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Effect of previous photoactivation of the adhesive system on the color stability and mechanical properties of resin components in ceramic laminate veneer luting

https://doi.org/10.1016/j.prosdent.2018.06.014Get rights and content

Abstract

Statement of problem

The color stability and mechanical properties of luting agents influence the esthetics and longevity of ceramic restorations. However, studies evaluating the color changes and mechanical properties of luting agents under ceramic laminates activated by using different methods are lacking.

Purpose

The purpose of this in vitro study was to evaluate the effects of different modes of photoactivation on the nanohardness and elastic modulus of resin cements and dental adhesives and on the color stability of ceramic laminate veneers.

Material and methods

Forty-four lithium disilicate blocks (7×8×0.6 mm) were cemented onto bovine enamel and divided into 4 groups according to the polymerization light (Radii-Cal or Valo) used and the mode of activation of the dental adhesive (no previous photoactivation or previous photoactivation). Single Bond Universal dental adhesive and RelyX Veneer resin cement were used in all experimental groups. Color stability was measured using a UV-2450 ultraviolet-visible spectrophotometer before and after ultraviolet-B artificial accelerated aging (n=8). The nanohardness and the elastic modulus of the adhesive and resin cement were measured using a nanohardness tester (n=3). The color stability and mechanical properties were measured and analyzed using ANOVA and the Tukey least significant difference test (α=.05).

Results

No difference in color stability or mechanical properties of the resin cement among the polymerization lights was detected (P>.05). Specimens that underwent previous photoactivation of the adhesive using the Valo polywave unit exhibited higher elastic modulus values than those that did not undergo previous photoactivation (P<.001).

Conclusions

The Valo polywave polymerization light improved mechanical properties and color stability more than the Radii-Cal unit. Previous activation of the dental adhesive in the dental enamel with the Valo polywave polymerization light yielded more satisfactory results.

Section snippets

Material and Methods

The materials used in this study are listed in Table 1. This study was approved by the Ethics Committee of the Araçatuba School of Dentistry, São Paulo State University (#2015-00673).

Forty-four lithium disilicate slices (7×8×0.6 mm) were made from high-translucency lithium disilicate blocks, shade B1 (IPS e.max CAD; Ivoclar Vivadent AG), using a low-speed diamond saw under water cooling (IsoMet 5000; Buehler). The ceramic slices were sintered in the manufacturer's furnace (Programat EP 5000;

Results

Table 2 shows the analysis of the color stability, which revealed no differences between the polymerization lights under the same experimental conditions (P>.05). After 252 hours of aging, the group with no previous photoactivation exhibited more chromatic alteration of the dental enamel than the group that was previously polymerized using Valo polywave (P=.023). There was more chromatic alteration after 756 hours than after 252 hours in both protocols for the dental adhesive when the Valo

Discussion

The mode of activation of the dental adhesive influenced the color stability and mechanical properties of the dental adhesive and the resin cement, and so the first null hypothesis was rejected. The use of different polymerization lights resulted in differences in color stability, HIT, and Eit* values, thus the third null hypothesis was rejected. Finally, analysis of the effects of different aging times on the color stability of ceramic laminates led to a rejection of the second null hypothesis.

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

  • 1.

    Nanohardness and elastic modulus were influenced by different polymerization lights, and the Valo polywave improved mechanical properties compared with the Radii-Cal single-wave polymerization light.

  • 2.

    The polymerization light had no effect on color stability.

  • 3.

    Previous photoactivation of dental adhesive in enamel using the Valo polywave yielded more satisfactory results.

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  • Cited by (0)

    Funding: This study was supported by the São Paulo Research Foundation (FAPESP) (grant #2015/06355-0).

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