Title: Comparison of Dimensional Accuracy of Additive and Subtractive Manufacturing of Dental Restorations after Digital Intra-oral Impression: An In Vitro Study.
Dr. Mohammed Yehea serves as a Lecturer and clinical instructor in at Qassim University, College of dentistry, Qassim, Saudi Arabia. He maintains his enthusiasm for education. His lectures cover topics including digital dentistry, advanced restorative dentistry and tooth colored restorations and he is published in few acclaimed dental journals. He is a Prosthodontist and has an excellent reputation for carrying out his clinical work to the highest level of precision and expertise. Dr. Yehea obtained his Master Degree (M.Sc) in Fixed and Removable Prosthodontics from Jordan University of Science and Technology. Irbid, Jordan. His research focus is in Digital impression and CAD-CAM produced prosthesis, both single, multiple and metal framework for fixed and removable partial dentures, through a variety of manufacturing techniques; additive (3D printing) and subtractive technologies.
Purpose: The dimensional accuracy of recently introduced dental restoration taken by digital intra-oral impression initially and then fabricated by additive manufacturing or the so-called 3D-printing technique is not well established and it may play a significant role in the future of dental technology.
Materials and Methods: This in vitro study presents a comparative experimental evaluation of dimensional accuracy of all-ceramic crown (fig 1) restorations fabricated by using two approaches: additive and subtractive manufacturing. The all-ceramic crown is digitally designed on molar die by using Computer-aided design (CAD) software. Samples are fabricated by using six different methods ( n=12 each group, total N=72), including three additive manufacturing techniques, stereolithography apparatus (SLA, fig 2), digital light processing (DLP, fig 3) and photopolymer jetting (PPJ, fig 4) ; and three subtractive techniques, wax, acrylic and e.max ceramic milling. The samples are scanned by using a high resolution optical surface dental scanner and then compared by overlapping reference data. The dimensional accuracy are evaluated by 3D-deviation analysis method. The 3D digital files of the scanned fabricated all-ceramic crowns (test model) are exported in standard tessellation language (STL) format and superimposed with the STL file of the designed all-ceramic crowns (reference model) using Geomagic Studio (3D Systems). The results are statistically analyzed using a one-way analysis of variance (a=0.05). Moreover, the surface morphology of one randomly selected sample from each group are evaluated using a digital microscope.
Results: The root mean square estimate value and color map results suggest that after digital intra-oral impression, additive and subtractive manufacturing have an influence on the dimensional accuracy of 3D-printed crown restorations. Among the tested groups, the SLA group showed a minimal deviation of 0.029 mm for thin support and 0.031 mm for DLP group, indicating an accurate fit between the test and reference models. Furthermore, the deviation pattern observed in the color map was homogenously distributed and located further away from the critical marginal area.
Conclusions: Within the limitations of this study, The results indicate that the accuracy of dental restorations htaken by digital intal-oral impression and fabricated using the additive manufacturing methods (SLA) is higher than that of subtractive methods. Therefore, this method is a viable alternative to subtractive methods.