Comparison of the virtual techniques in registering single implant position with a universal-coordinate system: An in vitro study.

OBJECTIVES: The aim of this in-vitro study was to compare the virtual techniques for registering single-implant position to the physical gold standard using a universal-coordinate system. MATERIALS AND METHODS: Thirty dentate maxillary resin models with a dental implant inserted in the incisor region were prepared. On each model, a tooth-supported acrylic stent with a 1 cm x 1 cm x 1 cm cubic-corner (CC) was prepared. The Cartesian x,y,z-coordinate of the implant neck and apex were measured physically by a coordinate-measuring machine (CMM) with reference to this CC and served as the gold-standard. The resin models were scanned by a benchtop scanner (Group BS), cone-beam computed tomography (Group CBCT), and intraoral scanner (Group IOS). Stone casts, poured from open-tray polyether impression of the resin models, were scanned by the benchtop scanner (Group BS-cast). The implant neck and apex coordinates with reference to the CC were measured and the differences in the coordinates (∆x, ∆y, ∆z) and distance r from the gold standard were calculated. The data were analyzed by one-sample t-test and one-way ANOVA/Kruskal-Wallis test with the level of significance set at 0.05. RESULTS: The implant neck and apex positions of Group BS were statistically different from that of the CMM, r>0 (p<0.001). Group IOS showed a significant less ∆z and r at the implant neck than Group BS-cast (p = 0.006). No significant difference was found in the coordinates and distance at implant apex among Groups BS, CBCT, IOS and BS-cast. CONCLUSIONS: The physical measurements could be adopted as the gold standard in assessing the single-implant positions. The IOS was more accurate in registering the single-implant neck positions than scanning of the cast. CLINICAL SIGNIFICANCE: A universal-coordinate system defined by the cubic-corner allows comparing the virtual techniques in registering single-implant positions to the physical gold standard.

Evaluation of laboratory scanner accuracy by a novel calibration block for complete-arch implant rehabilitation.

OBJECTIVES: To compare the accuracies of 4 laboratory scanners using a new custom-made block for complete-arch implant rehabilitation. MATERIALS AND METHODS: A block comprised 4 cylinders, with 2 in the anterior (0° angulation) and 2 in the posterior region (45° distal angulation) (Experimental group) and a standard block with 2 parallel cones in 16° taper (ISO group), were fabricated. Both blocks were scanned consecutively for 15 times by 4 laboratory scanners: IScan, Zfx, 3Shape, and KaVo. Measurements were also made by a coordinate measuring machine (CMM) as the reference. Acquired digital models were inspected with a metrology software. Linear and angular distortions were computed evaluation of trueness, precision and expanded uncertainty of scanners. Effects of blocks and scanners on the scanning trueness and precision were analyzed by Two-way ANOVA (α = 0.05). RESULTS: The linear trueness and precision of scanners was significantly poorer when the Experimental block instead of ISO block was used. Significant greater distortions were noticed at the 45° sites than the 0° sites and no significant effect of inter-implant distance on the scanning accuracy was found. Zfx, IScan and 3Shape exhibited comparable expanded uncertainties (10.6∼11.8) but KaVo showed the greatest (19.3) in complete-arch implant scans. CONCLUSION: The ISO block might not be more suitable than the Experimental block for evaluating the accuracy of laboratory scanner for complete-arch implant scanning. All the scanners tested except one demonstrated acceptable accuracy for complete-arch implant digitization. Scanning accuracy was compromised by unfavourable angulation of implants. CLINICAL SIGNIFICANCE: It is questionable whether the laboratory scanners validated for tooth-borne cases could also perform well for implant cases. It might be necessary to develop a new calibration object specifically for complete-arch implant scenarios to verify the capability of laboratory scanners in the implant workflow.

Reproducibility of laboratory scanning of multiple implants in complete edentulous arch: Effect of scan bodies.

OBJECTIVES: To evaluate the reproducibility of complete arch scanning with multiple implant scan bodies using a laboratory scanner. METHODS: A master model of edentulous maxillary arch with 6 implants was fabricated. PEEK scan bodies were inserted into the model and consecutively scanned using a dental laboratory scanner (N = 10, Group C). Another 10 scans were performed with each scan body detached and reinserted into the same site between each scan (Group CR). The last group of scanning was performed with the scan bodies detached and randomly repositioned between each scan (N = 10, Group RR). Virtual models were created and the inter-implant distances and angles were measured using an inspection software. Accuracy of the complete arch scans was calculated and compared using Two-Way ANOVA (⍺ = 0.05). RESULTS: Significant greater distance distortion was found in CR (27.6 ±â€¯18.9 µm) and RR (34.2 ±â€¯25.0 µm). No significant difference in angular distortion was found among 3 groups. The greatest distance distortion was found in the anterior and cross-arch region of the arch. The smallest angular distortion was found in the first scanned sextant, with increasing distortion along the scanning path of the arch. The distance precision was significantly reduced in group CR and RR, while the angular precision was significantly reduced in group RR only. CONCLUSION: Reproducibility of complete arch scanning was significantly affected by repositioning of the scan bodies using a laboratory scanner. Repeated and random repositioning of the scan bodies would decrease the reproducibility of the spatial position and angle of the virtual implant. The distortion appeared to be small and within the clinical tolerance. CLINICAL SIGNIFICANCE: High-precision transfer of the implant information from intra-oral environment to dental laboratory is a prerequisite for the success of implant-supported prosthesis. Although laboratory scanners seem to be accurate, their accuracy is also affected by the precision and attachment procedure of the implant scan bodies and that has always been overlooked.