Investigation of digital and conventional methods for verifying the fitness of CAD/CAM crowns on abutments with different shapes

Abstract

Purpose: To evaluate the marginal and internal compatibility of computer-aided design and computer-aided manufacturing crowns produced via a digital workflow using an intraoral scanner, and to compare this digital-detection technique with the conventional fit test using silicone rubber (silicone-compatibility technique) on various abutments.

Methods: Implant bodies were placed in the maxillary right central incisor and mandibular right first molar of reference models. Digital scans were acquired using an intraoral scanner, and abutments were prepared. Twenty-four crowns with a cement space of 70 μm were fabricated from the digital file of the abutment. The crown's inner surface, abutment, and occlusal surface were scanned. The gaps between the crown and abutment were measured using stereoscopic image analysis software based on standard triangulated language data, and the accuracy of the fit was verified using silicone rubber.

Results: Significant differences (P < 0.05) were observed between the silicone-compatibility and digital-detection techniques for the maxillary central incisor at the incisal edge and the palatal lower region, and for the mandibular first molar at the occlusal surface and the center of lingual axis. The digital-detection technique yielded values closer to 70 μm for the cement space. The values measured using the silicone-compatibility technique exhibited greater variation than those measured using the digital-detection technique.

Conclusions: The novel digital-detection technique had superior or equivalent performance compared to the silicone-compatibility technique and could be beneficial for verifying crown fitness accuracy.

Keywords: CAD/CAM technology; Digital scan; Dimensional accuracy; Intraoral scan.

Fig. 1

Reference model. A, Maxillary right central incisor. B, Mandibular right first molar

Fig. 2

A, Titanium abutment in the maxillary right central incisor. B, Titanium abutment in the mandibular right first molar. Black line: a total convergence of 6 degrees, and a rounded shoulder finish line of 0.5- mm with rounded line angles. Red line: a total convergence of 7 degrees, and a rounded shoulder finish line of 1- mm with rounded line angles

Fig. 3

Schematic drawing of Cement Space. CAD/CAM crown was fabricated by 70 μm cement space setting

Fig. 4

Silicone-compatibility technique. A, Optical impressions of the abutment. B, Optical impressions of the pressure-indicating silicone material remaining on the abutment. C, Superimposed image of implant abutment and pressure-indicating silicone material. D, E, Slice sections. (n = 6 for each group)

Fig. 5

Digital-detection technique. A, Optical impressions of the crown inner surface and margin. B, Optical impressions of the abutment. C, Optical impressions of the crown attached to the abutment. D, E, Slice section. (n = 6 for each group)

Fig. 6

Stereoscopic image analysis using software. The STL data for the silicone-compatibility technique and digital-detection techniques were acquired and transferred to the software for stereoscopic image analysis to measure the gap between the crown and the abutment

Fig. 7

Measurement site. A, Maxillary right central incisor: the labial margin (a), the center of the labial tooth axis (b), the center of the incisal edge (c), the upper region of the palatal access hole (d), the lower region of the palatal access hole (e), and the palatal margin (f). B, Abutment cut (orange line) in the buccolingual direction. C, LR6: Buccal margin (a), center of the buccal tooth axis (b), corner of the buccal occlusal surface (c), buccal region of the access hole (d), lingual region of the access hole (e), corner of the lingual occlusal surface (f), center of the lingual tooth axis (g), and lingual margin (h). D, Abutment cut (orange line) in the buccolingual direction

Fig. 8

Maxillary Right Central Incisor Measurement Results. Blue bar graph; silicone compatibility technique/ total convergence of 6 degrees, a rounded shoulder finish line of 0.5 mm, Orange bar graph; digital detection technique/ total convergence of 6 degrees, a rounded shoulder finish line of 0.5 mm, Silver bar graph; silicone compatibility technique/ total convergence of 7 degrees, a rounded shoulder finish line of 1 mm, Yellow bar graph; digital detection technique/ total convergence of 7 degrees, a rounded shoulder finish line of 1 mm. Significant differences (P < 0.05) were found between the values of silicone-compatibility and the digital-detection techniques at measurement sites c (center of the incisal edge: P = 0.0006/0.5 mm and 1 mm) and e (lower region of the palatal access hole: P = 0.0000/0.5 mm). b, c, d, e by ANOVA, a, f by Kruskal-Wallis test

Fig. 9

Mandibular Right First Molar Measurement Results. Blue bar graph; silicone compatibility technique/ total convergence of 6 degrees, a rounded shoulder finish line of 0.5 mm, Orange bar graph; digital detection technique/ total convergence of 6 degrees, a rounded shoulder finish line of 0.5 mm, Silver bar graph; silicone compatibility technique/ total convergence of 6 degrees, a rounded shoulder finish line of 1 mm, Yellow bar graph; digital detection technique/ total convergence of 6 degrees, a rounded shoulder finish line of 1 mm. Significant differences (P < 0.05) were found between values of the silicone-compatibility and digital-detection techniques at measurement sites d (the buccal region of the access hole: P = 0.0000/0.5 mm, P = 0.0010/1 mm) and g (the center of the lingual tooth axis: P = 0.0085/0.5 mm). a, b, d, g by ANOVA, c, e, f, h by Kruskal-Wallis test. The values obtained using the digital-detection technique were closer to the set cement spacing of 70 μm

Fig. 10

Comparison of abutment-tooth morphology by the digital-detection technique. A, Maxillary right central incisor. A significant difference (P < 0.05) was found between the values of the 0.5 mm and 1 mm abutment forms at measurement sites a (labial margin: P = 0.005678), c (center of the incisal edge: P = 0.000449), and e (lower region of the palatal access hole: P = 0.001134). a, b, c, d, e by Paired t test, f by Welch’s t test. B, mandibular right first molar. A significant difference (P < 0.05) was found between the values of the 0.5 mm and 1 mm abutment forms at measurement sites d (buccal region of the access hole: P = 0.00015) and g (center of the lingual tooth axis: P = 0.04856). a, b, c, d, e, f, g by Paired t test, h by Welch’s t test