Aging effect of pH on the mechanical and tribological properties of dental composite resins

Evaluation of the Mechanical Properties of Different Dental Resin-Based Materials After Submersion in Acidic Beverages

Background: The aim of this study was to evaluate the influence of acidic beverages on the mechanical properties of various dental resin-based materials. Methods: A total number of 160 samples were prepared using four types of resin-based materials-Group A (n = 40): flowable composite, Group B (n = 40): heavy-flow composite, Group C (n = 40): resin-based sealant and Group D (n = 40): nano-hybrid composite. Then, the samples were distributed into four subgroups according to the submersion solution: a (n = 10): artificial saliva, b (n = 10): coffee, c (n = 10): cola and d (n = 10): red wine. The Vickers microhardness, Young's modulus of elasticity and scratch resistance were assessed using a CETR UMT-2 tribometer. Results: The obtained results showed that 14-day submersion of the resin-based materials in coffee, cola and red wine solutions significantly (p < 0.05) decreased the microhardness values (VHN), Young's modulus of elasticity and scratch resistance. Fourteen days of storage in coffee decreased the microhardness values of flow resin from 117.5 to 81.59 VHN (p < 0.001) whereas the values of the nanohybrid resin decreased from 125.5 to 89.4 (p < 0.001). The elasticity modulus of the heavy flow resin showed a decline from 15.57 to 10.50 GPa after 14 days' submersion in coffee (p < 0.001), and from 21.29 to 13.10 GPa for the nanohybrid resin after immersion in cola (p < 0.001). For the scratch test, the resin-based sealant showed a significant decrease after 14 days of storage in coffee, from 0.34 to 0.02 units. Conclusions: The submersion of conventional nanohybrid, flowable, heavy-flow composite resins and resin-based sealants in coffee, cola and red wine solutions changes the mechanical properties (Young's modulus of elasticity, Vickers microhardness and scratch resistance). The most resistant resin-based material to acid attack was the conventional nanohybrid composite resin, followed by heavy flow resin, flowable resin and resin-based sealant.

Fatigue behaviour of a self-healing dental composite

OBJECTIVE

Novel self-healing resin-based composites containing microcapsules have been developed to improve the mechanical performance of dental restorations. However, the long-term fatigue behaviour of these self-healing composites has still been hardly investigated. Therefore, this manuscript studied the fatigue behaviour of self-healing composites containing microcapsules by subjecting the specimens to traditional staircase tests and ageing in a custom-designed chewing simulator (Rub&Roll) to simulate oral ageing physiologically relevant conditions.

METHODS

To prepare self-healing composite, poly(urea-formaldehyde) microcapsules containing acrylic self-healing liquids were synthesized. Subsequently, these microcapsules (10 wt%) and initiator (benzoyl peroxide, BPO, 2 wt%) were incorporated into a commercial flowable resin-based composite. Microcapsule-free resin-based composites with and without BPO were also prepared as control specimens. A three-point flexural test was used to measure the initial flexural strength (Sinitial). Subsequently, half of the specimens were used for fatigue testing using a common staircase approach to measure the fatigue strengths (FS). In addition, the other specimens were aged in the Rub&Roll machine for four weeks where after the final flexural strength (Sfinal) was measured.

RESULTS

Compared to Sinitial, FS of all tested specimens significantly decreased as measured through staircase testing. After 4 weeks of ageing in the Rub&Roll machine, Sfinal was significantly reduced compared to Sinitial for microcapsule-free resin-based composites, but not for the self-healing composites (p = 0.3658). However, the self-healing composites are still in the experimental phase characterized by a low mechanical strength, which still impedes further clinical translation.

SIGNIFICANCE

Self-healing composites containing microcapsules exhibit improved fatigue resistance compared to microcapsule-free non-self-healing composites.

Application of Tribology Concept in Dental Composites Field: A Scoping Review

Tribology is the discipline concerning the application of friction, lubrication, and wear concepts of interacting surfaces in relative motion. A growing interest has developed in tribology application in medical biomaterials, such as resin composites used in restorative dentistry. Yet, the keywords "tribology" and "biotribology" are little applied in the pertinent publications. The aim of this scoping review was to offer an overview of tribology application in dental composites research and to identify knowledge gaps and address future research. A literature search was conducted on Pubmed and Scopus databases and the studies investigating the tribological behavior of resin composites were included for qualitative synthesis. The majority of studies on dental tribology were published in the research areas of mechanical engineering/nanotechnology and differed in several methodological aspects. The preponderant engineering approach and the lack of standardized testing make the laboratory findings poorly informative for clinicians. Future research should focus on the tribological behavior of dental materials composites by means of an integrated approach, i.e., engineering and clinical, for improving development and advancement in this field of research.

