The Effect of Different Intermediary Layer Materials Under Resin Composite Restorations on Volumetric Cuspal Deflection, Gap Formation, and Fracture Strength.

This study investigated the effect of different intermediary layer materials under class II mesio-occluso-distal (MOD) resin composite restorations on volumetric cuspal deflection, gap formation, and fracture strength. In total, 32 sound human maxillary premolars were used. After large, standardized Class II MOD cavities were prepared, a universal adhesive (Clearfil Universal Bond Quick, Kuraray) was applied. The premolars were randomly allocated into four groups according to different intermediary layer materials (n=8): Group Z250 (control)/micro-hybrid composite (Filtek Z250, 3M ESPE); Group EST/low-viscosity bulk-fill resin composite (Estelite Bulk Fill Flow, Tokuyama Dental Corp) + micro-hybrid composite; Group NOV/nanofiber-reinforced low-viscosity composite (NovaPro Flow, Nanova) + micro-hybrid composite; and Group RIB/polyethylene fiber [Ribbond, Ribbond Inc] + micro-hybrid composite. Distilled water was used for storage for 24 hours. Using microcomputed tomography (micro-CT), the teeth were scanned immediately after cavity preparation (T0), then 24 hours after restorative procedures (T1). Volumetric cuspal deflection in cubic millimeters (mm3) was analyzed on the palatal and buccal regions of each restoration individually at T0 and T1 scans. Gap formation (mm3) was evaluated to quantify the volume of black spaces at the tooth-resin interface on the T1 scan. After these scans, using a universal testing machine, the teeth were subjected to a fracture strength test (0.5 millimeters/minute [mm/min]). The fracture surfaces were analyzed with a stereomicroscope. The data were analyzed using the Kruskal-Wallis, one-way analysis of variance (ANOVA), and Dunn's tests (p< 0.05). No significant differences in volumetric cuspal deflection and fracture strength were detected for all tested groups (p>0.05). Group RIB exhibited significantly higher gap formation values in comparison with all other groups (p<0.05). Predominant failure mode was favorable.

The Effect of Different Polishing Systems on the Surface Roughness of Nanocomposites: Contact Profilometry and SEM Analyses.

The aim of this study was to evaluate the effects of different polishing systems on the surface roughness of different nanocomposite resins using various analysis methods. Three types of nanocomposite resins were investigated in this study: supra-nanohybrid (Estelite Asteria), nanohybrid (GrandioSo), and nanoceramic composite resins (Ceram-X Spheretec One). Forty-eight disc-shaped specimens (4 mm in diameter, 2 mm in thickness) were fabricated using a Teflon mold and divided into four groups according to the different polishing systems (n=12). All specimens were processed with one of the following methods: Mylar strip (control), one-step polishers (Opti1step), two-step polishers (Clearfil TwistDia), or multistep polishers (Sof-Lex XT Pop-on). The surface roughness (Ra, µm) was measured by contact profilometry (Mahr, Marsurf PS1) (n=10) and scanning electron microscopy (SEM) (Thermo Fisher Scientific, Phenom XL) at 400× magnification (n=2). The data were statistically analyzed using Kruskal-Wallis and Bonferroni correction tests (p<0.05). In addition, the surface morphology and elemental content were examined by SEM and energy dispersive x-ray spectroscopy (EDS) analyses. Under SEM evaluation, in terms of the polishing systems, there were no significant differences in the surface roughness for supra-nanohybrid composite resin (p>0.05). The multistep polishers created lower surface roughness than the one-step polishers for nanohybrid and nanoceramic composites. In terms of the composite resins, supra-nanohybrid composite exhibited lower surface roughness than nanohybrid composite for all polishing systems (p<0.05). The SEM observations confirmed the surface roughness measurements related to the surface morphology. One-step and two-step polishers created porosity on the surface of nanohybrid and nanoceramic composites. EDS analysis indicated the elemental composition of the particles in the porous zones was quite close to diamond abrasives and glass fillers.