Sebastian Wille

Purpose: This study aimed to investigate whether different surface treatments applied to 3 mol% yttria‐stabilized tetragonal zirconia polycrystals (3Y‐TZP), with comparable mean roughness ( R _a ) values, result in comparable values of additional surface roughness parameters, and to evaluate the influence of zirconia surface topography on vertical substance loss of two opposing restorative materials: polymethacrylate‐based resin (PR) and lithium disilicate ceramic (LD). Materials and Methods: Ninety‐six zirconia discs were assigned to 12 groups ( n = 8) according to surface treatment using airborne‐particle abrasion, diamond burs, or silicon‐carbide‐coated abrasive papers applied before and/or after sintering, resulting in defined R _a surface roughness ranges ( R _a = 0.3–0.8 µm). Linear roughness parameters were verified by laser scanning microscopy. Ninety‐six conical antagonist specimens (PR or LD; n = 48) were prepared. The zirconia specimens (agonists) were subjected to mechanical loading for 1.2 million cycles, and vertical material loss was evaluated. Statistical analysis was performed using Kruskal–Wallis and Mann–Whitney tests followed by Bonferroni–Holm correction at a significance level of α = 0.05. Results: Despite comparable R _a values, different surface treatments resulted in significantly different roughness parameters ( R _p , R _z , R _c , R _t ; p ≤ 0.05), with airborne‐particle abrasion exhibiting the roughest surfaces. Agonist's roughness did not influence antagonist wear ( p = 0.739). However, the antagonist material LD, with median values up to 460 µm, showed a greater vertical material loss ( p = 0.019) compared to PR. Conclusions: Within the range of surface treatments investigated, the R _a of 3Y‐TZP might be sufficient to characterize surface topography with regard to wear behavior. LD, when opposed to 3Y‐TZP, may exhibit greater vertical material loss than PR.

This study examined whether short water rinsing after hydrofluoric acid (HF) etching achieves comparable total bond strength (TBS) to more advanced cleaning protocols. Ninety-six lithium disilicate specimens were etched with 5% HF and then assigned to one of six post-etch cleaning methods: a 15 s water spray, 60 s water spray, brushing with a toothbrush, an ultrasonic bath with distilled water, an ultrasonic bath with 99% isopropanol, or a 37% phosphoric acid followed by an ultrasonic bath. The specimens were then bonded to acrylic tubes filled with composite resin. Half of the specimens were stored in water at 37 °C for three days, and the other half were stored for 150 days with 37,500 thermal cycles (5 °C/55 °C). TBS testing, failure mode evaluation, and microleakage testing were performed. Two-way ANOVA and Tukey’s test were used for statistical evaluation. Aging for 150 days significantly reduced TBS in all groups. Cleaning with a 60 s water spray resulted in significantly higher TBS than phosphoric acid plus ultrasonic cleaning, regardless of storage time. No significant differences were found among the other cleaning methods. There was no change in microleakage among the different groups; the failure was predominantly cohesive. A 15 s water spray after HF etching was as effective as more complex cleaning protocols in terms of TBS and SEM-observed surface characteristics.

Directly printed aligners represent a promising alternative to conventional thermoformed aligners. The aim of this in vitro study was to compare the effects of water on the mechanical properties of directly printed aligners with those of conventionally manufactured thermoformed PET-G foils. Dental LT Clear V2 (LT), V Print Splint Comfort (VP), and TC-85 DAC (TC) were examined. Biolon (BL), a conventional PET-G material, served as the thermoplastic reference material. All samples were tested before and after 14 days of water storage at 37 °C. We performed a three-point bending test and an indentation test, and examined changes in the abrasion resistance and hygroscopic volume. The resistance of all printed specimens decreased significantly after water storage. VP and TC were less resilient than BL overall. LT and BL exhibited the lowest indentation creep (BL: 0.08 ± 0.01, LT: 0.13 ± 0.02, VP: 0.21 ± 0.02, TC: 0.24 ± 0.02). Furthermore, the abrasion of LT (0.72 ± 0.21 mm³) was significantly lower than that of BL (1.12 ± 0.37 mm³). In conclusion, the water sorption of the printed test specimens had a significant influence on the mechanical properties, with a reduction in the flexural modulus, Martens hardness, and plastic hardness.

This study was conducted to evaluate the material properties of polymer-infiltrated zinc oxide networks (PICN) and the effect of using a phosphate monomer-containing primer applied before polymer infiltration. A total of 148 ZnO-network (zinc oxide) specimens were produced: n = 74 were treated with a primer before polymer infiltration and light curing, while the remaining specimens were untreated. Each group was divided into two subgroups (n = 37) based on the infiltrating polymer: UDMA (aliphatic urethane-dimethacrylates)-TEGDMA (triethylene glycol-dimethacrylate) or BisGMA (bisphenol A-glycidyl-methacrylate)-TEGDMA. Additionally, n = 7 specimens of each polymer type were prepared for comparison. Then, biaxial flexural strength was measured before and after 150 days of water storage at 37 °C, including 37,500 thermal cycles (5 °C to 55 °C). The Vickers hardness, surface roughness, and water absorption at 37 °C were also tested. The initial biaxial flexural strength was reduced in the ZnO network specimens compared to in the pure polymers. Primer application improved the flexural strength, though the strength of BisGMA-TEGDMA significantly decreased after water storage. The ZnO network increased hardness, and the polymer-infiltrated networks showed higher roughness post-grinding and absorbed less water than the pure polymer groups. The ZnO networks did not improve the flexural strength over that of the pure polymers. However, the primer’s positive impact and the network’s long-term stability suggest potential if the network structure can be modified to contain thicker, more stable branches.

Objectives: The study investigated the influence of retention grooves and material thickness of the retainer wing on the retentive strength of resin-bonded attachments (RBAs). Materials and methods: Sixty-four extracted human molars were used. Each tooth received a preparation limited to the enamel for the retainer wings of the RBAs. The specimens were divided into eight groups, each containing eight specimens. The groups varied based on the number of conical retention grooves (0, 1, 2, or 4) and the thickness of the CoCr retainer wings (0.4 mm and 0.8 mm). Before testing the retentive strength of the RBAs, the specimens underwent 37,500 thermal cycles followed by dynamic loading of 1,200,000 cycles on the RBAs’ patrices using a chewing simulator. The debonding test was conducted using a universal testing machine at a crosshead speed of 2 mm/min. Results: The mean retentive strength ranged from 326 ± 96 N to 440 ± 77 N. Only a small portion of specimens (10.9%) exhibited adhesive failure, while the remainder demonstrated cohesive failure within the tooth structure. Neither the number of retention grooves, the thickness of the retainer wings, nor the size of the bonding surface significantly affected retentive strength. Conclusions: The findings suggest that reducing the number of retention grooves and the material thickness does not influence the retentive strength of RBAs. Clinical relevance: The retention of RBAs appears promising, supporting the clinical application of this treatment modality.

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.