Research and Education
Mechanical properties and internal fit of 4 CAD-CAM block materials

https://doi.org/10.1016/j.prosdent.2017.03.001Get rights and content

Abstract

Statement of problem

Recent polymer-based computer-assisted design and computer-assisted manufacturing (CAD-CAM) materials have been commercialized for inlay restorations, a polymer-infiltrated ceramic-network (PICN) and composite resin nanoceramics. Little independent evidence regarding their mechanical properties exists. Internal adaptation is an important factor for the clinical success and longevity of a restoration, and data concerning this parameter for inlays made with these blocks are scarce.

Purpose

The purpose of this in vitro study was to evaluate and compare the mechanical properties (flexural strength, flexural modulus, Vickers hardness, fracture toughness) and the internal adaptation of these recent polymer-based blocks with a lithium disilicate glass-ceramic block.

Material and methods

The materials tested in this study were a PICN material (Vita Enamic), 2 composite resin nanoceramics (Lava Ultimate; 3M ESPE and Cerasmart; GCDental Products), and a lithium disilicate glass-ceramic (IPS e.max CAD). Mechanical properties were evaluated according to ISO norm DIS 6872:2013. Bar-shaped specimens (18×3×3 mm) were prepared and submitted to a 3-point bend test using a universal testing machine at a cross-head speed of 0.5 mm/min. In addition, identical cavities were prepared in 60 human mandibular extracted molars (n=15) and optically scanned to receive mesioocclusodistal inlays milled with the 4 materials tested in a CEREC Inlab milling machine. The replica technique and a stereomicroscope (×20) were used to measure the internal fit of the inlays at 9 preselected locations. All data were statistically analyzed using 1-way ANOVA and the post hoc Tukey multiple comparison or Games-Howell test (α=.05).

Results

The mean flexural strength of the tested blocks ranged from 148.7 ±9.5 MPa (Vita Enamic) to 216.5 ±28.3 MPa (Cerasmart). The mean flexural modulus ranged from 23.3 ±6.4 GPa (Vita Enamic) to 52.8 ±10.5 GPa (IPS e.max CAD). The mean Vickers hardness ranged from 0.66 ±0.02 GPa (Cerasmart) to 5.98 ±0.69 GPa (IPS e.max CAD). The mean fracture toughness ranged from 1.2 ±0.17 MPa.m1/2 (Cerasmart) to 1.8 ±0.29 MPa.m1/2 (IPS e.max CAD). The values for internal discrepancy ranged from 119 ±55 μm to 234 ±51 μm. The mean internal discrepancy was significantly higher for Lava Ultimate (P<.05) than IPS e.max CAD and Cerasmart but not for Vita Enamic. The factor ‘‘material’’ was statistically significant in relation to the mechanical properties evaluated in this study (P<.05). The Pearson correlation was negative between the flexural strength results and the internal discrepancy of the materials tested (R2=0.941; P<.05).

Conclusions

The mechanical properties of the CAD-CAM block materials tested were within the acceptable range for fabrication of single restorations according to the ISO standard for ceramics (ISO 6872:2008). IPS e.max CAD and Cerasmart were observed to have superior flexural strength and better internal fit.

Section snippets

Material and Methods

The 4 materials tested in this study and their compositions are listed in Table 1. The IPS e.max CAD specimens used in this study were not fritted. Flexural strength and modulus evaluation were done according to International Organization for Standardization (ISO) standard 6872.30 Bar-shaped specimens (18×3×3 mm; n=16) were subjected to a 3-point bend test, using a universal testing machine at a cross-head speed of 0.5 mm/min. The flexural strength was calculated in megapascals (MPa) from the

Results

Results for the flexural strength, flexural modulus, fracture toughness, and Vickers hardness are presented in Figure 1, Figure 2, Figure 3, Figure 4. Cerasmart (216.5 ±28 MPa) and IPS e.max CAD (210.2 ±14 MPa) have significantly higher flexural strength results than Lava Ultimate or Vita Enamic (P<.05). The highest flexural modulus values were for IPS e.max CAD (52.8 ±10.5 GPa), which was significantly higher than the other materials tested (P<.05). The lowest Vickers hardness values were for

Discussion

This study investigated the mechanical properties of a dense ceramic, a PICN material, and 2 composite resin nanoceramic blocks. Additionally, the internal adaptation of MOD inlays prepared from these materials was evaluated. Correlation between the mechanical properties and the machinability of each of these block materials was investigated.

The IPS e.max CAD specimens were not fritted, because the main purpose was to evaluate the impact of mechanical properties on its machinability, which

Conclusions

Within the limitations of this in vitro study, the following conclusions were drawn:

  • 1.

    The mean flexural strength of Cerasmart and IPS e.max CAD was significantly higher than that of Lava Ultimate or Vita Enamic.

  • 2.

    The mean flexural modulus and Vickers hardness of IPS e.max CAD were significantly higher than those of Cerasmart, Lava Ultimate or Vita Enamic.

  • 3.

    The mean fracture toughness of IPS e.max CAD and Lava Ultimate was significantly higher than that of Vita Enamic or Cerasmart.

  • 4.

    The mechanical

Acknowledgments

The authors thank L. Viriot and B. Thivichon, Institute of Functional Genomics Lyon (UMR CNRS 5242), for assistance with stereomicroscopy and imaging studies and L. Scalone for the English language verification.

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Supported by GC Europe, Ivoclar Vivadent AG, Vita Zahnfabrik, and 3M ESPE.

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