Wear characteristics of current aesthetic dental restorative CAD/CAM materials: Two-body wear, gloss retention, roughness and martens hardness

TLDR: All permanent aesthetic CAD/CAM block materials tested behave similarly or better with respect to two-body wear and toothbrushing wear than human enamel, which is not true for temporary polymer CAD/Csam block materials.

Abstract: Objectives This study determined the two-body wear and toothbrushing wear parameters, including gloss and roughness measurements and additionally Martens hardness, of nine aesthetic CAD/CAM materials, one direct resin-based nanocomposite plus that of human enamel as a control group. Materials and methods Two-body wear was investigated in a computer-controlled chewing simulator (1.2 million loadings, 49 N at 1.7 Hz; 3000 thermocycles 5/50 °C). Each of the 11 groups consisted of 12 specimens and 12 enamel antagonists. Quantitative analysis of wear was carried out with a 3D-surface analyser. Gloss and roughness measurements were evaluated using a glossmeter and an inductive surface profilometer before and after abrasive toothbrushing of machine-polished specimens. Additionally Martens hardness was measured. Statistically significant differences were calculated with one-way ANOVA (analysis of variance). Results Statistically significant differences were found for two-body wear, gloss, surface roughness and hardness. Zirconium dioxide ceramics showed no material wear and low wear of the enamel antagonist. Two-body wear of CAD/CAM-silicate and -lithium disilicate ceramics, -hybrid ceramics and -nanocomposite as well as direct nanocomposite did not differ significantly from that of human enamel. Temporary polymers showed significantly higher material wear than permanent materials. Abrasive toothbrushing significantly reduced gloss and increased roughness of all materials except zirconium dioxide ceramics. Gloss retention was highest with zirconium dioxide ceramics, silicate ceramics, hybrid ceramics and nanocomposites. Temporary polymers showed least gloss retention. Martens hardness differed significantly among ceramics, between ceramics and composites, and between resin composites and acrylic block materials as well. Conclusions All permanent aesthetic CAD/CAM block materials tested behave similarly or better with respect to two-body wear and toothbrushing wear than human enamel, which is not true for temporary polymer CAD/CAM block materials. Ceramics show the best gloss retention compared to hybrid ceramics, composites and acrylic polymers.

Frequently asked questions

Q1. What are the contributions in "Wear characteristics of current aesthetic dental restorative cad/cam materials: two-body wear, gloss retention, roughness and martens’ hardness" ?

A range of CAD/CAM block materials with flexural strength below 200 MPa are available this paper. 

Q2. What was the method used to dry the antagonists?

To prevent antagonists from drying, tape (Tesa, Beiersdorf, Hamburg, Germany) was luted circularly to the carriers and filled with tap water. 

Q3. What is the effect of the CAD/CAM composite on the wear behaviour of porcelain crowns?

for overlay restorations, the elastic properties of a CAD/CAM composite proved to be beneficial compared to the performance of ceramics (Magne and Knezevic, 2009). 

Q4. What is the effect of the elasticity of composites on the wear behaviour of composites?

While the wear behaviour of both nanocomposites poses no problem, as shown in the present study (Figs 3c and 3d), possibly the low modulus of the elasticity of composites (10–15 GPa, 3M ESPE,2011) under load may contribute to the loosening of composite crowns after some clinical service time, while the higher E-moduli of ceramics do not (Kelly, 2011; Vanoorbeek et al., 2010). 

Q5. What is the effect of toothbrushing on the enamel?

Toothbrushing influences the wear of enamel and of restorations, mainly by the abrasivity of the toothpaste slurry and by the structure of the restorative materials (Da Costa et al., 2010; Lee et al., 2010; Wiegand et al., 2008). 

Q6. What is the contact area of the LU CAD/CAM nanocomposite specimen?

In h) the contact area of the FI direct nanocomposite specimen shows the margin zone of the contact area exhibiting circular cracking as well as some microporosity and pitting. 

Q7. What is the average vertical loss of enamel?

The normal vertical loss of enamel from physiological wear was estimated to be approximately 20–38 µm per annum (Lambrechts et al., 1989).