J Adv Prosthodont.  2014 Feb;6(1):1-7. 10.4047/jap.2014.6.1.1.

Comparison of the accuracy of digitally fabricated polyurethane model and conventional gypsum model

• Kim SY
• Lee SH
• Cho SK
• Jeong CM
• Jeon YC
• Yun MJ
• Huh JB

• KMID: 2176563
• DOI: http://doi.org/10.4047/jap.2014.6.1.1

Abstract

PURPOSE
The accuracy of a gypsum model (GM), which was taken using a conventional silicone impression technique, was compared with that of a polyurethane model (PM), which was taken using an iTero(TM) digital impression system.
MATERIALS AND METHODS
The maxillary first molar artificial tooth was selected as the reference tooth. The GMs were fabricated through a silicone impression of a reference tooth, and PMs were fabricated by a digital impression (n=9, in each group). The reference tooth and experimental models were scanned using a 3 shape convince(TM) scan system. Each GM and PM image was superimposed on the registered reference model (RM) and 2D images were obtained. The discrepancies of the points registered on the superimposed images were measured and defined as GM-RM group and PM-RM group. Statistical analysis was performed using a Student's T-test (alpha=0.05).
RESULTS
A comparison of the absolute value of the discrepancy revealed a significant difference between the two groups only at the occlusal surface. The GM group showed a smaller mean discrepancy than the PM group. Significant differences in the GM-RM group and PM-RM group were observed in the margins (point a and f), mesial mid-axial wall (point b) and occlusal surfaces (point c and d).
CONCLUSION
Under the conditions examined, the digitally fabricated polyurethane model showed a tendency for a reduced size in the margin than the reference tooth. The conventional gypsum model showed a smaller discrepancy on the occlusal surface than the polyurethane model.

Keyword

Intraoral scanner; Digital impression; Aaccuracy; Gypsum; Polyurethane; 3D scanning

MeSH Terms

Calcium Sulfate*
Models, Theoretical
Molar
Polyurethanes*
Silicones
Tooth
Tooth, Artificial
Calcium Sulfate
Polyurethanes
Silicones

Figure

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  Fig. 1 (A) Reference tooth: artificial tooth with a chamfer margin and a six-degree-taper axial wall, (B) Gypsum models (GMs), (C) Polyurethane models (PMs).

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  Fig. 2 3D image superimposed GM image of the reference model.

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  Fig. 3 Registered points to measure the discrepancy.

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  Fig. 4 2D images converted from a 3D image using Convince software. The green boxes present the discrepancy at each registered point.

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  Fig. 5 Means and SD of the absolute discrepancies at three zones (*P<.05).

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  Fig. 6 Means and SD of the discrepancies at the registered points on the buccolingual section (*P<.05).

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  Fig. 7 Means and SD of the discrepancies at the registered points on the mesiodistal section (*P<.05).

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  Fig. 8 Schematic diagram of distortion using the mean values at the registered points. The size of the discrepancy is expressed by the size of the arrow (left: comparison of GM and reference tooth, right: comparison of PM and reference tooth).

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