Ulf Örtengren

Yttria-stabilized zirconia (YSZ) has become indispensable in restorative dentistry; however, the influence of yttria content on its crystalline phases and fine structure remains incompletely understood. This study investigated how variations in yttria content (3–8 mol%) and low-temperature degradation (LTD) influence the crystalline phase composition and local atomic structures of dental zirconia using synchrotron-based X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) spectroscopy. Forty-two sintered disc-shaped specimens were prepared from zirconia powders stabilized with 3–8 mol% yttria (3–8YSZ). Half of the specimens were polished, while the other half underwent autoclaving to induce LTD. Synchrotron XRD showed that 3–5YSZ contained 2 tetragonal ( t and t′ ) phases, while 8YSZ contained a cubic ( c ) phase. The t -phase fraction decreased markedly with increasing yttria content, from 83.1 mass% in 3YSZ to 25.3 mass% in 5YSZ. LTD induced monoclinic ( m ) and rhombohedral ( r ) phases in 3YSZ and 4YSZ but not in 5YSZ, indicating improved LTD resistance at higher yttria contents. XAFS showed that the dual-peak white-line profile of zirconia specimens varied with yttria content, reflecting the t -to- t′ phase transition, and transformed into a single broadened peak after LTD, consistent with structural disorder induced by phase transformation. Fine structural analysis revealed 2 main coordination shells, Zr–O and Zr–Zr. In the Zr–Zr shell, the Debye–Waller factors changed systematically with yttria content, reflecting structural disorder associated with oxygen vacancies. In conclusion, a combined synchrotron XRD and XAFS approach elucidated the phase composition and atomic-scale structural disorder in dental zirconia across different yttria contents. These insights provide a foundation for the rational design of next-generation translucent dental zirconia, in which crystalline phase composition and local atomic disorder are deliberately tailored to achieve durable clinical performance.

The research exploiting the ability of dental materials to induce or prevent secondary caries (SC) development still seems inconclusive. Controlling bacterial adhesion by releasing bacteriostatic ions and improving the surface structure has been suggested to reduce the occurrence of SC. This paper analyses the impact of five distinctively composed dental materials on cariogenic biofilm formation. Forty-five specimens of three composites (CeramX Spectra ST, Admira Fusion, Beautifil II) and two glass–ionomers (Fuji II LC, Caredyne Restore), respectively, were incubated in bacterial suspension composed of Streptococcus mutans, Lactobacillus acidophilus, Streptococcus mitis, Streptococcus sanguinis, and Streptococcus salivarius at pH 7.0 and 5.5. Coverslips were used as a control. Adhered bacteria were collected after 2, 4, 6, 12, 24, and 48 h and analyzed using quantitative polymerase chain reaction (qPCR). Fluoride leakage was measured at each collection. The specimens’ surface topography was assessed using interferometry. In the present study, surface roughness seemed to have a partial role in bacterial adhesion and biofilm formation, together with chemical composition of the materials tested. Despite differences in fluoride leakage, biofilm accumulation was similar across materials, but the number of adhered bacteria differed significantly. A release of other ions may also affect adhesion. These variations suggest that certain materials may be more prone to initiating secondary caries.

Dental resin-based composites used as direct restorative treatment show increased water susceptibility depending on the monomer blend and radiant exposure. The current project aimed to investigate the mechanical properties of two contemporary dental resin-based composites with two different monomer mixtures and suboptimal light-curing after 30 and 90 days of water storage. Forty-eight samples of each material were made. Twenty-four samples were made using 5 s of 715 mW/cm2 irradiance (“low-cure” group) and compared to samples that were light-cured for 20 s with 1317 mW/cm2 (“high-cure” group). The samples were stored either in water or air for 30- and 90-days post-cure. After storage, the samples were tested using piston-on-ring biaxial flexure and analysed with differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. Both materials tested showed a reduction in maximal stress at fracture after 90 days compared to the 30 days samples. Furthermore, the “low-cure” sample groups exposed to water for 90 days underwent surface erosion for both materials. For all samples stored in air, the glass transition temperature (fictive temperature) was equal to the storage temperature (37±2 °C), and a hysteresis peak indicated physical ageing. For one of the materials tested, the “low-cure” samples stored in water showed smaller hysteresis peaks and a double glass transition, indicating a difference in curing between the organic filler particles used in the material and the polymer matrix.

