Exposure of Biomimetic Composite Materials to Acidic Challenges: Influence on Flexural Resistance and Elastic Modulus

The Influence of Beverages on Resin Composites: An In Vitro Study

Dental composites, through their structural diversity, represent the biomaterials frequently used in dental reconstructive therapy. The aim of our study was to observe the influence of different beverage environment conditions on seven types of obturation dental materials with different compositions. Our research focused on the surface modification analysis of the materials after the immersion in the different beverages; in this regard, we used the EDAX technique correlated with the energy-dispersive X-ray fluorescence (XRF). The pH of the drinks and that of the simulated saliva solution were determined by the titrimetric method, a sodium hydroxide solution 0.1 mol/dm3 was prepared and used for the titration. An amount of 5 mL of each analyzed solution was added to 15 mL of distilled water to obtain a dilution, to which 3 drops of phenolphthalein (as a color indicator-Phenolphthalein, 3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone, C20H14O4 Mw: 318.32, purchased from Merck) were added for each analysis. For each solution, the experiment was repeated three times in order to obtain accurate results. The results of our study materialized into a real plea for modifying the patients' behavior in terms of diet and preferences for acidic drinks, so that their quality-of-life valence can be improved by keeping the composite materials in a long-term unalterable state on the one hand; on the other hand, systemic damage can be prevented as well.

Influence of Storing Composite Filling Materials in a Low-pH Artificial Saliva on Their Mechanical Properties-An In Vitro Study

Restorative composites are subjected to various influences in the oral cavity environment, such as high or low temperatures, the mechanical force generated during mastication, colonization of various microorganisms, and low pH, which may result from ingested food and the influence of microbial flora. This study aimed to investigate the effect of a recently developed commercial artificial saliva (pH = 4, highly acidic) on 17 commercially available restorative materials. After polymerization, the samples were stored in an artificial solution for 3 and 60 days and subjected to crushing resistance and flexural strength tests. The surface additions of the materials were examined in terms of the shapes and sizes of the fillers and elemental composition. When stored in an acidic environment, the resistance of the composite materials was reduced by 2-12%. Larger compressive and flexural strength resistance values were observed for composites that could be bonded to microfilled materials (invented before 2000). This may result from the filler structure taking an irregular form, which results in a faster hydrolysis of silane bonds. All composite materials meet the standard requirements when stored for a long period in an acidic environment. However, storage of the materials in an acid environment has a destructive impact on the materials' properties.

The Impact of Simulated Bruxism Forces and Surface Aging Treatments on Two Dental Nano-Biocomposites-A Radiographic and Tomographic Analysis

Background and Objectives: Nowadays, indication of composite materials for various clinical situations has increased significantly. However, in the oral environment, these biomaterials are subjected (abnormal occlusal forces, external bleaching, consumption of carbonated beverages, etc.) to changes in their functional and mechanical behavior when indicated primarily for patients with masticatory habits. The study aimed to recreate in our lab one of the most common situations nowadays-in-office activity of a young patient suffering from specific parafunctional occlusal stress (bruxism) who consumes acidic beverages and is using at-home dental bleaching. Materials and Methods: Sixty standardized class II cavities were restored with two nanohybrid biocomposite materials (Filtek Z550, 3M ESPE, and Evetric, Ivoclar Vivadent); the restored teeth were immersed in sports drinks and carbonated beverages and exposed to an at-home teeth bleaching agent. The samples were subjected to parafunctional mechanical loads using a dual-axis chewing simulator. A grading evaluation system was conducted to assess the defects of the restorations using different examination devices: a CBCT, a high-resolution digital camera, and periapical X-rays. Results: Before mechanical loading, the CBCT analysis revealed substantially fewer interfacial defects between the two resin-based composites (p > 0.05), whereas, after bruxism forces simulation, significantly more defects were identified (p < 0.05). Qualitative examination of the restorations showed more occlusal defects for the Evetric than the other nanohybrid composite. Conclusions: There were different behaviors observed regarding the studied nanocomposites when simulation of parafunctional masticatory forces was associated with aging treatments.

