The effect of different storage media on the monomer elution and hardness of CAD/CAM composite blocks

Effects of printing orientation and artificial ageing on martens hardness and indentation modulus of 3D printed restorative resin materials

BACKGROUND

Three-dimensional (3D) printing is increasingly used to fabricate dental restorations due to its enhanced precision, consistency and time and cost-saving advantages. The properties of 3D-printed resin materials can be influenced by the chosen printing orientation which can impact the mechanical characteristics of the final products.

PURPOSE

The objective of this study was to evaluate the influence of printing orientation and artificial ageing on the Martens hardness (HM) and indentation modulus (EIT) of 3D-printed definitive and temporary dental restorative resins.

METHODS

Disk specimens (20 mm diameter × 2 mm height) were additively manufactured in three printing orientations (0°, 45°, 90°) using five 3D-printable resins: VarseoSmile Crownplus (VCP), Crowntec (CT), Nextdent C&B MFH (ND), Dima C&B temp (DT), and GC temp print (GC). The specimens were printed using a DLP 3D-printer (ASIGA MAX UV), while LavaTM Ultimate (LU) and Telio CAD (TC) served as milled control materials. Martens hardness (HM) and indentation modulus (EIT) were tested both before and after storage in distilled water and artificial saliva for 1, 30, and 90 days at 37 °C.

RESULTS

90° printed specimens exhibited higher HM than the other orientations at certain time points, but no significant differences were observed in HM and EIT between orientations for all 3D-printed materials after 90 days of ageing in both aging media. LU milled control material exhibited the highest HM and EIT among the tested materials, while TC, the other milled control, showed similar values to the 3D printed resins. CT and VCP (definitive resins) and ND displayed higher Martens parameters compared to DT and GC (temporary resins). The hardness of the 3D-printed materials was significantly impacted by artificial ageing compared to the controls, with ND having the least hardness reduction percentage amongst all 3D-printed materials. The hardness reduction percentage in distilled water and artificial saliva was similar for all materials except for TC, where higher reduction was noted in artificial saliva.

SIGNIFICANCE

The used 3D printed resins cannot yet be considered viable alternatives to milled materials intended for definitive restorations but are preferable for use as temporary restorations.

The effect of in-office bleaching agents on the Vickers hardness and surface topography of polished and unpolished CAD/CAM composite materials

In-office bleaching, using hydrogen peroxide, is effective to remove dental enamel stains. However, bleaching agents can deteriorate surface properties of CAD-CAM materials. This in vitro study aimed to investigate the effect of in-office bleaching agents on Vickers hardness and surface topography of polished and unpolished dental CAD-CAM composite materials (Grandio blocs, Lava Ultimate, BRILLIANT Crios, Cerasmart), and a polymer-infiltrated ceramic network block (Vita Enamic). The specimens were randomly divided into two groups: unpolished or polished. The micro-hardness and surface topography of each group were measured before bleaching, after a 60 min bleaching period, and 24-h and one-month post-bleaching. In-office bleaching significantly influenced the Vickers hardness of both the polished and unpolished CAD/CAM composite blocks, with Vita Enamic exhibiting the least hardness stability among all groups. Furthermore, in-office bleaching significantly influenced the surface roughness of unpolished CAD/CAM composite blocks. There was a significant difference in hardness reduction between the polished and unpolished specimens for most of the investigated materials at different time points. The bleaching did not influence the surface roughness of the investigated polished group, except for Vita Enamic and Lava Ultimate. However, it did influence the surface roughness of the investigated materials in the unpolished group.

Evaluation of Physical-Chemical Properties of Contemporary CAD/CAM Materials with Chromatic Transition "Multicolor"

