Dimensional accuracy and surface characteristics of complete-arch cast manufactured by six 3D printers

Abstract

Objective: This in vitro study aimed to quantitatively and qualitatively evaluate and compare the horizontal and vertical accuracies of complete-arch casts produced by six 3D printers with different printing principles and resolutions using a low-viscosity resin material.

Methods: A reference cast was designed by CAD software. The 3D printers used were DLPa (Asiga MAX), DLPk (cara Print 4.0), LCD2o (Ondemand 2 K Printer), LCD2p (Photon Mono X), LCD4s (SONIC 4 K), and SLA (ZENITH U). Ten casts were printed for each 3D printer using a low-viscosity resin. The accuracy of each printed cast was evaluated using shell-to-shell deviations, 12 linear, one angular, and five height deviations, with a reference cast as the control. The surface features of the casts were examined using field-emission scanning electron microscopy (FE-SEM) and digital cameras.

Results: The evaluation of shell-to-shell deviation revealed that DLPa and SLA printers exhibited low trueness values, whereas LCD printers displayed high trueness values. Among the LCD printers, LCD4s and LCD2o exhibited the lowest and highest trueness values, respectively. DLPa printers showed lower trueness values for intercanine and intermolar distances, whereas LCD printers generally demonstrated high trueness values. However, LCD4s exhibited similar trueness values to those of SLA and DLPk. The height deviation was smallest in the anterior area, whereas the largest height deviation occurred in the canine teeth. The surface characteristics indicated that the SLA casts had greater light reflection and blunt canine tips. The FE-SEM observations highlighted that the LCD and DLP printers exhibited varying layer characteristics, with some presenting rough and uneven borders in the anterior lingual area.

Significance: The accuracy of 3D printed casts varied among the 3D printer groups: DLPa and SLA were accurate for shell-to-shell deviation, with DLPa being the most accurate for linear and angular deviations. Regardless of the XY resolution, the DLP printers outperformed the LCD printers. Among the LCD group of 3D printers, higher-resolution LCD4s demonstrated increased accuracy. The SLA exhibited soft layer borders in the FE-SEM owing to its laser spot characteristics and prominent light reflection in the digital camera images.

Keywords: 3D printing principle; Low viscosity; Photopolymerization resin; Resolution.

Fig. 1

Reference cast design. A. CAD design, and B. 3D printed cast.

Fig. 2

Reference points, lines, and angulation on reference cast. $\overline{\text{BD}}$, intercanine width; $\overline{\text{BC}}$, right half of intercanine width; $\overline{\text{CD}}$, left half of the intercanine width; $\overline{\text{EG}}$, intermolar width; $\overline{\text{EF}}$, right half of the intermolar width; $\overline{\text{FG}}$, left half of the intermolar width; $\overline{\text{AC}}$, anterior arch length; $\overline{\text{AF}}$, total arch length; $\overline{\text{AB}}$, right anterior circumferential length; $\overline{\text{AD}}$, left anterior circumferential length; $\overline{\text{BE}}$, right posterior circumferential length; $\overline{\text{DG}}$, left posterior circumferential length; ∠EAG, arch convexity.

Fig. 3

Three-dimensional structure of individual tooth with measuring length. hA, height of the point between central incisors; hB, right canine height; hD, left canine height; hE, height of the mesiobuccal cusp of the right first molar; hG, height of the mesiobuccal cusp of the left first molar.

Fig. 4

Bar diagram showing the median values for trueness of shell-to-shell (reference versus printed casts) measured from scanned casts of each 3D printer group. Different uppercase letters on the right side indicate statistical differences among 3D printers (P < 0.05). RMS, root mean square; 3D, 3-dimensional; DLP, digital light processing; LCD, liquid crystal display; SLA, stereolithography.

Fig. 5

Deviation of 3D printed casts relative to reference cast. The range of deviation was color-coded from −300 μm (blue) to 300 μm (red) and the allowable tolerance option was set to zero. DLP, digital light processing; LCD, liquid crystal display; SLA, stereolithography.

Fig. 6

Box plot diagram shows median values for trueness of distances and angulation measured from scanned casts of each 3D printer group. Different uppercase letters on the right side indicate statistical differences among 3D printers (P < 0.01). A. linear deviation, B. angular deviation, C. height deviation. 3D, 3-dimensional; DLP, digital light processing; LCD, liquid crystal display; SLA, stereolithography.

Fig. 7

Photographed casts at various angles. A. labial view of anterior teeth (upper) and lingual view of canine and premolar (lower), B. buccal view (upper) and occlusal view (lower) of molars. DLP, digital light processing; LCD, liquid crystal display; SLA, stereolithography.

Fig. 8

FE-SEM(Field Emission Scanning Electron Microscope, Apreo S; Thermo Fisher Scientific) x250. A. lingual surface of the anterior part, B. tip of the canine, C. central fossa of the molar. DLP, digital light processing; LCD, liquid crystal display; SLA, stereolithography.