Physical and Mechanical Properties of Bulk-Fill, Conventional, and Flowable Resin Composites Stored Dry and Wet

Comparison of mechanical and surface properties of two 3D printed composite resins for definitive restoration

STATEMENT OF PROBLEM

Additive manufacturing (AM) technology is emerging as an innovative approach in the dental field. In recent years, manufacturers have introduced 3-dimensionally printed composite resins (3D-CRs) that are specifically designed for the AM of definitive prostheses; however, the mechanical and surface properties of these materials require investigation.

PURPOSE

The purpose of this in vitro study was to assess and compare the mechanical and surface properties of 2 commercially available 3D-CRs for definitive restoration after artificial aging.

MATERIAL AND METHODS

Saremco print Crowntec; Saremco Dental AG and Varseo Smile Crown Plus; Bego GmbH were printed with a layer thickness of 50 µm at a 90-degree angle. A total of 20 bar-shaped specimens (25×2×2 mm) were produced from each material to measure the flexural strength (σf) and elastic modulus (E) using a 3-point bend test, and 5 disk-shaped specimens (Ø15×3 mm) from each material were used to measure the surface microhardness using a microhardness test. Half of the specimens were tested under dry conditions, while the other half were immersed in distilled water for 30 days. Five disk-shaped specimens (Ø15×3 mm) from each material were used to evaluate surface roughness before and after undergoing toothbrushing simulations. Additionally, 5 disk-shaped specimens (Ø15×1 mm) were used to assess water sorption (wsp) and solubility (wsl) over 28 days. Statistical analyses were conducted using the Wilcoxon matched-pairs signed-rank test (1-tailed) with 90% power (α=.05).

RESULTS

The mean ±standard deviation flexural strength values were 123.4 ±8.7 MPa for Saremco print Crowntec and 109.9 ±15.8 MPa for Varseo Smile Crown Plus. After aging, these values were 97.5 ±15.2 MPa for Saremco print Crowntec and 94.2 ±11.7 MPa for Varseo Smile Crown Plus. The mean Vickers hardness values were 33.2 ±0.8 N/mm2 for Saremco print Crowntec and 31.5 ±0.6 N/mm2 for Varseo Smile Crown Plus. After aging, the mean values were 31.7 ±0.9 N/mm2 for Saremco print Crowntec and 29.6 ±1.0 N/mm2 for Varseo Smile Crown Plus. The mean modulus of elasticity was 4.2 ±0.3 GPa for Saremco print Crowntec and 3.82 ±0.2 GPa for Varseo Smile Crown Plus. After 21 days, the mean sorption values were 11.52 ±0.6 mg/mm3 for Saremco print Crowntec and 12.43 ±0.4 mg/mm3 for Varseo Smile Crown Plus. After 28 days, the mean solubility values were 1.36 ±0.4 mg/mm3 for Saremco print Crowntec and 0.98 ±0.3 mg/mm3 for Varseo Smile Crown Plus. Significant differences were found between the 2 3D-CRs in flexural strength in the dry state (P=.03), in Young modulus after 30 days of water immersion (P=.023), and in Vickers hardness in the dry state (P=.01) and after 30 days of water immersion (P=.018).

CONCLUSIONS

Both 3D-CRs provided good in vitro performance and the mechanical properties required for long-term clinical application. Artificial aging decreased the flexural strength of both 3D-CRs.

Maximizing Dental Composite Performance: Strength and Hardness Enhanced by Innovative Polymer-Coated MgO Nanoparticles

INTRODUCTION

Zein-incorporated magnesium oxide nanoparticles (zMgO NPs) can influence the mechanical properties of dental materials. However, the effect of this addition on the mechanical properties of resin composite has yet to be investigated. The objective of this study was to add various concentrations of zMgO NPs to conventional, flowable, and bulk-fill composite and assess the effect on the compressive strength, flexural strength, and microhardness.

METHODOLOGY

150 samples each of conventional composite, flowable composite, and bulk-fill composite (n=450) were enhanced with concentrations of zMgO NPs at 0%, 0.3%, 0.5%, 1%, and 2% (n=30). 10 samples of each group were randomly allotted to the compressive strength, flexural strength, or hardness test. Characterization of the specimens was performed by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Two-way ANOVA test was used to compare between groups, and one-way ANOVA followed by Tukey's test was done at p=0.05 to determine significance.

