Quantification of porosity in composite resins delivered by injectable syringes using X-ray microtomography

The effect of contouring instruments on immediate quality and porosity of direct restorations

OBJECTIVE

The study aims to evaluate the effect of contouring instruments on the porosity and immediate quality of direct dental restorations.

MATERIALS AND METHODS

Fifteen human molars with 30 Class II and 10 Class V cavities were restored by five voluntary dentists using three contouring instruments (conventional steel, silicone-tipped and diamond-like carbon coated-instruments) and three filling materials (Admira Fusion, Filtek Supreme XTE and Fuji II LC). The restorations were evaluated for immediate quality, porosity and number of pores using stereomicroscope and micro-computed tomography. Statistical analysis included the Shapiro‒Wilk test for normality, one-way ANOVA with Holm‒Sidak post hoc test for normal data, Kruskal‒Wallis ANOVA and Dunn's test for non-normal data, and Fisher's exact test for restoration quality comparisons. Statistical significance level was set at p < 0.05.

RESULTS

The proportion of restorations with acceptable immediate quality was higher for the restorations that had been contoured using a diamond-coated non-stick contouring instrument compared to the restorations that had been contoured using a conventional steel instrument (p = 0.033). The number of pores and porosity were similar for restorations that had been contoured with different contouring instruments. However, the number of pores and porosity were lowest in the restorations made of Filtek Supreme XTE followed by Admira Fusion and Fuji II LC.

CONCLUSION

The use of diamond-like carbon-coated contouring instruments increased the proportion of acceptable composite restorations compared to conventional steel instruments.

CLINICAL RELEVANCE

Non-stick contouring instruments should be considered for wider use.

Margin quality, homogeneity, and internal porosity assessment of experimental short fiber-reinforced CAD/CAM composite

OBJECTIVES

The aim of this study was to evaluate the margin quality of anterior crowns made of experimental short fiber-reinforced CAD/CAM composite (SFRC CAD) block before and after cyclic fatigue aging. Moreover, to investigate the microstructure, homogeneity, and porosity of the SFRC CAD compared with other commercial CAD/CAM materials.

METHODS

40 anterior crowns were milled from five CAD/CAM blocks divided into five groups (n = 8/group). The first group was made of lithium disilicate ceramic blocks (EM), the second of zirconia-reinforced lithium disilicate blocks (CD), the third of hybrid polymer-infiltrated ceramic network blocks (VE), the fourth of hybrid nanoparticle-filled resin blocks (CS), and the last of SFRC CAD blocks (SFRC). Crowns were inspected with stereomicroscope and margins irregularities were measured using FIJI software. Specimens were scanned using micro-CT to investigate porosity and homogeneity. Crowns were then subjected to cyclic fatigue aging (120,000 cycles, Fmax = 220 N) and margin irregularities were measured again. SEM/EDS and XPS analyses were employed.

RESULTS

SFRC CAD group resulted in the least margin irregularity values compared to other groups before and after cyclic fatigue aging, and lithium disilicate group resulted in the highest margin irregularity values (p < 0.05). Micro-CT scanning revealed a homogenous distribution of fillers of tested materials with low internal porosity.

SIGNIFICANCE

Material type and fatigue aging significantly affect crown margin irregularities. Hybrid and resin-based groups resulted in less margins irregularities than ceramic-based ones. All tested materials have homogenous structures with low internal porosity within the range of imaging resolution.

Evolution of the Guided Direct Composite Resin Technique in Restorative Dentistry: A Systematic Review

OBJECTIVE

This systematic review aims to understand the limitations and benefits of the guided direct restorative technique, to optimize the final outcomes, considering the evolution from analog to digital, including planning, the diversification of guides, and the different resins employed.

METHODOLOGY

A search was conducted in the electronic databases PubMed, Cochrane, and through manual searches, initiated in May 2023 and updated in April 2024. The following search strategy was used: ((injectable composite resin) OR (direct pressed composite)) OR (3D-guided), utilizing the PICO framework.

