Researchers from the Japanese Graduate School of Dentistry at Tohoku University conducted a study which resulted in the conclusion that 3D printing from light-cured resins using the DLP method is a more effective method of producing dental crowns than conventional CNC milling. The published scientific article describes 3D printing and wet milling of crowns of the same prosthetic models and their comparison in terms of dimensional accuracy and process efficiency. Through several test cycles, the team concluded that the 3D prints showed “higher accuracy” and “smaller discrepancies” than the milled alternatives, seeing DLP as having more promise for creating dental crowns.
For some time now, the prosthetic industry has been shifting from the production of metal crowns to resin crowns due to the relatively high wear resistance and color stability. At the same time, using CAD design software and a patient’s tooth impression, this approach allows the development of custom implants before using a milling machine to grind them from a ceramic block. However, the Tohoku University research team described problems with the use of the CNC method in terms of deterioration in the quality of the milling bar and relatively high material consumption. The researchers also point out that CNC milling forces dentists to adhere to rigid preparation requirements, and even if they stick to them, furrows can form on the inner surfaces of crowns.
These problems do not occur with 3D printing with light-curing resins. 3D printing offers durable crowns with higher dimensional accuracy, however, it remains unclear which process is better suited to prosthetic work. Scientists at Tohoku University decided to find out through a series of experiments …
The test samples were produced from a 3D scan of the abutment tooth model, then milled from a hybrid composite block and 3D printed using an Asiga Max 3D printer. Once both models were ready, each was compared to the original design models using an industrial 3D scanner that collected the data needed to identify any deviations.
Preliminary results showed a significant difference between crowns designed to conform to the line angles of the models and a non-displaced prosthesis with an observed gap of 100–200 µm. While the printed models showed high fidelity, the deviation was more pronounced in the milled parts where the team observed a distinct internal groove which they attributed to the brittle base material of the crowns.
Interestingly, the researchers also found that the 62 µm pixel resolution of their 3D printer is lower than that of the inner nodule region of non-displaced crowns. This made the system precise enough to make accurate models, while during milling, they discovered that grooves left on the inner surfaces of the crowns could lead to a poor fit and were due to the technological limitations of the subtractive method.
At the same time, the team concluded that while the results clearly show that DLP 3D printing is better suited to making crowns than CNC milling, more research is needed on different systems and parameters. Likewise, dentists have called for more research into the fracture resistance and biocompatibility of 3D-printed implants, which they believe can now be used to restore sharp teeth such as incisors.
Source: www.jstage.jst.go.jp via www.3dprintingindustry.com
Cover photo: own resources – not part of the described scientific document