Mechanical and Biomimetic Characteristics of Bulk-Fill Resin Dental Composites Following Exposure in a Simulated Acidic Oral Environment

During the last 10 years, various companies have marketed different "bulk-fill" resin dental composites for the restoration of posterior stress-bearing teeth; however, the impact of acidic conditions on these relatively newer materials has not been thoroughly investigated. Therefore, an attempt was made to evaluate the effect of acidic beverages on the mechanical biomimetic characteristics of four bulk-fill and one conventional nanohybrid resin-based dental composites (RBCs). The specimens of each RBC were stored in two acidic beverages namely 'Orange Juice' and 'Coca-Cola', whereas 'dry' and 'distilled water' storage of specimens served as controls. After 1 week of storage, flexural and surface hardness properties of specimens were determined using a universal testing machine and Vickers hardness tester, respectively. In general, the 'Coca-Cola' beverage caused the greatest degradation of flexural strength, flexural modulus, and surface hardness characteristics in all RBCs in contrast to the 'dry', 'distilled water' controls and 'Orange Juice' storage conditions. However, the overall mechanical biomimetic performance of nanohybrid RBCs was relatively better than all other bulk-fill RBCs and may, therefore, be considered a suitable candidate for the restoration of posterior stress-bearing permanent dentition.

Influence of margin design and restorative material on the stress distribution of endocrowns: a 3D finite element analysis

Background

This study aimed to evaluate the stress distributions in endocrown restorations as applied to endodontically treated teeth (ETT), according to the factors of “margin design” (four levels) and “restorative material” (six levels).

Methods

Four 3D-finite elements models were constructed for endocrown restored molars considering different margin designs. Model A was prepared with a flat butt joint margin and received an endocrown with a 2.0-mm occlusal thickness. Model B was prepared with a 20° bevel margin and received an endocrown with a 2.0-mm occlusal thickness. Model C was prepared with an axial reduction and 1-mm shoulder margin and received an endocrown with a 2.0-mm occlusal thickness. Model D was prepared with an anatomic margin and received an endocrown with a 2.0-mm occlusal thickness. The following endocrown materials were used: In-Ceram Zirconia (Zr), Vita Suprinity (VS), IPS Empress (IE), Grandio blocs (GR), VisCalor bulk (VS), and CopraPeek Light (CP). The Load application (600 N) was performed at the food bolus and tooth surface during the closing phase of the chewing cycle. The results for the endocrown and tooth remnants were determined according to the von Mises stress. The failure risk of the cement layer was also calculated based on the normal stress criterion.

Results

Model D (with an anatomic margin) showed the greatest stress concentrations, especially in the irregular and sharp angles of the restoration and tooth remnants. The stress concentrated on the dentin was significantly lower in Model B with a 20° bevel margin (20.86 MPa), i.e., 1.3 times lower than the other three margin designs (27.80 MPa). Restorative materials with higher elastic moduli present higher stress concentrations inside the endocrown and transmit less stress to the cement layer, resulting in lower bonding failure risks. In contrast, materials with an elastic modulus similar to that of dentin presented with a more homogeneous stress distribution on the whole structure.

Conclusions

An endocrown with a 20° bevel margin design could be a favorable preparation option for ETT. Composite resins (GR and VC) exhibit a more even stress distribution, and seem to be more promising materials for endocrown molars.

Biomimetic Nanotechnology Vol. 2

Biomimetic nanotechnology relates to the most basic aspects of living systems, and the transfer of their properties to human applications [...]

