By Tony Edwards, DrBicuspid.com editor in chief

June 28, 2018 -- Manufacturers have claimed that CAD/CAM dentures possess superior mechanical properties compared with conventional heat-cured dentures. In a new study, researchers compared two CAD/CAM denture specimens with a heat-cured specimen to see if the claims held up.

They found that the CAD/CAM specimens made from prepolymerized polymethyl methacrylate (PMMA) acrylic resins were stronger and had more flexibility than the heat-cured denture. Their study was published in the Journal of Prosthodontics (June 13, 2018).

"As CAD/CAM PMMA specimens exhibited improved flexural strength, flexural modulus, and impact strength in comparison to the conventional heat-cured groups, CAD/CAM dentures are expected to be more durable," the authors wrote.

The study was led by Ziad Al-Dwairi, BDS, of the department of prosthodontics at the Jordan University of Science and Technology Faculty of Dentistry in Irbid, Jordan.

Denture fabrication

Using CAD/CAM technology, dental practitioners can now fabricate complete dentures from blocks of PMMA acrylic resins. While these blocks are reported to have better mechanical properties than heat-cured PMMA blocks, there are no published reports to verify these claims, the study authors noted.

The researchers sought to fill this gap by comparing flexural strength, impact strength, and flexural modulus of two brands of CAD/CAM PMMA and a conventional heat-cured brand PMMA.

They fabricated 45 rectangular (65 x 10 x 3 mm) specimens:

“CAD/CAM dentures are expected to be more durable.”
— Ziad Al-Dwairi, BDS, and colleagues

The specimens were sprayed with a fitting spray, then stabilized on a custom-made stone base and mounted on a Ceramill Map 400+ CAD/CAM scanner (Amann Girrbach).

The researchers put the specimens through three-point bending and impact strength tests. They then studied the fractured specimens under a scanning electron microscope.

The Tizian (CAD/CAM) specimens showed the highest mean flexural strength and impact strength (see table below). The AvaDent (CAD/CAM) group had the highest mean flexural modulus. The Meliodent (heat-cured) group showed the lowest mean flexural strength, impact strength, and flexural modulus.

The flexural properties differences between the CAD/CAM specimens were not statistically significant (p > 0.05), the researchers noted.

CAD/CAM vs. heat-cured dentures
  Meliodent
(Heat-cured)
AvaDent
(CAD/CAM)
Tizian
(CAD/CAM)
Flexural strength 93.33 MPa 123.11 MPa 130.67 MPa
Flexural modulus 2,117.2 MPa 2,519.6 MPa 2,474.7 MPa
Impact strength 14.756 kg/m2 24.556 kg/m2 29.56 kg/m2
MPa = megapascal

The researchers attributed the improved flexural strength, flexural modulus, and impact strength in the CAD/CAM groups to the unique processing method of the CAD/CAM PMMA pucks in which high temperatures and pressure values are used for CAD/CAM PMMA polymerization.

Better performance

The researchers noted that this study involved in an vitro evaluation of the materials. They recommended more studies, especially ones including control groups and a greater range of materials.

However, the study results of the CAD/CAM PMMA disks backed the manufacturers' claims of better performance.

"Significant differences were reported between the conventional heat-cured PMMA and the CAD/CAM PMMA groups," the authors concluded.


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