RESULTS

Initially, 739 articles were retrieved. After applying inclusion and exclusion criteria, 33 studies were considered suitable for data extraction, including 12 in vitro studies and 21 case reports or technique descriptions. The articles focused on comparisons of techniques, flowable, heated, and conventional resins, as well as various technique reports with variations in guides, materials, and planning, potentially aiding clinicians in more effective and safer execution of this restorative technique.

CONCLUSION

The utilization of digital workflows presents greater solutions to the challenges of the guided direct restorative technique. Understanding the properties of the resins used is crucial for the results and should be chosen according to the patient's needs.

CLINICAL SIGNIFICANCE

A guided direct restorative procedure can deliver previously planned dental treatment based on individualized planning. This method ensures greater reproducibility in aesthetics and occlusion, resulting in superior quality work for the patient.

Effects of various beverages on characteristics of provisional restoration materials

OBJECTIVE

To investigate the effect of common beverages on four currently used provisional restoration materials: Protemp®4, Integrity®, polymethyl methacrylate (PMMA) block, and acrylic resin. Flowable resin composite is included as a control group.

MATERIALS AND METHODS

Each material was formed into disks of 10-mm diameter and 4-mm thickness (N = 40) by loading the material into acrylic molds. The exposed surface in the mold was covered using a glass slide to prevent an oxygen inhibition layer, and polymerization then proceeded. The solidified disks were placed in distilled water for 24 h. These samples (n = 8) were then immersed for 14 days in one of four different beverages: water, orange juice, cola, and coffee. Changes in color dimension, hardness, and roughness were observed and then analyzed using two-way repeated analysis of variance.

RESULTS

The provisional materials had more obvious changes in all three color dimensions than the flowable resin composite. Integrity showed the biggest changes, followed by acrylic resin and PMMA block, whereas Protemp had the smallest changes. The hardness of all the materials significantly decreased after immersion in any of the beverages for 14 days. There were no changes in surface roughness when the materials were immersed in distilled water. The surface roughness of the PMMA block significantly decreased in orange juice whereas that of Integrity and acrylic resin significantly increased in cola.

CONCLUSION

Different kinds of provisional materials had different degrees of staining due to their composition. Moisture had a significant influence on the hardness of materials, and the acidity of cola significantly roughened the surface of the provisional materials.

Assessment of internal porosities for different placement techniques of bulk-fill resin-based composites: a micro-computed tomography study

OBJECTIVES

The aim was to compare the porosity of different bulk-fill resin-based composites (RBCs) placement techniques to the conventional incremental technique using microcomputed tomography (μ-CT).

MATERIAL AND METHODS

Occlusal cavities were prepared on extracted human molars, divided into five groups based on the placement technique (n = 10/group). Techniques examined were Monoblock-two-step (SureFil SDR flow + Ceram.X), Monoblock-two-step (Tetric EvoFlow Bulk-Fill + Tetric EvoCeram Bulk-Fill), Monoblock-one-step (Tetric EvoCeram Bulk-Fill), Monoblock with sonic activation (SonicFill2), and incremental technique (Filtek Z250). μ-CT scanning (SkyScan, Bruker, Belgium) assessed the number, volume of closed pores, and total porosity. Analysis of variance on ranks was used (Student-Newman-Keuls method and Mann-Whitney rank-sum test), to determine the significance of RBC viscosity and the sonication placement technique. The Spearman correlation method assessed the correlation between porosity characteristics (α = 0.05).

RESULTS

The SonicFill2 presented a higher number of closed pores than the other groups (p < 0.05). The overall porosity within the restoration seemed greater in this order: Filtek Z250 > SonicFill2 > Tetric EvoFlow Bulk-Fill + Tetric EvoCeram Bulk-Fill > Tetric EvoCeram Bulk-Fill > SureFil SDR Flow + Ceram.X. Sonication was associated with increased number (p = 0.005) and volume (p = 0.036) of closed pores. A strong correlation was observed between the number and volume of closed pores (R2 = 0.549, p < 001).