In Vitro Weight Loss of Dental Composite Resins and Glass-Ionomer Cements Exposed to a Challenge Simulating the Oral Intake of Acidic Drinks and Foods

Specific conditions of the oral cavity, such as intake of acidic drinks, foods, and drugs, represent a damage both for teeth as well as restorative materials. The aim of this in vitro study is to assess the influence of an acidic challenge on the weight loss of biomimetic restorative dental materials (composite resins and glass-ionomer cements, respectively). Seven products recently available in the marked have been tested in this study for the two kinds of materials, respectively. Resin composites were divided into Groups 1A–7A, whereas glass-ionomer cements into Groups 1B–7B. A total of six samples was considered for each group, among which two were stored into distilled water (control samples) whereas the other four were immersed into soft drink (Coca-Cola, Coca-Cola Company, Milano, Italy) for 7 days. Respectively, after 1, 3 and 7 days, weight was assessed for each sample and the percentage weight loss was calculated. For all the composite resins (Groups 1A–7A), no significant intergroup or intragroup differences occurred for the weight loss values (p > 0.05). Conversely, all glass-ionomers (Groups 1B–7B) showed a significant and progressive weight loss after 1, 3, and 7 days of acid challenge (p < 0.05) (intragroup differences). This reduction was significantly lower in case of GC Equia Forte + Coat and ChemFil Rock, with respect to the other cements (p < 0.05) (intergroup differences). In conclusions, all the biomimetic composite resins showed a reliable behavior when exposed to acidic erosion, whereas glass-ionomers cements generally tended to solubilize. However, the additional use of a protective layer above these latter materials could reduce this event. Despite these results appear to be interesting from a clinical point of view, future morphological evaluations should be conducted to evaluate the superficial changes of the materials after acidic explosion.

The Influence of Popular Beverages on Mechanical Properties of Composite Resins

Currently, composite resins are used in many restorative procedures. Previous studies showed that drinking beverages may affect the mechanical properties such as microhardness or flexural strength of dental composite resins. The aim of the present study was to investigate the influence of common beverages on the mechanical properties of composite resins. Samples of the materials were prepared according to the ISO 4049:2010 standard and producer’s recommendations. The samples were next conditioned in tested fluids: distilled water, sparkling water, Coca-Cola, Red Bull and orange juice for 7 days. Vickers microhardness and flexural strength testing was performed after 7 days. Performed statistic tests confirmed the significance of microhardness changes of the tested materials in terms of both different conditioning of the samples and different composite materials. The mean flexural strength of composites was highest in distilled water and it was reduced after one week in different beverages. We conclude that all tested beverages influenced on Vickers microhardness of tested composite resins. Flexural strength only in one material was statistically significantly influenced by tested beverages. The results of this study should be taken into consideration by a dentist preparing recommendations for the patients after dental treatment with usage of composite material or after cementing composite based fixed dentures.

Influence of Polymeric Restorative Materials on the Stress Distribution in Posterior Fixed Partial Dentures: 3D Finite Element Analysis

Background: This study evaluated the effect of interim restorative materials (acrylic resin (AR), resin composite (RC) or polyetheretherketone (PEEK) for dental computer-aided design/computer-aided manufacturing (CAD/CAM)) on the stress distribution of a posterior three-unit fixed partial denture. Methods: The abutment teeth (first molar and first premolar) were modeled using the BioCAD protocol containing 1.5 mm of axial reduction and converging axial walls. A static structural analysis was performed in the computer-aided engineering software, and the Maximum Principal Stress criterion was used to analyze the prosthesis and the cement layers of both abutment teeth. The materials were considered isotropic, linearly elastic, homogeneous and with bonded contacts. An axial load (600 N) was applied to the occlusal surface of the second premolar. Results: Regardless of the restorative material, the region of the prosthetic connectors showed the highest tensile stress magnitude. The highest stress peak was observed with the use of RC (129 MPa) compared to PEEK and AR. For the cement layers, RC showed the lowest values in the occlusal region (7 MPa) and the highest values for the cervical margin (14 MPa) compared to PEEK (21 and 12 MPa) and AR (21 and 13 MPa). Conclusions: Different interim restorative materials for posterior fixed partial dentures present different biomechanical behavior. The use of resin composite can attenuate the stress magnitude on the cement layer, and the use of acrylic resin can attenuate the stress magnitude on the connector region.