Recent Advances in the Development of Antimicrobial and Antifouling Biocompatible Materials for Dental Applications

The risk of secondary bacterial infections resulting from dental procedures has driven the design of antimicrobial and antifouling dental materials to curb pathogenic microbial growth, biofilm formation and subsequent oral and dental diseases. Studies have investigated approaches based primarily on contact-killing or release-killing materials. These materials are designed for addition into dental resins, adhesives and fillings or as immobilized coatings on tooth surfaces, titanium implants and dental prosthetics. This review discusses the recent developments in the different classes of biomaterials for antimicrobial and antifouling dental applications: polymeric drug-releasing materials, polymeric and metallic nanoparticles, polymeric biocides and antimicrobial peptides. With modifications to improve cytotoxicity and mechanical properties, contact-killing and anti-adhesion materials show potential for incorporation into dental materials for long-term clinical use as opposed to short-lived antimicrobial release-based coatings. However, extended durations of biocompatibility testing, and adjustment of essential biomaterial features to enhance material longevity in the oral cavity require further investigations to confirm suitability and safety of these materials in the clinical setting. The continuous exposure of dental restorative and regenerative materials to pathogenic microbes necessitates the implementation of antimicrobial and antifouling materials to either replace antibiotics or improve its rational use, especially in the day and age of the ever-increasing problem of antimicrobial resistance.

The Effect of Thermocycling on Surface Layer Properties of Light Cured Polymer Matrix Ceramic Composites (PMCCs) Used in Sliding Friction Pair

This paper discusses the problem of thermocycling effect of light-curing polymer–ceramic composites. Cyclic thermal shocks were simulated in laboratory conditions. As a rule, these loads were supposed to reproduce the actual conditions of biomaterials exploitation. Periodically variable stresses occurring in dental restorations are associated with the wear of cold and hot foods and beverages. They lead to changes in the properties of composites, including the properties of the surface layer. The aim of the work was to assess the impact of cyclic hydrothermal interactions on the properties of the surface layer of composites relevant to the operational quality. Two commercial materials manufactured by the world’s leading producer (3M ESPE)—Filtek Z550, Filtek Flow and two experimental, micro-hybrid and flow type composites marked Ex-mhyb(P) and Ex-flow(P), respectively. All tests were carried out before and after hydro-thermal cycles (flowing water thermocycling). Micro-hardness test using the Vickers method, indentation hardness, and resistance to tribological wear in a ball–disc system in sliding friction conditions were performed. In addition, observations of the surface layer of composites on the SEM (scanning electron microscope) were carried out. It was noticed that semi-liquid composites, containing a smaller amount of filler, retain higher stability of mechanical and tribological properties of the surface layer under cyclic hydro-thermal loads. Coefficient of friction of samples after hydro-thermal cycles increased for micro-hybrid materials and Filtek Flow (FFlow) composite. In the case of Ex-flow(P) material, the coefficient of friction decreased. The microhardness of composites also changed, the variability of this size depended on the type of material. Composites with a higher content of filler particles were characterized by greater variability of microhardness under the influence of thermocycles. The resistance to tribological wear also changed in a similar way. Composites containing higher volume fraction of inorganic filler showed higher tribological wear after thermocycling. The wear resistance of flow composites changed to a lesser extent, after thermocycling increased. The paper also showed that, in real kinematic nodes, the surface layer of light-curing ceramic–polymer composites is exposed to significant non-tribological (erosive, thermal, and chemical) defects that synergize with tribological ones. In slip pairs loaded dynamically, under mixed friction conditions, tribological wear of PMCCs (polymer matrix ceramic composites) is manifested by spalling (spalling of the material flakes, in particular the polymer phase) and pitting (crushing wear caused by wear products, in particular large filler particles or clusters, previously adhesively extracted).

TEGDMA releasing in resin composites with different filler contents and its correlation with mitochondrial mediated cytotoxicity in human gingival fibroblasts

Compositions of resin composite exhibit cytotoxicity, especially Triethylene-glycol-dimethacrylate (TEGDMA), yet the underlying mechanisms and its relationship with filler content are poorly understood. Here, specimens of five composites (VITA LC, VITA ZETA, Z350, Filtek P60, and AP-X), containing different filler size and weight, were immersed into culture medium for 72 h. After TEGDMA quantification, the resin composite eluates were used to incubate HGFs. Cellular viability was evaluated. Total reactive oxygen species (ROS) and mitochondrial ROS were detected to assess oxidative stress. Adenosine triphosphate and cytochrome c oxidase (CcO) activity, mitochondrial membrane potential and morphology, mitochondrial biogenesis regulators were analyzed to evaluate mitochondrial functions. Results showed that TEGDMA release negatively correlated to filler size and weight of tested composites. Although cell viability reduction was not significant, total and mitochondrial ROS production showed a positive relationship with the amount of TEGDMA in composite eluates. Furthermore, the expression of mitochondrial biogenesis markers and mitochondrial fusion protein, were markedly elevated in TEGDMA rich eluates, especially in VITA-LC group, shown as elongated mitochondrial morphology and aberrant mitochondrial functions. Overall, TEGDMA could elute easier from those resin composites with less filler content and cause oxidative stress in HGFs via mitochondria dysregulation. These data can be instructive to optimize the synthesis of resin composites from the perspective of biocompatibility. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1132-1142, 2019.