How do splint materials for bite splints that were manufactured using different CAD/CAM manufacturing methods (milling processes, 3D printing processes) differ in terms of their abrasion resistance?
Felix Schmeiser M.Eng, Munich
Bite splints must meet a wide range of requirements. In addition to the general stress caused by the chewing mechanism, the splints made of the appropriate materials must withstand forces of up to 770 N if the chewing system malfunctions. With regard to production, various processes can be used, e.g. B. CAD/CAM milling, 3D Print. Due to the advantages in terms of material consumption, manufacturing time and associated costs compared to conventional and subtractive manufacturing, additive manufacturing already covers a large area of rail manufacturing.
Left: milled crowns made of THERMEO (pro3dure medical GmbH), right: chewing simulation with the CS-4 chewing simulator (SD-Mechatronik GmbH).
In the literature, subtractive splint materials have so far been able to prevail over additive splint materials due to lower abrasion losses. However, promising insights into the influencing factors of additive manufacturing were gained, which means that optimization is constantly progressing. In addition, higher accuracy was observed in the production of dentures using additive manufacturing.
Subtraction and additively manufactured rails made from different materials
Aim of the investigation
The aim of the study was to evaluate the influence of the manufacturing technology of splint materials based on the abrasion resistance of subtractively and additively manufactured crowns. In addition to the quantitative assessment of the results, microscopic images of all crowns were analyzed in order to also incorporate qualitative assessment principles.
Material and method
Investigation of abrasion resistance (two-body wear)
To carry out the abrasion examinations, crowns were created based on the geometry of a first mandibular molar using subtractive (Thermeo, pro3dure medical GmbH; CLEARsplint, Astron Dental) and additive (GR22 flex, pro3dure medical GmbH; KeySplint soft, Mycone Dental Supply, Co., Inc .) Manufactured and placed on appropriate dies. In order to compensate for post-polymerization effects, 3D printing was always carried out exactly 7 days before the chewing simulation.
The surface of the stump as well as the inside of the crowns were blasted with aluminum powder with a medium grain size of 110 µm at a pressure of 1,5 bar and adhesively attached.
The chewing simulation took place under the following conditions:
- Antagonists from natural teeth
- Number of chewing cycles = 120.000 x (in Viva approx. 6 months)
- Force = 50 N
- Horizontal sliding movement = 0,7 mm (=> frequency = 1,3 Hz)
- Constant temperature (37°C)
Microscopic examination and determination of abrasion losses
After the chewing simulation, the crowns were assessed under a digital light microscope to gain a qualitative impression of the abrasion surfaces and then scanned with a laser scanner. Assuming that there was no breakthrough or fracture of the crowns, the digitized surface was evaluated using matching software.
Vertical abrasion losses of the rail materials examined
Based on the examinations of the rail materials, no differences in abrasion resistance were found. However, it has been shown that the milled crowns show pure abrasion on the surface more often than the printed crowns. In connection with this, the damage patterns in milled crowns result in the antagonist breaking through the surface, but in printed crowns the entire structure fractures.
Manufacturing of bite splints: conclusion
As part of the investigation, the following conclusions can be drawn:
- No significant differences in material loss were found between all occlusion device materials.
- Three-dimensionally printed bite splints were more likely to show a fracture, while CAM-milled bite splints were more likely to show a breakthrough.