Abstract
ObjectivesThe aim of this study was to compare the occlusal precision of computer-aided-design/ computer-assisted-manufacturing (CAD/CAM) milled versus 3D printed polymethylmethacrylate (PMMA) temporary prosthetic crowns , starting from the same digital CAD design. Materials and methodsThe study sample included 34 patients presenting 34 premolars in need of prosthetic rehabilitation: a total of 68 temporary crowns were manufactured, 34 of which milled and 34 printed. Immediately after manufacturing, the milled and printed provisionals were scanned with a desktop scanner (E1, 3Shape) to obtain STL files, that were superimposed to the original CAD design in order to identify the occlusal trueness (Analysis A). A second occlusal comparison was performed by scanning both kind of provisional after being placed intraorally with Trios scanner (3 Shape); intraoral scans were obtained in order to compare STL files of provisionals before and after occlusal adjustments (Analysis B). The occlusal trueness was identified at three reference points, P1 (vestibular cusp), P2 (palatal / lingual cusp), P3 (central fossa). The statistical analysis was performed using the R 3.4.3 statistical software (The R Foundation for Statistical Computing), with a significance level of p <0.05. ResultsOverall, the printed crowns showed lower occlusal differences than the milled crowns, when compared to the CAD design file, with a statistically significant difference in P1 (difference of 0.025 ± 0.046 mm), P2 (difference of 0.027 ± 0 0.044 mm) and P3 ( difference of 0.018 ± 0.050) for Analysis A (p <0.05). In the Analysis B the direct comparison between the degree of average difference between the pre-adjustment and the post-occlusal adjustment of the milled and printed crowns shows that the printed crowns have lower occlusal mean difference values in all three points compared to the milled ones (difference of 0.146 ± 0.273 mm in P1, 0.285 ± 0.360 mm in P2 and 0.257 ± 0.277 mm in P3). ConclusionsWithin the limitation of this study, the data obtained showed a better occlusal surface dimensional accuracy of the 3D printed provisional crowns, when compared to the milled ones. Comparing the results obtained, it is possible to assume that the intraoral scans also had a contribution to occlusion, beside the manufacturing method. 3D printing can be successfully applied for manufacturing temporary PMMA crowns.
Highlights
Temporary restorations are an essential part of fixed prosthetic treatments [1]
In the period of time that goes from tooth preparation to final restoration delivery, the dental abutments need to be protected from the oral environment and to maintain their relationship with the adjacent and antagonist teeth [2]
The most adopted computer-aided-design/ computerassisted-manufacturing (CAD/CAM) method is the subtractive one; this process use milling machines equipped with power-driven tools that mechanically cut material blocks or disks into a tooth shape or other specific geom etries, while every step is controlled by a computer [7,8]
Summary
Temporary restorations are an essential part of fixed prosthetic treatments [1]. In the period of time that goes from tooth preparation to final restoration delivery, the dental abutments need to be protected from the oral environment and to maintain their relationship with the adjacent and antagonist teeth [2]. The provisional is shaped directly onto the abutment, while the conventional indirect technique requires several laboratory steps starting from a dental cast, tooth wax up and temporary crown realization by the dental technician [4,5]. There has been an increased use of digital CAD/CAM (computer aided design/ computer aided manufacture) technology for provisional crown manufacturing, both with subtractive (CAD/CAM milling ma chine) and additive techniques (3D printer) [6]. The most adopted CAD/CAM method is the subtractive one; this process use milling machines equipped with power-driven tools that mechanically cut material blocks or disks into a tooth shape or other specific geom etries, while every step is controlled by a computer [7,8]. There are different types of 3D printing but the most currently used are stereolithographic sys tems (SLA), digital light processing(DLP) and material jetting (MJ) [9]
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