Materials that hardly lose their strength after grinding


Swiss researchers examined the damages that are made by diamond grits of three grades to some restorative materials. Five materials were taken for the examination. Dentsply Sirona, a special milling unit was utilized for the examination. In the result, it appeared that some ‘soft’ materials lost their strength less than the ceramic materials, which were represented in the test in the amount of three units. 

The investigation took place in Geneva University and Geneva University Hospitals.

Losing strength                                         

Now polishing and multistep grinding are widely used in restoration process. This is connected with the wide CAD/CAM popularity, since this technique is very convenient for restoring crowns, veneers etc. The researchers tried to evaluate the damage grinding can make to ceramics and what part of strength is lost by the materials used.

The Doctors note that there is no danger for the patient after the restoration is actually ground. The possible cracks in the restoration can just lead to failure of the process itself. This is why they decided to see what materials exactly can more certainly have those possible cracks after grinding.

The following materials assigned for restoration were used:

  • Leucite glass-ceramic;
  • Lithium disilicate glass-ceramic;
  • Composite reinforced with nanoceramics;
  • Feldspar ceramic;
  • Feldspar ceramic-resin infiltrated.

Three diamonds with various grind levels (75 µm, 54 µm, 18 µm) were utilized for the test. Small slices of every material were cut, after that they underwent grinding and polishing, both processes were multistep.  

Then the grounding of the surfaces took place. For that purpose diamond disks on a turntable were utilized. The surfaces were polished with special diamond pastes (6 µm, 3 µm, 1 µm) with different rotation speed level 150rpm. Each surface was rotated during three minutes. Then the researchers had a chance to examine with the help of a microscope if any damages were done to the surfaces.

They calculated what number of cracks and fractures appeared on each material and compared the damage numbers to the material strength claimed by the manufacturer. Thus, loss of strength of each material was estimated. As it turned out, not all the materials have equal strength, some of them lose it more likely.

The researchers represented a table that shows chip sizes with mean deviation for all the materials.



Average chip sizes

Brand 75 µm diamond grinding damage 54 µm diamond grinding damage 18 µm diamond grinding damage
E.max CAD 100.2 ± 35.9 µm 84.1 ± 44.7 µm 42.8 ± 13.8 µm
Empress CAD 94.2 ± 34.0 µm 59.6 ± 19.4 µm 15.1 ± 7.6 µm
Vita Mark II 106.5 ± 53.1 µm 51.3 ± 12.8 µm 10.2 ± 3.6 µm
Enamic 25.8 ± 10.8 µm 18.3 ± 6.3 µm 7.0 ± 1.3 µm
Lava Ultimate 16.6 ± 7.5 µm 7.1 ± 2.0 µm 4.8 ± 1.5 µm