Universal Chromatic Resin-Based Composites: Aging Behavior Quantified by Quasi-Static and Viscoelastic Behavior Analysis

Abstract

Universal chromatic dental resin-based composites were recently developed in an attempt to speed up the restoration process with the aim of making it easier for the practitioner to decide on a suitable shade and to avoid time-consuming matching and mixing of materials. The way in which color is created in the analyzed universal chromatic materials is innovative, as it is not only induced by selective light absorption via pigments (Venus Diamond ONE, Venus Pearl ONE), as is usual in regular composites (Charisma Classic, Charisma Topaz, Venus, Venus Diamond), but also by selective light reflection via particularized microstructures (Omnichroma). Material properties were assessed at 24 h post-polymerization and after artificial aging. Flexural strength (n = 20) and modulus were measured in a 3-point-bending test and complemented with fractography and Weibull analysis. Quasi-static (Martens, Vickers, and indentation hardness; elastic and total indentation work; creep, indentation depth) and viscoelastic (storage, loss, and indentation moduli; loss factor) behavior (n = 6) was measured by a depth-sensing indentation test equipped with a DMA module. The nanoscale silica/zirconia polymer core-shell structure in the structural-colored material induces similar or poorer mechanical properties compared with pigment-colored materials, which is related to the higher polymer content. For all materials, aging shows a clear influence on the measured properties, with the degree of degradation depending on the measurement scale.

Keywords: DMA; aging; quasi-static; structural-coloring; universal chromatic resin-based composite; viscoelastic.

Figure 1

Flexural strength as a function of RBC and aging (mean values with 95% confidence interval).

Figure 2

Flexural modulus as a function of RBC and aging (mean values with 95% confidence interval).

Figure 3

Fracture origin as a function of RBC and aging.

Figure 3

Fracture origin as a function of RBC and aging.

Figure 4

Representative images of the three identified fracture origins in the analyzed materials, from left to right: corner (surface), sub-surface (volume), and edge defect (surface). The fracture mirror (smooth surface in the initial part of the fracture created when the crack is accelerated) is marked by a dashed line, with arrows pointing to the origin of the fracture. The rougher surface adjacent to the mirror (mist) is followed by crack propagation in different directions, resulting in radial striations (hackle lines).

Figure 5

Example of a Weibull plot representing the empirical cumulative distribution function of strength data at 24 h post-curing. Linear regression was used to numerically assess the goodness-of-fit and estimate the parameters of the Weibull distribution, as described in Table 2.

Figure 6

Variation of the Vickers hardness (HV) as a function of RBC and aging conditions (mean values with 95% confidence interval).

Figure 7

Variation of the Martens hardness (HM) as a function of RBC and aging conditions (mean values with 95% confidence interval).

Figure 8

Variation of the indentation modulus as a function of RBC and aging conditions (mean values with 95% confidence interval).

Figure 9

Variation of the indentation hardness as a function of material and frequency in (a) unaged and (b) after 6 months’ immersion in artificial saliva.

Figure 9

Variation of the indentation hardness as a function of material and frequency in (a) unaged and (b) after 6 months’ immersion in artificial saliva.

Figure 10

Variation of the indentation modulus as a function of material and frequency in (a) unaged and (b) after 6 months’ immersion in artificial saliva.

Figure 10

Variation of the indentation modulus as a function of material and frequency in (a) unaged and (b) after 6 months’ immersion in artificial saliva.

Figure 11

Viscoelastic material behavior: Variation of the loss factor (tan delta) as a function of material and frequency in (a) unaged and (b) after 6 months’ immersion in artificial saliva.

Figure 11

Viscoelastic material behavior: Variation of the loss factor (tan delta) as a function of material and frequency in (a) unaged and (b) after 6 months’ immersion in artificial saliva.