid ceramic blocks, one-step and two-step systems achieved this on composite blocks (p<0.05). In all test groups, the supplementary polishing performed after regular polishing procedures helped us reduce the surface roughness and color change on CAD/CAM blocks. Conclusions: The findings obtained in this study suggest that one and two-step polishing systems are more suitable for resin-based composite CAD/CAM blocks; for hybrid ceramic CAD/CAM blocks, on the other hand, two and multi-step finishing and polishing systems seem to be more efficient concerning lower surface roughness and resistance to color changes.