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Root Canal Taper and the Accuracy of Intraoral Scanners for Post Space Measurement: An In Vitro Study
Dusit Nantanapiboon1,2,3,4, Porawit Kamnoedboon1,5, Chawalid Pianmee6
1Clinic of General, Special Care, and Geriatric Dentistry, Center for Dental Medicine, University of Zurich, Zurich, Switzerland.
Objective:
The aim of the study is to evaluate the accuracy (trueness and precision) of two intraoral scanners (IOSs) for measuring post space length and area deviation in root canal-treated teeth with differing canal tapers, using a caliper as the reference standard.
Materials And Methods:
Fifteen endodontically treated resin teeth (n = 5 per group; maxillary central incisor, first premolar, and first molar) received 10 mm post spaces with sizes No. 2, No. 0.5, and No. 1, respectively. Each specimen was measured 10 times using each method: a digital caliper (reference), a conventional polyvinyl siloxane impression digitized with an extraoral scanner (inEos X5), and two IOSs, IOS-1 (Trios 4) and IOS-2 (CEREC Primescan). STL files were superimposed in OraCheck 5.0 to measure post space length and area deviation. The 10 scans were treated as replicates nested within each specimen in linear mixed-effects models; equivalence was tested using two one-sided tests against a ± 0.10 mm margin, and precision was expressed as the repeatability coefficient.
Results:
Conventional impressions matched the caliper in every group and were equivalent within ± 0.10 mm. For Tooth 21, both scanners also met the equivalence margin. Both scanners underestimated Tooth 24 (IOS-1 -0.90 mm; IOS-2 -0.61 mm) and overestimated Tooth 26 (IOS-1 +0.28 mm; IOS-2 +0.25 mm), and neither met the equivalence margin (p <0.001). The two scanners did not differ in area deviation, which varied by tooth type only (Tooth 21 lowest). Conventional impressions were far more repeatable than the scanners (repeatability coefficient 0.08 to 0.14 mm vs. 0.29 mm for IOS-2 and 0.61 mm for IOS-1).
Conclusion:
Canal taper appeared to influence IOS accuracy: the widest-taper incisor was captured accurately by both scanners, whereas the narrower-taper groups were not. Because tooth type, taper, and post diameter varied together, taper cannot be isolated as the sole cause. Clinicians should be cautious when using IOS post space data in narrow or less-tapered canals.