Ion-releasing materials (containing fluoride and boron, for example) have shown caries-preventive effects in vitro. The purpose of the present study was to investigate the impact of multi-ion-releasing coating material on pH stabilisation, plaque accumulation and the bacterial composition of dental plaque during a time period of 90 days. The null hypothesis tested here was that the evaluated material would not show any differences in pH stabilisation, plaque accumulation or bacterial composition compared with control material.The study was carried out as a double-blind, split-mouth, randomised, controlled clinical trial in 28 volunteers. Over the evaluation period (days 4, 30, 60 and 90), pH measurements, plaque index and plaque sampling for bacterial analyses were conducted in a calibrated, standardized manner. The study received ethical permission and was carried out in accordance with the Helsinki Declaration.A significant difference was observed, with less plaque accumulation over time in the subjects in whom the ion-releasing material was applied in comparison to the non-active group. No significant difference was evident in terms of either pH stabilisation or plaque levels of mutans streptococci.The null hypothesis relating to plaque accumulation was rejected, with a lower plaque index shown for the test group up to 60–90 days. No adverse effects during the observation period were observed. Since the studied cohort was healthy from a caries perspective, more clinical studies are needed to further evaluate the caries-prevention potential of the ion-releasing material in other patient groups.

Objective: The study aimed to investigate factors contributing to heat development during light curing of a flowable bulk-fill resin-based composite (SDR^TM, Lot # 602000876, Dentsply Sirona, Konstanz, Germany) (RBC). Materials and Methods: Temperatures were measured with calibrated thermocouples. A multi-wave light-emitting diode (LED) light curing unit (LCU) was used (Ivoclar Vivadent, Schaan, Lichtenstein). In all experiments, the RBC was first cured (cured) for 30 s and, after 5 min of recovery time, received a second LCU irradiation (post-cured) for 30 s. The exothermic reaction was measured by calculating the Δ temperature between cured and post-cured RBC. In a cylinder-shaped polymer mold, temperature was recorded inside of RBC during curing (part 1) and light transmission through RBC during curing was investigated (part 2). Pulpal temperatures were assessed in an extracted third molar during light curing (part 3). Data were statistically analyzed using one-way ANOVA (α=0.05). Results: Increased thickness of RBC led to decreased pulp chamber temperatures. Inside RBC, there was a large variation in heat development between the cured and post-cured groups (p< 0.05). The cured group absorbed more LCU irradiation than the post-cured group. Conclusion: The irradiance of the LCU seemed to be a more important factor than exothermic reaction of RBCs for pulp chamber heat development. Flowable bulk-fill RBCs can act as a pulpal insulator against LCU irradiation, despite their exothermic curing reaction.

The water sorption and solubility of two polymer resin‐based dental composite materials were assessed in order to evaluate the effects of immediate post‐cure water exposure on the water sensitivity of the composites. Each material was tested with two different light curing setups. The radiant exposure of the two curing setups differed by a factor of 5. After exposure to water and subsequent drying, the Knoop surface hardness was measured. The change in the degree of conversion in both water and air storage medium within the first 24 h after curing was monitored by Raman spectroscopy. No significant differences in the degree of conversion were detected 24 h after curing. Samples exposed to the lower irradiation dose showed higher solubility and a lower surface hardness than the samples exposed to the higher irradiation dose. Early exposure to water did not cause detectable differences in the ongoing polymerization process. Increase in radiant exposure reduced the fraction of unbound constituents and increased the crosslink density, thereby reducing the plasticity of the material.

Triethylene glycol dimethacrylate (TEGDMA) is commonly used in polymer resin‐based dental materials. This study investigated the molecular mechanisms of TEGDMA toxicity by identifying its time‐ and dose‐dependent effects on the proteome of human THP‐1 monocytes. The effects of different concentrations (0.07–5 mM) and exposure times (0–72 h) of TEGDMA on cell viability, proliferation, and morphology were determined using a real‐time viability assay, automated cell counting, and electron microscopy, and laid the fundament for choice of exposure scenarios in the proteomic experiments. Solvents were not used, as TEGDMA is soluble in cell culture medium (determined by photon correlation spectroscopy). Cells were metabolically labeled [using the stable isotope labeled amino acids in cell culture (SILAC) strategy], and exposed to 0, 0.3 or 2.5 mM TEGDMA for 6 or 16 h before liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) analyses. Regulated proteins were analyzed in the STRING database. Cells exposed to 0.3 mM TEGDMA showed increased viability and time‐dependent upregulation of proteins associated with stress/oxidative stress, autophagy, and cytoprotective functions. Cells exposed to 2.5 mM TEGDMA showed diminished viability and a protein expression profile associated with oxidative stress, DNA damage, mitochondrial dysfunction, and cell cycle inhibition. Altered expression of immune genes was observed in both groups. The study provides novel knowledge about TEGDMA toxicity at the proteomic level. Of note, even low doses of TEGDMA induced a substantial cellular response.