Evaluation of Colour Changes in Nanocomposite-Based Bulk-Fill and Universal Composite Using Different Polishing Systems.

PURPOSE: Resins composites are widely used in modern dentistry because of their aesthetic and physical properties. However, discoloration of anterior tooth restorations is a common complaint. Understanding the factors affecting the colour stability of resin composites can lead to longer-lasting repairs. This study aimed to evaluate and compare the colour changes of nanocomposite-based bulk-fill and universal resin composites after immersion in coffee using various polishing systems. MATERIALS AND METHODS: A total of 160 samples were prepared using four different composite groups, with 40 pieces for each combined group. Based on the finishing procedure, the samples were divided into four subgroups for each composite group. Three different polishing procedures were applied to the samples according to the manufacturer's instructions. The control group was not subjected to any treatment. Initial colour measurements were performed using a VITA Easyshade V spectrophotometer. After the initial measurements, the samples were immersed in a Nescafe coffee solution for seven days, followed by colour measurements. Data were analysed using the Kolmogorov-Smirnov test and two-way analysis of variance. Tukey's honest significant difference (HSD) test was used to determine differences between subgroups. RESULTS: The results indicate that bulk-fill resins exhibit more discolouration than universal composites; however, this difference was not statistically significant. The resin group with the smallest discolouration was Ceram X, and the most effective polishing method was Twist polishing. CONCLUSION: Final surface polishing significantly reduced the composites' discolouration. These findings support the selection of appropriate materials and polishing techniques to achieve aesthetic outcomes and colour stability in dental restorations.

Fracture strength of different veneers on polyetheretherketone (PEEK) frameworks in implant-supported single crowns.

PURPOSE: To evaluate the fracture strength of polyetheretherketone (PEEK) single crowns veneered with different materials produced by computer-aided design (CAD)-computer-aided manufacture (CAM) after aging. METHODS: 60 stainless-steel master dies were prepared with a 1 mm-wide deep chamfer. Sixty PEEK frameworks were produced with a CAD-CAM system for the right maxillary first molar tooth on the dies. PEEK frameworks were divided into six groups (n= 10) according to veneering materials (five CAD-CAM materials and a resin composite). Group ZR: monolithic zirconia (Upcera ST-Color); Group EC: lithium disilicate glass-ceramic (IPS e.max CAD); Group LU: resin nano-ceramic (Lava Ultimate); Group VM: feldspathic ceramic (Vitablocs Mark II); Group VS: zirconia-reinforced lithium silicate glass-ceramic (VITA Suprinity); and Group CR: indirect resin composite (Gradia). All samples were subjected to a fracture strength test in a universal test device after thermo-mechanical aging and then the results were analyzed statistically using one-way ANOVA and Tukey's post hoc test. In addition, post-fracture analyses of all samples were performed with a stereomicroscope. RESULTS: The differences in fracture strength values of different veneer materials in single crowns with a PEEK framework were statistically significant (P< 0.05). Fracture strength was highest in Group ZR (1665 N), followed by Groups LU (1440 N), EC (1249 N), CR (918 N), VS (754 N), and VM (655 N). CLINICAL SIGNIFICANCE: PEEK frameworks may have the potential to be used with many veneer materials of different content and properties in fixed partial prostheses.

Bond strength of ceramic or resin CAD-CAM laminate veneers.

PURPOSE: To compare the bond strength of ceramic or resin laminate veneers produced using computer assisted design/computer assisted machining (CAD-CAM). METHODS: 80 teeth were prepared for laminate veneer, and divided into eight groups of different CAD-CAM blocks in each group. Each group was restored with the manufacturers' recommended procedures. After cementation of the veneers, all samples were thermocycled (1,000 cycles); the crowns of the teeth were embedded vertically into acrylic blocks and subjected to shear bond strength in a universal tester. Shear bond strength was determined in Newtons (N). RESULTS: The tests showed 52.5% cohesive failure, 30% adhesive failure, and 17.5% adhesive-cohesive failure (mixed). Lava Ultimate had the highest bond strength average and the Cerec blocks had the lowest with 82.2N. Lava Ultimate, Cerasmart, and E-Max's shear bond strength values were statistically different compared to Vitablocs Mark II, Cerec Blocs, GC Initial LRF Blocks (P< 0.05). The difference between the Vitablocs Mark II and Cerec Blocs and the Vita Enamic block was statistically significant. There was no statistically significant difference among the other groups. The selected CAD-CAM material affected the shear bond strength of the laminate veneers. CLINICAL SIGNIFICANCE: The results of this study can assist clinicians in selecting materials with a high bond strength for laminate veneers.