RESULTS

Characterization yielded a uniform distribution of nanoparticles in the matrix and the formation of a new hybrid composite that maintained its properties. Composite of all types enhanced with 0.3% and 0.5% zMgO NPs demonstrated a statistically significant increase in compressive strength, flexural strength, and hardness when compared to the control (p<0.05). The bulk-fill composite with zMgO NPs concentrations of all groups demonstrated a statistically significant increase (p<0.05) in hardness when compared to the control.

CONCLUSION

The modified composites' compressive strength, flexural strength, and hardness improved or remained consistent.

CLINICAL SIGNIFICANCE

An improved dental resin composite will enhance the quality of care and patient experience. The augmented strength and hardness of resin composite is desirable in prolonging the durability of the restoration.

Influence of etching mode on bonding performance of self-adhesive flowable resin composites to bovine teeth

This study aimed to evaluate the bonding performance of self-adhesive flowable resin composites (SARs) to bovine teeth. Three SARs, one experimental, and two commercially available products, were used. The study parameters were shear bond strength (SBS), microleakage, and scanning electron microscopy (SEM) evaluation of bonding interfaces. The SBS of the materials was 14.1-15.1 MPa to enamel, 22.2-23.2 MPa to etched enamel, and 7.4-10.7 MPa to dentin. Specimens with pre-etching showed lower microleakage scores than those without pre-etching. SEM images of the interfaces of the materials showed excellent adaptation regardless of the substrate or etching mode. The study results indicate that enamel pre-etching can improve the bonding performance of SARs.

Influence of Layer Thickness and Shade on the Transmission of Light through Contemporary Resin Composites

BACKGROUND

Material-dependent parameters have an important impact on the efficiency of light polymerization. The present in vitro study aimed to investigate the influence of the increment thickness and shade of nano- and nanohybrid resin composites on the transmission of curing light.

METHODS

Three contemporary resin composites were evaluated: Tetric EvoCeram® (TEC); Venus Diamond® (VD); and Filtek Supreme XTE® (FS XTE). Light transmission (LT) was recorded in accordance with the sample thickness (0.5 to 2.7 mm) and the shade. Polymerized samples were irradiated for 10 s each using the high-power LED curing light Celalux 2 (1900 mW/cm2). LT was simultaneously recorded using the MARC Patient Simulator (MARC-PS).

RESULTS

LT was strongly influenced by the composite layer thickness. For 0.5 mm-thick samples, a mean power density of 735 mW/cm2 was recorded at the bottom side. For the 2.7 mm samples, a mean power density of 107 mW/cm2 was measured. Only LT was markedly reduced in the case of darker shades. From A1 to A4, LT decreased by 39.3% for FS XTE and 50.8% for TEC. Dentin shades of FS XTE and TEC (A2, A4) showed the lowest LT.

CONCLUSIONS

The thickness and shade of resin composite increments strongly influences the transmission of curing light. More precise information about these parameters should be included in the manufacture manual.

Performance Assessment of Three Similar Dental Restorative Composite Materials via Raman Spectroscopy Supported by Complementary Methods Such as Hardness and Density Measurements

(1) Background: A widespread problem in oral health is cavities produced by cariogenic bacteria that consume fermentable carbohydrates and lower pH to 5.5-6.5, thus extracting Ca2+ and phosphate ions (PO43-) from teeth. Dental restorative materials based on polymers are used to fill the gaps in damaged teeth, but their properties are different from those of dental enamel. Therefore, a question is raised about the similarity between dental composites and natural teeth in terms of density and hardness. (2) Methods: We have used Raman spectroscopy and density and microhardness measurements to compare physical characteristics of several restorative dental composites at different polymerization intervals. (3) Results: XRVHerculite®, Optishade®, and VertiseFlow® showed the very different characteristics of the physical properties following four polymerization intervals. Of the three composites, OptiShade showed the highest polymerization rate. (4) Conclusions: Only fully polymerized composites can be used in teeth restoring, because incomplete polymerization would result in cracks, pitting, and lead finally to failure.