The use of materials for computer-aided design/computer-aided manufacturing (CAD/CAM) has been rapidly increasing in daily practice. However, one of the main issues regarding modern CAD/CAM materials is their aging in the oral environment, which may lead to significant changes in their overall properties. The aim of this study was to compare the flexural strength, water sorption, cross-link density (softening ratio%), surface roughness, and SEM analysis of three modern CAD/CAM "multicolor" composites. Grandio (Grandio disc multicolor-VOCO GmbH, Cuxhaven, Germany), Shofu (Shofu Block HC-Shofu Inc., Kyoto, Japan), and Vita (Vita Enamic multiColor-Vita Zahnfabrik, Bad Sackingen, Germany) were tested in this study. They were prepared in stick-shaped specimens and submitted to different tests after several aging protocols, such as thermocycling and mechanical cycle loading challenge. Further disc-shaped specimens were also created and tested for water sorption, cross-link density, surface roughness, and SEM ultramorphology, before and after storage in an ethanol-based solution. For flexural strength and ultimate tensile strength, Grandio showed the greatest values both at baseline and after aging (p < 0.05). Grandio and Vita Enamic presented the highest modulus of elasticity and the lowest water sorption (p < 0.05). A significant reduction (p < 0.05) in microhardness after ethanol storage (softening ratio%) was observed especially in Shofu. Grandio had the lowest roughness parameters compared to the other tested CAD/CAM materials, while ethanol storage significantly increased the Ra and RSm values in Shofu (p < 0.05). Despite the comparable modulus of elasticity of Vita and Grandio, this latter showed greater flexural strength and ultimate tensile strength both at baseline and after aging. Hence, Grandio and Vita Enamic may be employed for the anterior teeth and for those restorations requiring load-bearing capacity. Conversely, aging seems to affect several properties of Shofu, so its use for permanent restorations should be well-pondered based on the clinical situation.

The influence of different storage media on Vickers hardness and surface roughness of CAD/CAM resin composites

INTRODUCTION

This study examined Vickers hardness as well as surface characteristics of different computer-aided design/computer-aided manufacturing (CAD/CAM) resin composites prior to and after storage in various media.

MATERIALS AND METHODS

CAD/CAM resin composite blocks (Grandio Blocs (GB), Lava Ultimate (LU), Brilliant Crios (BC), Cerasmart (GC), Shofu Block HC (SB), Tetric CAD (TC), Luxacam Composite (LC); incl. different translucency variants) were prepared, polished and surface free energy was determined. The specimens were divided into four groups: dry conditions for 24 h (25 °C), demineralized water (37 °C), Pepsi Cola (37 °C) and 75% ethanol (37 °C). After seven and 28 days of storage, Vickers hardness was determined. Surface roughness was measured after the entire storage period.

RESULTS AND DISCUSSION

Vickers hardness was in the range of about 150 HV for GB, around 115 HV for LU, and 80-100 HV for BC, GC, SB, TC and LC. Only minor differences (total: 50.2 (6.4)-56.2 (3.2) mN/m) in surface free energy could be detected. No relationship was observed between surface free energy and filler content. However, a correlation between filler content and Vickers hardness was evident. Artificial aging caused a decrease of Vickers hardness (up to -40 HV or 35%) depending on storage media, duration and material. The changes in surface texture after immersion in different media were below a value of ΔSa = 0.015 µm.

CONCLUSION

Artificial aging of CAD/CAM resin composites leads to a significant decrease of Vickers hardness for most materials, while only small changes in surface roughness were identified.

Monomers Release from Direct and Indirect Resin-Based Restorations after Immersion in Common Beverages

Impurities or degradation of the components of resin-based materials have been throughout investigated by the dental scientific community. The aim of this study is to examine if there is a release of monomers from resin-based materials when they are immersed in common beverage materials which are consumed by the population in large quantities. Three representative dental materials were used for this study, one resin composite indicated for direct restorations and two Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) materials with different methods of fabrication. Forty specimens were fabricated from each material using a low-speed precision sectioning blade 12 × 14 × 2 mm in size and immersed in wine, coffee or cola for 48 h and 12 days, equivalent to 1 month and 1 year of consumption. The materials released more monomers when the materials were immersed in the wine solution (p < 0.05). CAD/CAM materials release less monomers compared to the resin composite material indicated for direct restorations (p < 0.05). The CAD/CAM materials leach a limited quantity of monomers when they are immersed in common beverages due to the manufacturing process which includes high-temperature/high-pressure polymerization.

