Matthias Kern

The aim of this study was to evaluate the influence of weight ratio, the shape of the precursor particles, and the application of a phosphate-monomer-containing primer on the mechanical properties of polymer infiltrated ceramic networks (PICNs) using zinc oxide. Two different types of zinc oxide particles were used as precursors to produce zinc oxide networks by sintering, each with two different densities resulting in two different weight ratios of the PICNs. For each of these different networks, two subgroups were built: one involving the application of a phosphate-monomer-containing primer prior to the infiltration of Bis-GMA/TEGDMA and one without. Elastic modulus and flexural strength were determined by using the three-point bending test. Vertical substance loss determined by the chewing simulation was evaluated with a laser scanning microscope. There was a statistically significant influence of the type of precursor particles on the flexural strength and in some cases on the elastic modulus. The application of a primer lead to a significant increase in the flexural strength and in most cases also in the elastic modulus. A higher weight ratio of zinc oxide led to a significantly higher elastic modulus. Few statistically significant differences were found for the vertical substance loss. By varying the shape of the particles and the weight fraction of zinc oxide, the mechanical properties of the investigated PICN can be controlled. The use of a phosphate-monomer-containing primer strengthens the bond between the infiltrated polymer and the zinc oxide, thus increasing the strength of the composite.

Objective To investigate the effects of sterilization, conditioning method, and thermal aging on the retentive strength of two‐piece zirconia abutments. Materials and Methods In total, 128 stock zirconia abutments were divided into four groups ( n = 32) according to the conditioning parameters: (A) air‐abrasion using 50 μm alumina particles/1.0 bar, (B) 50 μm/2.0 bar, (C) 100 μm/1.0 bar, and (D) 100 μm/2.0 bar. All abutments were bonded onto titanium bases using DTK adhesive resin and stored in water bath (37°C) for 72 h. Each group was subdivided into two subgroups ( n = 16), group 1 was disinfected, whereas group 2 followed disinfection and autoclave sterilization. Half of the specimens of each subgroup ( n &amp;#x02009;=&amp;#x02009;8) was directly subjected to the axial retention test (groups N), while the other half was first subjected to 150&amp;#x02009;days of thermocycling followed by retention test (groups T). Statistical analysis was performed with three‐way ANOVA, additional statistical analysis was performed by using separate one‐way ANOVAs followed by the Tukey's post‐hoc test for post hoc pairwise comparisons among groups. Results The highest median retention strength was recorded for group B2N (1390 N), whereas the lowest strength was recorded for group C1T (688 N). No significant interaction ( p ≥ 0.05) was detected between the different variables; conditioning method, sterilization, and the thermal cycling regarding the effect on the resulting retention. However, the sterilization always showed a positive effect. Thermocycling presented an adversely significant effect only in the absence of sterilization ( p < 0.05), with the exception of subgroups A. For the sterilized groups, thermocycling had no statistically significant effect on the retention. Conclusion Steam autoclaving increased the retention of hybrid zirconia abutments. DTK adhesive resin for two‐piece zirconia abutments performed well after sterilization and thermocycling.