Feldspathic ceramic scores highest in composite hardness testing

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Researchers wanted to see which CAD/CAM composites for molars were hardest and held up best after toothbrush abrasion testing. After putting six composites through rigorous testing, they discovered that feldspathic ceramic scored the highest in hardness, but some of the composites might need periodic repolishing.

The researchers tested four blocks used for molars, one block for premolars, and a feldspathic ceramic and reported their findings in the Journal of Oral Science (June 2019, Vol. 61:2, pp. 358-363).

The Knoop hardness value and gloss were measured before and after toothbrush abrasion testing for six different CAD/CAM composites:

Researchers used a diamond disk to create seven plate-shaped specimens with a thickness of 2.5 mm from each block. They polished and cleaned the samples before testing. Each specimen was tested for Knoop hardness value and put through a toothbrush abrasion test. Before and after the abrasion test, the researchers measured the gloss and surface roughness.

Vitablocs Mark II had the highest Knoop hardness value, while the researchers found no significant differences between Vitablocs, Katana, and Shofu in gloss after the abrasion test. However, the gloss of Estelite P block and KZR-CAD HR3 Gammatheta was greatly decreased and surface roughness greatly increased after testing (see table below).

Testing results for 6 CAD/CAM composites
  Cerasmart 300 Estelite P block Katana Avencia P block KZR-CAD HR3 Shofu block HC Hard Vitablocs Mark II
Knoop hardness value 81.3 113.2 127.0 76.8 93.6 599.8
Gloss before toothbrush abrasion test 90.7 92.4 89.5 88.8 91.4 95.0
Gloss after toothbrush abrasion test 65.9 34.7 75.4 35.3 75.6 81.0

The authors listed no study limitations, but periodic recall and repolishing might be necessary when these products are used clinically, they concluded.

"Products that show greatly decreased gloss and increased surface roughness after toothbrush abrasion testing should be used with care," wrote the study authors, led by Kentaro Okamura of the division of applied oral sciences at the Nihon University Graduate School of Dentistry in Matsudo, Japan.

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