Print angle affects veneer quality according to research

Anisha Hall Hoppe, Dental Tribune International

Fri. 2. August 2024

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ISTANBUL, Turkey: Being able to accurately replicate intra-oral conditions is vital for successful restorative treatments. Although digital workflows have reduced the need for stone casts produced from conventional impressions, for cases that need physical casts, 3D printing is far superior in terms of sustainability in both material wastage and time. Researchers at Biruni University have evaluated how different 3D-printing technologies, specifically digital light processing (DLP) and stereolithography (SLA), as well as printing orientation affect the trueness of 3D-printed definitive casts for various tooth preparations. They found that both the type of 3D printer and the printing orientation significantly influenced trueness.

As clinicians transition away from relying on stone casts to evaluate case conditions and create dental restorations, digital workflows may offer greater precision, but have an equal need for correct technique and are not without their weaknesses. Human error can often be mitigated through assistive software, and the array of 3D-printing technologies offer their own unique benefits depending on the object being fabricated. However, clinicians need to be mindful of the various requirements of the respective printing processes of the various 3D-printing technologies, in addition to the nature of the materials used. Understanding the nature of the printing technologies is vital to troubleshooting the potential failures in printing a clinician might experience.

Both SLA and DLP polymerise a liquid photopolymer resin to build the object being printed. DLP uses a light projection system to polymerise a single layer in entirety at a time. SLA uses a single laser to create a continuous line of polymerised material in the resin bed, which also results in great precision, though it takes longer than DLP to polymerise each layer.

The researchers used an industrial scanner to digitise a maxillary typodont with tooth preparations for a posterior three-unit fixed partial denture, a lateral incisor crown, central incisor and canine veneers, first premolar and second molar inlays, and a first molar crown. The digital model was printed using both DLP and SLA technologies at four printing orientations: 0°, 30°, 45° and 90°. Seven casts were printed per orientation per technology.

The post-processed casts were scanned, and deviations from the original digital model were measured. It was found that the 3D printer type and printing orientation together significantly affected the deviations in most preparation regions, excluding the lateral incisor crown and canine veneer.

According to the researchers, the DLP printer generally outperformed the SLA printer in trueness, likely due to DLP’s simultaneous layer polymerisation, resulting in more uniform layers. SLA’s point-by-point polymerisation can introduce more variability. Overall, the 90° orientation consistently resulted in the lowest trueness across most preparations, attributable to increased staircase effects—the step-like pattern on the surface of a 3D-printed object—and fewer supports. Horizontal orientations (0° and 30°) minimised these effects, enhancing trueness.

These results do align with existing literature, emphasising the importance of optimal printing orientation for minimising layer-based inaccuracies and ensuring better restoration fit. The deviations observed were mostly within clinically acceptable ranges (< 200 µm), except for DLP-90° casts, underscoring the need for careful selection of printing parameters.

For dental clinicians, particularly in cosmetic dentistry, these insights highlight the importance of selecting the appropriate 3D-printing technology and orientation. Adjusting these parameters can lead to significant improvements in the fit and accuracy of restorations. Specifically, avoiding the 90° orientation with DLP printers is advisable owing to its tendency to produce less accurate casts.

The study, titled “Effect of 3D printing technology and print orientation on the trueness of additively manufactured definitive casts with different tooth preparations”, was published in the September 2024 issue of the Journal of Dentistry.