Egyptian researchers Passent Aly and Cherif Mohsen compare the benefits of 3D printing with conventional techniques for the production of prosthetic dental casts, releasing the findings of their study in ‘Comparison of the Accuracy of Three-Dimensional Printed Casts, Digital, and Conventional Casts: An In Vitro Study.’
In relation to oral and jaw restoration, prosthetics can be critical to the health of many patients. In this study, Aly and Mohsen match conventional stone casts with prosthetic casts 3D printed using stereolithography (SLA), as well as with “digital casts,” that is, 3D scans of existing stone casts. While digital technology is becoming increasingly popular for items like casts—replacing traditional methods with 3D printing for prototyping and creating functional parts—the authors point out that, for clinical practice, such processes must be heavily evaluated first.
In testing the effectiveness of digital casts in this study, Aly and Mohsen used a light desktop scanner to fabricate prototypes. For reference in comparison during experimentation, the researchers used a set of maxillary and mandibular ivory teeth. Five stone casts were made from polyvinylsiloxane impressions.
“The typodont casts (reference casts) were scanned using intraoral dental scanner (Trios 3Shape) in the following three steps: first maxillary and mandibular casts were scanned separately; the second step involved articulating the maxillary and mandibular arches by utilizing the ‘bite registration algorithm.’ Third and finally, digital casts (n = 5) were exported in STL file format to be integrated into space analysis software,” explained the researchers.
The digital casts were then printed on a ProJet 6000, using VisiJet SL Clear resin.
“The following linear measurements were taken: mesiodistal (MD) and occlusocervical (OC) for first molar, first premolar and canine in addition to intermolar width (IMW) and intercanine width (ICW) on both arches and sides by the same operator,” stated the researchers.
Errors occurred as follows:
“The errors ranged from 0.003 to 0.142 mm for different measurements. In OC, the errors of digital cast were significantly higher than the errors of the other two groups, where the mean of the digital cast = 0.016 compared with 0.004 and 0.007 for the other two groups (p < 0.0001). Similarly, in MD measurements, the error of digital casts (mean = 0.006) was significantly greater than the error of printed casts (mean = 0.003) but similar to those of conventional casts (mean = 0.005) with overall significant difference (p = 0.02). For IMW and ICW, digital casts had significantly greater errors (mean = 0.142 in IMW and 0.113 in ICW) compared with the two other groups (means= 0.019 and 0.008 in IMW and mean = 0.021 and 0.011 in ICW), p < 0.0001.”
Overall, only a ‘minor error’ was noted in accuracy of the 3D-printed casts as compared to the stone casts. The authors were able to confirm the advantages of using SLA printing in that area. They did, however, note a ‘significant difference’ in accuracy for SLA casts compared to digital casts:
“The cause of this error in the arch width measurements is due to the overestimation of digital measurements in comparison to stone and printed casts. Also, distortion of arch happens during scanning of dental casts,” concluded the authors. “But this error is still within the acceptable clinical range which comes in agreement with other studies.”
“This study used only one type of intraoral scanners and one type of 3D printers. Also, it is an in vitro study not simulating the conditions in the oral cavity, such as saliva, bleeding, limited mouth openings, and difficulty in vision, which are considered limitations of the current study. Thus, further studies are needed to evaluate the accuracy of other scanners and printers in comparison with the types used in this study. In addition, there is a need for future in vivo studies simulating oral conditions.”
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