Influence of Acidic Environment on the Hardness, Surface Roughness and Wear Ability of CAD/CAM Resin-Matrix Ceramics

This study aimed to measure the effect of storage environment on the hardness, surface roughness and wear ability of CAD/CAM resin-matrix ceramics. A total of 200 rectangular-shaped specimens were obtained by sectioning 5 CAD/CAM blocks; Crystal Ultra (CU), Vita Enamic (VE), Lava Ultimate (LU), Cerasmart (CS) and Vita blocks Mark II (MII). Microhardness and surface roughness were measured at baseline and after 7 days of immersion either in saliva or cola (n = 10). The wear ability of the CAD/CAM materials against steatite-ceramics antagonist was determined using a chewing simulator. The data were statistically analyzed using factorial ANOVA followed by post hoc Bonferroni multiple comparison tests (p < 0.05). The independent factors significantly influenced the microhardness and surface roughness (p < 0.05). The highest VHN was observed in MII at baseline (586.97 ± 13.95), while CU showed the lowest VHN after 7 days of immersion in cola (68.3 ± 1.89). On the contrary, the highest Ra was observed after 120,000 chewing cycles for the VE specimens (1.09 ± 0.43 µm) immersed in cola, while LU showed the lowest Ra at baseline (0.07 ± 0.01 µm). The highest % mass loss of the antagonist was observed with MII immersed in cola (1.801%), while CS demonstrated the lowest % mass loss of 0.004% and 0.007% in AS and cola, respectively. This study confirms that the surface properties of tested CAD/CAM materials are susceptible to degradation in an acidic environment except for hardness and wear of CS material.

Surface Characteristics and Color Stability of Dental PEEK Related to Water Saturation and Thermal Cycling

(1) Background: The study was undertaken to evaluate the surface characteristics, microhardness, and color stability of PEEK materials related to water saturation and in vitro aging. (2) Methods: Custom specimens of unmodified and modified PEEK CAD/CAM materials were investigated: BioHPP, a ceramic reinforced PEEK, and Finoframe PEEK and Juvora medical PEEK, 100% PEEK materials. Forty-eight plates were sectioned in rectangular slices. The specimens were immersed in distilled water at 37 °C for a period of 28 days, and then subjected to aging by thermal cycling (10,000 cycles). Surface roughness was measured with a contact profilometer; nanosurface topographic characterization was made by Atomic Force Microscopy; Vickers hardness measurements were performed with a micro-hardness tester; color changes were calculated. All registrations were made before immersion in water and then subsequently once a week for 4 weeks, and after thermocycling. (3) Results: The studied reinforced and unfilled PEEK materials reached water saturation after the first week of immersion, without significant differences between them. The most affected from this point of view was the reinforced PEEK material. Thermocycling induces a significant increase inmicroroughness, without significant differences between the studied materials. In relation to the nanosurface topography and roughness, the reinforced PEEK material was the least modified by aging. The color changes after 4 weeks of water immersion and one year of simulated in vitro aging ranged from extremely slight to slight, for all materials. (4) Conclusions: Water absorption was associated with a decrease in microhardness. Surface characteristics are affected by water immersion and thermocycling. Perceivable or marked color changes of the materials were not detected during the study.

Meta-analytical analysis on components released from resin-based dental materials

OBJECTIVES

Resin-based materials are applied in every branch of dentistry. Due to their tendency to release substances in the oral environment, doubts have been raised about their actual safety. This review aims to provide a comprehensive analysis of the last decade literature regarding the concentrations of elutable substances released from dental resin-based materials in different type of solvents.

MATERIALS AND METHODS

All the literature published on dental journals between January 2010 and April 2022 was searched using international databases (PubMed, Scopus, Web of Science). Due to strict inclusion criteria, only 23 papers out of 877 were considered eligible. The concentration of eluted substances related to surface and volume of the sample was analyzed, considering data at 24 h as a reference. The total cumulative release was examined as well.

RESULTS

The most eluted substances were HEMA, TEGDMA, and BPA, while the less eluted were Bis-GMA and UDMA. Organic solvents caused significantly higher release of substances than water-based ones. A statistically significant inverse correlation between the release of molecules and their molecular mass was observed. A statistically significant positive correlation between the amount of released molecule and the specimen surface area was detected, as well as a weak positive correlation between the release and the specimen volume.

CONCLUSIONS

Type of solvent, molecular mass of eluates, and specimen surface and volume affect substances release from materials.

CLINICAL RELEVANCE

It could be advisable to rely on materials based on monomers with a reduced elution tendency for clinical procedures.