Radiopacity of computer-aided design/computer-aided manufacturing composite resin blocks

A Comparative Evaluation of the Radiopacity of Contemporary Restorative CAD/CAM Blocks Using Digital Radiography Based on the Impact of Material Composition

Purpose

The main purpose of this study was to assess the radiopacity of contemporary restorative computer-aided design (CAD)/computer-aided manufacturing (CAM) materials and the impact of material composition as measured by energy-dispersive X-ray spectrophotometry (EDX) on radiopacity.

Materials and Methods

Ten specimens of six CAD/CAM materials with 1 mm thickness were produced and then digitally radiographed with an aluminum (Al) step-wedge (SW) and 1 mm thick tooth slice. The specimen mean gray values (MGVs) were recorded in pixels and compared to an Al-SW, dentin, and enamel of equal thickness. For the elementary analysis of the composition of the materials, EDX was performed.

Results

The recorded MGVs ranged between 21.20 ± 4.94 and 238.5 ± 13.61 pixels. Materials were sorted according to the MGVs descendingly, Prettau, Vita Suprinity, Vita Enamic, Shofu, Pekkton, and BioHPP. Prettau and Vita Suprinity had significantly higher MGV than dentin and 1 mm thick Al. In comparison, Vita Enamic had a slightly higher value than dentin and 1 mm thick Al. Although Pekkton and BioHPP had MGV significantly lower than dentin and 1 mm thick Al, Shofu had a significantly lower value than dentin and nonsignificantly lower than 1 mm thick Al (p < 0.05). According to EDX analysis, the examined materials contained several components in varying quantities of radiopacity.

Conclusions

The radiopacity of only three studied materials exceeded the International Organization for Standardization's minimum standards (ISO).

Radiopacity of resin-based CAD/CAM blocks assessed by areal grayscale pixel value measurement

PURPOSE

This study assessed radiopacity of resin-based computer-aided-design/computer-aided-manufacturing (CAD/CAM) materials by areal grayscale pixel value measurement.

METHODS

Radiopacities of six resin-based CAD/CAM block materials and resin composite were evaluated and compared to that of enamel and dentin. Specimens of 1-mm thickness were placed on photostimulable phosphor plate and irradiated with digital x-ray unit. On the radiographic image, regions of interests were determined for each specimen and areal grayscale pixel values were measured. Elemental analysis was performed with energy-dispersive x-ray spectroscopy (EDS) on field emission scanning electron microscope (FESEM) images of the specimens. Data were analyzed statistically (α = 0.05).

RESULTS

Radiopacity values of the restorative materials were significantly different from each other (P < 0.05). Radiopacity values of two resin-based CAD/CAM materials were significantly lower than that of dentin (P < 0.05). All tested restorative materials contain zirconium, three materials contain barium, and only resin composite contains lanthanum.

CONCLUSION

Four CAD/CAM materials with higher amounts of zirconia or barium (>18%) had radiopacity values significantly higher than the dentin; while two materials with lower amounts of zirconia (<4%) and/or no-barium, had radiopacity values significantly lower than the dentin. EDS analysis suggests materials containing elements with higher atom numbers such as zirconia and barium could exhibit higher radiopacity.

Characterisation of the Filler Fraction in CAD/CAM Resin-Based Composites

The performance of dental resin-based composites (RBCs) heavily depends on the characteristic properties of the individual filler fraction. As specific information regarding the properties of the filler fraction is often missing, the current study aims to characterize the filler fractions of several contemporary computer-aided design/computer-aided manufacturing (CAD/CAM) RBCs from a material science point of view. The filler fractions of seven commercially available CAD/CAM RBCs featuring different translucency variants were analysed using Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS), Micro-X-ray Computed Tomography (µXCT), Thermogravimetric Analysis (TG) and X-ray Diffractometry (XRD). All CAD/CAM RBCs investigated included midifill hybrid type filler fractions, and the size of the individual particles was clearly larger than the individual specifications of the manufacturer. The fillers in Shofu Block HC featured a sphericity of ≈0.8, while it was <0.7 in all other RBCs. All RBCs featured only X-ray amorphous phases. However, in Lava Ultimate, zircon crystals with low crystallinity were detected. In some CAD/CAM RBCs, inhomogeneities (X-ray opaque fillers or pores) with a size <80 µm were identified, but the effects were minor in relation to the total volume (<0.01 vol.%). The characteristic parameters of the filler fraction in RBCs are essential for the interpretation of the individual material's mechanical and optical properties.

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.

Evaluation of radiopacities of CAD/CAM restorative materials and resin cements by digital radiography

OBJECTIVE

This study aims to compare the radiopacities of computer-aided design/computer-aided manufacture (CAD/CAM) blocks and the adhesive cements used for their bonding.

MATERIALS AND METHODS

1 ± 0.2 mm thick specimens were obtained from six different CAD/CAM blocks (Incoris TZI, IPS e.max CAD, Vita Mark II, Cerasmart, Vita Enamic, and Vita Suprinity), four different adhesive resin cements (Panavia F2.0, Variolink Esthetic DC, RelyX Unicem Aplicap, G-CEM LinkAce), and a tooth. Radiographs of the specimens from each group, a tooth section, and an aluminum (Al) step-wedge were acquired. The radiopacity values of the materials were calculated as equivalents of Al thickness using the gray level values. The data were statistically analyzed using one-way ANOVA and Tukey HSD tests.

RESULTS

All the materials except Cerasmart and Vita Enamic had significantly higher radiopacity values than dentin (p < 0.05). Of the assessed blocks, the highest radiopacity value was observed in Incoris TZI, and the lowest radiopacity value was observed in Vita Enamic. Variolink Esthetic DC and RelyX Unicem Aplicap showed significantly higher radiopacity (p < 0.05) than the other adhesive cements, including enamel and dentin.

CONCLUSIONS

In this study, the majority of the CAD/CAM materials and all the adhesive resin cements were found to have sufficient radiopacity for prosthetic restorations according to the criteria set by the International Organization for Standardization (ISO).

CLINICAL RELEVANCE

From a clinical and biological point of view, materials should be chosen according to their radiopacity and other properties, such as biocompatibility and esthetics. If the selected restorative CAD/CAM blocks have a radiopacity value less than or equal to dentin, cements with higher radiopacity values are recommended to facilitate radiological diagnoses for periphery and interface of restorations.