Research and Education
Mechanical performance of monolithic materials cemented to a dentin-like substrate

Presented at the Annual Meeting of the Academy of Dental Materials, in Porto de Galinhas, Brazil, October 4th to 6th, 2018.
https://doi.org/10.1016/j.prosdent.2019.12.021Get rights and content

Abstract

Statement of problem

Studies on the mechanical behavior of restorative materials bonded to tooth structure and considering the properties of the material and the bonding between both substrates are lacking.

Purpose

The purpose of this in vitro study was to evaluate the hardness, fracture toughness, load-to-failure, cyclic fatigue, and stress distribution of 4 computer-aided design and computer-aided manufacturing (CAD-CAM) materials when bonded to a substrate similar to dentin (G10).

Material and methods

Disks (11×1.2 mm) of lithium disilicate (LD), feldspathic ceramic (FC), polymer-infiltrated ceramic (PC), and a nanohybrid composite resin (NC) were fabricated (n=45) and had their surfaces polished. Microhardness was measured by the Knoop indentation (19.61 N, 12 seconds, n=5). Indented specimens were subjected to biaxial flexural strength testing, and the fracture origin defect was measured to calculate fracture toughness (n=5). Forty disks from each material were adhesively bonded to G10. Half of the specimens were subjected to load-to-failure testing, and remaining specimens (n=20) were subjected to cyclic fatigue (400 N, 106 cycles). The test was suspended every 200 000 cycles, and specimens were examined for cracks, debonding, or catastrophic failure. Obtained data were evaluated by analysis of variance and the Tukey post hoc test (α=.05). Weibull analysis was also performed. A 3D model of the tested specimens was constructed in a design software program, and the stress distribution was evaluated by finite element analysis, with the application of a 100-N load normal to the restoration surface.

Results

Hardness values with statistically significant differences were LD (540.4)>FC (474.6)>PC (176.6)>NC (58.26). Fracture toughness vales (MPa.m1/2) and statistical significance were as follows: LD (2.25)=NC (2.46)>FC (1.14)=PC (1.18). Load-to-failure values (N) were LD (2881.6)=FC (2881.6)=PC (3200.6)>NC (2367.5). A specimen each of LD and NC fractured during the fatigue test, and LD and PC had a high percentage of subsurface cracks (55% and 75%, respectively). The FC had the lowest debonding rate after load-to-failure testing and no catastrophic fractures or cracks during fatigue.

Conclusions

The materials tested had different mechanical behaviors depending on the tests performed. Feldspathic ceramic had the best fatigue behavior when cemented to a dentin-like substrate.

Section snippets

Material and methods

Four CAD-CAM materials were tested: lithium disilicate ceramic (LD) (IPS e.max CAD; Ivoclar Vivadent AG), feldspathic ceramic (FC) (VitaBlocs Mark II; Vita Zahnfabrik), polymer-infiltrated ceramic (PC) (Vita Enamic; Vita Zahnfabrik), and a nanohybrid composite (NC) (Brava Block; FGM). The Knoop indentation test was used to determine the hardness and fracture toughness of materials. Load-to-failure and cyclic fatigue were evaluated by using adhesively bonding disks of the materials to a

Results

LD ceramic had the highest microhardness, while NC had the lowest microhardness (F=510.58; P<.001). NC and LD materials had the highest fracture toughness (F=17.58; P<.001) (Table 3).

NC had the lowest load-to-failure values (F=10.78; P<.001) (Table 4). The most common type of failure for NC (observed in 90% of the specimens) was the complete debonding of the restorative material from the G10 base. The other tested materials had debonding of more than half of the restorative disk after testing (

Discussion

In this study, the hardness and fracture toughness of the tested CAD-CAM materials, as well as the load-to-failure, cyclic fatigue, and stress distribution when cemented to a dentin-like material, were investigated. The null hypothesis was rejected. LD and FC materials had the highest values of hardness, and LD and NC had the highest values of fracture toughness. NC had the lowest value of load-to-failure, and FC exhibited the best performance in mechanical cyclic fatigue with no fractures or

Conclusions

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

  • 1.

    Among the tested CAD-CAM materials, feldspathic ceramic exhibited the best behavior under fatigue in terms of the absence of fractures, internal cracks, and debonding.

  • 2.

    Lithium disilicate had the highest values of hardness and fracture toughness.

  • 3.

    However, 55% of the lithium disilicate specimens and 75% of the polymer-infiltrated ceramic specimens had internal cracks after fatigue.

  • 4.

    When the nanohybrid composite was

Acknowledgments

The authors extend their thanks to Sao Paulo Research Foundation (FAPESP 2016/22317-4) for the research grant.

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    • Supported by Sao Paulo Research Foundation (FAPESP), grant number 2016/22317-4.

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