Abstract
Statement of problem
Intraoral scanning has benefits over conventional impression making, but whether scanning
is sufficiently accurate for multiple implants is unclear.
Purpose
The purpose of this in vitro study was to compare the trueness of digital scans acquired
by using intraoral scanners from a small range to a complete arch with the conventional
impression technique and to determine the influence of 2 different evaluation methods
(best-fit algorithm versus absolute linear deviation) on the outcomes of accuracy
assessment.
Material and methods
A mandibular model with 8 implants (A-H) around an edentulous arch was used as the
master model. Open-format standard tessellation language (STL) data sets (1 reference
file from a highly accurate dental laboratory scanner, 10 files from an intraoral
scanner, and 10 files from digitized conventional impressions at room temperature)
were imported to a metrology software program, and 5 groups of scanning ranges (AB,
FGH, CDEF, BCDEFG, and ABCDEFGH) were identified simulating different clinical situations.
Two evaluation methods—root mean square values calculated from the best-fit algorithm
and average value of linear discrepancies from absolute linear deviation—were used
to describe the trueness values. The impacts of different scanning or impression methods,
ranges, and evaluation methods were tested by using a 3-way ANOVA. The effect of the
scanning range on accuracy was further identified with 1-way ANOVA. The paired-sample
t test was used to determine the differences of trueness values between the 2 methods
in different groups.
Results
The trueness values of the implant impressions were significantly affected by different
scanning or impression methods (P<.001), evaluation methods (P<.001), and scanning ranges (P<.001) as independent variables. With use of the best-fit algorithm, deviations from
the digital scans were significantly greater than those from the conventional impressions
in cross-arch situations (groups CDEF, BCDEFG, and ABCDEFGH). With use of the absolute
linear deviation method, statistically significant lower accuracy was found when larger
areas were encountered (groups BCDEFG and ABCDEFGH). Use of the absolute linear deviation
method resulted in a higher mean score of inaccuracy than that from the best-fit algorithm
method in most situations.
Conclusions
Scanning or impression methods, ranges, and evaluation methods affected the dimensional
accuracy (trueness) of scans or impressions with multiple implants. Digital scans
had worse trueness values compared with those made with the conventional splinting
open-tray technique when cross-arch implant impressions were acquired.
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Article info
Publication history
Published online: February 24, 2021
Footnotes
Supported by Program for New Clinical Techniques and Therapies of Peking University School and Hospital of Stomatology, Grant/Award Number: PKUSSNCT-18A13 and Capital’s Funds for Health Improvement and Research, Grant/Award Number: 2018-2-4102.
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© 2021 by the Editorial Council for the Journal of Prosthetic Dentistry.
