Surface Characterisation of Dental Resin Composites Related to Conditioning and Finishing

Bacterial adhesion to composite resins produced by additive and subtractive manufacturing

The aim of this study was to evaluate the surface roughness and contact angle of composite resins produced by CAD/CAM milling and three-dimensional (3D) printing for permanent restorations as well as the adhesion of S. mutans and S. sanguinis bacteria to these composites. Three CAD/CAM milling composite resins (Vita Enamic-VE, Cerasmart-CE, Lava Ultimate-LU) and three 3D printing resins (Varseo Smile Crown plus-VSC, Saremco print Crowntech-SPC, Formlabs 3B Permanent crown-FLP) were selected. Twenty samples were prepared for each group. Using a contact profilometer, the surface roughness was determined, and an optical goniometer was used to quantify the contact angle. To evaluate the bacterial adhesion, composite specimens were immersed in mucin containing artificial saliva. All samples were incubated for 24 h at 37°C in 5% CO2. CFUs were determined by counting colonies after the incubation period. Surface roughness values of test samples were the highest in the Group VSC [0.46 (0.14) µm], whereas the lowest values were found in the Group LU [0.23 (0.05) µm]. There was no statistically significant difference between the groups in contact angle values (p > 0.05). The S. mutans adhesion extent on the Group SPC was statistically higher compared to all other materials with p < 0.05. For S. sanguinis, the lowest bacterial adhesion value was recorded in Group CE (3.00 × 104 CFU/ml) and statistically significant differences were found with Group VE and VSC (p < 0.05). Different digital manufacturing techniques and material compositions can affect the surface roughnesses of composite resins. All composite resin samples have hydrophobic characteristics. Microbial adhesion of the tested composite resins may be varied depending on the bacterial species. S. mutans showed much more adhesion to these materials than S. sanguinis.

Effect of the addition of silver nanoparticles on the mechanical properties of an orthodontic adhesive

Objectives

This study evaluated the effects of adding silver nanoparticles on the shear bond strength, microhardness, and surface roughness of orthodontic adhesives.

Material and Methods

Fifty upper premolars were randomly allocated to five groups (n = 10). Orthodontic brackets were bonded with silver nanoparticle (AgNP)-modified adhesives (1 %, 0.5 %, 0.1 %, 0.05 %), and conventional adhesive was used as a control. The shear bond strength was recorded using a universal testing machine, and the adhesive remnant index was evaluated using a stereomicroscope. Ten discs of each adhesive were subjected to the microhardness and surface roughness tests. The Vickers microhardness values were measured under a constant load of 100 g for 30 s using a microhardness tester. The samples were analyzed using a surface profilometer, and the arithmetic average roughness was used as the measurement parameter. Data were analyzed using one-way analysis of variance and chi-square tests. A significance level of 5 % was considered significant.

Results

AgNP concentration > 0.1 % significantly reduced the shear bond strength (p < 0.05). At higher AgNP concentration, the bonding failure pattern occurred mainly at the bracket-resin interface. The Vickers microhardness increased with increasing concentration, and significant differences were observed between the group with 1 % AgNP and the other groups (p < 0.05). The average roughness values were similar between the groups with AgNP concentrations > 0.1 % (p > 0.05).

Conclusion

The incorporation of AgNP into an orthodontic adhesive has the potential to decrease the shear bond strength while increasing the microhardness and surface roughness.

Effect of aging on color, gloss and surface roughness of CAD/CAM composite materials

OBJECTIVES

To assess the effect of aging procedures on color, gloss and surface roughness of CAD/CAM composite materials.

METHODS

6 CAD/CAM composite materials (Brilliant CRIOS, Cerasmart, Lava Ultimate, Tetric CAD, Shofu Block HC, Grandio Blocs) were tested. 10 CAD/CAM fabricated specimens of each material polished according to manufacturers' recommendations, were subjected to one of the following aging procedures; immersion in coffee (30 days, 37^οC), water thermocycling (5000 cycles, 5-55 °C) and photoaging (150,000 kJ/m²). Color, gloss and surface roughness measurements were performed before and after aging and the respective changes were calculated. Kruskal-Wallis tests, paired t-tests, one-way ANOVA and Bonferroni post-hoc tests were used for statistical analysis (a = 0.05).

