Edina Lempel

Objectives: Evaluate and compare the internal gap (IG), closed porosity (CP), and degree of conversion (DC) of short fibre-reinforced composite (SFRC) restorations applied using various techniques in an in vitro model. Materials and methods: Five restorative protocols were tested ( n = 20/group): (1) flowable bulk-fill SFRC; (2) flowable liner + flowable bulk-fill SFRC; (3) polyethylene fibre mesh + flowable liner + flowable bulk-fill SFRC; (4) flowable bulk-fill SFRC + high-viscosity SFRC (snowplow technique); and (5) conventional layered resin-based composite (RBC). IG (gap volume/interface volume) and CP (void volume/restoration volume) were assessed by micro-CT. DC was measured at three depths using micro-Raman spectroscopy. Data were analyzed using ANOVA, General Linear Model, and correlation tests (α = 0.05). Results: Significant differences were found among groups for IG, CP, and DC ( p < 0.001). Groups 1, 2, and 4 showed significantly lower IG (0.46–0.53%) than Group 3 (2.78%) and Group 5 (1.09%). Group 1 demonstrated the lowest CP (0.11%), while Group 4 exhibited the highest (0.5%). DC ranged from 74.8 to 88.4%, with significant depth-related variations. Group 2 and Group 5 did not differ in average DC ( p = 0.99). Conclusions: The flowable bulk-fill SFRC techniques demonstrated favorable internal adaptation, low CP, and acceptable DC, supporting their potential use in deep cavities. In contrast, polyethylene fibre mesh reinforcement increased IG formation, whereas the snowplow technique achieved high DC at the expense of increased CP. Clinical Relevance: Flowable bulk-fill SFRC may improve internal adaptation, reduce porosity, and achieve acceptable DC in deep cavities. Polyethylene fibre mesh and snowplow techniques exhibit technique-dependent limitations.

Preheated restorative resin-based composites (RBCs) have been suggested as alternative luting agents for ceramic restorations; however, their polymerization and long-term degradation behavior require further clarification. This study compared a preheated RBC with conventional light-cured and dual-cured adhesive resin cements regarding degree of conversion (DC%), monomer elution, water sorption (WSo), and solubility (Sol). Standardized lithium disilicate overlays were luted to ceramic abutments using preheated Estelite Σ Quick (EQ_55°C), Variolink Esthetic LC (VE_LC), or Variolink Esthetic DC (VE_DC). DC% was assessed by micro-Raman spectroscopy, monomer elution using high-performance liquid chromatography at 3, 10, and 17 days, and WSo/Sol per ISO 4049 at 30, 60, and 90 days. VE_DC showed the highest DC% (72.1%), while EQ_55°C presented the lowest (59.9%). Monomer elution was significantly higher for VE_LC and VE_DC compared to EQ_55°C and decreased over time for all groups. WSo peaked at day 60 but remained significantly lower for EQ_55°C. Sol followed the pattern VE_DC > VE_LC > EQ_55°C, decreasing progressively with time. These results indicate that the preheated RBC demonstrated reduced monomer release and lower hydrolytic degradation, supporting its potential use as a stable luting alternative for indirect ceramic restorations.

Reliable adaptation in Class II resin-based composite (RBC) restorations with margins on cementum remains challenging. This study compared the internal adaptation (IA) and closed porosity (CP) of three restorative strategies for such cavities, using either total-etch or self-etch adhesive approaches. Standardized box-only cavities were prepared on both proximal surfaces of 30 extracted molars, applying self-etch on mesial and total-etch on distal cavities. Group 1 used a layered microhybrid RBC; Group 2 used a flowable RBC base beneath a layered microhybrid RBC; and Group 3 used a thermoviscous RBC in a 4 mm bulk increment. Micro-computed tomography was employed to assess IA and CP. ANOVA, Tukey post hoc, and univariate analyses were used to evaluate group differences and the effects of adhesive/restorative strategies. Group 2 demonstrated the best adaptation (0.10%), whereas Group 3 exhibited the highest internal gap ratio (0.63%) and the lowest CP (p = 0.006). Total-etch adhesive significantly improved IA compared to self-etch (p < 0.001). These findings emphasize the impact of material selection and adhesive technique on the quality of restorations in cementum-located Class II cavities.

This study aimed to evaluate the nanomechanical surface properties and water uptake of a flowable short-fiber-reinforced composite (SFRC) using various restorative techniques in order to assess its potential as a standalone restorative material. Nanoindentation and compressive creep testing were employed to characterize material performance. Three resin composites were examined: a flowable SFRC (everX Flow), a bulk-fill particulate filler composite (PFC), and a conventional PFC. Five experimental groups were established based on the restorative technique: layered PFC, layered SFRC, bulk SFRC, bulk PFC, and a bi-structure combining SFRC and PFC. Ninety standardized specimens (n = 18/group) were fabricated. Static and creep nanoindentation tests were conducted to assess surface properties, and water uptake was measured over a 30-day period. Data were analyzed using one-way ANOVA and Bonferroni post hoc tests. Nanoindentation revealed significant differences in hardness, with bulk PFC exhibiting the lowest values (p < 0.001). Creep testing indicated changes in modulus and viscosity following water storage. Notably, bulk SFRC showed the lowest water absorption (p < 0.001). Overall, bulk-applied SFRC demonstrated favorable nanomechanical properties and reduced water uptake, demonstrating its suitability as a standalone restorative material. Further clinical investigations are recommended to validate its long-term performance.

Resin-based dental composites (RBC) release cytotoxic components, however the extent of the elution from preheated RBCs is barely investigated. The aim was therefore to determine the cytotoxic effect of preheated conventional, bulk, and thermoviscous RBCs of clinically relevant sizes using different cell viability methods in a contact-free model. Samples (6 × 4 mm) were prepared from conventional [Estelite Sigma Quick (ESQ), Filtek Z250 (FZ)] and bulk-filled [Filtek One BulkFill Restorative (FOB), SDR Plus Bulk Flow (SDR), VisCalor Bulk (VCB)] RBCs. The pre-polymerization temperature was set to room temperature (RT) and 55/65 °C. Pulp cells were cultured, followed by a 2-day exposure to monomers released from solid RBC specimens suspended in the culture medium. Cytotoxicity was assessed using a WST-1, MTT, and LDH colorimetric viability assays. Data were analyzed using one-way ANOVA, Tukey’s post hoc test, multivariate analysis, and independent t-test. The effect size (ƞp²) of material and temperature factors was also assessed. All the RBCs demonstrated cytotoxic effect upon exposure to pulp cells, but to a varying extent (ESQ >> VCB > FZ = FOB = SDR). The effect of pre-polymerization temperature was insignificant (ƞp² < 0.03), except for the thermoviscous RBC, which showed inconsistent findings when subjected to distinct viability tests. Cell viability was predominantly dependent on the type of material used (p < 0.001) which showed a large effect size (ƞp² > 0.90). Irrespective of the pre-polymerization temperature, RBC samples in a clinically relevant size can release monomers to such an extent, which can substantially decrease the cytocompatibility.