Influence of Ambient Air and Different Surface Treatments on the Bonding Performance of a CAD/CAM Composite Block

Aesthetic impact of resin infiltration and its mechanical effect on ceramic bonding for white spot lesions

BACKGROUND

Treating white spot lesions (WSLs) with resin infiltration alone may not be sufficient, raising questions about its compatibility with other treatments amid controversial or incomplete data. Therefore, this study aimed to assess the aesthetic feasibility of resin infiltration combined with bleaching, as well as its potential mechanical effect on ceramic bonding to WSLs.

METHODS

One hundred and fifty flat enamel surfaces of bovine incisors were prepared. Ninety specimens were deminerailized and randomly assigned to three groups(n = 30): post-bleaching resin infiltration (Bl-R), pre-bleaching resin infiltration (R-Bl), and only resin infiltration (R). Color, surface roughness and microhardness were assessed in immediate, thermocycling and pigmentation tests. The remaining sixty samples were randomly assigned to three groups (n = 20): control (Ctrl), bonding (Bo), pre-bonding resin infiltration (R-Bo). Shear bonding strength, failure mode, micro-leakage depth and interface morphology were evaluated after ceramic bonding. The Tukey test and analysis of variance (ANOVA) were used for statistical analysis.

RESULTS

For the effect of resin infiltration and bleaching on WSLs, the R-Bl group showed the worst chromic masking ability, with the highest |ΔL|, |Δa|, |Δb|, and ΔE values after treatment. Compared with those in the Bl-R group, the R-Bl and R groups showed significant time-dependent staining, which is possibly attributed to their surface roughness. For the effect of resin infiltration on the adhesive properties of WSLs, resin infiltration reduced the staining penetration depth of WSLs from 2393.54 ± 1118.86 μm to 188.46 ± 89.96 μm (P < 0.05) while reducing WSLs porosity in SEM observation.

CONCLUSIONS

Post-bleaching resin infiltration proved to be advantageous in the aesthetic treatment of WSLs. Resin infiltration did not compromise bonding strength but it did reduce microleakage and enhance marginal sealing. Overall, resin infiltration can effectively enhance the chromatic results of treated WSLs and prevent long-term bonding failure between ceramics and enamel. Based on these findings, the use of post-bleaching resin infiltration is recommended, and resin infiltration before ceramic bonding is deemed viable in clinical practice.

Effects of Two Different Acid Etching and Surface Washing Methods on Bond Strength on Different CAD-CAM Blocks under Aging Protocols

Aim. The purpose of this study is to investigate the effects of hydrofluoric acid and one-component ceramic primer and silane (Monobond Etch and Prime (MEP)) applications on lithium disilicate glass ceramics and zirconium-infiltrated lithium silicate glass ceramics, as well as the effect of ultrasonic and phosphoric acid surface washing methods on bond strength. Materials and Method. A total of 240 ceramic samples were prepared using two different CAD-CAM material blocks with a thickness of 2 mm made of lithium disilicate glass-ceramic (IPS e.max CAD) and zirconium-infiltrated lithium silicate glass ceramic blocks (Celtra Duo). The samples were cemented to the composite discs (Tetric N-Ceram) after two different acid treatments, and surface washing processes were applied to them. As such, 24 groups were formed, each with two different acid applications, three different washing processes, two different CAD-CAM blocks, and two different aging procedures ( $n=10$ ). Following the application of the acid, different washing processes are used. These were HF acid and washing only (HF + W), HF acid and ultrasonic washing (HF + US), HF acid and phosphoric acid (HF + PA), MEP with washing only (MEP + W), MEP and ultrasonic washing (MEP + US), and MEP and phosphoric acid (MEP + PA). The composite discs were cemented with dual cure adhesive cement (Multilink Automix) after the determined surface treatments were applied to the blocks. After surface applications, SEM analysis was conducted. Following exposure to two different thermal procedures, long-term (TL) and short-term (TS), bond strengths were measured using an Instron universal test device. SPSS version 23.0 software was used to perform the statistical analyses. Histogram graphs and the Kolmogorov-Smirnov/Shapiro-Wilk test were used to assess the variables’ conformity to the normal distribution. Results. The bond strength values of TS and TL in the Celtra Duo block were significantly higher than those in the e.max CAD block ( $p<0.05$ ). The TS-TL bonding strength value difference in the e.max CAD block was significantly higher than the surface measurements in the Celtra Duo block. While the highest bond strength value HF + US for TS in e.max CAD was $20.07\pm .31$ , the values of HF + US in Celtra Duo were significantly higher in terms of TL values when compared to other groups. Conclusion. Celtra Duo material demonstrated higher bond strength values after a short and long thermal cycle than e.max CAD material. In general, groups bonded with HF were less affected by the thermal cycle than groups treated with MEP.

UV-Mediated Photofunctionalization of Indirect Restorative Materials Enhances Bonding to a Resin-Based Luting Agent

Purpose

The potential of UV-mediated photofunctionalization to enhance the resin-based luting agent bonding performance to aged materials was investigated.

Methods

Sixty samples of each material were prepared. Yttria-stabilized zirconia (YZr) and Pd-Au alloy (Pd-Au) plates were fabricated and sandblasted. Lithium disilicate glass-ceramic (LDS) was CAD-CAM prepared and ground with #800 SiC paper. Half of the specimens were immersed in machine oil for 24 h to simulate the carbon adsorption. Then, all of the specimens (noncarbon- and carbon-adsorbed) were submitted to UV-mediated photofunctionalization with a 15 W UV-LED (265 nm, 300 mA, 7692 μW/cm²) for 0 (control groups), 5, and 15 min and subjected to contact angle (Ɵ) measurement and bonded using a resin cement (Panavia™ V5, Kuraray Noritake, Japan). The tensile bond strength (TBS) test was performed after 24 h. The Ɵ (°) and TBS (MPa) data were statistically analyzed using two-way ANOVA and Bonferroni correction tests (α = 0.05).

Results

In the carbon-adsorbed groups, UV-mediated photofunctionalization for 5 min significantly decreased Ɵ of all materials and increased TBS of YZr, and UV for 15 min significantly increased the TBS of LDS and Pd-Au. In noncarbon-adsorbed groups, UV-photofunctionalization did not significantly change the Ɵ or TBS except YZr specimens UV-photofunctionalized for 15 min.

Conclusion

UV-mediated photofunctionalization might have removed the adsorbed hydrocarbon molecules from the materials' surfaces and enhanced bond strengths of Panavia™ V5 to YZr, LDS, and Pd-Au. Additionally, UV-mediated photofunctionalization improved the overall TBS of YZr. Further investigation on the optimum conditions of UV photofunctionalization on indirect restorative materials should be conducted.