RESULTS

Color changes ranged from 3.03 to 4.13 after coffee immersion, from 1.33 to 2.55 after thermocycling and from 1.02 to 2.75 after photoaging. No statistically significant differences for ΔE*_ab were found among materials after coffee immersion and thermocycling (p>0.05). Gloss changes ranged from -5.7 to -1.6 GU after coffee immersion, from -2.3 to 0.1 GU after thermocycling and from -4.4 to 0.5 GU after photoaging. No significant differences in gloss changes were found among materials after aging (p>0.05). Tetric CAD demonstrated the significantly lower gloss and the higher surface roughness after polishing. Except for gloss after thermocycling, aging procedures caused significant alteration of gloss and surface roughness parameters from baseline levels.

CONCLUSIONS

Aging procedures caused perceptible but acceptable color changes and small but visible gloss changes, while surface roughness parameters of the tested CAD/CAM composite materials were significantly affected by aging.

CLINICAL SIGNIFICANCE

Aging procedures affected CAD/CAM composite materials indicating that these materials may be prone to color and surface alterations in the oral environment that could compromise the esthetics and the performance of the restorations. Clinical studies are needed to investigate the long-term behavior of the newly introduced CAD/CAM materials.

Surface Characteristics of High Translucent Multilayered Dental Zirconia Related to Aging

(1) Background: The purpose of this study was to evaluate the differences in terms of surface characteristics (roughness, topography, microhardness) among layers for multi-layered high translucent and super-high translucent zirconia and the influence of finishing and aging on surface characteristics and microstructure. (2) Methods: Three types of translucent multilayer zirconia were evaluated: STML (4Y-TZP); IPS e.maxZirCAD CEREC/in Lab MT Multi (4Y-TZP + 5Y-TZP); CeramillZolidfx ML (5Y-TZP). Ninety-six plate-shaped samples (32 for a material), 16 mm × 14 mm × 1 mm size, were cut with a precision disc, polished on both sides with sand papers and sintered respecting the manufacturer’s protocol. Half of the specimens (16) were finished by polishing and the other half by glazing and then equally divided into one control group and one group subject to aging by autoclaving (1 h, 134 °C, 0.2 MPa), resulting in four groups of eight samples, for each zirconia. The specimens were evaluated in three areas: cervical, medium, incisal-of each glazed or polished surface, before and after aging. Tests were performed to determine the surface roughness using a profilometer; the surface topography by an atomic force microscope (AFM) and a scanning electron microscope (SEM). Microhardness was recorded using a microhardness tester. Statistical analyses were performed using two-way ANOVA test, unpaired sample t-Test, paired sample t-Test (α = 0.05) and Pearson’s correlation. (3) Results: Before and after autoclaving, for glazed samples significance (p < 0.05) higher surface roughness, respectively lower microhardness in comparison with the polished group was assessed. No significant differences (p > 0.05) were reported between the three areas, on glazed or polished surfaces of a material. Although, after aging an increase in surface roughness was observed both on glazed and polished samples, statistical differences were found for STML (p < 0.05). No significant differences (p> 0.05) concerning microhardness among the same areas, on glazed and polished surfaces, recorded before and after aging, except CeramillZolidfx ML glazed samples. (4) Conclusions: For tested zirconia materials no significant differences among layers were registered regarding surface characteristics. Surface treatment (glazing or polishing) has a significant impact on surface roughness and microhardness. Both before and after aging, the surface roughness values for the glazed samples were higher than for those polished. The super translucent 4Y-TZP material was more affected by aging compared to the super-high translucent 5Y-TZP material. The combined material revealed similarities for each layer corresponding to the microstructure.

Optical Behavior and Surface Analysis of Dental Resin Matrix Ceramics Related to Thermocycling and Finishing

Color preservation of esthetic dental restorative materials in the oral environment represents, besides longevity, a concern, and there is still limited knowledge related to the effect of aging on the optical behavior of resin matrix ceramics. The study analyzed the finishing and thermocycling of resin matrix ceramic material surfaces, in order to assess their consequences on optical properties. Five resin matrix CAD/CAM ceramics, namely a polymer-infiltrated ceramic and four types of nanoparticle-filled resins, were selected for the study, and finished by polishing and glazing. Thermocycling was chosen as the in vitro aging method. Surface microroughness, optical and hardness evaluations were achieved before and after artificial aging. Statistical analyses were performed with IBM SPSS Statistics software at a significance value of p < 0.05. Micro-roughness values increased after thermocycling, but were kept under the clinically accepted values. The optical characteristics of resin matrix ceramics were not significantly modified by thermocycling. Values of the glazed samples became closer to those of the polished ones, after hydrothermal aging, even if the differences were insignificant. Thermocycling significantly decreased the microhardness, mainly for glazed samples. This could be the consequence of glaze removal during thermocycling, which means that glazes provide a surface protection for a limited time.