CONCLUSIONS

The monoblock technique with sonic activation showed significantly more internal porosity than the other placement techniques. Sonication during application contributed to the higher number and volume of closed pores than the passive bulk-fill application.

CLINICAL RELEVANCE

Using bulk-fill materials enhances efficiency, yet void formation remains an issue, depending on viscosity and active/passive delivery of materials. Clinicians must familiarize themselves with effective placement techniques to reduce void formation and optimizing treatment outcomes.

Damping Behaviour and Mechanical Properties of Restorative Materials for Primary Teeth

The energy dissipation capacity and damping ability of restorative materials used to restore deciduous teeth were assessed compared to common mechanical properties. Mechanical properties (flexural strength, modulus of elasticity, modulus of toughness) for Compoglass F, Dyract eXtra, SDR flow, Tetric Evo Ceram, Tetric Evo Ceram Bulk Fill, and Venus Diamond were determined using a 4-point bending test. Vickers hardness and Martens hardness, together with its plastic index (η_ITdis), were recorded using instrumented indentation testing. Leeb hardness (HLD) and its deduced energy dissipation data (HLD_dis) were likewise determined. The reliability of materials was assessed using Weibull analysis. For common mechanical properties, Venus Diamond always exhibited the significantly highest results and SDR flow the lowest, except for flexural strength. Independently determined damping parameters (modulus of toughness, HLD_dis, η_ITdis) invariably disclosed the highest values for SDR flow. Composite materials, including SDR flow, showed markedly higher reliabilities (Weibull modulus) than Compoglass F and Dyract eXtra. SDR flow showed pronounced energy dissipation and damping characteristics, making it the most promising material for a biomimetic restoration of viscoelastic dentin structures in deciduous teeth. Future developments in composite technology should implement improved resin structures that facilitate damping effects in artificial restorative materials.

Contemporary Approach to the Porosity of Dental Materials and Methods of Its Measurement

Porosity is an important parameter for characterizing the microstructure of solids that corresponds to the volume of the void space, which may contain fluid or air, over the total volume of the material. Many materials of natural and technically manufactured origin have a large number of voids in their internal structure, relatively small in size, compared to the characteristic dimensions of the body itself. Thus, porosity is an important feature of industrial materials, but also of biological ones. The porous structure affects a number of material properties, such as sorption capacity, as well as mechanical, thermal, and electrical properties. Porosity of materials is an important factor in research on biomaterials. The most popular materials used to rebuild damaged tooth tissues are composites and ceramics, whilst titanium alloys are used in the production of implants that replace the tooth root. Research indicates that the most comprehensive approach to examining such materials should involve an analysis using several complementary methods covering the widest possible range of pore sizes. In addition to the constantly observed increase in the resolution capabilities of devices, the development of computational models and algorithms improving the quality of the measurement signal remains a big challenge.

Is Micro X-ray Computer Tomography a Suitable Non-Destructive Method for the Characterisation of Dental Materials?

The aim of the study was to investigate the effect of X-rays used in micro X-ray computer tomography (µXCT) on the mechanical performance and microstructure of a variety of dental materials. Standardised bending beams (2 × 2 × 25 mm3) were forwarded to irradiation with an industrial tomograph. Using three-dimensional datasets, the porosity of the materials was quantified and flexural strength was investigated prior to and after irradiation. The thermal properties of irradiated and unirradiated materials were analysed and compared by means of differential scanning calorimetry (DSC). Single µXCT measurements led to a significant decrease in flexural strength of polycarbonate with acrylnitril-butadien-styrol (PC-ABS). No significant influence in flexural strength was identified for resin-based composites (RBCs), poly(methyl methacrylate) (PMMA), and zinc phosphate cement (HAR) after a single irradiation by measurement. However, DSC results suggest that changes in the microstructure of PMMA are possible with increasing radiation doses (multiple measurements, longer measurements, higher output power from the X-ray tube). In summary, it must be assumed that X-ray radiation during µXCT measurement at high doses can lead to changes in the structure and properties of certain polymers.