Background Erosive acids might create surface flaws and deteriorate the mechanical properties of CAD-CAM materials. This invitro study aimed to investigate the effect of simulated gastric HCl and extrinsic erosive acids on surface microhardness and fracture toughness of CAD-CAM materials. Methods 400 bar-shaped specimens (17×4×2 mm3) were prepared from 4 different CAD-CAM dental materials (n = 100/group); monolithic zirconia (Ceramill Zolid HT+, Amanngirbach, Austria), lithium disilicate ceramic (IPS e.max CAD, Ivoclar Vivadent, Liechtenstein), nanohybrid resin composite (Grandio Blocs, VOCO) and polymer-infiltrated glass network (Vita Enamic, VITA Zahnfabrik). Specimens from each material type were further subdivided into 5 groups (n = 20) according to the erosive media applied (simulated gastric HCl, white wine, Coca-Cola®, orange juice, and artificial saliva that served as a control). Specimens were immersed for 24 h in an incubator at 37 ℃, then ultrasonically cleaned in distilled water and air-dried. Half of the specimens were tested for Vickers microhardness (VHN) at parameters of 500 gf for 10 s, while the rest of the specimens underwent 3-point flexure till fracture. Fractured surfaces were examined under a scanning electron microscope (SEM) for fracture toughness (KIC) calculation using the quantitative fractographic analysis method. Data collected were statistically analyzed using two-way analysis of variance (α = 0.05) after verification of data normality and homogeneity of variances. Results Erosive media created surface flaws that lowered the surface microhardness of the material and initiated the fracture pattern under different loads according to material type. The material type was a more predominant factor than erosive media that affected either the microhardness or the fracture toughness of CAD-CAM dental materials. The highest VHN and KIC values were found among Ceramill Zolid HT+ groups followed by IPS e.max CAD and Grandio Blocs regardless of the erosive media employed. Erosive media significantly reduced the VHN and KIC in Vita Enamic specimens compared to the rest of the material types. Conclusion All CAD-CAM materials used, except Vita Enamic, showed high resistance against the erosive acids indicating higher longevity of the material in patients frequently exposed to either extrinsic or intrinsic acid.

Aim. The aim of this study was to compare the microshear bond strength of ceramic veneers with digital die spacer settings at 20, 40, and 100 µm. Materials and Methods. Eighteen milled lithium disilicate microdiscs (IPS e.max CAD, Ivoclar Vivadent) were divided into three groups (n = 6) according to their digital die spacer settings: group A = 20 µm, group B = 40 µm, and group C = 100 µm. Six randomly selected sound maxillary premolars received three microdiscs each. Each microdisc was 1 mm in diameter and 1 mm in height. The buccal surfaces of the premolars were prepared with a 0.5 mm depth in enamel. After cementation, the specimens were thermocycled for 2,500 cycles between 5 and 55°C. Microshear bond strength testing was performed using a universal testing machine until bonding failure. Failure modes were evaluated using a stereomicroscope. Statistical analyses included one-way ANOVA, Tukey’s post hoc test, and chi-square test with a 5% alpha error and 80% study power. Results. The mean microshear bond strength values were calculated in MPa for group A = 31.91 ± 12.41, group B = 29.58 ± 5.03, and group C = 13.85 ± 4.12. One-way ANOVA ( p ≤ 0.05 ) showed a statistically significant difference in microshear bond strength among the three groups. Tukey’s post hoc test showed significant differences between groups A and C ( p = 0.004 ) and between groups B and C ( p = 0.011 ). The failure modes were presented as cohesive, adhesive, and mixed failures. Chi-square test indicated that the failure mode distribution was not significantly different among the three groups ( p = 0.970 ). Conclusion. Higher digital die spacer settings decrease the microshear bond strength of CAD/CAM lithium disilicate veneers.

INTRODUCTION: One of the main causes of composite replacement is its discoloration after prolonged exposure to the oral environment. In an effort to fulfill the patient esthetic desire, harmonize composite material have been introduced with limited studies regarding its esthetic properties and color stability. OBJECTIVES: To study the effect of coffee on the color stability of two nanohybrid composites with different monomers. MATERIALS AND METHODS: The resin composites tested were Venus diamond and Harmonize. A custom made disk-shaped mold (4mm thickness x 8 mm diameter) used to prepare 12 composite specimens. They were divided into 2 groups (n=6) according to the resin based composite that was used as follow: Group A restored with Urethane dimethacrylate based composite (Venus diamond, Heraeus Kulzer) and Group B restored with Bisphenol A diglycidil dimethacrylate based composite (Harmonize, Kerr). The specimens were finished using (Multi fluted tungsten carbide finishing bur for fifteen seconds) followed by polishing using (HiLuster, Kerr) polishing system. After that, the specimens were immersed in coffee solution for 7 days. Color difference ∆E was calculated before and after immersion of specimens for 48 hours and after 7 days using spectrophotometer (VITA easy shade). RESULTS: Mann Whitney U test showed significant difference in ∆E among composite restorative materials (p < 0.05). Venus diamond composite resin was found to be more stain-resistant than Harmonize composite resin after both 48 hours and 7 days. CONCLUSION: Different monomer compositions, immersion time and solution may have direct effect on the color stability of nanohybrid restorative materials.

No abstract

INTRODUCTION: Any esthetic restorative material largely depends on the color match and the color stability of the material in long term use. Also the smooth surface appear to be critical for composite performance and it's aesthetic outcome. However resin composites are materials that can show color changing when exposed to staining media. OBJECTIVES: The aim of this invitro study is to evaluate the color stability, change in opacity and change in surface roughness of an ORMOCER, and two methacrylate based composites after being immersed in different staining solutions with different time intervals. MATERIALS AND METHODS: A total of one hundred twenty disc specimens (10mm in diameter and 2mm in thickness) were prepared from three composite resins, A bulk fill ORMOCER based (Admira fusion X-tra) and a bulk fill methacrylate based (X-tra fill) and an incremental fill methacrylate based (Esthet-X HD) composite resins (n = 40). Specimens of each type were divided in to four groups according to immersion solutions (n = 10). Group A= Specimens were immersed in coffee (Nescafe classic, Nestle, Egypt), Group B= Specimen were immersed in tea (Lipton yellow lable, Unilever brand, Egypt), Group C = Specimen were immersed in cola (Coca cola company, Egypt) and Group D= Specimen were immersed in distilled water as a control group. Color evaluation was done at base line before staining and then at periods of 7 days, 14 days, 28 days using spectrophotometer. Change in color (∆E*) and opacity (∆Op) were obtained using the CIE L*a*b* system. Surface roughness was evaluated using Atomic Force microscopy at baseline before staining and then at 28 days from immersion in staining solutions. RESULTS: All composite used showed change in color values at the end of the time intervals after 28 days of immersion in staining solutions. Group A (coffee) was the highest effecting group (ΔE >3.3) and Admira fusion X tra was the material with the highest change in color. Surface roughness also increased especially in group C (cola) for all materials after 28 days with no statistically significant difference between groups (p>0.05). CONCLUSIONS: Coffee has a higher effect on staining composite resin than tea and cola. While cola affected the surface roughness of the composite resins used more than the other solution used.