Color Stability of Resin Cements after Water Aging

The color stability of resin cements plays a key role in the achievement of esthetically-pleasant restorations. Resin luting materials can be mainly divided into two main classes: adhesive (relying on previous application of adhesive systems) or self-adhesive (also known as one-step cements). The different chemical compositions determine their physio-mechanical characteristics which, in turns, influence their color stability. To evaluate the color variations of different dual-cured resin cements after water aging, 80 disc-shaped specimens (15 mm in diameter and 1.2 mm thick) were obtained from the following resin cements (n = 10): (1) Maxcem Elite Universal, MCU (Kerr); (2) RelyX Universal, RXU (3M); (3) Calibra Ceram, CAL (Dentsply); (4) Multilink, MUL (Ivoclar-Vivadent); (5) Panavia V5, PAN (Kuraray); (6) Calibra Universal, CUN (Dentsply); (7) SpeedCEM Plus, SCP (Ivoclar); and (8) Panavia SA, PSA (Kuraray). After light-polymerization, the specimens were measured with a spectrophotometer and CIELab* values were recorded. The specimens were then placed in a digitally controlled thermostatic water bath at 60° for 30 days and afterwards the color measurements were repeated. Color differences were calculated for each specimen before and after water-aging procedures with ΔEab formula and the data were statistically analyzed (p < 0.05). The type of cement statistically influenced the ΔEab (p < 0.05), with MCU showing the lowest color variations (4.3 ± 0.7) whereas RXU and PSA the highest (16.9 ± 1.6 and 16.8 ± 1.2, respectively). No differences were observed between CAL, CUN and SCP (p = 0.05). Color stability is related to the chemical composition of the resinous luting materials, thus material dependent.

Protective effect of a nanofilled resin-based coating on wear resistance of glass ionomer cement restorative materials

BACKGROUND

The effect of nanofilled resin-based coating on the wear resistance of glass ionomer cements (GICs) is still controversial. This study aims to compare the wear resistance of four encapsulated GICs including two conventional and two resin-modified, and to evaluate the effect of G-Coat Plus on the wear resistance of GICs.

METHODS

A total of 80 disk-shaped specimens were prepared from two CGICs (riva self cure (SDI) and Equia Forte Fil (GC) and two RM- GICs (Ketac Nano (3 M/ESPE) and Fuji II LC (GC). The specimens of each material were divided into two groups (n = 10) based on the surface protection: no coating (NC), and coating with G-Coat Plus (GCP). All specimens were then placed in distilled water for 24 h at 37 °C. The specimens were subjected to thermocycling for 120,000 cycles using a chewing simulator. Wear resistance was measured using a specific formula. Data was analyzed using Kruskal-Wallis test.

RESULTS

There was no significant difference in volume loss (mm³) between coated and uncoated groups for all materials (P > 0.05). Ketac Nano showed significantly lower volume loss (0.65 ± 0.12) compared to all other groups (P < 0.05) among uncoated specimen, and significantly lower than Fuji II LC (P = 0.035) and Equia Forte Fil (P = 0.040) among coated groups. However, no statically significant difference was observed between volume loss of coated Ketac Nano with that of riva self cure (P = 0.087).

CONCLUSIONS

Coating with GCP did not affect the wear depth of GICs, and Ketac Nano showed significantly lower volume loss regardless of coating.

Microhardness Evaluation of Microhybrid Versus Nanofilled Resin Composite After Exposure to Acidic Drinks

Objective

To investigate the effect of two acidic agents on microhardness of nanofilled and microhybrid resin composite materials.

Materials and Methods

70 resin composite discs (10 mm diameter and 2 mm thick) were prepared from 2 resin composites (35 from each type), nanofilled (Z350XT) and microhybrid (Z250), 3M/ESPE. Ten discs (5 from each group) were used as control (tested at 1 h before immersion). Each group was divided into 3 subgroups (n = 10) according to the storage media: distilled water (control), box-type cola and orange juice. Each subgroup was further subdivided into 2 divisions (n = 5) according to microhardness testing at 24 h and 7days after immersions. Digital Vickers Microhardness Tester (FM-7, Future Tech, Tokyo, Japan) was used to measure surface microhardness with a Vickers diamond indenter. The surface of the specimens received a load of 200 g for 10 seconds. Three indentations not less than 1 mm from each other were placed on the surface of all specimens. Vickers hardness number (VHN) was calculated for each indentation Data were statistically analyzed using one- way ANOVA followed by Newman-keuls tests (P ≤ 0.05).

Results

Orange juice showed statistically significantly the lowest VHN mean value (92.7) followed by the Cola group (95.15) then the water group (104.02) compared to the control group (117.4). Microhybrid composite groups showed statistically significant higher VHN mean value (108.1) than the nanofilled composite (100.2). The 7days groups showed statistically significant lower VHN mean value (97.3) than 24h groups (106.6).

Conclusions

All storage media reduced hardness of resin composites with orange juice showing the highest reduction in hardness values. Microhybrid is more resistant to degradation than nanofilled composite. Over time, microhardness of resin composites decreased progressively.